Abstracts

Organophosphate (OP) compounds are chemical threat agents and include pesticides and chemical warfare nerve agents. OP exposure could lead to rapid onset of status epilepticus (SE) and survival following standard-of-care (SOC) treatment is associated with neuronal injury, memory impairment, and chronic spontaneous recurrent seizures (SRS). We recently demonstrated that adjunct therapy with atenolol and levetiracetam (AT+LV) along with SOC significantly reduces the mortality associated with OP-SE. In this study we investigated the effect of AT+LV treatment on chronic behavior and seizure outcomes following survival from OP paraoxon (POX)-induced SE.

Male Sprague-Dawley rats were injected with POX (2 mg/kg, s.c). One minute later, atropine sulfate (0.5 mg/kg, i.m.) and 2-PAM (25 mg/kg, i.m) were injected. At 1-h post SE onset, midazolam (1.78 mg/kg, i.m.) was used to terminate SE. Following POX-SE, rats were treated for seven days with AT+LV (AT, 5 mg/kg, LV 50 mg/kg, i.m., b.i.d for seven days) or saline (CON).  Approximately, three months post POX-SE, rats were assessed for mood and memory function using the Barnes Maze (BM). Around six months following POX-SE, rats were screened for the presence of SRS using video and video/EEG analysis.

OP intoxication produced rapid onset of SE and increased survival was noted with AT+LV intervention along with the SOC. On the BM, during the acquisition-phase, latency to escape and the number of errors were significantly lower in AT+LV-treated rats compared to CON. During the probe trial, AT+LV-treated rats spent significantly more time in the target quadrant and made significantly more visits to the escape zone compared to CON rats. Video-EEG monitoring revealed the presence of POX SE-induced SRS in 73.3% of control rats while only 56.2% of AT+LV treated rats exhibited SRS.  Additionally, in all rats displaying SRS, AT+LV resulted in a significant decrease in seizure frequencies from 7.5± 9.6 SZs/day to 1.7±2.2 SZs/day when compare to CON (n=24 CON, n=8 AT+LV, p≤ 0.01, Welch’s test).

Our results indicate that a long-term consequence of AT+LV treatment is of significant improvement in memory outcomes and a significant decrease in SRS occurrence following POX-SE in rats. Sustained release of Ca2+ from intracellular stores has been implicated as a major mechanism for neuronal injury and plasticity changes following SE and OP-SE. Given the role of calcium in signaling neuro-degradative and neuroplasticity pathways, LV’s action on lowering the elevated Ca2+ following OP-SE exerts a neuroprotective effect and improves memory and SRS outcomes following POX-SE. AT+LV combination therapy could be an effective treatment option for lowering the mortality and morbidities associated with lethal OP-SE.