Academic literature on the topic 'Motoneurones'

Bath application of the muscarinic agonist pilocarpine onto the deafferented stick insect thoracic nerve cord induced long-lasting rhythmic activity in leg motoneurones. Rhythmicity was induced at concentrations as low as 1x10(-4) mol l-1 pilocarpine. The most stable rhythms were reliably elicited at concentrations from 2x10(-3) mol l-1 to 5x10(-3) mol l-1. Rhythmicity could be completely abolished by application of atropine. The rhythm in antagonistic motoneurone pools of the three proximal leg joints, the subcoxal, the coxo-trochanteral (CT) and the femoro-tibial (FT), was strictly alternating. In the subcoxal motoneurones, the rhythm was characterised by the retractor burst duration being correlated with cycle period, whereas the protractor burst duration was almost independent of it. The cycle periods of the rhythms in the subcoxal and CT motoneurone pools were in a similar range for a given preparation. In contrast, the rhythm exhibited by motoneurones supplying the FT joint often had about half the duration. The pilocarpine-induced rhythm was generated independently in each hemiganglion. There was no strict intersegmental coupling, although the protractor motoneurone pools of the three thoracic ganglia tended to be active in phase. There was no stereotyped cycle-to-cycle coupling in the activities of the motoneurone pools of the subcoxal joint, the CT joint and the FT joint in an isolated mesothoracic ganglion. However, three distinct 'spontaneous, recurrent patterns' (SRPs) of motoneuronal activity were reliably generated. Within each pattern, there was strong coupling of the activity of the motoneurone pools. The SRPs resembled the motor output during step-phase transitions in walking: for example, the most often generated SRP (SRP1) was exclusively exhibited coincident with a burst of the fast depressor trochanteris motoneurone. During this burst, there was a switch from subcoxal protractor to retractor activity after a constant latency. The activity of the FT joint extensor motoneurones was strongly decreased during SRP1. SRP1 thus qualitatively resembled the motoneuronal activity during the transition from swing to stance of the middle legs in forward walking. Hence, we refer to SRPs as 'fictive step-phase transitions'. In intact, restrained animals, application of pilocarpine also induced alternating activity in antagonistic motoneurone pools supplying the proximal leg joints. However, there were marked differences from the deafferented preparation. For example, SRP1 was not generated in the latter situation. However, if the ipsilateral main leg nerve was cut, SRP1s reliably occurred. Our results on the rhythmicity in leg motoneurone pools of deafferented preparations demonstrate central coupling in the activity of the leg motoneurones that might be incorporated into the generation of locomotion in vivo.

In adults, muscle fibres match the functional requirements of the motoneurone that supplies them. During early stages of postnatal development of the rat neither muscle fibre properties, nor activity patterns of motoneurones supplying fast and slow muscles have completed their differentiation. Nevertheless, even at this early stage of development the muscles have characteristic properties that are well matched to the activity patterns of immature motoneurones. With further development differentiation of motoneurone activity and muscle fibre properties goes hand in hand. If during this period of linked differentiation, connections between the motoneurones and muscle fibres are disrupted, the development of fast muscles is permanently impaired.

An adaptive gain control system of a proprioceptive feedback system, the femur­tibia control loop, is investigated. It enables the joint control loop to work with a high gain but it prevents instability oscillations. In the inactive stick insect, the realisation of specific changes in gain is described for tibial torque, for extensor tibiae muscle force and for motoneuronal activity. In open-loop experiments, sinusoidal stimuli are applied to the femoral chordotonal organ (fCO). Changes in gain that depend on fCO stimulus parameters (such as amplitude, frequency and repetition rate), are investigated. Furthermore, spontaneous and touch-induced changes in gain that resemble the behavioural state of the animal are described. Changes in gain in motoneurones are always realised as changes in the amplitude of modulation of their discharge frequency. Nevertheless, depending on the stimulus situation, two different mechanisms underlie gain changes in motoneurones. (i) Changes in gain can be based on changes in the strength of the sensorimotor pathways that transmit stimulus-modulated information from the fCO to the motoneurones. (ii) Changes in gain can be based on changes in the mean activity of a motoneurone by means of its spike threshold: when, during the modulation, the discharge of a motoneurone is inhibited for part of the stimulus cycle, then a change in mean activity subsequently causes a change in modulation amplitude and gain. A new neuronal mechanism is described that helps to compensate the low-pass filter characteristics of the muscles by an increased activation, especially by a sharper distribution of spikes in the stimulus cycle at high fCO stimulus frequencies.

Stereotyped responses were evoked in a number of motoneurones in the appendages of semi-intact crayfish when the command neurones for escape behaviour were activated. The medial giant neurones mediated short latency responses in pereiopod common inhibitor, promotor and extensor motoneurones, several abdominal first root neurones and one uropod exopodite promotor motoneurone. The lateral giant neurones mediated short latency responses in the pereiopod common inhibitor neurones, the same abdominal first root neurones and one uropod protopodite promotor motoneurone. These responses can be correlated with stereotyped movements of the appendages which occur in the normal escape behaviour of crayfish. Note:

In spite of our knowledge of activity related adaptations in supraspinal neurones and skeletal muscles, very little is known concerning adaptations in α-motoneurones to alterations in chronic activity levels. Recent evidence shows that the biophysical properties of α-motoneurones are plastic and adapt to both increases and decreases in chronic activation. The nature of the adaptations-in resting membrane potential, spike threshold, afterhyperpolarization amplitude, and rate of depolarization during spike generation-point to involvement of density, type, location, and/or metabolic modulation of ion conductance channels in the motoneuronal membrane. These changes will have significant effects on how motoneurones respond when activated during the generation of movements, and on the effort required to sustain activation during prolonged exercise. Since the adaptations most likely involve structural changes in the motoneurones and changes in protein synthesis, and change the output response of the cells to input, they are considered to be learning responses. Future research directions for examining this issue are outlined. Key words: α-motoneurones, exercise, training, spinal cord, learning, disuse, spinal cord transection

The actions of serotonin and norepinephrine were investigated on spinal motoneurones in isolated, hemisected rat and frog spinal cords. Serotonin and norepinephrine induced slowly developing depolarizations of spinal motoneurones which were frequently preceded by brief, low amplitude hyperpolarizations. Neither the depolarizations nor the hyperpolarizations were attenuated by 20 mM Mg2+ or tetrodotoxin, although synaptic transmission was blocked in both cases. It thus appears unlikely that the action of serotonin and norepinephrine on spinal motoneurone polarization and results from an indirect action via interneurones.

Motoneurones that drive the closing of the lateral teeth during gastric mill rhythms in spiny lobsters start firing before the motoneurones that drive the medial tooth powerstroke. This has the expected behavioural interpretation that the lateral teeth must close on a food particle before the medial tooth is pulled across it. The neural basis of the teeth coordination was examined. Experiments were made during gastric rhythms in in vitro preparations comprising the stomatogastric, oesophageal and (paired) commissural ganglia. Identified neurones in the stomatogastric ganglion were polarized to study their functional effects on the phasing and amplitude of bursts in other cells. Evoked firing of the lateral teeth closer motoneurones (especially LC) would evoke a discharge in the medial tooth powerstroke (GM) motoneurones, and suppress the firing of the medial tooth returnstroke (CP) motoneurone. Therefore the coordination pathway starts directly with the lateral teeth closer motoneurones. The CI interneurone was found to be an important link in the coordination pathway. It exerted opposite effects on the medial tooth motoneurones, suppressing firing of the powerstroke GM cells while evoking bursts in the returnstroke CP cell. CI affected other features of the pattern as well. Non-spiking inhibition from the lateral teeth closer motoneurones (LC and GP) to the lateral teeth opener motoneurones (LGs) was found to occur conjointly with spike-mediated IPSPs. Hyperpolarization of the LC, GP or CI neurones could temporarily abolish the gastric rhythm, but bursting in some or all of the other cells would eventually return, although in some cases the phase pattern was altered. It appears that no individual neurone in the gastric network is necessary for rhythm production. The coordination system can be viewed as several ‘levels’ of synaptic connections, each level being redundant and synergistic with the others.

Motoneurone disease (MND or amyotrophic lateral sclerosis) is a paralysing disease of unknown cause involving progressive, widespread muscle atrophy due to degeneration of spinal and other motoneurones and an accompanying loss of Betz cells in the motor cortex. A current hypothesis attributes the disease to the loss of a muscle-derived neurotrophic factor acting in concert with the normal age-related deterioration and loss of motoneurones. The roots of this hypothesis are traced through research based mainly on the developing neuromuscular system, and in particular on the age-related processes of natural motoneurone death during embryogenesis: the neonatal reduction of polyneuronal innervation and the age-dependent variations in motor nerve terminal sprouting in response to partial denervation. A consideration of the disease process itself in association with the review of earlier work provide the background for the present work which reexamines ultrastructurally the chromatolytic and later responses to axotomy and the muscle-dependent factors responsible for the reformation of the Nissl bodies.

The role of centrally located motoneurones in producing the whole-body withdrawal response of Lymnaea stagnalis (L.) was investigated. The motoneurones innervating the muscles used during whole-body withdrawal, the columellar muscle (CM) and the dorsal longitudinal muscle (DLM) were cells with a high resting potential (−60 to −70 mV) and thus a high threshold for spike initiation. In both semi-intact and isolated brain preparations these motoneurones showed very little spontaneous spike activity. When spontaneous firing was seen it could be correlated with the occurrence of two types of spontaneous excitatory postsynaptic potential (EPSP). One was a unitary EPSP that occasionally caused the initiation of single action potentials. The second was a larger-amplitude, long-duration (presumably compound) EPSP that caused the motoneurones to fire a burst of high-frequency action potentials. This second type of EPSP activity was associated with spontaneous longitudinal contractions of the body in semi-intact preparations. Tactile stimulation of the skin of Lymnaea evoked EPSPs in the CM and DLM motoneurones and in some other identified cells. These EPSPs summated and usually caused the motoneurone to fire action potentials, thus activating the withdrawal response muscles and causing longitudinal contraction of the semi-intact animal. Stimulating different areas of the body wall demonstrated that there was considerable sensory convergence on the side of the body ipsilateral to stimulation, but less on the contralateral side. Photic (light off) stimulation of the skin of Lymnaea also initiated EPSPs in CM and DLM motoneurones and in some other identified cells in the central nervous system (CNS). Cutting central nerves demonstrated that the reception of this sensory input was mediated by dermal photoreceptors distributed throughout the epidermis. The activation of the CM and DLM motoneurones by sensory input of the modalities that normally cause the whole-body withdrawal of the intact animal demonstrates that these motoneurones have the appropriate electrophysiological properties for the role of mediating whole-body withdrawal.

One of the postural reflexes of crayfish, the uropod steering response, is elicited by specific sensory inputs while the animal is walking. It is not elicited, however, by the same inputs when the animal is at rest. To clarify the neuronal mechanisms underlying this facilitatory control of body posture in the active animals, we used intracellular recordings to analyse the synaptic activities of uropod motor system neurones in an unanaesthetized whole-animal preparation. Several uropod motoneurones were found to receive sustained depolarizing inputs during walking, whereas the walking leg motoneurones sampled always showed rhythmic activity. The membrane conductance of the uropod motoneurones increased during the sustained synaptic activity. Premotor nonspiking interneurones showed depolarizing or hyperpolarizing membrane potential changes during walking that were also accompanied by increases in membrane conductance. Some of these interneurones enhanced uropod motoneurone activity, whereas others suppressed it during walking. These results suggest that the background excitability of uropod motoneurones is kept at an intermediate level during walking by the antagonistic inputs from premotor nonspiking interneurones so that the uropod motor system can be responsive to both further excitatory and inhibitory inputs resulting from postural changes. <P>

L'Atròfia Muscular Espinal (AME) és una malaltia neurodegenerativa greu i la primera causa genètica de mort infantil. S'origina per la pèrdua o mutació del gen Survival Motor Neuron 1 (SMN1) que causa una deficiència de la proteïna de Survival Motor Neuron (SMN). La reducció d'aquesta proteïna condueix principalment a la degeneració de les motoneurones (MNs) de la medul·la espinal i, en conseqüència, produeix atròfia i feblesa del múscul esquelètic. Actualment, només es coneix parcialment quins mecanismes cel·lulars i moleculars exactes són els responsables de la pèrdua de funció de les MNs. La reducció de SMN causa degeneració de les neurites i mort cel·lular sense característiques apoptótiques clàssiques. L'autofàgia és un procés important i altament regulat, essencial per a l'eliminació d'orgànuls danyats i substàncies o proteïnes tòxiques a través de la degradació amb els lisosomes. L'autofàgia és especialment important en cèl·lules post-mitòtiques, com les MNs, on l'acumulació d’autofagosomes provoca la interrupció del transport axonal, la interferència del trànsit intracel·lular i la degeneració de les neurites. El que és ben sabut en l'AME és que el nivell intracel·lular de proteïna SMN defineix l'inici i la gravetat de la malaltia i això està parcialment determinat pel nombre de còpies del gen SMN2, la duplicació centromérica de SMN i el principal modificador de l'AME. Per aquesta raó, comprendre els processos que regulen la degradació de SMN amb la finalitat d'identificar compostos que augmentin els nivells de proteïnes és el principal objectiu en el desenvolupament terapèutic per a l’AME. Les calpaínes són una família de proteases dependents de calci que s'han relacionat amb trastorns musculars i malalties neurodegeneratives. Específicament, s'ha descrit en el múscul que SMN pot ser proteolizada per calpaína. L'activitat de la calpaína també està involucrada en la regulació de l'autofàgia mitjançant la modulació de múltiples de les proteïnes involucrades en el procés. L'objectiu en el present treball ha estat analitzar la desregulació de l'autofàgia i determinar la participació de la calpaína en la regulació de la proteïna SMN en les MNs per a aprofundir en l'origen de la neurodegeneración i desenvolupar un nou enfocament terapèutic per a l'AME. Per aquesta finalitat, hem analitzat marcadors autofágics en diferents models in vitro d’AME, tant de ratolí com d'humà. Els resultats van mostrar que, tant els autofagosomes com els nivells de LC3 es troben augmentats en les mostres d’AME en comparació amb els controls, la qual cosa suggereix una desregulació del procés d'autofàgia al llarg de la progressió de la malaltia. A més, la reducció dels nivells endògens de calpaína utilitzant un shRNA van mostrar un augment dels nivells de Smn i LC3, alhora que prevenia la degeneració neurítica que es produeix en les MNs de ratolí afectats per AME. Es van obtenir resultats similars en experiments in vitro utilitzant un inhibidor farmacològic de calpaína, la calpeptina. Tanmateix, l'activació de la calpaína produïda per condicions despolarizants induïa la proteólisis de l’α-fodrina i de SMN, la qual cosa confirma que calpain regula directament els nivells de proteïna SMN en les MNs. A més, el tractament amb calpeptina in vivo va millorar significativament l'esperança de vida i la funció motora de dos models de ratolins amb AME, la qual cosa demostra la utilitat potencial dels inhibidors de la calpaína en la teràpia per a la malaltia. Finalment, l'anàlisi de la via de la calpaína en ratolins i models cel·lulars humans d’AME va indicar un augment de l'activitat de la calpaína en les MNs amb nivells reduïts de SMN. Per tant, els nostres resultats demostren que l'activitat de la calpaína es troba sobreactivada en les MNs d’AME i que la seva inhibició pot tenir un efecte beneficiós sobre el fenotip de la malaltia a través de l'augment de SMN i la regulació del procés d'autofàgia en les MNs de la medul·la espinal.
La atrofia muscular espinal (AME) es una enfermedad neurodegenerativa grave y la primera causa genética de muerte infantil. Se origina por la pérdida o mutación del gen Survival Motor Neuron 1 (SMN1) que causa una deficiencia de la proteína de Survival Motor Neuron (SMN). La reducción de esta proteína conduce predominantemente a la degeneración de las motoneuronas (MNs) de la médula espinal y, en consecuencia, produce atrofia y debilidad del músculo esquelético. Actualmente, solo se conoce parcialmente que mecanismos celulares y moleculares exactos son los responsables de la pérdida de función de las MNs. La reducción de SMN causa degeneración de neuritas y muerte celular sin características apoptóticas clásicas. La autofagia es un proceso importante y altamente regulado, esencial para la eliminación de orgánulos dañados y sustancias o proteínas tóxicas a través de la degradación con los lisosomas. La autofagia es especialmente importante en células post-mitóticas, como las MNs, donde la acumulación de autofagosomas provoca la interrupción del transporte axonal, la interferencia del tráfico intracelular y la degeneración de las neuritas. Lo que es bien sabido en la AME es que el nivel intracelular de proteína SMN define el inicio y la gravedad de la enfermedad y esto está parcialmente determinado por el número de copias del gen SMN2, la duplicación centromérica de SMN y el principal modificador de la AME. Por esa razón, comprender los procesos que regulan la degradación de SMN con la finalidad de identificar compuestos que aumentan los niveles de proteínas es el principal objetivo en el desarrollo terapéutico de AME. Las calpaínas son una familia de proteasas dependientes de calcio que se han relacionado con trastornos musculares y enfermedades neurodegenerativas. Específicamente, se ha descrito en el músculo que SMN puede ser proteolizada por calpaína. La actividad de la calpaína también está involucrada en la regulación de la autofagia mediante la modulación de múltiples de las proteínas involucradas en el proceso. El objetivo en el presente trabajo ha sido analizar la desregulación de la autofagia y determinar la participación de la calpaína en la regulación de la proteína SMN en las MNs para profundizar en el origen de la neurodegeneración y desarrollar un nuevo enfoque terapéutico para la AME. Con este fin, hemos analizado marcadores autofágicos en diferentes modelos in vitro de AME, tanto de ratón como de humano. Los resultados mostraron que los autofagosomas y los niveles de LC3 se encuentran aumentados en las muestras de AME en comparación con los controles, lo que sugiere una desregulación del proceso de autofagia a lo largo de la progresión de la enfermedad. Además, la reducción de los niveles endógenos de calpaína utilizando un shRNA muestraron un aumento de los niveles de Smn y LC3, a la vez que previene la degeneración neuritica que se produce en las MNs de ratón afectados por AME. Se obtuvieron resultados similares en experimentos in vitro utilizando un inhibidor farmacológico de calpaína, la calpeptina. Asimismo, la activación de calpaína producida por condiciones despolarizantes inducia la proteólisis de α-fodrina y de SMN, lo que confirma que calpain regula directamente los niveles de proteína SMN en las MNs. Además, el tratamiento con calpeptina in vivo mejoró significativamente la esperanza de vida y la función motora de dos modelos de ratones con AME, lo que demuestra la utilidad potencial de los inhibidores de la calpaína en la terapia para la enfermedad. Finalmente, el análisis de la vía de la calpaína en ratones y modelos celulares humanos de AME indicó un aumento de la actividad de la calpaína en las MNs con niveles reducidos de SMN. Por lo tanto, nuestros resultados demuestran que la actividad de la calpaína se encuentra sobreactivada en las MNs de AME y su inhibición puede tener un efecto beneficioso sobre el fenotipo de la enfermedad a través del aumento de SMN y la regulación del proceso de autofagia en las MNs de la médula espinal.
Spinal Muscular Atrophy (SMA) is a severe neurodegenerative disease and the first genetic cause of infant death. It is originated by the deletion or mutation of Survival Motor Neuron 1 (SMN1) gene causing a Survival Motor Neuron (SMN) protein deficiency. The reduction of this protein predominantly leads to the degeneration of spinal cord motoneurons (MNs) and consequently produces skeletal muscle atrophy and weakness. The exact cellular and molecular mechanisms responsible for MN loss of function are only partially known. SMN reduction causes neurite degeneration and cell death without classical apoptotic features. Autophagy is an important and highly regulated process, essential for the removal of damaged organelles and toxic substances or proteins through lysosome degradation. This mechanism is specifically important in post-mitotic cells like MNs where autophagosome accumulation causes axonal transport disruption, interference of intracellular space trafficking, and neurite degeneration. What is well known in SMA is that intracellular SMN protein levels are critical to define the disease onset and severity, and this is partially determined by the number of copies of SMN2, the centromeric duplication of the SMN gene and the main modifier of SMA. For that reason, understanding the processes of SMN stability and degradation to identify compounds that increase protein levels is a major goal in SMA therapeutics development. Calpains are a family of calcium-dependent proteases that have been related to muscle disorders and neurodegenerative diseases. Specifically, it has been described in muscle that SMN can be a proteolytic target of calpain. Calpain activity is also involved in autophagy regulation by modulation of multiple proteins involved in the process. The objectives in the present work have been to analyze the autophagy deregulation and determine the involvement of calpain in SMN protein regulation on MNs, in order to deepen in the origin of neurodegeneration and to develop a new therapeutic approach for SMA disease. To this end, we have analyzed autophagic markers in different mouse and human SMA in vitro models. The results showed that autophagosomes and LC3 levels were increased in SMA samples compared to controls, suggesting a deregulation of the autophagy process throughout the disease progression. Moreover, calpain knockdown using an shRNA approach showed an increase of both, Smn and LC3 levels and prevented neurite degeneration occurred in SMA affected mouse MNs. Similar results were obtained in in vitro experiments using a pharmacological calpain inhibitor, calpeptin. Likewise, calpain activation produced by depolarized conditions induced α-fodrin and SMN proteolysis, confirming that calpain directly regulates the SMN protein level in MNs. Additionally, calpeptin in vivo treatment significantly improved the lifespan and motor function of two severe SMA mouse models, demonstrating the potential utility of calpain inhibitors in SMA therapeutics. Finally, the analysis of calpain pathway members in mice and human cellular SMA models indicated an increase of calpain activity in SMN-reduced MNs. Thus, our results show that calpain activity is increased in SMA MNs and its inhibition may have a beneficial effect on the SMA phenotype through the increase of SMN and the regulation of the autophagy process in spinal cord MNs.

La deuxième semaine qui suit la naissance est critique pour le développement du système locomoteur de la souris. C’est pendant cette semaine que les souriceaux acquièrent leur posture et commencent à marcher. Cette transformation implique une réorganisation en profondeur des éléments composant les unités motrices. Cependant, nous ne savons encore que peu de choses sur la différenciation des propriétés intrinsèques des motoneurones innervant les fibres musculaires. Contrairement à l’adulte, où la décharge démarre au début de la stimulation, les motoneurones de souriceaux déchargent de façon hétérogène. En effet, une stimulation au seuil induit chez certains motoneurones une décharge commençant au début du créneau alors que la décharge est retardée dans d’autres motoneurones. Par des enregistrements de motoneurones sur des tranches de moelle épinière à P6-P10, j’ai dans un premier temps caractérisé les courants sous‐tendant la décharge retardée et j’ai constaté que deux conductances potassiques (l’une ressemblant au courant de type A et l’autre très lente) étaient activées autour du seuil de décharge. Lorsqu’elles s’activent, ces conductances sont capables d’hyperpolariser le potentiel de membrane et d’empêcher le motoneurone de décharger. Puis, en s’inactivant, la membrane se dépolarise et le neurone commence à décharger avec un retard pouvant aller jusqu’à plusieurs secondes après le début du créneau. En outre, les deux populations de motoneurones présentent des propriétés électro-physiologiques et morphologiques différentes. Les motoneurones à décharge retardée possèdent un arbre dendritique plus ramifié que ceux à décharge immédiate. En conséquence, les motoneurones à décharge retardée possèdent une conductance d’entrée et un seuil de recrutement plus faible. De plus le temps de relaxation de l’hyperpolarisation suivant chaque potentiel d’action (AHP) est plus long dans les motoneurones à décharge immédiate. Enfin, une partie des motoneurones à décharge retardée exprime la protéine chondrolectine récemment décrite comme un marqueur moléculaire des motoneurones de type rapide. L’ensemble de nos résultats nous permet de faire l’hypothèse que les motoneurones à décharge retardée sont des motoneurones innervant les unités motrices de type rapide alors que ceux à décharge immédiate innervent les unités motrices de type lent. Dans un second temps, j’ai étudié l’effet de la mutation SOD1 G93A, un modèle murin de la sclérose latérale amyotrophique, sur les motoneurones spinaux à P6‐P10. Sachant que cette maladie affecte les motoneurones de façon différente à l’âge adulte, j’ai cherché à savoir si, chez les souriceaux SOD1 G93A, les motoneurones à décharge retardée et immédiate étaient affectés de la même façon. Mes résultats montrent que seuls les motoneurones à décharge immédiate sont hyperexcitables. Pour ces motoneurones, le seuil de décharge est plus hyperpolarisé et leurs dendrites sont plus courtes de 35%. Ces résultats amènent à reconsidérer le lien supposé entre hyperexcitabilité et dégénérescence des motoneurones
In the second postnatal week, the locomotor behavior of mice changes from crawling to walking. This is made possible by profound changes in motor units. Yet, how the discharge properties of spinal motoneurons evolve during post-­‐natal maturation and whether they have an effect on the motor unit maturation remains an open question. In neonates, the spinal motoneurons display two modes of discharge. For threshold pulses, 33% of the motoneurons have a discharge that start at the current onset and adapts during the pulse (“immediate firing motoneurons”). The remaining 66% motoneurons fire with a large delay and the discharge then accelerates throughout the pulse (“delayed firing motoneurons”). Though the delayed firing pattern is quite common in spinal motoneurons of neonates, the ionic mechanisms that elicit this mode of discharge have received little attention. Using the patch-clamp technique to record P6‐P10 mouse motoneurons in a spinal cord slice preparation, I characterized the ionic currents that underlie the delayed firing pattern. This is caused by a combination of an A-like potassium current that acts on a short time scale and a slow‐inactivating potassium current that delays the discharge on a much longer time scale. I then investigated how these two potassium currents contribute to the recruitment threshold and how they shape the F-I function of delayed motoneurons in neonatal mice. The slow inactivating potassium current induces memory effects that have a strong impact on motoneuron excitability and on its discharge. Building on these results, I tried to correlate the discharge pattern to known physiological sub‐types. The delayed firing motoneurons have a larger input conductance, a higher rheobase, a narrower action potential, a shorter AHP and a more complex dendritic arbor than the immediate firing motoneurons. Additionally, only a sub-­‐population of the delayed firing motoneurons expressed the chondrolectin protein, a fast motoneuron marker. Based on this body of corroborating evidence, the immediate firing motoneurons would be slow type motoneurons whereas the delayed firing motoneurons would be fast type motoneurons. Finally, numerous electrical and geometrical abnormalities have been observed in spinal motoneurons of SOD1 G934 mice (model of the amyotrophic lateral sclerosis) during the second post-natal week but the results were somehow contradictory. In relation to the known differential sensitivity to the disease exhibited by slow and fast motoneurons, I investigated whether the immediate and delayed firing motoneurons are equally affected by the SOD1 mutation. This is not the case. I found that the SOD1 mutation induced a decrease in the rheobase and a hyperpolarization of the voltage threshold only in the immediate firing motoneurons, thereby making them more excitable than in WT mice. Furthermore, the dendrites of the immediate firing motoneurons are substantially shorter (about 35%) in the mutant than in the WT. In sharp contrast, the excitability of the delayed firing motoneurons is unchanged and the dendritic tree is nearly unaffected (the dendrites only undergo a 10% elongation). These results allow for reconsidering the link between hyperexcitability and degenerescence of the motoneurons

L’Esclerosi Lateral Amiotròfica (ELA o ALS) és una malaltia neuromuscular caracteritzada per la degeneració selectiva de les motoneurones (MN) superiors e inferiors del còrtex motor, el tronc de l’encèfal i la medul•la espinal, que resulta en una debilitat, espasticitat i atròfia progressives de la musculatura. Menys del 10% dels casos corresponen a la forma familiar de la malaltia, i un 20% d’aquests estan relacionats a mutacions en el gen de l’enzim superòxid dismutasa 1 (mSOD1). La resta de casos corresponen a la forma esporàdica. Les causes implicades en la degeneració selectiva de les MN en la ELA són encara desconegudes. La seva patogènesi s’ha atribuït a diversos mecanismes com serien l’estrès oxidatiu, l’agregació proteica anormal, la disfunció mitocondrial, el transport axonal aberrant, la neuroinflamació, l’autoimmunitat o l’excitotoxicitat per glutamat. En el present estudi hem treballat amb dues d’aquestes hipòtesis en avaluar l’efecte dels sèrums de pacients amb ELA i altres malalties de la MN sobre l’activitat del receptor ionotròpic de glutamat de tipus N-metil-D-Aspartat (NMDAR), expressat en el model d’oòcit de Xenopus laevis. Mitjançant assaigs de ELISA hem analitzat la presència d’autoanticossos associats a ELA en el sèrum de pacients. L’acció dels sèrums control i patològics en els oòcits de Xenopus produïa la generació de corrents oscil•latoris de clorur (Cl-). Aquests corrents havien estat prèviament descrits en aquestes cèl•lules i són deguts a l’activació dels canals de Cl- dependents de calci (Ca2+), endògens en els oòcits de Xenopus, a causa de la mobilització de Ca2+ intracel•lular. L’alliberació de Ca2+ dels compartiments intracel•lulars es activada per l’acció d’un factor sèric, anomenat àcid lisofosfatídic o lisofosfatidat (LPA), sobre el seu receptor, present en la membrana dels oòcits, i a través d’una via de senyalització de segons missatgers. Així doncs, en aquest model, la generació de corrents oscil•latoris de Cl- és una mesura indirecta de la mobilització intracel•lular de Ca2+. En presència del NMDAR, les respostes generades pel sèrum ELA eren significativament superiors a les activades pel sèrum d’individus sans i d’altres malalties de la MN. La resposta generada pel sèrum ELA presentava una dependència respecte de la presència de les dues subunitats del NMDAR i era sensible al bloqueig del receptor amb MK-801, un antagonista no competitiu. Vàrem reproduir els experiments amb sèrums del model de rata transgènica mSOD1 G93A, considerat un model de la forma familiar de la malaltia. Les mostres de sèrum mSOD1 G93A generaven, en presència del NMDAR, respostes significativament superiors a les activades pel sèrum de rata WT. En analitzar l’acció de la fracció de IgG purificada dels sèrums control i patològics en el model d’oòcit de Xenopus, es generaven corrents transitoris d’entrada de tipus no oscil•latori, els quals diferien dels generats en el cas del sèrum complet. La resposta activada per IgG de pacients amb ELA en presència del NMDAR era també significativament superior a la generada per les IgG d’individus sans. En la segona part d’aquest estudi s’ha comprovat la presència d’anticossos contra la proteïna Semaforina 3A (Sema3A) en alguns sèrums de ELA i Lower Motor Neuron Disease (LMND), una altra forma comuna de malaltia de la MN. La Sema3A és una molècula quimiotàctica de guia axonal recentment relacionada amb la patologia de la ELA en detectar-se una sobreexpressió d’aquesta proteïna en cèl•lules de Schwann terminals del model de ratolí mSOD1 G93A. Tot i descartar-se que els anticossos contra Sema3A siguin un marcador específic de la ELA, al no detectar-se en tots el sèrums de pacients, i alhora, al estar presents també en algunes mostres LMND, aquests autoanticossos podrien tenir un efecte defensiu contra les senyals nocives exercides per Sema3A sobre els axons de les MN.
Amyotrophic lateral sclerosis (ALS) is a devastating neuromuscular disease, characterized by the selective degeneration of the superior motor neurons in the motor cortex and of the inferior motor neurons in the brain-stem and spinal cord. The familial form of the illness is associated with the mutation of the superoxide dismutase enzyme (SOD-1). This and other mutations accounts for fewer than 10% of cases; the rest, more than 90%, correspond to the sporadic form. In this study we tested the effect of sera from sporadic ALS patients and from mutated human SOD-1 (mSOD1 G93A) transgenic rats on N-methyl-D-aspartate receptors (NMDAR). We hypothesize that an endogenous excitotoxic factor is implicated in neuronal death in ALS, mediated by the activation of NMDAR noncanonical signalling pathways. Sera from ALS patients or healthy subjects were pretreated to inactivate complement pathways and dialysed to remove glutamate. Sera from mSOD1 G93A rats were obtained at different stages of the neurodegenerative progression. Sera from transgenic rats were also pretreated to eliminate complement system and glutamate. Immunoglobulins G (IgGs) from ALS patients and healthy subjects were obtained by affinity chromatography and dialyzed against phosphate-buffered saline. Human NMDAR were expressed in Xenopus laevis oocytes, and glutamate-induced currents were recorded using the two electrode voltage clamp technique. We observed that sera from sporadic ALS patients induced transient oscillatory currents in Xenopus oocytes expressing NMDAR with a total electric charge significantly higher than the electric charge carried by currents induced by sera from healthy subjects. The currents were inhibited by MK-801, a noncompetitive blocker of NMDAR. Results of sera from mSOD1 G93A transgenic rats were similar to those of sera from ALS patients; samples from patients with another type of neuromuscular disease did not exert this effect. IgG from ALS patients have a significant effect on NMDAR-injected oocytes and that response was doubled respect to the observed in the case of IgG from healthy subjects. Our data agree with the view that ALS patients sera contain some soluble factors that activates NMDAR, not opening directly the ionic conductance, but activating a non-canonical pathway.

La posture, composante statique du contrôle moteur permettant une position érigée du corps, repose sur une décharge tonique des motoneurones innervant nos muscles antigravitaires. La décharge prend la forme de « potentiel de plateau » au niveau de motoneurones matures chez de nombreux vertébrés. Pour déterminer une éventuelle concordance entre l'émergence des propriétés de plateau et le développement postural, notre travail a eu pour but d'étudier la maturation et la nature ionique des potentiels de plateau des motoneurones innervant le muscle triceps surae (extenseur de la cheville) chez le rat nouveau-né.La réalisation de ces travaux de thèse nous a permis de dégager un mécanisme fondamental dans la genèse des propriétés de plateau des motoneurones lombaires. Ce mécanisme dont le fondement repose sur l'activation d'un « ménage à trois » jouerait un rôle majeur dans le développement moteur chez le rat. Dans la mesure où les potentiels de plateau des motoneurones sont fortement perturbés à la suite d'une lésion médullaire, cette avancée scientifique permettra éventuellement de mieux comprendre l'origine de certains déficits sensori-moteurs (spasticité, hyperalgésie...) et le développement de nouvelles stratégies thérapeutiques
Posture allowing an erect posture of the body relies on spiking activity of motoneurons innervating antigravitary muscle. Discharge could take the form of plateau potential on mature motoneurons of numerous vertebrates. To determine a possible concordance between the emergence of plateau potential and postural control development, we studied the maturation and ionic nature of plateau potential of motoneurons innervating triceps surae muscle of neonatal rat.The conclusion of our work allows us to propose a fundamental mechanism in the genesis of plateau potential on lumbar motoneurons. This mechanism based on a "ménage a trois" seems to play an important role in the neonatal motor development. This scientific advance could eventually lead to a better understanding of the origin of some sensori-motor impairments (spasticity, hyperalgesia...) and development of therapeutic strategies

Dans la moelle lombaire de chat adulte, deux populations de motoneurones se distinguent par leur cible musculaire: les motoneurones alpha et gamma. Dans ce travail, les questions suivantes ont ete abordees: 1) les motoneurones sont-ils des la naissance identifiables comme alpha ou gamma ? pour repondre a cette question, nous avons utilise les criteres ultrastructuraux d'identification etablis chez le chat adulte. 2) comment l'equipement synaptique des motoneurones est-il remanie pendant le developpement postnatal ? dans une premiere etape, nous avons examine en microscopie electronique les motoneurones du muscle peroneus brevis chez des chatons ages de 1 et 3 semaines. Deux resultats originaux se degagent: 1) malgre la presence de motoneurones alpha et gamma identifies, certains motoneurones presentent des signes d'immaturite tels que leur identification est impossible. 2) le nombre de terminaisons sur le compartiment somatique ne varie pas apres la naissance. Cependant, une elimination synaptique peut etre masquee par l'arrivee de nouvelles synapses. Dans une deuxieme etape, nous avons effectue une analyse quantitative sur coupes semi-fines des terminaisons gaba et/ou glycine-immunoreactives contactant les motoneurones alpha pendant la periode postnatale et chez l'adulte. Une etude immunocytochimique ultrastructurale a ete realisee en parallele. Deux resultats principaux se degagent: 1) alors que le systeme glycinergique afferent aux motoneurones alpha est le systeme inhibiteur preponderant chez l'adulte, les systemes gabaergique et glycinergique ont des poids similaires aux stades 1 et 3 semaines postnatales. La proportion des terminaisons contenant les deux neurotransmetteurs augmente entre les stades 1 et 3 semaines et diminue ensuite. 2) les synapses p gabaergiques, correlats morphologiques de l'inhibition presynaptique de la connexion monosynaptique des fibres afferentes ia avec les motoneurones alpha, sont presentes des la premiere semaine postnatale. Les profils gaba-immunoreactifs en contact avec les motoneurones correspondent a des synapses qui sont majoritairement de type f

La sclérose latérale amyotrophique (SLA) est une maladie neurodégénérative fatale de l'âge adulte, caractérisée par une perte de motoneurones, conduisant à une atrophie et une faiblesse musculaires. Des mutations de la superoxyde dismutase-1 (SOD1) provoquent une forme génétique de SLA. Comme chez les patients atteints de SLA, le modèle animal de SLA, SOD1 mutant, révèle que tous les motoneurones sont inégalement sensibles à l'évolution de la maladie. Les mitochondries, centrales énergétiques des cellules, sont des organelles précocement touchées dans la pathologie de la SLA. Un mécanisme attrayant qui sous-tend la susceptibilité différentielle est la nécessité bioénergétique variable de sous-ensembles distincts de motoneurones. Cela implique que dans le système nerveux central, la demande bioénergétique pourrait moduler le seuil pathologique. Même en l'absence de perte bioénergétique, on peut imaginer une situation dans laquelle une contrainte pathologique modifie le niveau à partir duquel la production ou la livraison de l'ATP devient insuffisant, précipitant la chute des neurones les plus vulnérables. Dans les neurones, la majorité de l'ATP est produite par les mitochondries et l'homéostasie des gradients d'ions est le procédé le plus énergivore. La fonction mitochondriale est moindre pour modifier les propriétés électriques des motoneurones si la disponibilité en ATP devient insuffisante pour permettre aux pompes ioniques de maintenir des gradients appropriés. Nous avons démontré que la concentration intracellulaire basale d’ATP dans des cultures de neurones moteurs est diminuée dans les cellules mutées SOD1 par rapport au type sauvage. Paradoxalement à ce résultat, le taux de consommation d'oxygène des mitochondries est augmenté dans les motoneurones SOD1m et il n'existe aucune preuve d'une augmentation de la consommation. Nos résultats appuient l'hypothèse intéressante qu'il y a un découplage entre la chaîne respiratoire et la production d'ATP. Ce découplage peut être utilisé comme une stratégie pour minimiser les propriétés toxiques des mitochondries hyper stimulées
Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset neurodegenerative disorder characterized by a loss of motor neurons, leading to muscle wasting and weakness. Mutations in superoxide dismutase-1 (SOD1) cause a form of ALS. As in ALS patients, the mutant SOD1 animal model of ALS reveals that not all motor neurons are equally susceptible to the disease process. An attractive mechanism underlying differential susceptibility is the variable bioenergetics need of distinct subsets of motor neurons. This implies that within the CNS, bioenergetics can modulate the pathological threshold. Even in the absence of loss in bioenergetics, one can envision a situation in which a pathological stress alters the level at which either the production or delivery of ATP becomes insufficient, precipitating the demise of the most vulnerable neuron types. In neurons, majority of ATP is produced by mitochondria and the homeostasis of ion gradients is the most energy-consuming process. Reduced mitochondrial function will modify the electrical properties of motor neurons if ATP availability becomes insufficient to allow ion pumps to maintain appropriate gradients. We demonstrated that the basal ATP intra-cellular concentration in motor neuron cultures lower in SOD1 mutated cells compared to wild type. Paradoxically to this result, the oxygen consumption rate of mitochondria is increase in mSOD1 cells and there is no evidence for an increase of consumption. Our results support the interesting hypothesis that there is an uncoupling between the respiratory chain and the ATP production. This uncoupling might be used as a strategy to minor the toxic properties of hyper stimulated mitochondrion

Introduction: Compressive root lesions are characterized by changes in the spinal cord microenvironment, which include motoneuron chromatolysis and degeneration, chronic gliosis, and glutamatergic excitotoxicity. Since excessive NMDAr stimulation by glutamate leads to neuronal degeneration, the use of NMDAr antagonists has been proposed as a promissing treatment central and peripheral nerve injuries. Objective: The present study aimed to investigate the neuroprotective effects of memantine, following compressive spinal root axotomy. Methods: Adult C57BL/6J mice were subjected to unilateral ventral root crush (VRC) and divided into four groups: VRC+Vehicle, VRC+Memantine 30 mg/kg, 45 mg/kg, and 60 mg/kg. The treatment was administered orally for 14 days, starting immediately after injury. Twenty-eight days after the lesion, lumbar intumescences were collected and processed for motoneuron counting (toluidine blue staining), together with astrogliosis and microglial reaction assessment (immunohistochemistry for GFAP and Iba-1, respectively). The protocols for animal use and handling were approved by the local ethical committee (CEUA/UNICAMP, protocol no 5740-1). Results: Memantine rescued spinal motoneurons at all the studied doses when compared with the vehicle counterpart, being the 45 mg/kg group the most effective (P < 0.001). Memantine also downregulated microglial reactions at the doses of 45 mg/kg and 60 mg/kg (P < 0.01, and P < 0.05, respectively). Astrogliosis also decreased in all treated groups as compared to the control (P < 0.01). Conclusions: The memantine has a significant antiinflammatory effect on glial cells, coupled with neuroprotection of motoneurons, indicating a possible translation to the clinic.