In vivo presynaptic modulation of serotonergic neurotransmission in the rat hippocampus by diazepam

The effect of the benzodiazepine agonist, diazepam, on serotonergic (5-HT) neurotransmission was assessed in in vivo electrophysiological experiments. Diazepam enhanced, in a dose-dependent manner (0.05-2 mg/kg i.v.), the effect of electrical stimulation of the ascending 5-HT pathway on the firing activity of dorsal hippocampus pyramidal neurons. This effect was blocked by the benzodiazepine antagonist, flumazenil. Diazepam did not modify the efficacy of microiontophoretic application of 5-HT and GABA. The results indicate that the activation of benzodiazepine receptors facilitates of 5-HT neurotransmission, presumably through a presynaptic modulatory mechanism.