Skeletal muscle is composed of a heterogeneous mixture of several fibre types, each with specific physiological properties. In equine muscle, identification of these individual fibres (fibre typing) is important for both exercise physiology and pathological studies. Traditionally, fibre typing has been achieved by adenosine triphosphatase (ATPase) histochemistry or by immunoperoxidase labelling with antibodies directed at myosin heavy chain isoforms. ATPase histochemistry can be temperamental and lacks specificity, and both techniques require staining of serial cryosections to reveal the entire fibre type compliment of a single sample, which is time consuming and prone to inaccuracy. Here we describe an immunofluorescence labelling technique that enables rapid, accurate and specific identification of the 3 mature equine muscle fibre types in a single cryosection.
Summary
A 5‐week‐old American Miniature filly was referred due to intermittent neurological signs of 4 weeks' duration. Clinicopathological findings showed increased ammonia and bile acids in venous blood samples. Abdominal ultrasonography detailed a portosystemic shunt (PSS). The foal underwent laparotomy and operative mesenteric portovenography, which further defined the PSS as extrahepatic portocaval in configuration. The PSS was occluded and intraoperative portovenography confirmed successful shunt occlusion. The foal made a good recovery from surgery and had a successful showing career until she succumbed to colic just over 3 years after surgery.
The laryngeal tie-forward (LTF) procedure has been shown to move the larynx rostrally and dorsally whilst repositioning the basihyoid bone caudally and dorsally. Other studies have shown that the position of the hyoid bones influences the size of the nasopharynx. The effect of the LTF procedure on the size of the nasopharynx is unknown. It was hypothesised that the LTF procedure would result in a decrease in dorsoventral nasopharyngeal diameter. Twenty-five thoroughbred horses which underwent LTF with or without soft palate cautery (LTF±SPC) for treatment of dorsal displacement of the soft palate were included in this study. Preoperative and postoperative lateral radiographs were used to determine changes in laryngohyoid position and nasopharyngeal diameter. The LTF±SPC procedure resulted in a significant reduction (14-17 per cent) in dorsoventral nasopharyngeal diameter (P<0.001). The LTF procedure decreases nasopharyngeal diameter. The impact on upper respiratory tract function during exercise remains unclear.
Reasons for performing study
Recurrent laryngeal neuropathy (RLN) is a common equine distal axonopathy associated with neurogenic atrophy of intrinsic laryngeal muscles (particularly the left) causing laryngeal paresis and poor performance. An objective, reliable method of assessing changes in structure that correlates with laryngeal muscle function in vivo is necessary to determine response to novel treatments, including functional electrical stimulation. This study aimed to determine whether laryngeal muscle and nerve morphology (determined by CT and histopathology) correlated with laryngeal function.
Study design
Prospective cohort study.
Methods
Resting (grades 1–4) and exercising (grades A–C) laryngeal function was graded in adult Thoroughbred horses. Standing CT of the larynx was performed to compare volume, cross‐sectional area (XSA) and tissue density between left and right cricoarytenoideus dorsalis (CAD) muscles in 22 horses. CAD muscles and recurrent laryngeal nerves were collected in a subgroup of 10 horses and analysed for fibrosis, fat infiltration and nerve fibre density (axons/μm2).
Results
Horses with grade C RLN on exercising endoscopy had significantly (P<0.005) smaller left CAD muscles and reduced nerve fibre density than horses with grades A or B. Horses with grade 4 RLN on resting endoscopy had significantly (P<0.005) smaller left CAD muscles than horses with grades 1 or 2. Left CAD muscles had significantly more collagen than the right in horses with grade C RLN. CT measurements of the CAD muscles were significantly associated with % collagen/fat and nerve fibre density (P<0.05).
Conclusions
Laryngeal CT results correlate with laryngeal function at rest and exercise in the horse and provide a noninvasive method of monitoring changes in CAD morphology in response to novel treatments. CAD CT appearance is dependent on % collagen and fat in the muscle and is associated with nerve fibre density.
Ethical animal research: Horses destined for euthanasia were recruited for this study with approval of the Institutional Ethical Committee and under UK Home Office Licence. Sources of funding: Med‐El Elektro‐medizinische Geräte GmbH, Innsbruck, Austria. Competing interests: None.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.