Pineal nitric oxide synthase, but not heme oxygenase, mRNA is suppressed by continuous exposure to light

We have previously shown that exposure of rats to constant light (LL) induc ed a decrease in NO synthase (NOS) activity in the pineal gland. We report here that the use of the sensitive technique of RT-PCR has demonstrated tha t mRNA for neuronal NOS is present in the pineal, and that it is photoneura lly regulated. There was a marked decrease in pineal neuronal NOS mRNA leve ls in continuous light conditions, similar to the changes seen in NOS enzym e activity. Inducible NOS was not present in the pineal, and there was evid ence that the photoregulatable form was not endothelial NOS. The mRNA for t wo isoforms of heme oxygenase, the enzyme responsible for the generation of the putative neuromodulator carbon monoxide, was also present in the pinea l, but neither isoform was photoregulated. Using immunodetection, it was no t possible to identify the presence of NOS protein, other than to a minimal extent, even though NOS activity was clearly present. NADPH-diaphorase sta ining and in situ hybridization were carried out in an attempt to identify the precise location of neuronal NOS message. A strong NADPH-diaphorase rea ction was present in sympathetic nerve fibers of the pineal, but pinealocyt es showed no or only very weak labelling. In situ hybridization was also un able to identify neuronal NOS message in pinealocytes. These data thus also suggest the possible presence of a pineal-specific NOS isoenzyme. (C) 1999 Elsevier Science B.V. All rights reserved.