Visualization of subunit-specific delivery of glutamate receptors to postsynaptic membrane during hippocampal long-term potentiation.

An increase in the number of AMPA-type glutamate receptors (AMPARs) is critical for long-term potentiation (LTP), synaptic plasticity regarded as a basal mechanism of learning and memory. However, when and how each type of AMPAR reaches the postsynaptic membrane remain unclear. We have developed experimental methods to form postsynaptic-like membrane (PSLM) on a glass surface to precisely visualize the location and movement of receptors. We observed fluorescence-labeled AMPAR subunits (GluA1-3) around PSLM with total internal reflection fluorescence microscopy. The increases of GluA1, 2, and 3 in PSLM showed different time courses after LTP induction. GluA1 increased first, and was exocytosed to the periphery of PSLM soon after LTP induction. GluA2 and GluA3 initially decreased, and then increased. Exocytosis of GluA2 and GluA3 occurred primarily in non-PSLM, and later than exocytosis of GluA1. Thus, GluA1-3 appear to increase in the postsynaptic membrane through distinct pathways during LTP.