Abstracts

Rationale: Anti-seizure medications (ASM) are the main treatment option for people with epilepsy. Unfortunately, one-third of people with epilepsy are resistant to their ASMs, and the mechanisms underlying this pharmacoresistance are unknown. Historically, animal seizure models such as the maximal electroshock (MES) and 6 Hz mouse seizure models have played a key role in identifying ASMs. These models produce distinct seizure types that are clinically relevant to human seizure phenotypes. For example, the 6 Hz test is a model of therapy-resistant focal seizures, while the MES test is a clinically validated model of generalized tonic-clonic seizures. Each model displays a differential ASM profile; however, the reasons underlying this are unknown. We hypothesize that ASM efficacy will result in reduced brain region activation during seizures induced by MES or 6 Hz stimulation.

Methods: Adult male CF-1™ mice were treated with 3 mechanistically distinct ASMs: levetiracetam (LEV, 500 mg/kg, IP), cenobamate (CBM, 40 mg/kg, IP), and phenytoin (PHT, 60 mg/kg, IP). At the time to peak pharmacodynamic effect (CBM, 15 min; LEV and PHT, 60 min) seizures were evoked with a 6 Hz stimulus at the 1.5xCC97 (32 mA equivalent, 3 sec) or the supramaximal current induced by the MES stimulus (50 mA, 0.2 sec) by corneal stimulation. Mice that didn’t display head nodding, jaw chomping, forelimb clonus (6 Hz) or tonic hindlimb extension (MES) were considered protected. Ninety minutes after stimulation, animals were euthanized and brains were processed for immunohistochemical labeling of cFOS, an early activation gene indicative of neuronal activity.

Results: LEV, CBM, and PHT were effective against 6 Hz seizures (n=4/group). Conversely, only CBM and PHT were effective at blocking tonic hindlimb extensions induced by MES stimulation (CBM:6/8; PHT:7/8), whereas LEV was marginally effective against the tonic extensions (LEV:2/8). Although there were no differences in protection between ASMs in the 6 Hz test, differences in cFOS immunoreactivity were noted; e.g., reduced cFOS expression in the piriform cortex of mice treated with CBM compared to PHT, and reduced cFOS expression in the somatosensory cortex of mice treated with CBM and LEV but not PHT. No significant differences in cFOS immunoreactivity were observed in protected and non-protected animals following an MES seizure.

Conclusions: While LEV displayed reduced protection against MES seizures compared to CBM and PHT, no differences in cFOS immunoreactivity were seen between the ASMs suggesting that these ASMs provide little protection against activation of these brain regions during an MES seizure, and may indicate that CBT and PHT block seizures downstream of brain activation. All ASMs in the 6 Hz test displayed complete protection, but differences in cFOS levels between ASMs and VEH were noted, suggesting that these ASMs provide protection against brain region activation during a 6 Hz seizure.

Funding: Unrestricted funding from the University of Washington Institute of Translational Health Sciences (M.G.)