AMPA and NMDA glutamate receptor trafficking: multiple roads for reaching and leaving the synapse.

Glutamate receptor trafficking in and out of synapses is one of the core mechanisms for rapid changes in the number of functional receptors during synaptic plasticity. Recent data have shown that the fast gain and loss of receptors from synaptic sites are accounted for by endocytic/exocytic processes and by their lateral diffusion in the plane of the membrane. These events are interdependent and regulated by neuronal activity and interactions with scaffolding proteins. We review here the main cellular steps for AMPA and NMDA receptor synthesis, traffic within intracellular organelles, membrane exocytosis/endocytosis and surface trafficking. We focus on new findings that shed light on the regulation of receptor cycling events and surface trafficking and the way that this might reshape our thinking about the specific regulation of receptor accumulation at synapses.