The synaptic excitation of Renshaw cells

Abstract

An analysis has been made in spinal cats anaesthetised with pentobarbitone of the firing of Renshaw cells induced by stimulation of ventral roots or by volleys entering the spinal cord via dorsal root fibres. The response to maximal ventral root stimulation consisted of an early high frequency discharge which was blocked by dihydro-β-erythroidine (nicotinic receptors), a depression of spontaneous firing and a subsequent late firing which was specifically depressed by atropine (muscarinic receptors). The intervening depression or pause was associated with a non-specific depression of the sensitivity of these neurones to both acetylcholine and excitant amino acids. It is proposed that these responses may be the consequence of the action of acetylcholine released simultaneously from all of the axon collateral endings upon a Renshaw cell and that the late response may have no functional role. Other possibilities are discussed. The spontaneous activity of these neurones appears to involve muscarinic receptors. The activation of Renshaw cells by dorsal root volleys, which is independent of the prior discharge of motoneurones, does not involve cholinergic mechanisms.