A model of chronic pain in the rat: high-resolution neuroanatomical approach identifies alterations in multiple opioid systems in the periaqueductal grey |
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Authors: | MJ Millan BJ Morris FC Colpaert A Herz |
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Institution: | 1. Neurophysiology Research Center, Hamadan University of Medical Sciences, P. O. Box 65178, 38678 Hamadan, Iran;2. Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, P.O. Box 19615, 1178 Tehran, Iran;1. Department of Psychology, University of New England, Biddeford, ME 04005, United States;2. Department of Biomedical Sciences, University of New England College of Osteopathic Medicine, Biddeford, ME 04005, United States;3. Center for Excellence in the Neurosciences, University of New England, United States;4. Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, United States |
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Abstract: | Inoculation of the tail base of rats with Mycobacterium butyricum led to an arthritic swelling and inflammation of the limbs which displayed a hyperalgesia to noxious pressure: these effects peaked at 3 weeks postinoculation. In vitro autoradiography of coronal sections of rat brain was used for a parallel determination of binding to mu-, delta- and kappa-opioid binding sites. In only two regions, the dorsomedial and dorsolateral parts of the periaqueductal grey (PAG), was a significant change seen: this comprised an increase in binding to kappa-sites, whereas mu- and delta-sites therein were unaffected. This region was analysed for opioid peptides derived from each of the three opioid peptide families known. While no change was seen in levels of immunoreactive (ir)-dynorphin1-17 A (DYN) and ir-Met-enkephalin, a decrease was detected in those of ir-beta-endorphin (beta-EP): this change was restricted to the PAG. These data demonstrate a highly localized and selective influence of chronic arthritic pain upon multiple opioid systems in the PAG of the rat, a structure playing a key role in the control of pain and in the expression of the antinociceptive actions of opioids. The data suggest a possible significance of PAG pools of beta-EP and kappa-receptors in the response to and modulation of chronic pain. |
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Keywords: | β -Endorphin Dynorphin Opioid Opioid receptor Pain Arthritis Periaqueductal grey |
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