Abstract
Glucocorticoid hormones stimulate catecholamine (CA) anabolism in a variety of adrenergic derivatives of the neural crest. We describe work performed to investigate the action of these steroids on the catecholaminergic differentiation of neural crest cells themselves. Crest was taken from the trunk level of 2-day quail embryos, before migration had begun, and was cultured in vitro. Adrenergic differentiation, characterized by the ability of the cultures to synthesize and store CA, was minimal and was not improved when glucocorticoids were added to the medium. In contrast, extensive adrenergic differentiation occurred when neural crest cells, removed from the embryo 24 hr later, toward the end of their migratory phase, were cultured with the sclerotomal component of the somite (their immediate embryonic microenvironment). This process was considerably stimulated by corticosteroids; the rate of conversion of [3H]tyrosine to intracellular CA (norepinephrine, epinephrine, and dopamine) was 2 to 3 times higher in cultures exposed for 7 days to 10(-6) to 10(-7) M hydrocortisone, corticosterone, or dexamethasone, and the diameter of the dense-core vesicles seen in cell bodies and processes after permanganate fixation was strikingly increased. The effect was specific for the adrenergic phenotype in that acetylcholine synthesis by the cultures was consistently unaffected by hormone treatment. We infer that glucocorticoids do not trigger adrenergic differentiation, but that they selectively enhance catecholaminergic properties in crest cells that have already been exposed to an appropriate signal of another kind. This conclusion is strengthened by the observation that glucocorticoids stimulated the development of CA-producing cells from premigratory crest grown in the presence of somites and notochord, postulated sources of factors initiating adrenergic differentiation in the embryo. Although the intervention of glucocorticoids in vivo at very early embryonic stages remains to be established, our results indicate that neural crest derivatives would be potentially responsive to these hormones as soon as the sympathetic ganglia form.
