Fig. 3. Axons of ganglion explants can synthesize protein autonomously. Proliferation of non-neuronal cells was suppressed by culture conditions (A-D). When chick sympathetic ganglia were grown for 4-5 days on a poly-L-lysine substratum with intermittent Ara-C treatment, they produced a large radial halo of axons (A) that was virtually devoid of cell bodies or non-neuronal cells, as revealed by DAPI staining (B). The dotted line in (B) indicates the approximate position where the cell body mass would be removed for metabolic labeling experiments. When grown on a laminin substratum and in the absence of Ara-C treatment, axonal halos contained abundant non-neuronal cells, revealed by their nuclei (C,D). Normal ganglia grown under the conditions shown in (A,B) were incubated with [³⁵S]-methionine/cysteine, subjected to emulsion autoradiography and viewed by dark-field microscopy. They revealed a bright signal in the cell body mass and a fainter one in the axonal halo (E). Axonal halos with the cell body mass meticulously removed prior to metabolic labeling also showed newly synthesized protein throughout the axons (F). This signal was eliminated by cycloheximide treatment (G) but was undiminished when chloramphenicol treatment accompanied metabolic labeling (H). Conditions of radiolabeling, autoradiography and photography were uniform, except that the photographic exposure of (E) was 25% that of F-H owing to the intensity of signal from the cell body mass. The dark area in the center of the cell body mass in E is an artefact of high radioactive signal damaging the emulsion. Scale bars, 200 µm (in D, for A-D; in H, for E-H).