Abstracts

Rationale: Exposure to organophosphates (OPs), such as pesticides and nerve agents, can result in prolonged repetitive seizures and status epilepticus (SE). As there is an unmet need for antiseizure drugs in children exposed to OPs, we have developed an animal model of OP-induced seizures using exposure to diisopropylfluorophosphate (DFP) in immature rats. Results for the effects of an anesthetic (propofol) and a barbiturate (phenobarbital) on DFP-induced seizures were previously presented (AES, 2016); here, we show findings from two benzodiazepines, midazolam and diazepam. Methods: Immature (P21 and 28) and adult rats (P70) were instrumented for EEG recording using miniature wireless telemetry transmitters (EpochTM, Epitel, Inc.). On the day of treatment, rats received pyridostigmine bromide (0.026 mg/kg) as a pretreatment. The rats were then administered DFP 30 min after the pretreatment. Rats received an admixture of atropine sulfate (0.1 mg/kg) and 2-PAM (25 mg/kg) 1 min later. Rats were given vehicle or an antiseizure drug treatment of midazolam (2 mg/kg) or diazepam (10 mg/kg) 60 min after the onset of electrographic seizures. SE was monitored for 24 h with continuous video-EEG recordings to observe both behavioral and electrographic seizure activity.  After 24 h, brain tissue was examined with Fluoro-Jade B, a marker for degenerating neurons. Results: Both midazolam and diazepam treatment resulted in a significant decrease in power in the gamma band for P21 and P70 in the hours following administration. This was also apparent for P28 pups treated with diazepam, and there was a trend for amelioration of seizure activity in P28 animals treated with midazolam. Initial studies showed midazolam conferred neuroprotection at P70, while diazepam-treated P28 and P70 animals had reduced neuronal death compared to age-matched vehicle-treated controls. Conclusions: As might be expected from antiseizure compounds tested in adults and approved for use in children, midazolam and diazepam reduced electrographic seizures and also offered neuroprotection to both adult and immature rats after OP-induced SE. Funding: Supported by CounterACT Program, National Institutes of Health Office of the Director (NIH OD), and the National Institute of Neurological Disorders (NINDS), Grant W81XWH-14-C-0093 as a subcontract from the Military Research Institute of Chemical Defense (MRICD).