Facilitation of transmission via inhibitory pathway 1a to spinal extensor motoneurons in response to stimulation of the forelimb nerves in cats.

Activation of forelimb flexor reflex afferent in cats anesthetized with a mixture of Chloralose and Nembutal evoked temporospatial facilitation in the reciprocal inhibitory pathways to spinal extensor motoneurons. The amplitude of disynaptic reciprocal 1a inhibitory postsynaptic potentials (IPSP) evoked in the extensor motoneurons by activation of the most excitable fibers of the nerve supplying the antagonist muscle increased several-fold using conditioning stimulation of the forelimb nerve. Facilitation of 1a IPSP occurred on a background of IPSP evoked by descending inter-limb discharges. Facilitation of 1a IPSP had a latent period of 18-20 msec and could last to 60 msec. The possible role of inhibitory 1a interneurons in interlimb coordination is discussed.