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Introduction: It is well established that thyroid hormones are essential for normal development of mammalian brain. Thyroid hormone deficiency during critical period of brain development can exert devastative and irreversible effects on neuronal functions as well as on learning abilities and memory. The aim of the present investigation was to investigate the effects of maternal hypothyroidism on the neuronal structures of the subiculum in an experimental model of cretinism. Methods: Twenty five female Wistar rats were divided into experimental groups 1 and 2 and control. The experimental groups were made hypothyroid (500 mg/L PTU in drinking water). The experimental group 2 received PTU+Levothyroxin (1mg/L in drinking water). The controls only received drinking water. After two weeks the animals were mated. During pregnancy and lactation, the treatment regime of all groups was continued as above. The brain of 20 days old newborns were dissected and fixed for histological preparation. The numerical density (NV) of subicular neurons was estimated by applying a stereological technique "dissector". Results: In addition to the effects of maternal hypothyroidism on the litter size and offspring weights, the results showed significant increase of subicular neuronal density in experimental group 1 when compared with control (p<0.001). There was also a significant difference (p<0.001) between the Nv of experimental groups 1 and 2. Conclusion: The increased of neuronal Nv in hypothyroid rats was probably due to the retardation of the neuronal normal growth and extension of their dendritic arborization. It seems that thyroxin therapy can improve the effects of hypothyroidism on the neuronal structure of subiculum.

Keywords: Maternal hypothyroidism, subiculum, PTU, rat

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