Figure 3. Disruption of CO₂/H⁺ dilation in the cNTS and ROb causes unstable breathing and apnea.

(A) Trace of external intercostal muscle EMG (Int_EMG) activity shows respiratory activity of an anesthetized wild type mouse breathing 2.5% CO₂ following injections of saline or U46619 (1 μM; 30 nL/region) into the cNTS and ROb. (B) Location of injections in the cNTS and ROb. (C) Representative Poincaré plot (50 breaths) shows breath‐to‐breath (T_TOT) interval variability following injections saline (black) or U46619 (red) conditions. (D-E) Summary data (N = 6 animals/group) shows effects of U46619 injections into the cNTS and ROb alone and in combination on the coefficient of variation of Int_EMG frequency (C) and Int_EMG frequency (E). (F) Summary data show that injections of U46619 injections into the cNTS and ROb lowered the CO₂ apneic threshold from 3.2 ± 0.3% to 2.1 ± 0.1% (N = 7 mice). *, Difference in Int_EMG activity under control conditions (saline) vs. during U46119 into the NTS and/or ROb (RM-ANOVA followed by Bonferroni multiple-comparison test, p<0.05). scale bar = 200 μm.