SUBCELLULAR-LOCALIZATION OF NITRIC-OXIDE SYNTHASE IN THE CEREBRAL VENTRICULAR SYSTEM, SUBFORNICAL ORGAN, AREA POSTREMA, AND BLOOD-VESSELS OF THE RAT-BRAIN

The distribution of neuronal nitric oxide synthase (nNOS) has been stu died in the more rostral portion of the lateral ventricle, subfornical organ, area postrema and blood vessels of the rat central nervous sys tem. nNOS was located by means of a specific polyclonal antibody, by u sing light and electron microscopy. Light microscopy showed immunoreac tive varicose nerve fibers and terminal boutons-like structures in the lateral ventricle, positioned in supra and subependimal areas. The sp atial relationships between immunoreactive neuronal processes and the wall of the intracerebral blood vessels were studied. Electron microsc opy showed numerous nerve fibers in the wall of the lateral ventricle; many were nNos-immunoreactive and established very close contact with ependymal cells. Immunoreactive neurons and processes were found in t he subependymal plate of the ventricular wall, the subfornical organ, the area postrema, and the circularis nucleus of the hypothalamus. In these last three areas, the immunoreactive neurons were found close to the perivascular space of fenestrated and nonfenestrated blood vessel s. The nNOS immunoreactivity was localized to the endoplasmic reticulu m, cisterns, ribosomes, neurotubules, and in the inner part of the ext ernal membrane. In the terminal boutons, the reaction product was foun d surrounding the vesicle membranes. This distribution showed nNOS as a predominantly membrane-bound protein. The nitrergic nerve fibers pre sent in the wall of the ventricular system might regulate metabolic fu nctions as well as neurotransmission in the subfornical organ, area po strema and circularis nucleus of the hypothalamus. (C) 1997 Wiley-Liss , Inc.