The relationship between physical activity and cocaine intake in mice Anthony Ferreira, Fernando Perez-Diaz, Charles Cohen-Salmon Journal of Clinical Sport Psychology, 2009 Human studies suggest the existence of an exercise dependency syndrome and a link between drug intake and intense physical activity. Our aim was to assess whether a link actually existed between running activity and cocaine intake in mice. Thirty male Swiss mice were used. Ten mice were used as controls, individually housed in cages without a wheel, and 20 mice were in cages with free access to a running wheel. Cocaine preference was estimated as the ratio (as percent) of cocaine solution intake over total fuid intake in the course of free oral access to cocaine solution versus water. High cocaine scores were only found with high wheel activity. The lowest activity scores were found with low cocaine preference. A group of “high runners” impervious to cocaine appetence and to the effects of exercise withdrawal were found, which may suggest that shared mechanisms could be involved in both dependence on sport and drug taking. Findings suggest that moderate activity seems to be associated with low cocaine preference, and cocaine intake could increase in cases of intense activity. The urge for physical activity (as seen with top-level professional athletes) may theoretically combine with different degrees of vulnerability to cocaine. The use of substances by those engaging in intense physical activity, for performance enhancement or recreational purposes, could potentially trigger a pattern of consumption and addiction. This pattern corresponds with the theory that there may be an addictive element in physical activity. Animal models could prove useful for identifying biological or behavioral predictors of such vulnerability and identifying persons either at risk or possessing resistance.
Exercise dependence and morphine addiction: Evidence from animal models Anthony Ferreira, Fabien Cornilleau, Fernando Perez-Diaz, Charles Cohen-Salmon Journal of Clinical Sport Psychology, 2008 This study used animal models to examine potential similarities between dependence on physical activity (i.e., exercise) and dependence on morphine. Using C57BL/6 mice, the study also tested the hypothesis that physical exercise (e.g., long-term wheel running) may enhance vulnerability to the development of morphine dependence. The existence of an endorphin-related dependence induced by physical activity was also assessed. Naloxone was used to precipitate morphine withdrawal in mice accustomed to morphine. Specifically, the study sought to assess the intensity of addiction provoked by injection of morphine in mice that engaged in wheel-running activity as opposed to inactive mice. After 25 days of free access to activity wheel, mice that engaged in wheel-running demonstrated increased vulnerability to naloxone-induced withdrawal symptoms, which may be linked to activation of peripheral, as opposed to central, opioid receptors. These results indicate a behavioral interaction in which engaging in wheel running appears to potentiate the effects of morphine addiction. Implications of these findings for understanding human behavior and exercise addiction are also discussed.
Spontaneous appetence for wheel-running: a model of dependency on physical activity in rat Anthony Ferreira, Stéphanie Lamarque, Patrice Boyer, Fernando Perez-Diaz, Roland Jouvent, Charles Cohen-Salmon European Psychiatry, 2006 According to human observations of a syndrome of physical activity dependence and its consequences, we tried to examine if running activity in a free activity paradigm, where rats had a free access to activity wheel, may present a valuable animal model for physical activity dependence and most generally to behavioral dependence. The pertinence of reactivity to novelty, a well-known pharmacological dependence predictor was also tested. Given the close linkage observed in human between physical activity and drugs use and abuse, the influence of free activity in activity wheels on reactivity to amphetamine injection and reactivity to novelty were also assessed. It appeared that (1) free access to wheel may be used as a valuable model for physical activity addiction, (2) two populations differing in activity amount also differed in dependence to wheel-running. (3) Reactivity to novelty did not appeared as a predictive factor for physical activity dependence (4) activity modified novelty reactivity and (5) subjects who exhibited a high appetence to wheel-running, presented a strong reactivity to amphetamine. These results propose a model of dependency on physical activity without any pharmacological intervention, and demonstrate the existence of individual differences in the development of this addiction. In addition, these data highlight the development of a likely vulnerability to pharmacological addiction after intense and sustained physical activity, as also described in man. This model could therefore prove pertinent for studying behavioral dependencies and the underlying neurobiological mechanisms. These results may influence the way psychiatrists view behavioral dependencies and phenomena such as doping in sport or addiction to sport itself.
