High impulsivity is associated with vulnerability to drug dependence, drug relapse, and treatment failure in cocaine addicts. Using a novel animal model, our laboratory has demonstrated that, remarkably, exposure to a cocaine-paired environmental context alone produces a state of increased impulsivity, indicated by greater delay discounting behavior (i.e., choice of a small immediately available reward over a larger reward available with a time delay) in a cocaine-paired context than in an unpaired control context . Based on additional exciting preliminary data and the existing impulsivity literature the proposed exploratory R21 project will test the overarching hypothesis that distinct neuronal ensembles within the lateral orbitofrontal cortex (lOFC) promote, whereas in the prelimbic cortex (PrL) oppose, drug context-induced impulsive decision making (DCIDM). Furthermore, bidirectional regulation of DCIDM arises from the differential activation of excitatory projection neurons and GABAergic interneurons within these neuronal ensembles upon exposure to the cocaine-paired context.
Specific Aim 1 will be to test the hypothesis that drug context-activated neuronal ensembles in the lOFC and PrL are critical for promoting and suppressing DCIDM, respectively. Experiments will use the Daun02 pharmacogenetic method to site-selectively lesion putative cocaine context-activated neuronal ensembles within the lOFC or PrL in c-fos-lacZ transgenic rats. We will evaluate the effects of these manipulations on delay discounting behavior in the cocaine-paired or an unpaired control context. We predict that lesion of cocaine context-reactive lOFC neuronal ensembles will inhibit, whereas lesion of cocaine context-reactive PrL neuronal ensembles will potentiate DCIDM.
Specific Aim 2 will be to characterize the phenotype of drug context-activated neuronal subpopulations within the neuronal ensembles that regulate DCIDM in c-fos-lacZ transgenic rats. We will use double-label immunohistochemistry with confocal microscopy to quantify Fos/CaMKII- and Fos/GAD67-immunoreactive (IR) cell bodies spared by Daun02 in the brains of rats from Aim 1. We predict that exposure to a cocaine-paired context elicits preferential excitatory neuronal activation in th lOFC, and preferential GABA-ergic neuronal activation in the PrL, neuronal ensembles of interest. This will be reflected by Daun02-induced preferential Fos/CaMKII-IR cell loss in the OFC and preferential Fos/GAD67-IR cell loss in the PrL, in tissue collected after cocaine-paired context exposure during the DCIDM test. Overall, this R21 project will explore the neurobiological underpinnings of the newly discovered DCIDM phenomenon using a novel animal model, state-of-the-art pharmacogenetic techniques, and double-label immunohistochemistry with confocal microscopy. This high risk/high gain proposal has the potential to initiate a new line of investigation, provide original insight into the consequences o cocaine abuse on impulsive decision making, and inform the development of treatments for cocaine addiction.
Impulsive decision making can be precipitated by exposure to a cocaine-associated environmental context and this likely facilitates drug relapse and the maintenance of addictive behavior. The studies in this R21 proposal will utilize a novel rodent model and a pharmacogenetic approach to explore putative neuronal ensembles that regulate drug context-induced impulsive decision making. This research has strong potential to enhance our understanding of the consequences of drug abuse on cognitive function and may provide critical insights into the neurobiological mechanisms of cocaine addiction and impulsive disorders in general.