Non-invasive stress assessment in male and female rats using infrared thermography

We used Infrared thermography (IRT) to collect continuous tail and eye temperature measurements of male and female rats (Rattus norvegicus), for 30 minutes after exposure to one of three stressors (small cage, encircling handling or rodent restraint cone) for one minute, and cross-validated the thermal response with plasma corticosterone (CORT) and behavioural assessment. To obtain individual baseline temperatures and thermal responses to stress, rats were imaged in a test arena (to which they were habituated) for 30 seconds before and 30 minutes after being exposed to the stressor. In response to the three stressors, tail temperature initially decreased and then recovered to, or overshot the baseline temperature. Tail temperature dynamics differed between stressors; being restrained in the small cage was associated with the smallest drop in temperature, in male rats, and the fastest thermal recovery, in both sexes. Increases in eye temperature only distinguished between stressors early in the response and only in females. The post stressor increase in eye temperature was greater in the right eye of males and the left eye of females. In both sexes encircling was associated with the largest increase in CORT. These results were in line with observed behavioural changes, with greater movement in rats exposed to the small cage and higher immobility after encircling. The female tail and eye temperature, as well as the CORT concentrations did not return to pre-stressor levels in the observation period, in conjunction with the greater occurrence of escape-related behaviours in female rats.

本研究采用红外热成像（Infrared Thermography, IRT）技术，对暴露于三种应激原（小笼束缚、环绕式抓握或啮齿类束缚锥）1分钟后的雌雄褐家鼠（Rattus norvegicus）开展连续30分钟的尾部与眼部温度数据采集，并通过血浆皮质酮（CORT）检测与行为学评估对热响应结果进行交叉验证。为获取个体基础温度及应激热响应特征，研究人员在大鼠暴露于应激原前后，于其已适应驯化的测试箱中进行热成像：于应激前30秒采集30秒数据以获得基础温度，于应激后连续30分钟采集温度数据以记录热响应过程。三种应激原作用下，大鼠尾部温度均先出现下降，随后恢复至基线水平甚至超出基线温度。尾部温度的动态变化因应激原类型而异：雄性大鼠在小笼束缚应激下的温度降幅最小，而两种性别的大鼠在此应激下的热恢复速度最快。眼部温度升高仅在应激早期可区分不同应激原，且该现象仅存在于雌性大鼠中。应激后，雄性大鼠右眼的温度升高幅度更大，而雌性大鼠则表现为左眼温度升高更为显著。两种性别的大鼠在经历环绕式抓握应激后，血浆皮质酮浓度均升高最为显著。上述结果与行为学观测结果一致：暴露于小笼应激的大鼠活动量更高，而经环绕式抓握应激后的大鼠则呈现出更高的静止不动状态。在整个观测周期内，雌性大鼠的尾部、眼部温度以及血浆皮质酮浓度均未恢复至应激前水平，这与雌性大鼠更频繁出现逃逸相关行为的现象相吻合。