Upregulation of nitric oxide synthase and galanin message-associated peptide in hypothalamic magnocellular neurons after hypophysectomy. Immunohistochemical and in situ hybridization studies

The expression of several bioactive molecules in magnocellular hypothalamic neurons is modified when the axons of these cells are transected. In this stuyd we have evaluated by means of immunocytochemistry and in situ by hybridization the effect of hypophysectomy on the expression of nitric oxide synthase (NOS)- and of galanin message-associated peptide (GMAP)-like immunoreactivities (-LIs) as well as on their respective mRNAs in hypothalamic magnocellular neurosecretory neurons. The results show a transient increase in NOS- and GMAP-LIs in magnocellular neurons of both the paraventricular and supraoptic nuclei when compared to normal animals. The maximal increase in staining was observed between 5 and 7 days, and by 14 days NOS-LI was back to normal levels, whereas strong GMP-LI could still be detected in a few cella. A similar picture was observed for the NOS and GMAP mRNAs. The functional significance of the present findings is unclear, but they indicate a possible role of nitric oxide and GMAP in neurosecretory neurons after injury.