LIGHT INDUCES EXPRESSION OF FOS-RELATED PROTEINS WITHIN GASTRIN-RELEASING PEPTIDE NEURONS IN THE RAT SUPRACHIASMATIC NUCLEUS

The present study was conducted to determine whether the photic induct ion of c-fos expression in the rat suprachiasmatic nucleus (SCN) occur s within neurons containing gastrin-releasing peptide (GRP) and/or vas oactive intestinal polypeptide (VIP) because these peptidergic cells a re closely associated with retinal projections to the ventrolateral su bfield. Using dual immunostaining and thin sectioning techniques, the ventrolateral SCN of light-exposed rats was examined for evidence of i ndividual neurons coexpressing nuclear immunostaining for c-fos protei ns (Fos) with cytoplasmic immunoreactivity for GRP or VIP. In all anim als, the photic induction of Fos expression in the SCN was mainly conf ined to cells segregated within the ventrolateral subfield and was evi dent in approximately 40% of the SCN neurons with cytoplasmic immunore activity for GRP. However, neurons coexpressing Fos and GRP comprised only a small fraction of the total number of cells within the ventrola teral SCN exhibiting light-induced Fos immunoreactivity. No sign of Fo s expression was detected within VIP-immunoreactive perikarya in the v entrolateral SCN of light-treated rats. These results,demonstrate that light induces Fos expression in a number of GRP-containing neurons wi thin the SCN, suggesting that these peptidergic cells may process phot ic information mediating circadian entrainment.