REDUCED NEUROPHYSIN IMMUNOREACTIVITY IN RAT SUPRACHIASMATIC NUCLEUS PARALLELS DISSOCIATION OF CIRCADIAN FEEDING RHYTHM IN CONSTANT LIGHT

Several distinct neuronal populations can be outlined in the suprachia smatic nucleus (SCN) by employing immunohistochemistry. Understanding their interaction may serve as the key to the proc esses involved in t he generation of circadian rhythms by the SCN. 15 adult rats were expo sed to constant dim light (LL) and 3 animals as controls to an LD 12:1 2 light schedule over 140 days. When sacrificed 10 of the LL-animals h ad lost their circadian feeding rhythm while 5 were free-running and t he controls kept an entrained rhythm. The brains were immunohistochemi cally stained for myelin basic protein, neurophysin (NPH), vasoactive intestinal peptide, neuropeptide Y, synaptophysin and the leucocyte ep itopes FAL and HNK-1. Demarcation of intensely and very intensely stai ned NPH-positive areas by subjective gray-leveldiscrimination and comp uterized area measurement revealed that in rhythmic rats (n=8) the are as containing the stained material were twice as large (0.06 +/- 0.03 mm2 vs. 0.028 +/- 0.027 mm2; p less than or equal to 0.05) than in arr hythmic animals. It is hypothesized that low NPH-contents in arrhythmi c animals reflect arrest of the 'clockwork' in the SCN at circadian ti me 12:00.