Localization and in situ quantification of 5-hydroxytryptamine and its receptor in rat submaxillary gland

5-Hydroxytryptamine (5-HT) and its receptor have been localized and quantified in the submaxillary gland of rats of various ages, using immunohistochemistry, in situ hybridization and in situ quantification. In male rats, the epithelial cells of serous acini, intercalated ducts, secretary tubes and excretory ducts all showed 5-HT and 5-HT receptor (5-HTR) immunoreactivity. Both 5-HT and 5-HTR reactive sites were found in the same cells of adjacent sections. 5-HT1A receptor mRNA hybridized signals could be detected in cytoplasm of these cells. The parasympathetic ganglia cells and endothelial cells of small vessels also showed 5-HT and 5-HTR immunoreactivity in the cytoplasm. However, in female rats, only the epithelial cells in excretory tubes showed 5-HT and 5-HTR immunoreactivity. The immunoreactivity was present in the same cells of adjacent sections. The relative content of 5-HT and its receptor increased during the first 60 postnatal days but remained constant from day 60 to day 90 postnatum. These results suggest that the submaxillary gland of rats possess autocrine 5-HT, which may regulate the function and development of the gland.