ABSTRACT
Objective To study the effects of iodine deficiency and hypothyroidism on protein expression of extracellular signal-regulate kinase(ERK1/2) in the cerebellum of rots. Methods Twenty-eight healthy Wistar rots, female, 60 days old, were randomly divided according to their body weight into control group, iodine deficient group and hypothyroidism groups. Hypothyroidism groups in accordance with drinking water containing propylthiouracil(PTU) were divided into doses of 5 mg/L and 15 mg/L groups, 7 rats in each group. Rats after pregnancy, iodine deficient rats were administered with iodine-deficient diet and hypothyroid rats were administered with PTU in drinking water. Pup's cerebellum in each group were weighed on day 14,21,28 and 42. Cerebellum tissue was observed for cerebellar morphology using silver staining and detected for ERK1/2 protein using immunohistochemistry on day 7,14,21,28 and 42. Results On day 14,21,28 and 42, cerebellum weight of pups from iodine-deficient[(0.0945±0.0233), (0.1347±0.0046), (0.1542±0.0094), (0.1949±0.0048)g]were significantly lighter than control[(0.1856±0.0123), (0.2049±0.0098), (0.2268±0.0065), (0.2606±0.0086)g, all P < 0.05]and hypothyroidism groups [for 5 mg/L group: (0.1741±0.0172), (0.1927±0.0103), (0.2181±0.0064), (0.2583±0.0054)g, all P<0.05; for 15 mg/L group: (0.1604±0.0083), (0.1682±0.0103), (0.1996±0.0073) and (0.2579±0.0067)g, all P< 0.05]the difference had statistical significance(F=6.325,8.870, 16.191 and 21.574, all P<0.05). Compared to the controls on day 7, iodine-deficient group didn't have clear layers; on day 21, disappearance of external granule cells from iodine-deficient and 15 mg/L groups was delayed, still two or three layer external granule cells remained; on day 28 and 42, molecular layer from 5, 15 mg/L and iodine-deficient groups and became thinner. Immunohistochemistry showed that on day 7, there was no statistical difference of integrated optical density average of ERK1/2, in all the groups(F=1.102, P>0.05); on day 14,21,28 and 42, integrated optical density average of ERK1/2 in iodine-deficient group[(7.3245±0.5070), (8.3606±1.0683), (9.1217±1.0402), (12.1587±0.7581), all P<0.01]and hypothyroidism groups [for 5 mg/L group: (11.4307±1.5200), (14.919±0.8497), (16.0082±1.1130), (15.7721±0.8293), all P< 0.01; for 15 mg/L group: (7.8538±0.9775), (11.2461±0.8138),(12.78±1.3783), (13.0871±1.1450), all P < 0.01]was significantly lower than those of controls [(16.2831±0.5143), (20.2653±0.9551), (22.7485±1.0267), (22.1725±0.9939), all P < 0.01], the difference having a statistical signifieance(F=16.131,13.543,26.953,41.583, all P<0.01). Conclusions Iodine deficiency and hypothyroidism during critical periods of brain development may change eerebellar morphology and down regulate the protein expression of ERK1/2, which may result in damage of cerebellum development.
