Development of status epilepticus, sustained calcium elevations and neuronal injury in a rat survival model of lethal paraoxon intoxication

Abstract

Paraoxon (POX) is an active metabolite of organophosphate (OP) pesticide parathion that has been weaponized and used against civilian populations. Exposure to POX produces high mortality. OP poisoning is often associated with chronic neurological disorders. In this study, we optimize a rat survival model of lethal POX exposures in order to mimic both acute and long-term effects of POX intoxication. Male Sprague-Dawley rats injected with POX (4 mg/kg, ice-cold PBS, s.c.) produced a rapid cholinergic crisis that evolved into status epilepticus (SE) and death within 6–8 min. The EEG profile for POX induced SE was characterized and showed clinical and electrographic seizures with 7–10 Hz spike activity. Treatment of 100% lethal POX intoxication with an optimized three drug regimen (atropine, 2 mg/kg, i.p., 2-PAM, 25 mg/kg, i.m. and diazepam, 5 mg/kg, i.p.) promptly stopped SE and reduced acute mortality to 12% and chronic mortality to 18%. This model is ideally suited to test effective countermeasures against lethal POX exposure. Animals that survived the POX SE manifested prolonged elevations in hippocampal [Ca2+]i (Ca2+ plateau) and significant multifocal neuronal injury. POX SE induced Ca2+ plateau had its origin in Ca2+ release from intracellular Ca2+ stores since inhibition of ryanodine/ IP3 receptor lowered elevated Ca2+ levels post SE. POX SE induced neuronal injury and alterations in Ca2+ dynamics may underlie some of the long term morbidity associated with OP toxicity.

Chronic Treatment with Naltrexone Prevents Memory Retention Deficits in Rats Poisoned with the Sarin Analog Diisopropylfluorophosphate (DFP) and Treated with Atropine and Pralidoxime

“…If toxicity developed, antidotal therapy was initiated with SC atropine (2 mg/kg in 0.40-0.45 ml) and SC pralidoxime (25 mg/kg in 0.20-0.30 ml) and repeated as needed. Doses chosen were the same used in other studies of OP intoxication [20] and also replicated those used in our prior study [6]. Twenty-four hours later, the rats that received DFP were then randomized to the DFPnaltrexone group to receive SC naltrexone (5 mg/kg/day in 0.2-0.3 ml; N=9) for 12 weeks, or the DFP-saline group to receive an equal volume of SC saline for the same time period (N=8).…”

Rapid Throughput Analysis Demonstrates that Chemicals with Distinct Seizurogenic Mechanisms Differentially Alter Ca2+ Dynamics in Networks Formed by Hippocampal Neurons in Culture

“…In animal models of epilepsy, patterns of dysregulated Ca 21 dynamics have been well established (McNamara et al, 2006;Deshpande et al, 2010Deshpande et al, , 2014Chen, 2012). Aberrant Ca 21 dynamics have been proposed to be a major, if not essential, contributor to seizure induction and pathophysiology (McNamara et al, 2006;Chen, 2012).…”

Chronic behavioral and cognitive deficits in a rat survival model of paraoxon toxicity

“…By optimizing the standard three-drug regimen of atropine, pralidoxime chloride (2-PAM), and diazepam we were able to achieve a significantly higher survival rates. We also observed multi-focal neuronal injury and protracted hippocampal Ca 2+ elevations following severe DFP and POX exposures (Deshpande et al, 2010, Deshpande et al, 2014). Given the critical role of Ca 2+ signaling in neuronal plasticity, these severe OP induced alterations in Ca 2+ dynamics could underlie some of the long-term plasticity changes associated with OP and nerve agent toxicity (Filbert et al, 2005).…”

“…We have recently reported the development of a rat survival model of severe OP intoxication using POX and DFP (Deshpande et al, 2010, Deshpande et al, 2014). The mortality, behavioral manifestations, and electroencephalogram profile for DFP and POX-induced cholinergic crisis were identical to those reported for human OP and nerve agent exposures.…”