Effect Of Hypothyroidism On Oxidative Stress Status And NNOS-positive Cell In Rat Cerebral Cortex

Objective: To study the effect of hypothyroisism on oxidative stress status and nNOS-positive cell in rat cerebral cortex and to explore the mechanism of impaired brain caused by hypothyroidism.Methods: Forty-two male, Sprague-Dauley ( SD ) rats, clean animal grade,were randomly divided into 2 groups:control group(n=18) and hypothyroidism group(n=24).Hypothyroidism group was induced by administering propylthiouracil(PTU) of 20 mg per 100g of body weight solution to the dams by gavage. The control group were given saline of the same volume.All the rats received common feed and free of drinking.The doses of PTU were adjusted by the body weight weighed once a week. The two groups were sacrificed on 25th,45th and 60th day. The learning and memory abilities were measured by y-maze.All the rats are exsanguinated the blood 5ml from femoral artery, spin the tubes at 2000r/min for 5min and put it in the refrigerator in -20℃for testing FT₃,FT₄,u-TSH. The brain tissue samples were homogenated in proportion of 10∶1 by phosphate bufffer (ph=7.40) in iced bath,then centrifugated 4000r/min for 15min and put it in the refrigerator in -70℃for testing SOD,MDA,GSH-Px and NO.The cortex was fixed by neutral polyformalin solution and routinely paraffin-embedded sections. The mean profile area(MPA) and grey level of nNOS positive cell were determined by using the immunohistochemical method combined with image analysis technique.Results:â‘ General conditions were compared between the two groups: The body mass of rats was obviously raised with the increase of week age in the control group.They were sensitive response, strong activity, luster hair, kiyosuke sound and stronger feeding activities.While the changes in the hypothyroidism group were dullness reaction,laggerdness action, sparse hair,clouding and clouding. With the progressive course of hypothyroidism, body weight gradually reduced.â‘¡The learning ability of rats compared the control group with hypothyroidism:The spatial study and memory of the rats in hypothyroidism group(P<0.05).â‘¢The difference between control group and hypothyroidism group in thyroid function: On the 25th day, the FT₃ and FT₄ levels in plasma in hypothyroidism group were decreased obviously than those in control group(P<0.05),the levels of u-TSH in plasma of hypothyroidism group were higher than control group(P<0.05). The model is made successfully.On the 45th and 60th day, the FT3 and FT4 levels in plasma in hypothyroidism group were decreased obviously than those in control group(P<0.01),the levels of u-TSH in plasma of hypothyroidism group were higher than control group(P<0.01).â‘£The effects on the oxidant stress in cerebral cortex compared control and hypothyroidism group: On the 25th day, the SOD and GSH-Px levels in cerebral cortex in hypothyroidism group were decreased obviously than those in control group(P<0.05).On the 45th and 60th day, the SOD and GSH-Px levels in hypothyroidism group were decreased obviously than those in control group(P<0.01).SOD and GSH-Px levels was reduced progressively along with progress. On the 25th day, the MDA and NO levels in cerebral cortex in hypothyroidism group were increased obviously than those in control group(P<0.05). On the 45th and 60th day, the MDA and NO levels in hypothyroidism group were increased obviously than those in control group(P<0.01).MDA and NO levels were increased progressively along with progress.⑤Analytic result of computer image: The nNOS immunoreactive neurons in the cerebral cortex of rats were round,oval shape,spindle and triangle.All nNOSimmunoreactive neurons had larger somata in size and have distinct processes. Immunohistochemistry analysis of nNOS immunoreactive neurons showed brown.Nucleus had no coloring. Compared with the control group, the color was lighter and gray value was significantly decreased in the hypothyroidism group(P<0.05). The same change was between the control and hypothyroidism on 45 th and 60th day(P<0.05).we found mean profile area(MPA) of nNOS immunopositive neurons of hypothyroidism group had no significant changes compared with control group.â‘¥Comparison and correlative analysis of index with thyroid gland function: FT3 had significant positive correlation with activities of SOD and GSH-Px(r=0.945, r=0.918,P<0.01). FT₃ had significant positive correlation with activities of MDA and NO ( r=-0.915,r=-0.956,P<0.01). FT₃ had significant positive correlation with gray value of nNOS immunoreactive neuron (r=0.958,P<0.01).FT₄ had significant positive correlation with activities of SOD and GSH-Px (r=0.942,r=0.905,P<0.01).FT4 had significant positive correlation with activities of MDA and NO (r=-0.951,r=-0.915,P<0.01).FT₄ had significant positive correlation with gray value of nNOS immunoreactive neurons (r=0.952,P<0.01). u-TSH had significant negative correlation with activities of SOD and GSH-Px(r=-0.906,r=-0.903,P<0.01).u-TSH had significant positive correlation with activities of MDA and NO (r=0.901,r=0.928,P<0.01).u-TSH had significant negative correlation with grey value of nNOS immunoreactive neurons (r=0.903,P<0.01).Conclusion: 1 The oxidative stress state of hypothyroidism had a change in cerebral cortex.The activities of SOD and GSH-Px were significantly decreased, activities of MDA and NO increased. The balance and destruction on lipid peroxidation and antioxidantion system caused brain damage.With the progress of oxidation, the damage was aggravated. 2 Grey value of nNOS immunoreactive neurons was significantly decreased in the hypothyroidism group, neurotoxicity of NO/nNOS may participate in the damage of learning and memory in hypothyroidism rats.