Effect of forced treadmill exercise and blocking of opioid receptors with naloxone on memory in male rats

The forced treadmill running can influence the opioid contents of the brain, through both effects of exercise and the effects of stress caused by coercion. Since opioids can cause negative effects on brain functions, this study aimed to evaluate the effect of forced treadmill exercise and blocking of opioid receptors with naloxone on memory in male rats.

Experimental groups were the control, the exercise, the naloxone, and the naloxone exercise. The exercise program was treadmill running at 22 m/min at 0° inclination for 50 min/day, 6 days/week, for 4 weeks. Naloxone (1 mg/kg) was injected 5 min before the treadmill running. Morris water maze and passive avoidance learning tests were used for evaluation of memory. Acquisition phase of both tests was performed before interventions, and memory was evaluated 1‑day and 1‑week after the last session of exercise and treatments.

Our data showed that forced exercise impaired performance in passive avoidance learning test (P < 0.05 and P < 0.01, 1‑day, and 1‑week after the last session of exercise and treatments, respectively). Spatial memory was only impaired after 1‑week in the exercise group. Naloxone had no significant effect on memory in the control group. However, it improved memory in the exercise group, as there was no significant difference between the control and the naloxone exercise in both tests.

The data correspond to the possibility that opioidergic system may have mediatory roles in exercise‑induced responses in forced exercise. These roles are likely harmful for memory.