Nerve agents are lethal chemical weapons that have been used in war and in terrorist attacks, with devastating consequences; the possibility that they will be used again against civilians is presently very high. One of the clinical manifestations of exposure to nerve agents is seizure activity progressing to status epilepticus (SE) which can lead to death, or brain damage with long-term neurological and behavioral consequences. The American Academy of Pediatrics have pointed out the reasons that children may be more vulnerable to nerve agent toxicity; yet, there is very little information on the appropriate countermeasures to protect the pediatric population, as data in immature animals are lacking. The FDA has approved diazepam as the anticonvulsant treatment for nerve agent-induced SE, irrespective of the age of the victim. However, there is sufficient evidence indicating that diazepam does not have good neuroprotective efficacy, and, in the developing brain, it may worsen the injury induced by the SE. Animal data are, therefore, needed to provide knowledge on how to protect the immature brain from damage in the event of nerve agent exposure, taking into account that GABAA receptor-mediated activity can be excitatory in the developing brain, while glutamatergic activity and particularly the activity of NMDA receptors, which are well known for their role in excitotoxicity, is very pronounced. We have already demonstrated the efficacy of LY293558, an AMPA/GluK1 receptor antagonist, in stopping seizures and significantly reducing neuropathology and long-term deficits in adult rats exposed to soman. We have also tested the combination of LY293558 with caramiphen, an antimuscarinic with NMDA receptor antagonistic properties, and found that it terminates soman-induced seizures faster than LY293558 alone, provides full protection from neuronal damage in all brain regions examined, and the recovery of the animals is swift with no weight loss. In the present application, we propose to test and compare the efficacy of LY293558+caramiphen with that of LY293558 alone, and with two benzodiazepines, diazepam and midazolam, against soman, in male and female rats of postnatal age 7, 12, and 21 days; anticonvulsant treatments will be administered 1 h after soman exposure. We hypothesize that LY293558+caramiphen will provide more benefits than LY293558 alone, and will prove to be far superior to both diazepam and midazolam in stopping soman-induced seizures, preventing neuronal degeneration, neuronal loss, GABAergic interneuronal loss, atrophy and pathophysiological alterations in the amygdala and hippocampus, as well as cognitive, behavioral, and neurological deficits studied up to 6 months postexposure. The data acquired will contribute immensely in developing safe and efficacious countermeasures for protecting the lives of infants and children and prevent long-term morbidities.
The anticonvulsant that is presently approved by the FDA for treating status epilepticus induced by nerve agent exposure is the benzodiazepine diazepam, irrespective of the age of the victim. However, evidence has been accumulating that benzodiazepines have little neuroprotective efficacy and may worsen the injury induced by seizures in the immature brain, possibly because of the excitatory nature of GABAA receptor-mediated activity during development. Considering the pronounced glutamatergic activity in the developing brain, and particularly that of NMDA receptors which are well known for their role in excitotoxicity, we propose to test a combination therapy consisting on an AMPA/GluK1 receptor antagonist, LY293558, which has been highly efficacious against the nerve agent soman in adult rats, along with the muscarinic caramiphen which has NMDA receptor antagonistic properties, in soman-exposed male and female rats of postnatal day 7, 12, and 21, and compare this combination treatment with LY293558 alone and two benzodiazepines, diazepam and midazolam. The data obtained from these studies will contribute immensely in developing safe and efficacious countermeasures for protecting the lives of infants and children and prevent long-term morbidities.
