Rationale:
Current epilepsy therapy screening for Dravet syndrome (DS) relies on hyperthermia-induced seizures in transgenic mice with Scn1a mutations. Although temperature thresholds are useful for differentiating drug effects, the cellular mechanisms of hyperthermia-induced seizures are not well defined, lack circuit specificity, and may not capture the mechanisms underlying drug-resistant spontaneous recurrent seizures in adulthood. Here, we introduce a novel epilepsy therapy screening platform for DS using optogenetically induced seizures in Scn1a+/− mice.
Methods:
The Opto-Dravet platform was generated by crossing female homozygous Thy1-ChR2-YFP (JAX:007612) with male heterozygous 129S Scn1a knockout (MMRRC 037107-JAX). Adult mice (~8 wks) were implanted with optical fibers targeting dorsal hippocampus and EEG electrodes (cortical screws, hippocampal wires). After recovery, baseline video-EEG (1 wk) captured spontaneous seizures. Blue-light trains (10 Hz) were then delivered to induce seizures. Stimulation parameters (power, duration) were optimized using a pre-set algorithm. Assay outcomes included seizure induction probability, duration, behavioral scores, and EEG features. Within-subject assays were performed before and after diazepam (DZP; 3 mg/kg), valproate (VPA; 300 mg/kg), levetiracetam (LEV; 400 mg/kg), or carbamazepine (CBZ; 20 mg/kg).
Results:
All six mice examined exhibited spontaneous seizures during baseline video-EEG recording. Optimized stimulation yielded safe (mortality rate < 1% per stimulation), repeatable seizures in adult DS mice. EEG seizure induction probability was ≥98% without drug treatment across six animals. Optogenetically evoked seizures showed gross similarity to spontaneous seizures in duration and propagation patterns. Pharmacological testing demonstrated translational utility: benzodiazepines reduced EEG seizure induction probability to 33% (p=0.031, Wilcoxon test) and decreased the Racine scale population average from 4.38 to 0.53 (p=0.0001, paired t-test); VPA reduced EEG seizure induction probability to 56% (p=0.031, Wilcoxon test) and the Racine scale from 4.5 to 2.3 (p=0.004, paired t-test); LEV produced mixed effects on EEG seizure induction probability (60%, p=0.250, Wilcoxon test) but reduced the Racine scale from 4.1 to 1.76 (p=0.020, paired t-test); CBZ had no effect on seizure induction probability (100%) or average Racine scale (~4.5). Within-subject designs further enabled generation of time-resolved pharmacodynamic profiles.
Conclusions:
The Opto-Dravet platform provides a rapid, reliable assay that reproduces DS-relevant electrographic and pharmacological responses. The induced seizure profiles closely mimic spontaneous seizures in duration and propagation patterns. As part of a broader Opto-X framework, this platform extends previous work on optogenetically induced seizures in the acquired hippocampal model (Opto-IHK) and is positioned for expansion to additional genetic epilepsies (e.g., CDKL5) and for benchmarking investigational therapies.
Funding:
This work is partially supported by NIH R01NS082046.