Fig. 4. Rate-meter recording (100 ms/bin) of the responses of the neuron shown in  figure 1 to increasing doses of the γ-aminobutyric acid type A antagonist bicuculline at 0 and 1 minimum alveolar concentration (MAC) sevoflurane. When the increase in peak neuronal frequency had reached a plateau, the bicuculline dose rate was increased at least one more time to ascertain that the bicuculline effect was saturated,  i.e. , that all γ-aminobutyric acid type A receptors were blocked. This frequency represents the overall excitatory drive (F^e) to the neuron. Stated are the maximal dose rates for bicuculline that were applied, while a maximal increase in neuronal discharge frequency was already achieved with much smaller dose rates. F^con= neuronal control frequency.