ABSTRACT
Objective To study the effects of thyroid hormone (TH) on synaptophysin (syn) expression in rat cortex and hippocampus during developing period. Methods The experimental animals were divided into four groups: (1) Hypothyroidism group: the pregnant maternal rats had been given 0.02% methimazole(MM)water since 5 days, the infant rats suffered from innate hypothyroidism. (2)T4 substitution group: innate 0 days. (4)Normal control group: The pregnant rats were given a normol diet and water, yielding infant rats used as normal matched control. The expression of synaptophysin mRNA were measured by in site hybridization. Results (1) In the normal control group synaptophysin expression showed a characteristics layer distribution in the cortex and hippocampus. The expression was very low at O day, the peak of expression was at 4 days. During the following days, the expression was reduced gradually, reaching nearly the level in the adulthood by 30 days. (2)Synaptophysin expressions in hypothyroidism group were significantly lower than those in normal control group(P＜0. 01). In hypothyroidism group the peak of synaptophysin expression was delayed by 3 days, attaining the high peak on 7 days. (3) Synaptophysin expressions in T4 substitution group were significantly higher than those in hypothyroidism group at 4 days, 7 days, 14 days, 21 days, and 30 days, but were still lower than the levels in normal group(P＜0.05 or P＜0.01, except 7 days synaptophysin expression at hippocampus DG,P＞0.05). (4)Synaptophysin expressions in T4 hyperthyroidism group were significantly higher than those in normal control group at 14 days、21 days、30 days(P＜0.05 or P＜0. 01). Conclusion The results suggested that reduced thyroid hormone, T4 substitution, and T4 hyperthyroidism led to the changes of synaptophysin expression in the rat cortex and hippocampus, resulting in an adverse effect on synapses occurrence and related nerve circuit establishment,with appearance of peerless neuronal place or mistaken nerve thoroughfare, thus hindering the development and function of the brain. Timely T4 substitution therapy is an important way to correct the disturbance in synapses development of the central nervous system due to deficient thyroid hormone.