Expression of synaptotagmin I and effect of thyroxine treatment in the prefrontal cortex of adult hypothyroid rats / 中国地方病学杂志

ABSTRACT

Objective To observe the expression of synaptotagmin I(syt I)protein in the prefrontal cortex of adult-onset hypothyroidism rats and the effects of replicated therapy in different doses of thyroid hormone on the syt I protein.Methods All 44 aduh male Sprague-Dawley rats were divided into 4 groups randomly according to their body masshypothyroidism group,routine dosage thyroxine treatment group,high dosage thyroxine treatment group and control group.The adult male Sprague-Dawley rats were replicated to the adult-onset hypothyroidism and treatment models with propyhhiouracil(PTU).The levels of serum T3,T4 were assayed by the radioimmunoassay method and the level of the syt I protein in the molecular layer,external granular layer,external pyramidal layer,internal granular layer and internal pyramidal layer in prefrontal cortex was analyzed by immunohistochemistry.Results In the hypothyroidism group,the levels of serum T3 and T4[(0.34±0.04),(43.01±2.95)nmol/L]were significantly lower than those in the control group[(0.65±0.15), (55.20±3.56)nmol/L, F value 6.026,5.940,4.503,P<0.05 or <0.01 ], the levels of the syt I protein in the molecular layer(0.018±0.010), external granular layer (0.020±0.007), external pyramidal layer(0.013±0.008), internal granular layer(0.011±0.005), internal pyramidal layer(0.024±0.013) of prefrontal lobe were significantly lower compared to the control group[(0.028±0.010,0.031 ± 0.010,0.028 ± 0.010,0.022 ± 0.008,0.038 ± 0.013), F value 5.697,8.965,14.668,13.597,6.807,P<0.05 or <0.01 ]. In the routine dosage of the thyroxine treatment group, the levels of serum T3,T4 [(0.63 ±0.05), (55.04 ± 3.77)nmol/L] were not significantly different compared to the control group(F value 3.162,0.367,all P>0.05), and the level of the syt I protein in the molecular layer, external granular layer, external pyramidal layer, internal granular layer and internal pyramidal layer in prefrontal cortex showed a significant improvement of the syt I protein(0.027 ± 0.013,0.025 ± 0.009,0.022 ± 0.008,0.020 ± 0.010,0.033 ± 0.010), which were similar to that of the control group(F value 0.094,2.208,2.467,0.350,0.693, all P>0.05). In the high dosage thyroxine thyroid hormone treatment group, the levels of serum T3 and T4[ (1.11 ± 0.10), (96.68 ± 6.42)nmoL/L] were higher than the control group(F value 6.291,12.031, all P<0.01), the expression of the syt I protein(0.028 ± 0.008,0.031 ±0.011,0.026 ± 0.012,0.023 ± 0.011,0.038 ± 0.010) were not significantly different compare to the control group (F value 0.001,0.019,0.111,0.061,0.001, all P>0.05). Conclusions The expression of the syt I protein in the prefrontal cortex of adult-onset hypothyroidism can be decreased, which can be reversed by routine dosage of thyroxine treatment.