Effect of Treadmill Running on Morphine Dependence Before and After Medial Prefrontal Cortex Lesion in Rats

Preventive effects of fixed and progressive forced exercises on memory and brain electrical activity in morphine-addicted rats

Exercise and addiction influence brain functions. The preventive effects of fixed and progressive forced exercises on both brain functions and body weight were investigated in morphine-addicted rats. Thirty-five rats were allocated to control, morphine, fixed exercise-morphine, and progressive exercise-morphine groups. Forced exercise was applied 1h/day for 21 days with morphine sulfate administered at doses of 10, 20, 30, 40, and 50 mg/kg for 5 consecutive days. The 50 mg/kg dose was repeated over the five subsequent days. Brain performance was evaluated using the passive avoidance test and EEG recordings. The passive avoidance test revealed no significant changes in brain functions (namely, latency, total dark stay time, and number of times entering the dark compartment). Compared to the control, the morphine group exhibited significantly lower alpha and beta waves but significantly higher delta and theta ones. Compared to the morphine group, the progressive and fixed exercise-morphine groups exhibited significant changes in their passive avoidance performance and only in the alpha wave of their EEG recordings. Progressive exercise improved learning, memory, and memory consolidation but reduced locomotor activity whereas fixed exercise affected EEG recordings in the addicted subjects. Clearly, different (fixed or progressive) exercise models produced different changes in brain functions.

Aerobic exercise as a promising nonpharmacological therapy for the treatment of substance use disorders

Despite the prevalence and public health impact of substance use disorders (SUDs), effective long-term treatments remain elusive. Aerobic exercise is a promising, nonpharmacological treatment currently under investigation as a strategy for preventing drug relapse. Aerobic exercise could be incorporated into the comprehensive treatment regimens for people with substance abuse disorders. Preclinical studies of SUD with animal models have shown that aerobic exercise diminishes drug-seeking behavior, which leads to relapse, in both male and female rats. Nevertheless, little is known regarding the effects of substance abuse-induced cellular and physiological adaptations believed to be responsible for drug-seeking behavior. Accordingly, the overall goal of this review is to provide a summary and an assessment of findings to date, highlighting evidence of the molecular and neurological effects of exercise on adaptations associated with SUD.

Increased sign-tracking behavior in adolescent rats

An autoshaping procedure was used to test the notion that conditioned stimuli (CSs) gain greater incentive salience during adolescence than young adulthood under conditions of social isolation rearing and food restriction. Rats were single-housed and placed on food restriction during 10 daily training sessions in which a lever (CS⁺ ) was presented then followed immediately by a food unconditioned stimulus (US). A second lever (CS^- ) was presented on intermixed trials and was not reinforced. Despite the fact that food delivery was not contingent on the rats' behavior, all rats exhibited behaviors directed towards the lever (i.e., sign-tracking). In the adolescent group, the rate of lever pressing and the percentage of trials with a lever press were higher than in young adults. Initially, group differences were observed when rats were retrained when the adolescents had reached young adulthood. These findings support the hypothesis that cues that come to predict reward become imbued with excessive motivational value in adolescents, perhaps contributing to the hyper-responsiveness to reward-related stimuli typically observed during this period of development.