Vehicle and route dependent effects of a pyrethroid insecticide, deltamethrin, on motor function in the rat

Deltamethrin is a potent neuroactive pyrethroid insecticide. Literature reports of the in vivo potency of deltamethrin, however, vary by greater than three orders of magnitude in studies employing numerous vehicles and routes of exposure. Therefore, the present study systematically compared IP and PO routes of exposure to deltamethrin (0.3-1000 mg/kg) delivered to adult rats in one of four different vehicles (corn oil, glycerol formal, Emulphor, or methylcellulose). A reduction in motor activity as measured in figure-8 mazes was used to index the potency of this pesticide on CNS function. Dose-effect and time-course determinations were made for each combination of vehicle and route. Results demonstrated that the potency of deltamethrin was dependent on both the route of administration and the vehicle. The ED50 for deltamethrin was 5.1 mg/kg when administered PO in corn oil, whereas, the ED50 was > 1000 mg/kg when administered PO in methylcellulose. Thus, reported discrepancies in the potency of deltamethrin on CNS function are at least partially attributable to route of administration and vehicle.