Spatiotemporal modeling reveals geometric dependence of AMPAR dynamics on dendritic spine morphology

Abstract

The modification of neural circuits depends on the strengthening and weakening of synaptic connections. Synaptic strength is often correlated to the density of the ionotropic, glutamateric receptors, AMPAR, (-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor) at the postsynaptic density (PSD). While AMPAR density is known to change based on complex biological signaling cascades, the effect of geometric factors such as dendritic spine shape, size, and curvature remain poorly understood. In this work, we developed a deterministic, spatiotemporal model to study the dynamics of AMPAR during long term potentiation (LTP). This model includes a minimal set of biochemical events that represent the upstream signaling events, trafficking of AMPAR to and from the PSD, lateral diffusion in the plane of the spine membrane, and the presence of an extrasynaptic AMPAR pool. Using idealized and realistic spine geometries, we show that the dynamics and increase of bound AMPAR at the PSD depends on a combination of endo- and exocytosis, membrane diffusion, availability of free AMPAR, and intracellular signaling interactions. We also found non-monotonic relationships between spine volume and change in AMPAR at the PSD, suggesting that spines restrict changes in AMPAR to optimize resources and prevent runaway potentiation. Significance StatementSynaptic plasticity involves dynamic biochemical and physical remodeling of small protrusions called dendritic spines along the dendrites of neurons. Proper synaptic functionality within these spines requires changes in receptor number at the synapse, which has implications for down-stream neural functions, such as learning and memory formation. In addition to being signaling subcompartments, spines also have unique morphological features that can play a role in regulating receptor dynamics on the synaptic surface. We have developed a spatiotemporal model that couples biochemical signaling and receptor trafficking modalities in idealized and realistic spine geometries to investigate the role of biochemical and biophysical factors in synaptic plasticity. Using this model, we highlight the importance of spine size and shape in regulating bound AMPAR dynamics that govern synaptic plasticity, and predict how spine shape might act to reset synaptic plasticity as a built-in resource optimization and regulation tool.