POSTSYNAPTIC INHIBITIONS OF TRIGEMINAL AND LUMBAR MOTONEURONS FROM THE SUPERFICIAL RADIAL NERVE IN THE CAT

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Abstract
In the decerebrate cat, an IPSP [inhibitory postsynaptic potential] was recorded intracellularly in the motoneurons of jaw-closing muscles and of lumbar flexor and extensor muscles after single shocks applied to the lowest threshold afferent fibers of the superficial radial nerve of both sides. The trigeminal IPSP had a latency of 8.5 msec, a rise time of about 5 msec and a decay time of about 30 msec. The lumbar IPSP had a latency of about 40 msec, a rise time of about 40 msec and a decay time of about 60 msec. When the monosynaptic reflexes of the masseter nerve and from peroneal or gastrocnemius-soleus nerve were conditioned by a superficial radial nerve, the depression of similar time course to the IPSP was seen. Evidence is shown that the presynaptic inhibitory mechanism is not involved in the depression of lumbar monosynaptic reflex activities.