NADPH‐Diaphorase (Nitric Oxide Synthase) Staining in the Rat Supraoptic Nucleus is Activity‐Dependent: Possible Functional Implications

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Abstract
NADPH-diaphorase has recently been shown to be the enzyme nitric oxide (NO) synthase, and to be present in the rat supraoptic nucleus (SON) and posterior pituitary. Investigations were carried out to assess whether there is any difference in the extent to which this enzyme is present, as assessed by light-microscopic histochemistry, in SON of normal and dehydrated male Wistar rats. In normal rats there was clear cellular heterogeneity; cells located in the ventral and caudal areas of the SON stained only weakly or not at all, while cells in the rostro-dorsal areas of the nucleus stained strongly. Dehydration of rats for 12 h caused a large and rapid increase in staining intensity of the nucleus, particularly of cells in its ventral and caudal parts. On the basis of its known biological actions, and the kinetics of its induction, it is suggested that NO would be a strong candidate as a modulator of SON and posterior pituitary morphology and function, with the potential to rapidly modulate blood flow, neuronal activity, and possibly astrocyte morphology, in response to changes in neuronal activity.