Chemodenervation of the rat hemilarynx with phenol

Glottic Closing Force Versus Laryngeal Adductory Pressure in the Canine Larynx

INTRODUCTION

The strength of glottic closure with recurrent laryngeal nerve (RLN) stimulation has been indirectly measured experimentally by determining the squeezing pressure on a balloon inserted between the vocal folds, termed laryngeal adductory pressure (LAP). In this study, we sought to measure glottic closing force (GCF) directly and compare these results to LAP measures obtained with identical stimulation parameters.

METHODS

In canines, a method for measuring GCF was developed in which a suture was looped through a lateral thyrotomy hole, around the vocal process and back, then attached to a force gauge. The RLN was maximally stimulated and GCF recorded. The LAP was then measured as previously described, using the same stimuli. This process was repeated at 9 stimulation frequencies in 10-Hz intervals from 20 to 100 Hz. The GCF and LAP were compared using Pearson's correlation coefficient (PCC).

RESULTS

Both sides were measured in 16 dogs, resulting in 32 data sets. The LAP measures were obtained at all frequencies, while GCF was obtained in 246 of 288 (85.4%) attempts. The maximum GCF for each dog typically occurred at 80 to 100 Hz and averaged 0.287 ± 0.106 newtons. Plotting GCF versus LAP for each hemilaryngeal preparation, the mean PCC was 0.932 ± .042 (range, 0.802-0.987). The mean PCC did not differ between control (n = 26) and postoperative (n = 6) hemilarynges.

CONCLUSION

This method for measuring GCF appears valid. The high Pearson's correlation coefficient indicates strong covariance between GCF and LAP, demonstrating that they are both measures of the same physical property. The LAP is easier to perform and more consistently obtained.

The effect of the Botulinum toxin-A on craniofacial development: an experimental study

In this study, we developed a novel experimental model to evaluate muscular action on bone formation and remodeling by the help of Botulinum toxin-A (BTX). Forty-nine 15-day-old male Wistar rats were put into 4 groups randomly. Group 1 was the control group. BTX 0.4 IU (0.05 mL) was injected into the right masseter muscle in group 2 and into right temporalis muscle in group 3. The same volume of sterile saline was given into the both above-mentioned muscles in group 4. At the end of the fourth month, all animals were killed. Histology and weight of the masseter and temporalis muscles were studied. Thirty different osteometric measurements were also taken from skulls. Significant atrophy in BTX injected muscles was observed in groups 2 and 3. In group 4 (saline injection), only few osteometric measurements were significantly reduced, indicating the effect of the injection itself. Both groups 2 and 3 have apparent decrease in nasal bone, premaxilla, maxilla, and zygomatic dimensions on the injected side. When masseter group was compared with control and saline groups, no significant difference was found in skull base dimensions and mandibular length. In contrast, temporal group has also shown significant decrease in skull base dimensions. Our conclusions are as follows: (1) With this model, it is possible to study muscular action on bone formation and modeling without any surgical intervention, that is, by avoiding surgical artifacts, such as scar and contracture; (2) denervation of the skeletal muscles with BTX during the growing phase does effect bone development in a negative way; (3) pediatric use of the BTX deserves reevaluation under the light of these findings.

Local neurotoxins for prevention of laryngeal synkinesis after recurrent laryngeal nerve injury

OBJECTIVES

Persistent vocal fold motion impairment after recurrent laryngeal nerve (RLN) injury is not characteristically due to absent reinnervation, but often results from spontaneous aberrant reinnervation (synkinesis). We administered local neurotoxins to selected laryngeal muscles after RLN injury to determine whether aberrant reinnervation could be selectively inhibited.

METHODS

Unilateral RLN transection was performed in 24 male rats. Three weeks later, the denervated laryngeal adductor complex was injected with phenol, high- or low-dose vincristine sulfate (VNC), or saline solution. One month later, rat larynges were evaluated via videolaryngoscopy and laryngeal electromyography (LEMG). Larynges from euthanized animals were analyzed via immunofluorescent staining for the presence of reinnervation.

RESULTS

One animal that received phenol and 3 animals that received high-dose VNC died of toxicity-related complications. In the surviving neurotoxin-treated animals, videolaryngoscopy showed increased lateralization of the immobile vocal fold. Only 1 phenol-injected rat had adductor complex motor recruitment (score of 3+) with LEMG. The other neurotoxin-treated animals demonstrated an absence of adductor complex reinnervation, with only insertional activity and fibrillations (no motor units/recruitment). Spontaneous ipsilateral abductor reinnervation was not affected by the adductor injections.

CONCLUSIONS

Low-dose VNC injections appear to be relatively safe and effective in selectively inhibiting spontaneous aberrant reinnervation after RLN injury in an animal model.

Functional study of four neurotoxins as inhibitors of post-traumatic nerve regeneration

OBJECTIVES/HYPOTHESIS

Chemical inhibition of nerve regeneration was studied as a potential adjunct in the treatment of injuries to the facial or recurrent laryngeal nerve. We propose that by treating selected muscles with an inhibitor of nerve regeneration shortly after injury, synkinesis may be controlled.

STUDY DESIGN

Nerve regeneration after crush injury was studied in the rat posterior tibial and sciatic nerves, well-established models for the study of peripheral nerve injuries.

METHODS

Four days after controlled crush injury to the posterior tibial nerve, the gastrocnemius muscle was injected with saline (control, n = 8), phenol (n = 6), doxorubicin (n = 6), or vincristine (n = 11). Injection without crush injury was performed using vincristine (n = 4) or botulinum toxin (n = 4). Four rats underwent crush injury to the sciatic nerve followed 4 days later by botulinum toxin injection to the gastrocnemius muscle. The percent of functional recovery (%FR) of the nerve was assessed using walking track analysis.

RESULTS

Vincristine significantly retarded nerve regeneration. Five weeks after injury, %FR returned to normal in controls, as well as in the phenol, doxorubicin, and botulinum toxin groups, while in the vincristine group %FR was less than 60% of baseline (P <.0001). Vincristine injections without crush injury showed no significant reduction in print length factor. Functional recovery in the botulinum/crush group was more rapid than the botulinum without crush group.

CONCLUSIONS

Application of vincristine to the gastrocnemius muscle significantly inhibits regeneration of the posterior tibial nerve after crush injury. Botulinum toxin does not prolong functional recovery after nerve injury; rather, crush injury protects against the prolonged chemodenervation seen with botulinum toxin. Doxorubicin and phenol injection did not prolong functional recovery at the doses tested.