Effect of temperature on the rapid retrograde transport of microscopically visible intra-axonal organelles

Abstract

Summary The effects of temperature on the retrograde axonal transport of microscopically visible intra-axonal organelles was studied in acutely isolated myelinated axons from bullfrog sciatic nerve. Dark-field microscopy, cinemicrophotography, and computer-based analytical methods were employed. More than 90% of the optically detectable particles move in the retrograde direction. In the range of 8–37°C, the average speed of these particles is highly temperature sensitive, with a Q10 of 2.5–3.5. Movement stops entirely at about 5°C. Our findings show that the effect of temperature must be taken into consideration when comparing rates of axonal transport reported for different experimental systems. The average organelle speeds in frog are similar to those reported by others in mature axons of other species, but are faster than the rates which have been measured in neurites in tissue culture. The mean speeds of the particles moving in the retrograde direction are similar to the rates of retrograde axonal transport estimated by other methods. The average particle speeds are less than half of the anterograde rapid transport rates reported in the literature. However, the fastest particles move (in the retrograde direction) at speeds which approach the anterograde rates. The standard deviation of the distribution of retrograde particle velocities also varies with temperature, but remains a constant fraction (about 36%) of the population mean at all temperatures. The same fractional standard deviation (i.e. S.D. of the mean= 0.36) has been reported by others in axons from other species and in neurites in tissue culture, and may reflect a fundamental property of the axonal transport process.