Ultrastructural demonstration of NADPH-diaphorase histochemical activity in the supraoptic nucleus of normal and dehydrated rats.

The ultrastructural location of the NADPH-diaphorase, likely to represent the nitric oxide synthase, was studied in the supraoptic nucleus of control and dehydrated rats. The NADPH-diaphorase activity was found in nuclear envelope, inner and outer membranes of mitochondria, Golgi apparatus, and endoplasmic reticulum in both neurons and astrocytes. We observed an increase in the number of stained mitochondria and an increased staining of the endoplasmic membranes in prolonged dehydration stress. Based on available data, the supraoptic NADPH-diaphorase/nitric oxide synthase seems to be involved in adaptative function of the hypothalamic neurosecretory system.