Spike-Driven Glutamate Electrodiffusion Triggers Synaptic Potentiation via a Homer-Dependent mGluR-NMDAR Link

Summary

Electric fields of synaptic currents can influence diffusion of charged neurotransmitters, such as glutamate, in the synaptic cleft. However, this phenomenon has hitherto been detected only through sustained depolarization of large principal neurons, and its adaptive significance remains unknown. Here, we find that in cerebellar synapses formed on electrically compact granule cells, a single postsynaptic action potential can retard escape of glutamate released into the cleft. This retardation boosts activation of perisynaptic group I metabotropic glutamate receptors (mGluRs), which in turn rapidly facilitates local NMDA receptor currents. The underlying mechanism relies on a Homer-containing protein scaffold, but not GPCR- or Ca ²⁺-dependent signaling. Through the mGluR-NMDAR interaction, the coincidence between a postsynaptic spike and glutamate release triggers a lasting enhancement of synaptic transmission that alters the basic integrate-and-spike rule in the circuitry. Our results thus reveal an electrodiffusion-driven synaptic memory mechanism that requires high-precision coincidence detection suitable for high-fidelity circuitries.

Highlights

► A single action potential decelerates diffusion escape of released glutamate ► Slowing down glutamate diffusion enhances activation of perisynaptic group I mGluRs ► Activation of mGluRs boosts local NMDAR currents in a Homer1-dependent manner ► Postsynaptic spike-release pairing induces NMDAR- and mGluR-dependent LTP

Abstract

Sylantyev et al. find that electric fields of postsynaptic spikes retard escape of glutamate from the synaptic cleft thus boosting activation of perisynaptic metabotropic receptors in cerebellar synapses. This leads to enhancement of synaptic NMDA receptor current leading to long-term potentiation of transmission.