Relative Potencies for Acute Effects of Pyrethroids on Motor Function in Rats

Abstract

The prevalence of pyrethroids in insecticide formulations has increased in the last decade. A common mode-of-action has been proposed for pyrethroids based on in vitro studies, which includes alterations in sodium channel dynamics in nervous system tissues, consequent disturbance of membrane polarization, and abnormal discharge in targeted neurons. The objective of this work was to characterize individual dose-response curves for in vivo motor function and calculate relative potencies for eleven commonly used pyrethroids. Acute oral dose-response functions were de-termined in adult male Long Evans rats for five Type I (bifenthrin, S-bioallethrin, permethrin, resmethrin, tefluthrin), five Type II (b-cyfluthrin, l-cyhalothrin, cypermethrin, deltamethrin, esfenvaler-ate) and one mixed Type I/II (fenpropathrin) pyrethroids (n = 8–18 per dose; 6–11 dose levels per chemical, vehicle = corn oil, at 1 ml/kg). Motor function was measured using figure-8 mazes