NGF increases brain astrocyte number in culture

Nerve growth factor (NGF) promotes survival and maintenance of peripheral and central neurons. In previous studies, we found that low-affinity NGF binding sites were associated with flat nonneuronal cells dissociated and cultured from the embryonic septum. These cells were also labeled with a monoclonal antibody to the NGF receptor, 192 IgG, suggesting that low-affinity NGF receptors are associated with a nonneuronal population. To define the potential effect of NGF on these nonneuronal cells, rat Embryonic Day 17 (E17) septa were dissociated and cultured in fully defined medium in the presence of NGF. Glial fibrillary acidic protein (GFAP) was used as a marker for the astrocyte population. NGF elicited a dramatic ninefold increase in the number of GFAP-positive cells after 7 days. NGF similarly increased astrocyte number in cultures grown from E18 hippocampi and E16 substantia nigra, suggesting that NGF acts on glia from multiple brain regions. To begin defining the mechanism of NGF action on astrocytes, we examined [3H]thymidine incorporation, which increased significantly, but by only 50%, upon exposure to the trophic factor. We tentatively conclude that NGF increases astrocyte number in culture by stimulating mitosis as well as enhancing survival or differentiation.