A fine-structural study of interstitial cell changes in the testes of Necturus maculosus during a portion of the annual cycle, and possible evidence for local feedback control by seminiferous epithelium.

The developmental stages of the interstitial cells of Leydig in Necturus maculosus were studied in testes of animals obtained in November and December. As a consequence of the caudal to cranial progression of the wave of spermatogenesis, samples obtained from cranial, central, and caudal portions of these testes exhibit regional differences in the morphology of their Leydig cells. In these samples, fibroblast-like stromal cells with large, dense, elongated nuclei and thin sheets of cytoplasm surround the cranial seminiferous lobules that usually contain spermatozoa. Such stromal cells possess a small juxtanuclear Golgi apparatus, profiles of smooth and rough endoplasmic reticulum, and mitochondria with tubular and shelf-like cristae. In the central area of the testis, interstitial cells with oval nuclear profiles and a finer chromatin pattern surround degenerating seminiferous lobules. The abundant cytoplasm of these cells contains predominantly smooth endoplasmic reticulum interspersed with a few lipid droplets. These cells contain mitochondria that are packed with tubular cristae. Inthe caudal part of the testis, the Leydig cells have a round nucleus with finely dispersed chromatin. Numerous lipid droplets accumulate in the ample cytoplasm, which is filled with smooth endoplasmic reticulum. The juxtanuclear Golgi apparatus becomes enlarged; associated with it are vesicles with an electron-dense content. The cristae of the mitochondria are more numerous and have tubules of 50-nm diameter mixed with arrays of small tubules 25-30 nm in diameter. The appearance of morphologically mature interstitial cells of Leydig only adjacent to degenerated seminiferous lobules inthe caudal portion of the testis suggests the possibility of local feedback control of Leydig-cell development.