Effect of Aerobic Exercise on Morphine Self-administration and Pain Modulation in Rats.

BACKGROUND

Exercise reverses retention deficit induced by morphine. The present study investigated the effect of aerobic exercise on tolerance to morphine usage and pain modulation.

MATERIALS AND METHODS

Male Wistar rats were divided into four groups as follows: (1) saline group (S), (2) morphine group (M), (3) saline + exercise (S + E), and (4) morphine + exercise group (M + E). The rats were initially trained to receive small pellets of food by pressing an active lever in the self-administration apparatus. The tail-flick and hot-plate tests were used for pain assessment. To perform the experiment, the jugular vein was exposed and cannulated. After recovery, the animals were placed in the self-administration apparatus and allowed to self-administer morphine in 2 h sessions over 11 consecutive days.

RESULTS

The morphine group was found to record a higher number of active lever pressings than did the saline one while this parameter decreased in the morphine + exercise group compared with the morphine one. Moreover, the morphine + exercise exhibited lowered pain sensitivity as evidenced to have reduced morphine use in the hot plate test.

CONCLUSION

The exercise might be suggested to reduce using of morphine and modulate pain probably through the release of endogenous opioid.