P2X3 (A), P2X5 (B), and P2Y4 (C) mRNA is expression is not detectable in microglia freshly-isolated from some ages of mice. 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 = 3–5; for primary cells n = 4–5 separate culture preparations. Values in parentheses are fold-changes of the lowly-expressed samples. # 0.05 < p ≤ 0.10; ** p ≤ 0.01; *** p ≤ 0.005. Primary cultures: ††† p ≤ 0.005 vs. all freshly-isolated microglia; a - p ≤ 0.05 vs. 21 d and 4 mo; b - p ≤ 0.05 vs. 12 mo; c - p ≤ 0.01 vs. 4 mo. N.D. = not detected.