Chemotactic response of nerve fiber elongation to nerve growth factor.

These studies seek to determine whether the locomotory behavior of the extending tip of growing nerve fibers exhibits chemotaxis to nerve growth factor (NGF). Sensory neurons from dissociated dorsal root gangha of chick embryos were cultured within semisolid agar matrices containing concentration gradients of NGF which diffused from an adjacent source. A preferential orientation of approximately 60% of the tips of nerve fibers and an enhanced extension of fibers up NGF gradients were observed. The initiation sites of nerve fibers on cell bodies were not consistently oriented by these NGF gradients. Orientation of nerve fiber extension toward the NGF source was observed in chambers with NGF sources ranging from 25 to 1000 rig/ml of /3NGF and from 400 to 5000 rig/ml of 7 S NGF, but no orientation was observed when the concentration of the NGF source was 15000 rig/ml of fi-NGF. This oriented response apparently is not a concentration-dependent trophic response to NGF. The evidence supports the notion that chemotaxis is a regulatory factor in neuronal morphogenesis.