Fig. 5

d-serine level reduction or NMDAR blockade decreases the respiratory response to hypercapnia in medullary brainstem slices and adult mice. a Integrated inspiratory burst recorded from the VRC in slices obtained from P4 neonates during isohydric normocapnia (basal, 5% CO₂, pH 7.4), hypercapnic acidosis (10% CO₂, pH 7.2), and recovery to basal conditions. b, d, f, h Exposure to 0.1 U ml⁻¹ DAAO + 260 U ml⁻¹ catalase (b, n = 7) to degrade d-serine, exposure to 50 µM MET-phen (d, n = 6) or 50 µM ET-phen (f, n = 7) to inhibit d-serine racemase, and exposure to 10 µM MK-801 (h, n = 7) for NMDAR blockade for 45 min each reduced the hypercapnia-induced fR response in medullary brainstem slices. Colored lines connect the fR values at pH 7.4 and 7.2 for each medullary brainstem slice before exposure (basal, first column of graphs), after 45 min of exposure (second column of graphs), and after 30 min of wash out (b, recovery). c, e, g, i Average changes in fR induced by hypercapnia under control conditions (basal, white bars); after 45 min of superfusion with aCSF containing DAAO (c, n = 7, blue bar), MET-phen (e, n = 6, cyan bar), ET-phen (g, n = 7, brown bar), or MK-801 (i, n = 7, purple bar); and after 30 min of recovery (second white bar in c). By contrast, 45 min superfusion with basal aCSF (slice responsiveness control) did not modify the fR (j, n = 6) or average responses (k, n = 6). Average data are presented as the mean + SEM (bars and vertical lines, respectively). Analysis for c: P = 0.0062, Friedman’s test; **, P < 0.01 Conover post hoc test. Analysis for b, d–k: ns not significant; * indicates P < 0.05, Wilcoxon signed-rank test. l Ventilatory response to hypercapnia in adult mice injected with saline (control) or saline with 9 mg kg⁻¹ MET-phen. m Average fR response to hypercapnia expressed as the percentage of the basal fR in mice injected with saline (n = 7, controls) and MET-phen (n = 12) at different time points after injection (P = 0.017, mixed ANOVA; *, P < 0.05 Bonferroni post hoc test)