Trans-synaptic signaling complex in amygdala pain mechanisms

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Summary: Pain is a serious clinical problem that affects more than 100 million Americans. The economic costs of pain have been estimated to be more than several hundred billion dollars including healthcare costs and lost productivity. Persistent pain may produce long-term disability and lead to precipitation of depression, anxiety and cognitive impairment. Currently used medications for chronic pain are not always effective and have limitations in terms of tolerance and abuse liability. Thus, identifying novel therapeutic targets is essential to address this clinical burden. Peripheral and central pathways that encode, transmit, and amplify or reduce pain signals have been identified, including the spinothalamic and spinoparabrachial pathways. Plasticity of glutamatergic synapses along key nodes in the spinoparabrachial-amygdala pathway plays an important role in pain modulation and in the transition from subacute to chronic pain. However, the mechanisms governing the development, maintenance and plasticity of this system and their role in persistence of pain behaviors remain poorly understood. The proposed research will advance the concept that the trans-synaptic signaling complex centered on glutamate delta 1 receptor regulates function of synapses in the laterocapsular region of central amygdala also known as “nociceptive amygdala” and contributes to persistent pain mechanisms. Specific Aim1 will define the cell type- and projection-specific distribution of these receptors and their role in regulating amygdala circuitry and nocifensive and averse-affective behavior under normal conditions. Specific Aim 2 will determine persistent/chronic pain-related changes in glutamate delta 1 signaling using inflammatory and neuropathic pain models and test the effect of a rescue strategy on synaptic neuroplasticity in pain models. Changes in ultrastructure of amygdala synapses in pain models will be evaluated using 3D-electron microscopy. Specific Aim 3 will determine the effect of restoring trans- synaptic signaling through the glutamate delta 1 receptor in mitigating nocifensive and averse-affective behaviors in pain models. Complementary experiments will address the effect of cell-type specific manipulation of central amygdala circuitry in mitigating pain. To accomplish these aims we will utilize a combination of brain slice electrophysiology, behavior, chemo- and opto-genetics, confocal and electron microscopy (immuno and 3D), and genetic approaches to determine the functional and structural mechanisms through which the glutamate delta 1 signaling complex regulates pain-related neuroplasticity and behaviors. This project is significant because it would identify a novel brain mechanism of pain that could be targeted for pain management. Scientific rigor of research design is established by the use of multiple methods and approaches, replication of experiments in independent laboratories, use of validated models and reagents, consideration of blinding, biological variables and sex in addition to other aspects of experimental design.