evidence from anesthetized rats that the spontaneous activity of midbrain dopamine neurons peaks during adolescence and then decreases (McCutcheon and Marinelli, 2009). Developmental changes in mesocorticolimbic dopamine circuitry and activity may underlie some differences in motivated behavior generally, as well as risk taking and addiction vulnerability in particular. Several studies have observed reduced psychomotor effects of stimulant drugs in adolescent animals but enhanced or similar reinforcing effects (Adriani et al., 1998; Adriani and Laviola, 2000; Badanich et al., 2006; Bolanos et al., 1998; Frantz et al., 2007; Laviola et al., 1999; Mathews and McCormick, 2007; Spear and Brake, 1983). In contrast, adolescents are more sensitive to the cataleptic effects of neuroleptics (e.g., haloperidol), which are antagonists for dopamine receptors (Spear and Brake, 1983; Spear et al., 1980; Teicher et al., 1993). Some have proposed that this pattern, along with the increased exploration and novelty-seeking, indicates that the adolescent dopamine system is near a “functional ceiling” at baseline (Chambers et al., 2003).
