Brain electrical activity (EEG) after repetitive exposure to chlorphenvinphos an organophosphate anticholinesterase: I. Rabbit.

Abstract

Cholinesterase (ChE) activity in blood and brain as well as the hippocampal and cortical EEG were investigated in rabbits exposed once a day for a period of two weeks to an organophosphate insecticide, chlorphenvinphos (CVP). The daily dose of CVP was 14.0 mg/kg i.p. ChE activity in plasma and erythrocytes decreased by 60 and 48%, respectively, by the end of exposure and returned to the preexposure level within 35 days. In the exposed animals, killed and dissected a day after, the ChE activity in blood had been found normal, the level of ChE activity in some parts of the brain was still significantly depressed. The spontaneous hippocampal EEG showed no changes as soon as 24 hours after the exposure. However, after a period sufficiently long for the normalization of ChE activity in blood, the hippocampal arousal response (theta rhythm) to click and to a tone associated with pain was found heightened in the exposed rabbits. Moreover, spectral analysis of 5 minute EEG samples revealed a decrease in the content of 7-13 Hz activity in the cortex of the exposed animals as compared to the control ones. The obtained data suggest that exposure to CVP may lead to functional changes in the brain outlasting the period of ChE depression.