Effects of intravenous diphenhydramine (1.0 and 3.0 mg/kg) administration on extracellular DA levels in dialysates from rats implanted with microdialysis probes in the NAc shell (filled circles) and core (filled squares). Note that the effect of diphenhydramine on dialysate DA from the shell is significantly greater than its effect on DA levels in the core. Results are means, with vertical bars representing SEM, of the amount of DA in 10-min dialysate samples, expressed as percentage of basal values. Basal DA values (fmoles/sample) and group size (n) were: 38.3 ± 8.5 (4), and 36.6 ± 2.8 (4) for 1 and 3 mg/kg groups in the NAc shell, and 57.13 ± 7.3 (4), and 49.8 ± 2.1 (4) for 1 and 3 mg/kg in the NAc core. *= P<0.05 compared to the corresponding time point in the core.