Differential trophic effects of basic fibroblast growth factor, insulin-like growth factor-1, and neurotrophin-3 on striatal neurons in culture.

We have examined the trophic effects of basic fibroblast growth factor (bFGF), truncated insulin-like growth factor-1 (tIGF), and neurotrophin-3 (NT-3) on embryonic striatal neurons grown under serum-free culture conditions. Striatal neurons were identified using immunocytochemistry for dopamine- and cyclic AMP-regulated phosphoprotein (DARPP-32). In our serum-free striatal cultures, the survival and the development of DARPP-32- containing neurons were dependent on initial plating density: relatively high density cultures yielded disproportionately increased number of harvested DARPP-32- positive neurons. All three growth factors, bFGF (10 ng/ml), tIGF-1 (50 ng/ml), and NT-3 (50 ng/ml), promoted the survival of DARPP-32-positive neurons, with bFGF being significantly more effective than tIGF-1 and NT-3. Exposure to bFGF also significantly increased the total cell number compared to control cultures, whereas there was only a tendency toward more (20-30%) surviving cells in cultures treated with either tIGF-1 or NT-3. With the concentrations used, only bFGF gave rise to a significant increase (80%) in the number of glial fibrillary acidic protein-immunopositive glia as compared to controls. The most pronounced effect on morphological development of DARPP-32-containing neurons was seen with NT-3, which increased the length of neurites, the number of branching points on the neurites, and the soma area. There was no alteration of the morphology of this neuronal population in bFGF-treated cultures. All of these growth factors were seen to be approximately equally efficient at protecting striatal neurons from N-methyl-D- aspartate-induced excitotoxicity. These data indicate that bFGF, tIGF-1, and NT3 exert different trophic activities on striatal neurons in vitro and suggest that these growth factors might also be involved in the regulation of neuronal development and maintenance in the striatum.