Fig. 1.

Effects of IGFs on neuron numbers in cultures of EGF-generated precursors. A, Increasing concentrations of IGF-I, IGF-II, and insulin induced a dose-dependent increase in neuron (β-tubulin-immunoreactive) production, expressed as a percentage of total cells derived from EGF-generated spheres. The rank order of potency, IGF-I > IGF-II > insulin, is characteristic of IGF-I receptor pharmacology (LeRoith et al., 1993) (see Results for further discussion). Growth factors were added at plating and were present for the entire culture period. Under the identical experimental conditions the percentages of astrocytes (GFAP-immunoreactive (B) and total cell number (C) were not affected significantly, other than total cell numbers at supersaturating (1 μm) concentrations of IGF-I or IGF-II. Data represent the mean ± SEM of four independent cultures; *p < 0.05.