Intrinsic innervation of the ileocaecal junction in the horse: preliminary study.

This study explores the intrinsic neural structure of the horse’s ileocaecal junction (ICJ), revealing its morphology, demographics, phenotypes, and projections. The findings can better inform surgical approaches in bowel diseases and contribute to the development of pharmaceutical treatments for motility disorders in the ICJ.

Methods

• The study involves two young horses who were anaesthetized and underwent midline laparotomy. A fluorescent tracer called Fast Blue (FB) was used to map the neurons controlling the ileocaecal junction (ICJ) – the connection between the small and large intestine.
• Following 30 days of post-surgery recovery time, the horses were euthanised and the ileum (an area of the small intestine) was removed along with a small portion of the caecum.
• The post-mortem investigation focused on identifying several key substances that are produced by neurons (ChAT, neuronal nitric oxide synthase, substance P and neurofilament NF200kDa), and the density, distribution, and projections of these neurons.

Results

• The Fast Blue-labelled neurons associated with the ICJ are found in two major plexuses of the intestines; the myenteric plexus and the submucosal plexus. They were distributed up to 48cm and 28cm respectively from the site of Fast Blue injection.
• Most of the neurons in these areas were observed to produce nitric oxide, acetylcholine, neurofilament, and substance P. The descending neurons in the submucosal plexus (SMP) also produced a further substance: calcitonin gene-related peptide.

Conclusion

• The study concludes that the neurons found in the ileum have a significant role in modulating the ICJ. As such, while treating bowel diseases requiring the resection of certain parts of the intestine, it is recommended to conserve as much of the ileum as possible.
• By identifying the phenotypical characteristics of the enteric nervous system (ENS) neurons in the ileum, the study can help guide the development of targeted pharmaceutical treatments for motility disorders in the ICJ.