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 3

Reduced network activity and APs in somatosensory cortex 48 hours after CCI.

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Reduced network activity and APs in somatosensory cortex 48 hours after ...
(A) Schematics of intracellular current-clamp recordings measuring up states (subthreshold local network events) and APs. (B) Representative traces of spontaneous membrane potential fluctuations from layer 2/3 pyramidal neurons. Scale bar: 10 mV, 1 second. Average up state IEI box-and-whisker plot showing no difference in frequency after injury (P > 0.05, 2-sided, unpaired t test; n = 12 neurons, n = 8–10 mice per group). (C) Plot of the mean AUC of up states showing a smaller area in the neurons of mice that underwent CCI (**P = 0.007, 2-sided, unpaired t test; n = 12 neurons, n = 8–10 mice per group). (D) Traces of AP firing. Scale bar: 20 mV, 10 seconds. Box-and-whisker plot shows a lower frequency of spontaneous APs in the neurons of CCI-treated mice (*P = 0.01, 2-sided Mann-Whitney U test; n = 4–5 neurons, n = 4–5 mice per group). (E) Schematic of the experimental design for in vivo whole-cell sensory stimulation experiments. Evoked activity was recorded in layer 2/3 of the somatosensory cortex (hind limb area). Thal., thalamus. (F) Typical traces of subthreshold responses evoked by contralateral hind paw stimulation at the RMP. Scale bar: 10 mV, 0.5 seconds. The population subthreshold voltage response is plotted as a function of the stimulus number (P < 0.0001, 2-way ANOVA; n = 6–9 neurons, n = 6–8 mice per group). We observed a decrease in amplitude for all responses in CCI neurons during a 5 Hz, 2 second train of hind paw stimuli. The plot on the right shows a response to first sensory stimuli in neurons of CCI-treated mice (**P = 0.003, unpaired t test; n = 6–9 neurons, n = 6–8 mice per group).