EFFECTS OF ILLUMINATION AND ENUCLEATION ON SUBSTANCE-P-IMMUNOREACTIVESTRUCTURES IN SUBCORTICAL VISUAL CENTERS OF GOLDEN-HAMSTER AND WISTARRAT

The undecapeptide substance P is found in different entities of the vi sual system that control eye movement and synchronize endogenous rhyth ms with the light cycle (i.e., superior colliculus, suprachiasmatic nu cleus, intergeniculate leaflet). Immunocytochemical methods were used to compare the reactivity to substance P in the brain of five groups o f golden hamsters and two groups of Wistar rats: (1) untreated hamster s kept under 14L:10D and sacrificed at noon; (2) identically maintaine d animals sacrificed at midnight; (3) enucleated animals kept under co ntrol conditions; (4) hamsters kept under constant darkness; (5) hamst ers kept under the same conditions as the controls, but intraventricul arly injected with colchicine. The results obtained in golden hamsters of groups (1) and (3) were compared with findings in Wistar rats trea ted accordingly [groups (6) and (7)]. Substance P-immunoreactive perik arya were found in the suprachiasmatic nucleus and superior colliculus of hamsters and Wistar rats. Substance P-immunoreactive nerve fibers were abundant in the hypothalamic area ventral to the paraventricular nucleus, in the intergeniculate leaflet, in some thalamic nuclei, and in the superior colliculus. Immunoreactivity to substance P in the sup rachiasmatic nucleus and intergeniculate leaflet did not vary among th e experimental groups. However, a conspicuous decrease in reactivity t o substance P was observed in the superficial layers of the superior c olliculus of enucleated hamsters and rats, compared with all other gro ups. These results indicate that substance P immunoreactivity in the s uperior colliculus, but not that in the suprachiasmatic nucleus or int ergeniculate leaflet, depends on the integrity of the retinal projecti on.