Hypoxia enhances miniature, Ca²⁺-independent, TTX-insensitive excitatory synaptic release. A, Plot of the frequency of sEPSCs as a function of time before, during, and after hypoxia. Eachsquare represents an averaged sEPSC frequency during 5 sec. A dashed line represents an average sEPSC frequency during the prehypoxic period. The effect of hypoxia on sEPSC frequency persists in the presence of 1 mm TTX (B) and when slices are bathed in nominally Ca²⁺-free solution (C).