光周期—褪黑素信号调控高原鼠兔精原细胞分化和季节性精子发生

高原鼠兔是青藏高原特有的小型哺乳动物，其繁殖活动呈现明显的季节性。成年雄性高原鼠兔在繁殖期睾丸重量显著增加，精子发生正常进行，而在非繁殖期睾丸退化，精子发生阻断在未分化精原细胞阶段。光周期控制实验显示，长光照（16h∶8h）诱导非繁殖期高原鼠兔重新启动精原细胞分化和精子发生；而短光照（8h∶16h）显著抑制繁殖期高原鼠兔精子发生。酶联免疫分析发现，褪黑素分泌水平在长日照条件下降低而在短日照条件下升高。非繁殖期高原鼠兔连续注射褪黑素拮抗剂能诱导生殖细胞发育和精子发生恢复。促性腺激素释放激素(GnRH)与黄体生成素(LH)在繁殖期鼠兔下丘脑垂体显著升高，促卵泡素（FSH）水平无显著差异。注射GnRH可以促进非繁殖期高原鼠兔精原细胞分化和精子发生，而褪黑素注射后抑制GnRH的分泌进而负调控性腺轴。综上，高原鼠兔季节性精子发生受光周期-褪黑素信号控制，后者主要通过控制GnRH、LH水平影响精原细胞分化。本研究对理解季节性动物精子发生的调控机制有重要借鉴意义。

Photoperiod-melatonin signal regulates seasonal spermatogenesis in plateau pikas（Ochotona curzoniae）

The plateau pika (Ochotona curzoniae) is a small mammal native to the Qinghai-Tibetan Plateau. Pikas breed in summer and become reproductively dormant in winter. Long-day stimulation (16h∶8h) induced spermatogonial differentiation and the resumption of spermatogenesis, while short-day treatment (8h∶16h) resulted in spermatogonial differentiation arrest. Melatonin content was significantly increased in short-day adapted animals and injection of melatonin inhibited the spermatogonial differentiation and development of advanced germ cells, while treatment with a melatonin receptor antagonist stimulated spermatogonial differentiation and spermatogenesis in the reproductively dormant animals. Levels of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) were significantly increased in reproductively active males while follicle-stimulating hormone (FSH) did not differ. Functional experiments revealed that GnRH injection stimulated germ cells development and initiation of spermatogenesis in non-breeding season. Furthermore, GnRH content in brain was decreased by melatonin administration. Together, data from the present demonstrated that the seasonal spermatogenesis of plateau pikas was directed by photoperiod-melatonin signal. These findings revealed a key mechanism underlying seasonal reproduction in Plateau Pikas and likely other animal species.