The effects of regular exercise on capsaicin-induced pulpal pain and pain-induced changes in passive avoidance learning and memory in rats

Abstract

Background: Pulpal pain is one of the most common and severe orofacial pain conditions with considerable adverse effects on physiological processes including learning and memory. Regular exercise is known to be effective on cognitive function as well as pain processing in the central nervous system. Here, the possible effects of regular exercise on pulpal pain response as well as pain-induced changes in learning and memory efficiency in rats were investigated.

Methods: Twenty-four male Wistar rats were randomly assigned to the control, capsaicin, exercise, and exercise plus capsaicin groups. Rats in exercise groups were forced to run on a treadmill with a moderate exercise protocol for 4 weeks. Capsaicin was used to induce dental pulp pain. Passive avoidance learning and memory performance was assessed by using a shuttle box apparatus.

Results: According to the results, regular exercise could decrease the time course of capsaicin-induced pulpal pain (P < 0.001). Moreover, in capsaicin-treated rats, passive avoidance acquisition was impaired as compared to the control (P < 0.05) and exercise (P < 0.001) groups. Additionally, regular exercise before capsaicin injection could attenuate capsaicin-induced memory impairments (P < 0.05).

Conclusions: Taken together, the present data showed that regular exercise has inhibitory effects on capsaicin-induced pulpal pain as well as pain-induced cognitive dysfunction in rats.

Keywords: Capsaicin; Dental pulp; Pain; Passive avoidance learning; Rat; Regular exercise.

Fig. 1. The effects of regular exercise training on the time of nociceptive behavior at each time block (A) and at the total time (B). Data are presented as means ± SEM. ^***P < 0.001, ^**P < 0.01, ^*P < 0.05 versus control group. ^###P < 0.001, ^##P < 0.01, ^#P < 0.05 versus capsaicin group.

Fig. 2. Effects of capsaicin and regular exercise on the number of trials to acquisition. Data are presented as mean ± SEM. ^**P < 0.01 versus control group. ^###P < 0.001 versus exercise group. ^&P < 0.05 versus capsaicin group.

Fig. 3. Effects of capsaicin and regular exercise on (A) step-through latency (STL), and (B) the time spent in the dark chamber (TDC) in the retention test. Data are presented as mean ± SEM. ^*P < 0.05 versus control group. ^###P < 0.001, ^#P < 0.05 versus exercise group. ^&P < 0.05 versus capsaicin group.