Abstracts

Rationale: Exposure to organophosphates (OP), or organophosphate nerve agents, can result in status epilepticus (SE), which can produce neuronal damage in the CNS. SE is potentially lethal; however, early control of seizure activity could minimize mortality, as well as neuronal damage. Currently, standard anti-seizure treatments for OP-induced SE are sub optimal; there is a need to develop new treatments that more effectively control seizure activity. In order to initially evaluate the efficacy of novel agents, rodent models of OP exposure are essential. Methods: Male, Sprague Dawley rats (150-200 g) were implanted with electrodes for recording of the electroencephalogram (EEG) 1 week prior to treatment. On treatment day, SE was induced by administration of diisopropyl fluorophosphate (DFP). One hour after the start of SE, rats were co-administered midazolam and phenobarbital (Phe, 30 and 100 mg/kg) or midazolam and memantine (Mem, 32 and 56 mg/kg) or midazolam and vehicle. EEG was recorded for 24 hours at which time the rats were perfused, brains were sectioned and labeled with Fluoro-Jade B. Neuropathology was assessed as the number of Fluoro-Jade B positive cells in 10 brain regions: dorsal CA1, dorsal CA3, hilus, ventral CA1, ventral CA3, amygdala, thalamus, and the parietal, entorhinal and piriform cortices. Results: DFP induces a rapid and robust electrographic SE within minutes of administration. The co-administration of a high dose of phenobarbital (100 mg/kg) and midazolam 1 hour after the start of electrographic SE was reduced the intensity of SE beyond the effect of midazolam alone. This effect was dose-dependent, as a lower dose of phenobarbital (30 mg/kg) had no effect. In contrast, co-administration of memantine (56 mg/kg) reduced the effect of midazolam, thereby exacerbating the intensity of DFP-induced SE. However, despite contrasting effects on seizure intensity, both compounds were neuroprotective, resulting in less neuronal death compared to midazolam alone. Conclusions: These data demonstrate the feasibility and usefulness of this screening protocol in the detection of compounds that reduce seizure intensity and/or are neuroprotective, compared to midazolam alone. Despite having opposite effects on seizure intensity, both compounds significantly reduced neuronal death, suggesting that drug effects on neuronal death can be pharmacologically separated from effects on seizure intensity during SE. In regard to the development of compounds for the treatment of SE, this result demonstrates the importance of measuring the drug-induced neuropathological effects in addition to the drug effect on seizure intensity. Funding: USAMRICD Award Number W81XWH14C0119