Neonatal exposure to DDT induces increased susceptibility to pyrethroid (bioallethrin) exposure at adult age.--Changes in cholinergic muscarinic receptor and behavioural variables.

We have recently reported that DDT and the pyrethroid bioallethrin cause similar changes in the brain muscarinic cholinergic receptors (MAChR) and behavioural disturbances in the neonatal and adult mouse when given to neonatal mice during the peak of rapid brain growth. In the present study the interaction between neonatal and adult exposure to DDT and bioallethrin, respectively, is explored. Ten-day-old NMRI mice received a single low oral dose of DDT (0.5 mg/kg body wt). At adult age (5 months) the mice received bioallethrin 0.7 mg/kg body wt./day per os for 7 days. Mice used as controls received a 20% fat emulsion vehicle. The spontaneous behavioural tests revealed significant differences, both in mice treated neonatally with DDT and receiving bioallethrin as adults and in mice receiving the vehicle as neonates and bioallethrin as adults, compared with their corresponding controls. However, the behavioural changes developed in mutually opposite directions. Significant changes in MAChR, assayed in the P2 fraction of the cerebral cortex by using the muscarinic antagonist, quinuclidinyl benzilate ([3H]QNB) and agonist carbachol, was only observed in animals receiving DDT as neonates and bioallethrin as adults. The present study indicates an increased susceptibility in the cholinergic muscarinic receptors and a different behaviour reaction in animals already exposed to DDT (at a physiologically relevant dose), when again exposed to a similar neurotoxic agent as adults.