Characterization of Cortical Glial Scars in the Diisopropylfluorophosphate (DFP) Rat Model of Epilepsy

Abstract

Glial scars have been observed following stab lesions in the spinal cord and brain but not observed and characterized in chemoconvulsant-induced epilepsy models. Epilepsy is a disorder characterized by spontaneous recurrent seizures and can be modeled in rodents. Diisopropylfluorophosphate (DFP) exposure, like other real-world organophosphate nerve agents (OPNAs) used in chemical warfare scenarios, can lead to the development of status epilepticus (SE). We have previously demonstrated that DFP-induced SE promotes epileptogenesis which is characterized by the development of spontaneous recurrent seizures (SRS), gliosis, and neurodegeneration. In this study, we report classical glial scars developed in the piriform cortex, but not in the hippocampus, by 8 days post-exposure. We challenged both male and female rats with 4–5 mg/kg DFP (s.c.) followed immediately by 2 mg/kg atropine sulfate (i.m.) and 25 mg/kg pralidoxime (i.m.) and one hour later by midazolam (i.m). Glial scars were present in the piriform cortex/amygdala region in 73% of the DFP treated animals. No scars were found in controls. Scars were characterized by a massive clustering of reactive microglia surrounded by hypertrophic reactive astrocytes. The core of the scars was filled with a significant increase of IBA1 and CD68 positive cells and a significant reduction in NeuN positive cells compared to the periphery of the scars. There was a significantly higher density of reactive GFAP, complement 3 (C3), and inducible nitric oxide synthase (iNOS) positive cells at the periphery of the scar compared to similar areas in controls. We found a significant increase in chondroitin sulfate proteoglycans (CS-56) in the periphery of the scars compared to a similar region in control brains. However, there was no change in TGF-β1 or TGF-β2 positive cells in or around the scars in DFP-exposed animals compared to controls. In contrast to stab-induced scars, we did not find fibroblasts (Thy1.1) in the scar core or periphery. There were sex differences with respect to the density of iNOS, CD68, NeuN, GFAP, C3 and CS-56 positive cells. This is the first report of cortical glial scars in rodents with systemic chemoconvulsant-induced SE. Further investigation could help to elucidate the mechanisms of scar development and mitigation strategies.

DFP-Induced Status Epilepticus Severity in Mixed-Sex Cohorts of Adult Rats Housed in the Same Room: Behavioral and EEG Comparisons

“…In subsequent studies, we challenged females with 5 mg/kg DFP rather than 4 mg/kg. We found no significant difference in initial SE severity in females treated with 5 mg/kg compared to males treated with 4 mg/kg ( Gage et al, 2021a ; Gage et al, 2022a ). Interestingly, females had less variable SE severity at 5 mg/kg than males at 4 mg/kg.…”

“…The source of the DFP was from the same company (Sigma Aldrich, United States ) for all our experiments, but the batches were different. In our previous studies, female rats always received higher doses than males to achieve a similar SE severity ( Gage et al, 2020 ; 2021a ; 2021b ; 2022a ). In this study, we also used the DFP from different batches but the same vendor as our previous studies.…”

“…However, a repeated-low-dose approach is not suitable for DFP, soman, or other OPNA models as it does not mimic the real-world exposure of OPNAs to the general public. We and others have demonstrated that both DFP and soman models demonstrated the classical features of epilepsy, such as the onset of spontaneously recurring CS, gliosis, and neurodegeneration ( Apland et al, 2014 ; Apland et al, 2018 ; Lumley et al, 2019 ; Putra et al, 2020a , 2020b ; Rojas et al, 2020 ; Gage et al, 2021a , 2022a , 2022b ; González et al, 2021 ; Reddy et al, 2021 ). Off note, some of these studies used pyridostigmine bromide (PB) or other medical countermeasures such as HI-6 or 2-PAM as a pretreatment to minimize mortality ( Anderson et al, 1992 ; Apland et al, 2014 ; de Araujo Furtado et al, 2010 ; Reddy et al, 2020 , 2021 ).…”

Repurposing the Memory-promoting Meclofenoxate Hydrochloride as a Treatment for Parkinson‘s Disease through Integrative Multi-omics analysis

“…The neuronal nuclear protein (NeuN) is often used as a positive marker for the functional state of postmitotic neurons. Thus, the NeuN-positive rate of neurons is usually used to assess neurodegeneration [49][50][51] was lower than that of the NC group (relative expression of TH=4.49) (P = 1.8× 10 -2 ).…”

Sex‐based structural and functional MRI outcomes in the rat brain after soman (GD) exposure‐induced status epilepticus

“…Organophosphate nerve agents (OPNAs) such as soman, sarin, tabun, VX, and cyclosarin are chemically weaponizable and pose potential threats to both civilians and military personnel worldwide. Following OPNA exposure, prolonged convulsive seizures or status epilepticus (SE) ensues, 1–5 with no effective treatments for the victims 6,7 . OPNAs are irreversible acetylcholinesterase (AChE) inhibitors that cause acute respiratory and cardiac symptoms 8–11 .…”