ENDOTHERMY AND BEHAVIORAL THERMOREGULATION IN INFANTS

哺乳动物幼崽在热、流体和心血管稳态方面投入了大量资源。PI实验室最近的工作表明，长期以来被认为温度调节能力差的幼鼠，因为它们在寒冷环境下的热量损失率很高，在适当的条件下进行测试时，实际上表现出许多成功调节体温的迹象。它们的成功取决于利用棕色脂肪组织（BAT）在体内产生热量的能力，以及将这种热量输送到心脏和其他温度敏感的器官的能力。我们已经了解到，具有吸热能力的婴儿（如大鼠）与不具有吸热能力的婴儿（如仓鼠）相比，对寒冷表现出明显不同的行为和生理反应。然而，我们仍然不了解这两个物种的婴儿是如何向温暖方向和移动的，以及内部产生热量的能力是否会干扰体温调节行为的表达。因此，这一建议代表了研究计划的下一步，即解决生物行为研究的基本问题，旨在更好地理解婴儿调节其内部热环境和选择其外部热环境的无数生理和行为机制。这项工作对早产儿和足月婴儿的热管理具有重要意义，无论是生病还是健康，他们的内源性产热能力不同，我们对他们的体温调节行为知之甚少。首先，随着我们对个体幼鼠体温调节能力的新认识，我们研究了蜷缩在一起的幼鼠在寒冷暴露时的行为和生理反应。在神经节阻断后的幼鼠、神经节阻断幼鼠的BAT产热选择性激活后，以及由幼鼠和仓鼠组成的混合团中，研究了群体调节行为。这些实验将揭示恒温动物如何促进群集行为的表达和有效性。其次，使用一种新开发的新型仪器来检查孤立个体的体温调节行为-一种由珀尔帖二极管组成的多瓦“棋盘”仪器-可以对热环境进行精细控制。此外，红外热像仪的使用提供了基本的热数据，而不干扰行为表达。这些方法的结合使我们处于一个理想的位置，以批判性地研究幼鼠和仓鼠在寒冷暴露时的行为唤醒、运动、定向和热偏好，以及恒温对这些行为过程的贡献。最后，后续的实验将探讨介导对寒冷行为反应的感觉和神经机制。

Infant mammals devote considerable resources to thermal, fluid, and cardiovascular homeostasis. Recent work in the PI's laboratory has shown that infant rats, long considered poor thermoregulators because of their high rates of heat loss during cold exposure, actually exhibit many signs of successful thermoregulation when tested under appropriate conditions. Their success depends on the ability to produce heat internally using brown adipose tissue (BAT), as well as the delivery of this heat to the heart and other temperature-sensitive organs. We have learned that infants that possess endothermic capabilities (i.e., rats) exhibit significantly different behavioral and physiological responses to cold than infants that do not (i.e., hamsters). We still do not understand, however, how infants of either species orient and locomote toward warmth and whether the ability to produce heat internally interferes with the expression of thermoregulatory behavior. Therefore, this proposal represents the logical next step in a research program that addresses basic issues in biobehavioral research and aims to develop a better understanding of the myriad physiological and behavioral mechanisms by which infants regulate their internal thermal environment and select their external thermal environment. This work has important implications for the thermal management of preterm and full-term human infants, sick or healthy, who differ in their abilities to produce heat endogenously and about whose thermoregulatory behavior we know very little. First, with our new appreciation of the thermoregulatory capabilities of individual infant rats, the behavioral and physiological responses of huddling rat pups during cold exposure are examined. Group regulatory behavior is examined in infant rats after ganglionic blockade, after selective activation of BAT thermogenesis in ganglionically blocked pups, and in mixed huddles comprised of infant rats and hamsters. These experiments will reveal how endothermy contributes to the expression and effectiveness of huddling behavior. Second, thermoregulatory behaviors in isolated individuals are examined using a newly- developed, novel apparatus - a multi-tiled "checkerboard" apparatus composed of peltier diodes - that provides fine control over the thermal environment. In addition, the use of infrared thermography provides essential thermal data without interfering with behavioral expression. The combination of these approaches places us in an ideal position to critically examine behavioral arousal, locomotion, orientation, and thermal preference in infant rats and hamsters during cold exposure, as well as the contributions of endothermy to each of these behavioral processes. Finally, subsequent experiments will address the sensory and neural mechanisms that mediate behavioral responses to cold.