P2X1 (A) and P2X4 (B) receptor mRNA expression in freshly-isolated mouse microglia varies with age and differs from cultured neonatal microglia. P2R mRNA levels in freshly-isolated microglia from male and female mice of different ages and mixed-sex primary neonatal microglial cultures were determined using qRT-PCR. Expression was normalized to β-actin and average folds (+/- SEM) are graphed relative to the 3d time point of each sex. n = 3–6; for primary cells n = 5 separate culture preparations. Values in parentheses are fold-changes of the lowly-expressed samples. # 0.05 < p ≤ 0.10, * p ≤ 0.05; ** p ≤ 0.01; *** p ≤ 0.005. Primary cultures: †† p ≤ 0.01 vs. all freshly-isolated microglia, a - p ≤ 0.01 vs. 7 wk and 12 mo.