Peripheral Patterns of Calcitonin-Gene-Related Peptide General Somatic Sensory Innervation: Cutaneous and Deep Terminations

The study examined the distribution of calcitonin-gene-related peptide (CGRP) immunoreactivity in the peripheral tissues of rats, focusing on its potential nociceptive roles. CGRP-IR was found in a large proportion of small- and medium-diameter sensory ganglion cells, which give rise to thinly myelinated and unmyelinated axons throughout the body. In the skin, CGRP-IR axons were associated with dermal blood vessels, sweat glands, and nerve endings, with a similar pattern observed in both glabrous and hairy skin. In deep tissues, CGRP-IR was primarily related to vasculature and motor end plates of striated muscle, with a notable presence in bone and joint capsules. The study suggested that the role of CGRP-IR axons in tissue maintenance and renewal might be more significant than their nociceptive function.