Monecke Stefanie, Wollnik Franziska
Biological Institute, Department of Animal Physiology, University of Stuttgart, 70550 Stuttgart, Germany.
Biol Reprod. 2004 May;70(5):1438-43. doi: 10.1095/biolreprod.103.023002. Epub 2004 Jan 21.
Annual rhythms of body weight and reproduction in the European hamster (Cricetus cricetus) are the result of an interaction between seasonal changes in day length (photoperiod) and seasonal changes in the responsiveness of animals to these photoperiods. The present study demonstrates that under natural conditions European hamsters are not able to perceive long photoperiods (i.e., a 16L:8D cycle) before mid-November. This is an important difference to other hamster species, in which regrowth of the gonads can be stimulated by exposure to long photoperiods at any stage of gonadal regression. The experiments also demonstrate the existence of an annual phase of sensitivity to long photoperiods that starts around mid-November and extends until March/April. During this phase of sensitivity, exposure to a long photoperiod (16L:8D) induced gonadal regrowth within 3 wk. Additional experiments with an accelerated photoperiodic lighting regimen indicated that a photoperiod of approximately 13 h is necessary to stimulate gonadal regrowth. Under natural light conditions in Stuttgart (48.46 degrees N), a photoperiod of 13 h is reached by the beginning of April, which fits well with the finding that the majority of animals kept under a natural light:dark cycle had well-developed gonads by the end of April. Nevertheless, these animals showed a rather variable timing of gonadal regrowth, ranging from early January to late April. This is most likely the result of two processes: first, an endogenous mechanism (photorefractoriness) that induces gonadal recrudescence without any photoperiodic information while the animals are still in their hibernation burrows, and second, a direct stimulatory effect of long photoperiods.
欧洲仓鼠（Cricetus cricetus）的体重和繁殖年度节律是日长（光周期）季节性变化与动物对这些光周期反应性季节性变化之间相互作用的结果。本研究表明，在自然条件下，欧洲仓鼠直到11月中旬之前都无法感知长光周期（即16小时光照：8小时黑暗周期）。这与其他仓鼠物种存在重要差异，在其他仓鼠物种中，性腺退化的任何阶段暴露于长光周期都可刺激性腺重新生长。实验还证明了对长光周期的年度敏感阶段的存在，该阶段始于11月中旬左右，一直持续到3月/4月。在这个敏感阶段，暴露于长光周期（16小时光照：8小时黑暗）会在3周内诱导性腺重新生长。采用加速光周期光照方案的额外实验表明，大约13小时的光周期对于刺激性腺重新生长是必要的。在斯图加特（北纬48.46度）的自然光条件下，到4月初达到13小时的光周期，这与大多数在自然光照：黑暗周期下饲养的动物到4月底性腺发育良好的发现非常吻合。然而，这些动物的性腺重新生长时间相当可变，从1月初到4月底不等。这很可能是两个过程的结果：第一，一种内源性机制（光不应性），在动物仍在冬眠洞穴时，无需任何光周期信息即可诱导性腺再发育；第二，长光周期的直接刺激作用。
