Influence of intoxication by anticholinesterase agents on core temperature in rats: relationships between hypothermia and acetylcholinesterase inhibition in different brain areas.

The early and late effect of three anticholinesterase agents (physostigmine, paraoxon and soman) on core temperature and brain acetylcholinesterase (AcChE) inhibition are compared. The study was performed in adult male rats using sublethal doses of all drugs. AcChE activity was determined by hypothalamus, striatum, hippocampus, medulla oblongata-pons and rest of the brain. The co-existence of intoxication symptoms, hypothermia and AcChE inhibitions was clearly shown by the early effects. However, no relationship was found between the degree of hypothermia and that of inhibition whatever brain area. In contrast, late AcChE inhibition was not accompanied by symptoms and lowering of core temperature. Several hypotheses have been suggested to explain this phenomenon: de novo synthesis of enzyme, decreased sensitivity of neurotransmitter or return to normal of brain acetylcholine level through a negative feed back at the presynaptic level. The present data suggest that this latter assumption is the most likely.