Postsynaptic action of kynurenic acid in the rat dentate gyrus

Quantal analysis was performed on excitatory postsynaptic potentials (EPSP) recorded with intracellular electrodes from granule cells of the rat dentate gyrus, before, during and after the iontophoretic application of kynurenic acid. In this way a reduction in the EPSP caused by kynurenic acid was shown to be accompanied by an appropriate reduction in quantal size whilst the average number of quanta released per impulse was unchanged. The reduction in quantal size parallelled the reduction in the amplitude of the EPSP and is thus consistent with an action of kynurenic acid at a postsynaptic site. In addition, on a number of cells kynurenic acid reduced the depolarization evoked by L-glutamate by an equivalent amount and it is thus proposed that the synaptic transmitter is glutamate-like.