Sensitizing exposure to amphetamine increases AMPA receptor phosphorylation without increasing cell surface expression in the rat nucleus accumbens
Exposure to psychostimulants like cocaine or amphetamine leads to long-lasting sensitization of their behavioral and neurochemical effects. Here we characterized changes in AMPA receptor distribution and phosphorylation state in the rat nucleus accumbens (NAcc) weeks after amphetamine exposure to assess their potential contribution to sensitization by this drug. Using protein cross-linking, biochemical, subcellular fractionation, and slice electrophysiological approaches in the NAcc, we found that, unlike cocaine, previous exposure to amphetamine did not increase cell surface levels of either GluA1 or GluA2 AMPA receptor subunits, redistribution of these subunits to the synaptic or perisynaptic cellular membrane domains, protein-protein associations required to support the accumulation and retention of AMPA receptors in the PSD, or the peak amplitude of AMPA receptor mediated mEPSCs recorded in NAcc slices. On the other hand, exposure to amphetamine significantly slowed mEPSC decay times and increased levels in the PSD of PKA and CaMKII as well as phosphorylation by these kinases of the GluA1 S845 and S831 residues selectively in this cellular compartment. As the latter effects are known to respectively regulate channel open probability and duration as well as conductance, they provide a novel mechanism that could contribute to the long-lasting AMPA receptor dependent expression of sensitization by amphetamine. Rather than increase the number of surface and synaptic AMPA receptors as with cocaine, this mechanism could increase NAcc medium spiny neuron reactivity to glutamate afferents by increasing the phosphorylation state of critical regulatory sites in the AMPA receptor GluA1 subunit in the PSD.