Muscarinic regulation of cyclic AMP metabolism in rat neostriatal cultures.

Muscarinic receptor expression and function were investigated in cultured rat neostriatum. Muscarinic receptor levels were determined from saturation binding experiments performed on intact cultures using [3]N-methylscopolamine. In cultures maintained for 3, 7 and 12-14 days in vitro, the Bmax was 2.3, 5.4 and 10.9 fmol/culture. The average number of receptors per neuron increased during the 2nd week in vitro. Carbachol (100 microM) had no significant effect on basal cAMP levels but reduced cAMP levels elevated by forskolin. Carbachol significantly reduced cAMP levels stimulated with dopamine only in cultures untreated with a phosphodiesterase inhibitor. Comparing equimolar doses, the carbachol response was more sensitive to the M1 selective antagonist pirenzepine than the cardioselective M2 antagonist AF-DX 116. These results suggest that the muscarinic receptors regulate cAMP levels in neostriatal neurons and, in so doing, provide a post-synaptic substrate for the interaction of dopamine and acetylcholine.