Abstract
Age-dependent decreases in the levels of ornithine decarboxylase activity were observed in the optic lobes, cerebral hemispheres, and midbrain-diencephalon of 6--17-day-old chick embryos. In dissociated cell cultures from chick embryonic brains a similar pattern of declining ornithine decarboxylase activity with time in culture was observed. Ornithine decarboxylase activity in the dissociated brain cell cultures was stimulated by changing the culture medium. The peak stimulatory effect was shown to occur 12 h after changing the medium. Although serum-free medium stimulated ornithine decarboxylase activity slightly, the presence of serum in the medium was the primary stimulatory factor. Both fetal calf serum and heat-inactivated fetal calf serum produced dose-dependent stimulation of ornithine decarboxylase activity. Dialyzed fetal calf sera stimulated ornithine decarboxylase, but to a lower level than that produced by nondialyzed sera. Insulin (0.5--10 microgram/ml) stimulated ornithine decarboxylase activity in a dose-dependent manner in serum free medium. In addition, 10(-2) M-L-asparagine stimulated ornithine decarboxylase activity in serum-free medium.
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