Fig. 2.

Agonist-induced regulation of cell proliferation is blocked by receptor-selective antagonists indicating positive regulation mediated by the muscarinic M1 receptor. a, BrdU⁺ cell counts in the DG and CA1 regions of the hippocampus following oxotremorine. Chronic intraventricular administration of the M1 receptor antagonist, pirenzepine, but not the nicotinic antagonist, mecamylamine, dose-dependently blocked oxotremorine-induced elevations in BrdU immunolabeling in both the DG and CA1. b, Chronic intraventricular administration of the M1 receptor antagonist, pirenzepine, also dose-dependently blocked low dose carbachol-induced elevations in BrdU immunolabeling. By contrast, the nicotinic receptor antagonist, mecamylamine, had no effect. As described earlier, a higher dose of carbachol (30 μg/h) failed to affect cell proliferation. Co-administration with mecamylamine, however, dose-dependently elevated BrdU immunolabeling while co-administration with pirenzepine significantly reduced BrdU immunolabeling. Each bar represents the mean (±S.E.M.) (n = 6) number of BrdU⁺ cells per mm³. ** sig. diff. from saline-treated controls, p < 0.001, *p < 0.05; ++ sig. diff. from oxotremorine alone, p < 0.001, +p < 0.05.