LOCALIZATION OF MUSCARINIC RECEPTOR SUBTYPES IN BRAIN-STEM AREAS REGULATING SLEEP

MUSCARINIC cholinergic receptors (mAChRs) within the pontine brain ste m play a key role in generating rapid eye movement (REM) sleep. Using an in vitro autoradiographic technique that permits selective labeling of mAChR subtypes by radioligand binding, this study provides the fir st quantitative map of mAChR subtypes in cat brain stem areas importan t for REM sleep generation. M1, M2 and M3 mAChR subtypes were distribu ted heterogeneously throughout the brain stem. For all 3 mAChR subtype s, the greatest levels of binding were found in the dorsal raphe and l ocus coeruleus, and the least amount of binding was in the reticular f ormation. These findings are consistent with data from in vivo studies showing that multiple mAChR subtypes are involved in REM sleep genera tion.