Substance P depresses bioelectrical responses evoked in the nucleus tractus solitarii: Interaction with γ-aminobutyric acid-ergic neurons

The effects of intracerebroventricular (i.c.v.) administration of substance P (SP) and γ-aminobutyric acid (GABA) on responses evoked in the nucleus tractus solitarii (NTS) by electrical stimulation of the ipsilateral sinusal nerve were studied in α-chloralose-anesthetized rats. Both SP (0.01-10 μg) and GABA (100 μg) significantly depressed the presumably C-fiber mediated, late negative wave of the response. The effects were almost completely prevented by bicuculline (10 μg 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. © 1992