A pharmacological study of the inhibition of ventral group Ia-excited spinal interneurones.

In cats anaesthetized with pentobarbitone a pharmacological investigation was made of the inhibition by volleys in afferent fibres and ventral roots of physiologically identified Ia interneurones in the ventral horn. The recurrent inhibition of Ia interneurones by Renshaw cells, and the "mutual" inhibition between Ia interneurones, were suppressed by electrophoretic strychnine and are presumably mediated by glycine. Short latency and duration inhibitions by impulses in muscle and cutaneous afferents were also suppressed by strychnine. Electrophoretic GABA inhibited the firing of Ia interneurones and the effects of bicuculline methochloride suggested that this amino acid mediates longer latency and duration inhibition produced by afferent impulses of muscle and cutaneous origin.