Ganglioside GM1 overcomes serum inhibition of neuritic outgrowth

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Abstract
Considerable variations in both neuritic and non-neuronal cell outgrowths of ganglionic expiant cultures are imposed when different substrata and medium supplements are used. Therefore, a neuritic response to exogenous agents such as gangliosides may be better, or exclusively revealed under selected combinations of medium and substratum. We have surveyed a number of different ganglia for their ability to display a neuritic response to ganglioside GM1 and the culture conditions under which such a display may take place. GM1 can recognizably promote neurite extension from embryonic day 8 chick dorsal root ganglia, day 11 sympathetic ganglia, and day 8 ciliary ganglia. Demonstration of such effects, however, requires an appropriate balance between promoting and inhibiting influences by other extrinsic influences (culture substrata, neuronotrophic factors, serum inhibitors) thereby allowing for improvement by the ganglioside. Different ganglia require different combinations of those influences. Ciliary ganglia, for example, will show a GM1 response on a polyornithine substratum in medium supplemented with the chick eye Ciliary Neuronotrophic Factor and 1% fetal calf serum, but not with 10% serum or no serum. The effective concentration range for GM1 is in accord with previously reported serum binding data. These, and other data are consistent with an action of GM1 in executing a neurite program, rather than an imposition of the program itself.