Fig. 4. The effects of CHC and midbrain transection on the acute hypercapnic ventilatory response recorded in vivo. Open symbols represent control (Cont) animals; closed symbols represent chronically hypercapnic (CHC) animals. Circles and squares represent values recorded prior to (intact) and following (transected) in vivo midbrain transection, respectively. (A) Breathing frequency; (B) breaths per episode; (C) episodes per minute; (D) breath amplitude; (E) total ventilation index; (F) breath duration. *Significant difference from the value at [CO₂]=0% within any given group; significant difference between the control and CHC groups; significant difference before and after transection in either group.