Gordon Christopher J, Aydin Cenk, Repasky Elizabeth A, Kokolus Kathleen M, Dheyongera Geoffrey, Johnstone Andrew F M
Toxicity Assessment Division, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA.
University of Uludag, Faculty of Veterinary Medicine, Department of Physiology, TR-16059 Bursa, Turkey.
J Therm Biol. 2014 Aug;44:41-6. doi: 10.1016/j.jtherbio.2014.06.006. Epub 2014 Jul 2.
Laboratory mice housed under standard vivarium conditions with an ambient temperature (Ta) of ~22°C are likely to be cold stressed because this Ta is below their thermoneutral zone (TNZ). Mice raised at Tas within the TNZ adapt to the warmer temperatures, developing smaller internal organs and longer tails compared to mice raised at 22°C. Since mice prefer Tas equal to their TNZ when housed in a thermocline, we hypothesized that mice reared for long periods (e.g., months) in a thermocline would undergo significant changes in organ development and tail length as a result of their thermoregulatory behavior. Groups of three female BALB/c mice at an age of 37 days were housed together in a thermocline consisting of a 90cm long aluminum runway with a floor temperature ranging from 23 to 39°C. Two side-by-side thermoclines allowed for a total of 6 mice to be tested simultaneously. Control mice were tested in isothermal runways maintained at a Ta of 22°C. All groups were given cotton pads for bedding/nest building. Mass of heart, lung, liver, kidney, brain, and tail length were assessed after 73 days of treatment. Mice in the thermocline and control (isothermal) runways were compared to cage control mice housed 3/cage with bedding under standard vivarium conditions. Mice in the thermocline generally remained in the warm end throughout the daytime with little evidence of nest building, suggesting a state of thermal comfort. Mice in the isothermal runway built elaborate nests and huddled together in the daytime. Mice housed in the thermocline had significantly smaller livers and kidneys and an increase in tail length compared to mice in the isothermal runway as well as when compared to the cage controls. These patterns of organ growth and tail length of mice in the thermocline are akin to warm adaptation. Thus, thermoregulatory behavior altered organ development, a process we term behaviorally mediated, warm adaptation. Moreover, the data suggest that the standard vivarium conditions are likely a cold stress that alters normal organ development relative to mice allowed to select their thermal preferendum.
饲养在标准动物饲养条件下、环境温度（Ta）约为22°C的实验小鼠很可能会受到冷应激，因为这个Ta低于它们的热中性区（TNZ）。与在22°C环境中饲养的小鼠相比，在TNZ内的Ta环境中饲养的小鼠适应了较高的温度，其内脏器官较小，尾巴较长。由于小鼠在温度梯度环境中饲养时更喜欢与TNZ相等的Ta，我们推测，在温度梯度环境中长期（如数月）饲养的小鼠，由于其体温调节行为，其器官发育和尾巴长度会发生显著变化。将三组37日龄的雌性BALB/c小鼠放在一个温度梯度环境中一起饲养，该温度梯度环境由一条90厘米长的铝制跑道组成，地面温度范围为23至39°C。两个并排的温度梯度环境可同时对总共6只小鼠进行测试。对照小鼠在保持Ta为22°C的等温跑道中进行测试。所有组都提供了用于铺垫/筑巢的棉垫。在处理73天后，评估心脏、肺、肝脏、肾脏、大脑的质量以及尾巴长度。将温度梯度环境中和对照（等温）跑道中的小鼠与在标准动物饲养条件下每笼3只并带有铺垫物饲养的笼养对照小鼠进行比较。温度梯度环境中的小鼠在白天通常会一直待在温暖的一端，几乎没有筑巢的迹象，这表明它们处于热舒适状态。等温跑道中的小鼠会精心筑巢，并在白天挤在一起。与等温跑道中的小鼠以及笼养对照小鼠相比，温度梯度环境中的小鼠肝脏和肾脏明显较小，尾巴长度增加。温度梯度环境中小鼠的这些器官生长和尾巴长度模式类似于热适应。因此，体温调节行为改变了器官发育，我们将这一过程称为行为介导的热适应。此外，数据表明，相对于能够选择自己偏好温度的小鼠，标准动物饲养条件可能是一种冷应激，会改变正常的器官发育。
