Fig. 5. (A,B) Breathing frequency (breaths min^-1), (C,D) integrated breath area (Vxs) and (E,F) total ventilation index (Vxs min^-1) as a function of the inspired CO₂ level recorded in vivo from control (A,C,E) and CHC (B,D,F) toads. Open circles (A,C,E) and open squares (B,D,F) represent animals with the olfactory nerves intact (OI). Filled circles (A,C,E) and filled squares (B,D,F) represent animals that underwent olfactory denervation (OD) prior to the 10-day period of CHC (or control conditions). The data are plotted as the mean ± 1 s.e.m. Letters (a-c) represent significant differences at the different inspired CO₂ levels within any group. A number sign (#) represents a difference between the OI and OD groups. A plus sign (+) represents a difference between the control and CHC groups (comparing panel A with B, C with D and E with F).