Kynurenic acid antagonism of kainate following mossy fibre lesions of rat hippocampus.

Cells in the CA3 region of rat hippocampal slices were approximately five times more sensitive to kainate than CA1 cells. After destruction of mossy fibres the sensitivity of CA3 cells was significantly diminished. Kynurenic acid antagonized the excitation of CA1 neurones by kainate, N-methyl-D-aspartate (NMDA) and quisqualate, but in CA3 of normal slices it blocked responses to NMDA selectively. After colchicine treatment kynurenate blocked responses to kainate and NMDA. The results confirm that the excitatory effect of kainate in CA3 is partly due to a presynaptic action. However they also raise the possibility that postsynaptic and presynaptic kainate receptors are pharmacologically distinguishable, only the former being sensitive to antagonism by kynurenate.