Deafferentation hyperactivity (DH) was provoked in the neurons of the subnucleus caudalis of the spinal trigeminal nucleus and the lateral reticular formation in cats by Gasserian ganglionectomy, and was used as a model of peripheral deafferentation pain. The influence of neurochemical substances upon DH was investigated. Neurotransmitters and their antagonists were applied topically around the soma of hyperactive neruons by the microiontophoretic technique, using a 7-barreled glass micropipette. Then the participation of inhibitory amino acids in the descending inhibitory systems, which were activated by deep brain stimulation (DBS), was investigated. Discharges of hyperactive neurons (n=75) were recorded extracellularly and analyzed using a spike density histogram. DH was suppressed by topically injected GABA and glycine, but not by met-enkephalin. The suppressive effects of GABA and glycine were almost completely antagonized by bicuculline and strychnine, respectively. Stimulation of the internal capsule or VPM suppressed DH, and this suppression was not affected by microiontophoretically injected bicuculline or strychnine. Intravenous injection of picrotoxin reduced the suppression, but intravenous strychnine did not. GABA may play an important role as an inhibitory neurotransmitter in the descending inhibitory systems activated by DBS.
descending inhibitory system