We examined the effects of cholinergic receptor blockers on changes in rapid eye movement (REM) sleep components. M1 and M2 muscarinic receptor antagonists or atropine were microinfused before an M2 muscarinic receptor agonist, and the effects on individual REM sleep components were assessed. All drugs were microinjected into the same locus within the medial pontine reticular formation in cats, and sleep recordings were made for at least 3 hours postinjection. Results suggest that desynchronized electroencephalogram (EEG) is influenced by the M1 muscarinic receptor, muscle atonia is influenced by the M2 muscarinic receptor, and ponto-geniculo-occipital (PGO) waves are affected by the nicotinic receptor.