Exposure to a cocaine-associated environment elicits craving and/or an increase in propensity for relapse in cocaine users. Persistent and reoccurring environmentally triggered motivation for cocaine is likely elicited by plasticity in associative learning, memory, motivation, and executive cognitive function, implicating the involvement of the hippocampal formation, amygdala, nucleus accumbens, and frontal cortex in this phenomenon. However, the neural bases of context-induced drug relapse have been largely uncharacterized in part due to the scarcity of animal models that can be used to assess the motivational effects of environmental stimuli predictive of drug availability, as opposed to the motivational effects of conditioned stimuli paired explicitly with cocaine infusions. Using a new animal model in which cocaine seeking is elicited by exposure to a context predictive of drug availability, we have recently demonstrated that the functional integrity of the dorsal hippocampus (DH), basolateral amygdala (BLA), dorsomedial prefrontal cortex (dmPFC) and nucleus accumbens core (NACc) is necessary for contextual reinstatement of cocaine seeking. Taking a systems neurobiological approach, the proposed project expands the mapping of this critical pathway by further examining the role of the hippocampal formation, specifically the involvement of the ventral hippocampus (VH), subiculum, and entorhinal cortex, in contextual reinstatement of cocaine and food seeking using the tetrodotoxin-induced reversible neural inactivation method. Using similar techniques, the project will also further investigate the involvement of the NACc and nucleus accumbens shell in contextual reinstatement of cocaine and food seeking, as the former structure is postulated to be the input structure of the relapse circuitry toward the basal ganglia (Aim 1). Reversible asymmetrical inactivation (i.e., disconnection) will then be used to test the hypothesis that, within the contextual relapse circuitry, sequential information processing occurs between the DH and dmPFC as well as between the BLA and dmPFC via parallel loops, and information is then sequentially processed by the dmPFC and NACc (Aim 2). Lastly, the project will test the hypotheses that AMPA and metabotropic glutamate (mGLU) receptors within the relapse circuitry play a critical role in contextual reinstatement and that cocaine-induced adaptations in these receptor systems facilitate cocaine seeking. To this end, the project will examine dose-dependent effects of locally infused selective AMPA, group 1 mGLU, and group 2 mGLU receptor antagonists and/or agonists on contextual reinstatement of cocaine and food seeking (Aim 3). In summary, the objective of the proposed project is to elucidate the neurobiological and neuropharmacological mechanisms of contextual cocaine seeking. The resulting data have the potential to provide a rationale for the development of novel treatments for cue-induced drug relapse.
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