Figure 4.

Food self-administration, heroin self-administration, and heroin relapse-related behaviors in Oprm1-Cre rats and wildtype littermates. A, Food self-administration. Acquisition (left) and fixed-ratio response (right). Mean ± SEM number of pellets consumed (left) and active lever presses (right). Wildtype (3 males, 6 females), Oprm1-Cre (4 males, 6 females); data were combined for males and females. B, Heroin self-administration. Mean ± SEM number of heroin infusions during heroin self-administration training (days 1-6, 0.1 mg/kg/infusion; days 7-12, 0.05 mg/kg/infusion). Extinction responding. Mean ± SEM number of active lever presses during the seven 6 h extinction sessions. Active lever presses led to contingent presentations of the tone-light cue, but not heroin. Context-induced reinstatement. Mean ± SEM number of active lever presses during the 6 h reinstatement tests in Contexts B and A. Active lever presses led to contingent presentations of the tone-light cue, but not heroin. Individual data points are depicted for males (blue) and females (red). Reacquisition. Mean ± SEM number of heroin infusions (0.05 mg/kg/infusion) per hour during reacquisition. Active lever presses led to the delivery of heroin infusions and the tone-light cue. Wildtype (6 males, 8 females), Oprm1-Cre (5 males, 8 females); data were combined for males and females.