Topographical Distribution and Morphology of Calcitonin Gene-Related Peptide (CGRP) Nociceptive Afferent Axons in the Flat-Mounts of the Whole Stomach in Male and Female Mice: Tracing, Digitization, and 3D Scaffold
Authors: Ma Jichao , Nguyen Duyen , Madas Jazune , Kwiat Andrew , Mistareehi Anas , Bendowski Kohlton , Bizanti Ariege , Zhang Yuanyuan , Heal Maci , Lin Mabelle , Hunter Peter , Chen Jin , Cheng Zixi 
Published: May 2023

Millions of Americans suffer from chronic pain in the gastrointestinal (GI) tract. However, nociceptive afferent axon innervation of the GI tract has not been thoroughly investigated. In this study, we topographically mapped the CGRP (nociceptive marker) afferent axons in the flat mounts of the whole stomach muscular layers of male and female mice (C57BL/6J, 3-5 months, n=6/group). Then, we used a confocal microscope and a Zeiss M2 Imager to scan the whole stomachs. Over 300 maximum projection images from the confocal/Zeiss microscopes were assembled to create a complete montage of each stomach. Furthermore, a Neurolucida 3D Digitization and Tracing System was used to trace CGRP-IR axons and terminals in the flat mounts. We found that 1) CGRP-IR axon bundles entered the stomach along blood vessels near the esophagus and along the lesser curvature. 2) CGRP-IR axons formed extensive terminal networks in both ventral and dorsal stomachs. 3) CGRP-IR axons densely innervated the blood vessels (arteries and veins). 4) In longitudinal and circular muscles, CGRP-IR varicose axons ran in parallel with the direction of the muscles. 5) CGRP-IR axons formed a complex network between the longitudinal and circular muscle layers. 6) In the myenteric ganglia, CGRP-IR axons formed varicose terminal contacts with myenteric neurons. 7) CGRP-IR myenteric neurons were not found, indicating that these axons had external origins. 8) The CGRP-IR axon innervation was much denser in the antrum and cardia regions than in the fundus and corpus. 9) CGRP-IR axons had a similar innervation pattern in male and female mice. 10) DiI retrograde tracer injection into the stomach wall revealed that the major extrinsic source of CGRP-IR afferent axons was from the T7-T11 dorsal root ganglia. 11) Using the novel Neurolucida 360 nerve tracking software and ABI Mapping Tool provided by MBF Bioscience and the SPARC Map-Core, the distribution of CGRP-IR axons in the flat-mounts was traced, digitized, and integrated into a stomach scaffold for a 3D map of nociceptive afferent axons (male and female). For the first time, our data provide a topographical map of the CGRP-IR innervation of the whole stomach at single cell/axon resolution. In addition, we have for the first time delivered a 3D stomach scaffold for gastric nociceptive afferent innervation. This work provides an anatomical foundation for functional studies of CGRP-IR axons in various regions of the This study was supported by NIH HEAL/SPARC U01 NS113867-01 (ZJC), NIH R15HL137143-01A1 (ZJC), NIH SPARC OT3OD025349-01 (PH). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.