NOCTURNAL DECREASES IN NITRIC-OXIDE AND CYCLIC-GMP CONTENTS IN THE CHICK BRAIN AND THEIR PREVENTION BY LIGHT

The diurnal variations in the contents of nitric oxide (NO) and cyclic GMP were studied in the chick brain. NO and cyclic GMP contents in th e chick brain were lower at night than during the day and were inverse ly correlated with high night-time tissue melatonin levels. Furthermor e, when animals were kept in light at night, tissue melatonin levels r emained at low diurnal values, whereas NO and cyclic GMP contents rema ined high. Since we have previously shown that physiological concentra tions of melatonin inhibit nitric oxide synthase (NOS) activity in dif ferent brain areas,he nocturnal decrease in brain NO and cyclic GMP co ntents may be, in part, a consequence of the nocturnal inhibitory effe ct of melatonin on NOS activity. Copyright (C) 1996 Elsevier Science L td.