Temperature‐dependence of rapid axonal transport in sympathetic nerves of the rabbit

Stop‐flow techniques were used to determine how temperature affected the axonal transport of dopamine‐β‐hydroxylase (DBH) activity in rabbit sciatic nerves in vitro. These nerves were cooled locally to 2°C for 1.5 hr, which caused a sharp peak of DBH activity to accumulate above the cooled region. Accumulated DBH was then allowed to resume migration at various temperatures. From direct measurements of the rate of migration, we found that the axonal transport velocity of DBH was a simple exponential function of temperature between 13°C and 42°C. Over this range of temperatures, the results were well described by the equation: V = 0.546(1.09)^T, where V is velocity in mm/hr, and T is temperature in degrees centigrade. The Q₁₀ between 13°C and 42°C was 2.33, and an Arrhenius plot of the natural logarithm of velocity versus the reciprocal of absolute temperature yielded an apparent activation energy of 14.8 kcal. Transport virtually halted when temperature was raised to 47°C, although only about half of the DBH activity disappeared during incubation at this temperature. Another transition occurred at 13°C; below this temperature, velocity fell precipitously. This was not an artifact peculiar to the stop‐flow system since the rate of accumulation of DBH activity proximal to a cold‐block also decreased abruptly when the temperature above the block was reduced below 13°C.