Thyroid Hormone Regulates SNAP-25 And Synaptotagmin 1 Expression In The Adult Rat Hippocampus

Objective To observe the expression of SNAP-25 and synaptotagmin 1 in adult onset hypothyroidism rat hippocampus and learn the effect of Levothyroxin treatment.Methods All rats were separated into 4 groups randomly: (1) hypothyroidism rats (Hypo group). Twelve hypothyroid rats were induced by daily intraperitoneal injection of PTU (dissolved in saline solution, 1 mg/100g body weight (BW)) for six weeks; (2) T4-5 group. Eleven rats were treated with PTU for six weeks as described above. But from the fifth week, they were also treated with intraperitoneally injected L-T4 (dissolved in saline solution, 50μg/kg BW) every day for two weeks; (3) T4-20 group. L-T4 treatment rats with high dose were treated as the same protocol as T4-5 group but the dose of L-T4 (200μg/kg BW); (4) C group. Control rats were treated with saline solution for six weeks. The radioimmunoassay kits were applied to assay the levels of serum T3 and T4, and west blot method was used to determine the levels SNAP-25 and synaptotagmin 1in dorsal hippocampi of rats from different groups.Results Body weight levels in the hypothyroidism group and therapy groups were significantly lower than those in the control group rats(P<0.05); In the hypothyroidism group rats, serum T3,T4 levels were significantly lower than those in the control group rats(P<0.05); and the level of SNAP-25 protein were significantly increased and the level of syt 1 protein was significantly decreased in the crude synaptosome of dorsal hippocampus compared to the control group(P<0.05); after giving common dosage of L-T4 treatment, the levels of serum T3,T4 were returned to the normal, the level of SNAP-25 and synaptotagmin 1 protein was ameliorated, but there was no significant alteration compared to the hypothyroidism group( P>0.05). The high dosage of L-T4 could restore the increase of SNAP-25 protein to the normal and normalize the hypoexpression of syt 1 protein, while the levels of serum T3 and T4 were higher than the C group.Conclusion These results suggested that adult-onset hypothyroidism can increase the expression of SNAP-25 and decrease the expression of syt 1 in the dorsal hippocampus. Levothyroxin could reverse this alteration, and high dose is superior to common dose in recorverying SNAP-25 and syt 1 expression.