Presence of depolarization-induced suppression of inhibition in a fraction of GABAergic synaptic connections in rat neocortical cultures.

Brief depolarization of postsynaptic neurons in hippocampus and cerebellum results in a transient depression of GABAergic inhibitory input, called "depolarization-induced suppression of inhibition" (DSI). We studied whether a similar phenomenon occurs in the rat neocortical neurons. Using patch-clamp technique in neocortical cell cultures, we examined the effects of a 5-second depolarization of postsynaptic neurons on evoked GABAergic inhibitory post-synaptic currents (IPSCs). We found that the depolarization evoked a suppression of IPSC amplitude in 6 out of 26 neuronal pairs tested. The suppression of IPSC amplitude lasted for approximately 70 seconds and was accompanied by changes of paired-pulse ratio and IPSC coefficient of variation (CV), which is suggestive of a presynaptic mechanism. These results are in agreement with previous observations in hippocampal cell cultures and suggest that neocortical neurons express DSI.