Hormonal control and signaling of the testis of the bat Molossus molossus during the processes of testicular maturation, regression, and recrudescence

Abstract Molossus molossus , a species of neotropical bat belonging to the Molossidae family, has an annual reproductive cycle that includes two peaks of spermatogenic activity, one in April and another in September, and a period of total testicular regression in December. Although testicular regression and recrudescence are common processes in hibernating bats, they are rarer in tropical species, making studies on the hormonal control of these phenomena scarce. Thus, this study aimed to analyze and characterize the hormonal control and signaling of the processes of testicular maturation, regression, and recrudescence in M. molossus . Histological, morphometric, and immunohistochemical analyses were performed on the testes of animals in four phases of the reproductive cycle (juvenile, active adult, regressing adult, and recrudescent adult). The animals' blood was subjected to hormonal dosage for testosterone and estradiol. Our results demonstrate that the transition from juvenile to adulthood in M. molossus is characterized by enhanced steroidogenic activity in Leydig cells and increased testosterone production, supporting the establishment of complete spermatogenesis. Conversely, testicular regression is associated with reduced expression of steroidogenic components and androgen signaling, accompanied by decreased circulating T and impairment of Sertoli cell function, ultimately leading to disruption of the seminiferous epithelium and suppression of spermatogenesis. During recrudescence, the recovery of Leydig cell steroidogenic activity precedes the complete restoration of seminiferous epithelium organization, indicating that reactivation of androgen production is a critical event in the re‐establishment of reproductive function in M. molossus .