Blank J L, Freeman D A
Department of Biological Sciences, Kent State University, Ohio 44242.
J Comp Physiol A. 1991 Oct;169(4):501-6. doi: 10.1007/BF00197662.
Inhibitory photoperiod differentially effects reproduction in deer mice (Peromyscus maniculatus nebrascensis). Pituitary-testicular function is arrested in about one-third of short-day exposed males (reproductively responsive mice), while an equal number remain fertile (reproductively nonresponsive mice). Both phenotypes are found in natural populations and their disparate reproductive responses have a genetic basis. To assess whether this difference is attributable to a prepineal/pineal or post-pineal mechanism, we compared spermatogenic responses of known and unknown phenotype to exogenous melatonin. Melatonin significantly reduced mean sperm number in long-day housed mice of unknown phenotype. But, individual responses ranged from azoospermia to normal spermatogenesis, and this range was not significantly different from that previously recorded for short-day exposed mice. Reproductively nonresponsive males were unaffected by melatonin administration when housed under long or short daylength. In contrast, melatonin significantly suppressed sperm production in reproductively responsive males housed under long photoperiod, but had no additional suppressive effect in short-day housed mice with regressed testes. These data demonstrate that melatonin is only effective in eliciting testicular regression in reproductively responsive males. Taken together, these results suggest that differential testicular response to photoperiod are caused by a post-pineal mechanism.
抑制性光周期对鹿鼠（Peromyscus maniculatus nebrascensis）的繁殖有不同影响。约三分之一暴露于短日照的雄性（生殖反应型小鼠）垂体-睾丸功能停止，而数量相等的雄性仍保持生育能力（生殖无反应型小鼠）。这两种表型都存在于自然种群中，它们不同的生殖反应有遗传基础。为了评估这种差异是归因于松果体前/松果体还是松果体后机制，我们比较了已知和未知表型对外源褪黑素的生精反应。褪黑素显著降低了长日照饲养的未知表型小鼠的平均精子数量。但是，个体反应范围从无精子症到正常精子发生，且该范围与先前记录的短日照暴露小鼠的范围无显著差异。当在长日照或短日照条件下饲养时，生殖无反应型雄性不受褪黑素给药的影响。相反，褪黑素显著抑制了长光周期饲养的生殖反应型雄性的精子产生，但对睾丸已退化的短日照饲养小鼠没有额外的抑制作用。这些数据表明，褪黑素仅在引发生殖反应型雄性的睾丸退化方面有效。综上所述，这些结果表明，睾丸对光周期的不同反应是由松果体后机制引起的。
