FIG. 1.

Respiratory regions in the brain stem and network model schematic. A: parasagittal section (Neutral Red stain) of the mature rat brain stem at the level of nucleus ambiguus (NA), ventral respiratory group (VRG), facial nucleus (7), and pons (5, trigeminal nucleus; 7, facial nucleus; 7n, facial nerve; BötC, Bötzinger complex; cVRG, caudal ventral respiratory group; NA, nucleus ambiguus; pre-BötC, pre-Bötzinger complex; RTN, retrotrapezoid nucleus; rVRG, rostral ventral respiratory group; scp, superior cerebellar peduncle; SO, superior olive). B: schematic of the 4-neuron core model of the brain stem respiratory network considered here. Spheres represent neurons (excitatory: red; inhibitory: blue); green triangles represent 3 sources of tonic excitatory drives (in pons, RTN, and raphé) to different neural populations. Excitatory and inhibitory synaptic connections are indicated by red or green arrows and small blue circles, respectively. See text for details. Vertical dot-dashed lines through both A and B indicate transections that delineate reduced preparations in A and reduced models in B. The “medullary preparation” in A and “medullary” model in B are obtained after transection 1 at the pontine–medullary junction. The pre-BötC preparation in A and pre-BötC model in B are obtained after transection 2 at the rostral boundary of the pre-BötC. Dimensions indicated are typical for a 4- to 5-wk-old rat (after Smith et al. 2007).