الفهرس 
Development and histogenesis of the cerebellumOnly 14 pages are availabe for public view
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Abstract
Thyroid diseases are the second commonest gestational endocrinal disorders. Maternal THs are necessary for the natural growth of the CNS before birth. During the pre-natal period, a shortage of THs will lead to irreversible damage to the brain so; there is an increasing demand to decrease the incidence of gestational hypothyroidism and so decreasing the development of cognitive disorders in early childhood life. The cerebellum is identified to be one of the targets of THs. It can be used for studying the effect of THs on the CNS. Carbimazole is an anti-thyroid drug used for the treatment of hyperthyroidism. It can pass the placental barrier and is excreted in the milk so; it is used for induction of hypothyroidism in rat. TH replacement is very effective in treating hypothyroidism. Levothyroxine (L-thyroxine) is a manufactured TH. It is the most effective treatment for hypothyroidism.
The aim of this work was to detect the effect of experimentally induced maternal hypothyroidism on the postnatal development of the cerebellar cortex in albino rat offsprings. It also compared between the effect thyroxin replacement to mothers during pregnancy and to offsprings postnatally.
24 sexually mature female albino rats and 12 male albino rats (for mating) of Sprague-Dawley strain, weighing between 200-250 gm were used in this study.
Each two of females’ rat were housed overnight with a sexually mature male for mating, and every morning vaginal smears were taken and microscopically examined for the presence of sperms. The microscopic detection of sperms in the smears was considered as the 1st day of gestation.
75 Newly born rats were divided into three groups as follows:
group I (Control group): included thirty offsprings. They were subdivided into
- Subgroup Ia (negative control): included fifteen offsprings; they were kept without any treatment till the end of the study.
- Subgroup Ib (positive control): included fifteen offsprings; they received 1ml of 0.9% saline/rat once daily subcutaneously till the end of the study.
group II (Hypothyroid group): included fifteen offsprings, their mothers were rendered hypothyroid by administration of carbimazole at a dose of 20 mg/kg /day dissolved in distilled water by gastric tube from day one of pregnancy to the 21st day of lactation. Confirmation of occurrence of hypothyroidism was done by measuring TSH, FT3 and FT4 in mothers’ sera 10 days after the beginning of administration of carbimazole.
group III (Thyroid hormone replacement group): was divided into:
- Subgroup IIIa: included fifteen offsprings, their mothers received carbimazole as group II and after confirmation of occurrence of hypothyroidism at day 10 of gestation by measuring TSH, FT3 and FT4, levothyroxine (T4) (20 μg/ kg B.W/day) was injected
Summary and Conclusion
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subcutaneously from the 10th day of gestation to the 21st day of lactation.
- Subgroup IIIb: included fifteen offsprings, their mothers received carbimazole (20 mg/ kg B.W/d) by gastric tube from the 1st day of pregnancy to the 21st day of lactation. Following birth, the offsprings received daily thyroxin replacement therapy at day 1 at a dose 20μg/kg B.W. subcutaneously till the targeted period.
At the end of the 1st, 2nd and 3rd postnatal weeks, the crown rump length was measured in newborns. Also, TSH, FT3 and FT4 levels were estimated then decapitation of newborns of control, hypothyroid and thyroxin replacement groups was done at the end of the 1st, 2nd and 3rd postnatal weeks under light diethyl ether anesthesia.
The skull of each animal was splitted, opened and the cerebellum was dissected out. Some specimens were preserved in 0.9% saline for qRT-PCR, others were fixed for 24 hours in 10% neutral buffered formalin then dehydrated in ascending grades of alcohol, cleared and embedded in paraffin. After deparaffinizing, the 3-5 microns thick tissue sections were cut by microtome and subjected to Hx. & E. for routine histological examination and Touldine blue stain to demonstrate Nissl substance.
Immunohistochemical studies were done using (NF) (200kDa & 68kDa): for immunohistochemical staining of intermediate filaments of neurons and their processes, MBP for immunohistochemical staining of myelin sheath protein and BCL2 for detection of apoptosis.
Morphometric studies were done using image analyzer software for calculating the thickness of the EGL and ML, The number of degenerated PCs and the surface area of the brown color of NF, MBP and BCL2 immunohistochemistry. Genetic study was done using qRT-PCR for detection of Reelin gene that regulates processes of neuronal migration and positioning in the developing brain.
Regarding the crown rump length, at all corresponding ages, group II showed a highly significant decrease on comparing it with the control group I. Subgroups IIIa and IIIb showed a highly significant increase in comparison with group II. No significant difference was detected between subgroup IIIa and the control group I but subgroup IIIb showed a significant decrease on comparing it with the control group I and subgroup IIIa.
Regarding biochemical results, group II showed a highly significant decrease in FT3, FT4 and a highly significant increase in serum levels of TSH in comparison with the control group I.
Subgroup IIIa and b showed a highly significant increase in serum levels of FT3, FT4 and a highly significant decrease in TSH levels in comparison with group II
There were no significant differences in the biochemical results between subgroup IIIa and the control group I.
Subgroup IIIb showed no significant difference in serum levels of FT3, FT4 in comparison with subgroup IIIa and the control group I but a significant increase in serum level of TSH was detected in subgroup IIIb in comparison with subgroup IIIa and the control group I.
Summary and Conclusion
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group I and subgroup IIIa showed similar histological results to the normal cerebellar cortex at the 1st, 2nd and 3rd weeks. They showed a strong positive immune reaction to NF, MBP and BCL2 at the 1st, 2nd and 3rd weeks except for MBP at the 1st week, which showed a negative reaction.
group II at the 1st week showed vacuolation in the EGL, loss of the linear arrangement of PCs and vacuolations in the IGL. At the 2nd week, it showed vacuolation in the EGL, reduction in the thickness of ML with vacuolation. PCL showed areas of PC loss and some PCs appeared degenerated. IGL cells were smaller in size, fewer in number and sparse. At the 3rd week, group II showed more deterioration in the form of persistent thick EGL with vacuolation, reduction in the thickness of ML with vacuolation. Most PCs were degenerated. They were haphazardly arranged. IGL cells were smaller in size, fewer in number and sparse. group II also showed a weak immune reaction to NF, MBP and BCL2 at the 1st, 2nd and 3rd weeks.
All the previous findings were improved in subgroup IIIb but not as subgroup IIIa. Some degenerated PCs were detected. The EGL at the 3rd week was still present.
Regarding the expression of reelin gene mRNA at the 1st, 2nd and 3rd weeks, group II showed a highly significant decrease when compared to the control group I. Subgroups IIIa and IIIb showed a highly significant increase in comparison with group II. No significant difference was detected between subgroup IIIa and the control group I.
Subgroup IIIb at the 1st and 2nd weeks showed a significant decrease in comparison with the control group I but no significant difference was detected between it and subgroup IIIa. Subgroup IIIb at the 3rd week showed no significant difference in comparison with the control group I and subgroup IIIa.