Time course of the effect of 20 Hz dorsal raphe nucleus (DRN) electrical stimulation on DA and DOPAC extracellular levels in the nucleus accumbens (NAC) and the striatum in sham-operated (unfilled circles) and 5,7-dihydroxytryptamine-lesioned (5,7-DHT, filled squares) rats. Each data point represents the mean percentage ± SEM of baseline values calculated from three samples before DRN stimulation, performed for a 15 min period as indicated by the horizontal bar. Each experiment was performed on five animals per group 18–21 d after intra-DRN injection of vehicle or 5,7-DHT. 5,7-DHT treatment reduced the overall effect of DRN stimulation on DA and DOPAC extracellular levels in both the NAC and the striatum (see Results). *p < 0.05 and **p < 0.01 as compared with the sham-operated group for each time point (Student’s t test).