Kainate receptor activation enhances both tonic and phasic GABA-ergic inhibition in CA1 hippocampal interneurons

Kainate receptor agonists are powerful convulsants and excitotoxins. It has been a lot of controversy around functions of these receptors in the brain. It is shown in this article that kainate enhances evoked GABAergic IPSC (phasic currents) in CA1 interneurons in concentration-dependent manner. The phenomenon is likely to be due to kainate-mediated lowering of the threshold for action potential generation in interneuron axons and increased number of terminals responding to the same stimulus strength. Kainate application also induced an enhancement in tonic GABAergic conductance. This phenomenon can be attributed to massive extracellular GABA accumulation caused by interneuron firing in the presence of kainate. Extracellular GABA also shunts synaptic currents by activating tonic conductance as well as desensitizing synaptic GABAA receptors. Thus, the enhancement of the evoked IPSCs by 1 microM kainate was complicated by early and transient decrease. The kainate receptor-mediated enhancement of GABAergic tonic and phasic signalling to interneurons can contribute to the depression of GABAergic transmission to pyramidal neurons. The consequence of this phenomenon may play a major role in the epileptogenic action of this agent.