Pars Distalis Of Anterior Pituitary Research Articles

Peptidergic innervation in pars distalis of the human anterior pituitary

It has been previously shown that the peptidergic nerve fibers are present in the anterior pituitary of monkeys, dogs and rats. In our study, which is reported here, thick nerve fiber bundles, large numbers of peptidergic nerve fibers and their varicosities, which are substance P (SP)-, calcitonin gene-related peptide (CGRP)- and galanin (GAL)-immunoreactive (ir), are found in the human pituitary stalk. All these peptidergic nerve fibers run along the pituitary stalk and enter the pars distalis, and some GAL-ir nerve fibers even reach the center of the human anterior pituitary as well as in parenchyma of adenohypophysis. The number of SP-ir nerve fibers is much more than that of other kinds of peptidergic nerve fibers. All these peptidergic nerve fibers are mainly located in the medial part of the gland and distributed in its dorsal-posterior region. A substantial amount of these peptidergic nerve fibers with numerous varicosities are found to be close to the glandular tissue in the pars distalis of the human anterior pituitary. Furthermore, same SP-ir and CGRP-ir cells have been demonstrated in the pars distalis of the anterior pituitary. More or less, these peptidergic nerve fibers came also from the meningeal shell and enter the parenchyma of the anterior pituitary. Whatever the function of peptidergic nerve fibers in the human anterior pituitary might be, the concept that the adenohypophysis is regulated only hormonally by way of the portal system could be challenged.

Brain and Pituitary Melatonin Receptors in Male Rat during Post‐Natal and Pubertal Development and the Effect of Pinealectomy and Testosterone Manipulation

Using quantitative autoradiography, melatonin receptors have been studied during post-natal and pubertal development of the rat in 2 brain and 2 pituitary structures. In the pars distalis of anterior pituitary, melatonin receptors decrease gradually in density after birth and disappear in 30 day-old animals. In contrast melatonin binding is only expressed in the paraventricular nuclei of the thalamus at the age of 21-23 days and is always present in adult animals. In the suprachiasmatic nuclei and in the pars tuberalis of the pituitary, melatonin receptor density decreases after birth, remains stable for approximately 1 month and increases again at puberty to reach the birth values in the adult. This increase was absent in pinealectomized and in castrated animals but present in castrated animals receiving testosterone suggesting that it depends upon circulating testosterone and melatonin levels. These results show that melatonin receptors are differentially regulated during post-natal development in each of the 4 structures studied, and that melatonin and testosterone are 2 factors which could be involved in the regulation of melatonin receptor density in the suprachiasmatic nuclei and pars tuberalis.