Abstract: 【Aim】 To explore the mechanisms of the NaF injury to the gonad of the lepidopteran model insect-the silkworm, Bombyx mori, we studied the effects of NaF on the testis and ovarian tissue structure, and the antioxidant enzyme activities and their gene expression in the silkworm. 【Methods】 B. mori larvae were fed with mulberry leaves soaked in different concentrations of NaF solution (0, 25, 50, 100 and 200 mg/L). The malondialdehyde (MDA) content, and the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) and their corresponding mRNA levels in the gonad of the 5th instar larvae of both sexes were evaluated, and the change in the anatomical structure of gonad was observed by paraffin section and Hematoxylin-Eosin (H&E) staining technique. 【Results】 The MDA contents in male and female larvae fed with mulberry leaves soaked in different concentrations of NaF solution significantly changed in a concentration-dependent manner, increasing with the NaF concentration, as compared with those in the control group. The activities of both SOD and CAT increased in B. mori larvae fed with mulberry leaves soaked in low dose of NaF, but successively decreased after high dose of NaF was added; the activities in the treatment groups, however, were still higher than those in the control group. According to the analysis of Pearson correlation, the SOD activity was positively correlated with the CAT activity (male: R=0.865, P=0.000; female: R=0.766, P=0.001), and the CAT activity had an obvious correlation with its mRNA level. The GSH-Px activities in gonads of male and female larvae changed in a concentration-dependent manner, increasing with the NaF exposure concentration, and the changes in GSH-Px activity showed a positive correlation with its mRNA level. The changes in the antioxidant enzyme activities in male larvae were more responsive than those in female larvae when they were fed with mulberry leaves soaked in NaF solution. Changes in the structure of gonads of male and female larvae were observed by using H&E staining. Such phenomena as abnormal morphology, enlarged cell vacuoles and relative less reproductive cells were observed. With the increase of NaF concentration, gonads were more seriously damaged. 【Conclusion】 NaF in mulberry leaves fed by B. mori larvae not only causes changes in gonadal structure of its male and female larvae, but also results in changes in the antioxidant enzyme activities and their mRNA transcriptional level in larval gonads.

Key words: Bombyx mori; sodium fluoride, reproductive damage, tissue sections, antioxidant enzyme, mRNA expression