Differentiation in vitro of sympathetic cells from chick embryo sensory ganglia

This study was carried out in order to determine what factors control the differentiation of certain neural crest cells in the chick embryo. Emphasis was placed on the morphologically and biochemically divergent sensory and sympathetic pathways of differentiation. Embryos were precisely stage according to Hamburger & Hamilton (1951) and it was observed that sensory ganglia with somites, explanted at stages 21-24, gave rise to cells showing formaldehyde-induced fluorescence in more than 25% of explants. These cells were identical in properties to the fluorescent cells of the sympathetic system of embryos of similar age, and appeared by 12 days in vitro. These fluorescent cells did not appear when somites and sensory ganglia explants were maintained separately. The incidence of fluorescent cells in combined explants was considerably reduced or absent when cultures were maintained for 7 days or less, or when the explants were obtained from stage 25-26 embryos. Furthermore, when neural tube was also included in the cultures, the appearance of fluorescent cells was markedly inhibited. The requirement for somitic tissue to induce fluorescent cells in combined explants can be repalced by forelimb-bud tissue. The origin of these cells and the factors that control their differentiation in vitro are discussed with reference to the neural crest origin of the sensory ganglion, and the possible conditions pertaining in vivo in this region.