Fig. 2.

Mean elevations over baseline in nucleus accumbens dopamine concentrations in rats receiving self-administered or experimenter-administered intravenous injections ofd-amphetamine. For each rat the mean dopamine concentration was calculated for the four samples before and after an injection occurred as well as for the sample during which the injection occurred. Only the results for dialysate samples collected after the first 60 min of the session were used. These data were then averaged within each group. The vertical dashed line represents the time of ad-amphetamine infusion.