Delayed development of GFA immunoreactivity in the parietal cortex during thyroid hormone deficiency

The influence of neonatal hypothyroidism on the development of immunoreactivity to glial fibrillary acidic protein (GFA) was studied in parietal cortex of rats treated from birth with the antithyroid agent propylthiouracil (PTU) for 3 or 8 weeks. Density of GFA immunoreactivity was evaluated in cryostate sections reacted with an antiserum specific for GFA. Three weeks postnatally, the density of GFA-immunoreactive structures in the cortical layers II-V was 70% lower in PTU-treated animals than in controls injected with the solvent. This marked difference between the groups was, however, not seen in either the molecular layer, layer VI or white matter. The inhibited development of GFA immunoreactivity was not persistent in animals treated with PTU for 8 weeks continuously. Plasma from animals treated with PTU for 1,2,3 and 8 weeks was collected and the TSH level in each group compared with samples from age-matched controls and newborn pups. The treatment with PTU resulted in a more than 10-fold increase in TSH level after 1 week of injections. In longterm groups of 8 weeks, the TSH level decreased in the PTU-treated animals, but stayed considerably higher than control values throughout the experiments. The results described in the present paper indicate a thyroid hormone dependent development of the GFA immunoreactivity in cortex cerebri astrocytes.