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Hyperalgesia in an immobilized rat hindlimb: Effect of treadmill exercise using non-immobilized limbs


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Title: Hyperalgesia in an immobilized rat hindlimb: Effect of treadmill exercise using non-immobilized limbs
Authors: Chuganji, Sayaka / Nakano, Jiro / Sekino, Yuki / Hamaue, Yohei / Sakamoto, Junya / Okita, Minoru
Issue Date: 1-Jan-2015
Publisher: Elsevier Ireland Ltd
Citation: Neuroscience Letters, 584, pp.66-70; 2015
Abstract: Cast immobilization of limbs causes hyperalgesia, which is a decline of the threshold of mechanical and thermal mechanical stimuli. The immobilization-induced hyperalgesia (IIH) can disturb rehabilitation and activities of daily living in patients with orthopedic disorders. However, it is unclear what therapeutic and preventive approaches can be used to alleviate IIH. Exercise that activates the descending pain modulatory system may be effective for IIH. The purpose of this study was to investigate the effects of treadmill exercise during the immobilization period, using the non-immobilized limbs, on IIH. Thirty-six 8-week-old Wistar rats were randomly divided into (1) control, (2) immobilization (Im), and (3) immobilization and treadmill exercise (Im. +. Ex) groups. In the Im and Im. +. Ex groups, the right ankle joints of each rat were immobilized in full plantar flexion with a plaster cast for an 8-week period. In the Im. +. Ex group, treadmill exercise (15. m/min, 30. min/day, 5 days/week) was administered during the immobilization period while the right hindlimb was kept immobilized. Mechanical hyperalgesia was measured using von Frey filaments every week. To investigate possible activation of the descending pain modulatory system, beta-endorphin expression levels in hypothalamus and midbrain periaqueductal gray were analyzed. Although IIH clearly occurred in the Im group, the hyperalgesia was partially but significantly reduced in the Im. +. Ex group. Beta-endorphin, which is one of the endogenous opioids, was selectively increased in the hypothalamus and midbrain periaqueductal gray of the Im. +. Ex group. Our data suggest that treadmill running using the non-immobilized limbs reduces the amount of hyperalgesia induced in the immobilized limb even if it is not freed. This ameliorating effect might be due to the descending pain modulatory system being activated by upregulation of beta-endorphin in the brain.
Keywords: Beta-endorphin / Hyperalgesia / Hypothalamus / Immobilization / Midbrain periaqueductal gray / Treadmill exercise
URI: http://hdl.handle.net/10069/34948
ISSN: 03043940
DOI: 10.1016/j.neulet.2014.09.054
Rights: © 2014 Elsevier Ireland Ltd. / NOTICE: this is the author’s version of a work that was accepted for publication in Neuroscience Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Neuroscience Letters, 584, (2015)
Type: Journal Article
Text Version: author
Appears in Collections:Articles in academic journal

Citable URI : http://hdl.handle.net/10069/34948

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