Neurotrophic factor for central neurons.

A serum-free culture of dissociated neurons from embryonic rat hippocampus has been established as a rapid and quantitative in vitro test system for neurotrophic signals in the mammalian brain. By means of this cell culture bioassay, a novel low molecular weight neurotrophic factor (NTF) could be identified. NTF is essential for in vitro brain neuron development, promoting survival and neurite outgrowth. The diffusible factor is synthesized and secreted into serum-free defined medium by cultured astrocytes from rat cerebral hemispheres. The number of viable neurons responding to NTF by neurite outgrowth is dependent on the concentration of the factor. Fractionation of astroglial conditioned medium by gel filtration on columns of Sephadex G-10 recovered biological activity of NTF in a single sharp peak corresponding to an apparent molecular weight of approximately equal to 500. NTF is stable to heat and cold and resistant to trypsin and pronase. Unlike nerve growth factor, NTF has no apparent effect on the neurite outgrowth of peripheral neurons. NTF-like activity is present in situ in the mammalian brain, in certain other nonneural tissues, and in C6 and B12 glioma cell conditioned media.