Autoradiographic localization of muscarinic cholinergic receptors in visual areas of cat brain: variations in sensitivity of N-[3H]methylscopolamine binding sites to carbachol and pirenzepine.

The distribution of muscarinic acetylcholine receptors (MChRs) was studied in visual areas of cat brain using in vitro quantitative autoradiography with 1 nM N-[3H]methylscopolamine ([3H]NMS) as a radioligand. The highest density of [3H]NMS binding was observed in lamina A of the lateral geniculate nucleus (LGN) and in layer II/III of the visual cortex. The lowest binding was seen in the stratum griseum intermediale of the superior colliculus (SC). The comparison of inhibition of [3H]NMS binding by 100 microM carbachol and 300 nM pirenzepine showed that the SC and LGN contain predominantly M2 sites. M1 sites constitute the main population of MChRs in the cortical areas studied.