Immunoprecipitated CaMKII (A) or spinophilin (B) from S2 and S3 were evaluated on the same gel and quantified to compare levels of association in each fraction. Two-way ANOVA results: A: fractionation effect P=0.0021, brain region effect P=0.0789, Interaction P=0.1086. B: fractionation effect P<0.0001, Brain region effect P=0.2281, Interaction P=0.1140. Post hoc testing used the uncorrected Fisher’s LSD post hoc test. Comparison to corresponding hippocampal fraction: *P<0.05. Comparison to S2 fraction of corresponding brain region: ###P<0.001, ####P<0.0001. C. Model of differential expression and interactions in extrasynaptic and synaptic fractions isolated from hippocampus and striatum. 1. Equal expression and interaction of proteins in striatum and hippocampus synaptic fraction. 2. More spinophilin, NMDAR, and CaMKII expression in hippocampus compared to striatum extrasynaptic fraction. 3. Greater striatal association of spinophilin, CaMKII and GluN2B in extrasynaptic fraction.