Recent data have shown that connections among these reward-relevant regions continue to be elaborated during adolescence. Consistent with the relatively delayed development of frontal cortical regions that continues through adolescence and into young adulthood (see Spear, 2007b), neurocircuitry connecting the PFC and subcortical reward-related regions likewise continues to develop through this period. For instance, glutaminergic projections from the basolateral amygdala to PFC continue to be elaborated in adolescence (Cunningham et al., 2008), even though overall synaptic density and excitatory drive to PFC decline notably during adolescence (see Spear, 2007b, for review and references). The number of DA fibers terminating in PFC also increases into adolescence (Benes et al., 2000), as does the inhibitory control of PFC activity by these DA afferents from VTA (Tseng & O’Donnell, 2007). Levels of the rate-limiting enzyme in the synthesis of DA, tyrosine hydroxylase, likewise increase through adolescence and into adulthood in the medial PFC and the NAc of rats (Mathews et al., 2009).
