Glycine-mediated inhibitory transmission of group 1A-excited inhibitory interneurones by Renshaw cells.

1. Electrophysiological and micro-electrophoretic studies were carried out in anaesthetized cats on spinal interneurones which were monosynaptically activated from group 1 muscle afferents and recurrently inhibited by Renshaw cells. 2. The recurrent inhibition was blocked by the iontophoretic administration of strychnine, which also blocked the action of glycine. 3. The time course of the block of synaptic inhibition by strychnine was slower than the block of glycine evoked inhibition. The significance of this observation in terms of the location of the inhibitory synapses is discussed. 4. The observation that recurrent inhibition of motoneurones and of interneurones is blocked by strychnine whereas the mutual inhibition of Renshaw cells is not is discussed in relation to the proposal that the nature of the post-synaptic inhibitory receptor is not determined solely by the innervating neurone, which is the Renshaw cell in all three instances. 5. The recurrent inhibition of the interneurones was not blocked by the iontophoretic administration of bicuculline, but difficulties were encountered in demonstrating that this agent consistently antagonized the inhibitory effects of GABA.