Evaluation of axonal injury in cultured neurons exposed to impulsive tensile strain

Abstract

Diffuse axonal injury (DAI) is caused by sudden inertial loading to the head associated with rapid deformation of brain tissue, resulting in the stretching of neural axons. Periodic swellings along axons and axonal bulbs at disconnected terminal ends of axons that are the morphological hallmarks of DAI pathology lead to the disconnection of neurons from tissues, resulting in cell death. The β-amyloid precursor protein (β-APP) that is conveyed by axonal transport and Tau protein that is associated with axonal microtubules accumulate where axonal transport is disrupted. In this study, the cultured rat brain neuronal cells were stretched to strains of 0.10–0.30 at strain rates of 4–50 s^-1 . The sham control is put in the stretching device without mechanical loading and then is incubated under conditions of 5% CO² and 100% humidity at 37°C. β-APP and Tau protein were stained at 3 h post-loading and observed using fluorescence microscopy. As a result, β-APP and Tau protein accumulated in swellings and bulbs following stretching and accumulated axons significantly increased following strains of more than 0.22 in a strain-dependent manner compared to sham control. However, there were slight changes with regards to the dependence of strain rates. These results suggest that the threshold of interruption of axonal transport is 0.22 strain.