Figure 1. Effect of prior chronic cocaine exposure on locomotor activity and Fosb induction in NAc and CPu upon reexposure to the drug. A, Rats were injected intraperitoneally twice daily with either saline (Drug Naive) or cocaine (15 mg/kg; Drug Experienced) for 10 d and, after 28 d of withdrawal, were treated with one (ΔFosB and FosB mRNA) or several (Locomotor activity; ΔFosB protein) challenge injections of cocaine (15 mg/kg, i.p). B, Animals were habituated in a locomotor chamber without any challenge injection for 1 h, and then monitored for locomotor activity after one saline injection (Injection 0, n = 16) or cocaine challenge injections (Injection 1, n = 12; Injection 2, n = 8). Data are expressed as sum of total number of beam breaks over 60 min after the saline or cocaine injection. C, After 28 d of withdrawal, cocaine-naive and -experienced rats were injected intraperitoneally once with saline (Injection 0, n = 3) and with 1, 3, or 6 cocaine challenge injections (n = 5 per group). Animals were killed 24 h after the last injection and ΔFosB protein was quantified immunohistochemically in NAc and CPu. Bonferroni posttests: ∧p < 0.001 (B), p < 0.05 (C), different from Drug Naive with no cocaine challenge; *p < 0.001 (B), p < 0.05 (C), different from Drug Naive with cocaine challenges. Images displayed are from NAc shell. D, Animals were killed 45, 90, or 180 min after a single saline or cocaine challenge (n = 7 per group). Bonferroni posttests: ∧p < 0.05, different from Drug Naive-Saline; *p < 0.05, %p = 0.08, different from Drug Naive-Cocaine. Data are expressed as mean ± SEM.