Effects of a single exposure to chlorphenvinphos, an organophosphate insecticide, on hot-plate behaviour in rats.

Effect of a single i.p. exposure to an organophosphate insecticide, chlorphenvinphos (CVP), in doses of 1.0 and 3.0 mg/kg (one third and one tenth LD50, respectively), on the latency of the paw-lick response (hot plate test) was investigated in rats before and after a short inescapable footshock. The test was repeated twice on the 18th and 19th days after the exposure, i.e. after a time sufficient for a full recovery of cholinesterase activity in the blood and brain. On the first day of testing the groups did not differ with respect to the paw-lick latency before footshock. However, the paw-lick latency after footshock (the index of stress-induced analgesia) was significantly longer in rats exposed to the higher dose of CVP (3.0 mg/kg) than in the control animals. Twenty four hours later, in the control animals, the paw-lick latencies before footshock were shortened in comparison with those recorded on the day before. An opposite effect was observed in the rats exposed to 3.0 mg/kg of CVP. The data suggest that some alterations in the brain functional state may outlast the CVP induced depression of cholinesterase activity.