Effects of MPEP, a selective metabotropic glutamate mGlu5 ligand, on sleep and wakefulness in the rat.

Metabotropic glutamate receptors (mGlu) have been implicated in the regulation of physiological and behavioral processes. Pharmacological evidence involves group I mGlu receptors in the regulation of emotional states and antagonism of these receptors has been proposed as a novel class of anxiolytic drugs having also antidepressant effects. Here, the effects of mGlu5 receptor selective modulation on sleep and wake states are explored. 32 male Wistar rats were implanted with electrodes for recording sleep and wake states. 2-Methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP hydrochloride, 5, 10, and 20 mg/kg, i.p.), a potent, selective and systemically active mGlu5 receptor negative allosteric modulator, or vehicle was administered 1 h after the beginning of the light period. Sleep recordings were conducted for 3 h. MPEP (5, 10, and 20 mg/kg) significantly suppressed rapid eye movement (REM) sleep, decreasing the number of episodes and mean episode duration, and increased its latency. A reduction of light and deep slow wave sleep (SWS) latency was observed in the groups receiving 10 or 20 mg/kg, increasing latency to first wakefulness episode. 10 mg/kg of MPEP also increased non rapid eye movement sleep (NREM). The present results suggest that mGlu5 receptors might be involved in sleep regulation, more specifically in REM sleep, and drugs that block these receptors could potentially benefit the treatment of pathologies were REM sleep is enhanced.