Figure 6. PC-evoked upregulation of astrocytic HIF-1α and EPO require the P2X7 receptor. A–C, Immunohistochemical analysis of HIF-1α in the ipsilateral striatum. Typical pictures and quantitative data are shown in A–C, respectively. Representative immunohistochemical pictures stained with anti-HIF-1α (red), anti-GFAP (green), and anti-NeuN (green) antibodies in the ipsilateral striatum. At 1 d after PC, HIF-1α expression was increased mainly in neurons, and this upregulation was independent of the activation of P2X7 receptors; i.e., upregulation of HIF-1α was observed in both WT and P2X7−/− mice. In contrast, 3 and 6 d after PC, HIF-1α expression was increased in astrocytes. This upregulation was dependent on the P2X7 receptor; i.e., astrocytic upregulation of HIF-1α on day 3 and 6 after PC was significantly higher in WT mice than in P2X7−/− mice. For quantitative analysis, we used the index of percentage of HIF-1α-positive cells (see the Materials and Methods section for details). Scale bars: A, B, main images, 30 μm; insets, 12 μm. Values are shown as means ± SEM; **p < 0.01 versus WT-d3; ##p < 0.01 versus WT-d6; n = 3–6. sh, Sham-operated mice; D, PC significantly upregulated mRNA for EPO, a well known target molecule of HIF-1α, at 3 and 6 d after PC in WT mice, but not in P2X7−/− mice. Values are shown as means ± SEM; *p < 0.05, **p < 0.01; n = 3–6. nv, Naive mice.