Identification and localization of muscarinic acetylcholine receptor proteins in brain with subtype-specific antibodies

Abstract

mRNAs encoding five genetically distinct muscarinic ACh receptors are present in the CNS. Because of their pharmacological similarities, it has not been possible to detect the individual encoded proteins; thus, their physiological functions are not well defined. To characterize the family of proteins, a panel of subtype-selective antibodies was generated against recombinant muscarinic receptor proteins and shown to bind specifically to each of the cloned receptors. Using immunoprecipitation, three receptor proteins (m1, m2, and m4) accounted for the vast majority of the total solubilized muscarinic binding sites in rat brain. These receptor subtypes had marked differences in regional and cellular localization as shown by immunocytochemistry. The m1-protein was present in cortex and striatum and was localized to cell bodies and neurites, consistent with its role as a major postsynaptic muscarinic receptor. The m2-receptor protein was abundant in basal forebrain, scattered striatal neurons, mesopontine tegmentum, and cranial motor nuclei; this distribution is similar to that of cholinergic neurons and suggests that m2 is an autoreceptor. However, m2 was also present in noncholinergic cortical and subcortical structures, providing evidence that this subtype may presynaptically modulate release of other neurotransmitters and/or function postsynaptically. The m4-receptor was enriched in neostriatum, olfactory tubercle, and islands of Calleja, indicating an important role in extrapyramidal function. These results clarify the roles of these genetically defined receptor proteins in cholinergic transmission in brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential Effects of the Muscarinic M1 Receptor Agonist RS-86 and the Acetylcholine-Esterase Inhibitor Donepezil on REM Sleep Regulation in Healthy Volunteers

“…Furthermore, the frequently used parameter REM density is less adequate to reflect alterations in the generation of REMs itself since it depends on the REM sleep duration. Given that the M 1 and M 2 mAChR subtype are the most abundant AChR subtypes in the mammalian cortex (Levey et al, 1991), and given that there is broad evidence from preclinical studies indicating that the number of REMs and REM maintenance are predominantly mediated by M 2 mAChR activity in the brain stem (VelazquezMoctezuma et al, 1991;Coleman et al, 2004), it is likely to assume that the increases in the number of REMs and REM sleep duration observed after the administration of donepezil in the present study are mediated, to a large extent, by M 2 mAChR activation at the brain stem level.…”

“…In a widely accepted view, mAChRs are more relevant for REM sleep regulation than nicotinic AChRs (reviewed in Baghdoyan and Lydic, 2002). Actually, five mAChRs (M 1 -M 5 ) have been molecularly and pharmacologically identified (Caulfield and Birdsall, 1998), with the M 1 and M 2 mAChRs being the most abundant subtypes in mammalian cortex (Levey et al, 1991). The lack of specific ligands for each subtype makes pharmacological studies difficult, but inferences can be made for a specific function by comparing the potencies of different compounds with known affinities for M 1 -M 5 mAChRs.…”

The Role of Acetylcholine in Cocaine Addiction

“…In contrast, M 2 and M 4 receptors (M 2 -like) are coupled to G i proteins and inhibit adenylyl cyclase. Within the mesostriatal pathway, M 5 receptors are primarily found in the midbrain (Weiner et al, 1990), whereas M 1 and M 4 (and some M 2 ) are in the striatum (Levey et al, 1991). Neuronal nicotinic receptor subtypes include a and b subunits loosely categorized as two types: a-b subunit combinations (a 2 -a 6 , a 10 , and b 2 -b 4 ) and homo-oligomeric combinations (a 7 -a 9 ).…”

Tetrahydroaminoacridine and Physostigmine Increase Cerebral Glucose Utilization in Specific Cortical and Subcortical Regions in the Rat

“…Regions with strong THA effects have either a low (medial sep tum, superior colliculus, thalamic nuclei) or a high (cingular and retrosplenial cortices) M, receptor density (Mash and Potter, 1986;Spencer et aI., 1986;Levey et aI. , 1991).…”