Etude histophysiologique du système hypothalamo-hypophysaire de Scyliorhinus caniculus (L.) en état de mélanodispersion permanente

Abstract

Cases of permanent darkening, obtained in the course of experiments on the hypophysis and related hypothalamic structures of the spotted dogfish Scyliorhinus caniculus (L.), were submitted to histological examination after 4 months rearing. A series of experiments of short duration was also carried out. Melanization (due to melanophore dispersion) appears after every injury to the hypothalamo-hypophyseal tract, specifically the preoptico-hypophyseal tract. Neurosecretory accumulation appears after either direct (transverse cut) or indicrect (extirpation of various lobes) injury; disappearance of neurosecretory material was generally complete at 4 months after the operation. The structure of the neurointermediate lobe remained normal in 14 out of 15 cases in which pigmentation remained normal, and in 5 out of 18 cases in which melanization resulted. The other 13 of the 18 cases of permanent darkening exhibited profound changes of the neurointermediate lobe; the MSH-cells became degranulated and their ergastoplasm increased as a consequence of chronic hyperactivity. Marked regressive degeneration and functional inactivity of the preoptic nucleus were observed in 9 of the 13 cases. The same changes occurred in autografts of the lobe. With regard to the inhibitory control of the pars intermedia by the brain, these findings agree with those of Abramowitz (1939), Etkin (1941), and others. The bihormonal theory of the control of color change is refuted as far as Elasmobranchs are concerned.