LACK OF RETROGRADE AXONAL-TRANSPORT OF THE HEPARIN-BINDING GROWTH-FACTORS BY CHICK CILIARY NEURONS

In view of the likelihood that the heparin-binding growth factors of fibroblast growth factors are neurotrophic for the neurones of the chick ciliary ganglion a study has been made of the retrograde axonal transport of the acidic and basic fibroblast growth factors by these neurones. No high capacity retrograde axonal transport of these molecules was seen. The amount of transport was equivalent to the low level seen with many proteins such as horse radish peroxidase or bovine serum albumin rather than the convincing transport seen for nerve growth factor in the sympathetic system. The iodinated proteins retained their ability to bind to neuronal receptors. Thus, if the fibroblast growth factors are neurotrophic in the ciliary ganglion, they may exert their action by mechanisms other than the retrograde axonal transport of the factor itself.