Pain, Nociception and the Amygdala

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DESCRIPTION (provided by applicant): Arthritic pain is significantly associated with negative affect, such as depression and anxiety. The amygdala plays a key role in emotionality and affective disorders. In the previous grant period we delineated the laterocapsular part of the central nucleus of the amygdala (CeA) as the "nociceptive amygdala". We showed that in a model of arthritic pain multireceptive neurons in the CeA develop nociceptive plasticity, which is mediated by and dependent on the enhanced function of glutamate receptors: nociceptive transmission is enhanced through presynaptic metabotropic glutamate receptors of the mGluR1 subtype and neuronal excitability is increased through protein kinase A (PKA)-dependent phosphorylation of postsynaptic N-methyl-D-aspartate (NMDA) receptors in the CeA. The mechanism of PKA activation, however, is unknown. The proposed studies will analyze the role of two major non-opioid neuropeptides, calcitonin gene-related peptide (CGRP) and corticotropin releasing factor (CRF), in the amygdala in our kaolin/carrageenan arthritis pain model. CGRP and CRF are present at particularly high levels in the amygdala and their G-protein-coupled receptors are directly linked to the PKA signal transduction pathway. We will use an innovative and integrative pharmacological approach that combines behavioral tests and in vivo and in vitro electrophysiology to define, at the systems and cellular levels, the role of CGRP, CRF and their receptors in nociceptive processing and pain-related plasticity in the CeA. We will measure spontaneous exploratory behavior and audible and ultrasonic vocalizations in awake rats and use extracellular single-unit recordings in anesthetized rats in vivo and whole-cell patch-clamp in rat brain slices in vitro to test the hypotheses that: 1. CGRP produces pro-nociceptive effects through CGRP1 receptors and is required for nociceptive plasticity in the CeA in arthritis pain. 2. CRF has anti-nociceptive effects through CRF1 receptors and pro-nociceptive effects through CRF2 receptors in the CeA. The pro-nociceptive, but not anti-nociceptive, actions are enhanced and required for nociceptive plasticity in the CeA in arthritis pain. Specific aims are: 1. To analyze arthritis pain-related behavioral (a), electrophysiological in vivo (b) and in vitro (c) changes of CGRP receptor agonist and antagonist effects and their signal transduction mechanisms. 2. To define pro and anti-nociceptive effects and signal transduction mechanisms of CRF1 and CRF2 receptor agonists and antagonists on pain behavior (a) and electrophysiological in vivo (b) and in vitro (c) measures of nociceptive plasticity in the arthritis model. These studies will provide important new information on the role of non-opioid neuropeptides in pain mechanisms in the amygdala, a brain area that plays a key role in affective disorders, which are significantly associated with arthritic pain. The innovative and integrative behavioral and electrophysiological in vivo and in vitro approach will also contribute valuable insight into the potential therapeutic value of central non-opioid neuropeptide receptors as novel targets for pain relief.