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 suggests 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 examine the presence of three different 5-HT receptor subtypes in the suprachiasmatic 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 immunoreactivity, a lesser amount of 5-HT2a positive fibres and no staining with antiserum against the 5-HT7 receptor subtype. These results are compatible with previous pharmacological evidence obtained in our laboratory showing that serotonin acting through the 5-HT2c receptor subtype may be important in the phase shifting effects of light on the circadian system. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.