Melatonin modulates the sensitivity of 5-hydroxytryptamine-2 receptor-mediated sleep-wakefulness regulation in the rat.

The interaction between melatonin and two 5-hydroxytryptamine (5-HT2) compounds was studied on sleep patterns in rats. Administration of the 5-HT2 receptor antagonist ritanserin (0.63 mg/kg, i.p.) resulted in a significant increase of deep slow wave sleep (SWS2) and a decrease of paradoxical sleep (PS). The 5-HT2 receptor agonist DOM (1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane) (0.63 mg/kg, i.p.) produced a significant reduction of both SWS2 and PS. Melatonin (1 mg/kg, i.p.) alone did not alter sleep but counteracted the sleep effects induced by ritanserin as well as DOM. It is proposed that melatonin modulates the sensitivity of 5-HT2 receptor-mediated sleep response probably by an indirect route.