ENDOTHERMY AND BEHAVIORAL THERMOREGULATION IN INFANTS

幼年哺乳动物在体温、体液和心血管动态平衡方面投入了大量的资源。PI实验室最近的工作表明，幼鼠在适当的条件下进行测试时，实际上表现出了许多成功的体温调节迹象。长期以来，幼鼠被认为温度调节能力不佳，因为它们在寒冷环境中的热量损失率很高。它们的成功取决于利用棕色脂肪组织(BAT)在内部产生热量的能力，以及将这种热量传递到心脏和其他温度敏感器官的能力。我们了解到，具有吸热能力的婴儿(即大鼠)与没有吸热能力的婴儿(即仓鼠)对寒冷的行为和生理反应明显不同。然而，我们仍然不知道这两个物种的婴儿是如何定向和移动到温暖的，以及内部产生热量的能力是否干扰了体温调节行为的表达。因此，这项建议代表了一项研究计划的合乎逻辑的下一步，该计划旨在解决生物行为研究的基本问题，并旨在更好地了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。这项工作对于早产儿和足月儿的热管理具有重要的意义，无论是疾病还是健康的早产儿，他们内源性产热的能力不同，我们对他们的体温调节行为知之甚少。首先，随着我们对单个幼年大鼠体温调节能力的新认识，我们检查了在寒冷暴露期间缩成一团的小鼠的行为和生理反应。在神经节阻断后的幼鼠中，在神经节阻断的幼鼠中选择性地激活BAT产热之后，以及在由幼鼠和仓鼠组成的混合群体中，研究了群体调节行为。这些实验将揭示内温如何影响抱团行为的表达和有效性。其次，使用一种新开发的、新颖的设备--由珀尔蒂埃二极管组成的多层棋盘式设备--来检查孤立个体的体温调节行为，该设备提供了对热环境的精细控制。此外，红外热像仪的使用提供了基本的热数据，而不会干扰行为表达。这些方法的结合使我们处于一个理想的位置来批判性地检查冷暴露期间幼鼠和仓鼠的行为唤醒、运动、定向和热偏好，以及吸热对每个行为过程的贡献。最后，后续实验将解决调节对寒冷的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.