24-HOUR RHYTHMICITY OF NADPH-DIAPHORASE ACTIVITY IN THE NEUROPIL OF RAT VISUAL-CORTEX

In the present study we examined the daytime-dependent alterations of nitric oxide synthase in the visual cortex of the rat. For this purpos e, the activity of the nicotinamide adenine dinucleotide phosphate-dia phorase (NADPH-d), an enzyme equivalent to nitric oxide synthase, was measured histochemically in rat visual cortex at 0600, 1200, 1800, and 2400 h using a photometric scanning method, Our results show daytime- dependent changes of the NADPH-d activity in the neuropil of the visua l cortex, This was highest at 0600 h and decreased between 1200 h and 1800 h (unimodal profile of circadian activity), The number of NADPH-d -positive neuronal somata was not found to vary at the different time points. (C) 1997 Elsevier Science Inc.