Accumulating evidence indicates that various neurotrophic factors (NTFs) exist and function in the brain. In the mature mammalian brain, NTF expression is exclusively restricted to neurons. However, astrocytes activated by various cytokines, including fibroblast growth factor and interleukin-1̄, produce a significant amount of nerve growth factor (NGF) in vitro. Furthermore, non-NGF type NTF expression in astrocytes is also activated by the cytokines. The cytokines also enhance both release of ciliary neurotrophic factor from and expression of high-molecular weight basic fibroblast growth factor (FGF) in astrocytes. In the early phase following brain injury, cytokine-activated astrocytes rescue the damaged neurons via NTFs and other biologically active molecules.
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