Synaptic connections increase during brain development, reaching a developmental peak associated with high levels of plasticity that mature to lower stable adults levels. To investigate broad changes in neurotransmitter gene expression during adolescent brain maturation to young adulthood (P38 - P88), we used an RT-PCR Superarray™ of 84 neurotransmitter-specific mRNAs. Eleven genes were removed from the analysis due to insufficient yield (Table S1). Interestingly, there was a significant main effect of age on the expression of neurotransmitter-specific genes in controls across the entire array from P38 to P88(Figure 2A; average reduction of 56%, p<0.0001, F=282.4). The expression of thirty-five mRNAs was lower in P88 young adults as compared to P38 adolescents (Table 1; t-test, *p<0.05, **p<0.01, § p<0.05 Bonferroni post-test). Only six of the 73 neurotransmitter-specific mRNA did not decline between P38 and P88 (See Figure 2A). Adolescent brain maturation showed large decreases in peptide, γ-amino-butyric acid (GABA), cholinergic and dopaminergic gene expression (Fig. 3,Fig. 4 and Table 1). Examples include peptides such as NPY and somatostatin receptors, which decreased 70-80% during brain maturation across receptor subtypes (Table 1). These
