Role of GluA1 in the Escalation of Alcohol Drinking in Nicotine-Dependent Animals

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Project Summary ______ Drugs of abuse (including alcohol) are frequently used and abused in combination, and there is a substantial association of nicotine and alcohol use disorders in particular. Interest in the biobehavioral mechanisms underlying nicotine and alcohol interactions has recently grown, although information on neuronal signaling and behavioral adaptations that occur in animals exposed to both nicotine and alcohol remains limited compared to the abundance of studies on these substances in isolation. Nicotine use increases alcohol drinking, suggesting that the combination of these drugs may produce synergistic effects in activating brain reward circuitry. Alternatively, use of either of these substances may facilitate the development of cross- tolerance to the other to promote intake escalation. Our preliminary data demonstrates that alcohol self- administration is increased in animals made dependent on nicotine via chronic, intermittent nicotine vapor (CINV) exposure. While these data are consistent with previous reports, the neurobiological mechanisms that underlie this interaction remain largely unknown. Chronic drug-induced modifications of AMPA channel activity alter excitatory neurotransmission that functionally associates with excessive drug use and relapse. Several of these effects occur through phosphorylation of GluA1 AMPA subunits, which increases AMPA channel function via facilitation of membrane trafficking or channel activity. This phosphorylation event is thought to be essential for the modulation of synaptic plasticity that may underlie several key aspects of the persistence of drug addiction. Our preliminary molecular results demonstrate that nicotine exposure and alcohol challenge interactively produce neuroadaptations in GluA1 phosphorylation in a brain region-dependent manner. Alcohol robustly increases PKA-mediated phosphorylation of GluA1 in multiple regions. However, this neuroadaptation is largely absent in two areas (dorsomedial prefrontal cortex and central amygdala) in nicotine-experienced animals. This interactive effect suggests a molecular tolerance to alcohol-stimulated phosphorylation of GluA1 in the context of nicotine dependence. Nicotine may thus facilitate the reinforcing effects of alcohol by altering glutamate signaling in a region-specific manner, thereby leading to increased drinking in heavy smokers. The goal of this proposal is to test the central hypothesis that escalated drinking in nicotine-dependent male and female rats will be reduced by increasing AMPA signaling via local, HSV-mediated GluA1 overexpression in specific brain areas (dorsomedial prefrontal cortex and central amygdala) or by pharmacological stimulation of AMPA receptors via hydroxynorketamine (HNK). Results from this R21 will provide valuable insights into the neurobiological mechanisms associated with the co-abuse of nicotine and alcohol. These data may also provide new therapeutic avenues for treating problematic alcohol drinking in nicotine-dependent individuals.