INCREASED NEURONAL EXCITABILITY DURING DEPOLARIZATION-INDUCED SUPPRESSION OF INHIBITION IN RAT HIPPOCAMPUS

1. Depolarization-induced suppression of inhibition (DSI) is a form of plasticity of gamma-aminobutyric acid (GABA(A))-mediated (henceforth 'GABAergic') responses in the CNS. We made whole-cell recordings from CA1 pyramidal neurons to investigate the effects of DSI on excitatory synaptic transmission in the hippocampal slice preparation. 2. Signifi cant enhancement of the voltage-clamped excitatory postsynaptic curren t (EPSC) occurs during DSI of the temporally overlapping inhibitory po stsynaptic current. Viiith high levels of calcium chelators in the pip ette solution, or bath application of bicuculline, EPSC enhancement is blocked, suggesting that it results from DSI and that the DSI process selectively affects GABAergic, but not glutamatergic, transmission. 3 . The probability of synaptically evoked action potential firing is in creased during DSI under current clamp. DSI could influence other exci tatory phenomena as well.