Quisqualate and N-methyl-d-aspartate (NMDA) receptors in induction of hippocampal long-term facilitation using conditioning solution

Brief electrical high-frequency stimulation (tetanus) via the synapses induces long-term potentiation (LTP) in hippocampal neurons. In order to elucidate how LTP is produced, we attempted to induce long-term facilitation (LTF) by perfusing a conditioning solution (CS) instead of the tetanus. A 5 min perfusion of hippocampal slices with a CS containing glutamate, K⁺ at high concentration and no Mg²⁺ resulted in the generation of LTF in CA1 and dentate neurons. CS lacking one of these 3 factors failed to produce LTF. When the glutamate of the CS was substituted by both quisqualate and N-methyl-d-aspartate (NMDA), LTF was initiated. This indicates that both quisqualate and NMDA receptors play an important role in the induction of LTP.