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American Society for Action on Pain

UI - 000095

AU - Millan MJ

AU - Morris BJ

AU - Colpaert FC

AU - Herz A

TI - A model of chronic pain in the rat: high-resolution neuroanatomical approach identifies

alterations in multiple opioid systems in the periaqueductal grey

AB - 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

SO - Brain Research 1987;416:349-353