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Altérations des entrées synaptiques et origine de la vacuolisation dans les motoneurones de souris sod1g93a, modèle de la sclérose latérale amyotrophique

Abstract : Glutamate excitotoxicity arising from excessive entry of calcium in the cell, has long been suggested to contribute to the degeneration of motoneurons in Amyotrophic Lateral Sclerosis (ALS). This hypothesis is enhanced by the observation of vacuoles on motoneurones dendritic tree. Such vacuoles were previously observed on neurons under excitotoxic stress. Excitotoxicity may stem from an intrinsic hyperexcitability of the motoneurons or from a shift of the balance of excitatory / inhibitory inputs received by the motoneurons toward more excitation. Thanks to an in vivo preparation that allows us to make intracellular recordings of motoneurons in adult mice, it was shown that spinal motoneurons do not display an intrinsic hyperexcitability just prior to their degeneration in SOD1 G93A mice, the standard model of ALS. Thus, to study excitotoxicity hypothesis, we decided to study dendritic vacuoles and undersand their genesis, and then to study synaptic inputs on motoneurons, to decipher if there is a hyperexcitability. We have shown, with intracellular labelling and immunohistochemistry, that vacuoles grow with age, that they appear in the intermembrane space of mitochondria, and that deficiency in autophagy prevent their elimination. With electrophysiological recordings, we have shown that monosynaptic EPSP amplitude is reduced in SOD1 mice. IPSP were less numerous and inhibitory interneurons were less excitable. These alterations were not due to synapses numbers, however synapses are preferentially localised on dendritic places that vacuolate, suggesting a link between synaptic activity and vacuolation. These results suggest that excitotoxicity might not be the mecanism of motoneuron death.
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Clemence Martinot. Altérations des entrées synaptiques et origine de la vacuolisation dans les motoneurones de souris sod1g93a, modèle de la sclérose latérale amyotrophique. Neurosciences [q-bio.NC]. Université Sorbonne Paris Cité, 2017. Français. ⟨NNT : 2017USPCB259⟩. ⟨tel-02110521⟩

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