Rapid retrograde transport of dopamine-β-hydroxylase as examined by the stop-flow technique

We have studied the retrograde axonal transport of dopamine-β-hydroxylase (DBH) with the aid of a new stop-flow technique. Rabbit sciatic nerves in vitro were incubated in chambers which exposed different regions to oxygenated physiological saline solution at different temperatures. These chambers contained no mechanical barriers that could generate local compression or anoxia. When the proximal halves of nerves were cooled to 2°C while the distal halves were kept at 37°C, a peak of DBH activity began to accumulate in the middle. Accumulation was detectable after 1.5 h of proximal cooling, and the amount of activity in the peak increased linearly with time for up to 4.5 h. The rate of this accumulation was only about 20% of the rate at which DBH activity accumulates proximal to locally cooled regions. Retrograde accumulation of DBH activity is not an artifact that depends upon the simple juxtaposition of cooled and warmed regions; it does not occur when nerves are locally warmed to 37°C while being kept elsewhere at 2°C. When nerves that had been proximally cooled for 3 h were rewarmed, the accumulated DBH activity was asymmetrically displaced toward the proximal end. The migrating wave lacked a definite peak, but appeared as a shoulder with a well-defined front that moved steadily at about 12 mm/h. We take this as direct evidence for retrograde axonal transport of DBH. The maximum velocity of this transport is very similar to the velocity of orthograde transport previously determined by stop-flow techniques.