P2X1 (A), P2X4 (B), and P2X5 (C) mRNA expression is sexually dimorphic. P2R mRNA levels in freshly-isolated microglia from male and female mice of different ages were determined using qRT-PCR. Expression was normalized to β-actin and average folds (+/- SEM) are graphed relative to the males at each age. n = 3–6. # 0.05 < p ≤ 0.10; * p ≤ 0.05.