An M3-like muscarinic autoreceptor regulates the in vivo release of acetylcholine in rat striatum.

Selective muscarinic antagonists were used in an attempt to characterize the muscarinic autoreceptor modulating the release of acetylcholine in the striatum of the rat. In vivo microdialysis was applied to infuse atropine, 4-DAMP (4-diphenylacetoxy-N-methylpiperidine), pirenzepine or AF-DX 116 (11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5, 11-dihydro[2,3-b][1,4]benzodiazepine-6-one), leading to a dose-dependent increase in the overflow of acetylcholine, the order of potency being: atropine greater than 4-DAMP greater than pirenzepine greater than AF-DX 116. We conclude from these data that the muscarinic receptor modulating release in the striatum is of the M3 type.