Pivotal role of thalamic hypocretin transmission during EtOH seeking and relapse

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A central problem in the treatment of ethanol (EtOH) addiction is the prevalence of relapse to EtOH use even after protracted intervals of forced or self-imposed abstinence. Advances have been made in elucidating the neurocircuitry that mediates craving and EtOH seeking, which provides insights into the neurobiological basis of relapse. Functional brain imaging in humans and studies that use c-fos expression as a marker of neural activation in rodents implicate interconnected cortical and limbic brain regions in response to drug cue-, drug priming-, and stress-induced reinstatement. Major components of this circuitry include the medial prefrontal cortex (mPFC), basolateral amygdala (BLA), central nucleus of the amygdala (CeA), bed nucleus of the stria terminalis (BNST), ventral tegmental area (VTA), nucleus accumbens (NAC), hippocampus, thalamus (THAL), and dorsal striatum. The hypocretin (Hcrt) system regulates a wide range of physiological processes, including feeding, energy metabolism, and arousal, and is recruited by drugs of abuse, including EtOH. Of interest for the present proposal, recent studies have demonstrated a critical role of Hcrt in the modulation of stress and a possible anxiolytic effect of Hcrt receptor (Hcrt-r) antagonism. Hcrt neurons, located only in the hypothalamus, project to the major components of the neurocircuitry that mediates EtOH seeking and innervates densely the paraventricular nucleus of the thalamus (PVT). Recent evidence suggests that the PVT participates in the modulation of reward function in general and drug-directed behavior in particular. Furthermore, it has been shown that PVT is an important contributor in the regulation of stress, a critical factor that can induce intense craving and trigger relapse in abstinent individuals. Earlier findings demonstrated selective recruitment of the LH/DMH/PFA-PVT during EtOH seeking, and preliminary data suggest that a history of EtOH dependence dysregulates the Hcrt/Hcrt-r system. Thalamic impairments are a key feature of EtOH-related brain dysfunction in alcoholics, remaining to be determined are the extent to which a history of EtOH dependence dysregulates Hcrt and whether this dysfunction will predict maladaptive compulsive EtOH-seeking (relapse) that is precipitated by stress vs. normal (food-seeking) behavior. This proposal will test the hypothesis that a history of EtOH dependence dysregulates Hcrt and its interaction with the PVT, and that this dysfunction will predict compulsive EtOH seeking (relapse) precipitated by stress. Furthermore, using local gene silencing, this proposal will test the hypothesis that the permanent decrease in Hcrt production via a viral vector will prevent Hcrt transmission dysregulation in the PVT during dependence and therefore prevent exacerbated response to stress during EtOH abstinence. This project is likely to highlight a previously unrecognized mechanism in the etiology of compulsive EtOH seeking during abstinence; ultimately leading to the identification of novel therapeutic targets for the prevention of EtOH relapse.