The relative effects of selective M1 muscarinic antagonists on rapid eye movement sleep.

Three muscarinic antagonists, scopolamine, trihexyphenidyl and biperiden were systemically administered (0, 0.5, 1, 2 and 4 mg/kg) in rats. Scopolamine increased wakefulness and deceased sleep, both slow wave and REM. Trihexyphenidyl increased wakefulness and decreased REM sleep while biperiden decreased REM sleep selectively. The rank order REM-suppressing effect was roughly scopolamine and trihexyphenidyl having a greater suppressing effect than biperiden. These results suggest that the regulation of the sleep-wake cycle is at least partially controlled by the M1 muscarinic receptor.