Distribution of NADPH-diaphorase activity in the hypothalamo-hypophysial system of the frog, Rana esculenta.

Using nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase (ND) histochemistry, this study reports a wide distribution of ND activity in the hypothalamus, and for the first time in the median eminence (ME), the neural lobe (NL) and in the pars distalis (PD) of the frog, Rana esculenta. Perikarya are ND-active within the nucleus preopticus (NPO), the nucleus preopticus periventricularis (NPP), located around the preoptic recess (PR), the suprachiasmatic nucleus (SCN) and within five infundibular nuclei. Several ND-positive neurons of the nucleus infundibularis ventralis are cerebrospinal fluid-contacting in nature, while a few occupy a subependymal region. The infundibulum shows a thick sheet-like fiber plexus which receives fibers not only from its ND-active neurons, but also from the anterior and central thalamic nuclei. The ME, NL and most cells of the posterodorsal PD are ND-positive. The pituitary function may be mediated by nitric oxide through modulating the secretion of hormone-releasing factors of the hypothalamus. Possible functional significance of the ND-stained hypothalamic areas is discussed.