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BackgroundAfter facial nerve injury and surgical repair in rats, recovery of vibrissal whisking is associated with a high proportion of mono‐innervated neuro‐muscular junctions (NMJs). Our earlier work with Sprague Dawley (SD)/Royal College of Surgeons (RCS) rats, which are blind and spontaneously restore NMJ‐monoinnervation and whisking, showed correlations between functional recovery and increase of fibroblast growth factor‐2 (FGF2) and brain‐derived neurotrophic factor (BDNF) in denervated vibrissal muscles.MethodsWe used normally sighted rats (Wistar), in which NMJ‐polyinnervation is highly correlated with poor whisking recovery, and injected the vibrissal muscle levator labii superioris (LLS) with combinations of BDNF, anti‐BDNF, and FGF2 at different postoperative periods after facial nerve injury.ResultsRats receiving anti‐BDNF+FGF2 showed low NMJ‐polyinnervation and best recovery of whisking amplitude.ConclusionsRestoration of target reinnervation after peripheral nerve injury requires a complex mixture of trophic factors with a specific time course of availability for each of them.

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Objectives Treatment with botulinum toxin A (BoNT) is the therapy of choice for many patients with facial synkinesis. Repeated injections relieve hypertonicity and hyperkinesis of reinnervated mimic muscles. Aim of the study was to prove if the injection regime and dosage of BoNT change during long‐time therapy. Design Retrospective analysis of patients´ data, who were treated for synkinesis with BoNT from 1998 to 2018. Setting Tertiary referral facial nerve centre. Participants Injection pattern of BoNT was based on clinical symptoms, observations of the specialist and on previous treatment pattern. Onabotulinumtoxin (OnaBoNT), Incobotulinumtoxin (IncoBoNT) and Abobotulinumtoxin (AboBoNT) were available for treatment. Patients consulted our department for following treatment as soon as the symptoms re‐occurred. Main outcome measures Change in dosage and injection pattern, the time intervals between treatments over the entire therapy period. Results Seventy‐three patients were repeatedly injected. The median number of treatments was 18, the median treatment interval was 3.0 months. During the initial treatment, orbicularis oculi and the mentalis muscles were the most frequently injected muscles (94%). During repeated treatment, the number of injected muscles increased significantly (P < .0001), whereas the dose per muscle remained stable. The initial dose was 24 U (95%‐CI 22‐27 U) for OnaBoNT and IncoBoNT; 69 U for AboBoNT(95%‐CI 44‐94 U). We observed a significant increase in dosage for OnaBoNT and IncoBoNT (P < .0001) during the long‐term therapy. The time intervals between treatments were stable for all three BoNT preparations (P > .05). Conclusions We observed significant change in treatment dose and injection pattern of BoNT in patients with facial synkinesis. These results provide an orientation in dose finding and injection regimen of BoNT in the long‐term course of therapy.

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Insufficient recovery after injury of a peripheral motor nerve is due to (1) inappropriate pathfinding as a result of axonal regrowth to inappropriate targets, (2) excessive collateral axonal branching at the lesion site, and (3) polyinnervation of the neuromuscular junctions (NMJs). The rat facial nerve model is often used because of its simple and reliable readout to measure recovery of function (vibrissal whisking). Over the last decades scientists have concentrated their efforts to combat mostly NMJ polyinnervation, because it turned out to be very difficult to reduce collateral axonal branching and impossible to navigate thousands of axons toward the original fascicles. In the past, several groups of scientists concentrated their efforts to reduce the activity-dependent polyinnervation of NMJs by electrical stimulation of the muscles (square 0.1 msec pulses at 5 Hz). The results showed no recovery of functions and a severe reduction in the number of innervated NMJs to approximately one fifth of those observed in intact animals. More recent experiments, however, have shown that motor recovery improved significantly following mechanical stimulation of the denervated facial muscles (vibrissal and orbicularis oculi) and that restored functions could invariably be linked to reduced polyinnervation at the NMJ while the number of innervated NMJ remained the same. These results suggest that clinically feasible and effective therapies could be developed and tested in the near future.