Hypoxia-induced increase in sIPSC frequency persists in Ca²⁺-free bath solution.A, Plot of the frequency of sIPSCs as a function of time before, during, and after hypoxia. Each squarerepresents an averaged sIPSC frequency during 5 sec. A dashed line represents an average sIPSC frequency during the prehypoxic period. The effect of hypoxia on sIPSC frequency persists in the presence of 1 μm of TTX (B) and when slices are bathed in nominally Ca²⁺-free solution (C).