Distribution of AMPA receptor subunits and TARPs in synaptic and extrasynaptic membranes of the adult rat nucleus accumbens

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.

Research highlights▶ AMPAR subunits are more abundant in synaptic than extrasynaptic rat NAc membranes. ▶ GluA1 in NAc extrasynaptic membranes shows relatively greater S845 phosphorylation. ▶ GluA1 in NAc synaptic membranes shows relatively greater S831 phosphorylation. ▶ Homomeric GluA1 AMPARs are found in NAc extrasynaptic membranes. ▶ TARP y-2 is enriched in NAc synaptic membranes; y-4 is predominantly extrasynaptic.