Hut R A, Van der Zee E A, Jansen K, Gerkema M P, Daan S
Zoological Laboratory, University of Groningen, Haren, The Netherlands.
J Comp Physiol B. 2002 Jan;172(1):59-70. doi: 10.1007/s003600100227.
European ground squirrels (Spermophilus citellus) in outside enclosures show suppressed circadian rhythmicity in body temperature patterns during the first days of euthermia after hibernation. This may reflect either gradual reappearance of circadian rhythmicity following suppressed functioning of the circadian system during hibernation, or it may reflect transient days during re-entrainment of the circadian system which, during hibernation, has drifted out of phase with the environmental light-dark cycle. Here we report that animals kept under continuous dim light conditions also showed absence of circadian rhythmicity in activity and body temperature in the first 5-15 days after hibernation. After post-hibernation arrhythmicity, spontaneous circadian rhythms re-appeared gradually and increased daily body temperature range. Numbers of arginine-vasopressin immunoreactive neurons in the suprachiasmatic nuclei correlated positively with individual circadian rhythmicity and increased gradually over time after hibernation. Furthermore, circadian rhythmicity was enhanced rather than suppressed after exposure to a light-dark cycle but not after a single 1-h light pulse (1,700 lux). The results support the view that the functioning of the circadian system in the European ground squirrel is suppressed during hibernation at low temperatures and that it requires several days of euthermia to resume its summer function.
圈养在室外的欧洲地松鼠（Citellus citellus）在冬眠后恢复正常体温的头几天，其体温模式的昼夜节律受到抑制。这可能反映了在冬眠期间昼夜节律系统功能受到抑制后，昼夜节律逐渐重新出现；或者也可能反映了在冬眠期间与环境明暗周期不同步的昼夜节律系统重新同步的过渡阶段。在此我们报告，在持续昏暗光照条件下饲养的动物在冬眠后的前5 - 15天，其活动和体温也没有昼夜节律。在冬眠后无节律状态之后，自发的昼夜节律逐渐重新出现，且每日体温范围增加。视交叉上核中精氨酸加压素免疫反应性神经元的数量与个体昼夜节律呈正相关，并在冬眠后的一段时间内逐渐增加。此外，暴露于明暗周期后昼夜节律增强而非受到抑制，但单次1小时的光脉冲（1700勒克斯）照射后则不然。这些结果支持这样一种观点，即欧洲地松鼠的昼夜节律系统在低温冬眠期间功能受到抑制，需要几天的正常体温状态才能恢复其夏季功能。
