Impacts Of Thyroxine Combined With Donepezil On Hippocampal Ultrastructures And Expression Of Synaptotagmin-1 In Adult Rats With Hypothyroidism

Objective Adult hypothyroidism can cause hippocampal morphology and neurocognitive defects, involves the ultrastructure and synaptic related proteins in hippocampus, traditional thyroxine(T4) replacement therapy may not be able to restore the damage completely. The study aims to observe the impacts of thyroxine(T4) combined with donepezil(DON) on hippocampal ultrastructures and expression of synaptotagmin-1 in adult rats with hypothyroidism.Methods 60 healthy male SD rats, 3 months old, SPF grade, after adaptively fed for one week, all rats were randomly divided into five groups: the normal control group(CON), the hypothyroidism group(Hypo), the T4 treatment group(T4), the DON treatment group(DON) and the T4+DON combined treatment group(T4+DON). The total modeling time was six weeks, the CON group was fed with normal water, while the other four groups were given 0.05%(w/v) propylthiouracil(6-n-propyl-2-thiouracil, PTU) every day. From fifth week, the T4 group was intraperitoneally injected T4(6 μg / 100 g body weight), the DON group added 0.005% DON into the drinking water, and the T4+DON group was performed the above administration simultaneously. Meanwhile, the rest three groups were injected the same amount of saline as the alternative, weigh the weight of rats and record once a week. Application of radioimmunoassay luminescence method to detect each group of serum thyroid hormone(THs) levels in rats, JEM-1230 tele electron microscope(TEM) was used to observe the hippocampal ultrastructures of each group, Western Blot and real-time RT-q PCR were performed to analyze the protein and m RNA expressions of syt-1 in the hippocampus of each group.Results 1. Weight value in rats: After modelling successfully, The body weight of control group increased by 92.9%. Hypo, T4, DON, co-administration group were increased 39.0%, 62.8%, 36.1%, 64.2% respectively. Compared with the control group, added value of rats’ weight in orther groups were significantly ligther(P<0.01).2. Serum THs levels in rats: The serum radioimmunoassay test revealed that compared with the CON group, the mean T3 and T4 levels of the Hypo Group and the DON group were significantly lower(P < 0.01); while those of the T4 group and the T4+DON group were close to the CON group.3. Ultrastructure of hippocampus in rats: TEM revealed that the Hypo group exhibited the significant pathological alteration in the hippocampal neurons, the mitochondria were swelled, exhibited ridges broken and vacuolar degeneration, the free Golgi complex, rough endoplasmic reticulum, ribosomes were sparse, nuclear membrane around the lateral deposition lumps of high electron density anomaly, the presynaptic membrane and postsynaptic membrane structures were damaged, and the number of synaptic vesicles was reduced. The above injuries in the T4 or DON group were improved, and the performance of the T4+DON group was the most close to the CON group.4. Expression of syt-1 in rats: From the protein and m RNA levels, the dorsal hippocampal syt-1 expression of the Hypo group was significantly reduced(P<0.01), the expression was partially recovered after the T4 treatment(P<0.05), and the T4+DON combined treatment made the expression return to normal.Conclusion 1. Adult hypothyroidism could cause a series of pathological damages of hippocampal neurons and synaptic ultrastructures.2. The expression levels were downregulated of syt-1 mRNA and protein inside the synapses in SD rats with adult hypothyroidism.3. The aforementioned morpholog Ical and molecular biological damages were reversible in adult hypothyroidism, the T4+DON combined therapy were effective, and the roles were better than the single drug treatment.