Drug-paired lever responding during extinction and reinstatement testing. A. NVHL rats show significantly higher rates of cocaine-paired, but not inactive, lever responses during first two extinction test sessions relative to shams. B. The latency to reach extinction is prolonged in NVHL rats criteria (≤ 15 responses on cocaine-paired lever, ≤ 30 total on both levers in 2hr). C. Following achievement of extinction criteria, reinstatement induced by i.p. priming injections of cocaine is enhanced in NVHL relative to sham rats. Priming injections of saline or cocaine (5 and 15 mg/kg) were delivered after 2 h of additional extinction conditions in the test chambers. Two NVHL and one sham animal were excluded from the analysis due to high baseline responding (>30 total on both levers in second baseline hour). Data are presented as the mean ± SEM, *p < .05, **p < .01 by 2-way ANOVA, or by 2-tailed t-test.