Effects of single exposure to chlorphenvinphos, an organophosphate insecticide, on electrical activity (EEG) of the rat brain.

The effect of a single exposure to an agricultural insecticide, chlorphenvinphos (CVP), an organophosphorus anticholinesterase, on neocortical seizure activity induced or promoted by cardiazol, and on hippocampal and neocortical EEG was studied in rats. It was found that CVP, given intraperitoneally in doses of 1.0 and 3.0 mg/kg, resulted in no changes in the number and in the duration of epileptic bursts occurring spontaneously, as well as in the content of the hippocampal theta rhythm. The effect of cardiazol (12.5 mg/kg, i.p.) was slightly diminished when the drug was given 3 hours, but not 14 days, after the injection of CVP. I.p. injection of a carbamate cholinesterase inhibitor, physostigmine, in a dose of 1.0 mg/kg resulted in a dramatic increase of the theta content in the hippocampal EEG, and in the total disappearance of the spontaneous seizures. Determination of cholinesterase activity in blood and in the brain in a separate group of subjects showed that after injection of physostigmine (1.0 mg/kg), the inhibition of this enzyme does not exceed the inhibition after injecting CVP in the doses used. It has been suggested that the differences between CVP and physostigmine in their potential to reduce spontaneous epileptic activity and to induce the hippocampal theta rhythm may be due to somewhat antagonistic action of CVP on cholinergic postsynaptic receptors.