Hypoxia causes a rapid transient increase in the frequency of spontaneous EPSPs. A, A whole-cell current-clamp recording of sEPSPs from a representative layer 5 neuron under normoxic conditions. The cell was dialyzed with K gluconate-based solution (E_Cl = −70 mV) and held at voltage of approximately −70 mV with an injection of a small depolarizing current. B, Hypoxia within seconds markedly increases the frequency of spontaneous EPSPs. C, Starting from the second minute of hypoxia, the high-amplitude sEPSPs disappear; the frequency of the rest of the spontaneous events additionally increases. Note that the sEPSP amplitudes become progressively smaller, in parallel with decrease in neuronal input resistance. D, From the third minute of hypoxia, the sEPSPs become completely unresolvable from the noise.