A comparative histochemical study of intrinsic laryngeal muscles of ungulates and carnivores.

This study compares the muscle fibers in the larynx (voice box) of various herbivore and carnivore animals, including horses, donkeys, sheep, cattle, pigs, dogs, and cats. The research reveals differences in muscle fiber types and their proportions, which may indicate variations in the animals’ vocalization capabilities.

Study Technique and Main Findings

• The researchers used histochemical (tissue chemistry) exams to study the muscles’ fibers. They primarily looked for myosin ATPase (an enzyme helpful in muscle contraction), SDH (an enzyme involved in cell respiration), and M-alphaGPDH (another enzyme related to carbohydrates and fat metabolism).
• They discovered two main types of muscle fibers, referred to as betaR and alphaR, in all laryngeal muscles of the surveyed animals. These fiber types are associated with slow and fast-contracting, fatigue-resistant activity in muscle. They did not find the alphaW fiber type, which is usually found in fast contracting but not fatigue-resistant muscle.
• The dog and cat species demonstrated unique subgroupings of their alphaR fibers. These groups were distinguished by their myosin ATPase, oxidative, and glycolytic (breakdown of glucose) activities.
• Ox and pig exhibited atypical behavior in their muscle fibers, having as high myosin ATPase activity as the fast-contracting fibers but exhibiting acid resistance similar to slow-twitch fibers.

Species-Specific Observed Variations

• Certain laryngeal muscles, such as the CAD, more uniformly composed of slow-twitch fibers, especially for the studied species.
• The TA muscle, present in cats, sheep, and ox, showed a high percentage of fast-twitch fibers in its rostral portion with a gradual decrease towards the caudal portion. This indicated the possible separation of the TA muscle into two parts i.e., rostral (pars ventricularis) and caudal (pars vocalis), relating to the VE and VO muscles seen in dogs, horses, and donkeys.
• In VO muscle, slow-twitch fibers were more numerous than in the VE muscle. The two portions of the TA were not detected by histochemical methods in pigs. However, in pigs, the TA muscle exhibited the highest percentage of fast-twitch fibers.

Significance and Interpretation

• By examining and comparing the histology and chemistry of animal laryngeal muscle fibers, the study gives insights into the muscle composition and consequently possible vocalization characteristics of different species.
• The identified and elaborated on qualitative and quantitative data – alongside existing literature – may help bridge the gap between animals’ morphological structure and their vocal functionality. This can subsequently contribute to a more comprehensive understanding of the bio-mechanics involved in animal vocalization.