The Effect Of Monocrotophos On The Cholinergic System In The Early Development Of The Sea Urchin, Hemicentrotus Pulcherrimus

The organophosphorus pesticide (OPs) has been widely used in agriculture because of high efficiency and low toxicity. However, it remained in the environment a lot and showed potential threat to aquatic organisms and human health. Compared with the adult, the early developmental stage of organisms is more sensitive to the organophosphorus pesticide, and the effect is irreversible. Present study shows that, the main neurotoxicity of OPs restrain the activity of acetylcholinesterase (AChE). There are several components consist of the cholinergic system besides AChE, and they interact with each other complexly. As a result, it's not sufficient to explain the neurotoxicity of the whole cholinergic system just with AChE. Acetylcholine (ACh) is the important neurotransmitter of cholinergic system, and it is synthesized by choline acetyltransferase (ChAT). ChAT is often used to represent the content of ACh, for ACh is hard to detect. The early development of the sea urchin is an alternative model for mechanistic understanding of neurodevelopment, for it is easily observation, simply culture, and sensitive to pollutants. The OPs is able to disturb the early development of the sea urchin and lead to deformity by effect on the neurotransmitter and the cholinergic receptors.Therefore, AChE and ChAT was chosen as the researching object and sea urchin (Hemicentrotus pulcherrimus) as the experimental organism. The embryos of Hemicentrotus pulcherrimus were exposed to 0.001,0.01,0.10,1.00 and 10.0 mg·L-1 MCP. Then the activity and distribution of AChE and ChAT were examined at gastrulae stage, prism stage and 2-arm stage. The results are showed as follows:(1) The activity of AChE enhanced gradually with the development in the control group. As the monocrotophos concentration elevated, the AChE activity showed no significant change in gastrula stage while the activity of AChE in prism stage first increase and then declined. The activity of AChE in 2-arm stage showed a significant decline with the concentration of monocrotophos enhanced. It showed that among the early development stage tested in this thesis the activity of AChE in 2-arm stage is more sensitive to MCP.(2) Cuthiocholine method found that the AChE mainly localized in the areas where cells proliferation and the motile structure of the larva, such as the arm and cilia band. The distribution of AChE was inhibited in the MCP-treated group, and the exposed embryos appeared to be delayed and deformed.(3) The activity of ChAT dropped gradually during the development of the sea urchin. With the monocrotophos concentration increase, the ChAT activity was inspired initially in gastrula stage and then declined significantly, but in prism stage the ChAT activity goes down in the beginning and then improved in high concentration. In the 2-arm stage the ChAT activity showed no significant change after expose. These results indicated that among the three stages investigated in this thesis, the activity of ChAT in the gastrula stage is the most sensitive to the MCP, what's more, the activity of ChAT rises because of compensation in the low dose MCP group.(4) The ChAT mainly distribute along the gut wall cell. The distribution of ChAT was disturbed and the development of the larva was delayed and deformed in the MCP-treated larvae group.In conclusion, MCP not only restrains the activity and distribution of AChE in the early development stages of Hemicentrotus pulcherrimus, but also disturbs the activities and distribution of ChAT. The sensitivity of AChE and ChAT to MCP has stage differences. The AChE in the 2-arm stage larva was more sensitive to MCP while the activity of ChAT in the gastrula stage is more sensitive. With the comparison between AChE and ChAT, MCP restrains the activities of AChE firstly and then restrains the activities of ChAT in the early development stages of Hemicentrotus pulcherrimus. These effects illustrated that MCP has neurotoxicity in the early development stages of Hemicentrotus pulcherrimus, and showed a preliminary research to the toxic mechanism of organophosphorus pesticides on the cholinergic system.