The effects of IGF-I and IGF-II on cell growth and differentiation in the central nervous system.

Both IGF-I and IGF-II peptides have been localized to specific brain regions. The distribution of IGF-I is homogeneous whereas IGF-II appears to be more local. Two species of IGF receptors are found in the CNS. The type II (m6P) is similar to that in the periphery, but the type I has nearly the same affinity for IGF-I and IGF-II. IGF-I has now been shown to provide cell growth and survival as well as stimulate neurite outgrowth. Dorsal root ganglia and sympathetic neurons are sensitive to IGF-II and the action may be additive with NGF. Cells other than neurites, such as oligodendrocytes respond to the IGFs as well as primary and transformed lines. The mechanism of action has not been resolved but IDG-II appears to act via G-protein coupled activation of protein kinase C. Interaction between various growth factors and the IGFs may be due to up or down-regulation of the receptor predicated by the non-homologous peptide.