Tetanus-induced asynchronous GABA release in cultured hippocampal neurons.

Asynchronous GABA release was studied in cultured hippocampal neurons using paired whole-cell recordings. Tetanization of the presynaptic GABAergic neuron was accompanied by a train of IPSCs which showed tetanic depression. Asynchronous IPSCs (asIPSCs) also developed during the train and continued for 1.85+/-0.3 s after the stimulation. The threshold frequency for evoking asIPSCs was 10 Hz, while maximal asynchronous activity was achieved at 40 Hz. Perfusion with EGTA-AM blocked asIPSCs. The elevation of Ca(2+) that accompanies presynaptic action potential firing triggers asynchronous release of GABA vesicles, thereby counteracting tetanic depression of synchronous IPSCs.