Chronic aerobic exercise: Lack of effect on brain CB1 receptor levels in adult rats

Introduction: Exercise programs have been shown to be effective for both reducing risk for, and intervention following, substance abuse behaviors in both clinical and preclinical studies. Less is known, however, regarding the underlying neurobiological substrates involved in these changes in drug seeking behavior. In this study, we assessed cannabinoid receptor (CB1)levels throughout the brain which are key in endocannabinoid signaling following chronic aerobic exercise. Methods: Male and female Lewis young adult rats were grouped into exercise and sedentary groups at 8 weeks of age. Exercise rats ran on a treadmill at 10 m/min, 5 days/week, for 6 weeks, whereas sedentary rats remained in their home cage. Rats were euthanized after 6 weeks, and in vitro receptor autoradiography was performed using [³H]SR141716A to quantify CB1 receptors throughout the brain. Results: Exercise rats did not show significantly different [³H]SR141716A binding levels as compared to sedentary rats; however, an overall sex effect was found, where males had 29% higher [³H]SR141716A binding within the pyramidal layer of the hippocampus when compared to females. The chronic aerobic exercise regimen did not produce any changes in CB1 receptor levels. Conclusions: The present study found that chronic exercise during young adulthood did not alter cannabinoid CB1 receptor levels in the brain. Therefore, previously reported decreased cocaine preference in parallel treated cohorts did not involve exercise induced changes in CB1 levels which is key for endocannabinoid signaling.