Netrin-1 as A neural guidance protein in development and reinnervation of the larynx

Neural guidance proteins participate in motor neuron migration, axonal projection, and muscle fiber innervation during development. One of the guidance proteins that participates in axonal pathfinding is Netrin-1. Despite the well-known role of Netrin-1 in embryogenesis of central nervous tissue, it is still unclear how the expression of this guidance protein contributes to primary innervation of the periphery, as well as reinnervation. This is especially true in the larynx where Netrin-1 is upregulated within the intrinsic laryngeal muscles after nerve injury and where blocking of Netrin-1 alters the pattern of reinnervation of the intrinsic laryngeal muscles. Despite this consistent finding, it is unknown how Netrin-1 expression contributes to guidance of the axons towards the larynx. Improved knowledge of Netrin-1's role in nerve regeneration and reinnervation post-injury in comparison to its role in primary innervation during embryological development, may provide insights in the search for therapeutics to treat nerve injury. This paper reviews the known functions of Netrin-1 during the formation of the central nervous system and during cranial nerve primary innervation. It also describes the role of Netrin-1 in the formation of the larynx and during recurrent laryngeal reinnervation following nerve injury in the adult.

Immediate Ansa cervicalis-to-recurrent laryngeal nerve low-tension anastomosis: A new technique for phonation recovery and bilateral anastomoses to avoid tracheotomy

OBJECTIVE

This case series study investigated the outcomes of an innovative approach, ansa cervicalis nerve (ACN)-to-recurrent laryngeal nerve (RLN) low-tension anastomosis.

METHODS

Patients who received laryngeal nerve anastomosis between May 2015 and September 2021 at the facility were enrolled. The inclusion criteria were patients with RLN dissection and anastomosis immediately during thyroid surgery. Exclusion criteria were cases with anastomosis other than cervical loop-RLN anastomosis or pronunciation recovery time > 6 months. Patients admitted before January 2020 were assigned to group A which underwent the conventional tension-free anastomosis, and patients admitted after January 2020 were group B and underwent the innovative low-tension anastomosis (Dong's method).

RESULTS

A total of 13 patients were included, 11 patients received unilateral surgery, and 2 underwent bilateral surgery. For patients who underwent unilateral anastomosis, group B had a significantly higher percentage of normal pronunciation via GRBAS scale (83.3 % vs. 0 %, p = 0.015) and voice handicap index (66.7 % vs. 0 %, p = 0.002), and shorter recovery time in pronunciation (median: 1-day vs. 4 months, p = 0.001) than those in group A after surgery.

CONCLUSIONS

ACNs-to-RLN low-tension anastomosis with a laryngeal segment ≤1 cm (Dong's method) significantly improves postoperative pronunciation and recovery time. The results provide clinicians with a new strategy for ACN -to-RLN anastomosis during thyroid surgery.

Expression of trophic factors receptors during reinnervation after recurrent laryngeal nerve injury

OBJECTIVE

An injury of the recurrent laryngeal nerve (RLN) triggers axonal regeneration but results in a poor functional recovery. Netrin-1 and glial cell-derived neurotrophic factor (GDNF) expression are up-regulated in laryngeal muscles during RLN regeneration, but the role of their receptors produced in the nucleus ambiguus is unknown. The aim of this work was to determine the timing of the production of Netrin-1 and GDNF receptors during RLN regeneration and correlate this with the previously identified timing of up-regulation of their trophic factors in the laryngeal muscles.

STUDY DESIGN

Laboratory experiment with rat model.

METHODS

The right RLN was transected and dextran amine tracer applied. At 7, 14, and 21 days postinjury (DPI), brainstems were removed and harvested. Immunostaining was performed for Netrin-1 (deleted in colorectal carcinoma [DCC], UNC5A) and GDNF receptors (rearranged during transfection [Ret], glycosylphosphatidylinositol-linked cell surface receptors [GFRα1, GFRα2, GFRα3]). The timing and type of receptor production relative to injury as well as their position in the nucleus ambiguus was analyzed.

RESULTS

Netrin-1 UNC5A receptors were minimal in the nucleus ambiguus during RLN regeneration. DCC, the receptor that plays an attract role, was immunopositive from 7 to 21 DPI. All GDNF receptors, except GFRα2, were clearly positive from 7 to 14 DPI. No differences of production were observed according to the position of the motor neurons in the nucleus ambiguus.

CONCLUSION

An injury of the RLN leads to a higher production of Netrin-1 DCC and GDNF receptors in the nucleus ambiguus. The timing of receptor production is similar to up-regulation of their trophic factors in the laryngeal muscles.

LEVEL OF EVIDENCE

NA. Laryngoscope, 129:2537-2542, 2019.

Pre-Injection of Small Interfering RNA (siRNA) Promotes c-Jun Gene Silencing and Decreases the Survival Rate of Axotomy-Injured Spinal Motoneurons in Adult Mice

Brachial plexus injury is a common clinical peripheral nerve trauma. A series of genes in motoneurons were activated in the corresponding segments of the spinal cord after brachial plexus roots axotomy. The spatial and temporal expression of these genes directly affects the speed of motoneuron axon regeneration and precise target organ reinnervation. In a previous study, we observed the overexpression of c-Jun in motoneurons of the spinal cord ventral horn after brachial plexus injury in rats. However, the relevance of c-Jun expression with respect to the fate of axotomy-induced branchial plexus injury in adult mice remains unknown. In the present study, we explored the function of c-Jun in motoneuron recovery after axotomy. We pre-injected small interfering RNA (siRNA) to knockdown c-Jun expression in mice and examined the effects of the overexpression of c-Jun in motoneurons after the axotomy of the brachial plexus in vivo. Axotomy induced c-Jun overexpression in the ventral horn motoneurons of adult mice from 3 to 14 days after injury. In addition, the pre-injection of siRNA transiently inhibited c-Jun expression and decreased the survival rate of axotomy-injured motoneurons. These findings indicate that the axotomy-induced overexpression of c-Jun plays an important role in the survival of ventral horn motoneurons in adult mice. In addition, the pre-injection of c-Jun siRNA through the brachial plexus stem effectively adjusts c-Jun gene expression at the ipsilateral side.

Muscle specific nucleus ambiguus neurons isolation and culturing

BACKGROUND

Peripheral nerve injury leads to a regenerative state. However, the reinnervation process is highly non-selective. Growing axons are often misrouted and establish aberrant synapsis to abductor or adductor muscles. Determining the complex properties of abductor and adductor motoneurons in a neuron culture, may lay the groundwork for future studies on axon guidance, leading to a clinical treatment for a selective reinnervation.

NEW METHOD

In the present study we develop a neuron culture protocol to isolate recurrent laryngeal nerve abductor and adductor motoneurons in order to study their unique properties. Comparison with existing methods the best period to perform the present protocol for postnatal rat cranial motoneurons isolation was determined. In addition, the method allows identification of specific motoneurons from other primary motoneurons and interneurons within brainstem.

CONCLUSION

The present protocol will allow investigators to perform targeted and novel studies of the mechanisms of peripheral nerve regeneration.

Neuroregeneration in the nucleus ambiguus after recurrent laryngeal nerve avulsion in rats

OBJECTIVES

The objective was to investigate neuroregeneration, the origins of newborn cells and the proliferation of neuronal and glial cells in the nucleus ambiguus (NA) after ipsilateral recurrent laryngeal nerve (RLN) avulsion.

METHODS

All of the animals received a CM-Dil injection in the left lateral ventricle. Forty-five adult rats were subjected to a left RLN avulsion injury, while 9 rats were used as controls. 5-Bromo-2-deoxyuridine (BrdU) was injected intraperitoneally. Neuron quantification and immunohistochemical analysis were performed in the brain stems at different time points after RLN injury.

RESULTS

After RLN avulsion, CM-Dil labeled neural progenitor cells (NPCs) migrated to the ipsilateral NA and differentiated into astrocytes but not into neurons. In the NA, the neuronal cells re-expressed nestin. Only a small number of neuronal and glial cells in the NA showed BrdU immunoreactivity.

CONCLUSIONS

After RLN avulsion, the NPCs in the ependymal layer of the fourth ventricle or central canal are activated, migrate to the lesion in the NA and differentiate exclusively into astrocytes. The newborn neural stem cells in the NA may arise from the mature region neurons. The presence of both cell types in the NA may play a role in repairing RLN injuries.

Development of the rat larynx: a histological study

OBJECTIVES/HYPOTHESIS

To evaluate and describe the cartilaginous and muscular development of the rat larynx.

STUDY DESIGN

Histologic evaluation.

METHODS

The larynges of Sprague Dawley rats of embryonic day (E) 13, 15, 17, 19, 21, postnatal day 0, 14, and adult of 250 gm were collected. Four larynges of each age were harvested, cut into 15-μm serial sections, stained with hematoxylin and eosin, and evaluated under light microscopy. Representative digital images were recorded and evaluated at the preglottic (supraglottic in humans), glottic, and postglottic (subglottic in humans) levels.

RESULTS

Brachial arches were observed at E13. At E17, immature structures of the larynx, including skeletal muscle, cartilage, and the lumen were identifiable. Chondrification and muscle formation were clearly seen by E19. The muscular and cartilagenous components of the larynx were well established by E21. During the span between birth and adult maturation, the size of the larynx increased from a height of 1.10 mm to 2.90 mm, and from a width of 1.80 mm to 5.40 mm, and from a length of 1.38 mm to 4.77 mm in the stained section. Although developed at E21, the laryngeal structures continued to grow by approximately 30%.

CONCLUSION

Rat laryngeal development parallels that in mice and humans. In the rat, at E17 immature structures of the larynx are identifiable, they are well developed at birth and grow by approximately 30% into adulthood. Understanding the chronology and morphology of the embryogenesis of the rat laryngeal musculature is essential and will allow for further evaluation of the embryologic innervation of these muscles.