Methysergide blocks the sleep suppressant action of quipazine in rats

The aim of the present study was to examine the effect of methysergide, a 5-hydroxytryptamine (5-HT) receptor antagonist, on the sleep suppression produced by the 5-HT receptor agonist, quipazine. Treatment with methysergide maleate (5 mg/kg, IP) 15 min before the administration of quipazine blocked quipazine-induced suppression of flow-wave sleep (SWS), but failed to prevent the decrease in rapid-eye-movement sleep (REMS) produced by quipazine. Treatment with methysergide also prevented the head-shaking behavior induced by quipazine, a phenomenon associated with increased activity of the central serotonergic system. Furthermore, it was shown that administration of methysergide alone (1 or 5 mg/kg, IP) had little effect on sleep or head-shaking behavior. The present data provide pharmacological evidence that the suppression of SWS but not REMS by quipazine may be a result of stimulation of 5-HT receptors.