Hypothalamo-Neurohypophysial Neurosecretion After the Extirpation of Various Endocrine Glands

Abstract

The possible role of the hypothalamo-neurohypophysial system in regulating the release of the anterior pituitary hormones was studied in the rabbit and the rat. Thyroidectomy, gonadectomy and uni- and bilateral adrenalectomy were the experimental conditions used. The neurosecretory material (N. S. M.) was demonstrated by the aldehyde-fuchsin (AF) technique. Distinct differences were not seen in the different groups of rabbits on account of the great variation between individuals. In the rats, the thyroidectomy and gonadectomy groups often had slightly more N. S. M. in the median eminence around the portal vessels than the controls. Slight depletion of N. S. M. in the infundibular process was observed in unilaterally adrenalectomized rats. N. S. M. passing into the portal vascular system showed a tendency to increase. In the bilateral adrenalectomy group, N. S. M. was reduced in the supraoptic and paraventricular nuclei, in the hypothalamo-hypophysial tract and in the infundibular process. However, considerably more numerous neurosecretory nerve fibres passing towards the portal vessels than in the controls were found in the median eminence of this group. The conclusion drawn was that N. S. M. entering the hypophysial portal vessels in the median eminence may be of significance in the regulation of corticotrophin release.

Effect of Stress, Adrenalectomy, Hypophysectomy and Hydrocortisone on the Corticotropin-Releasing Activity of Rat Median Eminence

“…These findings are in agreement with the observations of Brodish and Long, who found elevated corticotropinreleasing activity in the peripheral blood of hypophysectomized-adrenalectomized rats (11). Using a different approach, Arko et al (12) have reported an increase in the number of neurohypophysial nerve fibers terminating in the portal vessels of the median eminence two and a half weeks after adrenalectomy-they interpret this as a sign of increased transport of the neurosecretory material into the portal vessels. Although the identity of this neurosecretory material has not yet been established, Rinne (13) believes it might have a role in regulating the release of ACTH.…”

Effect of Electrical Stimulation of the Neurohypophysis on ACTH Release in Rats with Hypothalamic Lesions

“…That the neurosecretory fibers originating in or run ning through the PVN and ending in the external zone of the median eminence may have a role in regulating the pituitary-adrenal axis has already been suggested on the basis of morphological investigations. So-called Gomoripositive 'CRF granules' in the external layer of the median eminence accumulated following adrenalectomy and de creased after dexamethasone treatment [2,3]. Such fibers show positive immunocytochemical reaction with neurophysine and vasopressin antibodies and originate mainly from the paraventricular nuclei [4, 39.…”

Effect of Diphenylhydantoin Treatment on the Release of Corticotrophin in Epileptic Patients

“…T h at the la tte r blockade could be overcome only by electrical stim ulation of the preoptic region of the hypothalam us argues in favour of an effect at the level of the central nervous system (Quinn 1965). An effect bearing on the hypothalam us in shown also by the finding th a t in the mouse di phenylhydantoin interferes w ith the liypothalam o-hypophysial neuro secretory system (Kivalo et al 1958) and this system m ay have a role in the regulation of ACTH release (see R inne 1960, 1965, Arko et al 1963, R inne and Sonninen 1964. I t is possible th a t diphenylhydantoin affects the hypothalam ic centres, which participate in the neuro hum oral control of the anterior p itu itary gland by lowering their activity in the same way as it reduces the excitability of the nerve tissue in general, possibly by way of Na turnover (see Sparberg 1963).…”