The effects of thyroid hormone on differentiation and neurofilament expression in rat brain aggregating cultures

The effects of thyroid hormone on neural development in vitro were studied using rat fetal forebrain aggregating cultures. They were examined morphologically after growth for 21 days in medium containing fetal calf serum (S+), in a chemically defined medium (S-), or in serum-free medium containing 30 nM triiodothyronine (T3). Aggregates grown in S+ showed certain morphological differences compared to those grown in the absence of serum: a glia limitans was present in the former, but not the latter, which were further characterized by a marginal zone rich in fibres and containing few cells. Immunocytochemistry using a monoclonal antibody against neurofilaments showed that immunostaining was most pronounced in aggregates grown in T3 (especially in the marginal zone) and weakest in those grown in S+. Quantitative estimation using an immunoadsorbent assay confirmed that T3 medium increased the amount of neurofilament protein in the aggregates, consistent with the view that thyroid hormone promotes neural development in vitro.