In a neuron dialyzed with Cs⁺ions, hypoxia causes a rapid and monotonic increase in sEPSC frequency.A, Voltage-clamp traces obtained with a Cs gluconate-containing pipette from a representative layer 5 neuron held at −70 mV under normoxic conditions. B, Thirty seconds after the onset of hypoxia, the frequency of sEPSCs increases; high-amplitude events are seen frequently. C, At the third minute of hypoxia, the high-amplitude sEPSCs disappear; the frequency of the rest of the spontaneous events additionally increases. Note that dialyzing neurons with Cs⁺ ions prevents a hypoxia-induced decrease in input resistance. Inset, A 100 msec segment of the record at an extended time scale to show the individual, superimposed sEPSCs. D, Reoxygenation rapidly suppresses the frequency of sEPSCs beyond the prehypoxic value.