The effects of methyl beta-carboline-3-carboxylate on social interaction and locomotor activity when microinjected into the nucleus raphé dorsalis of the rat.

Intraperitoneal and intracerebral injections of methyl beta-carboline-3-carboxylate (beta CCM) and intracerebral injections of RO 15-1788 were given to rats. The performance of the rats in the social interaction test was measured to determine if changes in social interaction induced by beta CCM were mediated in part by the nucleus raphé dorsalis (NRD). Intraperitoneal injections of beta CCM, 2 and 4 mg kg-1, reduced social interaction. Intracerebral microinjections of beta CCM (10-0.1 ng in 0.5 microliter) into the NRD reduced social interaction. Injections outside the NRD did not have this effect. Intracerebral microinjections of RO 15-1788 (1 ng in 0.5 microliters) into the NRD had no effect when given alone, but blocked the reduction in social interaction caused by intracerebral or intraperitoneal injections of beta CCM. No effect was observed when R 15-1788 was microinjected into sites outside the NRD. Changes in social interaction may reflect changes in anxiety. The NRD may be one of the important sites for the expression of the anxiogenic actions of beta CCM.