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Poster De Conférence Année : 2021

Homeostatic plasticity at the neuromuscular synapse

Gilles Ouanounou
Thierry Bal
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Résumé

Like sensory inputs in the thalamus, motor outputs, i.e. neuromuscular synapses, play a relay function that requires a homeostatic control. This control adapts the neurotransmitter release to the post-synaptic excitability, resulting in a unity synaptic gain (one post-synaptic action potential for one pre-synaptic action potential). For this control process, the post-synaptic cell evaluates the synaptic efficacy and exercises a retrograde feedback on the pre-synaptic terminals. We have shown previously (Ouanounou et al. eLife 2016;5:e12190) that the muscle cell senses the synaptic events and its own action potentials through two distinct calcium signals, i.e. the nicotinic receptor calcium permeability and the “depolarization-induced calcium release” (DICR) from internal stores respectively. The synaptic calcium signal triggers a positive feedback on the neurotransmitter release, while the DICR triggers a negative feedback. Balance in this homeostatic synaptic plasticity sets the neurotransmitter release to a level matching the post-synaptic excitability. Here we describe how dynamic the balance between homeostatic potentiation and depression is, and we show that this balance takes place primarily at the level of the post-synaptic calcium signals. The DICR signal follows the I/V curve of the L-Type voltage sensor of the muscle membrane, and consequently has the all or none characteristic of the action potential. Consequently, occurrence of the DICR depends on the muscle excitability threshold, but does not modulate the homeostatic balance in the supra-threshold range of the synaptic strength. In contrast, we show that the post-synaptic nicotinic calcium influx is strongly voltage-dependent and rectifies all along the physiological voltage range. The membrane parameters that appeared to modulate the nicotinic calcium influx were both the nicotinic conductance and the kinetics of repolarization, itself under the direct control of the input conductance. Therefore, the nicotinic calcium influx perfectly encodes the ratio between the nicotinic and the input conductances in both the sub- and supra-threshold ranges of the synaptic strength, and balances homeostatic plasticity in order to adapt the neurotransmitter release to the muscle excitability.
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Dates et versions

hal-04530850 , version 1 (03-04-2024)

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  • HAL Id : hal-04530850 , version 1

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Gilles Ouanounou, Thierry Bal. Homeostatic plasticity at the neuromuscular synapse. NeuroFrance 2021, Strasbourg International virtual meeting, May 2021, Strasbourg (100% virtuel), France. ⟨hal-04530850⟩
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