Recent clinical studies, including those of the Center, have shown that psychological stressors elevate drug craving and hypothalamic-pituitary-adrenal (HPA) axis activity, and that stress-induced HPA axis responses predict amounts of subsequent drug use. The hypothesis of this Project is: withdrawal from drugs of abuse and exposure to stress persistently alter gene expression levels of HPA axis and brain stress responsive systems in rodent extended amygdalar and mesocorticolimbic regions;critically contributing to persistent compulsive drug taking and relapse of drug seeking. During the current funding period, it has been found that a) arginine vasopressin (AVP) gene expression in the medial amygdala is activated during early withdrawal from heroin;and b) a selective AVP V1b receptor antagonist attenuates both reinstatement of heroin-seeking behaviors and HPA activation induced by stress in long-term heroin withdrawal. This suggests that amygdalar AVP/V1b receptor and HPA systems are critical components of the neural circuitry underlying the aversive emotional consequences of drug withdrawal, and the effect of negative emotional states on drug seeking behavior (negative reinforcing mechanism). Increases in AVP gene expression in the amygdala are further found in acute cocaine withdrawal, and are mediated via opioid receptor activation. Therefore, the first goal of this project is to determine the role of the AVP/V1b receptor systems in relapse to cocaine seeking and taking behaviors (Aim 1). The other main goals of this project are to characterize specific stress responsive genes with respect to: (a) dynamic and region-specific alterations after long-term withdrawal from chronic drug exposure after acute and chronic drug re-exposure (Aim 2) or after acute stress (Aim 3);(b) their correlations with stress-induced anxiety- or depression-like behaviors (Aim 3);(c) their correlations with stress-induced drug seeking or taking behaviors (Aim 1);and (d) potential epigenetic mechanisms underlying alterations of gene expression (Aim 4). The focus of this proposol is to study acute and chronic drug re-exposure after long-term withdrawal. The results will elucidate essential mechanisms for stress and opioid systems in the regulation of drug addictive-like states, which may lead to the identification of potentially novel therapeutic targets.
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