Stimulus-specific release of purinergic metabolites by NVU cells parallels microglial modulation of brain pH and hypercapnia-induced adenosine production. (a) CBF by laser Doppler flowmetry and tissue pH by pH-selective electrode were simultaneously assessed during hypercapnic challenge for 2 min. (b) Depleted mice show reduced extracellular brain pH. n = 10 and n = 16 measurements from six control and nine depleted mice; P < 0.0001, two-way ANOVA followed by Sidak’s multiple comparison (**, P = 0.0093, control versus depleted baseline; **, P = 0.0028, control versus depleted hypercapnia). (c) CBF response to hypercapnia is reduced in microglia-depleted mice. n = 6 control and 9 depleted mice; *, P = 0.012, Mann–Whitney test. (d) Effect of hypercapnia on levels of purinergic metabolites (ATP, ADP, AMP, and Ado [adenosine]) in primary endothelial, astrocyte, and microglia cultures as measured by HPLC. Endothelial cells: ATP: ****, P < 0.0001; ADP: ****, P < 0.0001; AMP: *, P = 0.01226, control versus hypercapnia; astrocytes: ATP: ***, P = 0.00029; Ado: ****, P = 0.000057, control versus hypercapnia; microglia; ADP: ***, P = 0.00134; Ado: ****, P < 0.0001, control versus hypercapnia; multiple t test. (e) Adenosine levels are significantly reduced in the cerebral cortex in the absence of microglia upon hypercapnic challenge. Adenosine was measured by HPLC in cortical brain tissue homogenates. n = 7 control and n = 7 depleted mice; *, P = 0.0142, unpaired t test. (f) Effect of hypoxia on levels of purinergic metabolites (ATP, ADP, AMP, and Ado) in primary endothelial, astrocyte, and microglia cultures as measured by HPLC. Endothelial cells: ATP: ***, P = 0.00054; AMP: ***, P = 0.00011, control versus hypercapnia; astrocytes: ADP: ****, P < 0.0001; AMP: *, P = 0.0148; Ado: **, P = 0.0059, control versus hypercapnia; microglia: ADP: ****, P < 0.0001, control versus hypercapnia; multiple t test. Data are expressed as mean ± SEM.