P2RX4 and major depressive disorder: Purinergic Receptor Transcripts: Among the purinergic P2X receptors, P2RX4 mRNA expression was significantly greater in the MDD-S compared to MDD-NS all subject analysis in the white matter (Kruskal–Wallis (KW) nonparametric test: KW statistic = 8.81, p = 0.01), with a significant main effect of disease observed (two-way ANOVA: F(2,14) = 4.46, p = 0.03, Figure 1C).