Fig. 2.
Striatal cell-specific overexpression of ΔFosB (filled circles and bars) facilitates acquisition of cocaine self-administration (FR1) at a low-threshold dose of cocaine (125 μg/kg per injection) (A) but not at a higher suprathreshold dose (250 μg/kg per injection) (B) compared with littermate bigenic controls maintained on doxycycline (open circles and bars). The numbers of cocaine injections (solid lines) and inactive lever presses (dashed lines) are shown at left, and the number of test sessions (latency) to achieve criteria for acquisition of cocaine self-administration are shown at right (for criteria, see Results). Each dose is tested for 5 d, followed by a higher training dose (500 μg/kg per injection) for days 6–10 to demonstrate a capacity for acquisition in all mice used in the analysis. Asterisks indicate that ΔFosB mice (n = 11, 7) differ from littermate controls (n = 13, 10) for threshold–dose cocaine self-administration by tests for simple effects (p < 0.05).