Synaptic activation of presynaptic kainate receptors on hippocampal mossy fiber synapses

Kainate receptors (KARs) are a poorly understood family of ionotropic gluta mate receptors. A role for these receptors in the presynaptic control of tr ansmitter release has been proposed but remains controversial. Here, KAR ag onists are shown to enhance fiber excitability, and a number of experiments show that this is a direct effect of KARs on the presynaptic fibers. In ad dition, KAR activation inhibits evoked transmitter release from mossy fiber synapses. Synaptic release of glutamate from either neighboring mossy fibe r synapses or associational/commisural (A/C) synapses results in the activa tion of these presynaptic ionotropic KARs. These results, along with previo us studies, indicate that KARs, through the endogenous release of glutamate , mediate excitatory postsynaptic potentials (EPSPs), alter presynaptic exc itability, and modulate transmitter release.