NITRIC-OXIDE SYNTHASE IN THE HYPOTHALAMIC SUPRACHIASMATIC NUCLEUS OF RAT - EVIDENCE FROM HISTOCHEMISTRY, IMMUNOHISTOCHEMISTRY AND WESTERN-BLOT - AND COLOCALIZATION WITH VIP

Nitric oxide (NO) is a neuroactive substance of high potency. Physiolo gical results revealed the involvement of NO in circadian regulation o f rats; Since neuronal structures containing NO-synthase (NOS) were pr eviously not found in the circadian oscillator, the hypothalamic supra chiasmatic nucleus (SCN), in this species but are present in the hamst er, we investigated the distribution of NO-producing structures in the rat SCN by Western blot analysis, immunohistochemistry of NOS, and by histochemistry (NADPH-diaphorase (NADPH-d) activity of NOS). Western blot analysis of SCN homogenates from rat (and, for comparison, hamste r) showed a NOS-like immunoreactive (-LI) protein band of apparent mol ecular mass of 150 kDa, consistent with the neuronal NOS molecule. In the rat SCN, perikarya exhibiting NADPH-d staining or NOS-LI with a co mplete overlapping of both were found. Double-immunofluorescence exper iments revealed that NOS cells are a subgroup of the neuronal SCN popu lation that is characterized by immunoreactivity to vasoactive intesti nal polypeptide. These data provide evidence for the existence of neur onal nitric oxide synthase in the rat SCN and may explain the involvem ent of NO in the mediation of photic information.