VEHICLE AND ROUTE DEPENDENT EFFECTS OF A PYRETHROID INSECTICIDE, DELTAMETHRIN, ON MOTOR FUNCTION IN THE RAT

Deltamethrin is a potent neuroactive pyrethroid insecticide. Literatur e reports of the in vivo potency of deltamethrin, however, vary by gre ater than three orders of magnitude in studies employing numerous vehi cles and routes of exposure. Therefore, the present study systematical ly 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 oi l, glycerol formal, Emulphor(R), or methylcellulose). A reduction in m otor activity as measured in figure-8 mazes was used to index the pote ncy of this pesticide on CNS function. Dose-effect and time-course det erminations were made for each combination of vehicle and route. Resul ts demonstrated that the potency of deltamethrin was dependent on both the route of administration and the vehicle. The ED(50) for deltameth rin was 5.1 mg/kg when administered PO in corn oil, whereas, the ED(50 ) was > 1000 mg/kg when administered PO in methylcellulose. Thus, repo rted discrepancies in the potency of deltamethrin on CNS function are at least partially attributable to route of administration and vehicle .