Figure 1.

Incubation of cocaine craving and β-endorphin extracellular levels. (a) Self-administration training: Number of active and inactive lever presses and cocaine infusions over the 10-day, 6 h/day self-administration sessions. Cocaine (0.75 mg/kg per infusion) induced intensive pressing on the active lever, whereas the amount of presses on the inactive lever was minimal. (b) Cue-induced drug-seeking behavior. The number of active lever presses in cocaine-trained rats tested on day 30 of abstinence was significantly higher than on day 1. Values are expressed as mean±SEM; n=9 rats per group. *p<0.001 vs day 1. (c) Cue-evoked β-endorphin levels in the NAc were significantly higher after 1 day of abstinence from cocaine than after 30 days. Values are expressed as mean±SEM; n=9 rats per group.*p<0.001 vs baseline and day 30. Top right corner: representative image for cannula placement in the NAc.