Intrinsic innervation of the ileocaecal junction in the horse: preliminary study.
Authors: Chiocchetti R, Bombardi C, Mongardi Fantaguzzi C, Russo D, Venturelli E, Montoneri C, Spadari A, Romagnoli N, Grandis A
Journal: Equine veterinary journal
Summary
# Editorial Summary: Intrinsic Innervation of the Ileocaecal Junction in the Horse The enteric nervous system controlling the ileocaecal junction (ICJ)—a critical anatomical bottleneck in equine hindgut function—has been largely uncharacterised until now, despite the clinical significance of ICJ dysfunction in colic and post-operative complications. Using retrograde neuronal tracing with Fast Blue injected directly into the ICJ wall, followed by immunohistochemical analysis 30 days post-injection, researchers identified and phenotyped neurons innervating this junction from both the myenteric and submucosal nerve plexuses of the ileum, mapping their projections up to 48 cm proximally. The results revealed that descending ileal neurons controlling the ICJ are predominantly nitrergic (54–68%), cholinergic (60–82%), and neurofilament-positive (54–78%), with approximately 20% expressing substance P and unique calcitonin gene-related peptide expression in submucosal neurons; notably, a substantial population (25–61%) co-expressed both nitric oxide synthase and acetylcholine transferase, suggesting complex functional modulation. These findings indicate that ileal neurons exert long-range control over ICJ motility and tone, which carries important surgical implications: preserving maximum ileal length during jejunocaecal anastomosis or ileal resection procedures may be crucial for maintaining postoperative ICJ function and reducing colic risk, whilst the neurochemical phenotypes identified provide logical targets for developing pharmacological treatments for ICJ dysfunction and associated motility disorders.
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Practical Takeaways
- •When surgical resection of terminal jejunum and proximal ileum is necessary, preserve as much ileum as possible to maintain neuronal control of ileocaecal function
- •Understanding ileal enteric nervous system phenotypes may guide future pharmaceutical treatments for ileocaecal motility disorders in horses
- •Avoid excessive ileal resection in colic cases where possible, as long-projecting neural pathways critical to sphincter function extend considerable distances proximally
Key Findings
- •Ileal neurons projecting to the ileocaecal junction extend up to 48 cm in the myenteric plexus and 28 cm in the submucosal plexus from the injection site
- •Descending myenteric and submucosal neurons were predominantly nitrergic (54% and 68%) and cholinergic (60% and 82%) with significant NF200 immunoreactivity
- •25% of myenteric and 61% of submucosal neurons coexpressed both nNOS and ChAT, suggesting complex neural modulation
- •Long-projecting ileal neurons innervating the ileocaecal junction play a critical role in sphincter modulation and control