An immunohistochemical and in situ hybridization study of insulin-like growth factor I within fetal neuron cell cultures.

Fetal neuron cell cultures (NCC) from 22 day gestation and 18 day gestation fetal rabbit brain were studied for the presence of insulin-like growth factor I (IGF I). The 22 day gestation NCC were incubated in an IGF I free/insulin free/serum free medium. The 18 day gestation NCC were incubated in: (1) IGF I free/insulin free/serum free medium, (2) IGF I containing medium (100 ng)/serum free medium, and (3) serum containing medium. The 22 day gestation NCC survived in the IGF I free/insulin free/serum free medium. Furthermore, IGF I was detected in the medium by RIA from day one to day ten of incubation. In contrast, the 18 day gestation NCC did not survive in the IGF I free/insulin free/serum medium, but survived in the serum medium. When the 18 day gestation NCC were incubated in the serum free medium containing 100 ng IGF I the cells survived for a period of 2-3 days. Immunoreactive IGF I was found within the 22 day gestation NCC incubated in the IGF I free/insulin free/serum free medium and 18 day gestation NCC in serum medium. Likewise, IGF I mRNA was found only within the 22 day gestation NCC. Internalization studies of IGF I have shown that the peptide was internalized from the medium by the two different gestational age NCC's studied. IGF I receptors were found in both 22 day gestation and 18 day gestation NCC. In conclusion IGF I may promote cell survival in early stages of brain development, and may be of exogenous origin. In contrast the 22 day gestation NCC are capable of producing and secreting IGF I, and indeed appear to respond to this growth factor in an autocrine fashion.