Evidence for a tonic GABAergic control of serotonin neurons in the median raphe nucleus

We examined whether serotonin (5-HT)-containing neurons of the midbrain raphe nuclei are subject to an inhibitory control by GABA. We found that injection into the median raphe nucleus of the GABA antagonists picrotoxin and bicuculline and the GABA agonist muscimol increase and decrease, respectively, the 5-HT turnover and the steady-state content of 5-hydroxyindoleacetic acid. The results provide evidence of a tonic inhibition by GABA of 5-HT neuronal activity in the median raphe nucleus; this inhibitory effect is potentiated by benzodiazepines.