Atypical plume-like events contribute to glutamate accumulation in metabolic stress conditions

Summary

Neural glutamate homeostasis is important for health and disease. Ischemic conditions, like stroke, cause imbalances in glutamate release and uptake due to energy depletion and depolarization. We here used the glutamate sensor SF-iGluSnFR(A184V) to probe how chemical ischemia affects the extracellular glutamate dynamics in slice cultures from mouse cortex. SF-iGluSnFR imaging showed spontaneous glutamate release indicating synchronous network activity, similar to calcium imaging with GCaMP6f. Glutamate imaging further revealed local, atypically large, and long-lasting plume-like release events. Plumes occurred with low frequency, independent of network activity, and persisted in tetrodotoxin (TTX). Blocking glutamate uptake with TFB-TBOA favored plumes, whereas blocking ionotropic glutamate receptors (iGluRs) suppressed plumes. During chemical ischemia plumes became more pronounced, overly abundant and contributed to large-scale glutamate accumulation. Similar plumes were previously observed in cortical spreading depression and migraine models, and they may thus be a more general consequence of glutamate uptake dysfunctions in neurological and neurodegenerative diseases.

Graphical abstract

Highlights

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  SF-iGluSnFR imaging shows plume-like glutamate release in cultured brain slices

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  Plumes are TTX-insensitive and occur independently of neuronal network activity

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  Plumes are favored by impaired glutamate uptake and suppressed by iGluR inhibition

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  Plumes persist and contribute to glutamate accumulation during chemical ischemia

Abstract

Small molecule; Molecular network; Molecular neuroscience; Specialized functions of cells