Pharmacological studies on inhibition in the cuneate nucleus of the cat

The effects of picrotoxin, strychnine, and pentobarbital on cuneate transmission were investigated in the cat. The positive wave, recordable at the surface of the cuneate nucleus and indicative of depolarization of cuneate afferent terminals, was reduced by picrotoxin. Picrotoxin also blocked the increase in excitability of cuneate presynaptic terminals produced by conditioning cortical or cutaneous volleys (applied 10–150 msec before the test volley). It reduced the inhibition of the lemniscal discharge by conditioning cutaneous sources. Pentobarbitone showed opposite effects and antagonized those of picrotoxin. Strychnine enhanced the increase in excitability of the cuneate terminals and increased the size of the test lemniscal response, but it further increased inhibition of that response by conditioning volleys applied 10–150 msec before the test volleys. The results give pharmacological evidence for the presence of presynaptic and postsynaptic inhibition in an important sensory nucleus.