Low-dose effects of paraoxon in adult mice exposed neonatally to DDT: changes in behavioural and cholinergic receptor variables.

This study revealed increased susceptibility in adult mice, exposed neonatally to a low dose of DDT (1,1,1-trichloro-2,2-bis( p-chlorofenyl)ethane), to develop changes in behaviour and cholinergic muscarinic receptors when exposed as adults to the organophosphorus insecticide paraoxon. 10-day-old NMRI male mice were given a single oral dose of DDT (0.5 mg/kg body weight). At the age of 5 months, paraoxon was administered by gavage as a single dose (0.7 or 1.4 mg/kg body weight) every 2nd day for 1 week. These doses caused approximately 15% and 45% inhibition of acetylcholinesterase respectively, 48 h after the last exposure. 24 h after the last paraoxon administration, a spontaneous motor activity test revealed no differences between any of the adult paraoxon-treated mice and their corresponding controls, though when the test was performed again 2 months later, mice exposed neonatally to DDT and given paraoxon as adults had developed changes in spontaneous behaviour. The density of muscarinic cholinergic receptors was significantly increased in this group. No significant changes were seen in either behaviour or muscarinic receptors in mice exposed neonatally to the vehicle and receiving paraoxon as adults and there were no significant differences in the muscarinic or nicotinic subpopulations investigated, between any of the treatment groups. These results show that a dose of paraoxon not having any effect in vehicle-treated animals can cause effects in animals neonatally exposed to DDT.