S-LAMININ AND N-ACETYLGALACTOSAMINE LOCATED AT THE SYNAPTIC BASAL LAMINA OF SKELETAL-MUSCLE ARE INVOLVED IN SYNAPTIC RECOGNITION BY GROWINGNEURITES

The purpose of the work reported here is to identify molecular compone nts of the synaptic basal lamina of skeletal muscle fibres which allow recognition of original synaptic sites by regenerating motor axons. W e focused on s-laminin and components recognized by the lectin Dolicho s biflorus agglutinin previously shown to be specifically located at t he synaptic basal lamina. We used a cryoculture bioassay in which chic k ciliary ganglion neurons grow on rat skeletal muscle cryostat sectio ns. In control cultures, neurites extended over the muscle sections in close association with the muscle cell surface. It was observed that most of the neurites that extended towards the endplate zone and reach ed an area of 40 mu m around the neuromuscular junction ceased to grow when they contacted the synaptic site. Masking either lectin receptor s or some s-laminin molecule epitopes prior to the culture of neurons alters the behaviour of growing neurites. On sections treated either w ith Dolichos biflorus agglutinin or anti s-laminin monoclonal antibodi es (D5 and C4) most of the neurites did not stop their growth at the s ynaptic regions. Moreover, treating muscle sections with Dolichos bifl orus agglutinin removed the gradient of substratum affinity around the endplate. These results indicate that the s-laminin and Dolichos bifl orus agglutinin receptors present on muscle cell surfaces may play a f unctional role in the interaction of growing neurites with original sy naptic sites in the process of neuromuscular regeneration.