Relationship of vasopressin with NADPH-diaphorase in the hypothalamo-neurohypophysial system

The relative anatomical distributions of vasopressin and the nitric oxide synthase, nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) were examined in the hypothalamo-neurohypophysial system using immunocytochemical and histochemical techniques. Double-labeled neurons were localized predominately to rostral aspects of the hypothalamo-neurohypophysial system. Only scattered double-labeled cells were found throughout the subdivisions of the supraoptic and paraventricular nuclei. Because previous investigations suggest that nitric oxide may play a critical role in neurotransmission and reductions in NADPH-d have been reported in the neural lobe of salt-loaded animals, the present report of its coexistence with the antidiuretic hormone vasopressin in the hypothalamo-neurohypophysial system further supports a role for these neuroactive substances in mechanisms modulating fluid homeostasis.