Serotonergic mediation of habenular self-stimulation in the rat

The possible involvement of serotonergic neurons in self-stimulation of the habenular complex was examined in 16 rats. Animals were implanted with bipolar electrodes into the habenula (Hb), lateral hypothalamus (LH), or median raphe (MR), and trained to touch a dry spout to receive electrical stimulation of the brain. Metergoline (5 mg/kg, IP), a serotonergic receptor blocking agent, produced a complete suppression of self-stimulation with Hb and MR electrodes, but significantly less suppression with LH electrodes, suggesting that the rewarding effect of habenular stimulation is mediated by serotonergic neurons. In contrast to the differential effects of metergoline, chlorpromazine (2 mg/kg, IP), a catecholamine receptor blocking agent, suppressed both Hb and LH self-stimulation in a similar manner.