Localization of sensory nerve terminals containing calcitonin gene-related peptide (CGRP) on striated muscle fibers in the rat esophagus: Evidence for triple innervation via motor endplates

Hirofumi Kuramoto; Mana Yabe; Ryo Morishita; Ryoichi Yoshimura; Hiroshi Sakamoto

doi:10.1016/j.autneu.2024.103177

Localization of sensory nerve terminals containing calcitonin gene-related peptide (CGRP) on striated muscle fibers in the rat esophagus: Evidence for triple innervation via motor endplates

Auton Neurosci. 2024 Apr 12:253:103177. doi: 10.1016/j.autneu.2024.103177. Online ahead of print.

Authors

Hirofumi Kuramoto¹, Mana Yabe², Ryo Morishita², Ryoichi Yoshimura², Hiroshi Sakamoto³

Affiliations

¹ Department of Applied Biology, Kyoto Institute of Technology, Kyoto 606-8585, Japan. Electronic address: kuramoto@kit.jp.
² Department of Applied Biology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
³ Department of Physical Therapy, Health Science University, Yamanashi 401-0380, Japan.

PMID: 38636284
DOI: 10.1016/j.autneu.2024.103177

Abstract

Background: Many esophageal striated muscles of mammals are dually innervated by the vagal and enteric nerves. Recently, substance P (SP)-sensory nerve terminals with calcitonin gene-related peptide (CGRP) were found on a few striated muscle fibers in the rat esophagus, implying that these muscle fibers are triply innervated. In this study, we examined the localization and origin of CGRP-nerve endings in striated muscles to consider their possible roles in the esophagus regarding triple innervation.

Methods: Wholemounts of the rat esophagus were immunolabeled to detect CGRP-nerve endings in striated muscles. Also, retrograde tracing was performed by injecting Fast Blue (FB) into the esophagus, and cryostat sections of the medulla oblongata, nodose ganglion (NG), and the tenth thoracic (T10) dorsal root ganglion (DRG) were immunostained to identify the origin of the CGRP-nerve endings.

Results: CGRP-fine, varicose nerve endings were localized in motor endplates on a few esophageal striated muscle fibers (4 %), most of which received nitric oxide (NO) synthase nerve terminals, and most of the CGRP nerve endings were SP- and transient receptor potential vanilloid member 1 (TRPV1)-positive. Retrograde tracing showed many FB-labeled CGRP-neurons positive for SP and TRPV1 in the NG and T10 DGR.

Conclusions: This study suggests that the CGRP-varicose nerve endings containing SP and TRPV1 in motor endplates are sensory, and a few esophageal striated muscle fibers are triply innervated. The nerve endings may detect acetylcholine-derived acetic acid from the vagal motor nerve endings and NO from esophageal intrinsic nerve terminals in the motor endplates to regulate esophageal motility.

Keywords: CGRP; Esophagus; Immunohistochemistry; Sensory nerves; Striated muscles; Triple innervation.