title: Persistent neuroinflammation and cognitive impairment in a rat model of acute diisopropylfluorophosphate intoxication.
abstract: Acute intoxication with organophosphorus (OP) cholinesterase inhibitors can trigger convulsions that progress to life-threatening status epilepticus. Survivors face long-term morbidity including mild-to-severe decline in memory. It is posited that neuroinflammation plays a key role in the pathogenesis of OP-induced neuropsychiatric deficits. Rigorous testing of this hypothesis requires preclinical models that recapitulate relevant phenotypic outcomes. Here, we describe a rat model of acute intoxication with the OP diisopropylfluorophosphate (DFP) that exhibits persistent neuroinflammation and cognitive impairment.
  
  
  
  Neuroinflammation, neurodegeneration, and cognitive function were compared in adult male Sprague Dawley rats injected with an acutely toxic dose of DFP vs. vehicle controls at multiple time points up to 36 days post-exposure. Neuroinflammation was quantified using immunohistochemical biomarkers of microglia (ionized calcium-binding adapter molecule 1, IBA1) and activated astrocytes (glial fibrillary acidic protein, GFAP) and positron emission tomography (PET) imaging of [11C]-(R)-PK11195, a ligand for the 18-kDa mitochondrial membrane translocator protein (TSPO). FluoroJade-B staining was used to assess neurodegeneration; Pavlovian conditioning, to assess cognitive function.
  
  
  
  Animals exhibited moderate-to-severe seizures within minutes of DFP injection that continued for up to 6 h post-injection. As indicated by IBA1 and GFAP immunoreactivity and by PET imaging of TSPO, acute DFP intoxication triggered neuroinflammation in the hippocampus and cortex during the first 3 days that peaked at 7 days and persisted to 21 days post-exposure in most animals. Neurodegeneration was detected in multiple brain regions from 1 to 14 days post-exposure. All DFP-intoxicated animals exhibited significant deficits in contextual fear conditioning at 9 and 20 days post-exposure compared to vehicle controls. Whole-brain TSPO labeling positively correlated with seizure severity score, but did not correlate with performance in the contextual fear-conditioning task.
  
  
  
  We describe a preclinical model in which acute DFP intoxication causes seizures, persistent neuroinflammation, neurodegeneration, and memory impairment. The extent of the neuroinflammatory response is influenced by seizure severity. However, the observation that a subset of animals with moderate seizures and minimal TSPO labeling exhibited cognitive deficits comparable to those of animals with severe seizures and significant TSPO labeling suggests that DFP may impair learning and memory circuitry via mechanisms independent of seizures or neuroinflammation.
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA.
authors.forename: Brenna M
authors.initials: BM
authors.lastname: Flannery
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA.
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bruun
authors.affiliation: Center for Molecular and Genomic Imaging, University of California-Davis, Davis, CA, 95616, USA.
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Rowland
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA.|Current address: Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Sacramento, CA, 95812, USA.
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Banks
authors.affiliation: Department of Pediatrics, University of California-Davis Medical Center, Sacramento, CA, 95817, USA.|Current address: Navistar, Inc., 2701 Navistar Drive, Lisle, IL, 60532, USA.
authors.forename: Adam T
authors.initials: AT
authors.lastname: Austin
authors.affiliation: Center for Molecular and Genomic Imaging, University of California-Davis, Davis, CA, 95616, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Kukis
authors.affiliation: Division of Biomedical Sciences, University of California-Riverside School of Medicine, Riverside, CA, 92521, USA.
authors.forename: Yonggang
authors.initials: Y
authors.lastname: Li
authors.affiliation: Division of Biomedical Sciences, University of California-Riverside School of Medicine, Riverside, CA, 92521, USA.
authors.forename: Byron D
authors.initials: BD
authors.lastname: Ford
authors.affiliation: Department of Pediatrics, University of California-Davis Medical Center, Sacramento, CA, 95817, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Tancredi
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of California-Davis Medical Center, Sacramento, CA, 95817, USA.
authors.forename: Jill L
authors.initials: JL
authors.lastname: Silverman
authors.affiliation: Center for Molecular and Genomic Imaging, University of California-Davis, Davis, CA, 95616, USA.
authors.forename: Simon R
authors.initials: SR
authors.lastname: Cherry
authors.affiliation: Department of Molecular Biosciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA. pjlein@ucdavis.edu.
authors.forename: Pamela J
authors.identifier: 0000-0001-7665-7584
authors.initials: PJ
authors.lastname: Lein
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002800:Cholinesterase Inhibitors / Q000633:toxicity*; D060825:Cognitive Dysfunction / Q000139:chemically induced* / Q000000981:diagnostic imaging; D003214:Conditioning, Classical / Q000187:drug effects; D004660:Encephalitis / Q000139:chemically induced* / Q000000981:diagnostic imaging; D005106:Exploratory Behavior / Q000187:drug effects; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D007531:Isoflurophate / Q000633:toxicity*; D008279:Magnetic Resonance Imaging; D008297:Male; D008840:Microfilament Proteins / Q000378:metabolism; D049268:Positron-Emission Tomography; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism; D012044:Regression Analysis; D013997:Time Factors
chemical_list: C100745:Aif1 protein, rat; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D002800:Cholinesterase Inhibitors; D005904:Glial Fibrillary Acidic Protein; D008840:Microfilament Proteins; D011963:Receptors, GABA-A; D007531:Isoflurophate; C069997:Tspo protein, rat
keywords: Cognitive deficits; Diisopropylfluorophosphate; Neurodegeneration; Neuroinflammation; Organophosphate neurotoxicity; PET imaging; Sublethal effects; TSPO