The differentiation of Leydig cells, steroidogenesis, and the spermatogenetic wave in the testis of Necturus maculosus

The study of seminiferous tubule--Leydig cell interactions in relation to specific germ cell stages during the cycle of the seminiferous epithelium is extremely difficult in most mammalian species due to the continual presence of different spermatogenetic stages in the testis from the onset of puberty. The problem is also compounded by the uniform distribution of both seminiferous tubules and interstitial tissue throughout the entire testis. This difficulty can be circumvented, however, by studying certain species where there is a topographical distribution of germ cell stages within the testis. The urodele amphibian Necturus maculosus exhibits a breeding cycle during which a longitudinal wave of spermatogenesis occurs along the length of the testis, resulting in a spatial and temporal segregation of differentiating germ cells. Moreover, this topographical pattern of spermatogenesis is also reflected in the degree of development of adjacent Leydig cells. This anatomical arrangement allows distinct testicular regions to be obtained using a dissecting microscope. The isolated zones, containing germ cells and Leydig cells in various stages of development, were analyzed for 17 alpha-hydroxylase, C-17,20-lyase, and aromatase activities (key enzymes for the synthesis of androgens and estrogen), estrogen binding, and cytochrome P-450 content. Functional parameters were then correlated with the morphology of Leydig cells in the various zones observed by both light and electron microscopy. It was found that there existed a distinct correlation between the state of differentiation of the leydig cells, their steroidogenic potential, and the distribution of estrogen receptors. These results in Necturus indicate indicate in this species, at least, the steroidal microenvironment of different germ cell associations may be quite specific.