Neurotransmission occurs at synapses, specialized points of contact between presynaptic nerve terminals and postsynaptic neurons. At excitatory synapses, receptors and downstream signaling enzymes are clustered in the postsynaptic density (PSD), a cytoskeletal web beneath the plasma membrane. Transmission at these excitatory synapses is mediated primarily by glutamate acting on two classes of ligand-gated ion channels: AMPA receptors and NMDA receptors. The AMPA receptors are involved in moment-to-moment signaling, whereas NMDA receptors play an important role in initiating synaptic plasticity.
Recent cell biological analyses have emphasized remarkable differences in regulation of the synaptic expression of these two classes of receptors (Malenka and Nicoll 1999; Malinow et al. 2000). NMDA receptors are stable components of the PSD, whereas AMPA receptors cycle on and off the synaptic membrane in a manner that is tightly controlled by neuronal activity (...
