Neuropeptide Y-immunoreactive structures in the telencephalon and diencephalon of the white sturgeon, Acipenser transmontanus, with special regard to the hypothalamo-hypophyseal system.
An immunohistochemical study using a streptavidin-biotin method demonstrated the extensive distribution of neuropeptide Y (NPY)-like immunoreactivity in the brain of the white sturgeon, Acipenser transmontanus, with the highest density in the basal telencephalon and diencephalon. Two labeled cell groups were found in the telencephalon, in mediobasal and dorsocaudal locations. Labeled fibers were considerably dense in the ventral area. The epithalamus displayed dense networks of varicose fibers in the ganglion habenulae, but only a few fibers were seen in the organon subcommissurale. In the thalamus, two groups of labeled cells were discerned in the periventricular gray matter: an anteroventral group largely composed of cerebrospinal fluid (CSF)-contacting neurons, and a dorsocaudal group consisting of non-CSF-contacting large neurons. The hypothalamus also contained a number of CSF-contacting neurons in the periventricular areas including the nucleus lobi inferioris, the nucleus lateralis tuberis and the nucleus recessus posterioris. Labeled varicose fibers were closely associated with the hypothalamo-hypophyseal complex, the organon vasculosum hypothalami, and the saccus vasculosus. Immunoreactive cells and fibers were also detected in the dorsal region of the adenohypophysis. These results suggest that NPY or a related molecule is involved in the hypothalamic neuroendocrine mechanisms of this primitive bony fish.