Stage-dependent topographical relationship of spermatogonia and early spermatocytes to Sertoli-Sertoli interspaces in the rat testis.

In the rat seminiferous epithelium the Sertoli-Sertoli interspaces can be regarded as ending at the surface of basal germ cells as well as at the basement membrane. The relationship between these basal endings (BEs) of the Sertoli-Sertoli interspaces and the basal germ cells was examined using the electron microscope. The number of BEs in a given area of the seminiferous epithelium was counted and found to be constant throughout the cycle of the seminiferous epithelium. Undifferentiated spermatogonia had contact with very few BEs while differentiating type A spermatogonia at stage VII and later during the cycle seemed to be associated with a maximum of BEs. As type A spermatogonia developed to intermediate spermatogonia, type B spermatogonia, and preleptotene spermatocytes, the average number of BEs per cell decreased exponentially. Thin, fingerlike cell projections emerged from the differentiating type A and intermediate spermatogonia along the basement membrane. These projections were associated with BEs. It is concluded that a specific stage-dependent topographical arrangement is established between Sertoli cells and germ cells long before the first synchronous division of type A spermatogonia takes place. The significance of this arrangement is discussed.