The sensitivity of the developing mammalian central nervous system (CNS) to organophosphorus (OP) nerve agents and the safety of antidotes such as atropine and pralidoxime, commonly used against acute OP toxicity, in pregnant women and the developing fetuses are hitherto unknown. Thus, during the 1995 terrorist attack with sarin in the Tokyo subway, pregnant women who sought medical attention after presenting mild signs of OP intoxication received no therapeutic treatment. The urgency of studies to investigate the developmental neurotoxicity of OP nerve agents is underscored by the recent report of the neurobehavioral teratogenicity of sarin in an avian model. In recent years, galantamine, a drug currently approved to treat Alzheimer's disease, emerged as an effective antidote against acute OP poisoning in neonatal, prepubertal, and adult guinea pigs. Treatment with galantamine was also shown to counteract the cognitive deficits and anxiety-like behavior seen months after a single exposure of prepubertal guinea pigs to 0.6-1.0xLD50 soman. The present project is, therefore, aimed at testing the central hypothesis that the developing mammalian CNS is exquisitely sensitive to the nerve agents sarin and soman and that galantamine or atropine will be effective medical countermeasures against the developmental neurotoxicity of these agents. The guinea pig will be the animal model of choice because: (i) brain development of guinea pigs closely resembles that of humans and non-human primates and (ii) like humans, guinea pigs have low levels of circulating carboxylesterases - the enzymes that metabolically inactivate OP compounds. The immediate goals of this project are: (i) to identify the effects of a prenatal exposure to soman or sarin on neurobehavior as well as functional, structural, and metabolic integrity of the brain of guinea pigs, and (ii) to assess the safety and effectiveness of galantamine or atropine, at doses that are compatible with human use, to counter the developmental toxicity of the nerve agents. Pregnant guinea pigs will receive, at a critical gestational period (GD 50-52), a subcutaneous injection of vehicle or a given dose (0.6x or 1.0xLD50) of soman or sarin. Subsequently (1 or 24 h later), the sows will be treated with saline (0.5 ml/kg, im) or a clinically relevant dose of galantamine (8 mg/kg, im) o atropine (0.5 mg/kg, im). On postnatal days 35-40 (prepuberty) and 120-125 (young adulthood), cognitive and emotional behavior of the animals will be analyzed. To examine the effects of the prenatal exposure to the nerve agents on electrical brain activity, electroencephalographic activity will be telemetrically monitored prior to the behavioral tests. Magnetic resonance imaging and spectroscopy will be used to identify deviations in brain structure and metabolism. The results of these translational, multidisciplinary studies will be far reaching as they will laythe groundwork necessary to advance research aimed at identifying safe and effective therapeutic strategies to treat even the most sensitive sector of the population in the event of a terrorist attack with sarin and soman.
The overarching goal of this project is to provide fundamental and timely input for assessment of the developmental toxicity of the nerve agents soman and sarin and identification of lead compounds for adequate treatment of neuropathologies that result from prenatal exposure to these agents.