The Experimental Research Of Iodine Deficiency Or Excess On The Morphological Changes Of Hippocampus And Cerebellum In Rats

ObjectivesTo observe the morphological changes of the neurons and the astrocytes in hippocampus, the pyramidal cells in internal pyramidal layer of the cerebral cortex motor area and the cerebellar neurons in adult Wistar rats after fed with different iodine concentration water for 3 months and 6 months. To study the effects of iodine deficiency or iodine excess on the morphology and functions of cerebral cortex, hippocampus and cerebellum in the adult rats.MethodsWistar rats at the age of two months, half of male and half of female, were divided into six groups randomly: low iodine group (LI group), normal iodine group (NI group), 5,10,50 and 100 folds of normal iodine intake groups (5HI, 10HI, 50HI and 100HI groups). The rats of the LI group were fed with the diet derived from endemic goiter area containing iodine concentration of less than 50μg/kg, and drank deironized water. The rats of the other five groups were fed with standard diet containing iodine of 300μg/kg. The rats of the NI group drank tap water containing iodine of 5μg/L, while the rats of the 5HI, 10HI, 50HI and 100HI groups drank different KIO3 concentration tap water respectively. According to intake of the water and the diet everyday, the rats' iodine intake of the whole day of the six groups are estimated as follows: <1μg/L(LI), 6.15μg/L(NI), 30.75μg/L(5HI), 61.5μg/L(10HI),307.5ng/L(50HI), 615ng/L(100HI). All rats were sacrificed at the end of the third and the sixth month respectively. About 10 rats were selected randomly from each group by us to observe the morphological changes of the hippocampus, cerebral cortex and the cerebellum. The whole brains were weighed. The expressions of NSE in the neurons of the hippocampus CA-s region , the expressions of GFAP in the hippocampal astrocytes were examined by immunohistochemistry, and volume density (Vv), numerical density on area (NA) and the mean of gray scale were measured. The pyramidal cells in internal pyramidal layer of the cerebral cortex motor area were also examined by silver impregnation technique, the dendrites arising from basal portions of the pyramidal cells were counted. After strained by the special purple dye, the area percentages of the molecular layer, Purkinje layer and granular layer, the medulla of the cerebellum were measured respectively. The area percentages of the Nissl bodies in the soma of the Purkinje cells in the Purkinje layer were also measured.Results1. Compared with NI group, the changes in brain weights in LI group and all iodine excess groups were insignificant at 3 month and 6month.2. Compared with NI group, the relative weights of the thyroid in LI group increase obviously (P<0.01)> but those in all iodine excess groups were of no statistical difference.3. Hippocampus : The changes of Vv, Na of the NSE expressed neurons in CA3 region were insignificant in all iodine excess groups. Only the changes of Na in LI group were significant. But the expressions of NSE in the neurons were different. In contrast to NI group, the mean of gray scale of the neurons werelower in 50HI group (P<0.05) at 6 month, were much lower in 100HI group (P<0.01) at 6 month and in LI (P<0.01) at both 3 month and 6 month. Compared with NI group, the changes of Vv, Na and the mean of gray scale of astrocytes in CA3 region in LJ group and all iodine excess groups were of no statistical difference(P>0.05).4. Cerebral cortex motor area: In silver impregnated slides, we found that the numbers of the dendrites arising from basal portions of the pyramidal cells in all groups varied insignificantly.5. Cerebellum: The area percentages of the molecular layer, Purkinjc layer and granular layer, the medulla of the cerebellum in all groups were without statistical difference(P>0.05). The area percentages of the Nissl bodies in the soma of the Purkinje cells in the Purkinje layer were without statistical difference yet.6. Concentrations of the thyroid hormone (T3 T4) in serum: The concentrations of T3 and T4 in serum in LI group were lower than those in NI group (P<().()5). The concentrations of the free Xjin 50HI and 100HI groups at 3 month increase, the concentrations of the total T4 and total T3 in 10HI and 50HI groups at 6 month were lower, and the concentrations of the total T3 in 100HI group at 6 month also decrease (P<0.05).ConclusionsIodine deficiency or iodine excess can not make significant morphological change of the neurons and the astrocytes in hippocampus, of the pyramidal cells in internal pyramidal layer of the cerebral cortex motor area, and of the cerebellar neurons in adult Wistar rats. But iodine deficiency or the concentration of iodine much morethan normal intake can weaken the function of the thyroid, as the result, the concentrations of T4 and T3 decrease. Therefore, the energy metabolism of the cerebral neurons will be lower. Both iodine deficiency and iodine excess (more than 50 times of normal intake) can affect on the function of the cerebral neurons.