Selective 5HT2A and 5HT6 Receptor Antagonists Promote Sleep in Rats

Abstract

Study Objectives

Serotonin (5-HT) has long been implicated in the control of sleep and wakefulness. This study evaluated the hypnotic efficacy of the 5-HT₆ antagonist RO4368554 (RO) and the 5-HT_2A receptor antagonist MDL100907 (MDL) relative to zolpidem.

Design

A randomized, repeated-measures design was utilized in which Wistar rats received intraperitoneal injections of RO (1.0, 3.0, and 10 mg/kg), MDL (0.1, 1.0 and 3.0 mg/kg), zolpidem (10 mg/kg), or vehicle in the middle of the dark (active) period. Electroencephalogram, electromyogram, body temperature (T_b) and locomotor activity were analyzed for 6 hours after injection.

Measurements and Results

RO, MDL, and zolpidem all produced significant increases in sleep and decreases in waking, compared with vehicle control. All 3 doses of MDL produced more consolidated sleep, increased non-rapid eye movement sleep (NREM) sleep, and increased electroencephalographic delta power during NREM sleep. The highest dose of RO (10.0 mg/kg) produced significant increases in sleep and decreases in waking during hour 2 following dosing. These increases in sleep duration were associated with greater delta power during NREM sleep. ZO Zolpidem induced sleep with the shortest latency and significantly increased NREM sleep and delta power but also suppressed rapid eye movement sleep sleep; in contrast, neither RO nor MDL affected rapid eye movement sleep. Whereas RO did not affect T_b, both zolpidem and MDL reduced T_b relative to vehicle-injected controls.

Conclusions

These results support a role for 5-HT_2A receptor modulation in NREM sleep and suggest a previously unrecognized role for 5-HT₆ receptors in sleep-wake regulation.

Keywords: Serotonin, zolpidem, sleep consolidation, EEG delta power, telemetry