Expression of hypothalamic peptides in mice lacking neuronal nitric oxide synthase: Reduced beta-END immunoreactivity in the arcuate nucleus

The gas nitric oxide (NO) is an important messenger in brain signaling. Alo ng with many other functions, NO is thought to influence the expression and /or release of various hypothalamic hormones (corticotropin-releasing hormo ne (CRH), gonadotropin-releasing hormone (GnRH) and vasopressin). To learn more about the role of NO in neuroendocrine mechanisms, we studied in mutan t mice lacking neuronal isoform of NO synthase (nNOS) the cellular expressi on of CRH, neurophysin (the carrier protein of vasopressin/oxytocin) and pr oopiomelanocortin (POMC), as well as of the POMC-derived peptides beta-endo rphin (beta-END), alpha-melanocyte-stimulating hormone (alpha-MSH) and cort icotropin (ACTH) by use of immunohistochemistry and in situ hybridization. Additionally, the remaining NO-generating capacities of the nNOS minus mice were investigated by NADPH-diaphorase histochemistry and citrulline immuno histochemistry as well as by immunohistochemical localization and Western b lot analysis of endothelial NOS (eNOS) and nNOS isoforms. Amongst all hypot halamic peptides under investigation, only beta-END was found to be altered in mutant mice. A morphometric analysis of beta-END producing neurons of t he arcuate nucleus revealed that significantly less cells were immunoreacti ve in mutant mice, whereas the expression of the precursor POMC as well as of other POMC-derived peptides was found to be unchanged. In addition to th at, fewer beta-END-immunoreactive fibers were found in the paraventricular nucleus of nNOS minus mice in comparison to wild-type animals. Hence, the r eduction of hypothalamic beta-END is probably a posttranslational event tha t might reflect a disturbed endorphinergic innervation of those hypothalami c neurons which normally express nNOS.