Hypothalamo-hypophysial Neurosecretory System in Normal and Hypophysectomised Catfish,Clarias Batrachus L

Abstract

Two neurosecretory centers, nucleus preopticus (NPO) and nucleus lateralis tuberis (NLT), are distinguished in the hypothalamus of Clarias batrachus L. The cell bodies of NPO are grouped into nucleus preopticus magnocellularis (NPM) and nucleus preopticus parvocellularis (NPP). The NLT is recognised into three divisions: pars rostralis, pars medialis and pars ventrolateralis. The neurons of both the NLT and NPO are aldehyde-fuchsin (AF) positive. The axons from NPO run into four or five bundles ventrolaterally and caudally for some distance before all of them from either side join ventromedially into a single thick cord of neurosecretory fibers which finally enters the pars intermedia to form the neurointermediate lobe. The fibers from NLT, which are separate from the neurosecretory fibers of the NPO, anastomose in the region of the pars distalis. The neurosecretory material (NSM) of NPO is transported by axonal route whereas that of NLT is by axonal as well as ependymovascular pathways. Hypophysectomy results in the increase of AF-positive material in the neurons of NPO shortly after the operation, but later on, the material begins to deplete in them. The AF-positive material at the cut end of neurosecretory fibers, however, accumulates. The AF-positive material in the cell bodies of NLT is also depleted, but the nuclei increase in size, after hypophysectomy.