On the development of behavioral tolerance to the organophosphate insecticide phosalone in rats

Abstract

Organophosphate pesticides exert their toxic effects by cholinesterase inhibition and the consequent proiongation of the undesirable effects of accumulation of acetylcholine. The signs of toxicity include tremors. convulsions. lachrymation. urination. defecation etc. However. prolonged cholinesterase inhibition through sustained administration of organophosphates could lead to the gradual disappearance of the in itial signs of toxicity in the course of time. termed behavioral tolerance. The present study was undertaken to examine in albino rats the development of behaviorai tolerance to phosalone. an organophosphate insecticide commonly used in agricultural operations. After determining the LD₅₀ dose, oral doses ranging between ½ LD₅₀ to ¹/₈ LD₅₀ (both inciusive) were . administered daily for a period of 15 days to six batches of rats (each batch of 12- 20 animals ), and changes in consummatory behavior (eating and drinking), body weight and cumulative mortality were monitored daily to assess the development of behavioral tolerance at a particu lar dose. The onset and disappearance and frequency of toxic signs and symptoms were also taken into consideration to arrive at a daily sublethal tolerable oral dose of phosalone. A dose of ¼LD₅₀ was finally selected for daily dosing for 15 days. The occurrence of tremors and convulsions was observed each day after dosing during a time period of 6h at intervals of ½h. 2h, 3h, and 6h. The study revealed that albino rats develop behavioral tolerance to phosalone toxicity. This may have implications in agricultural operations employing this insecticide.

Key words: Organophosphates. Phosalone. Albino rats, Behavioral tolerance.