Abstracts

Rationale: Status epilepticus (SE), an emergency condition with continuous seizure activity lasting more than 30 minutes, causes significant mortality and morbidity. SE can cause devastating damage to the limbic system leading to cognitive impairment and risk of epilepsy. Benzodiazepines are the first-line drugs for the treatment of SE. However, 35-50% patients exhibit partial or complete resistance to standard drugs, a condition known as refractory SE. Novel therapies are desperately needed for refractory SE, which is characterized by persistent seizures, progressive internalization of GABA-A receptors, and benzodiazepine resistance. However, there is currently no comparative analysis of animal models that recapitulates neurological features of refractory SE. In this study, we did comparative characterization of the organophosphate (OP)-intoxication and pilocarpine models of refractory SE using electrographic, behavioral and neuropathological approaches and by determining diazepam's ability to abort seizures and neurodegeneration. Methods: Persistent SE was induced chemically by lithium-pilocarpine regimen. OP intoxication was induced by exposure of rats to diisopropylfluorophosphate (DFP), an OP insecticide that, like nerve agents, causes SE and neuronal damage. One minute after DFP exposure, atropine sulfate and 2-PAM were administered to mimic available field treatment regimens. Diazepam was administered at 60 min after the onset of SE to attenuate seizures and ascertain benzodiazepine resistance. The onset and termination of SE was determined by video-EEG recordings for up to 24 h. Animals were perfused at 72 h for neuropathological studies. Histological assessment was made by Nissl and Fluoro-Jade-B staining. The extent of neurodegeneration of principal and interneurons was determined by the NeuN and NP-Y immunostaining, respectively. Results: Pilocarpine and DFP-treated animals exhibited electrographic and behavioral SE for over 8 h, which represent a state of refractory SE. Diazepam partially aborted seizures but sustained suppression of either behavioral or electrographic seizure activity was not evident, a profile indicative of refractoriness. At 72 h following SE induction, there was massive neuronal death in CA1, CA3 pyramidal regions, and in the dentate hilus regions. There was extensive neuronal damage in the amygdala, but such damage was not observed in the hypothalamus. The extent of neuronal damage was similar in pilocarpine and DFP models. Diazepam produced marginal protection against the SE-induced neurodegeneration in both models. Conclusions: Pilocarpine and DFP model are associated with refractory seizures and neurodegeneration. In the DFP model, persistent seizure activity and neurodegeneration was comparable to pilocarpine model, therefore providing a field model of refractory SE that can be used for the development of new treatment approaches. ** Supported by NIH grant NS076426 & NS051398 **