Astrocytic calcium release mediates peri-infarct depolarizations in a rodent stroke model
Cordula Rakers, Gabor C. Petzold
Cordula Rakers, Gabor C. Petzold
Published December 19, 2016
Citation Information: J Clin Invest. 2017;127(2):511-516. https://doi.org/10.1172/JCI89354.
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Brief Report Neuroscience

Astrocytic calcium release mediates peri-infarct depolarizations in a rodent stroke model

Abstract

Stroke is one of the most common diseases and a leading cause of death and disability. Cessation of cerebral blood flow (CBF) leads to cell death in the infarct core, but tissue surrounding the core has the potential to recover if local reductions in CBF are restored. In these areas, detrimental peri-infarct depolarizations (PIDs) contribute to secondary infarct growth and negatively affect stroke outcome. However, the cellular pathways underlying PIDs have remained unclear. Here, we have used in vivo multiphoton microscopy, laser speckle imaging of CBF, and electrophysiological recordings in a mouse model of focal ischemia to demonstrate that PIDs are associated with a strong increase of intracellular calcium in astrocytes and neurons. We found that astroglial calcium elevations during PIDs are mediated by inositol triphosphate receptor type 2–dependent (IP3R2-dependent) release from internal stores. Importantly, Ip3r2-deficient mice displayed a reduction of PID frequency and overall PID burden and showed increased neuronal survival after stroke. These effects were not related to local CBF changes in response to PIDs. However, we showed that the release and extracellular accumulation of glutamate during PIDs is strongly curtailed in Ip3r2-deficient mice, resulting in ameliorated calcium overload in neurons and astrocytes. Together, these data implicate astroglial calcium pathways as potential targets for stroke therapy.

Authors

Cordula Rakers, Gabor C. Petzold

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Figure 3

Astroglial IP3R2–mediated signaling contributes to glutamate kinetics during PIDs.

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Astroglial IP3R2–mediated signaling contributes to glutamate kinetics du...
(A) An average intensity projection of peri-infarct cortex showed specific and sufficient iGluSnFR expression in cortical astrocytes. The vasculature was visualized with Texas Red (TR) dextran. Scale bar: 50 μm. (B) There was a strong reduction of the duration of glutamate transients that was mostly caused by an attenuation of the second (sustained) phase of glutamate increase, indicated by a significantly shortened peak-to-baseline time and full duration at half-maximum (FDHM) (n = 48 cells from 9 Ip3r2–/– mice; n = 70 cells from 10 control mice). (C–E) Simultaneous imaging of glutamate (iGluSnFR) and calcium (Cal-590) in individual astrocytes (arrows) showed that the initial glutamate rise preceded the astroglial calcium transient, but that this calcium transient coincided with the secondary glutamate increase (n = 25 astrocytes from 5 Ip3r2–/– mice; n = 28 astrocytes from 5 control mice). Ip3r2–/– mice showed a shortened glutamate signal and an attenuated calcium rise. Δt, time difference. (F) Spearman’s rank correlation (ρ) between glutamate and calcium signal durations (FDHM) in overlapping ROIs (yellow lines represent linear regression). (G–I) Inhibition of mGluR groups I and II by MPEP/LY341495 (100 μM and 50 μM, respectively) left the glutamate rise time unchanged, but resulted in significantly shorter FDHM and smaller astroglial calcium amplitudes (n = 28 cells from 4 mice vs. n = 25 cells from 4 mice). P values in B, E, and G–I were determined by Mann-Whitney U test.