Attachment of Con A or extracellular matrix initiates rapid sprouting by cultured leech neurons.

The outgrowth of neurites by single identified leech neurons in culture is markedly influenced by the substrate. Extensive sprouting occurs within a few hours on the plant lectin Con A. In contrast, the same neurons grow far more slowly or not at all when plated on vertebrate extracellular matrix proteins, other lectins, or poly(L-lysine). Sprouting on Con A, unlike that on poly(L-lysine), is inhibited by the Con A-specific hapten sugar methyl alpha-D-mannoside. Another substrate, promoting even more extensive sprouting of leech neurons, is cell-free extracellular matrix obtained from leech ganglion capsules. Urea extracts of extracellular matrix retain full neurite-promoting activity when dialyzed and used to coat culture dishes. Soluble growth factors are not required, since sprouting occurs in medium without macromolecules. These results show that sprouting depends not simply on attachment to the substrate but, critically, on its molecular composition; moreover, the pattern of outgrowth is characteristic and distinguishable for each type of neuron.