Dynamics of fast axonal transport.

A phenomenological model of the process of fast axoplasmic transport is presented. The process was conceived of as occurring in two parts: (a) synthesis and storage of material in a cytoplasmic pool; (b) release from the pool and transport distally along the axon. Considering the fate of labeled proteins, the activity at points along the axon relfects events occurring earlier within the pool through the relationship: g(x,t) = const f(t - x/v); where g(x,t) represents axonal activity, f(t) the pool's activity, and v is the transport speed. Using the idea that when there is no further input of radioactivity into the pool its activity declines exponentially due to export of material to the axon. I generalized this concept to the case where activity enters and leaves the pool simultaneously. The model contains two parameters: the relative turnover rate of the pool, alpha, and T, an interval characteristic of the time of synthesis. From this model, the experimental data is unfolded and yields values for these parameters of alpha = 0.004 min-1 and T approximately 60 min.