Mechanistic studies of cAMP effectors in cocaine addiction

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Project Summary Cocaine addiction is a substantial medical and economic burden in the U.S. and worldwide. There currently are no FDA-approved medications for treating cocaine addiction. Repeated exposure to drugs of abuse including cocaine induces the upregulation of cAMP-dependent signaling in the mesolimbic system that initiates the transition to addiction. cAMP has three direct effectors: protein kinase A (PKA), exchange proteins activated by cAMP (Epac), and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Much work has been done to characterize the cAMP-PKA signaling pathway in the regulation of drug reinforcement and addictive behavior. However, few studies have addressed how the “other” cAMP effectors regulate the cellular and behavioral effects of drugs of abuse. During our prior NIH funding period, we provided the first evidence for Epac2-mediated modulation of cocaine-induced excitatory and inhibitory synaptic plasticity in dopamine neurons of the ventral tegmental area (VTA) and conditioned place preference. Drug self- administration has a high degree of face and predictive validity for abuse liability and is the gold standard for studying the reinforcing effects of drugs of abuse. However, whether and how Epac regulates cocaine self- administration remains unknown. Building on work from our previously funded grant period and our preliminary studies, the long-term goal of this R01 renewal is to test the hypothesis that Epac and HCN act via distinct but complementary mechanisms to regulate dopaminergic transmission and cocaine-induced long-term plasticity, and that these mechanisms contribute to cocaine reinforcement and seeking behavior. Using viral-mediated knockdown, conditional knockouts, fast-scan cyclic voltammetry (FSCV), electrophysiology, and cocaine self- administration, we will test this hypothesis via three Specific Aims. In Aims I and II, we will unravel the region- and cell type-specific mechanisms whereby Epac2 in the VTA and nucleus accumbens contribute to cocaine reinforcement and seeking behavior, respectively. In Aim III, we will determine how cocaine self-administration- induced, cAMP-mediated adaptations in HCN2 channels in VTA dopamine neurons contribute to cocaine reinforcement. These detailed, mechanistic studies are expected to provide first evidence that these under- studied cAMP effectors in the mesolimbic dopamine system regulate reinforced cocaine self-administration and drug seeking.