الفهرس 
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Abstract
The present study was carried out to study the effect of the induced hypothyroidism on the postnatal maturation of pyramidal and granule cells in albino rat hippocampus. Twenty pregnant dams were divided into two l groups; experimental and control. The experimental group received propylthiouracil drug. The control group rats received only distilled water. Three rats from each group were scarified at ages of 1, 7 ,15 ,22 and 30 days PN. The body weight of each rat was measured immediately before scarification .The animals were ,brain was carefully dissected out, then weighted and prepared for staining. Serum free T4 concentration was significantly reduced in hypothyroid rats since PN15. It was observed that hypothyroidism can disturb normal postnatal maturation of granule and pyramidal cells in the hippocampus , cells were smaller and their processes were diminished when compared to control rats .Cell death occurred since age of PN15 and till PN30.Hypothyroid rat were lighter in weight than control one , also brain and hippocampal weights were smaller when compared to control group. These changes indicate that early hypothyroidism not only retards the growth of the body but also retard the growth of the brain and hippocampus including maturation of pyramidal and granule cells. These finding reflect the importance of thyroid hormone for normal development of the hippocampus.