Colitis pain is clinically significant and not well understood. We hypothesize that an important mechanism in colitis pain is a novel signaling cascade in the amygdala. The amygdala, a key player in emotions and affective disorders, is emerging as an important pain center. We previously identified the latero-capsular division of the central nucleus of the amygdala (CeLC) as particularly important for pain processing and pain modulation in arthritis pain, but its role in visceral pain remains to be determined. The proposed three-step signaling cascade includes the activation of the MAP kinase ERK by group I metabotropic glutamate receptors (mGluRs) through reactive oxygen species (ROS). Our novel construct is that endogenous or exogenous activation of the mGluR->ROS->ERK signaling cascade in the amygdala contributes to visceral pain behavior and central sensitization in the spinal cord through descending pain control systems. To test this hypothesis we combine behavioral analyses, electrophysiology, pharmacology, neurochemistry and molecular biology. We use zymosan-induced colitis as a visceral pain model to determine the role of the mGluR-?ROS-?ERK signaling cascade in the amygdala (CeLC).
The Specific Aims assess the following endpoints. 1) Visceral pain-related sensitization of CeLC neurons, using extracellular single-unit recordings in anesthetized rats before and after intracolonic zymosan or saline injection. 2) Synaptic plasticity and neural excitability of CeLC neurons, using whole-cell patch-clamp in brain slices from rats with colitis and control rats. 3) Neurochemical changes in the CeLC, using immunocytochemistry and immunoblotting of group I mGluR and ERK expression, fluorescence imaging of mitochondrial ROS, and protein oxidation measurements in tissue samples from rats with colitis and control rats. 4) Visceral pain-related behavior, including audible and ultrasonic vocalizations and visceromotor reflexes in awake rats before and after intracolonic zymosan or saline injection. 5) Central sensitization of spinal dorsal horn neurons projecting to the CeLC, using extracellular single-unit recordings before and after intracolonic zymosan or saline injection. Group I mGluR agonists and antagonists, ROS donors and scavengers, and ERK inhibitors will be administered into the CeLC by microdialysis (Specific Aims 1, 4 and 5), superfused onto brain slices (Specific Aims 2 and 3), or administered intracellularly through the patch pipette (Specific Aim 2). These studies will determine the role of the novel mGluR->ROS-?ERK signaling cascade in the amygdala in visceral pain plasticity. This may be an important modulator of visceral pain via the amygdala. Thus, the amygdala modulates different levels of the central nervous system and contributes to the statedependent exacerbation and remission of visceral pain. This translational research will provide novel therapeutic targets for the management of visceral pain.
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