Abstracts

Rationale: Most people with epilepsy depend on anti-seizure drugs (ASDs) as their primary treatment option; however one-third of the patients with epilepsy are resistant to their medications. One integral tool for the identification of effective ASDs is the use of animal seizure models, including the maximal electroshock (MES) and the 6 Hz animal seizure models. Both models can provide important insight into the effectiveness of ASDs because they elicit different seizure types and are clinically relevant to different human seizure phenotypes. For example, the MES test is a clinically validated model of generalized tonic-clonic seizures that elicits maximum neuronal activity in both brain hemispheres, while the 6 Hz test invokes a focal seizure and is used as a model for therapy-resistant focal seizures. Previous studies have demonstrated the utility of these models for differentiating ASD pharmacology. However, the mechanisms underlying this phenomenon are not understood. The present study was designed to test the hypothesis that the different electrical stimulation paradigms used to evoke a seizure in these models will elicit the recruitment of different brain regions.

Methods: The characterization of brain region activation was performed in adult male CF-1™ mice following seizures evoked by either the CC97 (current sufficient to induce a stereotypic seizure in 97% of mice tested); i.e., xxx mA for 3 sec, in the 6 Hz test or a supramaximal current (50 mA, 0.2 sec duration) sufficient to induce a tonic clonic seizure in the MES test. Sham animals were used as controls in both experiments. Ninety minutes after stimulation, animals were euthanized and brains were extracted to be processed for immunohistochemical labeling of cFOS, an early activation gene that is indicative of neuronal activity. Ongoing studies are being completed to assess the pharmacological characterization of brain region activation following the treatment of three mechanistically distinct ASD’s; i.e., levetiracetam, phenytoin and cenobamate.

Results: Overall, cFOS immunoreactivity was differentially expressed in a seizure- and regional-dependent manner. Brains of animals following a MES seizure had robust cFOS labeling in the dentate gyrus of the hippocampus, whereas 6 Hz animals and sham controls had no staining in this region. cFOS labeling was significantly elevated in the piriform cortex, amygdala, thalamus and somatosensory cortex regions for both MES and 6 Hz animals. Sham controls had minimal cFOS labeling in any brain region suggesting that neuronal network activation is dependent on seizure activity.

Conclusions: These data suggest there is differential activation of brain regions following a 6 Hz or MES seizure, which is consistent with previously published literature. Ongoing studies are investigating the effects of mechanistically distinct ASD’s to block brain region recruitment of a 6 Hz or MES seizure and provide insight into the mechanisms of pharmacosensitivity of clinically used ASDs.

Funding: Please list any funding that was received in support of this abstract.: Unrestricted funding from the University of Washington Institute of Translational Health Sciences (MG).