IN THE RAT PINEAL-GLAND, BUT NOT IN THE SUPRACHIASMATIC NUCLEUS, THE AMOUNT OF CONSTITUTIVE NEURONAL NITRIC-OXIDE SYNTHASE IS REGULATED BY ENVIRONMENTAL LIGHTING CONDITIONS

To investigate whether the expression of neuronal isoform of nitric ox ide synthase is photoneurally regulated, we examined the amount of the enzyme by means of Western Blot analysis under different environmenta l lighting conditions in two photoneuronally regulated tissues, the pi neal gland and the suprachiasmatic nucleus of the rat. In the pineal g land nitric oxide synthase immunoreactivity was strikingly decreased w hen rats had been exposed for 8 days to light:dark 20:4 conditions or to constant light. The decline in nitric oxide synthase immunoreactivi ty following LL reversed after 4 days under light:dark 12:12. We concl ude that in the rat pineal the amount of neuronal nitric oxide synthas e is controlled by environmental lighting conditions. That it is not j ustified to extrapolate from the pineal to other photoneuronally regul ated centers is illustrated by the present finding that the suprachias matic nucleus did not reveal changes in the amount of neuronal nitric oxide synthase. (C) 1995 Academic Press, Inc.