Fig. 6. Effects of GABA_A/glycine antagonist mixture (bicuculline 1.25 µmol l^–1/strychnine 1.5 µmol l^–1) bath application on lung burst frequency under `baseline' and hypoxic conditions. The histograms show lung burst frequency measured at the end of the 10 min hypoxic period in the presence of the antagonist mixture. These experiments were performed on preparations from pre-metamorphic tadpoles (A; grey bars, N=6) and adult bullfrogs (B; black bars, N=6). (C) In adults, these experiments were also performed using low [HCO ^–₃] aCSF (tadpole) (N=4) to determine whether the composition of the aCSF contributes to the effect observed in B. Values are means ± s.e.m. ^*Value statistically different from baseline at P<0.05; values statistically different from corresponding mixture values at P<0.05.