The effect of histamine H3 receptor blokage on exercise-induced nociceptive response

In this study we investigated the effect of Thioperamide, a histamin H3 receptor bloker, on nociceptive response following exercise in sedentary and exercise trained rats. Sixteen male Wistar rats were equally assigned to one of two groups: sedentary control (C) and exercise-trained (T) groups. Thioperamide (Thio) was used at a dosage of 15 mg/kg, intraperitoneally (I.P.) Hot plate test was used to induce nociceptive stimulus, paw withdrawal latency was assessed, and paw latencies were repeated at rest, and following acute exercise. Exercise trained groups were subjected to eight weeks of motor-driven treadmill exercise. At the end of the experimental period, all rats were run on a motor-driven treadmill to measure exhaustion time, and paw withdrawal (hot plate) latencies were measured before, and following Thio injection. Beta endorphin (BE) concentrations from plasma, CSF (cerebrospinal fluid) and microdialysate samples collected at 30-min intervals for two hours from anterior cingulate cortex (ACC) of all rats were measured. Results were given as mean + SD, and t test was used to analyze the differences in hot plate latency, plasma and CSF BE levels between groups, and two way analysis of variance was used to analyze the differences in ACC BE levels in different time points and several administrations between groups. A level of p<0.05 was used to determine the statistical significance. Animals in T goup had significantly higher exhaustion time compared with C group, and Thio resulted a decrease in exhaustion time in T group. Hot plate latencies in C group were found to be prolonged following acute exercise, and although Thio resulted unaltered latency values, decreased latency values were found compared with the post-exercise latencies in C group. There were no significant differences in plasma, or CSF BE levels between groups. Increased BE levels from ACC were found following thermal stimulus, and Thio resulted a decrease in ACC BE levels in C group. Higher ACC BE levels were found following thermal stimulus compared with C group, but Thio is found to be uneffective on ACC BE levels in T group. The results of the present study demonstrated that Thioperamide, a histamin H3 receptor bloker, with a dose of 15 mg/kg resulted to decrease exercise-induced hypoalgesia and thermal stimulus-induced BE increase in ACC in sedentary rats.