IMMUNOHISTOCHEMICAL MAPPING OF NITRIC-OXIDE SYNTHASE IN THE RAT HYPOTHALAMUS AND COLOCALIZATION WITH NEUROPEPTIDES

The localization and distribution of nitric oxide synthase in the hypo thalamus have been studied with an immunohistochemical technique using antibodies to neuronal rat nitric oxide synthase. Subsequent double-l abeling experiments examined the colocalization patterns of nitric oxi de synthase and several peptides. Our results demonstrate a widespread occurrence of nitric oxide synthase-immunoreactive nerve cell bodies and processes throughout the hypothalamus, especially in various parts of the preoptic region, in the supraoptic and paraventricular nuclei, the lateral hypothalamic area, the ventromedial and dorsomedial nucle i, the arcuate nucleus and various parts of the mammillary region. Dou ble labeling experiments showed that nitric oxide synthase-like immuno reactivity coexists with substance P-like immunoreactivity in the medi al preoptic area, with oxytocin-, cholecystokinin- and galanin message -associated peptide-like immunoreactivity in the supraoptic nucleus, w ith enkephalin-, oxytocin- and corticotropin releasing factor-like imm unoreactivity in the paraventricular nucleus and with enkephalin-like immunoreactivity in the arcuate nucleus. Furthermore, in the ventromed ial nucleus, nitric oxide synthase-like immunoreactivity coexisted wit h enkephalin-, substance P-, and somatostatin-like immunoreactivity, a nd in the dorsomedial nucleus with enkephalin-, galanin message-associ ated peptide- and substance P-like immunoreactivity. In the mammillary region nitric oxide synthase-like immunoreactivity coexisted with enk ephalin-, cholecystokinin-, and substance P-like immunoreactivity. Amo ng these neuropeptides, enkephalin and substance P were most frequentl y found in nitric oxide synthase-immunoreactive neurons. We conclude t hat nitric oxide synthase immunoreactive neurons contain neuropeptides in various parts of the hypothalamus, and that nitric oxide in the hy pothalamus may be involved in a variety of neuroendocrine and autonomi c functions.