Inhibition of brain and plasma cholinesterase activity in zebra finches orally dosed with fenitrothion

Zebra finches (Poephila guttata) were given single oral doses of fenitrothion insecticide dissolved in soya bean oil. Brain and plasma cholinesterase (ChE) activities were measured periodically up to 10 d postexposure. Dosage rates of 1.04, 3.80 and 11.36 mg active ingredient/kg body weight resulted in maximum brain ChE inhibitions of 50, 70 and 75%, and maximum plasma ChE inhibitions of 78, 82 and 89%, respectively. Recovery of ChE activity in vivo followed an exponential pattern, with plasma ChE activity recovering more rapidly than brain ChE activity. At dosage rates of 1.04 and 3.80 mg/kg, plasma ChE activity recovered to normal in 1 to 2 d. Brain ChE activity was inhibited up to 10 d after dosing at 1.04 mg/kg. There was some mortality of exposed birds at the two higher dosage rates. Birds that died exhibited brain ChE inhibitions ranging from 3 to 84%.