Synaptic enhancement induced by NMDA and Qp receptors and presynaptic activity

Activity-dependent changes in synaptic efficacy may underlie the acquisition of memory. Much interest has centred on the involvement of NMDA (N-methyl-D-aspartate) receptors in the induction of long-term potentiation (LTP), but since activation of this receptor alone results only in short-term enhancement, other receptors are clearly involved. This paper describes a novel form of lasting synaptic enhancement requiring concomitant activation of both NMDA and metabotropic quisqualate, or Qp receptors for induction. Neither high frequency presynaptic activity, co-activation of many presynaptic axons, postsynaptic depolarization, nor blockade of inhibition were required. However, repetitive, though relatively low frequency activity of the presynaptic axon appeared to be necessary. We suggest, tentatively, that presynaptic activity may be directly involved in priming the recently active terminal to respond to postsynaptic changes.