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These spreading depolarization waves are induced by ionic imbalances in the wake of ischemia ().Because they impose an additional metabolic burden on the already compromised tissue, PIDs accelerate neurodegeneration and infarct core expansion in experimental models and clinical cases, essentially abrogating the “window of opportunity” for therapeutic interventions in the penumbra ().As previously reported ( (A and B) OGB-1 AM was injected into peri-infact cortex, and mice expressing ECFP under the Cx43 promoter were imaged using multiphoton microscopy. (C and D) The calcium amplitude in astrocytes from Cx43-ECFP Ip3r2 mice compared with controls, while the velocity remained unaltered (n = 104 cells from 5 mice vs. (G–I) High temporal and spatial resolution imaging of astrocytes (identified by ECFP expression) and neurons during PIDs showed that astrocytes lagged behind neighboring neurons by 1.29 ± 0.7 seconds in Cx43-ECFP Ip3r2 mice). Tukey’s box-and-whisker plots indicate the median (line), mean (circle), IQR (box), and 1.5 IQR (whiskers) in all figures.PIDs were identified by typical propagation of cellular calcium transients in neurons (n1–n4) and astrocytes (a1–a4; identified by their ECFP expression). All P values were determined by Mann-Whitney U test.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. 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.
Following p MCAO, we detected repetitive PIDs in the imaging region (Figure 1, A and B).However, the likelihood of neuronal survival and, hence, the chances for an acceptable clinical outcome strongly decline when metabolic demand in the penumbra exceeds the available energy resources.The most prominent example of this scenario is the occurrence of peri-infarct depolarizations (PIDs).However, if and how astrocytes contribute to the development of PIDs and whether there is an interplay between astrocytic calcium and glutamate accumulation have remained unknown.
Here, we show that IP3-mediated calcium release from internal stores in astrocytes not only mediates the majority of astroglial calcium changes during PIDs, but also has profound consequences for glutamate accumulation, neuronal calcium overload, PID burden and frequency, as well as neuronal survival and final infarct volume.Our data suggest that modulation of astroglial calcium pathways may represent a novel therapeutic target for further preclinical trials and potentially for stroke therapy.