Abstracts

Rationale: Exposure to organophosphorous chemical warfare nerve agents (CWNA) such as sarin (GB) is a threat to civilian population and deployed military personal and causes hyperactivation of the cholinergic system through inhibition of acetylcholinesterase leading to status epilepticus (SE). Exposure to 3.0 LCt50 GB results in onset of toxic signs within 15 min of exposure, and leads to SE and spontaneous recurrent seizures (SRS). Current treatment paradigms for the management of SE induced by CWNA fail to prevent SE and neuropathology from subjects exposed to CWNA, and treatment with diazepam (DZP) has been shown to be refractory. Pregnanolone (3 -hydroxy-5 pregnan-20-one; PREGN) is a neuroactive steroid that acts as a GABAA receptor positive allosteric modulator. PREGN is able to prevent mortality and reduce seizures and brain damage caused by soman exposure. This study was designed to evaluate the effects of PREGN therapy in a rat model of whole body exposure to GB.Methods: Male Sprague-Dawley rats were implanted with telemetry transmitters (DSI, St. Paul, MN) and cortical EEG was recorded 24 hours/day 1 week following recovery and for up to 90 days after GB exposure. Animals were exposed for 60 min to 3.0 LCt50 of GB and treated (i.m.) with an admix of atropine sulfate (ATR; 2 mg/kg) and HI-6 (93.6 mg/kg) at 1 minute post-exposure and with DZP (10 mg/kg, s.c.) and PREGN (2 or 4 mg/kg i.v.) or Vehicle (VEH; 30% 2-hydroxypropyl- -cyclodextrin) 30 min after seizure onset. Animals were evaluated at 1 and 3 months after exposure for spatial memory acquisition in the Morris water maze and euthanized 3 months after exposure for evaluation of brain pathology using silver staining.Results: The total duration and number of seizures in the period of up to 24 hours post-SE and 24-48 hours post-SE was reduced in the group treated with PREGN (4 mg/kg; PREGN4) when compared to VEH (p<0.05). Also, when considering the 72 h period post-SE, animals treated with PREGN4 showed a reduction in both total duration and number of seizures when compared to VEH (p<0.01 and p<0.05, respectively) . The percentage of animals presenting SRS was higher in the VEH group (33%; 2/6 rats) when compared to both PREGN4 (8%; 1/12 rats) and PREGN2 (0%; 0/4 rats), although this difference was not statistically significant. Rats exposed to GB had impaired acquisition of spatial memory in a Morris water maze test compared to air control (AC). Rats exposed to GB and treated with PREGN4 performed similar to AC at 1 and 3 months after exposure. At 3 months after exposure to GB and treatment with ATR, HI-6 and DZP, rats had brain pathology in fiber tracts, thalamus, amygdala, hippocampus and piriform cortex, while those that received PREGN2 or PREGN4 in addition to ATR, HI-6 and DZP had minimal or no brain pathology.Conclusions: This data showed that pregnanolone is effective against GB-induced initial SE, secondary episodes of SE and prevents GB-induced performance deficits and brain pathology. Neurosteroid treatment such as pregnanolone may be a feasible alternative to SE treatment that is refractory to DZP.