Changes of calcitonin gene-related peptide in primary sensory neurons and their central branch after nerve root compression of the dog

OBJECTIVE: To investigate changes in axonal flow after nerve root compression by using immunohistochemical techniques to detect calcitonin gene-related peptide (CGRP), which is thought to be involved in pain sensation. DESIGN: Experimental, controlled study. SETTING: University medical school in Japan. ANIMALS: Forty adult mongrel dogs (weight, 7-15kg). INTERVENTIONS: In dogs, the lumbar nerve roots were compressed using 4 types of clips with different pressures. Changes of CGRP levels in the spinal dorsal horn, dorsal root, and dorsal root ganglia (DRG) were examined immunohistochemically after compression for 24 hours or for 1 week. MAIN OUTCOME MEASURES: CGRP-positive neurons and CGRP-positive fibers. RESULTS: After compression, axonal flow in the dorsal root was impaired, accumulation of CGRP was observed distal to the site of compression, and the number of DRG cells showing positively for CGRP decreased. Compression for 1 week resulted in a decrease in the number of CGRP-positive fibers in the spinal dorsal horn. CONCLUSIONS: These findings indicate that CGRP dynamics are modified by nerve compression.