Tonically Active α ₅GABA _A Receptors Reduce Motoneuron Excitability and Decrease the Monosynaptic Reflex

摘要

Motoneurons, the final common path of the Central Nervous System (CNS), are under a complex control of its excitability in order to precisely translate the interneuronal pattern of activity into skeletal muscle contraction and relaxation. To fulfill this relevant function, motoneurons are provided with a vast repertoire of receptors and channels, including the extrasynaptic GABA_(A)receptors which have been poorly investigated. Here, we confirmed that extrasynaptic α5 subunit-containing GABA_(A)receptors localize with choline acetyltransferase (ChAT) positive cells, suggesting that these receptors are expressed in turtle motoneurons as previously reported in rodents. In these cells, α_(5)GABA_(A)receptors are activated by ambient GABA, producing a tonic shunt that reduces motoneurons’ membrane resistance and affects their action potential firing properties. In addition, α_(5)GABA_(A)receptors shunted the synaptic excitatory inputs depressing the monosynaptic reflex (MSR) induced by activation of primary afferents. Therefore, our results suggest that α_(5)GABA_(A)receptors may play a relevant physiological role in motor control.