The Toxicity Of The Herbicide Butchlor Effects On The Brain Of Toad Bufo Naddei Strauch In The Early Period Of Postembryonic Development

Objective: we investigate the morphological and behavior changes of the Bufo naddeiStrauch tadpoles in their early periods of postembryonic development after the exposureof Herbicide Butchlor, as well as the morphological and quantitative changes of neuronsin the brain, the changes of the ependymal thickness, with the acute and chronic toxicityexperiments of the Bufo naddei Strauch tadpoles. Aiming to reveal the impacts of theherbicide butachlor on the tadpoles brain in their early periods of postembryonicdevelopment, to provide more information for ecological protection.Methods: At first, we gave the Bufo naddei Strauch tadpoles （in gosner20,25,26 stagesrespectively） to acute exposure, to find their LC₅₀s, 95% confidence intervals and safeconcentrations, observing and recording the behavior and morphology changes oftadpoles; then in accordance with the 24hLC₅₀value calculated, we exposure the tadpoles（in gosner20,25,26 stages respectively） to butachlor solution, taking 4-5 tadpoles fromeach stage to do brain paraffin sections and Nissl staining, comparing the changes of braintissue with the control group. Then we took the tadpoles in gosner25 stage as our studyobject, giving them to the exposure experiment with the concentration gradient (the 1/51/10, 1/20, 1/50, 1/100 and 1/200 of its 24 hLC₅₀), recording body length and weight ofeach group after every 3 days, as well as taking 4-5 tadpoles of each group to do brainparaffin sections and Nissl staining to observe the toxic effects on the brain tissue.Results: The results showed that the values of LC₅₀s of Bufo naddei Strauch tadpoleswere increased as they developed. The morphological and behavioral changes wereobvious during our observations in the acute exposure of butchlor. The chronic exposurecaused significant diapauses effects on the Toad Bufo naddei Strauch tadpoles in the earlyperiod of postembryonic development, the body weight from day 6 and the body lengthfrom day 9 showed a significant difference between the exposed and control groups. Themorphology of the neurons in the tadpole brain were nearly not changed after acute andchronic exposure, but after 24h of acute exposure, the number of neurons in some areas ofthe brain decreased, in the 3rd day of chronic exposure, it all obviously decreased in thefour areas（Hippocampus; Diencephalon thalamus; The tectum of midbrain; Medullaoblongata） of the brain, while to the 12th day, the number of neurons in hippocampus andmedulla oblongata both decreased, the observations of the 21th day showed that thenumber of neurons of the four areas except midbrain were all beyond those of the controlgroup. In the acute and chronic exposure, the number of neurons in medulla oblongatadecreased most significantly. In the exposure process, the ependymal thickness of thelateral ventricles, third ventricle and fourth ventricle were all thickened significantly.Conclusion: The lactam Herbicide Butachior is moderately toxic to Bufo naddei Strauchtadpoles in the early period of postembryonic development, after exposure, the behavior and morphology of tadpoles were changed significantly, showing obvious diapauseseffect, and the effect on body weight compared with on body length was more obvious;The morphology of the neurons in the tadpole brain were nearly not affected by acute orchronic exposure, but the exposure made the ventricle ependymal produce a protectivereaction to rise its thickness; In the early period of exposure, the number of the neuronsdecreased, especially for the neurons in medulla oblongata, but followed the adaption oftheir own bodies, the number of neurons returned to normal levels again.