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 gest ation fetal rabbit brain were studied for the presence of insulin-like growth factor I (IGF I). The 22 day gestation NCC were incubated in a n 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 cont aining medium. The 22 day gestation NCC survived in the IGF I free/ins ulin free/serum free medium. Furthermore, IGF I was detected in the me dium 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/seru m 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 th e cells survived for a period of 2-3 days. Immunoreactive IGF I was fo und within the 22 day gestation NCC incubated in the IGF I free/insuli n free/serum free medium and 18 day gestation NCC in serum medium. Lik ewise, IGF I mRNA was found only within the 22 day gestation NCC. Inte rnalization studies of IGF I have shown that the peptide was internali zed 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 gesta tion NCC. In conclusion IGF I may promote cell survival in early stage s of brain development, and may be of exogenous origin. In contrast th e 22 day gestation NCC are capable of producing and secreting IGF I, a nd indeed appear to respond to this growth factor in an autocrine fash ion.