Pharmacological and functional characterization of muscarinic receptor subtypes in developing oligodendrocytes

This study focused on the molecular and pharmacological characterization of muscarinic acetylcholine receptors expressed by progenitors and differenti ated oligodendrocytes. We also analyzed the role of muscarinic receptors in regulating downstream signal transduction pathways and the functional sign ificance of receptor expression in oligodendrocytes. RT-PCR analysis reveal ed the expression of transcripts for M3, and to a lesser extent M4, followe d by M1, M2 and M5 receptor subtypes in both progenitors and differentiated oligodendrocytes. Competition binding experiments using [H-3]N-methylscopo lamine and several antagonists, as well as inhibition of carbachol-mediated phosphoinositide hydrolysis, showed that M3 is the main subtype expressed in these cells. In progenitors the activation of p42/44-mitogen-activated p rotein kinase (MAPK) and cAMP-response element binding protein (CREB) as we ll as c-fos mRNA expression were blocked by the M3 relatively selective ant agonist, 4-DAMP, and its irreversible analogue, 4-DAMP-mustard. Carbachol i ncreased proliferation of progenitors, an effect prevented by atropine and 4-DAMP, as well as by the MAPK kinase inhibitor PD98059. These results indi cate that carbachol modulates oligodendrocyte progenitor proliferation thro ugh M3 receptors, involving activation of a MARK signaling pathway. Recepto r density and phosphoinositide hydrolysis are down-regulated during oligode ndrocyte differentiation. Functional consequences of these events are a red uction in carbachol-stimulated p42/44(MAPK) and CREB phosphorylation, as we ll as induction of c-fos.