Assessing the Adolescent and Adult Prefrontal Cortex Proteome for Mechanisms of Enhanced Vulnerability to Alcoholism

Alcoholism is a debilitating neurobiological disorder affecting millions of people in the United States and around the globe. Treatment options for alcoholism are limited, due in part to incomplete understanding of the development and molecular mechanisms that lead to alcohol addiction. Age of drinking onset is one of the most significant predictors of lifetime alcoholism risk, with individuals initiating alcohol use during adolescence at substantially increased risk for developing alcoholism than those who initiate drinking during early adulthood. However, the specific neurobiological mechanisms responsible for this increased risk remain elusive. Synaptic plasticity is a critical component of adolescent brain development, and evidence suggests that alcohol and other drugs of abuse may induce aberrant plasticity in the brain, leading to long-term changes in the response to these drugs. Thus, the goals of this dissertation were to characterize the development of the adolescent and adult prefrontal cortex, a region known to be involved in adolescent maturation and drug taking behavior, and assess the differences in how the adolescent and adult prefrontal cortex respond to the presence of alcohol at the protein-expression level. Several of the proteins regulated by age and alcohol are involved in synaptic plasticity, including the protein phosphatase calcineurin (PPP3R1), which displays increased expression during adolescence and reduced expression following alcohol drinking in the adolescent but not adult prefrontal cortex. Systemic inhibition of PPP3R1 withthe drug FK506 reduced alcohol drinking more potently in adolescent versus adult mice, suggesting that PPP3R1 may be functionally involved in age differences in alcohol consumption. Next, to evaluate the role of PPP3R1 in long-term vulnerability to alcoholism following adolescent exposure to alcohol, a protocol for adolescent drinking and subsequent adult operant self-administration of alcohol was developed. Mice exposed to alcohol drinking during adolescence exhibited increased operant responding for alcohol during adulthood, and finding that was not evidenced in adult mice exposed to alcohol and subsequent operant self-administration. The increased responding for alcohol in adolescent alcohol exposure was reduced by the PPP3R1 inhibitor FK506. In contrast, operant responding for alcohol was not affected by FK506 in mice exposed to water during adolescence or adult mice exposed to either alcohol or water, demonstrating relative selectivity for the unique pattern of increased intake exhibited by mice exposed to alcohol during adolescence. The role of PPP3R1 in the prefrontal cortex was assessed via site-directed microinjection of FK506, which increased operant responding for alcohol in mice exposed to either alcohol or water during adolescence. Lastly, to examine brain regions known to be both regulated by input from the prefrontal cortex and involved in alcohol reinforcement, the amygdala, dorsal striatum and nucleus accumbens were all assessed for expression and phosphorylation of CaMKII, a protein critical for synaptic plasticity. Adolescent mice displayed reduced phosphorylation of CaMKII in the amygdala following voluntary alcohol drinking, whereas adult mice exhibited no changes in expression or phosphorylation. Conversely, phosphorylation of the AMPA receptor subunit GluA1 was increased in adult mice following alcohol consumption but reduced in adolescent mice. Finally, systemic administration of tianeptine, an atypical antidepressant that upregulates pGluA1 in a CaMKII-dependent manner, increased alcohol consumption in adolescent mice but decreased alcohol consumption in adult mice. Collectively, these experiments demonstrate that the adolescent and adult brains have noticeably different responses to alcohol consumption. The findings provide evidence that long-lasting alterations in synaptic plasticity may be responsible for the increased alcohol intake observed after adolescent exposure to alcohol.Doctor of Philosoph