The benzodiazepine receptor inverse agonist DMCM decreases serotonergic transmission in rat hippocampus: an in vivo electrophysiological study.

The intravenous administration of the benzodiazepine inverse agonist DMCM (6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylic acid methyl ester) dose-dependently reduced the efficacy of electrical stimulation of the 5-HT pathway in depressing the firing activity of rat hippocampus pyramidal neurons. This effect was prevented by the benzodiazepine receptor antagonist flumazenil and reversed by the benzodiazepine receptor agonist diazepam. This indicates that DMCM alters 5-HT transmission in the rat dorsal hippocampus via benzodiazepine receptors and that these receptors have both agonist and inverse agonist sites.