A large body of research indicates that steeply discounting the value of delayed outcomes is robustly correlated with addictive disorders, but at present we do not know if discounting plays a causal role in drug taking. If steeply devaluing the future is causal, then investing in therapies designed to decrease delay discounting could prevent the initiation, or aid in the treatment of substance-use disorders. If no causal relation exists, investments in other therapeutic approaches would be indicated. To evaluate this causation hypothesis requires, first, a nonhuman procedure to capture the intertemporal and inter-commodity dynamics of the human drug-choice milieu; specifically, choosing between immediate drug use and delayed non-drug rewards. This allomorphic choice procedure has been successfully employed in only one study, only with oxycodone, and only with male rats.
Specific Aim 1 will expand this procedure to cocaine self-administration and to male and female rats. Evaluating causation requires, second, a method of producing large and long-lasting reductions in impulsive choice. Building on past successes in male rats, Specific Aim 2 will evaluate the efficacy of this therapeutic method in female rats. Accomplishing these aims would pave the way for a follow-up R01-funded project designed to experimentally reduce delay discounting in males and female rats and then evaluating the effects of this reduction on allomorphic choice between immediate cocaine and delayed non-drug rewards. If rats trained to better tolerate delayed rewards self-administer less cocaine than control rats when non-drug rewards are increasingly delayed, then this would provide strong evidence for delay discounting as causal in the choice to consume a drug of abuse. Answering this question is important to the long-term mission of the National Institute on Drug Abuse as it will inform future translational research efforts to reduce substance use and dependence.
Considerable empirical evidence has revealed that individuals diagnosed with a substance-use-disorder more steeply devalue delayed events than matched non-drug-users. The proposed research will experimentally reduce this form of impulsivity in female rats (as our lab has done with males in past experiments) and expand an allomorphic choice procedure designed to model the intertemporal and inter-commodity dynamics of the human drug-taking milieu. Consistent with the public-health goals of the National Institute on Drug Abuse, accomplishing these aims will make possible important follow-up research investigating the causal role (if any) of delay discounting on problematic substance use.
