Presence of in vitro electrical activity in the ileum of horses with enteric nervous system pathology: equine dysautonomia (grass sickness).

The research investigates the impact of equine dysautonomia (grass sickness) on the intestine’s electrical properties in horses. The study highlights that while the neural elements face damage, the primary pacemaker function remains operational, albeit at a lesser efficiency and increased duration.

Research Objectives and Methodology

• The research aimed to understand and compare the in vitro (test tube or dish) electrical properties of the ileum (part of the small intestine) in horses suffering from grass sickness with horses having no gastrointestinal disease. The focus was on understanding how this potentially fatal disease impacts the electrical control of the intestines.
• Interstitial Cells of Cajal (ICC), considered the pacemakers of the gastrointestinal tract, were central to this study because any dysfunction in these cells can lead to intestinal disorders.
• The study was conducted on samples from 6 horses diagnosed with grass sickness and 8 other horses free of gastrointestinal disease. These horses were euthanised due to humanitarian reasons.
• Techniques used in the study included intracellular microelectrode recordings of the smooth muscle cells from equine’s ileum as well as histological assays using haematoxylin and eosin dye. Additionally, immunohistochemistry was carried out with c-Kit – a protein coding gene.

Findings

• Membrane potential oscillations (changes in electrical potential across the cell) were found in the ileal preparations from four of the six grass sickness horses and all normal horses. A pattern of waxing and waning (increasing and decreasing) of the said oscillation activity was noticed in some cells.
• Significant differences between sickness affected and normal horses were noticed, with the oscillations in the former having reduced frequency (P = 0.0001) and longer duration (P = 0.0002).
• Immunohistochemistry showed a reduction in ICC in the horses with grass sickness, providing insights into disturbed gastrointestinal functioning.
• At the same time, signs of depletion and pathology of the enteric neurons were confirmed in the tissues of grass sickness suffering horses via histological assessment.

Implications

• From the above findings, it can be concluded that while with the digestive disease, grass sickness, neural components in the horse’s intestine are severely damaged, the ICC-mediated pacemaker function, though compromised, remains functional. This is evident from the existing membrane potential oscillation activity observed in majorly all ileal preparations from grass sickness-affected horses.
• This research provides substantial insights into understanding how grass sickness impacts the intestinal conditions in horses, which can lead to future studies targeted towards developing effective treatment methods to combat this harmful disease.