Lateralized kappa opioid receptor signaling from the amygdala central nucleus promotes stress-induced functional pain

The response of diffuse noxious inhibitory controls (DNIC) is often decreased, or lost, in stress-related functional pain syndromes. Because the dynorphin/kappa opioid receptor (KOR) pathway is activated by stress, we determined its role in DNIC using a model of stress-induced functional pain. Male, Sprague-Dawley rats were primed for 7 days with systemic morphine resulting in opioid-induced hyperalgesia. Fourteen days after priming, when hyperalgesia was resolved, rats were exposed to environmental stress and DNIC was evaluated by measuring hind paw response threshold to noxious pressure (test stimulus) after capsaicin injection in the forepaw (conditioning stimulus). Morphine priming without stress did not alter DNIC. However, stress produced a loss of DNIC in morphine-primed rats in both hind paws that was abolished by systemic administration of the KOR antagonist, nor-binaltorphimine (nor-BNI). Microinjection of nor-BNI into the right, but not left, central nucleus of the amygdala (CeA) prevented the loss of DNIC in morphine-primed rats. Diffuse noxious inhibitory controls were not modulated by bilateral nor-BNI in the rostral ventromedial medulla. Stress increased dynorphin content in both the left and right CeA of primed rats, reaching significance only in the right CeA; no change was observed in the rostral ventromedial medulla or hypothalamus. Although morphine priming alone is not sufficient to influence DNIC, it establishes a state of latent sensitization that ampli...
Source: Pain - Category: Anesthesiology Tags: Research Paper Source Type: research

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American Journal of Roentgenology, Ahead of Print.
Source: American Journal of Roentgenology - Category: Radiology Authors: Source Type: research
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Source: International Journal of Surgery Case Reports - Category: Surgery Source Type: research
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Source: International Journal of Surgery Case Reports - Category: Surgery Source Type: research
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Source: International Journal of Surgery Case Reports - Category: Surgery Source Type: research
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Source: Hand Clinics - Category: Orthopaedics Authors: Tags: Preface Source Type: research
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Source: Gastroenterology Research and Practice - Category: Gastroenterology Tags: Gastroenterol Res Pract Source Type: research
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Source: Brain, Behavior, and Immunity - Category: Neurology Source Type: research
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Source: Internal Medicine - Category: Internal Medicine Tags: Intern Med Source Type: research
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Source: Internal Medicine - Category: Internal Medicine Tags: Intern Med Source Type: research
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