DIRECTED OUTGROWTH FROM A SUBSET OF COCHLEAR NUCLEUS FIBERS IN A COLLAGEN-GEL MATRIX

We have employed a collagen-gel co-culture system to evaluate the infl uence of the hindbrain floor-plate on initial axon outgrowth from the cochlear nucleus. After 2 days in vitro, cochlear nucleus explants exh ibited directed outgrowth towards co-cultured floor plate explants. Co mparisons with co-cultures of cochlear nucleus/forebrain or cochlear n ucleus/midbrain explants or with cochlear nucleus explants cultured al one suggest that the floor-plate has a specific chemoattractant effect on the outgrowth of the pioneer fibers of the hindbrain auditory comm issure. Fiber outgrowth was not directed towards a recombinant source of the chemoattractant molecule netrin suggesting that floor plate dir ected outgrowth in the cochlear nucleus is not solely dependent on net rin. In the present report, we present evidence for the first time tha t the floor-plate is a chemotropic source in pathfinding of second-ord er auditory fibers from the cochlear nucleus in the hindbrain. (C) 199 8 Elsevier Science B.V.