Although many cocaine addicts can abstain from drug use for short periods of time, relapse rates at longer periods of abstinence are remarkably high sometimes exceeding 90 percent. We have found that rats also exhibit an increased propensity for cocaine- seeking behavior in a model of prolonged abstinence. In this model, rats are trained to self-administer cocaine for 2-3 weeks, followed by short or long periods of forced abstinence when the animals are not allowed access to the self-administration chambers. At the end of each abstinence period, the level of cocaine-seeking behavior is measured by non-reinforced drug- paired lever responding during extinction and cue-induced reinstatement testing. Using this model, rats exhibit time- dependent increases in cocaine-seeking behavior from 1 day to 6 weeks of forced abstinence. This """"""""Cocaine Abstinence Effect"""""""" represents the phenomenon of incentive sensitization, whereby drug-associated memories gain motivational salience as abstinence proceeds. The proposed studies will utilize newly developed oligonucleotide microarrays to identify changes in gene expression in limbic brain regions that coincide with tune-dependent increase in cocaine-seeking behavior. Importantly, the behavioral model is designed to target changes in gene expression that are directly related to increased drug craving during prolonged abstinence, and not the multitude of changes that are produced by cocaine exposure and short-term withdrawal. The advent of microarray technology will allow for more than 7000 gene products to be measured simultaneously, a substantial improvement over previous expression profiling techniques. Changes in gene expression will be verified by real-time PCR and/or at the protein level by western blot. Secondary analysis of the most promising gene candidates will attempt to identify subpopulations of neurons within each broad region where expression changes occur by in situ hybridization and/or single cell PCR/microarray strategies. This forward genetic strategy is aimed at identifying novel and specific craving-related cellular changes in limbic brain regions that subsequently will determine reverse genetic or pharmalogical strategies to study their functional role in regulating drug- seeking behavior. Another major aim of these studies is to test the effects of early and late """"""""extinction training"""""""" on both the development and expression of molecular changes associated with prolonged abstinence.
This aim i s based on our recent studies showing that extinction training during abstinence reverses or normalizes many neuroadaptations associated with cocaine withdrawal, in addition to attenuating the ability of contextual cocaine-related stimuli to elicit drug-seeking. These studies will further our understanding of the complex interaction between drug craving and environmental context, and may suggest novel behavioral approaches to treatment.
