Ganglioside GM1 Antibodies and B‐Cholera Toxin Bind Specifically to Embryonic Chick Dorsal Root Ganglion Neurons but Do Not Modulate Neurite Regeneration

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Abstract
Polyclonal antibodies to ganglioside Gmi have been prepared and characterised by direct and competitive enzyme‐linked immunoassay. An immunoglobulin fraction was prepared from a rabbit antisera showing high specificity and antibody titre for GMI relative to the other major brain gangliosides. The anti‐GMI immunoglobulin fraction and B‐cholera toxin specifically labelled neurons in primary cultures of embryonic chick dorsal root ganglia and there was a good correlation between the relative increase in binding of anti‐GMI immunoglobulin and B‐cholera toxin following neuraminidase treatment of a variety of cell types. At antibody concentrations that show saturable binding to endogenous ganglioside in the neuronal membrane, the anti‐GM1 immunoglobulin fraction did not interfere with the nerve growth factor (NGF)‐mediated fibre outgrowth and neuronal survival as indexed by measurement of neu‐rofilament protein levels. Similarly, at levels in excess of those shown to stimulate thymocyte proliferation, B‐cholera toxin was also without effect. These data are not consistent with GMI in the neuronal membrane functioning as a receptor molecule for NGF and/or other differentiation factors present in the tissue culture media.