Fig. 5.

Mean changes in extracellular DA levels in the core and shell subregions in the NAcc (expressed as percentage of baseline ± SEM). A significant elevation in DA levels (*p < 0.05; **p < 0.01) compared with baseline levels was observed during the first CS+ presentations selectively in the core subregion. No significant changes in extracellular DA were seen in either region during the first 20 min of the self-administration session, which provided a measure of drug-seeking behavior unaffected by cocaine itself (gray shading). The ensuing cocaine infusions caused significant increases in DA levels in both core and shell subregions (arrows represent time points of cocaine infusions).