Ultrastructural study of the boar seminiferous epithelium: Changes in cryptorchidism

The present study compares the ultrastructural features of Sertoli cells an d germ cells between scrotal testes of healthy boars and abdominal testes o f unilateral and bilateral cryptorchid boars. In healthy boars, spermatogon ia are flat cells lying in close association with the basal lamina. As diff erentiation progresses, spermatogonia acquire an oval profile and lose thei r contact with the basal lamina. Spermatocytes are round cells moving from the basal compartment of the seminiferous epithelium to the luminal compart ment. Spermatids exhibit complex morphological changes leading to the forma tion of spermatozoa. Sertoli cells extend from the basal lamina to the tubu lar lumen. The nucleus encloses fine euchromatin and one or two nucleoli; t he nuclear envelope has a few deep infoldings. The lateral cell membranes f orm junctional specializations that constitute the blood-testis barrier. Th e cytoplasm encloses smooth endoplasmic reticulum, vesicles, aggregates, an d scattered mitochondria. The seminiferous epithelium of abdominal testes f rom unilateral and bilateral cryptorchid boars contains few spermatogonia w ith an abnormal appearance; the alteration in germ cell number is more seve re in the bilateral disease. In unilateral cryptorchid boars, spermatogonia appear as either large pyramidal cells or roundish cells; in bilateral cry ptorchid boars, spermatogonia show roundish profiles and degenerative patte rns. Abdominal testes of both unilateral and bilateral cryptorchid boars ar e constituted by immature Sertoli cells that show abnormal cytoplasmic cont ent, defective development of the blood-testis barrier, and atypical nuclea r appearance; in bilateral cryptorchid boars, immature Sertoli cells exhibi t degenerative signs. At postpubertal age, unilateral and bilateral cryptor chidism induce total arrest of spermatogenesis at spermatogonial stage as a result of an abnormal differentiation of the Sertoli cells. Moreover, the degeneration of abdominal testes initiates earlier in bilateral cryptorchid ism than in unilateral cryptorchidism. (C) 2000 Wiley-Liss, Inc.