Heat or Insulation: Behavioral Titration of Mouse Preference for Warmth or Access to a Nest

In laboratories, mice are housed at 20–24°C, which is below their lower critical temperature (≈30°C). This increased thermal stress has the potential to alter scientific outcomes. Nesting material should allow for improved behavioral thermoregulation and thus alleviate this thermal stress. Nesting behavior should change with temperature and material, and the choice between nesting or thermotaxis (movement in response to temperature) should also depend on the balance of these factors, such that mice titrate nesting material against temperature. Naïve CD-1, BALB/c, and C57BL/6 mice (36 male and 36 female/strain in groups of 3) were housed in a set of 2 connected cages, each maintained at a different temperature using a water bath. One cage in each set was 20°C (Nesting cage; NC) while the other was one of 6 temperatures (Temperature cage; TC: 20, 23, 26, 29, 32, or 35°C). The NC contained one of 6 nesting provisions (0, 2, 4, 6, 8, or 10g), changed daily. Food intake and nest scores were measured in both cages. As the difference in temperature between paired cages increased, feed consumption in NC increased. Nesting provision altered differences in nest scores between the 2 paired temperatures. Nest scores in NC increased with increasing provision. In addition, temperature pairings altered the difference in nest scores with the smallest difference between locations at 26°C and 29°C. Mice transferred material from NC to TC but the likelihood of transfer decreased with increasing provision. Overall, mice of different strains and sexes prefer temperatures between 26–29°C and the shift from thermotaxis to nest building is seen between 6 and 10 g of material. Our results suggest that under normal laboratory temperatures, mice should be provided with no less than 6 grams of nesting material, but up to 10 grams may be needed to alleviate thermal distress under typical temperatures.在实验室环境中，实验小鼠通常饲养于20–24℃的环境中，该温度低于其临界低温阈值（约30℃）。此类额外的热应激可能会影响实验结果的科学性与可靠性。提供筑巢材料可帮助小鼠通过行为调节体温，进而缓解此类热应激。筑巢行为会随环境温度与筑巢材料的变化而改变，而小鼠在筑巢与趋温性（thermotaxis，即响应温度变化的位移行为）之间的选择也取决于这两类因素的平衡，即小鼠会根据环境温度调整筑巢材料的使用量。本实验使用未经过实验处理的CD-1、BALB/c及C57BL/6品系小鼠，每一品系包含36只雄性与36只雌性个体，按每组3只进行饲养。实验小鼠被安置于一对相互连通的笼盒中，每个笼盒通过水浴控温系统维持于不同温度条件。每对笼盒中的一个维持在20℃，记为筑巢笼（Nesting cage; NC）；另一个则分别设置为6种温度梯度之一（温度笼；Temperature cage; TC：20、23、26、29、32或35℃）。筑巢笼内配备6种梯度的筑巢材料供应量（0、2、4、6、8或10g），且每日更换一次。研究人员对两个笼盒中的小鼠摄食量与筑巢评分进行了测定。随着成对笼盒间的温度差增大，筑巢笼内的小鼠摄食量随之升高。筑巢材料供应量会改变两组配对温度下的筑巢评分差异；筑巢笼内的筑巢评分随材料供应量的增加而升高。此外，不同的温度配对组合也会影响筑巢评分的差异，其中当两个笼盒的温度分别为26℃与29℃时，两地的评分差异最小。小鼠会将筑巢笼内的材料搬运至温度笼中，但该搬运行为的发生概率随筑巢材料供应量的增加而降低。综合来看，不同品系与性别的小鼠均偏好26–29℃的环境温度；且当筑巢材料供应量处于6~10g区间时，小鼠会从趋温行为转向筑巢行为。本研究结果表明，在常规实验室饲养温度下，应为小鼠提供不少于6g的筑巢材料；而若要在典型实验室温度下完全缓解小鼠的热应激，则可能需要最多10g的筑巢材料。