Developmental alterations in DA tone have also been reported in these reward-related regions. For instance, the elevation in DA tone (“hyperdopaminergic” state) postulated to be reached during late adolescence in NAc and dorsal striatum based on foskolin-induced cAMP accumulation data (Andersen, 2002) and estimated turnover rates (see Spear, 2000 for review) contrasts markedly with the (perhaps compensatory) blunting of the cAMP response to DA D1- and D2-R stimulation (suggestive of DA “hyposensitivity”) that is also seen in these areas during late adolescence (Andersen, 2002). Such compensatory responses have been long known to be rampant within DA systems (e.g., Zigmond et al., 1990) and even across systems. For an example of the latter, signs of increased DA transmission during adolescence were associated with compensatory changes in the cholinergic neurons to which they project in striatum, resulting in a functionally hyposensitive DA 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
