OBJECTIVETo study the acute effects of dimethoate on the muscarinic-receptors(M1, M2) in the brain of rats.

METHODS24 Sprague-Dawley rats were divided into 4 groups randomly. They were administered subcutaneously with 0, 25, 50, 100 mg/kg dimethoate, respectively. Brains were removed after 48 hours of administration. Radioligand binding assay was used to determine the density and affinity of M1 and M2 receptors.

RESULTSRats in the treated group showed low density of M1 and M2 receptors compared with the control rats. The brain M1 receptor density of the rats in the highest dosage group was significantly lower than that in the control group while brain M2 receptors density had a decrease trend with increasing dosage, but the difference showed no significance. However, there were no differences of the affinity of both M1 and M2 among different treated groups. Correlation analysis showed there is positive relationship between cholinesterase activity and density of M1 receptors(r = 0.583, P < 0.01).

CONCLUSIONM1 and M2 receptors density decreased with the increasing dosage of dimethoate. It is suggested that the alleviating of cholinergic symptoms may be due to the decrease of M1 and M2 receptors in rat brain.

Animals ; Brain ; drug effects ; metabolism ; Cholinesterases ; metabolism ; Dimethoate ; pharmacology ; Dose-Response Relationship, Drug ; Radioligand Assay ; Rats ; Rats, Sprague-Dawley ; Receptor, Muscarinic M1 ; analysis ; drug effects ; Receptor, Muscarinic M2 ; analysis ; drug effects