Brain acetylcholinesterase after acute parathion poisoning: a comparative quantitative histochemical analysis post mortem.

The postmortem distribution of acetylcholinesterase (AChE) inhibition was studied in the brains of 2 victims of lethal parathion intoxication and 2 control brains matched for age and sex. AChE activity in discrete brain regions was studied by quantitative histochemistry of 40-micron-thick sagittal or coronal cryostat sections from the 4 brains. Inhibition of human brain AChE by parathion is regionally selective. The biggest decreases (60-85%) were observed in the cerebellum, some thalamic nuclei, and the cortex. Only a moderate decrease (10-30%) was observed in the substantia nigra and basal ganglia, and no effect was seen in white matter. Detailed knowledge of the brain regions affected by parathion poisoning may explain some of the clinical manifestations of organophosphate poisoning.