On the mechanism of the uptake of horseradish peroxidase into the retrograde transport system of ligated postganglionic sympathetic nerves in vitro.

The mechanism of the uptake of horseradish peroxidase (HRP) by damaged post-ganglionic sympathetic axons was studied in vitro. HRP was applied to the damaged axons at the time of nerve injury or after a 3 hours or 17 hours delay. An interval of 3 hours or 17 hours between nerve injury and exposure to HRP had no effect on the localisation of the HRP in the damaged axons or on its retrograde transport to their perikarya. Evidence was found for the pinocytotic uptake of the enzyme by the damaged axons and its accumulation within those axons in elongated cisternae and larger rounded vesicles. In further experiments the damaged axons were treated with HRP at 0 degrees C and then washed in HRP-free medium. The tracer entered the axons in a diffuse form under these conditions but no pinocytotic uptake was observed. However, following 24 hours further incubation at 37 degrees C, HRP could not be found in the perikarya. Treatment at 0 degrees C did not produce any lasting damage to the retrograde transport mechanism. The results of these experiments are compatible with the involvement of pinocytosis in the uptake of HRP in a form suitable for retrograde transport.