Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA.
J Biol Rhythms. 2013 Jun;28(3):201-7. doi: 10.1177/0748730413490667.
A₁ adenosine receptor (A₁AR) activation within the central nervous system induces torpor, but in obligate hibernators such as the arctic ground squirrel (AGS; Urocitellus parryii), A₁AR stimulation induces torpor only during the hibernation season, suggesting a seasonal increase in sensitivity to A₁AR signaling. The purpose of this research was to investigate the relationship between body temperature (Tb) and sensitivity to an adenosine A1 receptor agonist in AGS. We tested the hypothesis that increased sensitivity in A₁AR signaling would lead to lower Tb in euthermic animals during the hibernation season when compared with the summer season. We further predicted that if a decrease in euthermic Tb reflects increased sensitivity to A₁AR activation, then it should likewise predict spontaneous torpor. We used subcutaneous IPTT-300 transponders to monitor Tb in AGS housed under constant ambient conditions (12:12 L:D, 18 °C) for up to 16 months. These animals displayed an obvious rhythm in euthermic Tb that cycled with a period of approximately 8 months. Synchrony in the Tb rhythm within the group was lost after several months of constant L:D conditions; however, individual rhythms in Tb continued to show clear sine wave-like waxing and waning. AGS displayed spontaneous torpor only during troughs in euthermic Tb. To assess sensitivity to A₁AR activation, AGS were administered the A₁AR agonist N(6)-cyclohexyladenosine (CHA, 0.1 mg/kg, ip), and subcutaneous Tb was monitored. AGS administered CHA during a seasonal minimum in euthermic Tb showed a greater drug-induced decrease in Tb (1.6 ± 0.3 °C) than did AGS administered CHA during a peak in euthermic Tb (0.4 ± 0.3 °C). These results provide evidence for a circannual rhythm in Tb that is associated with increased sensitivity to A₁AR signaling and correlates with the onset of torpor.
A₁ 腺苷受体 (A₁AR) 在中枢神经系统中的激活会诱导蛰伏，但在北极地松鼠 (AGS; Urocitellus parryii) 等强制性冬眠动物中，A₁AR 刺激仅在冬眠季节诱导蛰伏，这表明对 A₁AR 信号的敏感性随季节而增加。本研究的目的是研究 AGS 体温 (Tb) 与对腺苷 A1 受体激动剂敏感性之间的关系。我们假设，与夏季相比，在冬眠季节，A₁AR 信号转导敏感性增加会导致恒温动物动物的 Tb 降低。我们进一步预测，如果恒温动物 Tb 的降低反映了对 A₁AR 激活的敏感性增加，那么它也应该预测自发性蛰伏。我们使用皮下 IPTT-300 转发器监测在恒定环境条件 (12:12 L:D，18°C) 下饲养的 AGS 的 Tb，最长可达 16 个月。这些动物的恒温 Tb 显示出明显的节律，周期约为 8 个月。在恒定的 L:D 条件下几个月后，组内 Tb 节律的同步性丧失；然而，Tb 的个体节律继续显示出清晰的正弦波状盈亏。AGS 仅在恒温 Tb 的低谷时出现自发性蛰伏。为了评估对 A₁AR 激活的敏感性，AGS 给予 A₁AR 激动剂 N(6)-环已基腺苷 (CHA，0.1 mg/kg，ip)，并监测皮下 Tb。在恒温 Tb 的季节性最低点给予 CHA 的 AGS 显示出更大的药物诱导 Tb 下降 (1.6 ± 0.3°C)，而在恒温 Tb 的峰值时给予 CHA 的 AGS 则显示出较小的药物诱导 Tb 下降 (0.4 ± 0.3°C)。这些结果提供了 Tb 存在年周期节律的证据，该节律与 A₁AR 信号转导敏感性增加有关，并与蛰伏的开始相关。
