Neuronal nitric oxide synthase immunoreactivity in forebrain, pineal, and pituitary of Oreochromis mossambicus (Tilapia)

Abstract

Ultrastructural localization of neuronal nitric oxide synthase (nNOS) in olfactory receptor neurons (ORNs) and immunohistochemical detection of the enzyme in forebrain, pituitary, and pineal were undertaken in the teleost Oreochromis mossambicus. Application of post-embedding immunoelectron microscopy revealed nNOS-labeled gold particles on the cilia, microvilli, mitochondria, and Golgi complex of the ORNs. Gold particles were also seen adhered to microtubules in the axons that extend to the olfactory nerve layer in the olfactory bulb. With light microscopy, nNOS-immunoreactive neurons were seen in preoptic area, nucleus entopeduncularis, and parvocellular, and magnocellular subdivisions of nucleus preopticus (NPO). Numerous cerebrospinal fluid-contacting cells lining the wall of the third ventricle at the level of the NPO showed intense immunoreactivity. Intense to moderate immunoreactivity was observed in the neurons of suprachiasmatic nucleus, nucleus lateralis tuberis pars lateralis, and nucleus recessus lateralis. While several immunoreactive fibers were detected in medial olfactory tract, suprachiasmatic area, and hypothalamo-hypophyseal tract, a few were seen throughout the telencephalon, in the optic chiasma, tuberal area, and inferior lobes. In the pituitary, nNOS-containing fibers were seen in the neurohypophysis, rostral pars distalis, proximal pars distalis, and pars intermedia. While intense immunoreactivity was noticed in some cells in the pineal, immunoreactive fibers were detected in the pineal stalk as well as parenchyma. We suggest that nitric oxide may play a role in processing olfactory and photic information, circadian rhythms, and neuroendocrine regulation in tilapia.