Functional activity of 5-HT2 receptors in the modulation of the sleep/wakefulness states.

In the light of recent pharmacological investigations using agonists and antagonists that have potent actions on 5-hydroxytryptamine-2 (5-HT2) receptors, the possible functional role of 5-HT2 receptors in the modulation of the sleep/wakefulness states was examined. Data obtained from animals and from clinical studies suggest that serotonin may exert an inhibitory control on deep slow-wave sleep (SWS) through 5-HT2 receptors. In further investigations, the existence of a diurnal variation in the functional activity of 5-HT2 receptors, that depends on the day/night cycle and/or the melatonin rhythm, was revealed. Questions remain with regard to the physiological significance, of the 5-HT2 receptor-mediated deep SWS regulation, the anatomical site(s) of 5-HT2 receptors involved in this regulation and the mechanism underlying diurnal fluctuations in the functional activity of 5-HT2 receptors.