Thalamic GABAA Receptor Subunit Expression in the Stargazer Mouse Model of Absence Epilepsy

Absence epilepsy is a type of non-convulsive, generalized seizure, characterized by sudden and abrupt impairment of consciousness. It is the most common form of childhood onset epilepsies, with detrimental effects on childhood learning and physical safety. The clinical hallmark of absence epilepsy is 2.5-4Hz hypersynchronous brain signals on the electroencephalogram (EEG), referred to as “spike-wave discharges” (SWDs). Currently available anti-epileptic drugs (AEDs) for absence seizure control often lead to treatment failure due to severe side effects or lack of efficacy. In fact, AEDs can even exacerbate seizures in some cases, reflecting the complex and multifactorial mechanisms underlying the disorder. Hence it is vital to understand the source of hyperexcitability in absence seizures. It is well known that absence seizures generate from disturbances within the cortico-thalamocortical (CTC) network, but the precise underlying mechanism remains less well understood. Several human cases of absence epilepsy have been linked with point mutations at certain GABAA receptor (GABAAR) subunits, and recent experimental evidence from rodent absence epilepsy models suggests region-specific alterations in GABAAR mediated inhibition in the thalamus may contribute to hypersynchronous oscillatory activity in absence epilepsy. Therefore, the aim of this project was to investigate changes in GABAAR expression in the reticular thalamic nucleus (RTN) and ventral posterior (VP) region of the thalamus, using the well-established stargazer mouse model of absence epilepsy, which features absence seizures and SWDs on the EEG. Firstly, the localisation of different GABAAR subunits within the RTN and VP thalamic subregions was examined using immunofluorescence confocal microscopy, and the differences between control and epileptic stargazer mice was analysed using semi-quantitative Western blotting. Second part of the study utilized electron-microscopy immunogold cytochemistry (EM-ICC) in order to investigate synaptic changes in GABAAR subunits in the VP region. Third part of the study involved developmental investigation on juvenile control and epileptic mice to determine whether changes in GABAAR subunit levels occur pre-seizure and could contribute to the generation of SWDs, or are secondary effects that occur post-seizure. Overall, it was found that there are region-specific changes in both phasic and tonic GABAAR subunits expression in the thalamus of epileptic stargazer mice, which occur prior to seizure onset. Further investigation of GABAergic mechanisms that underlie generation of SWDs in absence epilepsy could be of immense importance for identifying novel drug targets for treatment of absence epilepsy, which has detrimental effects on childhood learning, social developments, and physical safety