Development of mammalian nerve-muscle synapses in culture: Lack of interference by antibodies to the neural cell adhesion molecule N-CAM and its L2/HNK-1 carbohydrate epitope

Rat myotubes were cultured with embryonic mouse spinal cord explants. After 4 days of co-culture, (miniature) endplate potentials, (M)EPPs, could be detected in 20-40% of the nerve-contacted myotubes. Polyclonal antibodies against the neural cell adhesion molecule N-CAM and monoclonal antiodies to its L2/HNK-1 carbohydrate epitope were tested for possible effects on synapse formation in this system. Co-cultures that were started and maintained in the presence of Fab fragments of these antibodies developed functional synapses to the same extent as did control cultures. Staining with an anti-IgG antibody demonstrated that added Fab fragments had bound to neurites and that an excess was present in the medium. These findings suggest that even if N-CAM and the L2/HNK-1 epitope were involved in early stages of muscle-nerve contact, they are not essential for the formation of electrophysiologically active synapses.