Long-term neuroadaptive and epigenetic changes that develop following chronic drug exposure are believed to underlie persistent behavioral changes that characterize addiction. Thus, one strategy for treating addiction is to focus on interventions that can reverse these changes, which would theoretically reverse the addiction process back to a level where the individual is no longer compulsively seeking drugs. We recently demonstrated that exercise during abstinence is one type of intervention that is able to reverse/block drug- induced neuroadaptations associated with relapse vulnerability. The goal of this R01 proposal is to determine the mechanism for the efficacy of exercise as an intervention for cocaine addiction focusing on epigenetic regulation of brain-derived neurotrophic factor (BDNF) in the prefrontal cortex (PFC). BDNF is one of the few markers that positively associates with relapse vulnerability in both humans and animal models. Evidence indicates that increasing BDNF during early cocaine abstinence, when levels are low, prevents its subsequent increase as well as the increase in relapse vulnerability. Exercise is known to both increase BDNF and to attenuate cocaine-seeking, with evidence to suggest that it exerts these effects through epigenetic regulation of Bdnf exon IV. Notably, we showed that wheel running, an animal model of exercise, beginning during early abstinence dose-dependently reduced subsequent cocaine-seeking and Bdnf exon IV expression in the PFC. Our recent data also show time-dependent effects of exercise where during early abstinence, but not during later abstinence, it effectively reduced subsequent cocaine-seeking. Therefore, we hypothesize that exercise, through epigenetic regulation, blocks cocaine-induced decreases in BDNF that are observed during early abstinence, thus preventing compensatory neuroadaptations that lead to enhanced cocaine-seeking. Based our recent findings showing that the efficacy of exercise at reducing cocaine-seeking differs between males and females and in females at different hormonal states, we further hypothesize that sex and hormone-specific differences in the effects of exercise on BDNF signaling and remodeling underlie its efficacy. These hypotheses will be tested using an animal model of cocaine relapse wherein following chronic cocaine self-administration, cocaine-seeking increases, or incubates, over protracted abstinence. To accomplish our goals, in Aim 1 we will first determine the markers of BDNF signaling and remodeling that are associated with the incubation effect in males and in females at different hormonal states, and then in Aim 2 we will determine the effects of exercise on these changes. Finally, in order to establish a causal mechanism for the efficacy of exercise, in Aim 3 we will assess the effects of site-specific manipulation of PFC BDNF alone and in combination with exercise. This is an understudied area of research and the results will greatly contribute to our understanding of not only exercise as a sex-specific intervention for cocaine addiction, but also how sex and ovarian hormones influence the process of addiction and recovery.
One strategy for treating addiction is to focus on interventions that can reverse drug-induced changes in the brain, which would theoretically reverse the addiction process back to a level where the individual is no longer compulsively seeking drugs. We have demonstrated that exercise during abstinence is one type of intervention that is able to reverse/block drug-induced changes in the brain. Now, in this R01 proposal, we will determine the mechanism for its efficacy in both males and females focusing on epigenetic regulation of brain-derived neurotrophic factor in the prefrontal cortex. Such information will help guide the development of exercise-based interventions alone or as an adjunct to other strategies for treating cocaine addiction in men and women.
