Psychopharmacology (2012) 219:313–326 Fig. 1 Effects of amphetamine (a), the selective DA reuptake inhibitor GBR12909 (b), the selective reuptake inhibitor atomoxetine (c) and the selective 5-HT reuptake inhibitor citalopram (d) on premature responding, i.e., impulsive action under baseline conditions (visual stimulus presented 5 s after trial initiation) in the 5-CSRTT. In total, n=16 animals were included in the analysis. Asterisk indicates p<0.05 and two asterisks indicates p<0.01 compared to vehicle treatment (paired samples t-test). All data are expressed as mean±SEM 317 no effect was found at the intermediate dose of 0.5 mg/kg and 1 mg/kg of amphetamine resulted in a significant increase (Table 1) [F(3,45) = 10.49, p < 0.001]. Systemic administration of the selective DA reuptake inhibitor GBR12909 resulted in enhanced premature and perseverative responses at a dose of 10 mg/kg (Fig. 1b and Table 1) [F(3,45) = 8.46, p < 0.007 and F(3,45) = 10.26, p < 0.004, respectively]. At this dose, the percentage of correct responses and response latency were reduced (Table 1) [F(3,45) = 6.02, p < 0.01 and F(3,45) = 3.93, p = 0.01, respectively]. GBR12909 had no effect on errors of omission [F(3,45) = 2.23, NS]. Atomoxetine, the selective reuptake inhibitor, enhanced the errors of omission and slowed response latency at all tested doses without affecting impulsive behavior (Fig. 1c and Table 1) [F(3,45) = 26.43, p < 0.001, F(3,45)= 23.22, p< 0.001, F(3,45)= 2.54, NS, respectively]. The other parameters of 5-CSRTT performance were unaffected by atomoxetine treatment under baseline con- ditions [correct responses: F(3,45)= 2.23, NS and persever- ative responses: F(3,45)= 0.8, NS]. Premature responding was decreased after treatment with the selective 5-HT reuptake inhibitor citalopram at the intermediate dose of 1.0 mg/kg (Fig. 1d) [F(3,45)=2.98, p<0.05], whereas the response latency was increased at a dose of 1.0 mg/kg and 3.0 mg/kg [F(3,45)=2.79, p=0.05]. Further comparisons indicated that accuracy, errors of omissions and perseverative responses were unaffected by citalopram [F(3,45)=0.23, NS, F(3,45)=0.99, NS, F(3,45)= 1.97, NS, respectively]. Effect of amphetamine and monoamine reuptake inhibitors on 5-CSRTT performance under long ITI conditions Under long ITI conditions in the 5-CSRTT, the effects of monoamine reuptake inhibitors were tested at a dose that affected impulsive behavior under baseline conditions, i.e., 10 mg/kg GBR12909 and 1 mg/kg citalopram. For atom- oxetine, which did not alter impulsive behavior under baseline conditions, the highest dose was used (i.e., 3 mg/ kg). An intermediate dose of amphetamine (0.5 mg/kg) was used as this dose had no effect on the errors of omission under baseline conditions but did markedly increase impulsive behavior in the 5-CSRTT (Table 1). Similar to baseline conditions, amphetamine (0.5 mg/kg) and GBR12909 (10 mg/kg) increased the amount of premature and perseverative responses and attenuated accuracy under long ITI conditions (Fig. 2a, b) [premature responses: df= 15, t = −4.07, p= 0.001 and df= 14, t = −3.49, p= 0.01, perseverative responses: df= 15, t = −3.21, p< 0.01 and df= 14, t= −2.50, p< 0.05, correct responses: df= 15, t= 2.70, p< 0.05 and df= 14, t= 2.52, p< 0.05, respectively]. In addition, GBR12909 (10 mg/kg) decreased response latency, whereas amphetamine had no effect on this parameter [df= 14, t = 2.91, p = 0.01 and df = 15, t = −0.44, NS, respective- ly]. No effect of amphetamine and GBR12909 was