Hypothalamic neurosecretory system of the spotted owlet, Athene brama Temminck
Singh, K.B.; Dominic, C.J.
Acta Anatomica 94(3): 414-430
1976
ISSN/ISBN: 0001-5180 PMID: 1032080 Document Number: 102157
The structure of the hypothalamic neurosecretory system of the spotted owlet as revealed in tissue sections was described. The paraventricular nucleus (PVN) is better developed than the supraoptic nucleus (SON), and is divided into periventricular and lateral divisions. The former is further divided into anteroventral and posterodorsal subdivisions. The neurons of the SON are grouped into preoptic, median and lateral divisions. The preoptic division is again divided into median and lateral subdivisions. The lateral division of the SON is likewise divided into anterolateral and posterolateral subdivisions. Neurons of the lateral division of the SON, which are embedded in the optic tract, form the so-called optic tract division. Scattered neurons connect the median division of the SON with the anteroventral subdivision of the periventricular division of the PVN and the lateral division of the SON with the lateral division of the PVN. There is no significant morphological difference between the neurons of the SON and of the PVN. Typically, the neurons are heavily loaded with neurosecretory material (NSM) and the cell nuclei appear poor in chromatin. Sometimes the NSM is the neurons is present in the form of one or more large granules. Occasionally, neurons loaded with NSM are seen in the process of distintegration; these may contribute to the large number of Herring bodies and neurosecretory granules which are found in the hypothalamic nuclei. Because of the paucity of the NSM, the proximal part of the hypothalamo-hypophyseal tract could not be traced. The tract bifurcates anterior to the median eminence. The dorsal branch proceeds to the neural lobe as the hypothalamo-neurohypophysial tract; the ventral branch passes to the zona externa of the anterior median eminence. The zona externa of the median eminence possesses an AF -positive anterior division and an AF-negative posterior division. The neural lobe is a thin-walled, sac-like structure with a large lumen. Its wall is heavily loaded with NSM and hence histological details are hardly visible.