Descending Vasomotor Pathways in Humans: Correlation between Axonal Preservation and Cardiovascular Dysfunction after Spinal Cord Injury

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Abstract
Cardiovascular dysfunction is common after cervical spinal cord injury (SCI) in humans. At least three spinal cord elements involved in cardiovascular control have been identified: descending vasomotor pathways (DVPs), sympathetic preganglionic neurons, and spinal afferents. However, little is known about the localization of the DVPs within the human spinal cord, which limits our understanding of the mechanisms of cardiovascular dysfunction after SCI. This study was undertaken to examine the association of cardiovascular abnormalities after SCI in humans with the severity of degeneration and axonal loss within the DVPs. A detailed chart review and histopathological examination of postmortem spinal cord tissue was conducted in individuals with cervical SCI (n = 7) and control individuals with an intact central nervous system (n = 5). Individuals with SCI were divided into group 1 (severe cardiovascular abnormalities) and group 2 (no/minor cardiovascular disturbances). The area of degeneration and the number of preserved axons within different areas of the spinal cord were quantitated using EMPIX imaging software. Two areas of possible localization of DVPs were investigated: area I, within the dorsal aspects of the lateral funiculus; and area II, within the white matter adjacent to the dorsolateral aspect of the lateral horn. Comparison of the extent of axonal degeneration in both SCI groups demonstrated that individuals in group 1 had more extensive axonal degeneration than those in group 2. The number of intact axons within areas I and II in individuals from group 1 was significantly lower than those from group 2 or control cases (p = 0.029; p = 0.028). The most dramatic axonal loss was observed within area I in individuals with cardiovascular dysfunction. We conclude that loss and degeneration of DVPs, which are localized within the dorsolateral aspects of the human spinal cord, contributes to abnormal cardiovascular control after SCI. This information adds to our knowledge of pathobiology of cardiovascular dysfunction after human SCI and may ultimately suggest novel therapeutic strategies as regenerative and reparative approaches become translated to the clinic.