Abstracts

Rationale: Acute repetitive seizures (ARS) are clinically defined by multiple seizures within a short time period (< 24 hours), with distinct bouts of seizure freedom that differentiate ARS from status epilepticus (SE). Further, ARS are sensitive to acute intervention with benzodiazepines (BDZ) whereas SE can become highly refractory to BDZ in a relatively short time window. ARS occurs in about 3% of the epilepsy patient population, whereas SE is a more frequent seizure emergency (4-16% of epilepsy patients). Nonetheless, ARS requires immediate intervention with BDZ to avoid the risk of potential subsequent SE onset and other medical complications. Preclinical models of ARS are presently lacking to understand how this clinical phenomenon differs from SE or how novel therapies may be developed to improve current first-line therapeutic options for ARS emergencies. To address this need, we present a novel model of ARS in mice. Methods: Male CF-1 mice (25-40 g; n = 8/treatment/time group) were divided into three treatment groups per time point. Phenytoin (PHT; 50 mg/kg, i.p.) was administered 1 hour prior to administration of the chemoconvulsant, pentylenetetrazol (PTZ; 100 mg/kg, s.c.). Acute continuous seizure activity (CSA) was defined as the onset of continuous myoclonic seizure activity and sustained, rhythmic generalized clonic “popcorn” seizures. Valproic acid (VPA; 300 mg/kg, i.p.), lorazepam (LZP; 4 mg/kg, i.p.), or vehicle (equivalent volume of 0.5% methylcellulose, i.p.) was then administered immediately (0 min) or 30 min after onset of CSA to define the BDZ sensitivity of the model. Mice were then monitored for 1 hour post-intervention for any recurrence of behavioral seizure activity and bodyweight change assessed 24-hours later. The extent of neurodegeneration was then assessed 24-hours later with FluoroJade-B staining. Results: VPA and LZP significantly attenuated time spent in CSA (F_(2,22)=18.22, p<0.0001). On average, VEH-treated mice spent 2531±1484 sec in CSA after intervention whereas VPA-treated mice spent 428.1±320.6 sec in CSA and LZP-treated mice spent 189.4±54.6 sec in CSA after intervention. Further, immediate intervention (0 min) with both VPA (100% survival) and LZP (100% survival) significantly improved 24-hour survival relative to VEH-treated control mice (50% survival; X²=9.6, p=0.0082). Interestingly, administration of LZP 30 min after CSA onset effectively arrested seizure activity (329.8±64.7 sec in CSA; F_(2,15)=1.694, p<0.026), suggesting a BDZ-sensitive model. The impact of delayed intervention on survival, bodyweight change, and neurodegeneration will be further discussed. Conclusions: PHT pre-treatment in the PTZ model of seizures precipitates CSA onset. These acute continuous seizures are BDZ sensitive; thereby representing an acute seizure emergency model with a distinct preclinical phenotype that is differentiated from that of SE. When administered immediately following CSA onset, both VPA and LZP halt seizures in this model and also promote improvements in 24-hour survival when compared to vehicle treated mice. Funding: This work was supported by the University of Washington School of Pharmacy.