Muscarinic acetylcholine receptor subtypes in rat visual cortex--a comparative study using quantitative receptor...

The laminar pattern of M1- and M2-muscarinic acetylcholine receptors (mAChR) in rat visual cortex has been compared with the distribution of the corresponding m1, m2, m3 and m4 receptor genes using both quantitative receptor autoradiography and in situ hybridization histochemistry. The laminar distribution of 3H-pirenzepine binding to M1-mAChRs in rat visual cortex shows a bimodal pattern with higher binding levels in upper layer III and deeper layer VI. In contrast, highest binding of 3H-AF-DX384 to M2-mAChRs was observed in upper layer IV (100%) and upper layer VI (about 80% of highest binding). The m1 receptor mRNA is almost homogeneously distributed throughout the visual cortex, whereas the m2mAChr mRNA predominates in layer IV with lower levels in layers I and V. The highest amounts of m3mAChR mRNA in rat visual cortex were observed in layer II, while the distribution of m4mAChR transcripts shows a bimodal pattern with peaks in layers III and upper layer VI. The distinct laminar pattern of mRNA muscarinic receptor subtypes in rat visual cortex suggest specific roles of the muscarinic receptor in visual function.