THE NATURE OF THE TROPHIC ACTION OF BRAIN-DERIVED NEUROTROPHIC FACTOR, DES(1-3)-INSULIN-LIKE GROWTH FACTOR-I, AND BASIC FIBROBLAST GROWTH-FACTOR ON MESENCEPHALIC DOPAMINERGIC-NEURONS DEVELOPING IN CULTURE

Brain-derived neurotrophic factor, basic fibroblast growth factor and des(I-3)-insulin-like growth factor-1, a brain specific form of insulin-like growth factor-1, were analysed, in the rat, for their influence on survival, morphological growth, and transmitter-specific differentiation of dopaminergic neurons in vitro. Brain-derived neurotrophic factor, des-insulin-like growth factor-1, and basic fibroblast growth factor were found to differentially regulate development of dopaminergic cells. Brain-derived neurotrophic factor stimulated survival, the formation of primary neurites and dopamine uptake activity. des-Insulin-like growth factor-1 was most effective in promoting survival, stimulated dopamine uptake less effectively than brain-derived neurotrophic factor and did not alter the morphology of dopaminergic cells. Basic fibroblast growth factor produced comparatively mild increases in survival and dopamine uptake, and slightly reduced neurite growth of the cells. None of the factors stimulated the expression of the tyrosine hydroxylase gene. These findings suggest that (i) effective growth factors may stimulate different, but partially overlapping, molecular pathways during developmental differentiation, (ii) none of the factors stimulates dopaminergic cell differentiation comparable to the pronounced trophic action of nerve growth factor on peripheral sympathetic or basal forebrain cholinergic neurons, and (iii) localization and effects of none of the factors are compatible with a role as target-derived survival-regulating neurotrophic factor.