TrkB agonists prevent postischemic emergence of refractory neonatal seizures in mice
Pavel A. Kipnis, Brennan J. Sullivan, Brandon M. Carter, Shilpa D. Kadam
Pavel A. Kipnis, Brennan J. Sullivan, Brandon M. Carter, Shilpa D. Kadam
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Research Article Development Neuroscience

TrkB agonists prevent postischemic emergence of refractory neonatal seizures in mice

Abstract

Refractory neonatal seizures do not respond to first-line antiseizure medications like phenobarbital (PB), a positive allosteric modulator for GABAA receptors. GABAA receptor–mediated inhibition is dependent upon electroneutral cation-chloride transporter KCC2, which mediates neuronal chloride extrusion and its age-dependent increase and postnatally shifts GABAergic signaling from depolarizing to hyperpolarizing. Brain-derived neurotropic factor–tyrosine receptor kinase B activation (BDNF–TrkB activation) after excitotoxic injury recruits downstream targets like PLCγ1, leading to KCC2 hypofunction. Here, the antiseizure efficacy of TrkB agonists LM22A-4, HIOC, and deoxygedunin (DG) on PB-refractory seizures and postischemic TrkB pathway activation was investigated in a mouse model (CD-1, P7) of refractory neonatal seizures. LM, a BDNF loop II mimetic, rescued PB-refractory seizures in a sexually dimorphic manner. Efficacy was associated with a substantial reduction in the postischemic phosphorylation of TrkB at Y816, a site known to mediate postischemic KCC2 hypofunction via PLCγ1 activation. LM rescued ischemia-induced phospho–KCC2-S940 dephosphorylation, preserving its membrane stability. Full TrkB agonists HIOC and DG similarly rescued PB refractoriness. Chemogenetic inactivation of TrkB substantially reduced postischemic neonatal seizure burdens at P7. Sex differences identified in developmental expression profiles of TrkB and KCC2 may underlie the sexually dimorphic efficacy of LM. These results support a potentially novel role for the TrkB receptor in the emergence of age-dependent refractory neonatal seizures.

Authors

Pavel A. Kipnis, Brennan J. Sullivan, Brandon M. Carter, Shilpa D. Kadam

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Figure 2

LM efficacy was sexually dimorphic and driven by significant reduction of ictal events, but not ictal durations, at both P7 and P10.

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LM efficacy was sexually dimorphic and driven by significant reduction o...
(A) EEG seizure burdens for ligate+PB–, post-LM0.25–, and pre-LM0.25–treated P7 pups. *P < 0.05 (second post-LM vs. first post-LM); ****P < 0.0001 (second pre-LM vs. first pre-LM) by 2-way ANOVA. (B) EEG seizure burdens for ligate+PB–, post-LM–, and pre-LM–treated P10 pups. ***P < 0.001 (second ligate+PB vs. first ligate+PB, and second post-LM vs. first post-LM); ****P < 0.0001 (second pre-LM vs. first pre-LM) by 2-way ANOVA. The @ indicates differences between P7 and P10; @@P < 0.01 by 2-tailed t test. (C) EEG ictal events for ligate+PB–, post-LM–, and pre-LM–treated P7 pups. **P < 0.001 (second ligate+PB vs. first ligate+PB, and second post-LM vs. first post-LM); ****P < 0.0001 (second pre-LM vs. first pre-LM) by 2-way ANOVA. (D) EEG ictal events for ligate+PB–, post-LM–, and pre-LM–treated P10 pups. ***P < 0.001 (second ligate+PB vs. first ligate+PB), ****P < 0.0001 (second post-LM vs. first post-LM, and second pre-LM vs. first pre-LM) by 2-way ANOVA. (E) EEG mean ictal durations for ligate+PB–, post-LM–, and pre-LM–treated P7 pups. *P < 0.05 (second ligate+PB vs. first ligate+PB) by 2-way ANOVA. (F) EEG mean ictal durations for ligate+PB–, post-LM–, and pre-LM–treated P10 pups. @@P < 0.01 by 2-tailed t test. (G) EEG seizure burdens by sex for ligate+PB–, post-LM–, and pre-LM–treated P7 pups. *P < 0.05 (second female post-LM vs. first female post-LM, and second male pre-LM vs. first male pre-LM); **P < 0.01 (second female pre-LM vs. first female pre-LM) by 2-way ANOVA. (H) EEG seizure burdens by sex for ligate+PB–, post-LM–, and pre-LM–treated P10 pups. *P < 0.05 (second male ligate+PB vs. first male ligate+PB, second female post-LM vs. first female post-LM, and second male pre-LM vs. first male pre-LM); ****P < 0.0001 (second female pre-LM vs. first female pre-LM) by 2-way ANOVA; @P < 0.05 by 2-tailed t test. (I) EEG ictal events by sex for ligate+PB–, post-LM–, and pre-LM–treated P7 and (J) P10 pups. (K) EEG mean ictal durations by sex for ligate+PB–, post-LM–, and pre-LM–treated P7 and (L) P10 pups. Number of P7 mice: n = 28 [16/12] (ligate+PB [M/F]), 26 [14/12] (post-LM), 27 [14/13] (pre-LM). Number of P10 mice: n = 11 [6/5] (ligate+PB), 13[6/7] (post-LM), 11 [5/6] (pre-LM). Box-and-whisker plots show quartiles with median with minima and maxima at the bottom and top whiskers, respectively.