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.