(A) Cartoons showing hypothesized network interactions (bottom) between putative independent lumbar (magenta square) and cervical (green circle) oscillators and unknown inhibitory interneurons, together generating two distinct temporal patterns of cervical (green) and lumbar (magenta) respiratory co-activation (top). These different networks produce motor outputs that differ in the relative time between their peaks (lumbar time-cervical time = τ, in ms). (B–D) Integrated and overlapped cervical and lumbar traces from 10 consecutive (B, WT–τ <150 ms), sequential but not consecutive (C, WT–τ ≥150 ms), or consecutive (D, Atoh1LacZ/LacZ [RL−/RTN−]) respiratory-related bursts aligned from the peak of cervical output (top–single burst, middle–average of 10 breaths, bottom–overlap of 10 bursts, numbers under traces = τ). Note the low level pre-inspiratory activity of the cervical trace during the lumbar burst as well as likely inhibition during the cervical burst in wild-type mice (C), but the strong simultaneous co-activation of lumbar and cervical outputs in Atoh1LacZ/LacZ mice (D). Partial peak delays are still present in E18.5 Phox2b-Cre; Atoh1LacZ/F (RL+/RTN−, E), and Phox2b-Cre;VGlut2F/F mice (RL+/RTNsilent, F) indicating Phox2b RTN neurons are not essential for temporal delay. (G–H) Histograms (12 ms bins) showing distributions of τ for WT (G–H) and Atoh1LacZ/LacZ (G and I) mice to determine whether loss of RL and RTN neurons affects τ. Distributions are scaled to same height for better comparison. Gray dashed line indicates τ = −150 ms cutoff. Note the clear differences in the peak and spread between baseline WT and Atoh1LacZ/LacZ distributions (G). WT but not Atoh1LacZ/LacZ distributions show increased temporal delay after application of 1 µM SP or 10−12M SST (H–I). Histogram color: WT (baseline–black, SP–red, SST–green), Atoh1LacZ/LacZ (baseline–cyan, SP–purple dashed, SST–orange dashed). See Figure 6—figure supplement 1 for traces showing the absence of effect of SP or SST on temporal delay (τ) in Atoh1LacZ/LacZ mice.