Alterations in spermatogenic activity and hormonal status in a seasonally breeding rat,Rattus fuscipes

The changes in the levels of serum FSH, LH, and testosterone have been studied during the seasonal reproductive cycle in males of the species Rattus fuscipes. In males captured in winter the seminiferous tubules were small, spermatogenesis was arrested at the primary spermatocyte stage, and the Sertoli cells contained increased numbers of lipid inclusions. The Leydig cells were atrophic and contained large crystalloids. The aspermatic state was accompanied by low levels of serum FSH, LH, and androgen. Reactivation of spermatogenesis occurred in spring and was accompanied by a rise in the levels of FSH, LH, and androgen. These hormonal changes were associated with a depletion of lipid inclusions from the Sertoli cells which paralleled the activation of spermatogenesis. The rising androgen levels were accompanied by the enlargement of Leydig cells and the disappearance of the crystalloids. In summer the fully active testes were associated with further increments of serum FSH and androgen levels above those seen during spring. It is concluded that the environmental cues controlling the seasonal reproductive cycle exert their influence on the testis through changes in gonadotrophin secretion by the pituitary gland.