Figure 4.

Locomotor sensitization is expressed on withdrawal day 14 (WD14), when AMPAR surface expression is enhanced in the NAc. Data are expressed as average number of beam breaks per 5 min interval during the first and last pretreatment sessions (a and b, respectively) and after saline or cocaine challenge on WD14 (c and d, respectively). The arrow indicates time of injection after habituation and the inset in (a) shows the total number of beam breaks (summed over the first 40 min after injection) across all eight pretreatment injections. Cocaine-pretreated rats showed a greater response to the last pretreatment injection of cocaine compared with the first (a, b; closed squares) and a greater response to cocaine challenge than saline-pretreated rats (d; closed squares vs open circles). Sal-Sal N=9, Sal-Coc N=12, Coc-Sal N=12, Coc-Coc N=12.