Antisense oligodeoxynucleotides against the muscarinic m2, but not m4, receptor supports its role as autoreceptors in the rat hippocampus

Antisense oligodeoxynucleotides against muscarinic m(2) and m(4) receptors were used to investigate the role of these receptor subtypes as negative autoreceptors in the regulation of acetylcholine (ACh) release in the rat hippocampus. Following the continuous infusion of antisenses into the third ventricle (1 mu g mu l(-1) h(-1), 3 days), H-3-AF-DX 384/muscarinic M-2-like binding was significantly decreased in the medial septum by the antisense against the m(2) receptor whereas M-2-like binding in the dorsal striatum was decreased by the antisense against the m(4) receptor. In contrast, H-3-pirenzepine/muscarinic M-1-like binding was unaffected by either antisense treatment in any of the brain areas investigated. When perfused into the hippocampus via a dialysis probe, the purported muscarinic M-2 receptor antagonist AF-DX 384 (100 nM) increased hippocampal ACh release in freely moving rats. This effect of AF-DX 384 was significantly attenuated by the m(2), but not the m(4), receptor antisense treatment. Hippocampal choline acetyltransferase activity was not affected by either antisense treatments. Taken together, these results suggest that the molecularly defined muscarinic m(2) receptor regulates hippocampal ACh release by acting as a negative autoreceptor. In contrast, the molecularly defined m(4) receptor is unlikely to be directly involved in the negative regulation of ACh release in the rat hippocampus. Therefore, inhibiting muscarinic m(2) receptor function may be an alternative approach to regulate the release of ACh in neurodegenerative diseases associated with impaired cholinergic functions. (C) 1999 Elsevier Science B.V. Ail rights reserved.