Inhibitory postsynaptic potentials of hypoglossal motoneurons of the cat

Abstract

The hypoglossal nerve of the cat contains some afferent fibers, but the role of these afferents in controlling hypoglossal motoneuron activity has not yet been analyzed. The effect of hypoglossal nerve stimulation on activity of hypoglossal motoneurons was investigated using microelectrode technique. Spontaneous discharges of hypoglossal motoneurons were inhibited by hypoglossal nerve stimulation, and during the period of this inhibition IPSP were recorded intracellularly. Threshold for evoking these IPSP was much higher than that for evoking antidromic action potentials in hypoglossal motoneurons. The mean latency of these IPSP was 14.4 msec and it was about twice as long as those of IPSP induced by lingual nerve stimulation. Therefore, these inhibitory effects by hypoglossal nerve stimulation are possibly due to excitation of high-threshold afferent fibers in the hypoglossal nerve and are not due to current spread to the lingual nerve. IPSP evoked by hypoglossal nerve stimulation were strychnine insensitive and picrotoxin sensitive. These hypoglossal IPSP were inhibited by lingual nerve stimulation, and this inhibition lasted for about 500 msec when supramaximal stimulation was applied to the lingual nerve. From these results we conclude that afferent fibers in the cat hypoglossal nerve exert inhibitory effects on hypoglossal motoneurons.