5-HT3 receptors augment neuronal, cholinergic contractions in guinea pig trachea

Localization of m3 mRNA, for the expression of the M3 muscarinic receptor, along the crypt-villus axis, was undertaken in rat jejunum by in situ hybridization. While enterocytes on the lower two-thirds of the villi showed the presence of m3 mRNA it was absent in the crypt enterocytes. This indicates that the final locus of muscarinically activated jejunal secretion is mediated by the M3 receptor on the enterocytes of the villi and not via the crypt cells.