A subset of RTN neurons from GPR4(H81F) mice lack pH sensitivity in acute slices. A, Schematic of experimental design to target GFP-labeled RTN neurons in slices from neonatal WT and H81F Phox2b::GFP (Jx99) mice (N = 40 and 41, P7–P13). B, Representative cell-attached recording from a GFP-expressing RTN neuron from a Jx99 mouse. C, Representative cell-attached recordings from pH-sensitive and pH-insensitive GFP⁺ RTN neurons from H81F-Jx99 mice. D, Frequency distribution of pH-sensitive and pH-insensitive RTN neurons from WT Jx99 (N = 40) and H81F-Jx99 mice (N = 41); the cutoff for designation into these two groups is indicated. E, The percentage of cells from each genotype that are either pH-sensitive or pH-insensitive (χ² analysis; numbers of cells from each group are provided within the bars). F, Averaged firing rates at different bath pH for RTN neurons from GPR4 WT Jx99 mice and for RTN neurons from H81F-Jx99 mice that were identified as either pH-sensitive or pH-insensitive (as in D, E). *compares Jx99 vs H81F-Jx99:pH-sensitive; †††compares Jx99 vs H81F-Jx99:pH-insensitive; #compares H81F-Jx99:pH-sensitive vs H81F-Jx99:pH-insensitive, by mixed-effect model with Tukey's test (for genotype F_(2,143)= 2.553; p = 0.0814; for pH × genotype F_(6,410)= 19.67; p < 0.0001). G, Whole-cell current–clamp records from representative RTN neurons in slices from WT (Jx99) and H81F-Jx99:pH-insensitive mice showing spontaneous action potential firing at resting membrane potential (G, −50 mV). H, Resting membrane potential (Em, left) and steady-state input resistance (R_N, right) of RTN neurons from Jx99 mice and pH-sensitive and pH-insensitive RTN neurons from H81F-Jx99 mice. I, Current-evoked firing during step current injections from a holding potential of −60 mV (indicated with dashed red line) in exemplar RTN neurons from WT (Jx99) and H81F-Jx99:pH-insensitive mice. J, Firing frequency during current injection in RTN neurons from the indicated mice.