Ganglioside GM1 Does Not Initiate, but Enhances Neurite Regeneration of Nerve Growth Factor-Dependent Sensory Neurones

An enzyme-linked immunoadsorbent assay (ELISA) for neurofilament protein was utilised to quantify the effect of exogenous ganglioside on neurite regeneration in cultures of dorsal root ganglion neurones. In contrast to nerve growth factor (NGF), ganglioside GM1 (100 micrograms/ml) failed to support neuronal survival and neurite regeneration as quantified by the ELISA assay and confirmed by morphological criteria. However, the simultaneous presence of GM1 (100 micrograms/ml) and NGF (0.5-5 ng/ml) throughout a 5-day period of culture resulted in an enhancement of previously reported NGF-induced increases in the expression of neurofilament protein. Further, the addition of GM1 (0-200 micrograms/ml) at 48 h in vitro to cultures initially established in the presence of 5 ng/ml NGF substantially increased the subsequent expression of neurofilament protein, this response being both independent of and not potentiated by NGF. The results in the present system suggest that GM1 cannot initiate a programme of neurite regeneration; however, GM1 can enhance this process with the response being secondary to the effect of NGF.