Cyclic Changes In The Hypothalamo Neurohypophysial System of Xenentodon Cancila (HAM.)

Abstract

The presence of functional hypothalamo-hypophysial neurosecretory system in vertebrates has led to revise earlier views regarding the hypothalamus-pituitary relationship. The hypothalamo-neurohypophysial system which consists of hypothalamic nuclei, their axonal fibres forming tractus preoptico-hypophyses and the neurohypophysis) works as a morphological as well as a physiological connection between the hypothalamus and the pituitary gland. In fishes, fibres from the neurosecretory hypothalamic nuclei terminate in the neurohypophysis, which remains inter digitized with the adenohypophysis and provides a very close association between the neurosecretory fibres and pars intermedia of the pituitary gland forming a neuro-intermediate lobe. Hypothalamo-Neurosecretory complex of Xenentodon cancila consists of Nucleus Pre-opticus (NPO), Nucleus Lateralis Tuberis (NLT) and their axonal tracts. NPO is a paired structure situated on either side of the third ventricle anterodorsal to the optic chiasma. NPO is divisible into a dorsal Pars Magnocellularis (PMC) consisting of large neurosecretory cells and Pars Parvocellularis (PPC) formed of smaller neurons. Neurons of PMC and PPC contribute beaded axons to form neurohypophysial tract. Herring bodies are seen in the anterior as well as posterior neurohypophysis.