The hypothalamo-hypophysial system in acipenseridae

Abstract

The peptidergic neurosecretory cells (NSC) of the nucleus praeopticus (NP) of male and female sturgeons, A. güldenstädti Brandt, were studied light microscopically at different stages of their life cycle and under experimental conditions. Four main NSC types reflecting different phases of secretory cycle and life course of the cell have been tentatively distinguished. The maximum percentage of the high and moderate active NSC are found in juvenile animals in the sea (stages I and I-II of gonadal maturity, sgm), in upstream migrating fish in spring before spawning, in down-stream migrating fish 1-1.5 months after spawning, and in experimental fish kept for 8.5 hours in a 32% sodium chloride solution. The least active NSC accumulating neurosecretory material (NSM) are characteristic of juvenile fish (sgm II) in the sea, sturgeons maintained in a sodium chloride solution for 3.5 or 6 hours and fish which remained in a net, thrown to the sea, for some hours before fixation. The lowest percentage of these cells is observed in autumn migrants, in females soon after spawning (sgm VI) and in fish kept for 8.5 hours in a sodium chloride solution. Cells rich in basophilic substance and poor in NSM occur in juvenile and in down-stream migrating fish. Cells reflecting the state of exhaustion after hyperactivity and "ageing" cells are seen in adults, expecially in sgm VI fish, and in autumn migrants. Pyknomorphous NSC are constantly present in all fish; they are most numerous in sturgeons found in a net. A diagram demonstrating the life course and the secretory cycle of the NSC is presented and the role of the hypothalamo-hypophysial neurosecretory system (HHNS) under stress conditions is discussed.