Prendergast B J, Hotchkiss A K, Wen J, Horton T H, Nelson R J
Department of Psychology and Institute for Mind and Biology, University of Chicago, Chicago, IL 60637, USA.
J Neuroendocrinol. 2006 May;18(5):339-48. doi: 10.1111/j.1365-2826.2006.01419.x.
Siberian hamsters (Phodopus sungorus) undergo reproductive involution following exposure to short winter day lengths. Following approximately 20 weeks of exposure to short day (SD) lengths, hamsters become refractory to the inhibitory effects of SD, and reproductive competence is restored in anticipation of spring. The extent to which changes in gonadal steroid-dependent and -independent regulation of gonadotrophin secretion participate in this vernal reactivation of the gonads is not known. This experiment tested whether tonic and gonadotrophin-releasing hormone (GnRH)-stimulated regulation of lutenising hormone (LH) secretion differs between photoresponsive and photorefractory Siberian hamsters. Male hamsters born into long day (LD) lengths were castrated or subjected to a sham-castration surgery at 17 days of age, implanted s.c. with blank or testosterone-filled capsules, and housed in LD or SD thereafter. Baseline LH and LH responses to GnRH (200 ng/kg, s.c) were measured at 14 (photoresponsive) and 40 (photorefractory) weeks of age. Despite lower circulating testosterone concentrations in gonadally regressed SD hamsters on week 14, tonic LH concentrations were comparable among all groups of gonad-intact hamsters on weeks 14 and 40; however, week 14 SD hamsters exhibited significantly higher GnRH-stimulated LH responses. Tonic LH concentrations were indistinguishable among all groups of castrated hamsters bearing empty implants on week 14, but prolonged exposure to LD led to a decrease in resting LH, whereas prolonged exposure to SD resulted in an increase in LH. In castrated hamsters bearing testosterone implants, baseline LH concentrations were comparable in all groups, but GnRH treatment resulted in significantly higher LH concentrations in photorefractory (week 40, SD) hamsters relative to all other groups. The data suggest that the development of photorefractoriness in Siberian hamsters is characterised by enhanced gonadal hormone-independent stimulation of LH secretion, and diminished sensitivity to inhibitory negative-feedback effects of testosterone on LH secretion. Decreases in responsiveness of gonadotrophin secretion to gonadal hormone negative feedback may contribute to the process of photorefractoriness and assist in maintaining the growth of reproductive organs during the process of gonadal recrudescence.
西伯利亚仓鼠（Phodopus sungorus）在暴露于冬季短日照后会经历生殖退化。在大约20周的短日照（SD）暴露后，仓鼠对SD的抑制作用变得不敏感，并且在春季来临前生殖能力得以恢复。促性腺激素分泌的性腺类固醇依赖性和非依赖性调节变化在性腺的春季再激活中所起的作用程度尚不清楚。本实验测试了光反应性和光不应性西伯利亚仓鼠之间，促性腺激素释放激素（GnRH）刺激下的促黄体生成素（LH）分泌的紧张性调节是否存在差异。出生在长日照（LD）条件下的雄性仓鼠在17日龄时接受去势或假去势手术，皮下植入空白或填充睾酮的胶囊，之后饲养在LD或SD条件下。在14周（光反应性）和40周（光不应性）龄时测量基础LH以及LH对GnRH（200 ng/kg，皮下注射）的反应。尽管在第14周时性腺退化的SD仓鼠循环睾酮浓度较低，但在第14周和40周时，所有性腺完整的仓鼠组中促性腺激素释放激素刺激的LH反应在第14周时显著更高。在第14周时，所有植入空胶囊的去势仓鼠组中促性腺激素释放激素刺激的LH反应无显著差异，但长期暴露于LD导致静息LH降低，而长期暴露于SD则导致LH升高。在植入睾酮的去势仓鼠中，所有组的基础LH浓度相当，但GnRH处理导致光不应性（第40周，SD）仓鼠的LH浓度相对于所有其他组显著更高。数据表明，西伯利亚仓鼠光不应性的发展特征是促性腺激素分泌的性腺激素非依赖性刺激增强，以及对睾酮对促性腺激素分泌的抑制性负反馈作用的敏感性降低。促性腺激素分泌对性腺激素负反馈反应性的降低可能有助于光不应性过程，并在性腺再发育过程中协助维持生殖器官的生长。
