Psychopharmacology (2012) 219:313–326 choice in rats. Thus, forebrain 5-HT lesions attenuated the ability of amphetamine to decrease impulsive behavior in a delay-discounting task, particularly in rats with high baseline levels of impulsivity, but did not themselves alter delay- discounting performance (Winstanley et al. 2003). Therefore, involvement of neurotransmitters other than DA, and 5- HT, respectively, in the behavioral effects of GBR12909, atomoxetine and citalopram cannot be excluded. In conclusion, the neuropharmacological manipulations presented here indicate a differential contribution of DA, and 5-HT in the modulation of two dimensions of impulsivity. Inhibition of the reuptake of DA exerted opposite effects on impulsive action (increase) and impulsive choice (decrease), whereas inhibition of and 5-HT reuptake reduced impulsive action but not impulsive choice. The current study, therefore, supports the well-established notion of the hetero- genous nature of impulsivity (Dalley et al. 2011; Eagle and Baunez 2010; Evenden 1999; Pattij and Vanderschuren 2008). The existence of independent processes of impulse control is exemplified in the psychiatric population, although it is difficult to relate certain forms of impulsivity with particular disorders (Moeller et al. 2001; Solanto et al. 2001; Sonuga-Barke 2003). Nevertheless, deficits in one of the subtypes of impulsivity or genetic variation in monoamine signaling (e.g., Colzato et al. 2010; Hamidovic et al. 2009) may contribute to the differential responsiveness and effectiveness of drug treatments in impulse control disorders. As such, understanding the contribution of different neuro- transmitter systems to distinct forms of impulsivity may contribute to the development of selectively tailored phar- macotherapeutic treatments of impulse control disorders. 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