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Investigators interested in studying the effect of thyroid
hormone on brain development over the past half century have used
a variety of animal models. One of the most popular has been the
neonatal rat (4). In the first 20-30 days postpartum thyroid
hormone exerts a profound effect on the neuronal cells involved
in brain development. Thyroid hormone regulates the migration of
cellular clusters, assures the myelination of nerve sheaths,
facilitates the assembly of microtubules and filaments, and
stimulates synaptogenesis as well as dendritic arborization.
The rat model is very useful since it is relatively easy to produce hypothyroidism in the fetal rat by simply administrating propylthiouracil or methimazole to the pregnant rat starting on gestational day 17. This will limit maternal and fetal production of hormone prior to day 21 when birth occurs. Further, the continued administration of antithyroid agents to the dam will result in the transmission of the agent to the newborn and thus block the synthesis of fetal thyroid hormone. |
