Simultaneous Expression of Long‐term Depression of NMDA and Long‐term Potentiation of AMPA Receptor‐mediated Synaptic Responses in the CA1 Area of the Kainic Acid‐lesioned Hippocampus

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Abstract
This study investigates the plasticity of the excitatory synapses in an experimental model of epilepsy, the kainic acid‐lesioned rat hippocampus. Stimulation of afferents in the CA1 area of lesioned hippocampi produced an epileptiform burst of action potentials, with an underlying synaptic potential composed of mixed α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA; 80%) and N‐methyl‐D‐aspartate (NMDA; 20%) receptor‐mediated components. Tetanic stimulation yielded a long‐term potentiation (LTP) of the mixed AMPA/NMDA receptor‐mediated population excitatory postsynaptic potentials. However, the same type of tetanus resulted in a long‐term depression (LTD) of pharmacologically isolated NMDA receptor‐mediated responses. This LTD occurred independently of the antagonism of AMPA receptors. This suggests that tetanic stimulation produced LTP of AMPA and LTD of NMDA receptor‐mediated responses simultaneously. Finally, both LTP and LTD were shown to be NMDA dependent. This property has profound functional implications for the control of excitatory networks in temporal lobe epilepsy. This work was supported by the Wellcome Trust and the Fondation Simone et Cino Del Duca.