Figure 8. Proposed respiratory network underlying temporal relationship between inspiratory and expiratory respiratory oscillators.
(A) Putative cervical (preBötC, green circle) and lumbar (RTN/pFRG, magenta square) oscillators contain Dbx1-derived neurons (blue filled circles) and drive expiratory (magenta, abdominals) and inspiratory (green, diaphragm) muscles. The preBötC is asymmetrically coupled to RTN/pFRG neurons via unknown inhibitory interneurons (gray filled circles). Phox2b RTN neurons (purple) provide excitatory drive to both oscillators. Atoh1 RL neurons (orange) excite the RTN/pFRG oscillator. Lines with circles indicate glutamatergic connections. Lines with arrowheads indicate inhibitory GABA/glycine connections. Black lines indicate strong synaptic connections. Dashed lines indicate weak synaptic connections. (B) EYFP-labeled neurons (green) within the BötC area of an Atoh1-Cre;R26 EYFP slice preparation. The recorded neuron was filled with Alexa 568 (magenta) through whole-cell patch dialysis. The merged pseudo-color fluorescence and transmitted light IR-DIC images of the recorded neuron are also shown. (C–F) Current-clamp recordings of BötC Atoh1 neurons (black, top). The corresponding integrated inspiratory activity is shown as ∫XII (bottom, green). The majority of Atoh1 neurons show tonic non-respiratory activity (C–D). (E) Recording of an expiratory Atoh1 neuron (from B) with rhythmic inhibition during inspiration. (F) Inhibitory inspiratory drive reverses with current bias to achieve a baseline membrane potential of −80 mV. Voltage scale bar = 20 mV. (G) Inhibitory inspiratory drive is eliminated with bath application of picrotoxin/strychnine. Scale bar = 1 s. (H–J) Cartoons showing hypothesized network reorganizations (bottom) underlying cervical (green) and lumbar (magenta) bursts (top). (H) Outputs without temporal lag are mediated by weak Atoh1 RL and inhibitory inputs and strong RTN/pFRG and preBötC excitatory coupling. (I) Fictive breaths with temporal delay between cervical and lumbar motor outputs have strong Atoh1 excitation of RTN/pFRG Dbx1 neurons and produce phasic inhibition of preBötC neurons. During the cervical burst, strong preBötC-mediated excitation of inhibitory interneurons leads to silencing of lumbar outputs. (J) Fictive breaths with lumbar inhibition during cervical bursts are due to weak Atoh1 RL neuron output and strong preBötC-mediated excitation of inhibitory interneurons leads to silencing of lumbar outputs. Lines define connectivity as in (A).