Calcitonin gene-related peptide immunoreactivity in chronic human spinal cord injury

Study Design: Histopathological study of the human spinal cord. Setting: International Collaboration on Repair Discoveries, Vancouver, BC, Canada. Rationale: In animals, primary dorsal root afferent fibers, which are immunoreactive for calcitonin gene-related peptide ( CGRP), sprout following spinal cord injury (SCI) into deeper laminas of the dorsal horn below the level of injury. It has been suggested that this aberrant sprouting plays a role in altering cardiovascular control after SCI and could be responsible for life-threatening episodes of autonomic dysreflexia (AD). Objectives: To observe the changes of CGRP distribution after SCI and compare the differences between normal and injured human spinal cord. Methods: Upper thoracic segments from individuals with chronic cervical SCI (n=4) and individuals with intact spinal cords (n=5) were processed immunocytochemically to identify CGRP fibers and histologically to identify the severity of degeneration. Results: Semiquantitative analysis showed a significant increase in CGRP immunoreactivity in the dorsal horns of individuals with chronic SCI (P < 0.001). Furthermore, one of the SCI individuals in this study displaying significant CGRP sprouting had well documented episodes of AD. Conclusions: Our observations suggest that SCI in humans results in significant sprouting of CGRP fibers. This aberrant sprouting of sensory fibers could contribute to the abnormal cardiovascular control and pain commonly observed following chronic human SCI.