We characterized the distribution of AMPA receptor (AMPAR) subunits and the transmembrane AMPA receptor regulatory proteins (TARPs) γ-2 and γ-4 in adult rat nucleus accumbens (NAc) using a method that separates plasma membranes into synaptic membrane-enriched and extrasynaptic membrane-enriched fractions. We also measured GluA1 phosphorylated at serine 845 (pS845 GluA1) and serine 831 (pS831 GluA1). GluA1-3 protein levels and pS831 GluA1/total GluA1 were higher in synaptic membranes. However, pS845 GluA1/total GluA1 was higher in extrasynaptic membranes, consistent with a role for S845 phosphorylation in GluA1 insertion at extrasynaptic sites. Homeric GluA1 receptors were detected in extrasynaptic membranes, consistent with evidence for extrasynaptic Ca2+-permeable AMPARs in other systems. The TARP γ-2 was enriched in synaptic membranes, whereas γ-4 was mainly found in extrasynaptic membranes, suggesting distinct roles for these proteins in the NAc. These experiments provide fundamental information that will aid in the interpretation of studies on AMPAR-related plasticity in the NAc.
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