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

The presence of functional hypothalamo-hypophysial neurosecretory system in vertebrates has led to reviseearlier views regarding the hypothalamus-pituitary relationship. The hypothalamo-neurohypophysialsystem which consists of hypothalamic nuclei, their axonal fibres forming tractus preoptico-hypophysesand the neurohypophysis) works as a morphological as well as a physiological connection between thehypothalamus and the pituitary gland. In fishes, fibres from the neurosecretory hypothalamic nucleiterminate in the neurohypophysis, which remains inter digitized with the adenohypophysis and provides avery close association between the neurosecretory fibres and pars intermedia of the pituitary gland forminga neuro-intermediate lobe. Hypothalamo-Neurosecretory complex of Xenentodon cancila consists ofNucleus Pre-opticus (NPO), Nucleus Lateralis Tuberis (NLT) and their axonal tracts. NPO is a pairedstructure situated on either side of the third ventricle anterodorsal to the optic chiasma. NPO is divisibleinto 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 formneurohypophysial tract. Herring bodies are seen in the anterior as well as posterior neurohypophysis.