Development of a Prolonged Calcium Plateau in Hippocampal Neurons in Rats Surviving Status Epilepticus Induced by the Organophosphate Diisopropylfluorophosphate

Abstract

Organophosphate (OP) compounds are among the most lethal chemical weapons ever developed and are irreversible inhibitors of acetylcholinesterase. Exposure to majority of OP produces status epilepticus (SE) and severe cholinergic symptoms that if left untreated are fatal. Survivors of OP intoxication often suffer from irreversible brain damage and chronic neurological disorders. Although pilocarpine has been used to model SE following OP exposure, there is a need to establish a SE model that uses an OP compound in order to realistically mimic both acute and long-term effects of nerve agent intoxication. Here we describe the development of a rat model of OP-induced SE using diisopropylfluorophosphate (DFP). The mortality, behavioral manifestations, and electroencephalogram (EEG) profile for DFP-induced SE (4 mg/kg, sc) were identical to those reported for nerve agents. However, significantly higher survival rates were achieved with an improved dose regimen of DFP and treatment with pralidoxime chloride (25 mg/kg, im), atropine (2 mg/kg, ip), and diazepam (5 mg/kg, ip) making this model ideal to study chronic effects of OP exposure. Further, DFP treatment produced N-methyl-D-aspartate (NMDA) receptor-mediated significant elevation in hippocampal neuronal [Ca(2+)](i) that lasted for weeks after the initial SE. These results provided direct evidence that DFP-induced SE altered Ca(2+) dynamics that could underlie some of the long-term plasticity changes associated with OP toxicity. This model is ideally suited to test effective countermeasures for OP exposure and study molecular mechanisms underlying neurological disorders following OP intoxication.

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).…”

Caramiphen edisylate as adjunct to standard therapy attenuates soman-induced seizures and cognitive deficits in rats

“…The increased activation of NMDA receptors by elevated concentrations of extracellular glutamate may be one of the mechanisms responsible for the accumulation of intracellular Ca 2+ and subsequent initiation of cell death (Delorenzo et al, 2005). This elevation of intracellular Ca 2+ in OP-exposed hippocampal neurons plateaus for more than a week following the initial exposure and is still elevated at 1 month (Deshpande et al, 2010). The impact of nerve agent-induced seizure activity on these two neurotransmitter systems suggests that drugs with anticholinergic and antiglutamatergic properties may be effective adjunct treatments for nerve agent exposure (Weissman and Raveh, 2008).…”

Long-term Continuous EEG Monitoring in Small Rodent Models of Human Disease Using the Epoch Wireless Transmitter System

“…Status epilepticus can be induced in adult rats by injecting the animals with the organophosphate, DFP 22,23 . The data in Figure 5 show repetitive EEG discharges, which are indicative of status epilepticus (see temporal expansions Figure 5A, B).…”

“…Multiple channels of recording allow for the recording of multi-modal biopotentials, such as electrocardiogram and electroencephalogram. Animal models of co-morbidities will benefit by the ability to record biopotentials during behavior [21][22][23] . Combining behavior with EEG monitoring will provide researchers with a better tool for research and pre-clinical studies.…”