Ann Rehabil Med.  2015 Jun;39(3):331-339. 10.5535/arm.2015.39.3.331.

Effect of Exercise on micro-Opioid Receptor Expression in the Rostral Ventromedial Medulla in Neuropathic Pain Rat Model

Affiliations
  • 1Department of Physical and Rehabilitation Medicine, Research Institute of Medical Sciences, Center for Aging and Geriatrics, and Regional Cardiocerebrovascular Center, Chonnam National University Hospital, Chonnam National University Medical School, Gwang

Abstract


OBJECTIVE
To investigate the effects of aerobic exercise on neuropathic pain and verify whether regular treadmill exercise alters opioid receptor expression in the rostral ventral medulla (RVM) in a neuropathic pain rat model.
METHODS
Thirty-two male Sprague-Dawley rats were used in the study. All rats were divided into 3 groups, i.e., group A, sham group (n=10); group B, chronic constriction injury (CCI) group (n=11); and group C, CCI+exercise group (n=11). Regular treadmill exercise was performed for 30 minutes a day, 5 days a week, for 4 weeks at the speed of 8 m/min for 5 minutes, 11 m/min for 5 minutes, and 22 m/min for 20 minutes. Withdrawal threshold and withdrawal latency were measured before and after the regular exercise program. Immunohistochemistry and Western blots analyses were performed using antibodies against micro-opioid receptor (MOR).
RESULTS
Body weight of group C was the lowest among all groups. Withdrawal thresholds and withdrawal latencies were increased with time in groups B and C. There were significant differences of withdrawal thresholds between group B and group C at 1st, 2nd, 3rd, and 4th weeks after exercise. There were significant differences of withdrawal latencies between group B and group C at 3rd and 4th weeks after exercise. MOR expression of group C was significantly decreased, as compared to that of group B in the RVM and spinal cord.
CONCLUSION
In neuropathic pain, exercise induced analgesia could be mediated by desensitization of central MOR by endogenous opioids, leading to the shift of RVM circuitry balance to pain inhibition.

Keyword

Exercise; Opioid receptors; Neuralgia; Medulla oblongata

MeSH Terms

Analgesia
Analgesics, Opioid
Animals
Antibodies
Blotting, Western
Body Weight
Constriction
Exercise
Humans
Immunohistochemistry
Male
Medulla Oblongata
Models, Animal*
Neuralgia*
Rats
Rats, Sprague-Dawley
Receptors, Opioid
Spinal Cord
Analgesics, Opioid
Antibodies
Receptors, Opioid

Figure

  • Fig. 1 The changes of body weight with time. There is increase in body weight with time in all groups. Body weight of group C was the lowest in all groups. There are significant differences of body weight between no exercise-CCI group and exercised CCI group at 2nd, 3rd, and 4th weeks after the beginning of the regular exercise program. *p<0.05 compared to group B. CCI, chronic constriction injury.

  • Fig. 2 The changes of withdrawal threshold to mechanical stimuli with time. Withdrawal thresholds are increased in group C, as compared to group B at every week after the beginning of the regular exercise program. *p<0.05 compared to group B.

  • Fig. 3 The changes of withdrawal latency to noxious heat stimuli with time. Withdrawal latencies are increased in group C, as compared to group B at 3rd and 4th weeks after the beginning of the regular exercise program. *p<0.05 compared to group B.

  • Fig. 4 Immunohistochemistry findings in the rostral ventromedial medulla (RVM, upper panel) and spinal cord (lower panel): (A, D) group A, (B, E) group B, (C, F) group C. Abundant stained neuronal perikarya (black arrow) are seen in the RVM and spinal cord (×200).

  • Fig. 5 The expression of µ-opioid receptor (MOR) by Western blots analysis. MOR protein expression of group C is significantly lower than that of group B in rostral ventromedial medulla (A) and spinal cord (B).


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