SUBSTANCE P-LIKE IMMUNOREACTIVITY IN THE SUPRACHIASMATIC NUCLEUS OF THE RAT

The content of substance P (SP)-like immunoreactivity (LI) within the suprachiasmatic nucleus (SCN) of rats was determined by enzyme immunoa ssay to evaluate the effect of light on SP-LI in the rat SCN. Male rat s were kept under various lighting conditions: light-dark cycles, cons tant darkness, continuous light exposure for 24 b or light pulse inter rupting constant darkness. Animals were also subjected to ocular enucl eation. The present study showed that SP-LI in the SCN was unaffected by environmental lighting conditions or by bilateral ocular enucleatio n. Immunohistochemical studies also confirmed that SP immunoreactivity , which was found in the ventrolateral (VL) subdivision of the SCN, wa s not reduced significantly even after ocular enucleation. These resul ts suggest that, in contrast to other neurotransmitters in the VL port ion of the SCN such as vasoactive intestinal polypeptide (VIP), gastri n releasing peptide (GRP) and neuropeptide Y (NPY), SP level in the SC N is quite stable to light and arises from an area other than the reti na.