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

M V Storozhuk,D Piomelli,S Y Ivanova

doi:10.1007/s11055-006-0077-x

Abstract

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.

Highlights

Title Presence of depolarization-induced suppression of inhibition in a fraction of GABAergic synaptic connections in rat neocortical cultures
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)
The suppression of IPSC amplitude lasted for ~70 seconds and was accompanied by changes of paired-pulse ratio and IPSC coefficient of variation (CV), which is suggestive of a presynaptic mechanism

Summary

Introduction

Title Presence of depolarization-induced suppression of inhibition in a fraction of GABAergic synaptic connections in rat neocortical cultures. The suppression of IPSC amplitude lasted for ~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. Postsynaptic spike firing or brief depolarization of the membrane of postsynaptic neuron results in a transient suppression of GABAergic synaptic transmission This phenomenon termed “depolarization-induced suppression of inhibition” (DSI), was California, USA. Recent studies have revealed that endocannabinoid substances play a key role in DSI These lipid mediators may be released from postsynaptic neurons and, travelling backward across synapses, activate CB1 receptors on axon terminals and suppress GABA release [6, 13, 23, 24]. We used cultures of neocortical neurons, a preparation which allowed us to study relatively responses evoked by the stimulation of a single presynaptic neuron

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