Chronic pain is a major health problem that afflicts one third of Americans. New research that can aid the development of new pain-relieving strategies is urgently needed. Our proposal focuses on identifying and validating a new central analgesic circuit. This project is based on a highly innovative hypothesis that the strong analgesic effect of general anesthesia (GA) is in part carried out by GA-mediated activation of the endogenous analgesic circuits. In preliminary studies, we discovered that a subset of GABAergic neurons located in the central amygdala (CeA) become strongly activated and express high level of the immediate early gene Fos under GA (hereafter referred to as CeAGA neurons). Excitingly, using our recently developed activity-dependent tagging system called CANE (Capturing Activated Neuronal Ensemble), we were able to capture CeAGA neurons and discovered that activating these neurons exerted profound pain-suppressing effects in an acute pain model and a chronic orofacial neuropathic pain model. Based on these exciting preliminary results, we propose to identify and validate CeAGA neurons? analgesic functions in multiple mouse pain models conducted in different labs (Wang and Ji, co-PI).
In aim 1, we will systematically activate and silencing CeAGA analgesic neurons and test the consequences of such bi- directional manipulations on regulating the sensory-discriminative and emotional-affective aspects of pain processing in nave mice and in several mouse models of acute and chronic pain models with cross validation between the two labs.
In aim 2, using the state-of-the-art in vivo imaging technology, we will test the hypothesis that the spontaneous activities of CeAGA analgesic neurons are severely reduced in various chronic pain models compared to nave conditions, leading to pain hypersensitivity in these models (due to the suppression of this endogenous analgesic circuit); and complimentary, we will use slice electrophysiology to examine changes in intrinsic and evoked properties of CeAGA analgesic neurons in normal and chronic pain conditions which may explain the altered in vivo activities.
In aim 3, based on preliminary results showing extensive axonal projections of CeAGA to many brain areas, we will identify the critical subsets of CeAGA projection pathway(s) for their analgesic effect in different chronic pain models. We expect to identify shared common pathways that need to suppressed by specific subtypes of CeAGA analgesic neurons in all models, and such information will be critical for developing precise CeAGA-based therapies. In summary, this research is expected to identify and validate a novel central analgesic circuit whose power can be harnessed to treat chronic pain.
Currently there is a complete lack of effective treatments for many chronic pain conditions. Our proposed research will precisely identify and validate a potent central analgesic/pain-suppressing circuit based on a highly innovative hypothesis and state-of-the-art viral genetic and system neuroscience technologies. Our research will not only provide much needed new insights into the brain's endogenous analgesic neural circuits but also lay down new ground for developing new drugs to treat chronic pain.
