Evidence for GABA mediation of sympathetic inhibition evoked from midline medullary depressor sites.

GABA antagonists blocked, and diazepam potentiated, inhibition of spontaneous sympathetic activity elicited by electrical stimulation of classic midline medullary depressor sites. Picrotoxin often converted inhibitory effects of raphe stimulation into sympathoexcitatory responses. Serotonin antagonists blocked these sympathoexcitatory responses. The midline medullary raphe complex is heterogeneous in respect to autonomic function with sympathoinhibitory elements mediated at least in part by GABA and sympathoexcitatory pathways mediated by serotonin.