BASIC FIBROBLAST GROWTH-FACTOR PROMOTES THE SURVIVAL OF EMBRYONIC VENTRAL MESENCEPHALIC DOPAMINERGIC-NEURONS .1. EFFECTS IN-VITRO

We have studied the effects of basic fibroblast growth factor on rat e mbryonic mesencephalic neurons in vitro. Basic fibroblast growth facto r promotes the survival of dopaminergic neurons in vitro, the effect i ncreasing with dose and reaching a maximum at 10 ng/ml. In the absence of basic fibroblast growth factor the number of tyrosine hydroxylase- stained (tyrosine hydroxylase positive) neurons declines to almost zer o within 14 days, whereas in the presence of basic fibroblast growth f actor numbers remain almost constant from three to 28 days in vitro. T his effect of basic fibroblast growth factor is abolished by preventin g non-neuronal cells from appearing in the cultures, apart from a basi c fibroblast growth factor-mediated increase in the numbers of tyrosin e hydroxylase-positive cells during the first two days in vitro. The p resence or absence of non-neuronal cells also influences dopaminergic neuronal morphology, the neurons having more, longer, and more varicos e processes in the absence of astrocytes. Survival of dopaminergic neu rons in vitro in the absence of basic fibroblast growth factor is very dependent on plating cell density, but in the presence of basic fibro blast growth factor this dependency vanishes. It is also possible to m ake survival independent of plating density by growing the cultures on inverted coverslips, which have the effect of concentrating secreted molecules in the thin layer of medium between coverslip and dish. Our conclusions from these experiments on plating density are that astrocy tes probably constitutively secrete a small amount of a trophic factor which promotes survival of dopaminergic neurons, and that the rate of production of this factor is greatly increased by basic fibroblast gr owth factor. If basic fibroblast growth factor is withdrawn from cultu res after two or seven days the dopaminergic neurons soon die. However , if basic fibroblast growth factor is withdrawn after 14 days, after the period of naturally occurring cell death of these neurons, there i s no increase in dopaminergic neuronal death compared to controls in w hich basic fibroblast growth factor treatment is maintained. If basic fibroblast growth factor is used to improve the survival of dopaminerg ic neurons grafted in vivo, it should therefore be sufficient to treat the grafts for 14 days.