This study aims to clarify the relation between axonal deformation and the onset
of axonal injury. Firstly, to examine the influence of strain rate on the
threshold for axonal injury, cultured neurons were subjected to 12 types of
stretching (strains were 0.10, 0.15, and 0.20 and strain rates were 10, 30, 50,
and 70 s-1). The formation of axonal swellings and bulbs increased
significantly at strain rates of 50 and 30 s-1 with strains of 0.15
and 0.20, respectively, even though those formations did not depend on strain
rates in cultures exposed to a strain of 0.10. Then, to examine the influence of
the strain along an axon on axonal injury, swellings were measured at every
axonal angle in the stretching direction. The axons that were parallel to
stretching direction were injured the most. Finally, we proposed an experimental
model that subjected an axon to more accurate strain. This model observed the
process of axonal injury formation by detecting the same neuron before and after
stretching. These results suggest that the strain-rate dependency of axonal
tolerance is induced by a higher magnitude of loading strain and an experiment
focusing on axonal strain is required for obtaining more detailed injury
criteria for an axon.