Changes in behavior and muscarinic receptor density after neonatal and adult exposure to bioallethrin.

Throughout life, mammals are exposed to environmental toxicants, some of which have acute effects on the nervous system. Early, low-dose exposure in combination with later re-exposure and possible interference with normal aging have been little studied. The present study revealed increased susceptibility in adult mice, exposed neonatally to a low dose of the insecticide bioallethrin, to renewed exposure to bioallethrin as adults. Ten-day-old Naval Medical Research Institute male mice received bioallethrin orally (0.7 mg per kg body weight per day for 7 days). When aged 5 months they were given the same dose of bioallethrin by gavage. Twenty-four hours after the last administration, a spontaneous motor activity test revealed significant aberrations in mice exposed both neonatally and as adults to bioallethrin. The density of muscarinic receptors was significantly increased. When aged 7 months, spontaneous behavioral disturbances and muscarinic receptor changes persisted and learning and memory deficits had developed. These results indicate that neonatal exposure to bioallethrin has the potential to increase susceptibility of the adult mouse to a new exposure at a dosage that does not have any effect in animals treated neonatally with vehicle.