Synaptic activation of kainate receptors on hippocampal interneurons

Although kainate receptor activation has been known to evoke epileptiform activity, little is known about the role of kainate receptors in synaptic transmission. Here we report that kainate (KA) receptors are present on interneurons and, when activated, cause a large increase in the frequency of spontaneous inhibitory postsynaptic currents (IPSCs) driven by action potentials. Stimulation of excitatory afferents generates a pharmacologically identifiable synaptic current mediated by KA receptors in interneurons. This synaptic current is similar to that mediated by AMPA receptors in its response to short stimulus trains, current-voltage relations and coefficient of variation, but it is much smaller in peak amplitude and much slower. KA application also considerably depresses evoked IPSCs. This depression seems to be in large part an indirect consequence of the repetitive firing evoked by the activation of the interneuronal somatic/dendritic KA receptors.