LIGHT AND ELECTRON MICROSCOPY AND ITS USE IN THE STUDY OF FACTORS INFLUENCING SPERMATOGENESIS IN THE RAT

SYNOPSIS The value of employing both light and electron microscopy in cytological research is discussed. It is pointed out, however, that depending upon the kind of problem being studied it may be necessary to employ a wide variety of experimental techniques. This is particularly true when attempting to relate structure to function. To emphasize this, and to present a synthesis of some recent work, observations made by the writer and collaborators on the testes of normal, irradiated and oestrogen‐treated rats are described. The following main results are reported: 1. The residual bodies, cast off by the newly‐formed spermatozoa, consist of basic cytoplasmic constituents; they are especially rich in R.N.A. 2. The residual bodies are phagocytosed by the Sertoli cells and degenerate. During the latter process their R.N.A. component is absorbed or dispersed. Their lipid, however, remains and probably constitutes the bulk of the lipid seen with the Sertoli cells during later stages of the seminiferous cycle. 3. A lipid cycle is shown both by the germ cells and the Sertoli cells. The germ cells contain most lipid during about stages 1–8. The Sertoli cells contain most lipid during about stages 9–14. The two cycles are essentially out of phase with each other. 4. The lipid of the germ cells, residual bodies and Sertoli cells, gives a negative reaction to Schultz's test for cholesterol. 5. High doses of radiation (10,000 rads; 50,000 rads) cause the germ cells to degenerate; they are then phagocytosed by the Sertoli cells. The degenerating germ cells form large amounts of lipid which comes to lie freely embedded within the Sertoli cytoplasm. This lipid gradually becomes markedly cholesterol‐positive. 6. Preliminary tests suggest that the cholesterol‐positive lipid of irradiated animals possesses progestin‐like activity. 7. During prolonged treatment with oestrogenic hormone, large amounts of lipid slowly accumulate within the Sertoli cells. This lipid gradually gives a strong positive cholesterol‐reaction. As a working hypothesis it is suggested that in normal animals the lipid within the Sertoli cells represents a steroid hormone or its precursor which it utilized by the germ cells at some particular stage, or stages, of their development. On this basis the residual bodies initiate the production of this hormone. Thus the well‐marked co‐ordination of spermatogenetic stages about a radial axis in seminiferous tubules of the rat may depend upon the phagocytosis of the residual bodies and the secretion of a steroid hormone by the Sertoli cells.