Pathways of AMPA receptor trafficking. AMPA receptors may cycle between intracellular stores and the cell surface rapidly and constitutively. AMPA receptors in plasma membrane may exchange between the extra-synaptic and synaptic membrane in a manner of lateral diffusion. The receptor-cycling event and lateral diffusion can regulate the number of AMPA receptors in synapses and further changes the synapse strength. PSD, post-synaptic density.