Figure 5.

Changes in breathing frequency during stimulation of RVLM-CA neurons is differentially occluded by hypoxia and hypercapnia. A, Initial respiratory effects of photostimulation (5 ms pulse at 20 Hz for 30 s) and poststimulus hypoventilation in a ChR2-mCherry-expressing DβH^Cre/0 mouse during hyperoxia (100% O₂, trace 1), hyperoxic hypercapnia (3 and 6% CO₂ balanced in O₂, traces 2 and 3, respectively), and a different mouse during normoxia (21% O₂ balanced in N₂, trace 4) and poikilocapnic hypoxia (15 and 10% O₂ balanced in N₂, traces 5 and 6). Arrows identify bouts of poststimulus hyperventilation. Note that the period of hypoventilation following the offset of the stimulus under hyperoxic and normoxic conditions is largely abolished when respiratory drive is increased by activating the chemoreceptors. B, Group data of the effects of photostimulation on f_R (B1), V_T (B2), and MV (B3) under hyperoxic and hyperoxic hypercapnic conditions. N = 9 for each condition, *p < 0.05, **p < 0.01, ***p < 0.001 for resting versus stimulated condition. C, Group data of the effects of photostimulation on f_R (C1), V_T (C2), and MV (C3) under normoxic and hypoxic conditions. N = 7 for each condition *p < 0.05, **p < 0.01 for resting versus stimulated condition. D, X-Y plot of the average change in f_R during stimulation in relation to prestimulus f_R under each gas mixture presented in B1 and C1 (p = 0.0001 for difference between slopes, hypercapnia r² = 0.44, hypoxia r² = 0.73; error bars indicate 95% CI). E, Change in f_R caused by RVLM-CA neuron stimulation and a brief CO₂ challenge (15 s of 15% CO₂) during graded hypoxia, normalized to the response f_R under normoxic conditions. **p < 0.01, ***p < 0.001 for stimulation versus CO₂ condition.