Neuronal chemotaxis: chick dorsal-root axons turn toward high concentrations of nerve growth factor.

Micropipettes containing 2 to 50 biological units of beta growth factor (NGF) were placed near growing axons of chick dorsal-root ganglion neurons in tissue culture. The axons turned and grew toward the NGF source within 21 minutes. This turning response to elevated concentrations of NGF appears to represent chemotactic guidance rather than a general enhancement of growth rate.