Development of glial fibrillary acidic protein immunoreactivity in thyroidectomized rats.

The majority of astroglia develop postnatally in rats. GFAP (glial fibrillary acidic protein)-immunoreactivity appears mainly during the 2nd and 3rd postnatal weeks throughout the brain. Hypothyroidism inhibits, among others, the cell proliferation, maturation, and migration of neurons. However, hardly any data on the effect of hypothyroidism on GFAP-immunoreactivity are available in the literature. In our experiments, thyroidectomy was performed between the 3rd and 5th postnatal days. Operated and control animals from the same litter were perfused transcardially and processed for immunohistochemistry in parallel after 2, 3, and 4 wk. On the basis of serial sections, the development of GFAP-immunoreactivity was not generally affected by hypothyroidism. We could observe only two phenomena that showed a tendency of retardation in the operated animals: (1) the decrease of the strong GFAP-immunopositivity of white matter tracts (for example, internal capsule and pyramidal tract) and (2) the gradual disappearance of the GFAP-immunoreactive radial fibers (for example, in the neocortex, in the olfactory bulb, and around the 3rd ventricle).