Developmental pyrethroid exposure causes long-term decreases of neuronal sodium channel expression

Pyrethroid insecticide use has increased over recent years because of their low to moderate acute toxicity in mammals. However, there is increasing concern over the potential detrimental effects of pyrethroids on developing animals. Most recently, we have shown that developmental exposure to deltamethrin results in long-term neurobehavioral effects. Pyrethroids exert their toxicity by acting on the voltage-gated sodium channel (Na_v), delaying channel inactivation and causing hyperexcitability in the nervous system. Previous in vitro studies found that exposure to agents that increase Na⁺ influx, including deltamethrin decreased Na_v mRNA expression. However, it is unknown whether this occurs in vivo. To determine whether developmental pyrethroid exposure decreases Na_v mRNA expression, pregnant mice were exposed to the pyrethroid deltamethrin (0 or 3mg/kg) every three days throughout gestation and lactation. Na_v mRNA expression was measured in the striatum and cortex of the offspring at 10-11 months of age, a time at which behavioral abnormalities were still observed. Developmental exposure to deltamethrin decreased expression of Na_v mRNA in a region- and isoform-specific fashion by 24-50%. Deltamethrin exposure also resulted in the persistent down-regulation of brain-derived neurotrophic factor (Bdnf) in the striatum by 66% but not in the cortex, suggesting a plausible mechanism for some of the associated behavioral effects observed previously. Taken together these data suggest that developmental deltamethrin exposure results in persistent deficits in Na_v and BDNF mRNA expression that may contribute to long-term behavioral deficits.