Simultaneous Reactive Change in Unmyelinated and Myelinated Axon Segments Following Experimental Diffuse Traumatic...

Area of Science:

• Neuroscience
• Traumatic Brain Injury Research
• Axonal Pathobiology

Background:

• Diffuse axonal injury (DAI) is a major cause of morbidity following traumatic brain injury (TBI).
• Previous research suggested unmyelinated axons are more susceptible to TBI than myelinated axons, with myelin potentially offering protection.
• DAI has been localized to the perisomatic domain, including the unmyelinated axon initial segment (AIS) and nodes of Ranvier.

Purpose of the Study:

• To investigate the hypothesis that unmyelinated axonal segments are selectively vulnerable to TBI-mediated forces.
• To examine the gray-white matter interface for initiating DAI pathology.
• To determine if myelin plays a protective role in diffuse TBI.

Main Methods:

• Utilized a murine midline fluid percussion injury model.
• Examined neocortical layer V pyramidal cell perisomatic domains using antibodies for cytoskeletal proteins and amyloid precursor protein (APP).
• Employed yellow fluorescent protein for enhanced visualization of axonal injury.

Main Results:

• Axonal swellings were observed simultaneously in both unmyelinated perisomatic segments (AIS, nodes) and adjacent myelinated segments.
• Findings indicate concomitant reactive axonal changes, suggesting non-selective axonal susceptibility.
• Myelin did not appear to confer protection against diffuse injury forces in this model.

Conclusions:

• Unmyelinated axonal segments may not be selectively vulnerable to TBI shear/tensile forces.
• Myelin may not protect axons from diffuse TBI, contrary to historical assumptions.
• DAI extends to the gray-white matter junction, impacting neuronal function and connectivity; further research is needed on shared pathological mechanisms between white and gray matter axons.