Glia-promoting factors (GPFs) are brain peptides which stimulate growth of specific macroglial populations in vitro. To identify the cellular sources of GPFs, we examined enriched brain cell cultures and cell lines derived from the nervous system for the production of growth factors. Ameboid microglia secreted astroglia-stimulating peptides, while growing neurons were the best source of the oligodendroglia-stimulating factors. These secretion products co-purified by gel filtration, anion exchange chromatography, and reverse-phase high performance liquid chromatography with GPFs isolated from goldfish and rat brain. Our findings suggest that glial growth in the central nervous system is regulated in part by a signaled release of peptides from specific secretory cells.

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