| Background and purpose: Iodine deficiency disorders (IDD) is characterized by mental retardation. However, even after supplementation of iodine salt for many years it was found that the patients of IDD (such as sub-cretinism) still frequently appeared. Epidetniological analysis revealed that iodine (lo) deficiency was usually associated with selenium (Se) deficiency. Therefore, Se deficiency was considered as a possible cause of the sub-cretinism besides lo deficiency. In this study the effects of Se and lo deficiency on the nervous development, especially on the learning and memory, was investigated by examining the neurobehavioral development and the synaptic ultrastructure of hippocampal CAS area which was related to learning and memory in rat model.Materials and methods: The rats of the third generation from established selenium deficiency rat model were used in this study. The rats were assigned into 4 groups: control group, Se- group, I- group and Se- plus I- group. These rats were fed the given diets with different levels of Se and lo, respectively . The automatic operant behavior tests were carried out in different days according to the experimental design .The Morris water maze was used to assess the ability of the spatial learning and memory of rats. The synaptic interface parameters of Gray- I inhippocampal CAS area were measured by stereology method to evaluate themorphologic plasticity of the synapse. Results:!. The early neurobehavioral development test: on the postnatal 4tk day the average score of Se-I- group in righting reflex test was lower than that of cbntrol group (P<0. 01). There was no significant difference of the scores among these groups on the postnatal 7th day. In the auditory startling reflex the appearance of the positive reflex in the rats of I-and Se- plus 1- groups was somewhat delayed in contrast with the control. On the postnatal 12th day, the hanging time in the rats of Se- plus I- groups was significantly longer than that of control group. And On the 14th day, so were in the rats of Se- and Se- plus 1- groups. In the walking ability test performed on the postnatal 12th day, the average scores of 1- and Se-plus I- groups were significantly lower than that of control group. 2. Morris water maze test: In the place navigation test, for the female rats the average latencies in Se- plus I- group were significantly longer than that of control group (P < 0. 05); the latency difference between period 1 and period 9 in the Se- plus I- group statistically significantly diminished compared with control group (P<0.01) . As to the straight and tendency strategy of finding the hidden platform used by female rats there was no significantly difference among all groups. For the male rats, the average latencies and the Latency differences between period 1 and period 9 in Se-, I-, Se- plus I- groups were significantly indifferent froa the control group. And the straight strategy used by the male rats significantly diminished comparing with control group (P<0. 05) .In the .spatial probe test there were no significant differences in staying time in different quadrants for four groups of both male and female rats. But the female rats of control group spend more time in target quadrant than the other three groups. There were no significant differences as to thetimes of passing through the platform position for the male rats of four groups, but the times for the female rats of Se- plus I- group significantly decreased.3 The synaptic ultrastructure parameters: The length of active zone and the thickness of PSD significantly decreased in Se- group, I- group and Se-I- group compared with control group, and so were the synaptic curvatures. The width of synaptic cleft in Se- plus I- was significantly decreased in contrast with control group, too (P<0. 01). Conclusions:1. The selenium or iodine deficiency and both demonstrated significant effects on the early neurobehavioral development in terms of the results of the neurobehavioral development tests.2. The result of Morris water maze test s... |
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