Background: Cytotoxic brain edema, marked by astrocyte swelling, develops early after acute ischemic stroke (AIS). While the ischemic core is irreversibly injured, the penumbra remains vulnerable to spreading depolarization (SD), which propagates through viable tissue and exacerbates lesion progression. Swollen astrocytes fail to maintain extracellular ion and glutamate homeostasis, thus facilitating SD initiation and promoting excitotoxicity. Using an acute brain slice model of stroke-related cytotoxic edema, we tested whether inhibiting astrocyte swelling limits SD and glutamate accumulation. Methods: Coronal brain slices (350 µm) from Wistar rats (n=28) were prepared. Cytotoxic edema was achieved by hypo-osmotic stress (NaCl 130→60 mM; HM60), SD was elicited by transient hypoxia (2.5 min). The spatio-temporal characteristics of SD were detected by local field potential and intrinsic optical signal recordings. Extracellular glutamate levels were measured by enzymatic biosensors. To counteract astrocyte swelling Bumetanide (Bum; 1 mM), TGN-020 (100 µM), and DCPIB (20 µM) were applied to inhibit sodium potassium chloride cotransporter 1 (NKCC1), aquaporin-4 (AQP4) and volume regulated anion channels (VRAC). Results: In HM60 the SD area affected nearly the entire cortex (82.5±11.5%) which was reduced by DCPIB and TGN-020+Bum treatments (45.1±11.6 and 44.8±13.2%). Surprisingly, despite limiting spatial spread, both treatments increased SD propagation velocity compared to HM60 (5.8±1.5 vs. 5.1±1.5 vs. 3.7±1.2 mm/min; DCPIB vs.TGN-020+Bum vs. HM60). SDs in HM60 were accompanied by a glutamate peak of 61.7±14.2 µM, which remained elevated during recovery (22±10 µM). DCPIB and TGN-020+Bum reduced the glutamate peak (25.4±6.6 and 21.7±7 µM), the post-SD glutamate accumulation (9.9±4.1 and 8.7±2.8 µM) and shortened the SD plateau (68±44 vs. 111.5±52.3 vs. 176.7±57.6 s; DCPIB vs.TGN-020+Bum vs. HM60), thereby reducing the overall duration of SD. Conclusion: Our results indicate that astrocyte swelling enhances SD propagation and glutamate excitotoxicity in a stroke-related cytotoxic edema model. Pharmacological inhibition of astrocyte swelling may help limit secondary injury and slow lesion progression during the acute phase of ischemic stroke.
Frank et al. (Thu,) studied this question.