Abstracts

Rationale: Nerve agents and some pesticides such as diisopropylfluorophosphate (DFP) cause neurotoxic manifestations that include seizures and status epilepticus (SE), which are potentially lethal and carry long-term neurological morbidity. Current antidotes for OP intoxication include atropine, 2-PAM and diazepam (a benzodiazepine for treating seizures and SE). There is some evidence for partial or complete loss of diazepam anticonvulsant efficacy when given 30 min later after exposure to an OP; this condition is known as refractory SE. Effective therapies for OP-induced SE are lacking and it is unclear why current therapies do not work.  In this study, we investigated the time-dependent efficacy of diazepam in the nerve agent surrogate DFP model of OP intoxication on seizure suppression and neuroprotection in rats, following an early and late therapy.  Methods: The surrogate DFP model was used for OP intoxication in rats. Rats were given a standard antidote regimen (atropine methylnitrate and 2-PAM) after DFP. Diazepam (5 mg/kg, im) was given at 10, 60 or 120 min after DFP exposure. Rats were monitored for behavioral and EEG seizures for 24 h and then perfused at 72 h for brain histology.  Results: Diazepam controlled seizures when given 10 min after DFP exposure (“early”), but it was completely ineffective at 60 or 120 min (“late”) after DFP. DFP-induced neuronal injury, neuroinflammation, and neurodegeneration of principal cells and GABAergic interneurons were significantly reduced by early but not late therapy.  Conclusions: These findings demonstrate that diazepam failed to control seizures, SE and neuronal injury when given 60 min or later after DFP exposure, confirming the benzodiazepine refractory SE and brain damage after OP intoxication. In addition, this study indicates that degeneration of inhibitory interneurons and inflammatory glial activation are potential mechanisms underlying these morbid outcomes of OP intoxication. Therefore, novel anticonvulsants, superior to benzodiazepines, are desperately needed for controlling refractory SE and brain injury. Funding: Supported by NIH CounterACT grants U01 NS083460 & R21 NS099009.