Characteristics of the retrograde axonal transport system for nerve growth factor in the sympathetic nervous system

Retrograde axonal transport of ¹²⁵I labeled nerve growth factor (NGF) occurs in the adrenergic neurons of the sympathetic nervous system of rats as well as mice. This transport is saturable, it can be blocked by an excess of unlabeled NGF and shows a specificity for the biologically active form of the protein. Other proteins such as serum albumin, chymotrypsin or insulin are transported in varying, but much smaller, amounts. Although the transport of albumin is blocked by an excess of NGF, the opposite is not true, again suggesting a specific mechanism. NGF antibody, injected subcutaneously, prevents retrograde transport in neonatal but not in more mature animals and the relative resistance of the latter to the action of NGF antiserum may be related to this phenomenon.