Microinjections of methyl-beta-carboline-3-carboxylate into the dorsal raphe nucleus: behavioural consequences.

Very small quantities (0.01-10 ng) of the inverse benzodiazepine receptor agonist, methyl-beta-carboline-3-carboxylate (beta-CCM) microinjected into the dorsal raphe nucleus (DRN) of the rat selectively reduced social interaction, an effect consistent with an increase in anxiety. Similarly, intraperitoneally injected beta-CCM, within a limited dose range, reduced social interaction without affecting locomotor activity. The benzodiazepine receptor antagonist, RO15-1788 (1 ng) microinjected into the DRN, reversed the suppression of social interaction induced by either intra-raphe or intraperitoneal beta-CCM. Histological examination of the beta-CCM microinjection sites showed that locations within the DRN were almost invariably associated with decreases in social interaction; microinjections failing to decrease social interaction were located primarily outside the DRN. We conclude that the DRN has a major role in expressing the anxiogenic effect of beta-CCM and it may therefore be an important area in the neuronal system controlling anxiety.