Intracranial self-stimulation motivates treadmill running in rats

Most animal running models have traditionally used aversive motivators to induce exercise tasks. This study demonstrates treadmill running motivated by reinforcement of intracranial self-stimulation (ICSS), providing an alternative model with which to study physiological responses to exercise. Twenty-nine male Sprague-Dawley rats were stereotaxically implanted with bipolar electrodes aimed at the ventral tegmental area of the brain. After 7 days of operant lever-press training for ICSS, rats that pressed at least 50 presses/min were randomly divided into three conditions: exercise-reinforcing brain stimulation (Ex-St), exercise-aversive shock (Ex-Sh), and sedentary controls (C). Ex-St and Ex-Sh ran for 30 min at 25 m/min at 5% grade for 2 wk with ICSS and electric shock as the motivator, respectively, while C did not run. At the end of 2 wk, Ex-St and Ex-Sh performed an endurance run. Results show that Ex-St ran longer than Ex-Sh [63 +/- 10 vs. 42 +/- 10 (SD) min; P less than 0.05]. HR was higher in Ex-St than in C (P less than 0.05). Rectal temperature increased similarly in both exercise groups. This model provides a highly effective method to motivate treadmill running in rats and as such can be used to characterize physiological responses to exercise without the potentially confounding influence of stress associated with an aversive shock motivator.