Long-term potentiation and long-term depression (LTP/LTD) can be elicited by activating N-methyl-D-aspartate (NMDA)-type glutamate receptors, typically by the coincident activity of pre-and postsynaptic neurons. The early phases of expression are mediated by a redistribution of AMPA-type glutamate receptors: More receptors are added to potentiate the synapse or receptors are removed to weaken synapses. With time, structural changes become apparent, which in general require the synthesis of new proteins. The investigation of the molecular and cellular mechanisms underlying these forms of synaptic plasticity has received much attention, because NMDA receptor-dependent LTP and LTD may constitute cellular substrates of learning and memory.L ong-term synaptic plasticity is a generic term that applies to a long-lasting experience-dependent change in the efficacy of synaptic transmission. Here we will focus on N-methyl-D-aspartate (NMDA) receptor-dependent synaptic potentiation (LTP) and depression (LTD), two forms of activity-dependent long-term changes in synaptic efficacy that have been extensively studied. Because both LTP and LTD are believed to represent cellular correlates of learning and memory, they have attracted considerable interest. In this article we will focus on the molecular and cellular mechanisms associated with LTP and LTD. As for other forms of long-term synaptic plasticity, a characterization of LTP and LTD involves describing the molecular mechanisms that are required to elicit the change (induction), followed by an investigation of the mechanism of expression (hours) and maintenance (days). The best-characterized form of NMDA receptor (NMDAR)-dependent LTP occurs between CA3 and CA1 pyramidal neurons of the hippocampus (Fig. 1). Throughout the chapter we will mostly refer to this specific form of LTP. At these CA3-CA1 Schaffer collateral synapses, the loci of both induction and expression are situated in the postsynaptic neuron.
AMPA-TYPE AND NMDA-TYPE GLUTAMATE RECEPTORSAfter exocytotic release of the content of the synaptic vesicle from the presynaptic specialization (see Castillo 2012), the neurotransmitter