Immunohistochemical localization of serotonin receptors in the rat suprachiasmatic nucleus

Serotonin (5-HT) has been implicated in the regulation of circadian rhythms through its actions on the suprachiasmatic nucleus (SCN). Recent data sugg ests that, along with excitatory amino acids, serotonin may be important in the neural pathway that mediates the transmission of photic information to the circadian system. The present study uses immunohistochemistry to exami ne the presence of three different 5-HT receptor subtypes in the suprachias matic nucleus (5-HT2a, 5-HT2c and 5-HT7) in male albino Wistar rats. In the SCN, there was a considerable amount of 5-HT2c-receptor-like immunoreactiv ity, a lesser amount of 5-HT2a positive fibres and no staining with antiser um against the 5-HT7 receptor subtype. These results are compatible with pr evious pharmacological evidence obtained in our laboratory showing that ser otonin acting through the 5-HT2c receptor subtype may be important in the p hase shifting effects of light on the circadian system. (C) 1999 Elsevier S cience Ireland Ltd. All rights reserved.