Localization of substance P (SP)-immunoreactivity in the myenteric plexus of the rat esophagus

Substance P release from rat dura mater is inversely correlated with CGRP release- experiments using glycerol trinitrate and anti-CGRP antibodies

BACKGROUND

The neuropeptides calcitonin gene-related peptide (CGRP) and substance P are important mediators of neurogenic inflammation when they are released from activated primary nociceptive afferents. It is long evident that neuropeptides play an important role in migraine pathophysiology, but the significance of neurogenic inflammation is still debated.

METHODS

In an approved hemisected rodent head preparation, we measured CGRP release from the cranial dura mater in parallel with substance P release using animals pre-treated with anti-CGRP antibodies or control solutions.

RESULTS

Apart from the known decrease in CGRP release following antibody treatment, we found a significant inverse correlation of basal and stimulated CGRP versus substance P release across all experiments. The results are discussed in connection with our previously published data.

CONCLUSIONS

An increase in CGRP release seems to inhibit substance P release in meningeal structures possibly decreasing substance P-dependent plasma extravasation, which argues against a significant role of neurogenic inflammation in migraine.

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

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.