Exposure to constant light during testis development increases daily sperm production in adult Wistar rats

Testis histometry and daily sperm production (DSP) were evaluated in adult (160-day-old) Wistar rats exposed to constant light for the first 25 days after birth, and compared with control animals which were exposed to a 12 h-light-12 h-dark light regimen. Significantly greater (P < 0.05) numbers of Sertoli cell nucleoli and round spermatids per cross-section of seminiferous tubule were found in animals exposed to constant light. In addition, epididymis weight, DSP per testis and per gram of testis, as well as Leydig cell compartment volume, were significantly increased in treated animals. Although there was a clear trend toward an increased Sertoli cell population per testis in animals exposed to constant light, this difference was not statistically significant (P < 0.05). The number of round spermatids as expressed per Sertoli cell was the same in both groups. Surprisingly, the diameter and volume of round spermatid nucleus at stages I and VII of the cycle of seminiferous epithelium were significantly lower (P < 0.05) in treated animals. In conclusion, constant illumination during neonatal testis development increased sperm production and Leydig cell compartment volume in adult rats probably through a mechanism involving elevated follicle stimulating hormone and luteinizing hormone during the prepubertal period. To our knowledge, this is the first study showing that altering the light regimen can affect sperm production in non-seasonal breeders.