Abstract: Objective：To explore the effects of thyroid hormone, given to the hypothyroidism pregnant rats, on the expression of synaptophysin in the offspring hippocampus. Methods：Eighty Wistar rats (female)were randomly divided into eight groups: normal group, hypothyroidism control group, hypothyroidism with pregnancy (1-17 d) + thyroid hormone (high, medium and low dosage) groups, and hypothyroidism with pregnancy (18-20 d) + thyroid hormone (high,medium and low dosage) groups. Rats were fed with low-iodine diet. Rats of normal group were given KIO3 solution, and rats of other groups were given deionized water. Rats were mated with normal male rats (n=80) after three months of feeding. According to 100 g of rat body weight, the concentrations of thyroid hormone for high, medium and low dosage were 3.5, 2.0, 0.5 μg/d.The hippocampus samples were taken from new-born, 7-day-old, 14-day-old,21-day-old and 28-day-old offspring rats in eight groups. Immunohistochemistry method and image analysis technique were used to detect the expression of synaptophysin in the hippocampus . Results：In different period rats , the expression level of synaptophysin was higher in normal group than that of hypothyroidism control group（P＜0.01）. In the newborn rats ,there was no significant difference in the expression level of synaptophysin between hypothyroidism with pregnancy (18-20 d) group supplied with medium dosage of thyroid hormone and hypothyroidism control group (P > 0.05), the expression level of synaptophysin was lower in hypothyroidism with pregnancy (1-17 d,18-20d) groups supplied with low dosage of thyroid hormone than that of hypothyroidism control group （P＜0.05）, the expression level of synaptophysin was higer in hypothyroidism with pregnancy (1-17 d) group supplied with thyroid hormone (me?dium ,high dosage)and hypothyroidism with pregnancy (18-20 d) group supplied with high dosage of thyroid hormone than that of hypothyroidism control group（P＜0.01）. In the 7-day-old,14-day-old，21-day-old and 28-day-old offspring rats, there was no significant difference in the expression level of synaptophysin between hypothyroidism with pregnancy (1-17 d,18-20d) groups supplied with low dosage of thyroid hormone and low-iodine control group (P > 0.05), the expression level of synaptophysin was higher in other groups than that of hypothyroidism control group（P＜0.05）.Conclusion：Hypothyroidism of pregnant rats results in the low expression of synaptophysin in off-spring hippocampus,the expression of synaptophysin in off-spring hippocampus is highly related to the supply dosage and supply time of thyroid hormone in hypothyroidism pregnant rats.

Key words: Thyroxine, Hypothyroidism, Synaptophysin, Rat, Imunohistochemistry