Cholinergic antagonists and REM sleep generation.

In this study we extended our observations on the role of M1 and M2 muscarinic receptors in mediating the cholinergic induction of REM sleep. Cats were chronically implanted with sleep recording electrodes and microinjections of Ringer's or muscarinic antagonists followed by the relatively specific M2 muscarinic agonist, cis-methyl-dioxolane (cisdioxo), were made into the medial pontine reticular formation (mPRF). The microinjection of Ringer's followed by cisdioxo significantly increased REM sleep percentage. Atropine, a mixed muscarinic receptor antagonist, administered before cisdioxo blocked the REM sleep increase while pirenzepine, a selective M1 muscarinic antagonist, did not block the cisdioxo-induced increase in REM sleep. Gallamine, a nicotinic and a putative M2 antagonist, tended to inhibit the cisdioxo-induced increase in REM sleep. These results support the hypothesis that the cholinergic stimulation-induced REM sleep in the medial pontine reticular formation is mediated by a non-M1 muscarinic receptor subtype.