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Mark Pitcher 2015 Mitchell Max Award Recipient
2015 Mitchell Max Awardee:
Mark Pitcher, Ph.D.
Visiting Postdoctoral Fellow, National Center for Complementary and Integrative Health

Dr. Pitcher earned a B.A. in Psychology at Bishop’s University, an M.Sc. in neuroscience at McGill University with Terence Coderre and a Ph.D. with Fernando Cervero, also at McGill University. Mark is currently a Visiting Postdoctoral Fellow in M. Catherine Bushnell’s 'Pain and Integrative Neuroscience' (PAIN) laboratory at the National Center for Complementary and Integrative Health. His work at NCCIH focuses on exercise-induced analgesia as well as the development of novel rodent assays to measure the impact of persistent pain on motivational and affective behavior.


ABSTRACT:
Effect of voluntary exercise in a rat model of persistent inflammatory pain

Pitcher MH, Tarum F, Rauf IZ, Bushnell MC

Laboratory of Pain and Integrative Neuroscience, NCCIH, NIH

Aerobic exercise improves health outcomes in a variety of chronic conditions including depression, diabetes and osteoarthritis. Mechanistic studies focusing on exercise-induced analgesia in rodents also find beneficial effects of aerobic exercise. However, to better control exercise parameters, these studies commonly use forced exercise (i.e. treadmill running with electric shock reinforcement), an approach known to provoke stress responses that may interfere with exercise-induced analgesia. Here, we assessed the effectiveness of voluntary exercise in attenuating hypersensitivity, stress and peripheral inflammation in a rat model of persistent inflammation.

Male Long Evans rats (175-200g; n=12/group) were either sedentary or given access to a running wheel for three weeks (2hrs/day, 4days/wk) following intra-articular injection of Complete Freund’s Adjuvant (CFA) or sham injection. We measured ankle swelling (peripheral inflammation), weight bearing capacity of ipsilateral and contralateral hind paws (hypersensitivity), plasma corticosterone (stress) and the level of running exercise. At three weeks post-inflammation, sedentary rats continued to exhibit significant hypersensitivity, with 58.4±6.8% less weight bearing capacity compared to baseline (p<0.001), as well as significantly elevated corticosterone levels (1931±421.5pg/ml vs. 838±121.4pg/ml in sham rats; p<0.05). Rats in the voluntary exercise group ran approximately 1500-2000m/week. By week 3 post-CFA, weight-bearing deficits in the exercise group had returned to baseline levels (97.6±7.4% weight bearing capacity compared to baseline) and plasma corticosterone was comparable to sham levels (875±127.7pg/ml vs. 838±121.4pg/ml in sham rats). Nonetheless, CFA-induced ankle swelling was unchanged by exercise (120.2% of baseline ankle size in exercise group vs. 122.9% in sedentary group; p=0.61). Our findings demonstrate that voluntary exercise effectively reverses both pain and stress in a rodent model of persistent inflammatory pain, without altering peripheral inflammation.