Figure 3.

Stimulation of μ receptors in the ventral pallidum induces the reinstatement of cocaine seeking. A, Morphine in the ventral pallidum reinstated lever pressing in cocaine-trained subjects. Extinguished subjects were microinjected with saline or morphine to reinstate lever pressing. Active lever extinction baseline was as follows: ventral pallidum, 13 ± 2; nucleus accumbens, 9 ± 3. Data were evaluated using a mixed-regression analysis, and each rat had a maximum of two reinstatement trials (ventral pallidum, F_(4,11) = 8.45, p = 0.002; nucleus accumbens, F_(4,11) = 1.92, p = 0.181). B, The reinstatement by morphine (MS; 10 μg) microinjection into the ventral pallidum was blocked by co-microinjection with CTAP (3 μg). Each animal received all three reinstatement trials in random order, and the data were evaluated using a one-way ANOVA with repeated measures over treatment: extinction baseline, 13 ± 2; F_(2,10) = 29.04; p < 0.001. C, The effect of intra-ventral pallidum morphine and systemic cocaine (Coc; 5 mg/kg, i.p.) in reinstating drug seeking. Each animal received a maximum of two reinstatement trials, and the data were evaluated using a mixed-regression analysis: extinction baseline, 16 ± 1; F_(3,9) = 11.699; p = 0.002. D, Intra-pallidal injection of high-dose morphine (10 μg) inhibits cocaine-primed (10 mg/kg, i.p.) reinstatement. Each rat received both treatments in random order, and the data were evaluated using a paired Student's t test. ^*p < 0.05 compared with CTAP in A, cocaine in B, vehicle (Veh) + Veh in C, and Veh + Coc in D.