Moderate Alcohol Drinking and the Amygdala Proteome: Identification and Validation of Calcium/Calmodulin Dependent Kinase II and AMPA Receptor Activity as Novel Molecular Mechanisms of the Positive Reinforcing Effects of Alcohol
BACKGROUND Despite worldwide consumption of moderate amounts of alcohol, the neural mechanisms that mediate the transition from use to abuse are not fully understood. METHODS Here, we conducted a high throughput screen of the amygdala proteome in mice after moderate alcohol drinking (n 12/group) followed by behavioral studies (n 6 8/group) to uncover novel molecular mechanisms of the positive reinforcing properties of alcohol that strongly influence the development of addiction. RESULTS Two dimensional difference in gel electrophoresis with matrix assisted laser desorption ionization tandem time of flight identified 29 differentially expressed proteins in the amygdala of nondependent C57BL/6J mice following 24 days of alcohol drinking. Alcohol sensitive proteins included calcium/calmodulin dependent protein kinase II alpha (CaMKIIa) and a network of functionally linked proteins that regulate neural plasticity and glutamate mediated synaptic activity. Accordingly, alcohol drinking increased a amino 3 hydroxy 5 methyl 4 isooxazole receptor (AMPAR) in central amygdala (CeA) and phosphorylation of AMPAR GluA1 subunit at a CaMKII locus (GluA1 Ser831) in CeA and lateral amygdala. Further, CaMKIIa Thr286 and GluA1 Ser831 phosphorylation was increased in CeA and lateral amygdala of mice that lever pressed for alcohol versus the nondrug reinforcer sucrose. Mechanistic studies showed that targeted pharmacologic inhibition of amygdala CaMKII or AMPAR activity specifically inhibited the positive reinforcing properties of alcohol but not sucrose. CONCLUSIONS Moderate alcohol drinking increases the activity and function of plasticity linked protein networks in the amygdala that regulate the positive reinforcing effects of the drug. Given the prominence of positive reinforcement in the etiology of addiction, we propose that alcohol induced adaptations in CaMKIIa and AMPAR signaling in the amygdala may serve as a molecular gateway from use to abuse.
Biological Psychiatry