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. Physiological results revealed the involvement of NO in circadian regulation of rats. Since neuronal structures containing NO-synthase (NOS) were previously not found in the circadian oscillator, the hypothalamic suprachiasmatic nucleus (SCN), in this species but are present in the hamster, 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, hamster) showed a NOS-like immunoreactive (-LI) protein band of apparent mo…