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1
GAMBARDELLA, Cristina. « Caratterizzazione della corrente h in neuroni dopaminergici della substantia nigra pars compacta ». Doctoral thesis, Università degli studi di Ferrara, 2011. http://hdl.handle.net/11392/2388763.
Texte intégralRésumé :
1. Introduzione
I neuroni dopaminergici (DA) della substantia nigra pars compacta (SNc) sono tra i più studiati nel sistema nervoso centrale per la loro implicazione nella malattia del Parkinson. Essi presentano un ampio corredo di correnti voltaggio-dipendenti, tra le quali emerge una tipica corrente attivata da iperpolarizzazione, la Ih. Diversamente dalla maggior parte delle cellule nervose, i neuroni dopaminergici della SNc presentano una attività spontanea regolare dopo isolamento o riduzione degli input sinaptici, e non è, quindi, sorprendente che numerosi lavori abbiano indagato il ruolo della Ih nell'attività spontanea. Tuttavia il ruolo della Ih non è stato ancora ben compreso, dal momento che il blocco di questa corrente non sembra comportare nessuna alterazione significativa della frequenza di scarica.
Abbiamo, allora, riesaminato il problema studiando la corrente h, in fette sottili di cervello, in condizioni sperimentali che si differenziano dalla maggior parte degli studi precedenti per tre aspetti fondamentali:
i) abbiamo utilizzato topi transgenici che esprimono una proteina reporter (GFP) sotto il promotore tirosina idrossilasi (TH), per identificare i neuroni DA della SNc;
ii) abbiamo effettuato le registrazioni elettrofisiologiche a 37°C;
iii) abbiamo eseguito la maggior parte degli esperimenti in condizioni di patch perforato al fine di lasciare inalterato l’ambiente fisiologico intracellulare.
2. Risultati
Il nostro primo obiettivo è stato quello di effettuare un'analisi dettagliata della dipendenza della cinetica e dell’ampiezza della Ih dalla temperatura. Il protocollo di attivazione della corrente h prevedeva una serie di comandi iperpolarizzanti della durata di 4s e le registrazioni erano effettuate a 27°C e 37°C. Abbiamo calcolato che il coefficiente di temperatura (Q10) per la variazione di ampiezza della corrente h è pari 3,73, mentre i valori di Q10 relativi alle velocità di attivazione e deattivazione sono rispettivamente pari a 10,8 e 3,17. Il V50 è di -94,9 ± 1,07 mV a 27°C (n = 13) e -84,2 ± 1,31 mV a 37°C (n = 18).
Abbiamo, successivamente, esaminato la modulazione da parte dei nucleotidi ciclici in condizioni di patch perforato a 37°C, in presenza di forskolina (10 μM), un attivatore della adenilato ciclasi, e IBMX (0.1 mM), un inibitore delle fosfodiesterasi, i quali, insieme, inducono un aumento della concentrazione intracellulare di adenosina monofosfato ciclico (cAMP). In queste
condizioni abbiamo registrato un aumento dell'ampiezza Ih (da -178,53 ± 23,48 pA in condizioni di controllo a -227,01 ± 34,17 pA con forskolina a -130 mV, n = 8), uno spostamento del V50 di + 4,80 ± 0,68 mV (n = 8) e una riduzione delle costanti di tempo di attivazione di circa il 25%.
Dato che questa modulazione è il risultato di un’interazione diretta del cAMP con il canale, abbiamo studiato gli effetti sulla Ih di diversi neurotrasmettitori accoppiati a proteine Gi o Gs, in particolare abbiamo testato la dopamina, la serotonina (5-HT) e la noradrenalina (NA). Il quinpirolo, un agonista dei recettori dopaminergici D2 (30 μM, dopo 3 minuti di applicazione nel bagno), ha indotto una diminuzione dell'ampiezza della Ih del 15% a -130 mV (n = 6), mentre il sulpiride, un antagonista dei recettori dopaminergici D2 (20 μM), ne ha determinato un aumento (n = 5). L'effetto sulla Ih della 5HT (100 μM), dopo 3 minuti di applicazione nel bagno, è stato una riduzione dell’ampiezza del 20% (n = 5); al contrario, l'applicazione nel bagno della NA (100 μM), ne ha indotto un aumento di circa il 12% (n = 8).
Infine, abbiamo analizzato il ruolo della corrente h sull’autoritmicità. L'ivabradina (10 μM), bloccante del Ih, ha determinato una marcata iperpolarizzazione (circa -10 mV), che di fatto ha silenziato le cellule; tuttavia, questo effetto sull’attività spontanea era indiretto, poiché se la membrana era ripolarizzata, l’autoritmicità si ripristinava.
3. Conclusioni
Gli studi eseguiti a temperatura ambiente sul ruolo e le proprietà della corrente h nei neuroni dopaminergici della SNc sono scarsamente informativi perché, in queste condizioni sperimentali, la corrente è sottovalutato in ampiezza, velocità e, in ultima analisi, nella sua capacità di svolgere alcun ruolo a potenziali fisiologici. Le registrazioni elettrofisiologiche a 37°C, invece, restituiscono un profilo più accurato e veritiero della Ih.
La modulazione della corrente h ad opera di sistemi a secondo messaggero, un processo scarsamente esplorato nei neuroni dopaminergici della SNc, sembra essere rilevante, e suggerisce l'esistenza di diversi pathways importanti per il controllo dell’eccitabilità neuronale.
La corrente h è, in ultima analisi, molto importante nell’autorimicità perché stabilizza il potenziale di membrana di riposo dei neuroni dopaminergici della SNc in uno stato depolarizzato, ma non ricopre un ruolo di principale nell’attività pacemaker.
Questi risultati sono interessanti perché aprono nuove prospettive sul ruolo del canale HCN nei neuroni dopaminergici della substantia nigra pars compacta.
2
GIUSTIZIERI, MICHELA. « Meccanismi di modulazione presinaptica nei neuroni dopaminergici della substantia nigra pars compacta ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/561.
Texte intégralRésumé :
L’inibizione presinaptica è un meccanismo di modulazione sinaptica comunemente osservato nelle sinapsi del sistema nervoso centrale e periferico. Questo processo inizia in risposta all’attivazione di un’ampia varietà di recettori presinaptici e porta ad una riduzione della probabilità di fusione delle vescicole con la membrana del terminale sinaptico. Uno dei più comuni meccanismi d’azione consiste nell’inibizione dei canali del calcio voltaggio dipendenti (VDCCs) localizzati nei bottoni presinaptici. Tuttavia, esistono altre forme di inibizione presinaptica con meccanismi che coinvolgono direttamente la machinery di rilascio vescicolare. In questa tesi ho studiato il meccanismo di inibizione presinaptica mediata dal recettore metabotropico del glutammato del tipo III (mGluRs) e dal recettore GABAB nella trasmissione GABAergica dei neuroni dopaminergici della substantia nigra pars compacta (SNc) di ratto. L’AP-4 (100 μM), agonista selettivo del recettore metabotropico del glutammato del tipo III, e il baclofen (10 μM), agonista selettivo del recettore GABAB, riducono reversibilmente la frequenza delle correnti spontanee inibitorie post-sinaptiche (sIPSCs) rispettivamente del 48.5 ± 3.7 % e del 83.6 ± 2.3 % rispetto al controllo, senza avere alcun effetto sull’ampiezza della corrente. L’AP-4, non deprime la frequenza delle correnti inibitorie miniature post-sinaptiche (mIPSCs), registrate in tetrodotossina (TTX, 1 μM) e cadmio (100 μM), mentre è in grado di ridurre la frequenza delle mIPSCs del 75.3 ± 2.8 % rispetto al controllo, in presenza di TTX (1 μM) e bario (1 mM). Al contrario, il baclofen riduce la frequenza delle mIPSCs sia in cadmio (70.0 ± 6.7 % del controllo) sia in bario (52.3 ± 2.9 % del controllo). In TTX e ionomicina (2 μM), il baclofen riduce significativamente la frequenza delle mIPSCs del 71.8 ± 6.9 % del controllo, mentre l’AP-4 non ha effetto. In maniera simile, in presenza di TTX e α-latrotossina (α-LTX, 0.3 nM), la frequenza delle mIPSCs è diminuita del 64.5 ± 4.8 % del controllo dal baclofen, mentre mantiene gli stessi valori in presenza di AP-4. Infine, in continua presenza di baclofen, l’AP-4 non causa un ulteriore riduzione della frequenza delle sIPSCs. La conclusione di questi studi è che i recettori metabotropici del glutammato del tipo III deprimono il rilascio di GABA dai neuroni dopaminergici della SNc , attraverso l’inibizione dei VDCC, mentre i recettori presinaptici GABAB coinvolgono direttamente il rilascio vescicolare del neurotrasmettitore. Inoltre questi due diversi meccanismi di inibizione pre-sinaptica coesistono nello stesso terminale sinaptico. Questa caratterizzazione fornisce nuove conoscenze sul ruolo di questi recettori presinaptici nello studio della fisiologia della substantia nigra e nel loro potenziale uso come target nel trattamento farmacologico di malattie neurodegenerative come il morbo di Parkinson.Presynaptic inhibition is a mechanism of synaptic modulation normally observed in the synapses of the nervous system. This process starts upon activation of a large number of presynaptic receptors and leads to the decreased probability of vesicles to fuse to the cell membrane. One of the most common mechanism consists in the inhibition of the voltage dependent calcium channels (VDCC) located on the active zone of the presynaptic neuron. However, there is evidence for another form of presynaptic inhibition with a direct impairment of the vescicular release machinery. In my thesis I have investigated the mechanisms of presynaptic inhibition by group III metabotropic glutamate receptors (mGluRs) and GABAB receptors of the GABAergic neurotransmission to dopamine (DA) neurones of the rat substantia nigra pars compacta (SNc). The group III mGluRs agonist L-(+)-2-amino-4-phosphonobutyric acid (AP4, 100 μM) and the GABAB receptor agonist baclofen (10 μM) reversibly depressed the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) to 48.5 ± 3.7 % and 83.6 ± 2.3 % of control, respectively, with no effect in their amplitude. AP4 did not affect miniature inhibitory postsynaptic currents (mIPSCs) recorded in tetrodotoxin (TTX, 1 μM) and cadmium (100 μM), while in TTX (1 μM) and barium (1 mM), mIPSCs frequency was reduced to 75.3 ± 2.8 % of control. In contrast, baclofen reduced mIPSCs frequency either in cadmium (70.0 ± 6.7 % of control) or barium (52.3 ± 2.9 % of control). In TTX and ionomycin (2 μM), baclofen significantly reduced mIPSCs frequency to 71.8 ± 6.9 % of control, while AP4 had no effect. Similarly, in TTX and α-latrotoxin (α-LTX, 0.3 nM), the frequency of mIPSCs was reduced by baclofen to 64.5 ± 4.8 % of control, but was insensitive to AP4. Finally, in the continuous presence of baclofen, AP4 failed to produce any further reduction of sIPSCs frequency. The conclusion of this study is that group III mGluRs depress GABA release to DA neurons of the SNc through inhibition of presynaptic voltage-dependent calcium channels, while presynaptic GABAB receptors also impair transmitter exocytosis, and both mechanisms coexist on the same synapses. This characterization provides new insights about the role of these presynaptic receptors in the physiology of the substantia nigra and their potential involvement in the treatment of neurodegenerative diseases such as Parkinson’s Disease.
3
LALLAI, VALERIA. « L’isolamento sociale riduce marcatamente la risposta dei neuroni dopaminergici mesocorticali agli stimoli piacevoli ». Doctoral thesis, Università degli Studi di Cagliari, 2015. http://hdl.handle.net/11584/266621.
Texte intégralRésumé :
The mesolimbic dopaminergic pathway plays an important role in the genesis of emotional arousal and behavioral activation in response to stimuli that provide a reward. This neural circuitry is also active in the early stages of learning and stabilization of addictive behavior due to substances abuse. Isolated animals have a different sensitivity to natural or artificial reinforcers. Accordingly, experimental evidences suggest that exposure to stress can deeply modify eating behavior. In light of these evidences the aim of this study was to investigate the influence of a chronic stress, like social isolation at weaning, on the sensitivity of mesocorticolimbic dopaminergic neurons to anticipation and consumption of food. Rats have been food restricted using a protocol that consists in training the animals to consume their meal for only two hours for day. Using vertical microdialysis, extracellular concentrations of dopamine in response to anticipation and consumption of food were measured both in the mPFC and the NAC.
In PFC of GH rats extracellular DA increased (+180%) 80 minutes before food presentation showing the maximal increase (+350%) during food intake. On the contrary, in the NAc of GH rats no significant changes were observed. In SI animals trained to food restriction the increase in mPFC DA output observed in GH animals was completely blunted, while, in the NAc, 40 min before the presentation of the food, a significant increase in extracellular concentrations of DA was observed.
Our results show that exposure to chronic stress modified the response of mesocortico-limbic dopaminergic neurons to an enjoyable stimulus and suggest that these changes might be important to explain the greater sensitivity to abuse that is observed in individuals subjected to stressful stimuli. This underlying alteration in brain function might be a crucial mechanism that predisposes individuals to impulsive behavior and increases the risk of developing addiction.
4
CUCCHIARONI, MARIA LETIZIA. « Meccanismi di vulnerabilità dei neuroni dopaminergici mesencefalici di ratto esposti a fattori neurotossici ambientali ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/848.
Texte intégralRésumé :
E’ sempre più accettata l’ipotesi secondo cui le malattie neurodegenerative come il morbo di Parkinson siano di origine multifattoriale (“multiple hit hypothesis”), cioè siano causate dalla concomitante o ripetitiva presenza di diversi fattori che cooperano alla morte cellulare. Tra questi quelli ambientali occupano un posto rilevante. Sebbene una grande varietà di processi neurologici potrebbero essere influenzati da neurotossine ambientali, il sistema dopaminergico sembra essere quello più colpito.
Negli ultimi 10 anni si è rivolta sempre maggiore attenzione alla L-BMAA (L-β-N-methylamino-L-alanine), un aminoacido non proteico trovato nei semi della Cycas micronesica, che sembra essere alla base dell’ “ALS-PDC complex”, una sindrome complessa caratterizzata da sintomatologie cliniche tipiche della sclerosi laterale amiotrofica (SLA), del morbo di Parkinson e dell’Alzheimer.
Recenti scoperte hanno dimostrato che questa tossina viene prodotta da una grande varietà di cianobatteri del genere Nostoc presenti in tutto il mondo. Pertanto, potenzialmente, tutta la popolazione umana potrebbe essere esposta a tale sostanza. Ciò potrebbe determinare il suo accumulo nell’organismo, sia in forma libera che legata alle proteine, da cui verrebbe poi rilasciata lentamente durante il catabolismo proteico.
Sulla base di queste considerazioni abbiamo voluto analizzare gli effetti di questo aminoacido sulle cellule dopaminergiche della SNc da un punto di vista elettrofisiologico, farmacologico, morfologico e tossicologico.
La BMAA (3 mM, 10 psi 1.0 s) causa una depolarizzazione dei neuroni dopaminergici della SNc inducendo una corrente entrante (media = 454.48 ± 34.65, n = 73) e aumenti transienti della concentrazione di calcio intracellulare (R medio = 0.368 ± 0.062, n = 13). Questi effetti sono mediati prevalentemente dall’attivazione dei recettori metabotropici del glutammato di gruppo I (mGluR1), in quanto vengono ridotti reversibilmente dall’antagonista selettivo, CPCCOEt (100 μM) (corrente: 41.56 ± 3.61 % del controllo, n = 24; calcio: 28.43 ± 5.96 % del controllo, n = 7). La corrente, ma non il calcio, indotta dalla BMAA è ridotta in piccola parte dal CNQX (10 μM) (corrente: 93,09 ± 1,97 % del controllo, n = 24; calcio: 100.17 ± 9.93 % del controllo, n=6), antagonista competitivo dei recettori AMPA.
Nelle cellule dopaminergiche della SNc gli aumenti di calcio indotti dall’attivazione dei recettori mGluR1 sono mediati dai canali SOCs/TRPC. Infatti, sia le correnti entranti che le variazioni di calcio intracellulare indotte dalla BMAA sono ridotte dagli antagonisti di tali canali, SKF 96365 (100 μM) (corrente: 42.125 ± 4.35 % del controllo, n = 8; calcio: 43.57 ± 7.9 % del controllo, n = 7) e Ruthenium Red (20 μM) (corrente: 27.05 ± 8.3 % del controllo, n = 6).
Inoltre, nonostante la BMAA in presenza di carbonato presenti una struttura chimica simile a quella dell’acido glutammico, essa non viene ricaptata dalla cellule dopaminergiche attraverso il trasportatore degli aminoacidi eccitatori EAAT.
E’ interessante notare che negli interneuroni GABAergici della SNc la BMAA attiva i recettori AMPA, ma non quelli metabotropici, senza indurre variazioni della concentrazione del calcio intracellulare. In queste cellule, tuttavia, l’agonista selettivo degli mGluR1, il DHPG (30 μM), evoca correnti entranti, a dimostrazione della presenza degli mGluR1 sugli interneuroni GABAergici.
A conferma della sua potenziale tossicità, esposizioni prolungate di fettine mesencefaliche (12, 20 e 30 minuti) alla BMAA inducono cambiamenti irreversibili su numerose proprietà cellulari. Tali modificazioni sono accompagnate dal rilascio massivo del citocromo C (Cyt C) nel citoplasma delle cellule dopaminergiche che viene completamente bloccato dall’aggiunta, nel mezzo di perfusione, di antagonisti dei recettori mGluR1 e AMPA.
I dati che ho riportato in questa tesi forniscono una chiara e plausibile dimostrazione di come la BMAA può essere tossica verso le cellule dopaminergiche della SNc, causando i sintomi neurologici della malattia di Parkinson.It is well known that several neurodegenerative diseases, such as Parkinson disease, have a multifactorial origin (multiple hit hypothesis), which suggests that neuronal loss is a result of multiple factors. Among them, environmental factors are the most important. Although a variety of neurological processes can be adversely affected, the dopaminergic system appears to be a major target for environmental neurotoxins. The hypothesis that L-BMAA (L-β-methylamino-L-alanine), a nonprotein amino acid found in the Cycas micronesica seeds in western pacific islands, is involved in the development of amyotrophic lateral sclerosis/Parkinson-dementia complex (ALS-PDC complex) has risen and fallen since its initial proposal in 1987. In the last ten years the interest for this toxin has grown due to the discovery that it can be produced by many strains of Nostoc cyanobacterias, present throughout the world. Moreover L-BMAA can bind proteins. This bound form may function as an endogenous neurotoxic reservoir, accumulating and being released during protein catabolism. In order to analyze the effects of this amino acid, we have performed electrophysiological, pharmacological, morphological and toxicological studies on dopaminergic neurons of SNc. In these neurons puff-application of L-BMAA (3 mM, 10 psi 1.0 s) causes an inward current (mean = 454.48 34.65, n = 73) and a transient increase of intracellular calcium (R mean = 0.368 ± 0.062, n = 13). These effects are mediated by the activation of group I metabotropic glutamate receptors (mGluR1) and they are reversibly blocked by the application of the antagonist CPCCOEt (100 μM) (current: 41.56 ± 3.61 % of control, n = 24; calcium: 28.43 ± 5.96 % of control, n = 7). Bath application of CNQX (10 μM), a competitive antagonist of AMPA receptors, partially inhibits the L-BMAA-induced current (current: 93,09 ± 1,97 % of control, n = 24) but it has no effect on the calcium concentration (100.17 ± 9.93 % of control, n = 6). SOCs/TRPC channels are present in the dopaminergic cells of SNc and they mediate the intracellular calcium increase due to the activation of mGluR1. Indeed SKF 96365 (100 μM) and Ruthenium Red (20 μM), two antagonists of TRPC channels, are able to reduce the L-BMAA-induced inward current (42.125 ± 4.35 % of control, n = 8 and 27.05 ± 8.3 % of control, n = 6 respectively). Moreover SKF 96365 (100 μM) reduces the intracellular calcium increase induced by L-BMAA (43.57 ± 7.9 % of control). It is known that L-BMAA, in the presence of carbonate, has a chemical structure similar to glutamic acid, however it is not re-uptaken by EAATs, the excitatory amino acid transporters. Interestingly, in GABAergic interneurons, L-BMAA activates AMPA receptors but not mGluR1, and this activation causes inward current without any change in intracellular calcium concentration. However mGluR1 are present in these neurons because application of DHPG (30 μM), the selective agonist, produces inward currents. In order to confirm the toxic effects of this amino acid we have treated midbrain slices with L-BMAA for 12, 20 and 30 minutes and we have seen irreversible modification of cellular properties (decrease in membrane resistance, inability to evoke firing, elevated intracellular calcium). As a consequence of the treatments, cytocrome C is released in the cytoplasm, but in the presence of AMPA and mGluR1 antagonists, this effect is blocked. In conclusion this study demonstrates that L-BMAA could be considered a possible toxic agent for the dopaminergic neurons and provides new insights into the role of this amino acid in the aetiology of Parkinson disease.
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ANGIONI, LAURA. « Ossitocina nella Sostanza Nera del ratto : azione sull'attività locomotoria e interazione con i neuroni dopaminergici, glutammatergici e GABAergici nigrali ». Doctoral thesis, Università degli Studi di Cagliari, 2016. http://hdl.handle.net/11584/266640.
Texte intégralRésumé :
Oxytocin, the neurohypophyseal hormone well-known for its hormonal role in lactation and parturition, also exerts a wide range of effects acting in the Central Nervous System as a neuromodulator or neurotransmitter. An increasing number of experimental studies have suggested that, in rodents, central oxytocin exerts also a modulatory role on locomotor activity, but little is known about the cerebral areas in which oxytocin might act to produce this effect.
The substantia nigra, a mesencephalic structure which is part of the basal ganglia, a group of interconnected nuclei involved in motor and non-motor functions, receives oxytocinergic projections from the parvocellular compartment of the paraventricular nucleus of the hypothalamus. Moreover, oxytocinergic receptors and oxytocin receptor messenger RNA have been shown to be present in human and rat substantia nigra, respectively. Furthermore, it has been demonstrated that a significant decrease in the number of oxytocin-immunoreactive neurons occurs in the paraventricular nucleus of patients suffering from Parkinson’s Disease, a progressive neurodegenerative movement disorder characterised by the degeneration of the cell bodies of nigrostriatal dopaminergic neurons projecting to the dorsal striatum.
In order to investigate the role of nigral oxytocin in locomotor activity, a combined approach comprehensive of immunohistochemical, behavioural and lesion studies, has been used in male rats. First, the effect on locomotor activity of low and high doses of oxytocin, given intraperitoneally or into the substantia nigra, and of d(CH2)5Tyr(Me)2-Orn8-vasotocin, a selective oxytocin receptor antagonist, given into the lateral ventricles or into the substantia nigra, were studied in male rats habituated to the experimental conditions in order to avoid novelty-induced behavioural effects. Second, the presence of nigral oxytocinergic fibres and their localization with respect to nigral neurons immunoreactive for tyrosine hydroxylase (TH) (a marker of dopaminergic neurons) was investigated by immunohistochemistry. Finally, the effect on spontaneous locomotor activity of the bilateral injection into the substantia nigra of oxytocin-saporin (OXY-SAP), a recently discovered neurotoxin that specifically destroys neurons presenting oxytocinergic receptors on their surface, was studied in relation to the modifications induced in the dopaminergic, glutamatergic and GABAergic systems, assessed by immunohistochemistry using antibodies against TH, vesicular glutamate transporters (VGluT1, VGluT2 and VGluT3) and glutamate decarboxylase (GAD). Together, the results of the above experiments with oxytocin and d(CH2)5Tyr(Me)2-Orn8-vasotocin and those with OXY-SAP, which revealed the existence of a correlation between the changes in locomotor activity found in OXY-SAP-treated rats and the extent of the changes in nigral TH, VGluT1, VGluT2 and VGluT3 immunoreactivities measured at 28 days after OXY-SAP injection, provide support for a modulatory role of oxytocin on locomotor activity at the level of the substantia nigra.
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ESPA, ELENA. « Meccanismo d'azione del Pramipexolo nella terapia della malattia di Parkinson ». Doctoral thesis, Università degli Studi di Cagliari, 2015. http://hdl.handle.net/11584/266366.
Texte intégralRésumé :
Pramipexole (PPX) is a dopamine (DA) D3 and D2 receptors agonist widely used alone or in combination with levodopa as Dopamine Replacement Therapy in Parkinson’s disease. In clinical and preclinical studies, PPX improved motor deficits, this evidence led to lowering daily dose of levodopa, delaying the motor side effects associated with its use. Recently, PPX administration has been associated to the development of addictive-like behaviors related to the DA Dysregulation Syndrome, particularly in a subpopulation of treated patients, characterized by impulsive-compulsive personality traits as well as previous addiction’s experience.
Based on these evidences, the aim of this study was twofold: first to investigate the pharmacological action of PPX, using a unilateral model of Parkinson’s disease in which 6-OHDA was injected in the medial forebrain bundle. After two weeks, we tested in primed and naive rats, the ability of three different doses of PPX (0,035; 0,1 and 0,35 mg/kg s.c.), to induce contralateral turning behavior as well c-fos expression after pretreatment of DA D1 antagonist SCH 39166. Next, we checked the ability of PPX to induce contralateral rotations after D2 (eticlopride) and D3 (S33084) DA antagonist pretreatment. In order to investigate the role of PPX (0,05 mg/kg s.c.) in behavioral sensitization, we tested its effect with S33084 pretreatment in levodopa sensitized rats.
Second, we assessed the correlation between PPX treatment, Parkinson’s disease and the onset of DA Dysregulation Syndrome on Conditioned Place Preference (CPP) paradigm. To do this, 6-OHDA was injected bilaterally in DA striatal terminals, in three different strains of rat: the addiction prone Lewis (LEW), the addiction resistant Fisher 344 (F344) inbred strains, and the Sprague Dawley (SD) outbred strain. Furthermore, to test its rewarding properties, PPX was directly infused in the nucleus accumbens shell (NAc), a DA mesolimbic region known to be involved in the rewarding effects of drugs of abuse, in healthy rats belonging to the above mentioned strains.
We discovered that in primed rats, PPX (0,35 mg/kg s.c.) induced turning behavior that was increased by SCH 39166 pretreatment (0,1 mg/kg s.c.). No effect was seen in naive rats both for turning behavior and c-fos expression. D2 receptors antagonist eticlopride (0,1 mg/kg s.c.) reduced PPX-induced turning behavior more than D3 receptors antagonist S33084 (0,5 mg/kg s.c.), also a previous levodopa sensitization increased PPX-induced turning behavior on its first administration. This suggests that PPX’s action could be related to D2 stimulation, and it seems to require a previous D1/D2 stimulation to observe a behavioral outcome.
PPX (1 mg/kg s.c.) was able to induce a significant CPP in SD and LEW lesioned rats but not in F344 and control rats, and the persistence of preference was stronger in LEW than in SD rats. When injected into the NAc shell, PPX (5 μg/0.5 μl) induced CPP in all rat strains, but the persistence of its effect was more strong in LEW compared to SD and F344 rats. These results suggest that the parkinsonian state might be more sensitive to the rewarding properties of PPX, which do not seem entirely influenced by phenotype.
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CAVALLERI, LAURA. « Generazione e caratterizzazione di neuroni dopaminergici mesencefalici umani derivati da cellule staminali pluripotenti indotte da utilizzarsi come componente di dispositivi terapeutici per parkinsonismi ». Doctoral thesis, Università degli studi di Modena e Reggio Emilia, 2022. http://hdl.handle.net/11380/1273446.
Texte intégralRésumé :
La degenerazione dei neuroni dopaminergici (DA) del mesencefalo ventrale è considerata uno dei segni distintivi della malattia di Parkinson (PD) e del Parkinsonismo. La loro suscettibilità al danno e la loro adattabilità e plasticità sono state inizialmente studiate in modelli animali per comprendere i meccanismi cellulari e molecolari e l'azione delle terapie farmacologiche. La recente introduzione della tecnologia delle cellule staminali pluripotenti indotte umane (iPSCs) e lo sviluppo di protocolli per la loro differenziazione in neuroni con un fenotipo DA ha permesso la valutazione diretta dei meccanismi cellulari del PD e del Parkinsonismo, il meccanismo d'azione dei farmaci antiparkinsoniani e le applicazioni esplorative di vari aspetti della terapia cellulare.
Lo scopo di questa tesi è la generazione e la caratterizzazione fenotipica di neuroni DA umani utilizzabili come strumento per lo sviluppo di una varietà di dispositivi terapeutici basati sulla terapia cellulare, in particolare dispositivi elettronici impiantabili interamente organici. Questi dispositivi sono stati progettati per essere impiantati in modelli animali di PD per una terapia loco-regionale guidata da stimoli elettrici e chimici per supportare l'attecchimento dei precursori dei neuroni DA, massimizzando la loro differenziazione e funzione.
Al fine di ottenere precursori di neuroni DA umani di alta qualità e riproducibili che siano in grado di differenziarsi e maturare in neuroni DA funzionali che rispondono a stimoli elettrici e chimici, questo lavoro è stato organizzato in quattro sottoprogetti principali.
Il primo sottoprogetto è stato dedicato all'ottimizzazione dei metodi di differenziazione delle iPSCs umane in precursori dei neuroni DA mesencefalici utilizzando un protocollo precedentemente pubblicato (Fedele et al. 2017). Questi precursori dei neuroni DA possono essere espansi per diversi passaggi e conservati in azoto liquido per qualsiasi uso futuro.
Il secondo sottoprogetto è stato dedicato alla differenziazione dei precursori DA mesencefalici in neuroni DA maturi che sono stati caratterizzati mediante immunofluorescenza, PCR quantitativa, HPLC ed analisi elettrofisiologiche. Il fenotipo DA dei neuroni è stato studiato testando la loro risposta a due agonisti dopaminergici (pramipexolo e piribedil) attualmente utilizzati per il trattamento del PD. Dati recenti hanno dimostrato un effetto neurotrofico prodotto da un agonista antiparkinsoniano del recettore DA D2/D3, il ropinirolo (Collo et al. 2018). Sulla base di questi risultati, sono stati valutati gli effetti cellulari e molecolari di pramipexolo e piribedil sui neuroni DA umani studiando i cambiamenti morfologici correlati alla plasticità strutturale e l'attivazione delle vie intracellulari. Sono state studiate anche le proprietà neuroprotettive e neurorigenerative di questi due agenti farmacologici.
Il terzo sottoprogetto è stato dedicato allo studio degli effetti della stimolazione elettrica sulla plasticità strutturale dei neuroni DA umani. Diversi lavori hanno dimostrato che la stimolazione elettrica può promuovere la differenziazione neuronale e la crescita dei neuriti di vari tipi di cellule neuronali in vitro, tra cui PC12 e cellule staminali neurali umane.
Il quarto sottoprogetto è stato dedicato alla generazione di iPSCs umane da cellule mononucleate del sangue periferico (PBMCs) donate da nuovi controlli sani e pazienti affetti da un Parkinsonismo, l’atrofia multisistemica (MSA). I cloni di iPSCs ottenuti dal controllo e dal paziente sono stati sottoposti a caratterizzazione fenotipica per esaminare la presenza di marcatori di pluripotenza mediante immunofluorescenza, PCR quantitativa, analisi del cariotipo, pluripotenza e capacità di differenziazione nei tre foglietti embrionali. Le iPSCs sono state successivamente differenziate in neuroni DA mesencefalici e valutate per la loro risposta farmacologica agli agonisti dopaminergici.The degeneration of dopaminergic (DA) neurons of the ventral mesencephalon is considered one of the hallmarks in Parkinson’s disease (PD) and Parkinsonism. Their susceptibility to damage and their adaptability and plasticity were initially studied in animal models in order to understand the cellular and molecular mechanisms and the action of pharmacological therapeutics. The recent introduction of human inducible pluripotent stem cells (iPSCs) technology and the development of protocols for their differentiation into neurons with a DA phenotype has permitted the direct evaluation of cellular mechanisms of PD and Parkinsonism, the mechanism of action of anti-parkinsonian drugs and the exploratory applications of various aspects of cell therapy. The aim of this thesis was the generation and phenotypic characterization of human DA neurons amenable to be used as a tool for the development of a variety of therapeutic devices based on cell therapy, in particular implantable whole-organic electronic devices. These devices were designed to be implanted in animal models of PD for a loco-regional therapy driven by electrical and chemical stimuli to support the engraftment of DA neuron precursors, maximizing their differentiation and function. In order to achieve high quality and reproducible human DA neuron precursors that are able to differentiate and mature into functional DA neurons that respond to electrical and chemical stimuli, therefore amenable to the above described use, this work was organized in four main subprojects. The first subproject was dedicated to the optimization of the methods of differentiation of human iPSCs into mesencephalic DA neuron precursors using a previously published protocol (Fedele et al. 2017). These DA neuron precursors can be expanded for several passages and stored in liquid nitrogen for any future use. The second subproject was dedicated to the differentiation of mesencephalic DA precursors into mature DA neurons that were characterized by immunofluorescence, quantitative PCR, HPLC and electrophysiological analyses. The DA phenotype of the neurons was investigated by testing their response to two dopaminergic agonists (i.e., pramipexole and piribedil) currently used for the treatment of PD. Recent data have demonstrated a neurotrophic effect produced by an anti-parkinsonian DA D2/D3 receptor (D2R/D3R) agonist, ropinirole (Collo et al. 2018). Based on these findings, the cellular and molecular effects of pramipexole and piribedil on human DA neurons were evaluated by studying morphological changes related to structural plasticity and the activation of intracellular pathways. The neuroprotective and neuroregenerative properties of these two pharmacological agents were also studied. The third subproject was dedicated to the study of the effects of the electrical stimulation on the structural plasticity of human DA neurons. Several reports have shown that electrical stimulation can promote neuronal differentiation and neurite growth of various neuronal cell types in vitro, including PC12 (Jing et al. 2019) and human neural stem cells (Stewart et al. 2015). The fourth subproject was dedicated to the generation of human iPSCs from peripheral blood mononuclear cells (PBMCs) donated from a novel set of healthy controls and patients affected by a Parkinsonism, i.e., the multiple system atrophy (MSA). The iPSC clones obtained from the control and the patient underwent a phenotypic characterization to examine the presence of pluripotency markers by immunofluorescence and quantitative PCR analysis, karyotype analysis, pluripotency and trilineage differentiation potential. The iPSCs were subsequently differentiated into mesencephalic DA neurons and assessed for their pharmacological response to dopaminergic agonists.
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SCIAMANNA, GIUSEPPE. « La disfunzione del recettore striatale D2 induce un’alterata trasmissione GABAergica in un modello murino di distonia DYT1 ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/849.
Texte intégralRésumé :
La distonia DYT1 è una grave forma di distonia generalizzata causata da una mutazione del gene DYT1 che codifica per la proteina TorsinA. La funzione di tale proteina rimane ancora poco chiara anche se è stato proposto che possa svolgere importanti funzioni nel traffico proteico intracellulare e nei processi secretori. Lo striato, all'interno dei gangli della base svolge un importante ruolo nella regolazione dell'attività motoria, ed alterazioni a carico di tale struttura appaiono essere coinvolti nella patogenesi della distonia. Ho registrato pertanto le correnti sinaptiche spontanee sia di tipo
GABAergico che glutamatergico in neuroni spinosi striatali (MSNs) da animali che sovraesprimevano la proteina umana mutata (hMT) confrontandoli poi con animali di controllo (CTRL) e con quelli che esprimevano la proteina umana non-mutata (hWT). Gli animali mutati presentavano
un significativo aumento nella frequenza degli eventi sinaptici GABAergici (sIPSCs) non accompagnato però da variazioni nell'ampiezza di tali correnti. Al contrario l'attività spontanea di tipo glutamatergico (sEPSC) risultava essere del tutto normale.
L'inibizione GABAergica striatale è di origine esclusivamente instrinseca e deriva da due distinte fonti. Una delle più importanti tuttavia fa capo agli interneuroni GABAergici Fast Spiking
(FS). Ho pertanto verificato l'ipotesi che tali cellule potessero presentare alterazioni nella loro normale funzionalità. Sia gli sIPSCs che gli sEPSC registrati risultavano tuttavia essere invariati fra
gli animali hMT, hWT e quelli di controllo.
In condizioni fisiologiche l'attivazione del recettore dopaminergico D2 agisce
presinapticamente inibendo il rilascio di GABA. Nei MSNs di animali di controllo e hWT, tale funzionalità risultava essere del tutto preservata. L'applicazione di quinpirolo (agonista D2-like)
portava infatti ad una significativa riduzione della frequenza degli sIPSCs misurati. Tale effetto
tuttavia era assente negli animali hMT. Inoltre sia MSNs sia FS di topi hMT non presentavano l'effetto inibitorio tipico del quinpirolo sulle correnti sinaptiche evocate tramite stimolazione elettrica (eIPSCs).
In conclusione il mio lavoro dimostra la presenza di un'alterata attività del circuito
GABAergico striatale in un modello animale di distonia DYT1, che può essere in parte giustificata da una disfunzione del recettore dopaminergico D2.DYT1 dystonia is a severe form of inherited generalized dystonia, caused by a deletion in the DYT1 gene encoding the protein torsinA. The physiological function of torsinA is unclear, though it has been proposed to perform chaperone-like functions, assist in protein trafficking, membrane fusion and participate in secretory processing. Alterations in GABAergic signaling have been involved in the pathogenesis of dystonia. I recorded GABA- and glutamate-mediated synaptic currents from striatal neurons obtained from a mouse model of DYT1 dystonia. In medium spiny neurons (MSNs) from mice expressing human mutant torsinA (hMT), we observed a significantly higher frequency, but not amplitude, of GABAergic spontaneous inhibitory postsynaptic currents (sIPSCs) and miniature currents (mIPSCs), whereas glutamatergic spontaneous excitatory synaptic potentials (sEPSCs) activity was normal. No alterations were found in mice overexpressing normal human torsinA (hWT). To identify the possible sources of the increased GABAergic tone, I recorded GABAergic Fast-Spiking (FS) interneurons that exert a feed-forward inhibition on MSNs. Both sEPSC and sIPSC recorded from hMT FS interneurons were comparable to hWT and controls.In physiological conditions, dopamine (DA) D2 receptor act presynaptically to reduce striatal GABA release. Notably, application of the D2-like receptor agonist quinpirole failed to reduce the frequency of sIPSCs in MSNs from hMT as compared to hWT and controls. Likewise, the inhibitory effect of quinpirole was lost on evoked IPSCs both in MSNs and FS interneurons from hMT mice. My findings demonstrate a disinhibition of GABAergic synaptic activity, that can be partially attributed to a D2 DA receptor dysregulation. A rise in GABA transmission would result in a profound alteration of striatal output, that might be relevant to the pathogenesis of dystonia.
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Bloomfield, Michael. « Dopaminergic mechanisms underlying psychosis ». Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/44332.
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Schizophrenia is a potentially devastating mental illness with a complex aetiology, in which the odds ratios for environmental risk factors for the disorder are greater than the odds ratios of any single gene hitherto identified. Within schizophrenia, striatal dopamine dysfunction has been proposed to underlie the development of psychosis. The Aberrant Salience hypothesis provides an explanatory model based on empirical findings to explain how psychotic symptoms may arise from striatal hyperdopaminergia, whereby multiple risk factors converge to elevate striatal dopamine synthesis capacity as the Final Common Pathway to psychosis. Two important epidemiological risk factors for the disorder are chronic cannabis use and longterm psychosocial stress, both of which have evidence supporting effects on the dopamine system. Environmental risk factors are by their very nature modifiable, and so this thesis examined whether these environmental risk factors were associated with the same dopaminergic abnormalities that have been observed in schizophrenia with 3,4-dihydroxy-6- [18F]-fluoro-l-phenylalanine Positron Emission Tomography. This thesis also examined whether cannabis users exhibit aberrant salience processing using a behavioural task, the Salience Attribution Task. This thesis found that long-term cannabis use was associated with reduced dopamine synthesis capacity and no relationship was found between striatal dopamine synthesis capacity and cannabis-induced psychotic-like symptoms. Whilst cannabis use was not associated with increased aberrant salience processing, there was a relationship between cannabis-induced psychotic-like symptoms and aberrant salience processing. This thesis found that long-term psychosocial stress is associated with reduced dopamine synthesis capacity, although this finding may be due confounding factors. However, a positive relationship was observed between childhood and recent adult stressors and dopamine synthesis capacity. These findings call into question the hypothesis that cannabis increases the risk of psychosis by inducing the same changes observed in schizophrenia, although there some evidence to support the hypothesis that psychosocial stressors do increase risk via this mechanism.
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Szostak, Carolyn Margaret. « Dopaminergic mechanisms in conditioned circling ». Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/29438.
Texte intégralRésumé :
After unilateral lesions of the mesotelencephalic dopamine (DA) system, the administration of DA receptor agonists results in circling. This response is believed to reflect an asymmetry in mesotelencephalic DA activity. Moreover, drug-induced circling is thought to be directed away from the projection of higher dopaminergic activity. Recently, it has been reported that circling can be established and maintained using operant procedures in surgically intact and drug naive rats. The phenomenon of conditioned circling has been associated with an asymmetrical change in DA metabolism within the striatum and nucleus accumbens. The present series of experiments was designed to characterize further the involvement of mesotelencephalic DA in conditioned circling.
Rats trained to circle for water according to a continuous schedule of reinforcement did not exhibit increased DA metabolism within either the striatum or the nucleus accumbens (Experiment I). However, a bilateral augmentation was observed when rates of responding were increased by implementing an intermittent schedule of reinforcement (Experiment II). Concurrent increases in the biosynthesis of DA, as estimated by accumulation of DOPA following the administration of a DOPA decarboxylase inhibitor, were not observed (Experiment III). Experiments IVa and IVb examined the extent to which inherent directional biases, which play a role in determining the magnitude and direction of drug-induced circling, influenced the acquisition and performance of the conditioned circling response. No effects were evident. Moreover, a symmetrical, bilateral enhancement in DA metabolism was observed in the striatum, irrespective of directional preferences. While conditioned circling can be established and maintained by reinforcing the response with food, food itself influenced DA metabolism and therefore precluded the detection of changes in DA metabolism specific to the circling response. Specifically, striatal and accumbens DA metabolism was augmented to a similar extent in animals given matched amounts of non-contingently presented food (Experiment V). Concentrations of DA, DOPAC and homovanillic acid (HVA) were found to be differentially distributed throughout the striatum (Experiment Via), suggesting a possible chemical basis for the heterogeneity of striatal DAergic functions. Changes in striatal DA metabolism associated with conditioned circling were observed only within localized regions of the anterior striatum (Experiment VIb). All changes noted were, however, bilateral in nature. Finally, unilateral lesions of the mesotelencephalic DA projection, following the establishment of the conditioned circling response, disrupted responding, irrespective of the relative locus of the lesion (i.e. ipsilateral or contralateral to the direction of turning) (Experiment VII). However, the extent of the behavioral deficit was more severe following contralaterally placed lesions.
It is concluded that circling, established and maintained by positive reinforcement, is subserved by a bilateral augmentation in DA metabolism within the nucleus accumbens and discrete regions of the striatum. However, lesion studies indicate an asymmetrical involvement of the ipsilateral and contralateral projections in this response.Medicine, Faculty of
Graduate
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Stopper, Colin Michael. « Dopaminergic mechanisms guiding probabilistic choice ». Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46395.
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Maci, Tiziana. « Dopaminergic System and cognitive function ». Thesis, Universita' degli Studi di Catania, 2011. http://hdl.handle.net/10761/100.
Texte intégralRésumé :
I pazienti con malattia di Parkinson (PD) presentano deficit di elaborazione temporale. Gli effetti della terapia con L-dopa sulla capacita' di stimare lo scorrere del tempo non sono ancora chiari in quanto sono stati osservati sia effetti positivi che negativi. Il presente studio e' stato progettato per analizzare la capacita' di stimare la durata di intervalli di tempo sia brevi che unghi in pazienti con PD, e l'effetto della somministrazione di L-dopa.
Dieci pazienti con PD sono stati confrontati con 10 soggetti sani appaiati per eta' e scolarita'. Abbiamo valutato la possibilita' di stimare gli intervalli di tempo tra 1 a 5 s (brevi intervalli di tempo), cosi' come intervalli di 40-90 s (lunghi intervalli di tempo). Per la stima del tempo, abbiamo utilizzato sia prove che richiedono conteggio mentale nonche' compiti che non lo consentono. Nei pazienti con PD, gli effetti della L-dopa sulla stima del tempo sono stati valutati confrontando i risultati ottenuti prima (OFF) e due ore dopo la somministrazione del farmaco (ON).
La stima di brevi intervalli di tempo, quando era possibile il conteggio mentale, ha dimostrato che i pazienti con PD in stato OFF percepivano, rispetto ai controlli, gli intervalli di tempo come piu' lunghi del normale. Questa condizione si normalizzava in stato ON, cosi' da non essere significativamente diversa dai controlli. Quando non e' stato consentito il conteggio mentale, i pazienti in stato OFF eseguivano la stima del tempo peggio dei soggetti normali e la somministrazione di L-dopa (stato ON), invece di normalizzare la condizione, ha aumentato il tasso di errore. Nella stima degli intervalli di tempo piu' lunghi, i pazienti con PD in stato OFF mostravano solo un errore modesto nella stima del tempo, che migliorava dopo assunzione di L-dopa, sia quando il conteggio mentale era possibile sia quando non lo era.
Nei pazienti con PD, la stima del tempo dipende dalla disponibilita' di dopamina. Per la stima di brevi intervalli di tempo, la L-dopa sembra avere una duplice azione paradossa: migliora la prestazione quando il conteggio e' possibile e peggiora la stima quando il conteggio mentale non e' possibile e, quindi, presumibilmente altri meccanismi cognitivi sono coinvolti. Pertanto, i diversi comportamenti osservati in seguito alla somministrazione di L-dopa sulla stima di brevi e lunghi intervalli indicano il coinvolgimento di diversi timer interni.Patients with Parkinson's disease (PD) have been reported to have deficient temporal processing. The effects of L-dopa therapy on time evaluation are not yet clear; in fact both positive and negative effects have been observed. The present investigation was designed to analyze the capability of estimating short as well as long time intervals in PD patients and the effect of dopamina replacement by L-dopa administration. Ten PD patients were compared with 10 age- and education-matched controls. We evaluated the capability of estimating time intervals in the range from 1 to 5 s (short intervals) as well as from 40 to 90 s (long intervals). For the time estimation, we used tasks requiring internal count as well as tasks that did not allow it. In PD patients, the effects of L-dopa on time estimation was assessed by comparing the results obtained before (OFF) and two hours after drug administration (ON). Time estimation of short intervals, when the internal count was allowed, demonstrated that patients with PD in OFF state perceived the time intervals longer than usual compared to normal controls. This condition normalized in ON state, being not significantly different from normal subjects. When internal counting was not allowed, PD patients in OFF state performed worse than normal subject, but L-dopa administration, instead to normalize the condition, increased the error rate in ON state. In the estimation of long time intervals, PD patients in OFF state displayed only a modest impairment, slightly improved by L-dopa intake, in both conditions (counting or not counting). In patients with PD, the time estimation is dependent from dopamine availability. For short time intervals estimation, L-dopa had a paradoxical dual action, ameliorating the estimates when motor mechanisms (internal counting) were presumably involved and worsening the estimates when other cognitive mechanisms were requested (qualitative evaluation). Moreover, the different behaviors following L-dopa administration observed for short and long estimates suggest the involvement of different internal timers.
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DE, SANCTIS Claudia. « MicroRNAs profiling in Dopaminergic neurons ». Doctoral thesis, Università degli studi del Molise, 2018. http://hdl.handle.net/11695/83499.
Texte intégralRésumé :
Lo sviluppo dei neuroni dopaminergici mesencefalici (mDA) è un fenomeno complesso e non ancora pienamente compreso. Molti studi hanno focalizzato la loro attenzione sul ruolo svolto da diversi fattori di trascrizione specifici e ben noti. L'obiettivo della mia tesi di dottorato è focalizzato su una classe relativamente nuova di regolatori post-trascrizionali denominati microRNA (miRNAs), in grado di regolare l'espressione genica legando le sequenze parzialmente complementari nelle regioni 3' non tradotte (UTR) degli mRNAs target.
Per studiare il ruolo svolto dai miRNAs durante la differenziazione dei neuroni mDA, abbiamo scelto di analizzare il profilo di espressione dei miRNA usando piattaforme di Array. A tale scopo, abbiamo utilizzato un protocollo ottimizzato da cellule staminali di epiblasto di topo (epiSC) differenziate in neuroni mDA (Jeager et al.,2011).
Dall'analisi bioinformatica dei dati dell'array, ottenuti dalle epiSC differenziate in neuroni mDA, abbiamo identificato alcuni candidati molto probabilmente implicati nella differenziazione e nella funzione dei neuroni DA. I miRNA candidati sono stati sottoposti a screening per la loro capacità di indurre il fenotipo DA. A questo scopo, ho generato vettori lentivirali inducibili per ciascun miRNAs e ho infettato colture primarie mesencefaliche di topo allo stadio E12.5. Tra tutti i miRNA candidati, miR-218 e miR-34b/c aumentano il numero di cellule TH + positive, suggerendo il loro possibile contributo nei neuroni mDA. Inoltre, miR-218 e miR-34b/c, risultano arricchiti sia nel mesencefalo dei topi (E13.5) che nelle cellule GFP + sortate al FACS, isolate da embrioni E13.5 Pitx3-GFP di topo, rispetto al controllo.
I dati ottenuti dal saggio di Luciferasi e dal saggio di reporter a doppia fluorescenza suggeriscono che miR-34b/c legano e sopprimono la 3'UTR di Wnt1 e viene espresso durante la differenziazione dei neuroni mDA.
Tramite analisi di ibridazione in situ e dati d’ immunoistochimica ho potuto verificare che miR-218 è espresso in particolare nel mesencefalo di topo allo stadio E14, dove co-localizza rostralmente con Isl-1 (marcatore di motoneuroni) e caudalmente con TH, Pitx3, Lmx1a (marcatori dopaminergico). Questi dati suggeriscono che miR-218 è espresso anche nei motoneuroni craniali, come descritto in altri recenti studi (Thiebes, K.P. et al., 2014; Amin, N.D et al., 2015).
Per comprendere ulteriormente il ruolo di miR-218 nello sviluppo e nella funzione dei neuroni dopaminergici ho generato topi knock-out condizionali (cKO) per miR-218-2. Accoppiando miR-218-2 flox / flox con topi En1Cre /+ che esprimono Cre sotto il controllo del promotore di Engrailed 1 (En1, marker pro-dopaminergico), sarò in grado di comprendere il contributo di miR-218 nel sistema dopaminergico. I topi miR-218-2 flox / flox En1Cre /+ da osservazioni preliminari, hanno mostrato un fenotipo con danno motorio, ma per confermare questi dati sto attualmente effettuando test comportamentali e analisi in vivo. Attraverso il profilo di espressione di miRNAs, siamo in grado di comprendere il meccanismo e la funzione del sistema dopaminergico, poiché i miRNAs sono regolatori chiave nelle reti di espressione genica, possono influenzare molti processi biologici e in futuro potrebbero essere utilizzati come biomarkers per diagnosticare patologie legate al sistema nervoso.Midbrain dopaminergic neurons (mDA) development is a complex and still not fully understood phenomenon. Many studies till now concentrated their attention on the roles played by several, specific and well-known transcription factors. The aim of my PhD thesis is focus on a relatively new class of post-transcriptional regulators named microRNAs (miRNAs) able to regulate gene expression by targeting partially complementary sequences in the 3’untranslated regions (UTRs) of the target mRNAs. To investigate the role played by miRNAs during mDA differentiation, we choose to analyze miRNAs expression profile by using miRNA Array platforms. To this purpose we used an optimized protocol from mouse Epiblast stem cells (epiSC) differentiated into DA neurons (Jeager et al. 2011). By bioinformatics analysis of the array data, obtained from epiSC differentiated into mDA neurons, we identified few candidates most likely implicated in the DA neurons differentiation and function. The candidate miRNAs were screened for their ability to induce DA phenotype. To this purpose, I generated inducible lentiviral vectors for each miRNA and I have infected mesencephalic primary cultures from mice at stage E12.5. Among all candidate miRNAs, miR-218 and miR-34b/c increase the number of TH+ positive cells, showing their possible contribution in the mDA neurons. Moreover, miR-218 and miR-34b/c, were enriched both in midbrain of mice (E13.5) and in FACS sorted GFP+ cells isolated from E13.5 Pitx3-GFP mice embryos when compared with control. Data obtained from Luciferase Assay and Dual Fluorescence Reporter Assay suggest that miR-34b/c target and suppress Wnt1 3’UTR and it is expressed during DA neurons differentiation. By performing In situ hybridization analysis and immunohistochemistry, I was able to detect miR-218 in particular in the mouse midbrain at stage E14, where co-localize rostrally with Isl-1 (motor neuron marker) and caudally with TH, Pitx3, Lmx1a (dopaminergic marker). This data suggests that miR-218 is expressed also in cranial motor neurons, as described in others recent studies (Thiebes, K.P. et al. 2014; Amin, N.D et al. 2015). To further understand the role of miR-218 in development and function of dopaminergic neurons I have generated the conditional knock-out (cKO) mice for miR-218-2. By mating miR-218-2 flox/flox with En1Cre/+ mice expressing the Cre under Engrailed 1 promoter (En1 is a pro-dopaminergic marker) I will be able to investigate the contribution of miR-218 in dopaminergic system. Preliminary observations on miR-218-2 flox/flox En1Cre/+ mice shown motor impairment phenotype, but to confirm this data I’m currently performing behavior tests and in vivo analysis. Through miRNA expression profiling we be able understand mechanism and function of dopaminergic system, because miRNAs are as key regulators in gene expression networks, can influence many biological processes and have also shown promise as biomarkers for neuro-disorders.
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Zietlow, Rike. « Factors affecting the survival of embryonic dopaminergic neurones after transplantation ». Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624313.
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Lak, Armin. « Encoding of economic value by midbrain dopamine neurons ». Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648342.
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PES, ROMINA. « Ruolo dei neurosteroidi nella modulazione dopaminergica ». Doctoral thesis, Università degli Studi di Cagliari, 2015. http://hdl.handle.net/11584/266803.
Texte intégralRésumé :
Cogent evidence shows that neurosteroids play a key role in the modulation of
dopaminergic responses in the brain. Several findings have shown that these
compounds can affect the severity of DRT- induced effects in well validated
animal models. Over the last few years, we have characterized that inhibition of
5 alpha- reductase (5AR), the key enzyme for androgen metabolism and
neurosteroid synthesis, elicts antidopaminergic effects. The 5AR inhibitor,
finasteride (FIN), is currently approved for the therapy of benign prostatic
hyperplasia and androgenic alopecia. We found that, in rodents, FIN attenuates
the severity of behavioral manifestations induced by dopaminergic agents,
including deficits of sensorimotor gating as well as repetitive and compulsive
responses. Unlike other antidopaminergic agents, however, FIN does not elicit
catalepsy or other extrapyramidal side-effects.
To extend these findings, this thesis is aimed at the assessment of the role of
other key neurosteroidogenic enzymes in PPI, such as 17α-hydroxylase/C17,20
lyase (CYP17A1), 3α- and 3β-hydroxysteroid dehydrogenase (HSD), in
Sprague-Dawley rats and we tested the drug like FIN in a reserpinized rat
probability discounting task, a behavioral paradigm aimed at capturing critical
behavioral aspect of gambling disorder, namely the preference for large,
uncertain rewards, rather than small certain rewards.
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Aron, Liviu. « Genetic analysis of dopaminergic neuron survival ». Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-117874.
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Racz, Karoly. « Peripheral dopaminergic mechanisms in experimental hypertension ». Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72776.
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Lokwan, S. J. A. « Excitatory regulation of central dopaminergic neurones ». Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637946.
Texte intégralRésumé :
The regulation of midbrain dopaminergic (DAergic) neurones by excitatory afferents, especially afferents which utilise excitatory amino acids (EAAs), was investigated using single unit extracellular recording and iontophoretic techniques in chloral hydrate anaesthetised rats. It is well documented that DAergic neurones fire action potentials in a pattern which consists of single spikes or bursts. Evidence suggests that tonically active EAAergic afferents induce burst firing in DAergic neurones. Since the pedunculopontine tegmental nucleus (PPTg) is one source of EAAergic afferents, its potential role in mediating burst firing in DAergic neurones was investigated. Single pulse electrical stimulation applied to the PPTg (and other sites in the rostral pons) elicited a response in the majority of DAergic neurones located in the substantia nigra pars compacta (A9 cell group), consisting of long-latency, long-duration excitations (E responses) or inhibition-excitations (IE responses). 37% of responses elicited by stimulation of the PPTg contained bursts closely time-locked to the stimulation: non-PPTg sites were less effective in this regard. The bursts themselves had a mean latency of 96.2 ms, which is shorter than that of bursts in A9 DAergic neurones elicited by stimulation of the medial prefrontal cortex (mPFC; 152 ms). Since the mPFC has been implicated in the production of bursts in DAergic neurones, the present results raise the possibility that bursts arise in these cells via a polysynaptic route which involves the PPTg. It has recently been hypothesised that bursts in DAergic neurones are initiated by a burst of activity in EAAergic afferent fibres. This burst activates receptors of the N-methyl-D-aspartate subtype of EAA receptor to produce a slow depolarising wave in the cell.
20
Fallon, S. J. « Dopaminergic modulation of planning and attention ». Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598929.
Texte intégralRésumé :
This thesis has explored the neurochemical and psychological basis of cognitive heterogeneity, particularly within the domains of planning and attention, and the relationship that deficits in these domains have between each other. The neurochemical basis of these deficits was examined by investigating the extent to which a genetic polymorphism in the Catechol O-methyltransferase (COMT) enzyme, an enzyme thought to modulate PFC dopamine levels, influenced participants’ cognitive performance. This thesis was able to establish that, whilst there appears to be an inverted-U shape function between putative PFC dopamine levels and attention set-formation (a measure of attentional structure), there is no evidence for supposing that such a relationship exists between PFC dopamine levels and planning ability. The psychological basis of cognitive heterogeneity in PD patients was probed by examining ability of PD patients to establish a demarcation between relevant and irrelevant information, and rapidly update this demarcation. Overall, it was found that PD patients did not have generic difficulty in distinguishing between relevant and irrelevant information, or in updating this distinction. Rather, such deficits were only found in certain experimental contexts, further underlying the specificity of attentional impairments in PD. Overall planning performance in PD patients and healthy older adults was not found to predict attentional dysfunction. Thus, there appears to be a separate, or relatively independent, basis for impairment in these two domains.
21
Dommett, Eleanor Jane. « Sensory regulation of midbrain dopaminergic neurons ». Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425614.
Texte intégral
22
Vander, Weele Caitlin Miya. « Dopaminergic modulation of prefrontal cortex subpopulations ». Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120628.
Texte intégralRésumé :
Thesis: Ph. D. in Neuroscience, Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2018.Cataloged from PDF version of thesis. Page 176 blank.
Includes bibliographical references (pages 159-175).
Despite abundant evidence that dopamine modulates medial prefrontal cortex (mPFC) activity to mediate diverse behavioral functions, the precise circuit computations remain elusive. One potentially unifying theoretical model by which dopamine can modulate functions from working memory to schizophrenia is that dopamine serves to increase the signal-to-noise ratio in mPFC neurons, where neuronal activity conveying sensory information (signal) are amplified relative to spontaneous firing (noise). To connect theory to biology, we lack direct evidence for dopaminergic modulation of signal-to-noise in neuronal firing patterns in vivo and a mechanistic explanation of how such computations would be transmitted downstream to instruct specific behavioral functions. Here, we demonstrate that dopamine increases signal-to-noise ratio in mPFC neurons projecting to the dorsal periaqueductal gray (dPAG) during the processing of an aversive stimulus. First, using electrochemical approaches, we reveal the precise time course of tail pinch-evoked dopamine release in the mPFC. Second, we show that dopamine signaling in the mPFC biases behavioral responses to punishment-predictive stimuli, rather than reward-predictive cues. Third, in contrast to the well-characterized mPFC-NAc projection, we show that activation of mPFC-dPAG neurons is sufficient to drive place avoidance and defensive behaviors. Fourth, to determine the natural dynamics of individual mPFC neurons, we performed single-cell projection-defined microendoscopic calcium imaging to reveal a robust preferential excitation of mPFC-dPAG, but not mPFC-NAc, neurons to aversive stimuli. Finally, photostimulation of VTA dopamine terminals in the mPFC revealed an increase in signal-to-noise ratio in mPFC-dPAG neuronal activity during the processing of aversive, but not rewarding stimuli. Together, these data unveil the utility of dopamine in the mPFC to effectively filter sensory information in a valence-specific manner.
by Caitlin Miya Vander Weele.
Ph. D. in Neuroscience
23
Mehta, Mitul Ashok. « Dopaminergic modulation of human cognitive function ». Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621792.
Texte intégral
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Decker, Amanda R. « TRPM7 function in zebrafish dopaminergic neurons ». Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/5927.
Texte intégralRésumé :
TRPM7 (Transient Receptor Potential Melastatin-like 7) is an ion channel necessary for the proper development of many cell types. Insight into the precise role of the channel in different cells has been hampered by the lethality of knocking out the gene in model organisms such as the mouse. Here I examine a zebrafish that has a loss-of-function mutation in the gene encoding Trpm7. First, I show that trpm7 is important for the function of developing dopaminergic neurons in the zebrafish. Second, I examine the interaction between trpm7 and the related gene vmat2 in order to develop a cellular mechanism of trpm7 function in presynaptic dopaminergic neurons. Finally, I investigate the necessity of the kinase and ion channel domains of trpm7 in their ability to promote pigmentation in melanophores as a model cell type. Based on the results from these experiments and observations from other researchers, I form a new hypothesis for Trpm7 function in protein sorting. These studies provide a detailed and novel analysis of the function of an ion channel that is necessary for life.
25
Yang, Wonsuk. « The bipyridyl herbicide paraquat-induced toxicity in human neuroblastoma SH-SY5Y cells : relevance to dopaminergic pathogenesis ». Texas A&M University, 2005. http://hdl.handle.net/1969.1/4384.
Texte intégralRésumé :
Paraquat (PQ) is a cationic non-selective bipyridyl herbicide widely used in
agriculture to control weeds and grasses. Epidemiologic studies indicate that exposure to
pesticides can be a risk factor in the incidence of Parkinson`s disease (PD). A strong
correlation has been reported between exposure to paraquat and PD incidence in Canada,
Taiwan, and United States. This correlation is supported by animal studies showing that
paraquat produces toxicity in dopaminergic neurons of the rat and mouse brain. However,
it is unclear how paraquat triggers toxicity in dopaminergic neurons. Based on the
previous reports, it was hypothesized that paraquat may induce oxidative stress and
proteasomal dysfunction-mediated toxicity in dopaminergic neurons. To explore this
possibility, dopaminergic SH-SY5Y human neuroblastoma cells were treated with
paraquat, and several biomarkers of oxidative stress or proteasomal dysfunction were
investigated. First, a specific dopamine transporter inhibitor GBR12909 significantly
protected SY5Y cells against the toxicity of paraquat, indicating that paraquat exerts its
toxicity by a mechanism involving the dopamine transporter (DAT). Second, paraquat increased the levels of reactive oxygen species (ROS) in SY5Y cells, but decreased the
levels of glutathione. Third, paraquat inhibited glutathione peroxidase activity, but did
not affect glutathione reductase activity. On the other hand, paraquat increased GST
activity by 24 hr, after which GST activity returned to the control value at 48 hr. Fourth,
paraquat decreased mitochondrial transmembrane potential (MTP). Fifth, paraquat
produced the increases in malondialdehyde (MDA) and protein carbonyls, as well as
DNA fragmentation, indicating oxidative damage to major cellular components. Sixth,
paraquat decreased proteasomal activity, the activities of mitochondrial complex I and V,
and intracellular ATP levels, but increased the activities of caspase 3 and 9, indicating
that proteasomal inhibition is linked to mitochondrial dysfunction accompanied by the
activation of apoptotic signaling pathway. Seventh, paraquat increased the protein levels
of heme oxygenase-1 (HO-1), p53, Bax, ñ-synuclein and ubiquitinated proteins. Eighth,
paraquat induced nuclear condensation. Taken together, these findings support the
hypothesis that paraquat produces oxidative stress and proteasomal dysfunctionmediated
toxicity in SY5Y cells. Thus, current findings suggest that paraquat may
induce the pathogenesis of dopaminergic neurons through oxidative stress and
proteasomal dysfunction.
26
Karakuyu, Dilek. « Dopaminergic and serotonergic modulation of working memory ». [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=970180993.
Texte intégral
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Korotkova, Tatiana. « Hypothalamic modulation of the midbrain dopaminergic system ». [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968537340.
Texte intégral
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St, Onge Jennifer Rose. « Dopaminergic modulation of risk-based decision making ». Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/1313.
Texte intégralRésumé :
Psychopharmacological studies have implicated the mesolimbic dopamine (DA) system in the mediation of cost/benefit evaluations about effort-related costs associated with larger rewards. However, the role of DA in risk-based decision making remains relatively unexplored. The present study investigated how systemic manipulations of DA transmission affect risky choice assessed with a probabilistic discounting task. Over discrete trials, rats between two levers; a press on the “small/certain” lever always delivered one reward pellet, whereas a press on the other, “large/risky” lever delivered four pellets, but the probability of receiving reward decreased across the four trial blocks (100%, 50%, 25%, 12.5%). In separate groups of well-trained rats we assessed the effects of the DA releaser amphetamine, as well as receptor selective agonists and antagonists. Amphetamine consistently increased preference for the large/risky lever; an effect that was blocked or attenuated by co-administration of either D₁ (SCH23390) or D₂ (eticlopride) receptors antagonists. Blockade of either of these receptors alone induced risk aversion. Conversely, stimulation of D₁ (SKF81297) or D₂ (bromocriptine) receptors also increased risky choice. In contrast, activation of D₃ receptors with PD128,907 induced risk aversion. Likewise, D₃ antagonism with nafadotride potentiated the amphetamine-induced increase in risky choice. Blockade or stimulation of D₄ receptors did not reliably alter patterns of choice. These findings indicate that DA plays a critical role in mediating risk-based decision making, where increased activation of D₁ and D₂ receptors biases choice towards larger, probabilistic rewards, whereas D₃ receptors appear to exert opposing effects on this form of decision making.
29
Hersi, Ali I. « Dopaminergic modulation of the septohippocampal cholinergic system ». Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40359.
Texte intégralRésumé :
The central cholinergic system is thought to be an integral component of the neural circuitry involved in mnemonic processes. The septohippocampal cholinergic pathway is considered crucial in this respect. In addition, however, other neurotransmitter systems are also likely involved in learning and memory either by interacting with the cholinergic system or on their own. Dopamine is postulated to be one such neurotransmitter. Accordingly, this thesis examines the possible interactions between dopamine and acetylcholine in the hippocampus, in particular in relation to cognitive processes.Using a fimbriaectomy/receptor autoradiography approach, we examined the location of hippocampal dopamine receptors and found that a proportion of dopamine D1-like receptors are likely located on cholinergic terminals in the hippocampus. Moreover, the stimulation of D1-like, but not D2-like, receptors enhanced in vivo hippocampal acetylcholine release, in a phasic manner. The loci for this action is apparently at the level of the cholinergic terminals within the hippocampus.
There are at least two members of the D1-like family of dopamine receptors, namely D1 and D5 subtypes. Owing to the unavailability of selective ligands, we utilized a combined antisense-in vivo dialysis approach in order to ascertain which of these two receptors is involved in modulating hippocampal acetylcholine release. It appears that the D5 receptor subtype is responsible for this function. Interestingly, this is the first evidence of a possible function for the dopamine D5 receptor subtype in the mammalian brain.
This dopaminergic modulation of hippocampal acetylcholine release is preserved as the animal ages. Interestingly, stimulation of D1-like receptors attenuated the memory deficits observed in aged rats in the Morris water maze task. Thus the hippocampal dopamine-acetylcholine interactions likely have a cognitive significance.
Finally, dopamine D1-like receptors were also found in the hippocampal formation of monkey and human brains. It is conceivable, therefore, that dopamine acting via these receptors might serve similar functions in primates as those described above for the rat.
Taken together, the results presented in this thesis provide information about the heteroregulation of the cholinergic synapses in the hippocampus. Most importantly, this work suggests a novel approach to alleviate age-associated memory deficits by stimulating D5 receptors.
30
Allman, Ava-Ann. « Dopaminergic effects on putative endophenotypes for schizophrenia ». Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114243.
Texte intégralRésumé :
Schizophrenia is a complex and devastating mental disorder. Genetic differences in brain function and environmental factors such as stress are thought to interact to produce the illness. In searching for genetic factors, researchers have used endophenotypes, i.e. covert differences in brain function that manifest even in the absence of a precipitating stressor. The present thesis presents three studies that look at dopamine (DA) transmission and putative endophenotypes for schizophrenia. In the first study, the effect of dextroamphetamine (D-amp), an indirect DA agonist, on eye movement tasks that may be endophenotypes for schizophrenia were studied in healthy controls. As there is some indication that the effect of DA manipulations on cognitive performance depends on initial DA levels (Barch, 2004), participants were divided into those with high or low initial performance as a proxy of their baseline DA levels (Robbins & Arnsten, 2009). D-amp was found to reduce the proportion of errors on the antisaccade task for all participants; its effect on antisaccade latency depended on initial performance, increasing correct antisaccade latency in those who initially had short latencies, and decreasing it in those who initially had long latencies. The drug had no effect on the predictive saccade task. Thus, antisaccade error rates, a putative endophenotype were reduced by DA agonists across groups, while for antisaccade latency there was evidence of an impact of initial DA level. In the second study, we examined the effects of another DA agonist, methylphenidate (MPH), on oculomotor tasks. We found that MPH had no effect on antisaccade performance. It increased the proportion of predictive saccades across all participants. The increase in predictive saccades was seen only in conditions with predictable timing, supporting a hypothesized effect of MPH on timing functions (Ben-Pazi et al, 2006; Rubia et al, 2003). Smooth pursuit, a putative oculomotor endophenotype, also improved with drug across all participants. We consider the differences between the effects of D-amp and MPH effects in terms of differences in drug action and differences between studies in terms of the implementation of the tasks. In the third study, DA system reactivity was assessed with a psychosocial stress task in a population with putative differences in DA system functioning, i.e. individuals at elevated risk for schizophrenia and healthy controls. Baseline DA and DA release were quantified with 11-C raclopride binding potential and positron emission tomography (PET) on separate days using the Montreal Imaging Stress Task and a non-stress control task. HPA axis reactivity and hippocampal volume were also assessed. Relatives had significantly lower binding potential than controls, suggestive of increased endogenous DA levels, consistent with findings in patients. Stress-induced DA release did not differ between the groups. DA release was negatively correlated with cortisol release. Hippocampal volume did not correlate with DA release but did correlate with cortisol release. Together, these findings indicate a role for DA in eye movement tasks that are putative endophenotypes for schizophrenia, and also suggest that DA system dysregulation at rest may itself be an endophenotype for the illness.La schizophrénie est un trouble mental complexe et dévastateur, considérée comme le résultat des facteurs environnementaux stressant et des troubles du système dopamine (DA). À la recherche de facteurs génétiques, les chercheurs utilisent des phénotypes intermédiaires, des différences cachées dans le fonctionnement de cerveau. La thèse suivante présente trois études examinant la transmission de DA ainsi que les phénotypes intermédiaires putatifs de la schizophrénie.Premièrement, l'effet de la dextroamphétamine (D-amp), un agoniste de DA, sur les tâches des mouvements oculaires a été étudié chez les participants sains. D-amp a réduit de la proportion des erreurs sur la tâche antisaccade mais n'a eu aucun effet sur la tâche saccade prédictive. On peut donc conclure que les taux d'erreurs chez les antisaccades, un phénotype intermédiaire putatif, ont été réduit par agoniste dopaminergiques. Nous avons ensuite examiné l'effet d'un autre agoniste de DA, le méthylphénidate (MPH), sur les tâches oculomotrices. Le MPH n'avait aucun effet sur la performance de l'antisaccade. Il augmentait la proportion des saccades prédictives uniquement chez des conditions de choix d'horaire prévisibles ; ceci appuie l'hypothèse de l'effet du MPH sur les fonctions de synchronisation. Le médicament améliore également une poursuite lisse et un phénotype intermédiaire oculomoteur putatif. Les différences entre les effets de la D-amp et le MPH sont considérées en termes de différences dans l'action des médications. Finalement, la réactivité du système DA a été évaluée avec l'aide d'une tâche de stress psychosocial chez des individus avec des risques élevés de schizophrénie et des participants sains. La DA au repos ainsi que la libération de la DA ont été quantifié avec [11]C raclopride et la tomographie par émission de positions (TEP) en utilisant la tâche du stress d'imagerie de Montréal. Ont été également évalué la réactivité de l'axe HPA et le volume l'hippocampe. Les individus avec des risques élevés avaient un pouvoir de fixation nettement plus faible que chez les participants sains, ce qui suggère un accroissement des niveaux de DA endogènes, cohérent avec les résultats chez les patients. Le stress induit par la libération de la DA ne différaient pas entre les groupes. La libération de la DA a été corrélé négativement avec la libération de cortisol. Même si le volume d'hippocampique a corrélé avec la libération de cortisol, elle n'a pas eu le même effet avec la libération de la DA. Les résultats indiquent un rôle de la DA dans les tâches des mouvements oculaires qui sont caractérisés comme étant des phénotypes intermédiaires putatifs pour la schizophrénie et suggèrent également que la dérégulation du système de la DA au repos pourrait être en soi un phénotype intermédiaire de la maladie.
31
Love, Rebecca Margaret. « Improving the survival of embryonic dopaminergic neurons ». Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343277.
Texte intégral
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McAfee, Ghia. « Smoking and brain dopaminergic neurochemistry / Ghia McAfee ». Thesis, North-West University, 2004. http://hdl.handle.net/10394/590.
Texte intégralRésumé :
Tobacco use is not only a major health concern worldwide but also a grotesque economic burden
on the smoker as well as the health care system. The most well-known and most researched
constituent of tobacco products is nicotine. There are a variety of products on the market that
ensure nicotine intake, including cigarettes, cigars, pipe tobacco and smokeless tobacco.
Once absorbed by the body, nicotine undergoes phase I metabolism by cytochrome P450 (CYP)
2A6 (humans) or CYP2B1 (rat) to cotinine, the major metabolite. Since nicotine is a blood flow
marker, its transport across the blood-brain barrier (BBB) has been well documented. However,
data on the BBB penetration of nicotine and cotinine in animals subject to chronic nicotine
exposure are limited. This gap in literature was identified and subsequently the focus of our first
objective. Our data indicate that neither nicotine or cotinine uptake by the BBB is altered after
chronic nicotine exposure in rat.
Nicotine exerts its effect by binding to nicotinic cholinergic receptors (nAChRs) on dopaminergic
neurons in the striatum and the ventral tegmental area (VTA). The addictive property of nicotine is
attributed to its effects on the mesocorticolimbic system, which serves a fundamental role in the
acquisition of behaviours. Smoking not only plays a role in addiction but also in Parkinson's disease
(PD), where epidemiological studies have shown that smokers have a lower incidence of PD as
opposed to non-smokers. Dopamine (DA) is one of the major neurotransmitters that plays a critical
role in addiction and PD. Centrally, the biosynthesis of DA occurs intraneuronally through the ratelimiting
enzyme, tyrosine hydroxylase (TH). DA undergoes metabolism by monoamine oxidase
(MAO) intraneuronally. DA, that is not metabolized by MAO, is subsequently transported into the
storage vesicles. After stimulation of nAChRs, DA is released into the synaptic cleft after
membrane depolarization. Released DA stimulates post-synaptic dopaminergic receptors, is
metabolized by catecholamine-0-methyl-transferase or transporter back into the pre-synaptic
neuron by DA transporter (DAT).
Little is known about the effects of whole cigarette smoke on the dopaminergic system. Therefore,
our second objective of this study was to determine the effect of whole cigarette smoke extract
(nicotine-containing and nicotine-free smoke extract), nicotine and cotinine on TH and DAT
expression in undifferentiated pheochromocytoma cells. Our third objective was closely developed
from our second. After investigating the effect in vitro, we determined the effect in vivo in rats after
28 day exposure of whole cigarette smoke extract (nicotine-containing and nicotine-free smoke
extract), nicotine and cotinine on TH and DAT regulation. Both the in vitro and in vivo TH as well
as the in vivo DAT regulation data implicated nicotine to be responsible for TH and DAT
upregulation.
It is known that nicotine releases DA from rat striatal synaptosomes. We therefore aimed to
determine whether a component of tobacco leaf extracts which is a MAO-A and MAO-B inhibitor,
2,3,6-trimethyl-I,4-naphthoquinone (TMN) release DA from rat striatal synaptosomes. We found
that TMN releases DA from synaptosomes, to a greater extent when compared to nicotine.
Our data conclude that cotinine does cross the BBB and that both nicotine and cotinine transport
do not vary after chronic nicotine exposure. We also found that nicotine, as the major constituent
of tobacco smoke, is responsible for increased DA synthesis and DA transport back into the
presynaptic neuron. TMN, is not only a MAO-A and MAO-B inhibitor but experiments from our
laboratory indicate that in striatal synaptosomes, TMN releases DA to a greater extent than
nicotine.Thesis (Ph.D. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2005.
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Chowdhury, R. « Dopaminergic enhancement of cognition in old age ». Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1388281/.
Texte intégralRésumé :
As humans age, the brain undergoes many changes. This includes loss of the neurotransmitter dopamine, which forms a bridging link between age and the ensuing changes in cognition. However many questions about the precise nature of this relationship with regards to brain structure and function remain unanswered. These questions are important given our expanding aging population, and the answers may help the discovery of new therapeutic interventions for age-related impairments as well as identify mechanisms to promote successful aging. Old age also provides a model for understanding the role of dopamine in many fundamental human behaviours. The aim of my research was to use a multimodal approach to explore the contribution of dopamine to learning and memory in healthy older age. In this thesis I present four studies in which I used a combination of behavioural testing, pharmacological manipulation, structural and functional magnetic resonance imaging in older adults. I show that dopamine boosts delayed episodic memory in a non-linear dose-dependent manner. Using functional MRI, I show this effect is mediated through consolidation rather than encoding by the hippocampus. In two further imaging studies conducted to explore the role of dopamine in reward-based learning, I show that the flexibility of learning depends on the structural integrity of the substantia nigra/ventral tegmental area (the origin of dopamine projections) and that pharmacological enhancement of dopamine levels can remediate abnormal reward processing in the ventral striatum. Individual differences in neural activity associated with reward prediction also relate to anatomical nigro-striatal connectivity, identified using diffusion tensor imaging. Finally, I show that in old age, valence influences decision-making in relation to ones own beliefs about the future, mediated by volume of the anterior cingulate cortex. I conclude this thesis with a brief discussion of the implications of these findings, study limitations and potential future studies.
34
Barrie, Elizabeth Stofko. « Genetic Factors Regulating Expression of Dopaminergic Genes ». The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406388433.
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Edman, Linda C. « Chemokines and their role in dopaminergic development ». Stockholm : Department of Medical Biochemistry and Biophysics, Karolinska Institutet, 2009. http://diss.kib.ki.se/2009/978-91-7409-688-0/.
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Rizvi, Nisha. « NOVEL DOPAMINERGIC SIGNALING MODULATING HIPPOCAMPAL SYNAPTIC TRANSMISSION ». OpenSIUC, 2015. https://opensiuc.lib.siu.edu/dissertations/1082.
Texte intégralRésumé :
Dopaminergic systems regulate many brain functions and dysfunction of dopaminergic neurotransmission is thought to underlie numerous disorders, including schizophrenia, attention deficit hyperactivity disorder (ADHD), depression and Alzheimer’s disease. In the hippocampus, a dopaminergic projection from the ventral tegmental area (VTA) is proposed to be essential for controlling entry of sensory information into long-term memory through novelty and salience detection. However, the effects of the VTA-dopamine system on hippocampal synaptic transmission are largely under-explored and the underlying mechanisms are unclear. The goal of this project was to investigate mechanisms involved in dopaminergic modulation of hippocampal neurophysiology. Specifically, I (1) examined if dopamine modulates hippocampal synaptic transmission in a region- and input-specific manner, and (2) studied the signaling mechanisms underlying such modulation. In the first aim for the study, I tested whether SKF38393, a dopamine D1-like receptor agonist, differentially affects excitatory synaptic transmission in perforant path synapses onto dentate gyrus granule cells and whether such effects differ from those at area CA1 synapses. I found that SKF38393 produced a concentration-dependent increase in field excitatory postsynaptic potential (fEPSP) in both subregions, but that higher concentrations were needed in the dentate gyrus to produce comparable effects. This synaptic enhancement was long-lasting and largely irreversible which suggests it may be a form of long term enhancement (LTP). Also, the increase in synaptic transmission at medial perforant path synapses was larger than in the lateral perforant path. Importantly, effects in the dentate gyrus, unlike those in CA1, differed substantially along the dorsoventral axis, with effects being significantly larger at the dorsal compared to the ventral pole. In the second aim, various combinations of D1 and D2-like receptor agonists and antagonists as well as inhibitors of second messenger systems, demonstrated that differential mechanisms were required for initiation and maintenance of SKF38393-mediated early and late-phase enhancement and that a novel non-canonical phospholipase-C (PLC) dependent signaling pathway may be involved. Based on recent discoveries in other brain regions, we hypothesized that multiple subcellular signaling pathways may contribute to PLC activation which may include but are not limited to D1(5)-D2 heteromers and Gβγ complex. In conclusion, this work uncovers novel dopaminergic signaling pathways regulating hippocampal physiology, which will lead to development of better (functionally selective) therapeutic agents.
37
Tuathaigh, Colm O. « Dopaminergic involvement in stimulus selection : a behavioural study ». Thesis, University of Leicester, 2001. http://hdl.handle.net/2381/31325.
Texte intégralRésumé :
People with schizophrenia show deficits in the inhibitory processes controlling stimulus selection. Overshadowing and the Kamin blocking effect provide examples of stimulus selection. Overshadowing refers to the phenomenon whereby greater learning accrues to the more salient stimulus of a compound presentation. Kamin blocking occurs when prior learning to a single stimulus in stage 1 disrupts learning to an added stimulus in stage 2, when both stimuli are presented in compound. Both paradigms measure the ability to select relevant and deselect irrelevant information from the stimulus environment, and are dependent upon cognitive processes hypothesised to be disrupted in schizophrenic patients. The study of the neural basis of such stimulus phenomena provides a putative model with construct validity for the information processing deficits seen in schizophrenia. A disturbance in central dopaminergic activity is thought to underlie the cognitive deficits of schizophrenia. In the present study, the effect of dopaminergic manipulations on Kamin blocking and overshadowing was assessed in the rat. The indirect dopamine agonist d-amphetamine (1.0 mg/kg, i.p.) disrupted Kamin blocking when administered at stage 2 conditioning. Amphetamine also abolished overshadowing when given at conditioning. It was concluded that amphetamine effects in both paradigms may consist of a selective increase in learning to the less salient stimulus. The DA antagonist haloperidol (0.2 mg/kg, i.p.) failed to reverse the attenuating effects of amphetamine (1.0 mg/kg i.p.) on overshadowing. However, haloperidol (0.2 mg/kg & 0.5 mg/kg, i.p.) successfully reversed amphetamine-induced hyperlocomotion. Neither the selective D2 receptor antagonist raclopride (0.5 mg/kg, i.p.) nor the selective D2 receptor antagonist sulpiride (50 & 100 mg/kg, i.p.) restored overshadowing in amphetamine - treated animals. SCH23390 (0.05 mg/kg, i.p.), the selective D1 receptor antagonist, restored overshadowing in amphetamine - treated rats. The D1 receptor agonist SKF 38393 (5 mg/kg i.p.) disrupted overshadowing in a manner similar to that observed following amphetamine treatment.
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Tripanichkul, Wanida 1962. « Associations between glia and sprouting of dopaminergic axons ». Monash University, Dept. of Medicine, 2002. http://arrow.monash.edu.au/hdl/1959.1/7630.
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Canales, Juan Jose. « Behavioural correlates of dopaminergic manipulations of the striatum ». Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364066.
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Livingstone, Phil. « Nicotinic modulation of dopaminergic signalling in the PFC ». Thesis, University of Bath, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.528111.
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Pöltl, Dominik [Verfasser]. « Degeneration mechanisms in human dopaminergic neurons / Dominik Pöltl ». Konstanz : Bibliothek der Universität Konstanz, 2012. http://d-nb.info/1025226135/34.
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Foy, Catherine Mary Louise. « The non dopaminergic neuropharmacology of idiopathic Parkinson's disease ». Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392537.
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Killcross, Andrew Simon. « Dopaminergic mechanisms and latent inhibition : implications for schizophrenia ». Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261541.
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Keeler, Joshua Finn. « Instrumental response sequencing : dopaminergic modulation and behavioural control ». Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648582.
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Kou, Jinghong. « The Neurotoxicity of Insecticides to Striatal Dopaminergic Pathway ». Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/77991.
Texte intégralRésumé :
Parkinson's disease (PD) is an age-related neurodegenerative disease, which is characterized by severe loss of dopaminergic neurons in the substantia nigra pars compacta (SNc) and consequent dopamine depletion in its projecting area. In this dissertation, I evaluated the neurotoxicity of several classes of insecticides/drugs/neurotoxins to the striatal dopaminergic pathway and their potential relationship to Parkinsonism in the C57BL/6 mouse model, using biochemical and molecular biology methods.
In the first objective, I investigated the neurotoxicity in striatal dopaminergic pathways following co-application of permethrin (PM), chlorpyrifos (CPF) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The study was done because pyrethroid and organophosphorus compounds are widely used insecticides and they have been implicated in Gulf War Syndrome. We found that short-term, high-dose exposure to PM or CPF had no significant effects on the expression of dopamine transporter (DAT), tyrosine hydroxylase (TH), or α-synuclein protein in striatal nerve terminals, but the insecticides slightly enhanced the neurotoxicity of MPTP in C57BL/6 mice at 28 days post-treatment. This finding indicates a slowly developing neurotoxicity may occur after termination of high-dose exposure. Long-term, low-dose exposure to PM did not show significant neurotoxicity to striatal dopaminergic pathways when given alone, nor did this injection of PM enhance the neutotoxicity of MPTP in C57BL/6 mice. In addition, experiments with pure cis or trans isomers of permethrin showed that both cis and trans isomers contributed equally to the neurotoxicity of PM in the short-term high dose study.
Previous studies demonstrated a deficiency in mitochondrial function in PD, and a high density of K⁺ATP channels are present in substantia nigra, which play an important role in the maintenance of the membrane potential under metabolic stress. Therefore, in the second objective, I investigated the effect of K⁺ATP channel blockage on the neurotoxicity of mitochondrial-directed neurotoxins to striatal dopaminergic pathways. I found that mitochondrial inhibitors are potent releasers of preloaded dopamine from striatal nerve terminals, with the most potent compounds active in the nanomolar range. Co-application of the K⁺ATP channel blocker glibenclamide selectively increased the dopamine-releasing effect by complex I inhibitors in vitro, and potentiated the neurotoxicity of MPTP (a complex I inhibitor) on DAT and TH expression, in vivo. Mechanistic studies demonstrated that mitochondrial inhibitor-induced dopamine release is Ca²⁺-dependent. In addition, the selectivity of glibenclamide is not correlated to ATP depletion, but associated with the generation of excessive reactive oxygen species at the site of complex I.
In the third objective, I conducted comparative studies on the mode of action of rotenone-/reserpine-/tetrabenzaine (TBZ)-induced depletion, in vitro, as these three compounds share some similarities in their chemical structures. I found that rotenone, reserpine and TBZ selectively released preloaded dopamine and serotonin (5-HT), with the rank order as rotenone>reserpine>TBZ. Mechanistic studies demonstrated more than one mechanism was involved in both rotenone- and reserpine-induced neurotransmitter release. Ca²⁺-stimulated vesicular release and neurotransmitter transporter-mediated release are the common mechanisms involved in rotenone- and reserpine-induced dopamine release.
Overall, the insecticides/drugs/neurotoxins tested in the above experiments all exhibited some effect on the nigrastrital dopaminergic pathway, either alone or by enhancing the toxicity of other chemicals in combination treatment.Ph. D.
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Kohls, Morgan Rae Kohls. « IDENTIFICATION OF DROSOPHILA DOPAMINERGIC NEURAL CIRCUITS USING MARCM ». Ohio University Art and Sciences Honors Theses / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ouashonors1461174612.
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Karuppagounder, Senthilkumar S. Dhanasekaran Muralikrishnan Suppiramaniam Vishnu. « Environmental toxins and dopaminergic neurotoxicity novel neuroprotective strategies / ». Auburn, Ala, 2009. http://hdl.handle.net/10415/1883.
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Gangarossa, Giuseppe <1983>. « Dopaminergic transmission in the mouse hippocampus : signaling studies ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3893/1/Gangarossa_Giuseppe_Tesi-1.pdf.
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Gangarossa, Giuseppe <1983>. « Dopaminergic transmission in the mouse hippocampus : signaling studies ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3893/.
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Patel, Jyotiben Chhitubhai. « Heterogeneous regulation of dopamine release in the rat striatum ». Thesis, Queen Mary, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325157.
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