Abstracts

Rationale: Intoxication with organophosphates (OPs) presents a significant global burden and can occur as a result of exposure to chemical weapons, agro-industrial poisoning, and even suicide attempts. OPs bind to the acetylcholinesterase preventing the breakdown of acetylcholine. Acute OP-intoxication leads to a cholinergic storm, status epilepticus (SE) and, in severe cases, death. Survivors can develop a persistent neuropathology including spontaneously recurring seizures (SRS) and long-term cognitive dysfunction. Standard-of-care (SOC) countermeasures including atropine, midazolam and an oxime can be lifesaving, however they do not fully protect against SE and the development of SRS. Therefore, it is crucial to determine the natural history of the development and progression of SRS and cognitive dysfunction following acute OP-intoxication to identify effective therapies. We hypothesized that acute intoxication with the OP-threat agent diisopropylfluorophosphate (DFP) would result in acute SE, the development of SRS, alterations to neural oscillations, and persistent learning and memory dysfunction.


Methods: Adult male (n=28) and female (n=42) Sprague Dawley rats were surgically implanted with intracranial electrodes in the dorsal and ventral hippocampus, prefrontal cortex, amygdala, and skull screws over prefrontal and posterior cortices. Continuous video-EEG monitoring occurred on days 1-21, 52-61 and 90-99 post-DFP, and was utilized for seizure quantification and analyses of neural oscillations. The Y-maze (48d post-DFP), novel object (NOR; 51d post-DFP), and Barnes maze (BM; 85-88d post-DFP) were used to evaluate cognitive function at chronic timepoints.


Results: Over 66% of male and female rats developed SRS within 2-weeks post-DFP and over 75% had an observed SRS by the end of the study. While seizure frequency peaked within the first three weeks, most animals continued to seize, with seizure duration increasing significantly (p< 0.05). While intoxicated male and female rats performed comparable to vehicle controls on the y-maze, there was a significant impairment in NOR performance in both sexes (p< 0.05). On the Barnes maze there was a trend toward a difference in performance in male rats (p=0.12) and a significant difference in performance in female rats (p< 0.05). However, when Barnes maze was re-analyzed separating out those male rats that experienced SRS, intoxicated with SRS performed significantly worse than both vehicle control and those DFP rats that did not develop SRS.


Conclusions: Our preliminary data support our proposed hypothesis that acute OP-intoxication results in the development of chronic SRS and cognitive dysfunction. Specifically, most rats experienced SRS within one week of acute-intoxication, and most animals continued to seizure throughout their lifetime. While rats did not perform differently on a working memory task (y-maze), they were significantly impaired in object recognition and spatial learning. Next steps will include evaluation of mechanism as well as testing of potential therapeutic compounds to determine whether spontaneous seizures are refractory and whether we can reduce seizures without worsening cognitive outcomes.


Funding: U54NS127758