The role of botulinum toxin type a-induced motor endplates after peripheral nerve repair

Botulinum toxin in the masseter muscle: Lingering effects of denervation

Botulinum neurotoxins (BoNTs) are paralytic agents used to treat a variety of conditions in jaw muscles. Although their effect is considered temporary, there are reports of persistent functional changes. Using rabbits that received BoNT injection in one masseter muscle, the recovery of neuromuscular connection was investigated using nerve stimulation to evoke an electromyographic (EMG) response, and the recovery of muscle fibers was investigated using histological morphometry and bromodeoxyuridine (BrdU) immunohistochemistry. One month after treatment, evoked EMG was greatly reduced in both amplitude and duration, indicating that little reinnervation had taken place. Muscle fibers were atrophied and collagenous tissue was increased. Three months after treatment, evoked EMG duration was normal, indicating that at least some neuromuscular junctions were functional. Histologically, some muscle fibers were hypertrophied, some were still atrophied, and some appeared to have died. Fibrosis was still apparent amid slight increases in dividing cells and regenerating fibers. The histological effects of BoNT were evident although attenuated at a distance of about 1 cm from the injection level, but no regional differences could be discerned for the evoked EMGs. In conclusion, there were persistent muscular deficits seen 3 months after BoNT treatment that may have been caused by the failure of some affected muscle fibers to become reinnervated.

Topical Application of Human Wharton's Jelly Mesenchymal Stem Cells Accelerates Mouse Sciatic Nerve Recovery and is Associated with Upregulated Neurotrophic Factor Expression

Peripheral nerve regeneration following injury is often slow and impaired, which results in weakened and denervated muscle with subsequent atrophy. Human Wharton's jelly mesenchymal stem cells (hWJ-MSC) have potential regenerative properties which, however, remain unknown in mouse nerve recovery. This study investigated the effect of the topical application of hWJ-MSC onto repairing transected sciatic nerves in a mouse model. Human adipocyte-derived stem cells (hADSC) were used as a positive control. The sciatic nerve of BALB/c mice was transected at a fixed point and repaired under the microscope using 10-0 sutures. hWJ-MSC and hADSC were applied to the site of repair and mice were followed up for 1 year. The hWJ-MSC group had significantly better functional recovery of five-toe spread and gait angles compared with the negative control and hADSC groups. hWJ-MSC improved sciatic nerve regeneration in a dose-dependent fashion. The hWJ-MSC group had a better quality of regenerated nerve with an increased number of myelinated axons throughout. hWJ-MSC appear to be safe in mice after 1 year of follow-up. hWJ-MSC also expressed higher levels of neurotrophic factor-3, brain-derived neurotrophic factor, and glial-derived neurotrophic factor than hADSC. hWJ-MSC may promote better nerve recovery than hADSC because of this upregulation of neurotrophic factors.

Contralateral Botulinum Toxin Improved Functional Recovery after Tibial Nerve Repair in Rats

BACKGROUND

There is clinical and experimental evidence that botulinum toxin applied to the healthy side of patients with facial paralysis positively affects functional recovery of the paralyzed side. The authors created an experimental model to study the effects of botulinum toxin injection in the gastrocnemius muscle contralateral to the side of tibial nerve lesion/repair in rats.

METHODS

Fifty rats were allocated into five groups: group I, control; group II, tibial nerve section; group III, tibial nerve section and immediate neurorrhaphy; group IV, tibial nerve section, immediate neurorrhaphy, and botulinum toxin injected into the contralateral gastrocnemius muscle; and group V, botulinum toxin injected into the gastrocnemius muscle and no surgery. Assessment tools included a walking track, electromyography, gastrocnemius muscle weight measurement, and histologic analysis of the nerve.

RESULTS

Paralysis in group V was transient, with function returning to normal at 8 weeks. At 12 weeks, group V had lower latency levels. At week 12, group IV showed higher functional outcomes and amplitude levels than group III, and lower muscle atrophy on the side injected with botulinum toxin compared with group V.

CONCLUSION

Transient paralysis of the contralateral gastrocnemius muscle by botulinum toxin type A improved functional recovery in rats that underwent section and repair of the tibial nerve.

Botulinum Toxin Conditioning Enhances Motor Axon Regeneration in Mouse and Human Preclinical Models

BACKGROUND

Peripheral axon regeneration is improved when the nerve lesion under consideration has recently been preceded by another nerve injury. This is known as the conditioning lesion effect (CLE). While the CLE is one of the most robust and well characterized means to enhance motor axon regeneration in experimental models, it is not considered a clinically feasible strategy. A pharmacological means to re-produce the CLE is highly desirable.

OBJECTIVE

To test whether chemodenervation with a clinical grade formulation of botulinum toxin A (BoTX) would be sufficient to reproduce the CLE.

METHODS

We examined the effects of a 1-week preconditioning administration of BoTX on motor axon regrowth in both a mouse tibial nerve injury and human embryonic stem cell (hESC)-based model. We assessed neuronal reinnervation in vivo (mice) with retrograde tracers and histological analysis of peripheral nerve tissue after injections into the triceps surae muscle group. We assessed motor neuron neurite outgrowth in vitro (hESC) after incubation in BoTX by immunohistochemistry and morphometric analysis.

RESULTS

We found that BoTX conditioning treatment significantly enhanced outgrowth of both murine motor axons in vivo and human MN neurites in vitro.

CONCLUSIONS

BoTX preconditioning represents a pharmacological candidate approach to enhance motor axon regeneration in specific clinical scenarios such as nerve transfer surgery. Further studies are needed to elucidate the molecular mechanism.