Extrinsic afferents supplying the ovine duodenum and ileum

Area of Science:

• Neuroscience
• Gastroenterology
• Immunohistochemistry

Background:

• Primary sensory neurons innervate the gastrointestinal tract, playing a role in visceral sensation.
• Understanding the distribution and neurochemical properties of these neurons is crucial for visceral pain research.

Purpose of the Study:

• To determine the distribution of primary sensory neurons projecting to the sheep duodenum and ileum.
• To characterize the neurochemical profile of these neurons, focusing on nitric oxide synthase (NOS) and associated markers.

Main Methods:

• Retrograde tracers Diamidino Yellow (DY) and Fast Blue (FB) were injected into the sheep duodenum and ileum.
• Immunofluorescence staining was performed on spinal ganglia (SG) and distal vagal ganglia (DVG) to detect NOS-IR, substance P (SP), calcitonin gene-related peptide (CGRP), neurofilament 200kDa (NF), and isolectin B(4) (IB4).

Main Results:

• DY-labeled cells were found in both DVG and SG (T9-L3); FB-labeled cells were predominantly in SG.
• The majority of SG duodenal projections were NOS-negative, while most SG ileal afferent neurons were NOS-positive.
• NOS-IR neurons in SG frequently co-expressed IB4, CGRP, and SP, but rarely NF.

Conclusions:

• Sensory innervation of the sheep ileum and duodenum differs in distribution and neurochemical phenotype.
• Ileal afferent neurons projecting to the SG are largely NOS-positive and express markers like IB4, CGRP, and SP, suggesting distinct roles in visceral processing.