| Organophosphorus pesticides, carbamate pesticides and pyrethroid pesticides have beenwidely used in the agriculture, forestry and health industry, because of their characteristics ofhigh efficiency, low toxicity and low residue. These three kinds of pesticide, being called neuralinhibitive pesticide, can act on the nervous system of animal, and then produce thecorresponding neurotoxicity. The.present research shows that, the organophosphorus pesticidesmainly exert toxic effects by the inhibition of acetylcholinesterase (AChE) activity and they alsocan directly inhibit activity muscarinic acetylcholine receptor (mAChR) and nicotinicacetylcholine receptor(nAChR); carbamate pesticides,which have similar inhibitory effect withthe Organophosphorus pesticide, also mainly inhibit the activity of acetylcholinesterase;Pyrethroid pesticides result in nerve toxicity, mainly by inhibiting the Na+channel on themembrane and damaging the nervous system. Danio rerio is an ideal model for the study ofvertebrate toxicity because of the characteristics of small individual, high reproductive rate, easyoperation and sensitive of the poison reaction.This paper selected the organophosphorus pesticide malathion, carbamate pesticidemethomyl and pyrethroid pesticide deltamethrin as toxic to adult Danio rerio. According to the50%Lethal Concentration(24h-LC50) to Danio rerio of the three pesticides, three concentrationgroups,0.5TU,1TU and2TU were setting. For analyzing the variation of the activity of twokinds of receptor in Danio rerio, the change trends of the mAChR and nAChR activity weredetermined with different time and different pesticides concentrations. The supportive data forthe further study of the influence mechanisms of neural inhibitive pesticide to cholinergic systemand cholinergic receptor activity was provided. The results showed that:1.24h acute toxicity test indicated that: the24h-LC50of malathion, methomyl anddeltamethrin on Danio rerio were9.48μg/L,2299.23μg/L and5.32μg/L. Malathion anddeltamethrin are highly toxic poisons to Danio rerio, but methomyl is a moderately toxic poison.Danio rerio mortality rate was positively correlated to the concentration of the three kinds ofpesticides, which had a high correlation coefficient, and this correlation has obvious dose-effect relationship. Danio rerio can exhibit significant behavioral changes by different poisons, whichis related to the adaptation of Danio rerio in toxic condition.2. Malathion, methomyl and deltamethrin have obvious inhibitory effects on mAChR ofDanio rerio. Methomyl has the biggest inhibitory effect, however in low concentration (0.5TU),the most significant inhibitor is deltamethrin. With the increase of exposure time, mAChRactivity of each concentrations was decreased, and basically conformed that the more exposureconcentration, the more obvious inhibitory effect. During exposure, rebound phenomenon ofaction could appear sometimes, which may be related to the adaptation of Danio rerio to toxicenvironment. Therefore, in the continuous exposure of different pesticides, mAChR activity maybe increased or decreased in different time, but the general trend is down.3. Malathion, methomyl and deltamethrin have certain inhibitory effects on nAChR ofDanio rerio, but overall, the inhibitory effect was less than that on mAChR. The most obviousinhibitory effect on the activity of nAChR was deltamethrin, up to39.88%. However, in0.5TUconcentrations, only malathion had significantly inhibitory effect by difference analysis. It is notobvious that the activity of nAChR was decreased with the exposure time; the inhibitory effectwas existed in the early age of exposure period in most concentrations, and this effect kept in acertain range, which explained that the effects of pesticides on the activity of nAChR had certainrestrictions. In sometimes，the phenomenon of recovery of nAChR the activity would appear,that may be related to the adaptation of Danio rerio to pesticide metabolism.4. The Change of the activity of mAChR and nAChR with time has a certain similarity withstepwise stress model. There was a phenomenon that the activity increased in early exposure andthe activity reduced after the early time; however there was a revertible process in activedecreased stage.In conclusion, these three kinds of pesticide could control the activity of mAChR andnAChR, of which, the inhibitory effect on mAChR activity was more obvious. These three kindsof pesticides have certain inhibitory effect on mAChR and nAChR, but the difference ofinhibition was obvious. This may be related to different pesticide toxicity mechanism. In lowconcentration, the activity of mAChR was more sensitive to deltamethrin, while the activity ofnAChR was more sensitive to malathion. Overall, the inhibition of cholinergic receptor ispositively correlated to the exposure concentration of pesticide and exposure time. There was a phenomenon of active recovery in a certain period of time, and this should be correlated to theadaption of Danio rerio to the drugs. |
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