The effects on behavior and cholinesterase (ChE) of an OP pesticide, dimethoate, were examined in wood mice under laboratory conditions. Mice were administered 0, 5, 15, or 50 mg/kg intraperitoneal dimethoate and their behavior was recorded in an open field for one hour. In a second experiment, using only the 0 and the 50 mg/kg dose, mice were subjected to 10-rain open field tests repeated at various time intervals during a 24-h period. Shortly after administration of dimethoate, there was a general, dose-dependent, behavioral depression that was characterized by increased inactivity and decreased grooming, rearing, and sniffing. The introduction of a novel object in the open field failed to elicit any reaction in mice treated with the two highest doses of dimethoate. The behavioral impairment completely disappeared 6 h after treatment. A stereotyped compulsive grooming was also observed in the first 30 rain after administration of the two highest doses. Exposure to dimethoate caused a dose-dependent decrease in ChE activity in the brain and in serum. Behavioral impairment was associated with maximum levels of ChE inhibition of 65-75% (brain) and 75-85% (serum). Recovery of ChE activity lagged behind that of behavioral impairment and started 3-6 h after dimethoate administration. The possible implications for free-living wood mice which inhabit cereal fields and may be exposed to OPs are discussed.
Exposure of vertebrates to organophosphate (OP) and carbamate pesticides results in the inhibition in the activity of cholinesterase (ChE) enzymes which are fundamental for the normal functioning of the cholinergic system. Sublethal depression of acetylcholinesterase (ACHE) activity in the brain has been related to several physiological effects in laboratory rodents, such as changes in nerve conductance , respiratory reflexes , and learning capabilities (Banks and