SPECIFIC [H-3] L-GLUTAMATE BINDING AND [H-3] D-ASPARTATE RELEASE IN THE HIPPOCAMPUS OF RAT AFTER PENTYLENETETRAZOL KINDLING AND LONG-TERM POTENTIATION

In the present study, the time-course of changes in glutamate binding and aspartate release in the rat hippocampus following tetanization of perforant pathway and of pentylenetetrazol-induced kindling was investigated. The K+ (48 mM)-stimulated [H-3]D-aspartate release from hippocampal slices and the specific [H-3]L-glutamate binding to crude synaptic membranes of the hippocampus were measured 1, 4 and 24 h after the last tetanization train or one, five and nine weeks after the last pentylenetetrazol injections, respectively. The tetanization of the fascia dentata was followed by a significant increase in K+-stimulated [H-3]D-aspartate release from hippocampal slices only 1 h after the last tetanization train, but the specific [H-3]L-glutamate binding was enhanced 4 h afterwards. No further deviations from controls have been seen 24 h after tetanization. After pentylenetetrazol kindling, the K+-stimulated amino acid release from hippocampal slices was not changed. However, at one week as well as at five and nine weeks after the pentylenetetrazol kindling the specific [H-3]L-glutamate binding in the hippocampus was significantly increased by about 50% compared to controls. From these findings it can be assumed that after long-term potentiation induction presynaptic transmitter release and post- (and/or pre-)synaptic glutamate binding are elevated with a different time course only in the early phase of potentiation. In contrast, kindling results in a long lasting increase in activity state of glutamatergic transmission. Therefore, it can be concluded that differences of the synaptic excitability following long-term potentiation and kindling are reflected by a different activation of glutamatergic system in the central nervous system.