Fig. 3. GABA_A receptors mediate hypoxia-induced neuronal depression. (A) When neurones were recorded at rest under normoxic conditions action potentials (APs) (at I), inhibitory postsynaptic potential (IPSPs; at II) and excitatory postsynaptic potential (EPSPs; at III) were observed. (B) Addition of 100 µmol l^-1 bicuculline to the perfusate induced a significant decrease in AP frequency (grey bars; N=7, P=0.003 paired t-test). When neurones underwent a normoxic to hypoxic transition in the presence of 100 µmol l^-1 bicuculline, there was no significant change in AP frequency (white bars; N=6, P=0.235 paired t-test). The hypoxia-mediated decrease in AP frequency is not significantly different from the decrease observed during the normoxic application of bicuculline (black hypoxia bars vs grey normoxia+bicuculline bars; P=0.844 unpaired t-test). Data sets denoted by a white triangle were taken from Fig. 2A for direct visual comparison.