Single molecule tracking of AMPA receptors shows the role of synaptic insertion during maintenance of chemical LTP

Abstract

Long term potentiation (LTP) likely contributes to memory formation. Early expression of LTP involves insertion of AMPA receptors (AMPARs) to the extrasynaptic membrane followed by their lateral diffusion into the synaptic membrane. However, whether a similar mechanism mediates the maintenance of LTP is unclear. Using single-molecule microscopy, we quantified that 6 GluA1- and 11 GluA2-containing endogenous AMPARs were added per synapse in cultured hippocampal neurons at 20 min following chemical LTP (cLTP) induction for 10 min, resulting in a 54% increase for both subunits. Single molecular tracking of transfected subunits revealed that the number of exocytosed subunits at the synapse increased by 15-18% from 5 to 20 min following cLTP induction, but their lateral exchange between synaptic and extrasynaptic membranes was minimal. These findings suggest that cLTP maintenance is contributed largely by synaptic insertion of AMPARs rather than the surface diffusion of exocytosed AMPARs from extrasynaptic to synaptic regions.

Fluorescence-Based Detection of Proteins and Their Interactions in Live Cells

“…While an increase in the number and conductance of postsynaptic AMPARs has been shown to mediate the expression of LTP, it is unclear how AMPARs are trafficked to the synapse during the early and maintenance phases of LTP. Jin et al 4 conducted a study to investigate the molecular mechanism underlying the expression and maintenance of LTP in the central nervous system. They used singlemolecule tracking with high localization resolution to quantitatively measure the numbers, percentages, and movements of synaptic AMPARs during both the early (0−10 min after induction of LTP) and maintenance phases (10−20 min) of LTP in living hippocampal cultured neurons at the singlesynapse and single-molecule level.…”

“…Recently, a modified version of the FIONA technique has been applied to investigate the trafficking of AMPARs during the early and maintenance phases of long-term potentiation (LTP) in living hippocampal cultured neurons. 4 Long-term potentiation (LTP) is a critical biological phenomenon which refers to the long-lasting strengthening of synaptic connections between neurons that occurs as a result of repeated stimulation and is thought to be a critical cellular mechanism underlying learning and memory in the brain. While an increase in the number and conductance of postsynaptic AMPARs has been shown to mediate the expression of LTP, it is unclear how AMPARs are trafficked to the synapse during the early and maintenance phases of LTP.…”