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Effect of thyroxine combined with donepezil on expression of synaptotagmin-1 and munc-18 in the frontal lobe of adult rats with hypothyroidism

Yanyan Wang, Zhangxiang Chen, Min Zhu, Zhangbi Wu, Hao Yang, Fen Wang, Defa Zhu

The aim of the current study was to observe the effect of thyroxine combined with donepezil on the expression of synaptotagmin-1 (syt-1) and mammalian uncoordinated-18 (munc-18) in the frontal lobe of adult rats with hypothyroidism and to explore the possible mechanisms of hypothyroidism-induced brain injuries. A total of 45 adult SD rats were randomly divided into a control group (CON), a hypothyroidism group (hypothyroidism), a thyroxine-treatment group (T4), a donepezil-treatment group (DON), and a T4+DON group. The rats were anesthetized with chloral hydrate and blood samples were collected from the abdominal aorta; then, levels of thyroid hormones T3 and T4 and of thyroid stimulating hormone (TSH) were measured in the centrifugal serum. The brain of each rat was sampled on ice and the prefrontal lobe was isolated and stored at -80°C to detect the expression of SYT-1 and munc-18. The expression of syt-1 and munc-18 in the rats’ frontal lobe was analyzed by a western blot analysis and reverse transcriptionpolymerase chain reaction (RT-PCR). Compared with the CON group, the expression of syt-1 and munc-18 in the hypothyroidism group was significantly decreased (P<0.01), even after T4 or DON treatment (P<0.05). However, after T4+DON treatment, expression levels returned to normal values. Hypothyroidism in adults can down-regulate syt-1 and munc-18 in the frontal lobe and a single treatment of either T4 or DON will not be effective. Protein expression can return to normal after a combined treatment with T4 and DON, suggesting that a combined therapy is more conducive to the recovery of damaged proteins in the region of hypothyroidism-induced brain injury.