Dissociation of systemic and hippocampal modulation of rat locomotor activity by 5-HT(2C) receptors

In the present study, the ability of 5-hydroxytryptamine(2C) (5-HT(2C)) receptors in the hippocampus to enhance locomotor activity in rats was investigated by local infusion. Intraperitoneal injection of the selective 5-HT(2C) antagonist SB 242084 (1 mg/kg) significantly increased rats motor activity, while the effects of non-selective 5-HT(2C) agonist m-chlorophenylpiperazine (m-CPP, 10 mg/kg; i.p.) on motor activity were lower than those of the control group. In the day hours, the local infusion of non-selective 5-HT(2C) agonist, m-CPP (1.0 mM) into the bilateral hippocampus via microdialysis probes increased locomotor activity in contrast with intraperitoneal injection. This increase was completely reversed by the combined infusion of the selective 5-HT(2C) antagonist SB 242084 (100 mM). In the night hours, the local infusion of SB 242084 (100 mM) into the bilateral hippocampus significantly inhibited the nocturnal hyperactivity, which was reversed by the combined infusion of m-CPP. The present study demonstrates that the 5-HT(2C) receptors in the hippocampus act to increase rat locomotor activity.