In the human, true myocutaneous junctions of skeletal muscle fibers are limited to the face

A Novel Rat Model for Muscle Regeneration and Fibrosis Studies in Surgical Lip Repair

OBJECTIVE

Lip muscle undergoes suboptimal regeneration after surgical repair, but the mechanism underlying this observation remains obscure. This study provided a rat model to investigate lip muscle regeneration after surgical intervention.

DESIGN

This work provided a detailed description of the rat orbicularis oris muscle anatomy, and a surgically injured model was established based on the muscle anatomy.

MAIN OUTCOME MEASURES

Morphological and histological features of the rat orbicularis oris muscle were characterized. The processes of myogenesis and fibrogenesis were examined between the untreated and surgically injured groups.

RESULTS

Rat orbicularis oris muscle is encapsulated by the vermilion and oral mucosa. Although it remains a thin layer of flat muscle with tight myocutaneous and myomucosal junctions, if accessed properly, the rat orbicularis oris muscle could be isolated as a cylindrical muscle bundle with considerable size, facilitating further surgical manipulations of the muscle fibers. Muscles in steady state and after surgical intervention demonstrated distinct molecular features in the myogenesis and fibrogenesis processes, which were quantifiable in tissue section analysis.

CONCLUSION

The orbicularis oris muscle dissection procedures and injury model provided in this work clarify the rat lip muscle anatomy. The injury model offered a platform to analyze the effects of surgical interventions commonly used in lip repair on orbicularis oris muscle regeneration.

Regeneration process of myotendinous junction injury induced by collagenase injection between Achilles tendon and soleus muscle in mice

Recently, it has become clear that peri-muscular tissues play a significant role in the deterioration of muscle function. Understanding the function and regeneration of muscle, as well as its surrounding tissues, is crucial to determining the causes of muscular illnesses. However, the regeneration process of the myotendinous junction (MTJ), the most closely related peri-muscular tissue, is still unknown. Therefore, we generated a mouse model of MTJ injury by collagenase injection and searched for the process of regeneration of the MTJ and its adjacent regions. The MTJ region was damaged by collagenase injection, which greatly increased the tendon cross sectional area. Collagenase injections increased the proportion of myofibers with a central nucleus, which is a characteristic of regenerating muscle. The collagenase injection group had myofibers with central nuclei and expressing MTJ markers. Additionally, we measured the length of MTJs using serial cross sections of the soleus muscle and discovered that MTJs at 2 weeks after collagenase injection were shorter compared to the control group, with a propensity to progressively recover their length over time. The results showed that MTJs undergo morphological regeneration even when severely damaged, and that this regeneration occurs in conjunction with muscle regeneration. We anticipate that these findings will be valuable in upcoming research on motor unit regeneration.

A review of the peripheral proprioceptive apparatus in the larynx

The larynx is an organ of the upper airway that participates in breathing, glutition, voice production, and airway protection. These complex functions depend on vocal fold (VF) movement, facilitated in turn by the action of the intrinsic laryngeal muscles (ILM). The necessary precise and near-instantaneous modulation of each ILM contraction relies on proprioceptive innervation of the larynx. Dysfunctional laryngeal proprioception likely contributes to disorders such as laryngeal dystonia, dysphagia, vocal fold paresis, and paralysis. While the proprioceptive system in skeletal muscle derived from somites is well described, the proprioceptive circuitry that governs head and neck structures such as VF has not been so well characterized. For over two centuries, researchers have investigated the question of whether canonical proprioceptive organs, muscle spindles, and Golgi tendon organs, exist in the ILM, with variable findings. The present work is a state-of-the-art review of the peripheral component of laryngeal proprioception, including current knowledge of canonical and possible alternative proprioceptive circuitry elements in the larynx.

Human Frontalis Muscle Innervation and Morphology

Due to its clinical importance and due to a suggestion regarding the afferent innervation, the microscopic appearance of the frontalis muscle was investigated.

Aponeurosis linguae-Myocutaneous or myotendinous junctions of skeletal muscle fibres in the human tongue?

The morphology of the more superficial tissue of the human tongue was investigated and discussed with the clinical appearance of fissures. Three regions could be distinguished according to the presence and shape of the aponeurosis linguae: the central region showed a thick aponeurotic plate with myotendinous muscle fibre insertions. The lateral region showed still an aponeurosis linguae but of reduced thickness and without muscle insertions. The edge-wise and lower region showed no aponeurosis linguae but a fatty subcutis and myocutaneous muscle fibre insertions lacking specific molecules of myotendinous junctions. This system of partially developed exoskeleton seems to underlie but not to be involved in tongue fissures, which are more superficial within the epidermis and dermis.