Objective To observe the change of Toxoplasma g ondii tachyziote in pseudocyst. Methods The mice infected by RH Toxoplasma were treated with mandelic acid (200 mg?kg -1 , twice daily) orally or intravenously, then ascites was taken out to smear in 24 h, 72 h and the time of death, with Giemsa dye and transmission electronic microscope (TEM), the survival time was c alculated. Results Under the light microscope, the cell mem brane of tachyzoite was tortous and broken, the bubble and pelletish material we re observed in cytoplasm, cell nucleus was split; but the cell membrane, organs and nucleus were destroyed more obviously under the TEM than those under the lig ht microscope. Meanwhile the living time of mice treated by mandelic acid (8.0 d ays in oral administration group and 6.8 days in intravenous administration grou p) was obviously longer than that in positive control group(5.5 days, P

【Objective】 To construct an acute toxoplasma encephalitis mouse model by observing the pathological changes in the hippocampus of mice infected with Toxoplasma gondii strain RH. 【Methods】 The quantitative RH Toxoplasma gondii (100, 500, and 1 000 trophozoites) were injected into the hippocampal CA1 region of mice by the stereotaxic surgery; the survival status of mice was observed. Giemsa staining was used to observe the changes of toxoplasma in mouse ascites and brain tissue homogenates. Nissl staining and HE staining were used to observe the pathological changes of hippocampal nerve tissue. The distribution of Toxoplasma gondii in brain tissue was observed by immunohistochemical ABC method. 【Results】 The RH Toxoplasma gondii infected mice showed obvious symptoms such as arched back, bristling hair, abdominal distension, subtle tremor and hemiplegia on the fourth day of infection. The survival of mice in 100 trophozoites group was longer, no trophozoites of Toxoplasma gondii were found in ascites, a few pseudocysts were found in brain tissue homogenates after infected for 96 hours, and more trophozoites were found after death. Nysl staining and HE staining showed more tissue necrosis foci and loss of nerve cells in CA1 area after infected 144 h. The injury aggravated with the prolongation of infection time. Toxoplasma trophozoites were found in ascites and brain homogenates of mice in 500 and 1000 trophozoites groups. Nissl staining revealed neuronal loss and massive necrosis in the hippocampus. HE staining showed necrosis and inflammatory cell infiltration. The brain tissue injury significantly aggravated compared with 100 trophozoites group. The distribution of Toxoplasma gondii in the necrotic foci was confirmed by immunohistochemistry. 【Conclusion】 The survival of 100 trophozoite mice infected with Toxoplasma gondii strain RH was longer, and the pathological changes of brain tissue gradually aggravated. The damage was relatively confined to the brain tissue, and the mice showed typical symptoms of toxoplasma encephalitis. Therefore, the mouse model of acute toxoplasma encephalitis can be constructed by localized infection of 100 toxoplasma trophozoites, which can lay a foundation for future research on the mechanism of toxoplasma injury to cranial nerves.