A single cocaine injection induces an increase in AMPAR/NMDAR ratio within 3 h in VTA neurons. A , Representative traces of AMPAR and NMDAR EPSCs from naive animals or animals pretreated 3–5 h earlier with a single injection of cocaine (15 mg/kg, i.p.) or equivalent amount of saline. B , Averaged AMPAR/NMDAR ratios. Cocaine-injected animals (n = 9) show a significantly increased ratio compared with saline-injected (n = 5) or naive (n = 5) animals. **p < 0.01. Error bars represent SEM.