Investigating excitatory GABAergic signalling & benzodiazepine resistance in an in vitro model of status epilepticus
Master Thesis
2018
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University of Cape Town
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Abstract
Status epilepticus (SE) describes a state of persistent seizures which are unrelenting. First- line treatment for status epilepticus uses a group of drugs, the benzodiazepines, that promote the action of the major inhibitory neurotransmitter within the brain, gamma (γ)-aminobutyric acid (GABA). In a subset of patients however, benzodiazepines prove to be ineffective in terminating SE. Previous data from in vitro models has demonstrated that during single seizures, instead of being inhibitory, activation of the GABAA receptor can have an excitatory effect on neurons. To date, it is unknown whether this shift in GABAergic function contributes to SE, nor how it may modulate the anticonvulsant properties of benzodiazepines. In this thesis I explore the role of excitatory GABAergic signaling in an in vitro model of SE and how this may affect the anticonvulsant efficacy of the benzodiazepine, diazepam. Firstly, I confirm that benzodiazepine-resistant SE is prevalent in a South African paediatric population. Secondly, consistent with its established mechanism of action, I show that diazepam enhances GABAAR synaptic currents. Thirdly, using the in vitro 0 Mg²⁺ model of status epilepticus I show that whilst early application of diazepam has anticonvulsant properties, this is lost when the drug is applied during prolonged epileptiform activity. Fourthly, to investigate this phenomenon I use optogenetic activation of GABAergic interneurons to show that interneurons can drive epileptiform discharges during SE-like activity in vitro. Finally, I confirm that during seizure-like events there is a transient shift in GABAergic signaling that is caused by activity driven changes in the transmembrane Cl⁻ gradient. This thesis provides insight into how excitatory GABAergic signaling during prolonged seizures may contribute towards benzodiazepine resistance in SE. I believe that these results are relevant for understanding of the pathophysiology of SE and may help inform optimal treatment protocols for this condition.
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Burman, R. 2018. Investigating excitatory GABAergic signalling & benzodiazepine resistance in an in vitro model of status epilepticus. University of Cape Town.