Dissertations / Theses on the topic 'Amygdala'

Thesis (Ph. D.)--Florida State University, 2009.
Advisor: Michael Meredith, Florida State University, College of Arts and Sciences, Dept. of Biological Science. Title and description from dissertation home page (viewed on May 4, 2010). Document formatted into pages; contains xv, 131 pages. Includes bibliographical references.

Research over the past several decades has revealed that the amygdala is involved in aversive, or fear, conditioning. However, the precise nature of this involvement remains a matter of debate. One hypothesis suggests that disrupting amygdala function eliminates the storage of memories formed during aversive conditioning, eliminating the production of internal responses that alter the expression of observable behaviors. Alternatively, lesions or inactivation of the amygdala may impair the modulation of memories in other brain regions and disrupt the ability to perform certain observable behaviors. The experiments reported in the present thesis examined these arguments by making multiple behavioral measures during exposure to unconditioned (US) or conditioned (CS) aversive cues. Amygdala activity was inferred from changes in c-Fos protein expression or activity was temporarily suppressed with muscimol injections. The relationship between the behavioral measures and the role of the amygdala in producing them was examined. Amygdala neurons expressing the c-Fos protein tracked exposure to the US and CS but did not coincide with expression of freezing. Temporary inactivation of the amygdala with muscimol injections before presentation of the US or exposure to the CS attenuated the expression of freezing and active place avoidance; two incompatible behaviors. Finally, temporary inactivation of amygdala activity blocked freezing, place avoidance, and memory modulation produced by the same posttraining exposure to an aversive CS. Since amygdala activation alone was not sufficient to produce freezing and inactivation of the amygdala eliminated freezing, place avoidance, and memory modulation, the results cannot be interpreted as reflecting a direct role for the amygdala in production of observable behaviors. The results also preclude the idea that memory modulation is the only function of the amygdala. Rather, the results of all three studies suggest that the amygdala stores an aversive representation of the US which promotes the expression of various behaviors, possibly through the production of internal responses reflecting an aversive affective state.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 54-61).
Threatening and rewarding stimuli evoke a set of distinct stereotyped behaviors, which can be categorized as negative and positive valence-related behaviors, respectively. The stereotypic nature of negative and positive valence-related behaviors suggests that threatening and rewarding stimuli engage evolutionarily predetermined neural circuits in the brain. The amygdala is an important mammalian brain region that is activated by negative and positive stimuli and mediates negative and positive valence-related behaviors. The current prevailing circuit model of the amygdala mainly considers negative behaviors and only recently has cell-type specific models have been proposed. Hence, the substrates, genetically distinct neuronal populations, for negative and positive behaviors are not known. The work presented here describes a genetically-defined amygdala circuit model for negative and positive behaviors. Development of a genetic-based circuit model of the amygdala revealed anatomical and genetic circuit motifs that underlie that amygdala circuits that mediate valence-specific behaviors.
NIH Pre-Doctoral Training Grant T32GM007287 RIKEN Brain Science Institute
by Joshua Kim.
Ph. D.

This thesis investigated the role of the amygdala in social cognition by examining variability in social-perceptual abilities within the normal population and via experiments with individuals who have Asperger's syndrome (AS). I found that a significant proportion of men from the general population had a fear recognition deficit akin to that seen in patients with bilateral amygdala lesion and that poor fear recognition was associated with poor theory of mind ability and with reduced activation of the amygdala and associated areas of the 'social brain'. Further experiments suggested a mechanism for these impairments - reduced fixation of the eye region of the face - similar to that exhibited by patient SM, who has suffered bilateral amygdala damage. Overall, I found that AS subjects also had a fear recognition deficit when compared with matched controls. However, there was great variability in responses, with scores ranging from normal to severely impaired. Again, an eyetracking experiment showed that low fear recognition was related to a reduced amount of time spent fixating the eyes. Informed by recent neurodevelopmental models of amygdala involvement in autistic- spectrum disorders, I conducted psychological, neurophysiological and neuroanatomical experiments in order to examine the cause of this failure to attend to the eyes in some AS subjects. As a whole, the findings support a 'hyper-active amygdala model', in which social stimuli induce an aversive level of arousal and so are avoided. I suggest that inattention to social stimuli, which could have a number of possible aetiologies, might be at the heart of a general route to social cognitive impairment, which could be shared by several distinct populations.

Fear is an emotion expressed by a subject which is under a threat or danger to secure itself.  It causes the “Fight or Flight” sensation in the being which is under attack. In previous studies, it is found that amygdala is the central unit in brain for fear stimuli. Here we have done two different neuroscience studies on fear with ultra high field MRI. Case 1: With ultra high field MRI brain images we visualised that there is a faster and short pathway to amygdala. Fear stimuli activate the amygdale even when the images are shown for a very short time of 50ms with which conscious recognition is not possible. This shows brain reacts to fear even before we recognise it consciously. Case 2: We investigated the influence of low and high spatial frequency fearful images in amygdala because of the contradiction in some previous studies. We compared low, high and broad spatial frequency images of fearful averted gaze faces, snakes and objects and found both high and low spatial frequency fear images affect the amygdale in the similar manner.

La Maladie de Huntington (MH) est une pathologie génétique neurodégénérative, causée par un nombre anormalement élevé de répétitions du codon CAG dans le gène codant pour la protéine huntingtine (htt). A un stade pré-symptomatique (avant les symptômes moteurs), des troubles émotionnels sont souvent observés chez les patients MH, tels une agitation, une anxiété, une irritabilité ainsi qu’une tendance à la dépression, une apathie et une perte du contrôle émotionnel. Dans le but d’étudier la physiopathologie sous-jacentes aux (dys)fonctions émotionnelles de la MH, nous analysons le rôle de l’amygdale (en particulier le noyau central (CeA)). Cette structure est connue pour être impliquée dans la régulation du processus émotionnel et avoir un volume réduit ainsi qu’un grand nombre d’agrégats chez les patients et chez des modèles animaux transgéniques. Afin d’étudier les symptômes émotionnels de la MH, nous avons utilisé un modèle de rats transgéniques récent, les BACHD. Nos résultats montrent que ces animaux sont hyper-anxieux et hyper-réactifs face aux situations menaçantes à un stade précoce de la maladie. Ces rats BACHD présentent également un nombre élevé d’agrégats de grande taille augmentant en fonction de l’âge spécifiquement dans le CeA par rapport au noyau basolateral (BLA). De plus, la modulation pharmacologique du CeA entraine un effet comportemental différentiel chez les rats BACHD par rapport aux rats normaux, attestant d’un défaut fonctionnel de cette structure à un stade précoce de la maladie. Finalement, l’hyper-activité cellulaire observée dans le CeA (partie médiane) des rats BACHD pourrait expliquer l’hyper-réactivité émotionnelle de ces animaux et participer aux troubles émotionnels de la MH
Huntington’s disease (HD) is a genetic neurodegenerative disorder, caused by an expanded CAG repeat in the gene encoding the huntingtin protein. At the presymptomatic phase, before motor symptoms occur, psychiatric and emotional disorders are observed with high prevalence in HD patients. Agitation, anxiety and irritability are often described but also depression and/or apathy, associated with a lack of emotional control.In search of the pathophysiology underlying the emotional (dys)functions of HD, we studied the role of the amygdala (especially the central nucleus (CeA)). This structure is known to be involved in emotional regulation and has a reduced volume and a large number of aggregates in both patients and transgenic rat models. To study the emotional symptoms of HD we used a recent model of transgenic rats, BACHD. Our results show that these animals are hyper-anxious and hyper-reactive to threatening situations at an early stage of the disease. BACHD rats also have a high number of large aggregates, increasing with age, specifically in the CeA compared to the basolateral nucleus (BLA). In addition, pharmacological modulation of the CeA induce differential behavioral effects in BACHD rats compared to WT rats, evidencing a functional deficit of the structure at an early stage of the disease. Finally, the cellular hyper-activity observed in the CeA (medial part) of BACHD rats could account for the emotional hyper-reactivity of these animals and participate of emotional disorders of HD

Thesis: Ph. D. in Neuroscience, Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references.
The amygdala is a structure well known for its role in fear and reward learning, but how these mechanisms are used for decision-making is not well understood. Decision-making involves the rapid updating of cue associations as well as the encoding of a value currency, both processes in which the amygdala has been implicated. In this thesis I develop a strategy to study value-guided decision making in rodents using an olfactory binary choice task. Using a logistic regression model, I show that the value of expected rewards is a strong influence on choice, and can bias perceptual decisions. In addition, I show that decisions are influenced by events in the near past, and a specific bias towards correct choices in the near past can be detected using this analysis. Using genetic targeting of a sub-population of amygdala neurons, I show that this population is required for the rapid learning of an olfactory decision making task. Using in-vivo calcium imaging of this population I show that these neurons are active during the inter-trial interval and modulated by choice history, suggesting a mechanism by which choice history can influence current decisions.
by Kean Jaime-Bustamante.
Ph. D. in Neuroscience

Includes bibliographical references.
Neuro-imaging studies have strongly implicated the basolateral amygdala in dreaming (e.g. Maquet et al., 1996). Various neuropsychological dream theorists (Domhoff, 2001; Hobson, Pace-Schott & Stickgold, 2000; Revonsuo, 2000) propose central roles for the amygdala in dreaming (particularly in the generation of dream affect); however, little empirical research on its function in dreaming exists. Urbach-Wiethe Disease (UWD) is a very rare genetic condition that can lead to calcifications in the medial temporal lobes. This study analysed 26 dream reports collected from eight adult UWD patients with fully calcified basolateral amygdalae bilaterally, and compared them to 58 dream reports collected from 17 matched controls. Dream affect and various other dream characteristics were examined. A number of significant results of small to moderate effect size were found. Notably, UWD patients’ dream reports had a significantly higher mean intensity of positive affect than controls’ dream reports, a significantly lower mean intensity of negative affect, a significantly higher mean intensity of PLAY, and a significantly lower mean intensity of RAGE. The UWD patients’ dream reports were also significantly more wish-fulfilling than the controls’ dream reports, were significantly less likely to be classified as nightmares, and had a significantly lower word count and narrative item count. These results are consistent with an extensive literature that implicates the basolateral amygdala in fear conditioning, emotional appraisal and in similar affective processes in waking life (e.g. LeDoux, 2003; Pessoa, 2010). The dream reports were also analysed for instances of threat and escape, as well as for approach and avoidance behaviour, in order to test some of the hypotheses central to Revonsuo’s (2000) threat simulation theory (TST) of dreaming. These analyses produced no significant results. Given that the amygdala is essential to Revonsuo’s (2000) conceptualisation of dreaming as an evolutionarily adaptive mechanism to safely simulate threat avoidance, these findings contradict some of TST’s central predictions. In general, these findings suggest that the average dream of persons with bilateral basolateral amygdalae damage is significantly simpler, more pleasant, less unpleasant, more wish-fulfilling and less likely to be a nightmare than the average control dream. As such, the dream reports of the UWD patients seem strikingly similar to the dreams of young children.

Social anxiety disorder (SAD) interferes with everyday life. It can, for instance, hinder careers, relationships, and leisure time. It is a common anxiety disorder that was neglected for decades. SAD individuals crave and fear social interactions simultaneously, leading to isolation in our highly social world. Therefore, research surrounding these kinds of disorders is essential. This systematic review has focused on the neural aspects and differences between SAD and healthy controls surrounding amygdala activation and connectivity. Functional magnetic resonance imaging (fMRI) studies conducted using social and emotional tasks were included. Findings include increased amygdala activation to fearful faces and words and a positive correlation between amygdala activation and symptom severity. Further, deficits in emotion regulation and a finding of gradual habituation have been found in SAD compared to healthy controls. Some limitations to this research are the small sample sizes used in the included articles and the use of both SAD and individuals with generalized SAD. The study is essential to assess future questions and directions regarding diagnosis, treatment, and understanding of SAD.

Opioid withdrawal induces long-lasting effects on neuronal function and synaptic transmission in opioid-sensitive neurons throughout the brain. These persistent changes are thought to drive drug-seeking and relapse behaviours during the withdrawal state and beyond into abstinence. Despite this, the mechanisms and circuits underlying the altered behaviours following opioid withdrawal are only partially understood, limiting the development of addiction treatments. Neural circuits within the amygdala mediate drug-seeking and relapse behaviours, thus, the current thesis hypothesised that neuroadaptations would manifest in opioid-sensitive amygdala cells during opioid withdrawal. Using patch-clamp electrophysiology in rat brain slices, the effects of opioid withdrawal on the highly opioid-sensitive intercalated amygdala neurons and their connections were investigated. The broad aims of this thesis were firstly, to define the activity and connections of the intercalated neurons and also their regulation by various neuromodulators under normal physiological conditions. Then, to determine whether opioid withdrawal induced any neuroadaptive changes to normal functioning. To this end, Chapter 3 defined that the activity of an enkephalin-degrading peptidase, neprilysin, was a key regulator of synaptic transmission in the main intercalated cell nucleus. Chapter 4 highlighted that the activity of neprilysin was increased in the intercalated cells during withdrawal, a change that reduced peptide control of synaptic transmission between amygdala nuclei. Finally, Chapter 5 revealed that the increased peptidase activity changed synaptic transmission onto a population of amygdala neurons that mediate the learning and memory processes that become maladaptive during withdrawal, potentially triggering drug-seeking behaviours during the withdrawal state and abstinence. As amygdala neural circuits are involved in the development of addiction behaviours, the current thesis has identified that peptide systems in the amygdala are viable targets for the development of novel pharmacotherapies for drug relapse, a feature of addiction that severely limits the efficacy of current treatment options. Restoring endogenous peptide activity within the amygdala during withdrawal may return synaptic transmission to normal, mitigate the withdrawal-induced neuroadaptations and rescue the addiction behaviours exhibited during opioid withdrawal and abstinence.

Pain is an important defense against dangers in our environment, however some clinical conditions produce pain that outlasts this useful role and persist even after the injury has healed. The experience of pain consists of somatosensory elements of intensity and location, negative emotional/aversive feelings and subsequent restrictions on lifestyle due to learning to associate certain activities with pain. The amygdala contributes negative emotional value to nociceptive sensory information and forms the association between an aversive response and the environment in which it occurs. It can form this association because it receives nociceptive information via the spino-parabrachio-amygdaloid pathway and polymodal sensory information via its basolateral nucleus (BLA) and cortical and thalamic inputs. Within the spino-parabrachio-amygdaloid pathway, nociceptive information is sent from the external lateral nucleus of the parabrachial nucleus (PB) to the laterocapsular region of the central nucleus of the amygdala (CeLC). The PB-CeLC synapse and other brain regions undergo synaptic plasticity in chronic pain conditions with ongoing injury. However very little is known about how plasticity occurs in conditions where pain persists even after the injury has healed. In the first study of this thesis, I used immunohistochemistry, electrophysiology and behavioural assays, to show that a brief nociceptive stimulus with no ongoing injury can produce long-lasting synaptic plasticity at the rat parabrachial-amygdala synapse. I show that this plasticity is caused by an increase in number of postsynaptic AMPARs with a transient change in AMPAR subunit, similar to long-term potentiation. Furthermore, repeated stimuli lengthened this plasticity. The potentiation could be representative of the initial changes that occur in the transition from an acute to a chronic pain state. This could mean greater association of a painful experience with the environment and context and could ultimately facilitate the negative association of certain activities and situations with pain, leading to limiting or avoidance of these activities/situations. The next studies of this thesis focused on potential neuromodulators of activity at the PB-CeLC synapse and the polymodal BLA inputs to the CeLC. Opioids and Calcitonin gene-related peptide (CGRP) were chosen because of their presence at synapses in the amygdala and their role in pain particularly in the affective component of pain. Opioids reduce pain intensity and the emotional unpleasantness of pain. Opioids inhibit some synapses in the amygdala, however whether opioids specifically modulate the PB-CeLC and the BLA-CeLC is unknown. I used electrophysiology and optogenetics to show that opioids inhibit two synapses important for pain modulation in the amygdala. Given the evidence of the opioid’s role in reducing pain affect, modulation of these synapses could be, in part, the site of opioid action. CGRP is expressed at all levels of the spino-parabrachio-amygdala pathway and modulates pain, as CGRP receptor antagonists injected into the amygdala inhibit nocifensive behaviours in animals. Additionally, CGRP antagonists reverse arthritis-induced synaptic plasticity at the PB-CeLC synapse. CGRP enhances synaptic transmission in the CeLC, however it is unknown whether it also directly regulates the excitability of CeLC neurons. Using electrophysiology, I show that CGRP directly ‘excites’ CeLC neurons even when fast synaptic transmission is blocked. This suggests that in normal physiology CGRP and opioids have opposing effects in the CeLC and the balance of activity in the CeLC will depend on which peptide has the bigger influence on the CeLC. This thesis addressed the question of whether plasticity can outlast a stimulus and the time course of the plasticity. This plasticity was seen in the amygdala, an area important for associative learning and the affective component of pain. This thesis also addressed how neuropeptides, opioids and CGRP regulate amygdala synapses in normal physiology. Knowledge of how these peptides modulate the amygdala synapses will provide information on how they could operate in a pain state.

Anxiety is a psychological disorder that negatively impacts an individual’s quality of life that has socioeconomic burden to society and the individual. Fear is a physiological learned and innate response that helps protect people and animals from danger. Dysregulation of fear can manifest in anxiety disorders, therefore, understanding fear in the brain may lead to a better understanding of the pathophysiology of anxiety and better treatment options. The amygdala is a brain region integral in fear responses. Intra-amygdala circuits underlie the association of negative outcomes to neutral stimuli, which then programs our mind and body to avoid dangerous situations. Extinction of fear, the loss of fear response once the danger has ceased, is also a process that is amygdala dependent. Impaired fear extinction manifests as PTSD. The intercalated cells, an inhibitory amygdala sub-nuclei, gates information within the amygdala to dampen overall excitability. Understanding regulation of intercalated function, therefore, may provide insight into promoting extinction of fear and treatment of disorders such as PTSD. Two key regulators of intercalated function are dopamine and opioids. This thesis therefore aimed to define the regulatory role of dopamine and opioids in the intercalated cells and how this may impact overall amygdala activity. Using electrophysiology, optogenetics, behavioural paradigms and immunohistochemistry I have found dopamine and opioids both inhibit local intercalated synapses, however, opioids but not dopamine inhibit all intercalated output synapses. I have also discovered a novel synaptic connection between the midbrain and the intercalated cells that may be the source of dopamine for intercalated function. This thesis concluded that although dopamine and opioids have similar inhibitory functions within the intercalated cells, the key differences means they will likely have opposing outcomes on fear behaviours- with dopamine preventing and opioids promoting fear behaviours.

En esta Tesis Doctoral hemos identificado los componentes de la amígdala extendida (EA) de aves, en base a su posición topológica, perfil genético y origen embrionario. En EA central de pollo y pinzón, identificamos las masas intercaladas y amígdala central, con células de origen estriatal dorsal y/o ventral, pero con subpoblaciones menores de otros orígenes. Además, el núcleo lateral de la estria terminal, de origen palidal, contiene subpoblaciones de células inmigrantes de origen estriatal, preóptico o eminencial. En EA medial del pinzón, hemos identificado distintas subpoblaciones celulares en la amígdala medial y el núcleo medial de la estria terminal con origen palidal, preóptico, hipotalámico o eminencial. Nuestros datos indican que EA está formada por múltiples corredores celulares con distinto origen y perfil genético, lo que supone un cambio de paradigma para entender la conectividad y función de cada tipo celular en el control de las emociones, motivación y comportamiento social.
In this Ph.D. Dissertation, we have identified the components of the avian extended amygdala (EA), based on their topological position, genetic profile and embryonic origin. In central EA of chicken and zebra finch, we identified the intercalated masses and the central amygdala, with cells derived from the dorsal and/or ventral striatal domains, but with minor subpopulations from other origins. Moreover, the lateral bed nucleus of the stria terminalis, with pallidal origin, contains subpopulations of immigrant cells with striatal, preoptic or eminential origins. In medial EA of zebra finch, we identified different cell subpopulations with pallidal, preoptic, hypothalamic or eminential origins. Our data indicate that EA is formed by multiple cell corridors with different origin and genetic profile, which opens new venues for investigating the connections and function of each neuron subtype in the control of emotions, motivation and social behavior.
En aquesta Tesi Doctoral hem identificat els components de l'amígdala estesa (EA) d'aus, en base a la seva posició topològica, perfil genètic i origen embrionari. En EA central de pollastre i pinsà, hem identificat les masses intercalades i l'amígdala central, amb cèl·lules estriatals dorsal i/o ventral, però amb subpoblacions menors d'altres orígens. A més, el nucli lateral de l’estria terminal, d'origen palidal, conté subpoblacions de cèl·lules immigrants d'origen estriatal, preòptic o eminèncial. En EA medial del pinsà, hem identificat diferents subpoblacions cel·lulars en l'amígdala medial i el nucli medial de l’estria terminal amb origen palidal, preòptic, hipotalàmic o eminèncial. Les nostres dades indiquen que EA està formada per múltiples corredors cel·lulars amb diferent origen i perfil genètic, la qual cosa suposa un canvi de paradigma per entendre la connectivitat i funció de cada tipus cel·lular en el control de les emocions, motivació i comportament social.

The underlying goal of this dissertation is to understand how the amygdala, a brain region involved in establishing the emotional significance of sensory input, contributes to the processing of complex sounds. The general hypothesis is that communication calls of big brown bats (Eptesicus fuscus) transmit relevant information about social context that is reflected in the activity of amygdalar neurons.

The first specific aim analyzed social vocalizations emitted under a variety of behavioral contexts, and related vocalizations to an objective measure of internal physiological state by monitoring the heart rate of vocalizing bats. These experiments revealed a complex acoustic communication system among big brown bats in which acoustic cues and call structure signal the emotional state of a sender.

The second specific aim characterized the responsiveness of single neurons in the basolateral amygdala to a range of social syllables. Neurons typically respond to the majority of tested syllables, but effectively discriminate among vocalizations by varying the response duration. This novel coding strategy underscores the importance of persistent firing in the general functioning of the amygdala.

The third specific aim examined the influence of acoustic context by characterizing both the behavioral and neurophysiological responses to natural vocal sequences. Vocal sequences differentially modify the internal affective state of a listening bat, with lower aggression vocalizations evoking the greatest change in heart rate. Amygdalar neurons employ two different coding strategies: low background neurons respond selectively to very few stimuli, whereas high background neurons respond broadly to stimuli but demonstrate variation in response magnitude and timing. Neurons appear to discriminate the valence of stimuli, with aggression sequences evoking robust population-level responses across all sound levels. Further, vocal sequences show improved discrimination among stimuli compared to isolated syllables, and this improved discrimination is expressed in part by the timing of action potentials.

Taken together, these data support the hypothesis that big brown bat social vocalizations transmit relevant information about the social context that is encoded within the discharge pattern of amygdalar neurons ultimately responsible for coordinating appropriate social behaviors. I further propose that vocalization-evoked amygdalar activity will have significant impact on subsequent sensory processing and plasticity.

Alcohol dependence is a global societal problem, yet current avenues for its treatment are largely ineffective in slowing its chronic-relapsing trajectory. Animal studies of alcohol dependence have described neuroadaptations in the amygdala that may play a central role in mechanisms of relapse. In this thesis, spontaneous amygdala network function was examined in abstinent alcohol dependent patients (ADP) using functional magnetic resonance imaging within the framework of a multi-site neuroimaging platform: ICCAM. Participants underwent five scans that included baseline, as well as scans under placebo, acute antagonism of μ-opioid, Dopamine D3 (DRD3) and Neurokinin-1 (NK1) receptor systems previously implicated in mechanisms of addiction. At baseline, amygdala – substantia nigra/ventral tegmental area (SN/VTA) resting state functional connectivity (RSFC) was elevated in abstinent ADP, despite widespread grey-matter (GM) volumetric atrophy, in both amygdala and SN/VTA, compared with age-matched healthy controls (HC). The strength of amygdala – SN/VTA RSFC in ADP was primarily associated with years of cumulative alcohol exposure, but not with amygdala or SN/VTA GM volume, length of abstinence, smoking status, or head motion. Amygdala RSFC with other regions showed sensitivity to core clinical features of ADP at baseline. Amygdala – frontoparietal (FPN) RSFC was inversely associated with abstinence length, with ADP in the first two months of abstinence showing significantly reduced amygdala – FPN RSFC compared with HC. Voxelwise comparison of amygdala RSFC between each drug session and placebo, did not reveal differential effects of receptor blockade on ADP and HC. Across both groups, however, the three drugs exhibited both overlapping and differential effects on distinct brain networks. Notably, amygdala RSFC in the superior temporal gyrus showed increases under NK1-antagonism, and decreases under naltrexone compared with placebo. Finally, amygdala – SN/VTA was significantly elevated in ADP relative to HC across all four sessions, suggesting that it may represent a stable neurophysiological feature of alcohol dependence.

Within the field of functional magnetic resonance imaging (fMRI) neurofeedback, most studies provide subjects with instructions or suggest strategies to regulate a particular brain area, while other neuro-/biofeedback approaches often do not. This study is the first to investigate the hypothesis that subjects are able to utilize fMRI neurofeedback to learn to differentially modulate the fMRI signal from the bilateral amygdala congruent with the prescribed regulation direction without an instructed or suggested strategy and apply what they learned even when feedback is no longer available. Thirty-two subjects were included in the analysis. Data were collected at 3 Tesla using blood oxygenation level dependent (BOLD)-sensitivity optimized multi-echo EPI. Based on the mean contrast between up- and down-regulation in the amygdala in a post-training scan without feedback following three neurofeedback sessions, subjects were able to regulate their amygdala congruent with the prescribed directions with a moderate effect size of Cohen’s d = 0.43 (95% conf. int. 0.23–0.64). This effect size would be reduced, however, through stricter exclusion criteria for subjects that show alterations in respiration. Regulation capacity was positively correlated with subjective arousal ratings and negatively correlated with agreeableness and susceptibility to anger. A learning effect over the training sessions was only observed with end-of-block feedback (EoBF) but not with continuous feedback (trend). The results confirm the above hypothesis. Further studies are needed to compare effect sizes of regulation capacity for approaches with and without instructed strategies.

Within the field of functional magnetic resonance imaging (fMRI) neurofeedback, most studies provide subjects with instructions or suggest strategies to regulate a particular brain area, while other neuro-/biofeedback approaches often do not. This study is the first to investigate the hypothesis that subjects are able to utilize fMRI neurofeedback to learn to differentially modulate the fMRI signal from the bilateral amygdala congruent with the prescribed regulation direction without an instructed or suggested strategy and apply what they learned even when feedback is no longer available. Thirty-two subjects were included in the analysis. Data were collected at 3 Tesla using blood oxygenation level dependent (BOLD)-sensitivity optimized multi-echo EPI. Based on the mean contrast between up- and down-regulation in the amygdala in a post-training scan without feedback following three neurofeedback sessions, subjects were able to regulate their amygdala congruent with the prescribed directions with a moderate effect size of Cohen’s d = 0.43 (95% conf. int. 0.23–0.64). This effect size would be reduced, however, through stricter exclusion criteria for subjects that show alterations in respiration. Regulation capacity was positively correlated with subjective arousal ratings and negatively correlated with agreeableness and susceptibility to anger. A learning effect over the training sessions was only observed with end-of-block feedback (EoBF) but not with continuous feedback (trend). The results confirm the above hypothesis. Further studies are needed to compare effect sizes of regulation capacity for approaches with and without instructed strategies.

Thesis (Ph.D.)--University of Cincinnati, 2007.
Advisor: Dr. Floyd R Sallee. Title from electronic thesis title page (viewed Mar. 29, 2009). Keywords: amygdala; neuropeptide; NPY receptor; CRH receptor; chronic stress; glucocorticoid; GIR. Includes abstract. Includes bibliographical references.

Emotional events are better remembered than neutral events. But what are the mechanisms behind this memory enhancing effect? It seems that they depend on the arousal level at the moment we experience the event to be remembered. The first study of the present thesis mapped the brain areas that changed their activity in a highly arousing situation in subjects with snake or spider phobia. Looking at pictures of their feared object engaged the amygdala, situated in the medial temporal lobe. This area has previously been demonstrated to be necessary for fear reactions. Here, the novel question was what other brain areas the amygdala engages when the brain is in a state of high arousal. Results suggest that the amygdala recruits other limbic and cortical areas known to be involved in motor behavior and object recognition. In contrast, when subjects watched fear-relevant but non-phobic pictures, amygdala activity was negatively correlated to the anterior cingulate cortex suggesting cortical inhibition. The final two studies aimed at explaining the physiological brain mechanisms behind arousal enhancement of memory. In the first one, epileptic patients with medial temporal lobe resections including the amygdala were compared to healthy controls on a recognition memory task where the pictures to be remembered varied in arousal intensities. Results suggested that the anterior medial temporal lobe including the amygdala is necessary for arousal enhancement of memory because the enhancement effect was abolished in resectioned patients. The last study related inter-individual differences in bodily arousal to amygdala-parahippocampal interaction. Results suggest that the beneficial effects of emotion on memory depend on arousal regulating mechanisms of the amygdala that in turn affects parahippocampal activity. Collectively, results suggest that the amygdala is regulating changes in arousal states of the brain and body during distressful situations. Further, arousal in turn determines memory strength through gating amygdala influences on the parahippocampal cortex. Thus, the amygdala is a node both in a fear and a memory network and arousal influences the amygdala to prepare for action and to enhance memory. This seems evolutionary sound.

Not so long ago the amygdala was an unclear region of the brain. Nowadays it is assumed that the amygdala is playing a key role in emotions, especially in the perception of fear. The amygdala is a crucial component that enables humans and animals to detect and to respond to threats. When the amygdala is damaged the ability to learn and respond to threats becomes impaired. This paper reviews data that highlights internal processes of the amygdala as well as external amygdala processes. Further, it discusses how the amygdala contributions to fear related emotions and memory. Additionally the paper discusses what the costs are to the concept of fear in humans and animals when the amygdala is damaged. In sum, the paper presents a variety of studies conducted both on humans and animals, using brain imaging machines and fear conditioning that confirms the importance of the amygdala in the perception of fear.

The Conditioned Cue Preference (CCP) task, which requires rats to differentiate between two widely separated locations on an 8-arm radial maze, was used to show that this ability is determined by a complex interaction between pre-exposure to the maze (without a reinforcer) and number of training trials (with a reinforcer). Lesion data suggested that the discrimination is learned by two parallel information processes involving different parts of the amygdala (together with other parts of the brain). When the rat has been pre-exposed to the maze, basolateral amygdala (BLA) mediates the CCP by associating neutral stimuli with the rewarding properties of the reinforcer (stimulus-outcome learning). When the rat has not been pre-exposed, the central amygdala (CeA) mediates the CCP by associating neutral stimuli with the responses elicited by the reinforcer (stimulus-response learning). Both of these pavlovian associations result in the identical arm discrimination in the CCP task.
Le Conditionnement par Préférence de Repères (CPR) demande aux rats de différencier deux endroits distincts et espacés dans un labyrinthe radial à huit branches. Ce type de conditionnement a été utilisé pour montrer que la capacité de différenciation est déterminée par une interaction complexe entre la pré-exposition au labyrinthe (sans renforcement) et le nombre de séances d'apprentissage (avec renforcement). Selon certaines études, la distinction entre les repères serait apprise par deux systèmes d'information parallèles impliquant différentes parties de l'amygdale (combinées à d'autres régions du cerveau). Lorsque les rats sont pré-exposés au labyrinthe, le noyau basolatéral de l'amygdale (BLA) influence le CPR en associant des stimuli neutres avec les propriétés motivantes du renforcement (apprentissage stimulus-résultat). Lorsque les rats ne sont pas pré-exposés au labyrinthe, le noyau central de l'amygdale (CeA) agit sur le CPR en associant des stimuli neutres à la réponse que suscite le renforcement (apprentissage stimulus-réponse). Ces deux types d'associations Pavloviennes résultent en une discrimination similare des branches dans le CPR.

The amygdala, in particular its basolateral part (BLA), plays a critical role in binding affective qualities to otherwise neutral stimuli, and in eliciting emotional behaviors. Plasticity of inputs to BLA projection neurons involved in emotional memory has been extensively studied. However, how BLA neurons collectively process sensory information to encode and stabilize emotional memories is unknown. Precise coordination of BLA network activities seems critical. Specifically, timed integration of salient stimuli, and synchrony with hippocampal theta oscillations appear to be important. Recent reports suggest that GABAergic neurons may be instrumental in shaping ensemble activity in the BLA. Studies of neocortex and hippocampus showed that diverse GABAergic interneuron types play highly specific roles in coordinating network operations. The presence of similar interneuron populations in the BLA suggests comparable mechanism may govern its activities. However, GABAergic cell types and their functions have not been characterized.

Reaction times (RTs) are a valuable measure for assessing cognitive processes. However, RTs are susceptible to confounds and therefore variable. Exposure to threat, for example, speeds up or slows down responses. Distinct task types to some extent account for differential effects of threat on RTs. But also do inter-individual differences like trait anxiety. In this functional magnetic resonance imaging (fMRI) study, we investigated whether activation within the amygdala, a brain region closely linked to the processing of threat, may also function as a predictor of RTs, similar to trait anxiety scores. After threat conditioning by means of aversive electric shocks, 45 participants performed a choice RT task during alternating 30 s blocks in the presence of the threat conditioned stimulus [CS+] or of the safe control stimulus [CS-]. Trait anxiety was assessed with the State-Trait Anxiety Inventory and participants were median split into a high- and a low-anxiety subgroup. We tested three hypotheses: (1) RTs will be faster during the exposure to threat compared to the safe condition in individuals with high trait anxiety. (2) The amygdala fMRI signal will be higher in the threat condition compared to the safe condition. (3) Amygdala fMRI signal prior to a RT trial will be correlated with the corresponding RT. We found that, the high-anxious subgroup showed faster responses in the threat condition compared to the safe condition, while the low-anxious subgroup showed no significant difference in RTs in the threat condition compared to the safe condition. Though the fMRI analysis did not reveal an effect of condition on amygdala activity, we found a trial-by-trial correlation between blood-oxygen-level-dependent signal within the right amygdala prior to the CRT task and the subsequent RT. Taken together, the results of this study showed that exposure to threat modulates task performance. This modulation is influenced by personality trait. Additionally and most importantly, activation in the amygdala predicts behavior in a simple task that is performed during the exposure to threat. This finding is in line with “attentional capture by threat”—a model that includes the amygdala as a key brain region for the process that causes the response slowing.

Reaction times (RTs) are a valuable measure for assessing cognitive processes. However, RTs are susceptible to confounds and therefore variable. Exposure to threat, for example, speeds up or slows down responses. Distinct task types to some extent account for differential effects of threat on RTs. But also do inter-individual differences like trait anxiety. In this functional magnetic resonance imaging (fMRI) study, we investigated whether activation within the amygdala, a brain region closely linked to the processing of threat, may also function as a predictor of RTs, similar to trait anxiety scores. After threat conditioning by means of aversive electric shocks, 45 participants performed a choice RT task during alternating 30 s blocks in the presence of the threat conditioned stimulus [CS+] or of the safe control stimulus [CS-]. Trait anxiety was assessed with the State-Trait Anxiety Inventory and participants were median split into a high- and a low-anxiety subgroup. We tested three hypotheses: (1) RTs will be faster during the exposure to threat compared to the safe condition in individuals with high trait anxiety. (2) The amygdala fMRI signal will be higher in the threat condition compared to the safe condition. (3) Amygdala fMRI signal prior to a RT trial will be correlated with the corresponding RT. We found that, the high-anxious subgroup showed faster responses in the threat condition compared to the safe condition, while the low-anxious subgroup showed no significant difference in RTs in the threat condition compared to the safe condition. Though the fMRI analysis did not reveal an effect of condition on amygdala activity, we found a trial-by-trial correlation between blood-oxygen-level-dependent signal within the right amygdala prior to the CRT task and the subsequent RT. Taken together, the results of this study showed that exposure to threat modulates task performance. This modulation is influenced by personality trait. Additionally and most importantly, activation in the amygdala predicts behavior in a simple task that is performed during the exposure to threat. This finding is in line with “attentional capture by threat”—a model that includes the amygdala as a key brain region for the process that causes the response slowing.

Previous research has indicated that the amygdala exerts a modulatory influence on multiple memory systems. Evidence also indicates that emotional state can influence the use of multiple memory systems and that this effect is mediated by the amygdala. Anxiogenic drugs administered during acquisition in a task that can be acquired either through hippocampus-dependent “place” learning or caudate dependent “response” learning, resulted in the predominant use of response learning. It is not known whether inducing anxiety at other behavioral time points will also influence the relative use of multiple memory systems. In experiment 1, male Long-Evans rats were trained to swim from the same start point to an escape platform constantly located in a goal arm. Prior to memory retrieval rats were administered either alpha- two adrenoceptor antagonist RS 79948-197, peripherally (0.03, 0.01, 0.3 mg/kg) or into the basolateral amygdala (0.1 µg), or saline vehicle. Rats treated with RS 79948-197 prior to memory retrieval exhibited caudate-dependent response learning. Previous studies examining the effects of RS 77948-197 on memory were conducted with rats trained in an anxiogenic state and subsequently probed in a drug free state. Experiment 2 examined whether state dependency may account for those results. Animals received peripheral (0.1 mg/kg) or intra-amygdala (0.1 µg) administration of RS 79948-197, prior to both acquisition and memory retrieval. Rats treated with RS 79948- 197 predominantly exhibited response learning. Finally, experiments 3 and 4 examined whether the use of response learning produced by RS79948-197 was due to the impairing effect on hippocampus-dependent memory. Rats that were administered peripheral (0.03 mg/kg) or intra-amygdala (0.1 µg) injections of RS 79948-197 displayed impaired acquisition of the single solution place task relative to control animals. This indicates that place learning was impaired. Over, all the present findings indicate 1) peripheral and intra-amygdala anxiogenic drug administration results in the use of habit memory at both acquisition and retrieval, 2) state dependency does not play a role in the influence of RS 799948-197 on memory system use, 3) the use of response learning produced by peripheral and intra-amygdala injections of RS 79948-197 may result from an impairing effect of hippocampusdependent memory.

Posttraumatiskt stressyndrom (PTSD) är en sjukdom som är traumarelaterad och svår att få en övergripande bild av då statistiken för antalet drabbade är bristfällig framför allt av ett stort mörkertal. Symtombilden vid denna sjukdom är mycket individuell och de upplevda symtomen är många, vilket skapar en svårighet i att diagnostisera sjukdomen. Vem som helst kan drabbas när som helst under sin livstid och att få en behandling som fungerar är problematisk då ingen exakt bot finns. Under ett trauma påverkas vårt alarmsystem i kroppen för att varna om fara och då har hjärnstrukturen amygdala en övergripande roll. Eftersom amygdala har stor betydelse för vår uppfattning om faror har därför denna studie valt att se om dessa traumatiska händelser orsakar symtomen vid PTSD. Mer specifikt var syftet med denna litteraturstudie att se om förändringar i amygdala och närliggande regioner kan vara bidragande till symtomen som upplevs av individer med PTSD samt vilka neurologiska förändringar som skett/finns i dessa hjärnregioner som kan ha en bidragande faktor till uppkomsten av sjukdomen. Av sex utvalda orginalartiklar kunde det sammantaget konstateras att vissa neurologiska förändringar som amygdala aktivitet och kortikal volym möjligtvis kan ha en koppling till vissa upplevda symtom som bland annat förhöjd vaksamhet och känsloregleringsförmåga. Artikel 1 visade på minskad volym av grå substans i premotorcortex och i främre cingulate cortex (p<0.05)samt att de med PTSD hade svårare att hantera vardagliga utmaningar, var mindre positiva och mer negativa (p<0.0001).Artikel 2 visade på att volymen av grå substans hade korrelationer med svårighetsgraden av PTSD samt symtombilden. Artikel 3 visade att individer med PTSD hade en minskad aktivitet i högra och vänstra amygdala och ventrala striatum (p<0.005). Där emotionellt avtrubbande hade korrelationer med högra ventrala striatum(p<0.05).Artikel 4 såg att de med PTSD hade förändrad cortex, i högra hemisfären var det åttaregioner och i den vänstra sex regionersom antagligen hade samband med totala CAPS poäng. Artikel 5visade att PTSD gruppen hade en ökad respons i högra amygdala vid syn av skrämmande ansikten (p<0.05) samt att högra amygdala aktiviteten hade samband med symtomet förhöjd vaksamhet. Artikel 6 visade att förmågan att reglera känslor var förändrad hos individer med PTSD. Både vid intensifiering av en känsla (amygdala (p<0.04), bakre cingulate cortex (p<0.01), främre cingulate cortex (p<0.04), middle cingulate cortex (p<0.02), vänstra inferior frontal cortex (p<0.04), vänstra putamen (p<0.04), bilaterala inferior parietal loben (p<0.03)) samt vid minskning av känsla (inferior frontal cortex (p<0.01), vänstra putamen (p<0.02), bilaterala inferior parietal loben (p<0.01), insula (p<0.03)).Denna studie kunde alltså inte påvisa tydliga hjärnområden, kopplade till amygdala, vilka hade förändringar som kan ha orsakat uppkomsten av ångestrelaterade besvär vid PTSD. Eftersom hjärnan är mycket komplex och kan bearbeta intryck på väldigt olika sätt kan dessa resultat kanske förklaras med hjälp av att de olika typer av trauman som individerna utsattes för i stor utsträckning påverkade skilda hjärnregioner. Det är alltså därför viktigt att fler studier, med större deltagarantal och likartade traumatiska händelser, fortsätter belysa PTSD symtom och deras koppling mot amygdala och närliggande hjärnregioner för att öka förståelsen för uppkomsten av PTSD. Eftersom kunskapen idag är begränsad vid behandling av PTSD-relaterad symtom behövs dessa frågeställningar klarläggas för att snabbare kunna ställa diagnos och kunna ge tidigbehandling till individer med PTSD.
Post-traumatic stress disorder (PTSD) is a trauma-related disorder that is difficult to get an overall picture of because of lack of statistics regarding affected individuals, most likely due to a large number of unrecorded cases. The symptoms of this disease are very individual and the perceived symptoms are many, which create a difficulty in diagnosing the disease. Anyone can be affected at any time during his or her lifetime, where effective treatment still needs to be developed. During a trauma our alarm systems in the body warns us of danger and then the brain structure amygdala has a central role. Because the amygdala is of great importance for our understanding of dangers, this study set out to examineif these traumatic events cause the symptoms of PTSD. More specifically, the purpose of this study was to examine if changes in the amygdala and nearby regions may contribute to the symptoms experienced by individuals with PTSD, as well as if the neurological changes that occurred in these brain regions may be a contributing factor to the onset of the disease. Of the six selected original articles it could be noted that certain neurological changes, including amygdala activity and cortical volume, could be linked to certain perceived symptoms together with heightened alertness and emotional regulation skills. Article 1 showed reduced volume of gray matter in the premotor cortex and the anterior cingulate cortex (p <0.05), and those individuals with PTSD had more difficulties handling everyday challenges together with less positive attitudes (p <0.0001). Article 2 showed that the volume of gray matter had correlations with the severity of PTSD and symptoms. Article 3 showed that individuals with PTSD had a decreased activity in the right and left amygdala and ventral striatum (p <0.005). There, emotional numbing had correlations with right ventral striatum (p <0.05). Article 4 showed that those with PTSD had altered cortex in the right hemisphere was the eight regions and in the left six regions that probably was associated with total CAPS score. Article 5 indicated that PTSD group had a higher response in the right amygdala at sight of the faces daunting (p <0.05) and the right amygdala activity was associated with elevated symptom vigilance. Article 6 showed that the ability to regulate emotions was altered in individuals with PTSD. Both the intensification of a sense (amygdala (p <0:04), the posterior cingulate cortex (p <0:01), anterior cingulate cortex (p <0:04), middle cingulate cortex (p <0:02), left inferior frontal cortex (p <0:04) left putamen (p <0.04), bilateral inferior parietal lobe (p <0.03)) and the reduction of sensation (the inferior frontal cortex (p <0.01), the left putamen (p<0.02), bilateral inferior parietal lobe (p <0.01 ), insula (p <0:03)). This study could thus not demonstrate distinct brain areas, linked to amygdala, which had changes that may have caused the onset of anxiety-related disorders in PTSD. Since the brain is very complex and can process impressions in very different ways, these results may be explained by the different types of trauma that the individuals were exposed to,which in turn could affect different brain regions. It is thus important that more studies with larger number of participants, and similar traumatic events, continues highlighting PTSD symptoms and their relationship to amygdala and related brain regions to increase understanding of the onset of PTSD. As knowledge today is limited in the treatment of PTSD-related symptoms, these issues must be continuously examined to develop earlier diagnosecriterias and finally propose proper treatments for individuals with PTSD.

Rhythmic network oscillations are observed in cortical structures during many cognitive states in vivo including memory formation, processing and consolidation and are implicated in the temporal coding of sensory information. The basolateral amygdala (BLA) has a fundamental role in affective memory processing.

This thesis investigates the roles of the amygdala and hippocampus in Pavlovian conditioning. Three questions are addressed. First, what is the involvement of discrete sub-nuclei of the amygdala in Pavlovian conditioning? Second, what molecular processes accompany the retrieval of Pavlovian associations? Third, what changes in gene expression are induced during the acquisition of a Pavlovian association? The basolateral region of the amygdala (BLA) is widely believed to represent the site of CS-US association in Pavlovian conditioning. Recent experiments have however suggested that the BLA may play a more restricted role in Pavlovian conditioning, and that other nuclei and within and outside the amygdala can support the formation of Pavlovian associations. In a first series of experiments the effect of BLA lesions on aversive Pavlovian conditioning were investigated. Lesions of the BLA were found to disrupt conditioning to both discrete and contextual stimuli, as assessed by conditioned freezing, but the effect of BLA lesions on contextual conditioning was ameliorated by additional training. In a second group of experiments the effect of amygdala lesions on the ability of Pavlovian cues to motivate instrumental responding (Pavlovian to instrumental transfer, PIT) was studied. Lesions of the BLA were found to be without effect on PIT, but lesions of the central nucleus of the amygdala (CeN) abolished this effect, as did lesions of the nucleus accumbens (NAcc) core. These results demonstrate that there are dissociable roles of the BLA and CeN within Pavlovian conditioning, and suggest that the CeN and NAcc core interact in PIT.

The amygdala central nucleus (CeN) is a heterogeneous structure lying within the medial temporal lobe and is known to be involved in the processing and reacting to emotional events. Traditionally, the CeN has been the focus of research investigating aversive Pavlovian conditioning, specifically in the acquisition and expression of fear responses. Here, a series of experiments have been conducted to examine the role of the CeN in appetitive instrumental conditioning. Generally in this type of learning, behaviours are initially goal-directed and sensitive to the outcome value, but after a period of training, behaviours shift to being habitual. The role of the CeN in habitual control of instrumental actions was investigated in an overtraining-induced habit in rats. It was found that the anterior region of the CeN (aCeN) is critical for habit acquisition. Furthermore, experiments to investigate interactions of the aCeN and its efferent and afferent structures were also conducted. Using asymmetrical lesions to disconnect regions of interest, it was found that the aCeN interacts with both the dorsolateral striatum (DLS) and the basolateral complex of the amygdala (BLAC) in habit acquisition in distinct and dissociable ways. These results are the first to implicate the CeN and its connection with the circuit involving the DLS and BLAC in habit learning. Furthermore, they imply that, in instrumental conditioning, regions of the amygdala parse the instrumental outcome into reward and reinforcement signals mediating goal-directed and habitual actions.

Pain places a great burden upon society, and a better understanding of pain circuitry will be critical to developing new therapies. Of interest is the connection between the medial nucleus of the central amygdala (CeM) and periaqueductal gray (PAG), due to its role in producing analgesia. Opioid and cannabinoid analgesics act upon this pathway, though their specific sites of action within amygdala pain circuitry has not been fully determined. Therefore, the present study aimed to address this using tract tracing and whole cell patch clamp electrophysiology. Retrograde tracer was injected into the rat PAG, and the effects of opioids and cannabinoids on inhibitory inputs to labelled and unidentified CeM neurons was recorded. Notably, while DAMGO reduced inhibitory input to the CeM in both unidentified and labelled projection neurons, deltorphin inhibited inputs to unidentified neurons alone, and U69593 to only projection neurons. DHPG also produced short-term inhibition of inhibitory inputs to CeM neurons, which was abolished by AM251 in unidentified but not labelled neurons. This inhibition was associated with an extended recovery time, which was reduced by AM251 in both populations. These findings suggest that pain processing amygdala circuitry is differentially modulated by opioid receptor agonists. DHPG also modulates this circuitry, however in projection neurons, short-term inhibition seemed to be cannabinoid-independent and longer-term inhibition to be cannabinoid-dependent, potentially indicative of cannabinoid-dependent long-term depression (LTD). Overall, this study is the first to electrophysiologically demonstrate a role for cannabinoids in modulating inputs to PAG-projecting CeM neurons, as well as for κ-receptor agonists in preferentially inhibiting these inputs. This broadens our understanding of how these analgesics interact with pain circuitry via the amygdala, and may lead to more successful manipulation of this pathway to effectively manage pain.

Diversos desordres neuropsiquiàtrics en humans estan relacionats amb una disfunció en el control de les emocions i del comportament social, i alguns d'ells estan associats a una alteració en el desenvolupament de l'amígdala. El control de les emocions i del comportament social estan, en particular, associats a la denominada amígdala estesa, un corredor de cèl·lules del telencèfal basal que s'estén des de l'amígdala centromedial al nucli del llit de l'estria terminal (BST), que constitueix l'estació d'eixida mes important cap a centres efectors de l'hipotàlem i tronc encefàlic. No obstant això, hi ha molts aspectes del desenvolupament de l'amígdala estesa que es desconeixen, incloent l'origen embrionari de les seves diferents subpoblacions de neurones. L'objectiu d'esta Tesi ha sigut investigar l'origen de les neurones de l'amígdala estesa en embrions de ratolí (E13.5-E16.5) per mitjà d'assajos de migració in vitro. Els resultats d'estos assajos es van combinar amb inmunofluorescencia per a analitzar el fenotip de les neurones que van migrar a l'amígdala des d'orígens distints, i es van comparar amb dades d'inmunohistoquímica (per a marcar distints neuropèptids, proteïnes o enzims) i hibridació in situ (per a detectar el RNAm de diferents factors de transcripció i altres proteïnes) per a ajudar en la delimitació de distints dominis embrionaris del prosencèfal i distintes subdivisions de l'amígdala estesa. En particular, esta Tesi està dedicada a l'estudi de l'origen embrionari de les neurones de les dos subdivisions (o subcorredors) principals de l'amígdala estesa, l'amígdala medial estesa (Capítol 2) i l'amígdala central estesa (Capítol 3). En relació a l'amígdala medial estesa (Capítol 2), la present Tesi proporciona evidència experimental de l'origen múltiple de les seves neurones principals, incloent les de l'amígdala medial i les del BST medial. En particular, aquest estudi aporta proves que indiquen que una gran part de les neurones de l'amígdala medial i el BST medial deriva de la part caudoventral de l'eminència ganglionar medial (MGEcv, prèviament coneguda com, o inclosa en, l'àrea peduncular anterior), formant un subcorredor de cèl·lules amb característiques moleculars semblants (expressió del factor de transcripció Lhx6 i la proteïna calbindina). La comparació amb altres dades indica que les neurones d'aquest subcorredor de cèl·lules que deriven de MGEcv estan interconnectades i projecten a les mateixes dianes de l'hipotàlem, involucrades en el control del comportament reproductor. Esta Tesi també aporta dades experimentals que demostren que el pal·li ventral produeix algunes neurones de l'amígdala medial, que pareixen expressar el factor de transcripció Lhx9. Els resultats també confirmen que algunes neurones de l'amígdala medial estesa s'originen en l'àrea preòptica (les nostres dades indiquen que s'originen específicament en l'àrea preòptica comissural o POC, i aquest origen es correlaciona amb expressió de la proteïna senyalitzadora Shh) i en el domini supraopto-paraventricular de l'hipotàlem (SPV, que dóna lloc a neurones amb expressió postmitòtica dels factors de transcripció Lhx5 i Otp). De forma semblant a les neurones que deriven de MGEcv, és possible que les neurones de l'amígdala medial estesa que deriven d'altres dominis embrionaris també formen distints subcorredors de cèl·lules amb funcions específiques. En relació a l'amígdala central estesa (Capítol 3), els resultats d'esta Tesi mostren que els seus principals components, incloent l'amígdala central i el BST lateral, són mosaics formats per distintes proporcions de neurones derivades de la part dorsal de l'eminència ganglionar lateral (LGEd), la part ventral de l'eminència ganglionar lateral (LGEv), o l'eminència ganglionar medial (MGE). La neurones derivades de LGEd expressen el factor de transcripció Pax6 i invadeixen preferentment les parts laterals de l'amígdala central, encara que unes poques també arriben al BST lateral. Basant-se en correlació amb el RNAm de pre-proencefalina i altres dades, moltes d'aquestes cèl·lules són probablement neurones de projecció encefalinèrgiques. Les neurones derivades de LGEv expressen el factor de transcripció Islet1 i invadeixen principalment la part central i medial de l'amígdala central, i part del BST lateral. La correlació amb altres estudis suggereix que aquestes cèl·lules són probablement les neurones de projecció que contenen el factor alliberador de la corticotropina. D'altra banda, MGE produeix la majoria de les neurones del BST lateral, però la part caudoventral del MGE (MGEcv) també produeix una important subpoblació de neurones de projecció que expressen somatostatina que invadeixen la part medial de l'amígdala central. Així, distints tipus de neurones de projecció s'originen en distints dominis embrionaris, però els mateixos dominis produeixen neurones per a quasi totes les parts de l'amígdala central estesa, la qual cosa podria explicar la similitud de les neurones en característiques neuroquímiques i connexions al llarg del corredor. Els resultats, junt amb altres dades publicades, també suggereixen l'existència de al menys tres subcorredors de cèl·lules en l'amígdala central estesa, cada un relacionat amb un origen embrionari distint i involucrat en el control d'un aspecte diferent de les respostes de por i ansietat. En resum, aquest estudi proporciona importants dades que aclareixen aspectes rellevants del desenvolupament i organització adulta de l'amígdala estesa, i ajuda a establir les bases per a una millor comprensió del control neural de les emocions i el comportament social en condicions normals i patològiques.
Varios desórdenes neuropsiquiátricos humanos están relacionados con una disfunción en el control de las emociones y del comportamiento social, y algunos de ellos están asociados a una alteración en el desarrollo de la amígdala. El control de las emociones y el comportamiento social están, en particular, asociados a la denominada amígdala extendida, un corredor de células del telencéfalo basal que se extiende desde la amígdala centromedial al núcleo del lecho de la estria terminal (BST), que constituye la estación de salida mas importante hacia centros efectores del hipotálamo y tronco encefálico. Sin embargo, existen muchos aspectos del desarrollo de la amígdala extendida que se desconocen, incluyendo el origen embrionario de sus diferentes subpoblaciones de neuronas. El objetivo de esta Tesis ha sido investigar el origen de las neuronas de la amígdala extendida en embriones de ratón (E13.5-E16.5) mediante ensayos de migración in vitro. Los resultados de estos ensayos se combinaron con inmunofluorescencia para analizar el fenotipo de las neuronas que migraron a la amígdala desde orígenes distintos, y se compararon con datos de inmunohistoquímica (para marcar distintos neuropéptidos, proteinas o enzimas) e hibridación in situ (para detectar el RNAm de diferentes factores de transcripción y otras proteinas) para ayudar en la delimitación de distintos dominios embrionarios del prosencéfalo y distintas subdivisiones de la amígdala extendida. En particular, esta Tesis está dedicada al estudio del origen embrionario de las neuronas de las dos subdivisiones (o subcorredores) principales de la amígdala extendida, la amígdala medial extendida (Capítulo 2) y la amígdala central extendida (Capítulo 3). En relación a la amígdala medial extendida (Capítulo 2), la presente Tesis proporciona evidencia experimental del origen múltiple de sus neuronas principales, incluyendo las de la amígdala medial y las del BST medial. En particular, este estudio aporta pruebas que indican que una gran parte de las neuronas de la amígdala medial y el BST medial deriva de la parte caudoventral de la eminencia ganglionar medial (MGEcv, previamente conocida como, o incluida en el área peduncular anterior), formando un subcorredor de células con características moleculares similares (expresión del factor de transcripción Lhx6 y la proteina calbindina). La comparación con otros datos indica que las neuronas de este subcorredor de células que derivan de MGEcv están interconectadas y proyectan a las mismas dianas del hipotálamo, involucradas en control del comportamiento reproductor. Esta Tesis también aporta datos experimentales que demuestran que el palio ventral produce algunas neuronas de la amígdala medial, que parecen expresar el factor de transcripción Lhx9. Los resultados también confirman que algunas neuronas de la amígdala medial extendida se originan en el área preóptica (nuestros datos indican que se originan específicamente en el área preóptica comisural o POC, y este origen se correlaciona con expresión de la proteina señalizadora Shh) y en el dominio supraopto-paraventricular del hipotálamo (SPV, que da lugar a neuronas con expresión postmitótica de los factores de transcripción Lhx5 y Otp). De forma similar a las neuronas que derivan de MGEcv, es posible que las neuronas de la amígdala medial extendida que derivan de otros dominios embrionarios también formen distintos subcorredores de células con funciones específicas. En relación a la amígdala central extendida (Capítulo 3), los resultados de esta Tesis muestran que sus principales componentes, incluyendo la amígdala central y el BST lateral, son mosaicos formados por distintas proporciones de neuronas derivadas de la parte dorsal de la eminencia ganglionar lateral (LGEd), la parte ventral de la eminencia ganglionar lateral (LGEv), o la eminencia ganglionar medial (MGE). La neuronas derivadas de LGEd expresan el factor de transcripción Pax6 e invaden preferentemente las partes laterales de la amígdala central, aunque unas pocas también alcanzan el BST lateral. En base a correlación con el RNAm de pre-proencefalina y otros datos, muchas de estas células son probablemente neuronas de proyección encefalinérgicas. Las neuronas derivadas de LGEv expresan el factor de transcripción Islet1 e invaden principalmente la parte central y medial de la amígdala central, y parte del BST lateral. La correlación con otros estudios sugiere que estas células son probablemente las neuronas de proyección que contienen el factor liberador de la corticotropina. Por otro lado, MGE produce la mayoría de las neuronas del BST lateral, pero la parte caudoventral del MGE (MGEcv) también produce una importante subpoblación de neuronas de proyección que expresan somatostatina que invaden la parte medial de la amígdala central. Así, distintos tipos de neuronas de proyección se originan en distintos dominios embrionarios, pero los mismos dominios producen neuronas para casi todas las partes de la amígdala central extendida, lo que podría explicar la similitud de las neuronas en características neuroquímicas y conexiones a lo largo del corredor. Los resultados, junto con otros datos publicados, también sugieren la existencia de al menos tres subcorredores de células en la amígdala central extendida, cada uno relacionado a un origen embrionario distinto e involucrado en el control de un aspecto diferente de las respuestas de miedo y ansiedad. En resumen, este estudio proporciona importantes datos que clarifican aspectos relevantes del desarrollo y organización adulta de la amígdala extendida, y ayuda a establecer las bases para una mejor comprensión del control neural de las emociones y el comportamiento social en condiciones normales y patológicas.
Dysfunctions in emotional control and social behavior are behind several human neuropsychiatric disorders, some of which are associated to an alteration of amygdalar development. The control of emotions and social behavior is particularly associated to the so-called extended amygdala, which is a cell corridor of the basal telencephalon extending from the centromedial amygdala to the bed nucleus of the stria terminalis (BST), that constitutes the major output station to effector centers of the hypothalamus and brainstem. However, many aspects of the development of the extended amygdala remain elusive, including the embryonic origin of its different neuron subpopulations. The aim of this Thesis has been to investigate the origin of the neurons of the extended amygdala in mouse embryos (E13.5-E16.5) by using in vitro migration assays. The fate mapping results were combined with immunofluorescence for analyzing the phenotype of the neurons that migrated to the amygdala from distinct origins, and were compared with data from immunohistochemistry (to label distinct neuropeptides, proteins or enzymes) and in situ hibridization (to detect the mRNA expression of different transcription factors and other proteins) which helped in the delineation of forebrain embryonic domains and extended amygdala subdivisions. In particular, this Thesis deals with studing the embryonic origin of the neurons of the two major subdivisions (or subcorridors) of the extended amygdala, the medial extended amygdala (Chapter 2) and the central extended amygdala (Chapter 3). Regarding the medial extended amygdala (Chapter 2), this Thesis provides experimental evidence for a multiple embryonic origin of its principal neurons, including those of the medial amygdala and medial BST. In particular, this study provides novel evidence indicating that a major part of the neurons of the medial amygdala and medial BST derives from the caudoventral part of the medial ganglionic eminence (MGEcv, previously called or included as part of the anterior peduncular area), forming a cell subcorridor with similar molecular features (expression of the transcription factor Lhx6 and the protein calbindin). Comparison to other data indicates that neurons along this MGEcv-related cell subcorridor are interconnected and project to the same hypothalamic targets, which are involved in reproductive behavior. This Thesis also provides novel experimental evidence indicating that the ventral pallium produces some neurons for the medial amygdala, which appear to express the transcription factor Lhx9. The results also confirm that some neurons of the medial extended amygdala originate in the preoptic area (our results indicate that these cells specifically originate in its commissural subdivision or POC and correlate to expression of the signaling protein Sonic hedgehog) and the supraopto-paraventricular domain of the hypothalamus (or SPV, which derived neurons express the transcription factors Lhx5 and Otp). Similarly to the neurons derived from MGEcv, it is possible that neurons of the medial extended amygdala derived from other embryonic domains also form distinct cell subcorridors related to specific functions. Regarding the central extended amygdala (Chapter 3), the results of this Thesis show that its major components, including central amygdala and lateral bed nucleus of the stria terminalis (BST), are mosaics formed by different proportions of dorsal lateral ganglionic eminence (LGE)-, ventral LGE- and medial ganglionic eminence (MGE)- derived neurons. Dorsal LGE-derived neurons express the transcription factor Pax6, and primarily populate lateral parts of the central amygdala, but a few also reach the lateral BST. Based on correlation with pre-proenkephalin mRNA and other data, many of these cells are likely enkephalinergic projection neurons. The ventral LGE-derived neurons express the transcription factor Islet1, and primariy populate the central and medial parts of the central amygdala, and part of the lateral BST. Correlation with other studies suggests that these cells represent projection neurons expressing corticotropin-releasing factor. The MGE produces the majority of neurons of lateral BST, but its caudoventral subdivision (MGEcv) also produces an important subpopulation of projection neurons containing somatostatin for medial aspects of the central amygdala. Thus, distinct principal neurons originate in different embryonic domains, but the same domains contribute neurons to most subdivisions of the central extended amygdala, which may explain the similarity in neurochemistry and connections along the corridor. The results, together with other published data, also suggest the existence of at least three subcorridors within the central extended amygdala, each related to a different embryonic origin and involved in the control of a different aspect of fear responses and anxiety. In conclusion, this study provides important data that clarify relevant aspects on the development and adult organization of the extended amygdala, and helps to set up the foundations for a better understanding of neural control of emotions and social behavior in normal and abnormal conditions.

Occasional stress is a normal aspect of mammalian life. However repeated or prolonged stress exposure dysregulates stress responses and contributes to the onset or exacerbation of affective disorders such as anxiety, depression and post-traumatic stress disorder (PTSD). Understanding the underlying mechanism of the effect of stress on affective behaviors is essential for effective prevention and treatment of these disorders.

All affective disorders share a deficit in the regulation of emotion. The amygdala plays crucial role in this regulation and is adversely affected by stress. This suggests that stress precipitates abnormal affective state by altering amygdala function. While the effect of acute stress on the amygdala has been well described, less is know about the impact of repeated stress nor its age-dependency. We hypothesized that repeated stress leads to a hyperactive amygdala and impairs the amygdala function in regulating affective behaviors, and such impacts are greater during prepubescence than during adulthood. In this study, we subjected prepubescent (postnatal day, PND ∼30) and adult rats (PND ∼65) to repeated restraint stress. We then measured the effect of stress on amygdala physiology and amygdala-dependent behavior in prepubescent (PND ∼40) and adult (PND ∼75) rats. The results were compared between age-matched non-restraint and repeated restraint groups and across age. Repeated restraint stress increased basolateral amygdala (BLA) spontaneous population activity in prepubescent rats whereas it enhanced individual neuron activity in adult rats. In parallel with these physiological changes, repeated restraint stress enhanced initial expression of conditioned fear in both age groups, but impaired within session fear extinction only in prepubescent rats. Further studies demonstrated that repeated restraint stress reduced the BLA projection neuron inhibition by exogenous GABA in prepubescent rats. However, repeated restraint stress enhanced the BLA projection neuron excitation by exogenous glutamate in adult rats. In addition, repeated restraint reduced basal GABA transmission and enhanced mPFC-induced excitation of spontaneously active BLA projection neurons in both age groups. Together, these findings indicate that repeated restraint results in a generalized hyperactive and hyper-responsive amygdala. The distinct changes in amygdala physiology at different developmental stages might underlie age-dependent effect of stress on affective behaviors. Overall, this study leads to a better understanding of the pathophysiology of stress-related affective disorders and provide insight into age-specific treatment of these disorders.