Figure 7.

Contribution of stretching to slow axonal transport in extreme stretch-grown axons. We applied our model to the study of Pfister et al. (7) to see how much stretching contributed to anterograde transport in cases of extreme stretch growth. In the study, axons were elongated at a rate of γ = 4 mm day⁻¹ for 12 days. These axons were free of adhesions along the length, so Eqs. 6 and 7 were applied. Parameter values A = 84.1 and C = 1.96 were derived using values listed in Table S1. (A) Flux profiles of anterograde transport at the beginning of the 12-day elongation period. Since A is much greater than C, the slope of the total flux profile is close to zero, and stretching is the dominant form of transport in the majority of the distal axon (x_1/2/L = 5.09). (B) After 12 days, stretching is still the dominant form of transport in the distal 41% (20 mm) of the axon (x_1/2/L = 5.89). (C) The relative contribution of stretching to anterograde momentum is given by the ratio p_U/p. Over the course of 12 days of elongation at 4 mm day⁻¹, this ratio declines from .491 to .411, showing that stretching accounts for a significant amount of anterograde transport (>40%) when axons are elongated by extreme stretch growth.