| Popis: |
The aim of the present study was to investigate persistent neurobehavioural effects of repeated low-level exposure to chlorphenvinphos ((2-chloro-1-(2,4-dichlorophenyl) vinyl diethyl phosphate-CVP) in rats. The rats received 10 i.p. injections of CVP at daily doses of 0.5 mg/kg or 1.0 mg/kg (one injection/day, five days/week) which corresponded to 1/20 and 1/10 of LD50, respectively, for this species. In a part of the rats, cholinesterase (ChE) activity in blood (plasma and erythrocytes), and in the selected brain regions was determined at arbitrarily chosen time after the last exposure. The determinations showed that the level of ChE inhibition was dose-related, but the compartments studied differed in the magnitude of this effect. The differences in the level of ChE inhibition between the compartments were particularly evident in rats which had received CVP at the 1.0 mg/kg dose; in these animals 3 h after exposure the ChE activity in erythrocytes, plasma and the brain corresponded to 78%, 48% and 67-70%, respectively, of the control value. Enzyme activity returned to the control level after 14 days in plasma and after 35 days in erythrocytes. In rats receiving CVP at daily doses of 0.5 mg/kg, ChE activity in plasma was decreased by 40.8% and that in erythrocytes by 21.4% 3 h after the last exposure. The activity of ChE in plasma returned to the control level within four days and that in erythrocytes within 14 days. In these rats, in all the brain regions studied except brainstem, ChE activity was not reduced significantly. In rats selected for behavioural tests, the following behavioural aspects were investigated: response to novelty in an open field, acquisition and extinction of a one-way active avoidance response, and the magnitude and persistence of the footshock-induced analgesia (hot-plate test). Testing in the open field was performed before the exposure and then 1, 3 and 6 weeks after the last exposure. The remaining tests were performed after the exposure. The interval between testing and the last CVP injection was sufficient for recovery of ChE activity. It has been found that in rats of both exposure groups the response to novelty in the open field, i.e. the increase in locomotor and exploratory activity in the presence of a new object, was reduced, albeit nonsignificantly, compared to the unexposed animals. In rats which received CVP at the dose of 1.0 mg/kg, acquisition of the one-way active avoidance response was facilitated. No differences between groups were found during extinction of this response. In the hot-plate test, in rats exposed repeatedly to 1.0 mg/kg CVP, the footshock-induced increase in the latency of the paw-lick response to heat (54.5 degrees C) was stronger and more persistent than in the unexposed animals. The above results show that some neurobehavioural effects of exposure to organophosphorous (OP) compounds may be detected after a time sufficient for recovery of ChE activity. |
