Regulation of neuroblast proliferation by hormones and growth factors in chemically defined medium

Pure neuronal cultures prepared from 6‐day‐old embryonic chick brains incorporated [ 3 H]‐thymidine in serum‐free medium up to the 4th day in culture. The addition of insulin any time within this culture period caused an increase in thymidine incorporation. This increase in [ 3 H]‐thymidine was correlated with an increase in cell number and percentage of labeling index. Triiodothyronine and endothelial cell growth factor were also active in stimulating [ 3 H]‐thymidine incorporation into chick neuroblasts. The effect of these trophic agents is unique since a variety of known mitogens tested were negative.