Differential effects of M1 and M2 muscarinic drugs on septohippocampal, hippocampal and cortical neurons in the rat.

The effects of muscarinic agonists (McN-A-343, pilocarpine, oxotremorine-M, carbachol) and antagonists (pirenzepine, gallamine) applied by iontophoresis were studied on several neuronal populations in the central nervous system of rats anesthetized with urethane. Septohippocampal neurons and neurons from hippocampus, subiculum and somatic sensory cortex were studied. Oxotremorine-M and carbachol had (almost exclusively) potent excitatory effects whereas pilocarpine had some and McN-A-343 had almost exclusively inhibitory effects on the 4 populations of neurons studied. Pirenzepine blocked more easily the effects of pilocarpine and McN-A-343 than those of oxotremorine-M or carbachol. These results suggest (i) that many central neurons may bear different functional muscarinic receptors and (ii) that the various agonists studied might act through (at least partially) different mechanisms.