Preventing neuronal edema increases network excitability after traumatic brain injury
Punam A. Sawant-Pokam, … , Nick O. McKean, K.C. Brennan
Punam A. Sawant-Pokam, … , Nick O. McKean, K.C. Brennan
Published October 12, 2020
Citation Information: J Clin Invest. 2020;130(11):6005-6020. https://doi.org/10.1172/JCI134793.
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Research Article Neuroscience

Preventing neuronal edema increases network excitability after traumatic brain injury

Abstract

Edema is an important target for clinical intervention after traumatic brain injury (TBI). We used in vivo cellular resolution imaging and electrophysiological recording to examine the ionic mechanisms underlying neuronal edema and their effects on neuronal and network excitability after controlled cortical impact (CCI) in mice. Unexpectedly, we found that neuronal edema 48 hours after CCI was associated with reduced cellular and network excitability, concurrent with an increase in the expression ratio of the cation-chloride cotransporters (CCCs) NKCC1 and KCC2. Treatment with the CCC blocker bumetanide prevented neuronal swelling via a reversal in the NKCC1/KCC2 expression ratio, identifying altered chloride flux as the mechanism of neuronal edema. Importantly, bumetanide treatment was associated with increased neuronal and network excitability after injury, including increased susceptibility to spreading depolarizations (SDs) and seizures, known agents of clinical worsening after TBI. Treatment with mannitol, a first-line edema treatment in clinical practice, was also associated with increased susceptibility to SDs and seizures after CCI, showing that neuronal volume reduction, regardless of mechanism, was associated with an excitability increase. Finally, we observed an increase in excitability when neuronal edema normalized by 1 week after CCI. We conclude that neuronal swelling may exert protective effects against damaging excitability in the aftermath of TBI and that treatment of edema has the potential to reverse these effects.

Authors

Punam A. Sawant-Pokam, Tyler J. Vail, Cameron S. Metcalf, Jamie L. Maguire, Thomas O. McKean, Nick O. McKean, K.C. Brennan

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Figure 8

The osmotic diuretic mannitol reduces neuronal swelling and increases network activity.

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The osmotic diuretic mannitol reduces neuronal swelling and increases ne...
(A) Images of representative neurons in layer 2/3 cortex during treatments. Scale bar: 25 μm. Plot of neuronal cross-sectional area shows that mannitol (Man) (3 g/kg; i.v.) reversed neuronal swelling in CCI-treated mice (P = 0.001, 1-way ANOVA with Bonferroni’s multiple-comparisons test; CCI-mannitol vs. vehicle: **P < 0.01; CCI-vehicle vs. sham-vehicle: **P < 0.01; n = 32–70 neurons, n = 4–5 mice per group). (B) Quantification of SD frequency based on 2-hour recordings in 1 M KCl solution showed a significant increase in SD susceptibility in CCI-mannitol– versus CCI-vehicle–treated animals (P = 0.03, Kruskal-Wallis with Dunn’s multiple-comparisons test; CCI-mannitol vs. vehicle: **P < 0.01; n = 6–10 mice per group). (C) Analysis of network excitability showed a significant increase in the percentage of animals with seizures in the CCI-mannitol–treated group relative to the CCI-vehicle–treated group (CCI-mannitol vs. vehicle: *P = 0.04; CCI-vehicle vs. sham-vehicle: *P = 0.02; χ2 test; n = 7–9 mice per group; the number of mice with seizures and group size are indicated for each group.).