SPATIAL AND TEMPORAL GROWTH-FACTOR INFLUENCES ON DEVELOPING MIDBRAIN DOPAMINERGIC-NEURONS

Despite the large number of growth factors shown to affect dopaminergi c cell survival and differentiation in vitro, presently little is know n about the role these growth factors play during normal in vivo devel opment of dopaminergic neurons. To address this issue, glia and neuron s of both the mesencephalic home region as well as the striatal and co rtical target areas have been screened for effects on dopaminergic cel l survival in serum-free dissociated cell cultures of the embryonic da y (E) 15 and E17 rat mesencephalon. In E15 mesencephalic cultures, the number of surviving tyrosine hydroxylase-immunoreactive dopaminergic neurons maximally increased 2.6-fold with medium conditioned by glia o f the E15-E20 mesencephalon, the E17-E20 striatum, or the E20 cortex. In marked contrast, all glial-conditioned media (CM) failed to affect dopaminergic cell survival in E17 mesencephalic cultures. Similarly, E 17 dopaminergic cell survival was not affected by CM derived from stri atal or mesencephalic neurons. This absence of survival-promoting effe cts was not due to a general lack of sensitivity of the late embryonic dopaminergic neurons to growth factors. Basal survival of cultured E1 7 dopaminergic neurons declined with PD98059 (20 mu M), a potent inhib itor of growth factor-activated microtubule-associated protein (MAP) k inase cascade. Moreover, irrespective of the age of the cultured mesen cephalic tissue, dopaminergic growth factors with potential autocrine functions such as brain-derived neurotrophic factor (BDNF; 50 ng/ml) a nd glial cell line-derived neurotrophic factor (GDNF; 10 ng/ml) promot ed dopaminergic cell survival 1.5- to 1.9-fold. These findings suggest that dopaminergic cell survival is predominantly affected by, as yet unknown, growth factors derived from mesencephalic, cortical, and stri atal glia during early embryonic development, and by autocrine-acting growth factors during late development stages. (C) 1998 Wiley-Liss,Inc .