Pain, Nociception and the Amygdala

描述（由申请人提供）：疼痛的多维特征提出了一个治疗挑战，需要更好地理解调节其复杂情绪-情感和认知方面的高级大脑功能（NIH PA-10-006）。这个项目将继续为这些更高级的大脑机制提供有价值的见解。杏仁核是大脑的情绪中枢，它的神经可塑性现在被认为是疼痛的情绪-情感维度的关键因素。疼痛中的杏仁核功能障碍也会通过损害内侧前额叶皮质（mPFC）功能而导致认知缺陷。因此，控制杏仁核活动是疼痛管理的理想治疗目标。在这里，我们提出了一个新的概念，即认知缺陷和皮层输出受损导致疼痛及其情绪的持续

DESCRIPTION (provided by applicant): The multidimensional character of pain presents a therapeutic challenge that calls for better understanding of higher brain functions that regulate its complex emotional-affective and cognitive aspects (NIH PA-10-006). This project will continue to provide valuable insight into these higher brain mechanisms. Neuroplasticity in the amygdala, an emotional brain center, is now recognized as a key factor in the emotional-affective dimension of pain. Amygdala dysfunction in pain also causes cognitive deficits by impairing medial prefrontal cortex (mPFC) function. For that reason, control of amygdala activity is a desirable therapeutic goal in pain management. Here we advance the novel concept that cognitive deficits and impaired cortical output result in the persistence of pain and its emotional affective component. Based on our previous studies and preliminary data we propose the novel hypothesis that the cognitive control system for negative emotions consists of mPFC-driven inhibition of excessive amygdala activity, which is impaired in pain but can be restored for pain relief. Three Specific Aims (SAs) will determine synaptic and cellular mechanisms and behavioral consequences of a vicious cycle in which abnormal deactivation of the mPFC in a rat model of arthritis pain causes failure of mPFC-driven inhibition of amygdala output. Cortical control of output neurons in the central nucleus of the amygdala (CeA) requires activation of inhibitory neurons in the intercalated cell mass (ITC) of the amygdala. The goal is to identify pharmacological targets that can restore cortical control of amygdala dysfunction in pain. These include metabotropic glutamate receptor mGluR5 to activate mPFC neurons, cannabinoid receptor CB1 to release excessive synaptic inhibition of mPFC neurons, and novel neuropeptide S (NPS) to activate selectively ITC cells that inhibit CeA neurons (feedforward inhibition). Behavioral experiments (SA1) will test the hypothesis that restoring mPFC-amygdala control pharmacologically will decrease pain and shorten its duration. Nocifensive, emotional-affective and cognitive behaviors will be measured. Electrophysiology in vivo (SA2) will examine dysfunction of the mPFC-ITC-CeA pathway in pain, measured as mPFC and ITC deactivation and CeA hyperactivity. Pharmacological rescue strategies will be tested. SA1 and SA2 will use stereotaxic and systemic drug applications. Patch-clamp studies in brain slices (SA3) will determine pain-related changes of synaptic and cellular modulation of mPFC output by mGluR5 and CB1 and of feedforward inhibition of CeA neurons by NPS. Patch-clamp analysis will clarify the usefulness of pharmacological targets to restore normal transmission at individual synapses of the mPFC-ITC-CeA circuitry. These conceptually novel studies will identify cortico-amygdala control deficits as an important mechanism of persistent pain. They will provide novel targets to restore cognitive control functions for pain relief. The mechanistic analysis of higher brain functions and drug targets in pain will boost basic science knowledge required for evidence-based medicine and provide new and improved strategies for pain management.