Low and infrequent expression of nitric oxide synthase/NADPH-diaphorase inneurons of the human supraoptic nucleus: a histochemical study

The gas nitric oxide is a messenger in brain signaling. In the hypothalamo- hypophyseal system nitric oxide is involved in the control of the expressio n and/or release of peptide hormones (corticotropin-releasing hormone, gona dotropin-releasing hormone, vasopressin and oxytocin). Nitric oxide synthas e (NOS), the enzyme generating nitric oxide, is abundantly present in the m agnocellular nuclei of the rat hypothalamus. Its localization in the human hypothalamus is less well studied. Hence, we investigated the anatomical di stribution of neuronal nitric oxide synthase in the human supraoptic nucleu s by use of immunohistochemical and enzyme histochemical techniques. The im munohistochemical localization of NOS was studied in 31 matched human hypot halami (13 control cases, eight depressed patients and ten schizophrenics). NADPH-diaphorase studies were carried out on seven additional hypothalami (three normal brains, four schizophrenics). Apparent inter-individual diffe rences exist with regard to the occurrence of the enzyme in supraoptic neur ons. In a majority of cases no immunostaining or histochemical reaction for the enzyme was observed. In seven cases (three controls, two schizophrenic s, two depressives) a population of nitrergic nerve cells was seen in the d orsomedial part of the nucleus. This group of cells also stained for NADPH- diaphorase. Also, there were a few NOS-immunopositive neurons scattered thr oughout the nucleus. Additionally, thin NADPH-diaphorase positive fibers we re observed to cross the nucleus. Our data show that, unlike the rat, the h uman supraoptic nucleus contains only a small number of nitrergic neurons. No correlation was found between the expression of the enzyme in supraoptic neurons and the psychiatric status of the patients. (C) 2000 Elsevier Scie nce B.V. All rights reserved.