关键词: 晚期日本血吸虫感染, 旷场试验, 高架十字迷宫试验, 焦虑

Abstract:

Objective To observe the behavioral characteristics of mice with late-stage schistosomiasis japonica and explore the relationship between late-stage infection of Schistosoma japonicum and anxiety. Methods Thirty 6-week-old male C57BL/6J mice were randomly divided into the infected group (n = 16) and the uninfected group (n = 14). The infected group was infected via abdominal skin contact with 20 cercariae of both sexes, and the uninfected group was treated with dechlorinated water without cercariae. Mice in both of groups were administered with praziquantel by gavage at 8 weeks post-infection. Additional 7 male APP/PS1 double transgenic mice (Alzheimer’s disease model) at 6 weeks of age were used as positive control (transgenic group) without any treatment. Three groups of mice were reared in the same environment until they were 10 months old, to observe their behavioral changes in an open-field test (OFT) and elevated-plus maze test (EPM). In OFT, the total distance, the travelling distance in the central zone, the percentage of travelling distance in the centrol zone, the number of locomotor activity, the duration of locomotor activity, the time percentage spent in the centrol zone, the mean speed, the mean speed in the centrol zone were measured, and in EPM, the locomotor distance, retention time and the number of entry in the open arms/close arms/central zone, and the percentage of locomotor distance, retention time and number of entry in the open arms were recorded to evaluate the anxiety-like behavior of the three mice groups. The mice of all groups were euthanized, and the livers were collected to observe gross morphology. The liver tissue sections were stained using hematoxylin & eosin (HE) and Masson’s trichrome stain for microscopic observation of pathological changes and collagen fiber hyperplasia. The content of liver hydroxyproline which is the specific amino acid constituent in collagen, was determined. The mRNA relative transcription levels of α-smooth muscle actin (α-SMA), transforming growth factor-β1 (TGF-β1), collagen Ⅰ(ColⅠ) and ColⅢ in the liver tissues of each group were detected by fluorescence quantitative PCR. SPSS 21.0 software was used for statistical analysis. Results The appaearance color of the mice livers from the infected group was darker compared to the uninfected group. There was a large number of eggs were deposited in the liver tissue, with surrounded infiltrating inflammatory cells and collagen fibres hyperplasia. The liver hydroxyproline content of the infected group (0.194 ± 0.040) μg/mg was significantly higher than that of the uninfected group (0.122 ± 0.016) μg/mg and transgenic group (0.124 ± 0.004) μg/mg (t = 0.79, 0.86, P < 0.05), with no significant difference between the uninfected and transgenic group. The mRNA expression levels of Col Ⅰ, α-SMA, TGF-β1, Col Ⅲ in the liver of the infected group were 3.55 ± 1.76, 2.01 ± 0.66, 2.21 ± 0.64, 4.51 ± 2.32,which is not significantly higher than those of the uninfected group (t = 0.76, 0.59, 0.17, 0.40,P > 0.05). The infected group’s activity time (346.77 ± 181.03) in OFT, the locomotor distance in the open arms (206.31 ± 282.52) mm, the percentage of locomotor distance in the open arms (7.51 ± 9.90)%, the number of entry in the open arms, closed arms and central zone (1.32 ± 1.51, 3.44 ± 3.10, 4.53 ± 4.21)(P < 0.01) in EPM were significantly increased compared to the uninfected group (t = 1.61, 2.24, 1.66, 1.83, 2.35, 2.22, P < 0.05 or P < 0.01), with no significant differences between the two groups for the other indexes. The infected group’s the number of locomotor activity (123.68 ± 50.23) in OFT was significantly decreased compared to the transgenic group (P < 0.05), but there was no significant difference between the two groups for other indexes of OFT. The infected group showed shorter retention time in the closed arm (232.85 ± 88.82) s than that in the transgenic group (295.38 ± 9.88）s(t = -2.81,P < 0.01), and higher values of the rest of the indexes in EPM than those in the transgenic group (P < 0.05 or P < 0.01). Conclusion Mice with late-stage of S. japonica infection did not show more serious level of anxiety than the uninfected mice, however, the anxiety extent presented a significant reducing-tendency, suggesting that the pathological process of S. japonica infection may not be directly correlated to the occurrence and development of anxiety.

Key words: Late-stage infection of Schistosoma japonicum, Open-field test, Elevated-plus maze test, Anxiety