RELATIONSHIP OF NEURONAL NITRIC-OXIDE SYNTHASE IMMUNOREACTIVITY TO GNRH NEURONS IN THE OVARIECTOMIZED AND INTACT FEMALE RAT

The present study has used a rat neuronal nitric oxide synthase (nNOS) antibody to examine the relationship of nNOS immunoreactivity to GnRH neurons in the ovariectomized and intact diestrous and proestrous rat . A striking band of nNOS-immunoreactive cells was identified in the r ostral preoptic area which began in the median preoptic nucleus and or ganum vasculosum of the lamina terminalis and formed an inverted Y-typ e distribution above the rostral third ventricle at the level of the a nteroventral periventricular nucleus. Another band of nNOS-immunoreact ivity was found extending through the internal zone of the median emin ence into the arcuate nucleus. Although nNOS immunoreactivity was not detected within GnRH neuronal cell bodies in any of the experimental g roups, GnRH perikarya located in the rostral preoptic area, but not el sewhere, were found to be surrounded by nNOS-containing cells, In the median eminence, nNOS and GnRH immunoreactivities were distributed sep arately in the internal and external zones, respectively. These result s provide evidence that, regardless of their pattern of activity, GnRH neurons in the female rat do not express nNOS. Instead, a close anato mical relationship between nNOS-immunoreactive cells and GnRH perikary a and fibers has been identified within specific sub-regions of the ro stral preoptic area and in the median eminence. Such findings are comp atible with a role for NO at both sites in regulating the release of G nRH throughout the estrous cycle.