system (Bolanos et al., 1998), along with the blunted psychomotor stimulant response to DA agonists frequently (e.g., Bolanos et al., 1998; Frantz et al., 2007; Mathews et al., 2009; Spear & Brake, 1983; Zombeck et al., 2008) but not always (Collins & Izenwasser, 2002; Niculescu et al., 2005; Smith & Morrell, 2008) seen when adolescent rats are compared with adults. Environmental variables (such as the amount of pretest manipulation or handling) may contribute to these different psychopharmacological findings across studies (Maldonado & Kirstein, 2005a,b; Doremus-Fitzwater & Spear, under revision), perhaps via their influence on mesocorticolimbic DA systems (Brake et al., 2004) adding further complexity.
