Authors :
Presenting Author: Anastasia Brodovskaya, PhD – University of Virginia
Nadia Adotevi, PhD – University of Virginia; Jaideep Kapur, MD, PhD – Director of the UVA Brain Institute, Professor of Neurology, Neurology, University of Virginia
Rationale:
Repeated generalized tonic-clonic seizures (GTCSs) are the single most significant risk factor for sudden unexpected death in epilepsy (SUDEP). Others have demonstrated that animals with ion channel mutations causing epilepsy have postictal apnea. We reported last year that repeated PTZ-induced seizures gradually lead to fatal postictal apnea, related to the plasticity of the GluA1 subunit of AMPA receptors. We tested whether similar mechanisms operate in the kindling model of temporal lobe epilepsy.
Methods:
We induced repeated GTCSs using the hippocampal kindling model. We generated global knockout (K.O.) mice of AMPA receptor subunit GluA1 and compared EEG, breathing, and heartbeat in GluA1 K.O. and W.T. littermates. Kindled mice underwent hypoxia (10% O2) and hypercarbia (5% CO2) gas challenge every other day before kindling from naïve to fully kindled states to determine if there are any gas sensitivity changes before apnea development. Breathing frequency and variability were recorded in plethysmography chambers. Next, we kindled activity reporter TRAP2 mice to label and map neuronal circuits active during postictal apnea. Because the amygdala has been shown to be involved in apnea, we injected Cre-dependent AAV9 GFP virus in the amygdala of TRAP2 mice that express Cre only in the activated neurons. Injection of 4-hydroxytamoxifen in these mice after postictal apnea allowed us to trace only activated anatomic projections from the amygdala through the brainstem during apnea. We used immunohistochemistry and NeuroInfo software to create a 3D brainstem reconstruction map of activated brainstem nuclei during postictal apnea.
Results:
We found that repeated hippocampal kindling-induced GTCSs also led to fatal postictal apnea. Mice without GluA1 subunit of AMPA receptors neither attained nor sustained GTCSs compared to W.T. littermates. Sixty percent of GluA1 K.O. mice remained unkindled despite stimulation, their seizure threshold was higher (GluA1 K.O.: 157.10 ± 37.65 µA, n = 10 mice; W.T.: 64.00 ± 14.70 µA, n = 10 mice; Mann Whitney test, p = 0.022), seizure severity lower (p < 0.05), seizure duration shorter, and none of them died compared to W.T.s. The experiments mapping neuronal circuits active during hippocampal GTCSs-induced apnea in TRAP2 mice and sensitivity to hypoxia and hypercarbia during kindling are ongoing.