After three weeks withdrawal from chronic cocaine or saline treatment mice were decapitated. The ventral striatum was dissected from the brain as described elsewhere (Szumlinski et al., 2004 (link)), and subcellular fractionation was performed as described previously with minor modifications (Toda et al., 2006 (link)). Briefly, fresh brain tissues were homogenized in cold buffer containing 0.32 M sucrose and 10 mM HEPES, pH 7.4. Homogenates were cleared two times at 1000 g for 10 min to remove nuclei and large debris (P1). The resulting supernatants were concentrated at 12 000 g for 20 min to obtain a crude membrane fraction (P2), which was rinsed twice (4 mM HEPES, 1 mM EDTA, pH=7.4; 20 min at 12 000g). Then, it was incubated (20 mM HEPES, 100 mM NaCl, 0.5% triton X, pH= 7.2) for 15 min and centrifuged at 12 000 g for 20 min to pellet the synaptosomal membrane fraction (LP1). The supernatant was considered the non-postsynaptic density membrane fraction (non-PSD), sometimes referred to as the triton soluble fraction. The pellet was then solubilized (20 mM HEPES, 0.15 mM NaCl, 1% triton X100, 1% deoxycholic acid, 1% SDS, pH= 7.5) for 1 h and centrifuged at 10 000 for 15min. The supernatant contained the postsynaptic density fraction (PSD) or triton insoluble fraction. The integrity of non-PSD and PSD fractions was verified by immunoblotting for PSD-95 which was enriched in PSD fraction, and synaptophysin which was enriched in non-PSD fraction (Supplemental Figure 1). All buffers were supplemented with protease inhibitors cocktail (Complete mini tablets, Roche). Protein concentration was measured using the Bradford assay (Pierce).