Abstract
Organophosphate (OP) threat agents can trigger seizures that progress to status epilepticus, resulting in persistent neuropathology and cognitive deficits in humans and preclinical models. However, it remains unclear whether patients who do not show overt seizure behavior develop neurological consequences. Therefore, this study compared two subpopulations of rats with a low versus high seizure response to diisopropylfluorophosphate (DFP) to evaluate whether acute OP intoxication causes persistent neuropathology in non-seizing individuals. Adult male Sprague Dawley rats administered DFP (4 mg/kg, sc), atropine sulfate (2 mg/kg, im), and pralidoxime (25 mg/kg, im) were monitored for seizure activity for 4 h post-exposure. Animals were separated into groups with low versus high seizure response based on behavioral criteria and electroencephalogram (EEG) recordings. Cholinesterase activity was evaluated by Ellman assay, and neuropathology was evaluated at 1, 2, 4, and 60 days post-exposure by Fluoro-Jade C (FJC) staining and micro-CT imaging. DFP significantly inhibited cholinesterase activity in the cortex, hippocampus, and amygdala to the same extent in low and high responders. FJC staining revealed significant neurodegeneration in DFP low responders albeit this response was delayed, less persistent, and decreased in magnitude compared to DFP high responders. Micro-CT scans at 60 days revealed extensive mineralization that was not significantly different between low versus high DFP responders. These findings highlight the importance of considering non-seizing patients for medical care in the event of acute OP intoxication. They also suggest that OP intoxication may induce neurological damage via seizure-independent mechanisms, which if identified, might provide insight into novel therapeutic targets.
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Abbreviations
- AChE:
-
Acetylcholinesterase
- AS:
-
Atropine sulfate
- BChE:
-
Butyrylcholinesterase
- ChE:
-
Cholinesterase
- CT:
-
Computed tomography
- DFP:
-
Diisopropylfluorophosphate
- EEG:
-
Electroencephalogram
- FJC:
-
Fluoro-Jade C
- im:
-
Intramuscular
- ip:
-
Intraperitoneal
- OP:
-
Organophosphate
- 2-PAM:
-
Pralidoxime
- PBS:
-
Phosphate-buffered saline
- ROI:
-
Region of interest
- sc:
-
Subcutaneous
- SE:
-
Status epilepticus
- T2w:
-
T2-weighted
- VEH:
-
Vehicle
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Acknowledgements
We thank Dr. Suzette Smiley-Jewell (UC Davis CounterACT Center) for her assistance in editing this manuscript. This work was supported by the CounterACT Program, National Institutes of Health Office of the Director and the National Institute of Neurological Disorders and Stroke [grant number U54 NS079202], predoctoral fellowships to E.A.G from the National Institute of Neurological Disorders and Stroke [grant number F31 NS110522] and the National Institutes of Health Initiative for Maximizing Student Development [grant number R25 GM5676520], and predoctoral fellowships to M.G. from the National Institute of General Medical Sciences [grant number T32 GM099608], and the David and Dana Loury Foundation. This project used core facilities supported by the UC Davis MIND Institute Intellectual and Developmental Disabilities Research Center (U54 HD079125). The sponsors were not involved in the study design, in the collection, analysis, or interpretation of data, in the writing of the report, or in the decision to submit the paper for publication.
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EG: Conceptualization, Methodology, Investigation, Writing-Original Draft, Visualization. AR: Conceptualization, Methodology, Investigation, Writing-Original Draft. MG: Methodology, Investigation, Writing-Review and Editing, Visualization. JC: Methodology, Investigation, Visualization. DB: Conceptualization, Investigation, Supervision, Data Curation. AD: Methodology, Investigation. PA: Investigation. NS: Formal Analysis, Writing-Review and Editing, Visualization. DR: Methodology, Investigation, Data Curation, Writing-Review and Editing. DH: Formal Analysis, Writing-Original Draft, Visualization. MR: Funding Acquisition. PL: Conceptualization, Writing-Review and Editing, Supervision, Project Administration, Funding Acquisition.
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González, E.A., Rindy, A.C., Guignet, M.A. et al. The chemical convulsant diisopropylfluorophosphate (DFP) causes persistent neuropathology in adult male rats independent of seizure activity. Arch Toxicol 94, 2149–2162 (2020). https://doi.org/10.1007/s00204-020-02747-w
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DOI: https://doi.org/10.1007/s00204-020-02747-w