ROLE OF LAMININ IN AXONAL EXTENSION FROM OLFACTORY RECEPTOR-CELLS

The role of laminin, an extracellular matrix molecule believed to be i nvolved in axon extension, was explored in the outgrowth of olfactory receptor cells and therefore in the maintenance of organization in the olfactory pathway. First, immunocytochemistry was used to examine lam inin expression in the olfactory nerve and bulb during development. La minin immunoreactivity was high in the olfactory nerve and glomerular layers. Although it declined in intensity, laminin expression continue d in the nerve and in single glomeruli of adults. Second, the influenc e of laminin on neurite outgrowth was examined in vitro using olfactor y receptor cells harvested from E14 rat embryos. We developed an in vi tro assay to quantify the substrate preference of outgrowing neurites. Cells were cultured for 48 h on coverslips coated with either poly-L- lysine alone, or poly-L-lysine overlaid with laminin. On laminin-coate d regions of coverslips, the primary neurites of olfactory receptor ce lls were 52% longer than on the poly-L-lysine control substrates. In a ddition, the direction of the neurite outgrowth was influenced by lami nin. Fifty-six percent of all receptor cells located in a defined area surrounding a laminin zone extended neurites onto laminin. In contras t, only 7% of all receptor cells located in the corresponding laminin zone extended a neurite onto poly-L-lysine. In summary, these data sug gest that laminin provides a favorable substrate far the extension of the primary neurite from olfactory receptor cells and the direction of their extension. Therefore, laminin may be a factor underlying contin uous olfactory receptor cell axon outgrowth and its pathfinding in the olfactory system. (C) 1997 John Wiley & Sons, Inc.