Functional Characterization of Parabrachial Circuits Processing Noxious Thermal Pain

 描述(申请人提供)：疼痛是一种主观体验，由大脑多个区域对伤害性刺激的神经反应而产生，具有辨别性和情感两个组成部分。疼痛通过触发反射(如戒断)来减少对有害刺激的暴露，从而在维持身体动态平衡方面发挥着至关重要的保护作用。然而，疼痛处理可能会变得异常，导致慢性病理情况。病理性慢性疼痛不仅是一种身体上的折磨，也是一种情绪消耗，而且对目前可用的治疗方法来说是难以接受的。因此，了解处理对疼痛刺激的情绪、情感和自主反应的神经通路对于形成理解和治疗病理性慢性疼痛的新基础至关重要。众所周知，情绪和情感痛通路涉及位于脑干的臂旁核，臂旁核可分为外侧臂旁核(PB-L)和内侧臂旁核(PB-m)。有害信息通过PB传递到边缘系统，产生情绪性和自主性反应。然而，由于缺乏分子工具，还不可能研究由特定疼痛刺激激活的不同PB神经元的精确连接和功能。在这个方案中，我使用了我们实验室最近开发的一项高度创新的新技术，专门研究了参与处理小鼠伤害性热痛(口面部疼痛)的PB神经回路。我要检验的假设是：热伤害性感受性PB-L和PB-m神经元集成嵌入不同的亚回路，在调节情感热(口面部)痛知觉方面具有不同的性质和不同的功能。具体地说，利用这项新技术，我将在由辣椒素激活的PB神经元中表达荧光蛋白或光遗传工具，辣椒素是有毒热刺激的替代品。我将确定轴突投射靶点和热伤害性PB-L和PB-m神经元的某些输入。我将用切片电生理学方法检测辣椒素激活的PB神经元的神经化学和电生理特性以及突触连接。最后，我将使用光遗传激活和抑制来确定辣椒素激活的PB神经元在使用操作性口面部疼痛行为感受伤害性热痛中的功能。这些研究有望填补PB神经通路的知识空白，并为处理对痛苦刺激的情绪、情感和自主反应的电路机制提供新的见解。

 DESCRIPTION (provided by applicant): Pain is a subjective experience that arises from neural responses to noxious stimuli in multiple brain regions and has both discriminative and emotional components. Pain plays a crucial, protective role in preserving bodily homeostasis by triggering a reflex, such as withdrawal, to reduce exposure to harmful stimuli. However, pain processing can become abnormal, resulting in chronic pathological conditions. Pathological chronic pain is not only a physical ordeal, but also an emotional drain, and is refractory to currently available treatments. Thus, understanding the neural pathways that process the emotional, affective, and autonomous responses to painful stimuli is essential in forming the new foundations for understanding and treating pathological chronic pains. It is known that the emotional and affective pain pathway involves the parabrachial nucleus (PB) located in the brainstem, which is subdivided into two major divisions: lateral PB (PB-l) and medial PB (PB- m). Noxious information is relayed through PB to the limbic system to generate affective and autonomous responses. However, due to the lack of molecular tools, it had not been possible to study the precise connectivity and functions of different PB neurons activated by selected painful stimuli. In this proposal, I am using a highly innovative novel technology recently developed in our lab to investigate specifically the PB neural circuits involved in processing noxious thermal (orofacial-) pain in mouse. The hypothesis that I am going to test is: thermal nociceptive PB-l and PB-m neuronal ensembles are embedded in different sub-circuits, have different properties and different functions in regulating affective thermal (orofacial) pain perception. Specifically, using the novel technique, I will express fluorescent proteins or optogenetic tools in PB neurons activated by capsaicin, a surrogate for noxious heat stimulus. I will identify the axonal projection targets and certain inputs of thermal nociceptive PB-l and PB-m neurons. I will examine the neurochemical and electrophysiological properties as well as synaptic connectivity of capsaicin- activated PB neurons with slice electrophysiology. Finally, I will use optogenetic activation and inhibition to determine the functions of capsaicin-activated PB neurons in noxious heat pain perception using an operant orofacial pain behavior. These studies are expected to fill the knowledge gap of the PB neural pathways, and provide new insights into the circuit mechanism that process the emotional, affective, and autonomous responses to painful stimuli.