The structure of the hypothalamic neurosecretory cells of Zoarces viviparus L. under the conditions of constant dark and light during the reproductive cycle

Summary

The Structure of the hypothalamic neurosecretory cells during their activity in continuous light and dark conditions and depending on the seasonal alteration has been investigated in Zoarces viviparus L. in the level of light and electron microscopy.

The depletion of AF- or AT-stainable material, of the elementary neurosecretory granules and the disappearance of smooth-surfaced vesicles occur during April and June. The accumulation of the stanable material as well as the elementary neurosecretory granules and the smooth-surfaced vesicles has been observed in the cell body in late September.

An excess increase in number of the smooth-surfaced vesicles of dark-induced animals and light-induced animals kept in a black stained tank is apparent. On the other hand, the disappearance of the elementary granules and the smooth-surfaced vesicles and an enlargement in the reletive nuclear surface of the neurosecretory cells of light-induced animals which were kept in a gray stained tank in April is also evident.

Taking into consideration the responsiveness of both the elementary neurosecretory granules and the smooth-surfaced vesicles in relation to the external environment as well as their topographical arrangement in the cell body the possible differences in their origin and function are discussed.

Numerous studies indicate that the physical environment is in part responsible for the functional properties of the hypothalamic neurosecretory centers of various vertebrates. In the level of light microscope, it has been repeatedly shown that the neurosecretory cells are activated in the animals subjected to continuous illumination, and in those subjected to long daily photo period (Oksche et al., 1958; Fiske and Greep, 1959; Öztan and Gorbman, 1960; Satyanesan, 1965). The enlargement of the nuclei and the amount of Gomori — or aldehyde fuchsin — stainable material, as well as the enzymatic activity, were used as the criteria of cellular activity in the histological preparation. In the level of electronmicroscope it has been shown that Gomori positive material (Bargmann, 1949) is represented as aggregated elementary neurosecretory granules in the ultrathin sections of neurohypophysis (Bargmann et al,. 1957). Although the fine structure of the hypothalamic neurosecretory cells of various fishes and higher vertebrates have been studied in normal and experimental conditions (Palay, 1960; Lederis, 1962, 1964; Follenius et Porte, 1962; Follenius, 1963; Murakami, 1961–1964; Gansler, 1965; Holmes, 1965) the type of granules and their function still remains as an open question (see Bargmann, 1963; Knowles, 1965).