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Stimulation of Peripheral Opioid Receptors during Acute Exercise Decreases Anxiety‐Like Behaviors in a Rat Model of Fibromyalgia
Author(s) -
Williams Emily R.,
Daniels Abigale B.,
Ford Caleb M.,
Horton Molly,
Stocks Silas,
Leal Anna K.
Publication year - 2018
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2018.32.1_supplement.588.2
Subject(s) - fibromyalgia , open field , anxiety , opioid , treadmill , stimulation , medicine , (+) naloxone , endocrinology , peripheral , saline , receptor , nociception , anesthesia , psychology , physical therapy , psychiatry
Patients with fibromyalgia often experience comorbid anxiety. Studies show exercise training can decrease pain in patients with fibromyalgia as well as decrease anxiety in healthy populations. Evidence suggests endorphins acting on opioid receptors contribute to exercise‐induced analgesia, but the role of these receptors on anxiety has not been determined in patients with fibromyalgia. The purpose of this study was to compare the effects of sedentary behavior and exercise training on anxiety in a rat model of fibromyalgia and to determine the contribution of peripheral opioid receptors to the exercise‐induced response. Female Sprague Dawley rats were induced with fibromyalgia by acidic saline injections (0.1 mL; pH 4). To assess anxiety‐like behaviors, rats were placed in an open field arena (90 × 90 cm) for two minutes. The arena floor was marked with 20.5 cm grids and the number of grids crossed during the observation period was recorded: a decrease in grids crossed indicated increased anxiety. A group of sedentary rats (SED; n=8) were tested for anxiety 5 days/week for 4 weeks. Another group of treadmill‐trained rats (NAL; n=5) received injections of the nonspecific opioid receptor antagonist naloxone (120 μg in 0.1 mL saline) in both gastrocnemius muscles ten minutes prior to moderate‐intensity (15 m/sec) treadmill running (4 weeks; 5 days/week; 30 min/day). NAL rats were observed in the open field arena before (PRE) and after (POST) each running bout. Mean grids crossed for SED rats in the open field were 21.3 ± 2.4 for week 1, 23.7 ± 2.9 for week 2, 29.7 ± 2.9 for week 3, and 28.0 ± 3.0 for week 4. While NAL PRE grids crossed were not different from SED grids crossed, the POST grids crossed for NAL rats decreased for all weeks: 16.5 ± 2.0 (PRE) and 10.1 ± 1.9 (POST) for week 1, 24.0 ± 1.9 (PRE) and 12.4 ± 1.4 (POST) for week 2, 21.8 ± 1.9 (PRE) and 10.4 ± 1.7 (POST) for week 3, and 23.6 ± 2.2 (PRE) and 13.2 ± 1.8 (POST) for week 4 (all p<0.05). Further, NAL POST grids crossed were significantly different from SED grids crossed for weeks 1, 2, 3 and 4 (p<0.05). While our data does not show a long‐term effect of exercise training on anxiety, it does suggest that stimulation of peripheral opioid receptors during acute exercise decreases anxiety‐like behaviors in the rat model. In conclusion, this study provides evidence that peripheral, in addition to central, opioid receptors contribute to an exercise‐induced decrease in anxiety and that even one exercise bout is beneficial when compared to sedentary behavior. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .