Influence of cell density and thyroid hormone on glial cell development in primary cultures of embryonic rat cerebral hemisphere

Abstract

The influence of cell density and thyroid hormone (TH) on the development of astrocytes and oligodendrocytes was investigated in primary cultures prepared from rat cerebral hemisphere on embryonic day (E)18. At the beginning of the culture, most of the cells were microtubule-associated protein 2 (MAP2)-positive neurons, whereas O1-positive oligodendrocytes and glial fibrillary acidic protein (GFAP)-positive astrocytes were rarely observed. After the cells were maintained in serum-free defined medium, astrocytes developed at high cell density but rarely at a low one. When leukemia inhibitory factor (LIF) was supplemented in low-density cultures, the levels of GFAP expression markedly increased to almost the same extent as in high-density culture without TH. This suggests that, in low-density cultures, astrocyte progenitors could not differentiate because of insufficient astrocyte-inducing factors. Interestingly, the addition of TH increased GFAP expression levels only at high density. The number of oligodendrocytes increased with TH addition at both cell densities, although the effects were more remarkable at high density. These results suggest that cell density and TH are pivotal factors in the development of both astrocytes and oligodendrocytes. It is also suggested that the effects of TH on glial cell development could be accelerated via cell-cell communications.