SUBSTANCE-P DEPRESSES BIOELECTRICAL RESPONSES EVOKED IN THE NUCLEUS-TRACTUS-SOLITARII - INTERACTION WITH GAMMA-AMINOBUTYRIC ACID-ERGIC NEURONS

The effects of intracerebroventricular (i.c.v.) administration of substance P (SP) and gamma-aminobutyric acid (GABA) on responses evoked in the nucleus tractus solitarii (NTS) by electrical stimulation of the ipsilateral sinusal nerve were studied in alpha-chloralose-anesthetized rats. Both SP (0.01-10-mu-g) and GABA (100-mu-g) significantly depressed the presumably C-fiber mediated, late negative wave of the response. The effects were almost completely prevented by bicuculline (10-mu-g i.c.v.). It is concluded that i.c.v. administered SP induces dose-dependent depression of baro- and/or chemosensory transmission in the NTS, via a mechanism involving interactions with GABAergic neurons of the NTS.