Impaired State-Dependent Potentiation of GABAergic Synaptic Currents Triggers Seizures in a Genetic Generalized Epilepsy Model

Abstract

Epileptic activity in genetic generalized epilepsy (GGE) patients preferentially appears during sleep and its mechanism remains unknown. Here, we found that sleep-like slow-wave oscillations (0.5 Hz SWOs) potentiated excitatory and inhibitory synaptic currents in layer V cortical pyramidal neurons from wild-type (wt) mouse brain slices. In contrast, SWOs potentiated excitatory, but not inhibitory, currents in cortical neurons from a heterozygous (het) knock-in (KI) Gabrg2+Q/390X model of Dravet epilepsy syndrome. This created an imbalance between evoked excitatory and inhibitory currents to effectively prompt neuronal action potential firings. Similarly, physiologically similar up-/down-state induction (present during slow-wave sleep) in cortical neurons also potentiated excitatory synaptic currents within brain slices from wt and het KI mice. Moreover, this state-dependent potentiation of excitatory synaptic currents entailed some signaling pathways of homeostatic synaptic plasticity. Consequently, in het KI mice, in vivo SWO induction (using optogenetic methods) triggered generalized epileptic spike-wave discharges (SWDs), being accompanied by sudden immobility, facial myoclonus, and vibrissa twitching. In contrast, in wt littermates, SWO induction did not cause epileptic SWDs and motor behaviors. To our knowledge, this is the first mechanism to explain why epileptic SWDs preferentially happen during non rapid eye-movement sleep and quiet-wakefulness in human GGE patients.

Sleep slow-wave oscillations trigger seizures in a genetic epilepsy model of Dravet syndrome

“…This is compatible with that DEAB injections (i.p.) (Chen et al, 2014;Zhang et al, 2021) only suppresses 70% of seizure incidence in het Gabrg2 +/Q390X KI mice. However, this SWOrelated mechanism might determine the seizure duration for status epilepiticus evolution (see Fig.…”

“…Sterile mouse surgery and EEG/multi-unit recordings in vivo With all procedures in accordance to guidelines set by the institutional animal care and use committee of Vanderbilt University Medical Center (VUMC), mouse EEG surgery was performed as our previous methods (Zhang et al, 2021). Briefly, both wt littermates and het Gabrg2 +/Q390X KI mice [by crossing het KI mice with mice #012334 from The Jackson Laboratory to express halorhodopsin (NpHR) protein in neurons (Gradinaru et al, 2008;Zhao et al, 2008)] underwent brain surgery (anesthesia 1-3% isoflurane (vol/vol)) to implant three EEG screw electrodes (each for one hemisphere and one for grounding over cerebellum, Pinnacle Technology, #8201), one concentric bipolar tungsten electrode in somatosensory cortex (S1 cortex, depth 0.8~1 mm in laminar V) and one fiber optic cannula (0.2-0.4 mm diameter, Thorlabs Inc., Newton, New Jersey) for laser light delivery in vivo (brain atlas coordinates: within somatosensory cortex range, anterior-posterior between -1.82 and -0.46 mm, midline-lateral between +2.0 and +4.0 mm reference to bregma, dorsal-ventral 0.7-1.1 mm reference to pia surface).…”

“…Based on our previous study ex vivo (Zhang et al, 2021), 4-(diethylamino)-benzaldehyde (DEAB, blocking retinoid acid synthesis) (Chen et al, 2014) was used as a drug to suppress SWO-induced homeostatic synaptic potentiation of excitatory currents in neurons in vivo. The DEAB was dissolved in DMSO/saline and injected (i.p.)…”

“…Currently, seizure onset mechanisms during sleep period still remain unknown. Our previous work has shown that the sleep-like state-dependent synaptic potentiation mechanism can trigger epileptic SWDs (Zhang et al, 2021). In this study, using one heterozygous (het) knock-in (KI) transgenic mice (GABA A receptor 2 subunit Gabrg2 Q390X mutation) and an optogenetic method, we hypothesized that slow-wave oscillations (SWOs) themselves in vivo could trigger epileptic seizures.…”

A comprehensive atlas of fetal splicing patterns in the brain of adult myotonic dystrophy type 1 patients

“…GABRG2 (Gamma-Aminobutyric Acid Type A Receptor Subunit Gamma 2) has been associated with a plethora of neuro(developmental) disorders, mostly related to epilepsy (56–58). GABRG2 is known to be differentially spliced during development, where the short variant is expressed in early development (59).…”