Abstract
The discovery and development of novel antiseizure drugs (ASDs) that are effective in controlling pharmacoresistant spontaneous recurrent seizures (SRSs) continues to represent a significant unmet clinical need. The Epilepsy Therapy Screening Program (ETSP) has undertaken efforts to address this need by adopting animal models that represent the salient features of human pharmacoresistant epilepsy and employing these models for preclinical testing of investigational ASDs. One such model that has garnered increased interest in recent years is the mouse variant of the Intra-Amygdala Kainate (IAK) microinjection model of mesial temporal lobe epilepsy (MTLE). In establishing a version of this model, several methodological variables were evaluated for their effect(s) on pertinent quantitative endpoints. Although administration of a benzodiazepine 40 minutes after kainate (KA) induced status epilepticus (SE) is commonly used to improve survival, data presented here demonstrates similar outcomes (mortality, hippocampal damage, latency periods, and 90-day SRS natural history) between mice given midazolam and those that were not. Using a version of this model that did not interrupt SE with a benzodiazepine, a 90-day natural history study was performed and survival, latency periods, SRS frequencies and durations, and SRS clustering data were quantified. Finally, an important step towards model adoption is to assess the sensitivities or resistances of SRSs to a panel of approved and clinically used ASDs. Accordingly, the following ASDs were evaluated for their effects on SRSs in these mice: phenytoin (20 mg/kg, b.i.d.), carbamazepine (30 mg/kg, t.i.d.), valproate (240 mg/kg, t.i.d.), diazepam (4 mg/kg, b.i.d.), and phenobarbital (25 and 50 mg/kg, b.i.d.). Valproate, diazepam, and phenobarbital significantly attenuated SRS frequency relative to vehicle controls at doses devoid of observable adverse behavioral effects. Only diazepam significantly increased seizure freedom. Neither phenytoin nor carbamazepine significantly altered SRS frequency or freedom under these experimental conditions. These data demonstrate that SRSs in this IAK model of MTLE are pharmacoresistant to two representative sodium channel-inhibiting ASDs (phenytoin and carbamazepine) but not to GABA receptor modulating ASDs (diazepam and phenobarbital) or a mixed-mechanism ASD (valproate). Accordingly, this model is being incorporated into the NINDS-funded ETSP testing platform for treatment resistant epilepsy.
Highlights
An intra-amygdala kainate model of TLE was evaluated for pharmacoresistant seizures
Administration of midazolam during status epilepticus did not affect mortality
Model characteristics were evaluated over a 90-day natural history study
Spontaneous seizures were resistant to phenytoin and carbamazepine
Spontaneous seizures were sensitive to valproic acid, diazepam, and phenobarbital
Competing Interest Statement
CSM serves as a consultant for a consultant for Sea Pharmaceuticals. KSW serves on the scientific advisory board of Mend Neuroscience and Blackfynn, Inc and is a consultant to Xenon Pharmaceuticals.
Footnotes
Declaration of Interest: CSM serves as a consultant for a consultant for Sea Pharmaceuticals. KSW serves on the scientific advisory board of Mend Neuroscience and Blackfynn, Inc and is a consultant to Xenon Pharmaceuticals.
Inclusion of additional data: Methods, SE, and seizure EEG characterization (new figure 1), behavioral seizure scores and durations (revised 90 day natural history figure), and pharmacology data for phenobarbital (25 and 50 mg/kg b.i.d., new figure 8).
- Abbreviations
- ASD
- antiseizure drugs
- BLA
- basolateral amygdala
- CBZ
- carbamazepine
- DZP
- diazepam
- EEG
- Electroencephalography
- ETSP
- Epilepsy Therapy Screening Program
- FJB
- FluoroJade B
- GABA
- gamma-Aminobutyric acid
- IAK
- Intra-Amygdala Kainate
- ILEA
- International League Against Epilepsy
- KA
- kainic acid
- LTG-R
- lamotrigine resistant
- MTLE
- mesial temporal lobe epilepsy
- NINDS
- National Institute of Neurological Disorders and Stroke
- PB
- phenobarbital
- PHT
- phenytoin
- SE
- status epilepticus
- SRS
- spontaneous recurrent seizure
- TLE
- temporal lobe epilepsy
- VEH
- vehicle
- VPA
- valproic acid / valproate