Interstitial cells of cajal of the equine gastrointestinal tract: development and disease

Gastrointestinal motility disorders constitute a substantial problem in the horse both in terms of welfare and economic cost. It is often difficult to identify the underlying cause as many horses recover spontaneously or with empirical medical treatment. Recently, the gastrointestinal pacemaker cells, the interstitial cells of Cajal (ICC), were identified in the horse. These cells initiate and coordinate gastrointestinal motility patterns through the generation of slow waves. This current study investigated the ICC in the equine intestine both in health and disease using immunohistochemical, electrophysiological and molecular biological techniques. The aim of these studies was to further our knowledge on the role of ICC in equine intestinal motility disorders.Using immunohistochemistry targeting a receptor tyrosine kinase, c-Kit, of the ICC, the ontogeny of these cells in the horse was described. This demonstrated a proximal to distal, as well as a transmural developmental gradient in the large intestine with evidence of ongoing postnatal development. Additionally, the density of ICC in healthy, adult horses was compared to that in horses with obstructive intestinal disease requiring surgical correction. This demonstrated a significant reduction in ICC density in horses with obstructive disorders of the large intestine compared to the control group. In addition, ICC density and distribution was investigated in recovered chronic equine grass sickness horses as well as in normal and diseased donkeys.The c-kit gene, encoding the c-Kit receptor of the ICC, was identified in intestinal tissue samples. The transcription levels of this gene were determined and comparisons made - 1 - between healthy and diseased horses using quantitative real-time PCR analysis. A parallel immunohistochemical assessment was also performed. These studies demonstrated no significant changes in gene transcription levels, although a reduction in ICC density (using c-Kit immunohistochemistry) in horses with an obstructive disorder of the large colon was evident, suggesting that future investigations of c-kit posttranscriptional control as well as c-Kit protein pathology are warranted.Investigation of the in vitro electrical activity of the equine large colon was carried out using intracellular microelectrode recording techniques in order to characterise slow waves and other electrical activities in this anatomical region from normal and diseased horses.It is hoped that this study will help improve our knowledge ofthe involvement of ICC in equine intestinal motility in health and disease. Furthermore, it may facilitate future studies investigating the involvement and function of the ICC in the equine gastrointestinal tract

High-Resolution Genotyping of Expressed Equine MHC Reveals a Highly Complex MHC Structure

The Major Histocompatibility Complex (MHC) genes play a key role in a number of biological processes, most notably in immunological responses. The MHCI and MHCII genes incorporate a complex set of highly polymorphic and polygenic series of genes, which, due to the technical limitations of previously available technologies, have only been partially characterized in non-model but economically important species such as the horse. The advent of high-throughput sequencing platforms has provided new opportunities to develop methods to generate high-resolution sequencing data on a large scale and apply them to the analysis of complex gene sets such as the MHC. In this study, we developed and applied a MiSeq-based approach for the combined analysis of the expressed MHCI and MHCII repertoires in cohorts of Thoroughbred, Icelandic, and Norwegian Fjord Horses. The approach enabled us to generate comprehensive MHCI/II data for all of the individuals ( n = 168) included in the study, identifying 152 and 117 novel MHCI and MHCII sequences, respectively. There was limited overlap in MHCI and MHCII haplotypes between the Thoroughbred and the Icelandic/Norwegian Fjord horses, showcasing the variation in MHC repertoire between genetically divergent breeds, and it can be inferred that there is much more MHC diversity in the global horse population. This study provided novel insights into the structure of the expressed equine MHC repertoire and highlighted unique features of the MHC in horses

Myenteric networks of interstitial cells of Cajal are reduced in horses with inflammatory bowel disease

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Myenteric networks of interstitial cells of Cajal are reduced in horses with inflammatory bowel disease

Background Inflammatory bowel disease (IBD) is a well‐recognised but poorly understood disease complex in the horse. Clinical signs may vary but often include weight loss, diarrhoea and colic. The effect this disease process may have on the gastrointestinal pacemaker cells (the interstitial cells of Cajal), enteric neurons and glial cells has not been previously evaluated in the horse. Objectives To compare the density of the interstitial cells of Cajal (ICC), enteric neurons and glial cells in horses with IBD to those of normal horses using immunohistochemical markers. Study design Retrospective, quantitative immunohistochemical study. Methods Ileal samples were collected during post‐mortem examinations from 14 horses with a clinical and histopathological diagnosis of IBD and from eight normal controls. All horses were Standardbreds 1–15 years of age. Six of the IBD cases had eosinophilic gastroenteritis (EG) while the remaining eight had granulomatous enteritis (GE). Tissue sections were labelled with anti‐CD117 (c‐Kit), anti‐TMEM16 (TMEM16), anti‐protein gene product (PGP9.5) and anti‐glial fibrillary acidic protein (GFAP) using standard immunohistochemical labelling techniques. Image analysis was performed to quantify the presence of ICC (CD117, TMEM16) as well as neuronal (PGP9.5) and enteroglial (GFAP) networks. Results Interstitial cells of Cajal networks were significantly reduced in the myenteric plexus (MP) region in IBD horses compared with the controls for both markers (P0.05). Main limitations The number of horses included in the study. Conclusions Disruption to ICC networks may contribute to the clinical signs of colic in some horses with IBD. Further studies are needed to establish the pathophysiological mechanisms involved and the functional effects of the reduced ICC networks

A bitless bridle does not limit or prevent Dynamic Laryngeal Collapse

Background: Bits have often been incriminated as a cause of upper respiratory tract obstruction in horses; however, no scientific studies are available to confirm or refute these allegations. Clinical signs of dynamic laryngeal collapse associated with poll flexion (DLC) are induced when susceptible horses are ridden or driven into the bit. Objective: To determine whether use of Dr Cook's™ Bitless Bridle, instead of a conventional snaffle bit bridle, would reduce the severity of DLC in affected horses measured objectively using inspiratory tracheal pressures. Study design: Intervention study using each horse as its own control in a block randomised order. Methods: Nine Norwegian Swedish Coldblooded trotters previously diagnosed with DLC were exercised on two consecutive days using a standardised high-speed treadmill protocol with either a conventional bridle with a snaffle bit, or Dr Cook's™ Bitless Bridle. Head and neck position, rein tension, inspiratory tracheal pressure measurements, and laryngeal videoendoscopy recordings were obtained. A heart rate greater than 200 bpm, and similar degrees of poll flexion/head height, had to be achieved in both bridles for the individual horse's data to be included for comparison. Results: Seven horses’ data met the inclusion criteria. The change in mean inspiratory tracheal pressure between free and flexion phases in the bitless bridle (−15.2 ± 12.3 cmH2O) was significantly greater (P < .001) than in the snaffle bit bridle (−9.8 ± 7.9 cmH2O). Mean inspiratory pressure during the free phase was significantly (P < .001) more negative with the snaffle bit bridle (−32.3 ± 6.3 cmH2O), vs the bitless bridle (−28.5 ± 6.9 cmH2O). Mean pressures in flexion phase, snaffle bridle (−42.1 ± 10.8 cmH2O), vs bitless bridle (−43.7 ± 15.6 cmH2O) where not significantly different between bridles (P = .2). Main limitation: Small sample size due to difficulty recruiting suitable clinical cases. Conclusions: This study could not provide any clear evidence that the effect of a snaffle bit in a horse's mouth influences the development or severity of DLC. Instead, head and neck angles induced by rein tension seem to be he key event in provoking DLC in suspectible horses.publishedVersio

A bitless bridle does not limit or prevent Dynamic Laryngeal Collapse

Background: Bits have often been incriminated as a cause of upper respiratory tract obstruction in horses; however, no scientific studies are available to confirm or refute these allegations. Clinical signs of dynamic laryngeal collapse associated with poll flexion (DLC) are induced when susceptible horses are ridden or driven into the bit. Objective: To determine whether use of Dr Cook's™ Bitless Bridle, instead of a conventional snaffle bit bridle, would reduce the severity of DLC in affected horses measured objectively using inspiratory tracheal pressures. Study design: Intervention study using each horse as its own control in a block randomised order. Methods: Nine Norwegian Swedish Coldblooded trotters previously diagnosed with DLC were exercised on two consecutive days using a standardised high-speed treadmill protocol with either a conventional bridle with a snaffle bit, or Dr Cook's™ Bitless Bridle. Head and neck position, rein tension, inspiratory tracheal pressure measurements, and laryngeal videoendoscopy recordings were obtained. A heart rate greater than 200 bpm, and similar degrees of poll flexion/head height, had to be achieved in both bridles for the individual horse's data to be included for comparison. Results: Seven horses’ data met the inclusion criteria. The change in mean inspiratory tracheal pressure between free and flexion phases in the bitless bridle (−15.2 ± 12.3 cmH2O) was significantly greater (P < .001) than in the snaffle bit bridle (−9.8 ± 7.9 cmH2O). Mean inspiratory pressure during the free phase was significantly (P < .001) more negative with the snaffle bit bridle (−32.3 ± 6.3 cmH2O), vs the bitless bridle (−28.5 ± 6.9 cmH2O). Mean pressures in flexion phase, snaffle bridle (−42.1 ± 10.8 cmH2O), vs bitless bridle (−43.7 ± 15.6 cmH2O) where not significantly different between bridles (P = .2). Main limitation: Small sample size due to difficulty recruiting suitable clinical cases. Conclusions: This study could not provide any clear evidence that the effect of a snaffle bit in a horse's mouth influences the development or severity of DLC. Instead, head and neck angles induced by rein tension seem to be he key event in provoking DLC in suspectible horses

Pre- and post-race serum cardiac troponin T concentrations in Standardbred racehorses

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Exercise induced laryngeal obstructions in humans and equines. A comparative review

Dynamic obstructions of the larynx are a set of disorders that occur during exercise in equines and humans. There are a number of similarities in presentation, diagnosis, pathophysiology and treatment. Both equines and humans present with exercise intolerance secondary to dyspnea. During laryngoscopy at rest, the larynx appears to function normally. Abnormalities are only revealed during laryngoscopy at exercise, seemingly triggered by increased ventilatory demands, and quickly resolve after cessation of exercise. Lower airway disease (asthma being the most prevalent condition), cardiac disease and lack of fitness are the major differentials in both species. Laryngoscopic examination during exercise should be performed from rest to peak exertion to allow for a comprehensive diagnosis, including where the airway collapse begins, and thereafter how it progresses. Dynamic disorders with most visual similarity between humans and equines are: aryepiglottic fold collapse (both species); equine dynamic laryngeal collapse (DLC) relative to some forms of human combined supraglottic/glottic collapse; and epiglottic retroversion (both species). Quantitative grading techniques, such as airway pressure measurement, that have proven effective in veterinary research are currently being piloted in human studies. Conditions that appear visually similar are treated in comparable ways. The similarities of anatomy and certain types of dynamic collapse would suggest that the equine larynx provides a good model for human upper respiratory tract obstruction during exercise. Thus, close collaboration between veterinarians and medical personal may lead to further advancements in understanding pathophysiologic processes, and enhance the development of improved diagnostic tests and treatments that will benefit both species