Hypothalamic Neurosecretion in Mink (Mustela vison Schreb.) Kept Under Various Photoperiodic Conditions

Abstract

The hypothalamo-hypophyseal neurosecretory system (HHNS) of male standard mink were studied cytomorphologically in November. The control (group I) was kept under natural photoperiodic conditions. For group II, daylight was prolonged from November 10–25 by 17 h. Group III was exposed to conditions simulating a halving of the natural light year; the day’s length was gradually decreased from July to September up to 7.30 h and then increased by the end of November up to 17.00 h. In mink of groups II and III, the numbers of nuclei and nucleoli of the neurosecretory cells of the supraoptic nucleus were increased. The neurosecretion content in the cells and fibers of the supraoptic, postoptic, and paraventricular nuclei and of the median eminence (ME) was reduced twofold. The glial and vascular elements of these areas were activated. A twofold reduction of neurosecretory material in the posterior pituitary (PP) was observed in mink of group II only. The cells of the arcuate nucleus demonstrated increases in the size of nuclei (insignificant) and nucleoli (significant) in mink of group III. In these mink, the glial elements of the ME were markedly hyperplastic (by 107%) and hypertrophic (by 139%). The glial cells of the ME of group II were slightly activated (by 28% and 36%, respectively). The proliferative processes in gonads of mink of group III were much more advanced than those of group II. It is possible that the regulatory effect of the peptidergic HHNS is exerted through the PP in mink of group II. This effect is exerted in mink of group III by the complex comprising the magnocellular and arcuate nuclei acting, largely, through the adenohypophysis.