Signalling organelle for retrograde axonal transport of internalized neurotrophins from the nerve terminal

The retrograde axonal transport of neurotrophins occurs after receptor-medi ated endocytosis into vesicles at the nerve terminal. We have been investig ating the process of targeting these vesicles for retrograde transport, by examining the transport of [I-125]-labelled neurotrophins from the eye to s ympathetic and sensory ganglia. With the aid of confocal microscopy, we exa mined the phenomena further in cultures of dissociated sympathetic ganglia to which rhodamine-labelled nerve growth factor (NGF) was added. We found t he label in large vesicles in the growth cone and axons. Light microscopic examination of the sympathetic nerve trunk in vivo also showed the retrogra dely transported material to be sporadically located in large structures in the axons. Ultrastructural examination of the sympathetic nerve trunk afte r the transport of NGF bound to gold particles showed the label to be conce ntrated in relatively few large organelles that consisted of accumulations of multivesicular bodies. These results suggest that in vivo NGF is transpo rted in specialized organelles that require assembly in the nerve terminal.