Heterosynaptic expression of depolarization-induced suppression of inhibition (DSI) in rat hippocampal cultures

Depolarization-induced suppression of inhibition (DSI) is a transient suppr ession of the inhibitory synaptic transmission, observed in the hippocampus and the cerebellum, upon postsynaptic depolarization. Using rat hippocampa l cultures, we examined whether DSI is confined to the inhibitory synapses on the depolarized neuron or, if DSI can spread to those on neighboring non -depolarized neurons. Whole-cell recordings were performed in 108 neuronal pairs with the following synaptic responses. Stimulation of one neuron evok ed the inhibitory autaptic currents (IACs) recurrently in that neuron and a lso elicited the inhibitory postsynaptic currents (IPSCs) orthodromically i n the other neuron. In 38 of 108 pairs, the postsynaptic depolarization cau sed transient suppression of IPSCs (homosynaptic DSI). In 11 of the 38 pair s exhibiting the homosynaptic DSI, the depolarization also induced suppress ion of IACs (heterosynaptic DSI). The heterospnaptic DSI, like the homosyna ptic DSI, depended on depolarizing pulse duration and was blocked by a phor bol eater. These results suggest that DSI can spread to the synapses on a n eighboring non-depolarized neuron in rat hippocampal cultures. (C) 2000 Els evier Science Ireland Ltd. All rights reserved.