Figure 2 - available via license: Creative Commons Attribution 3.0 Unported
Content may be subject to copyright.
Schema of the extratemporal facial nerve with the location of FG application and detection. (a) Proximal part of ETFN; (b) middle part of ETFN; (c) distal part of ETFN; (d) proximal part of the injection site. TB, temporal branch; ZB, zygomatic branch; BB, buccal branch; MMB, marginal mandibular branch; CB, cervical branch; SF, stylomastoid foramen.
Source publication
Understanding the microanatomy of the facial nerve is vital to functional restoration of facial nerve injury. This study aimed to locate the spatial orientation of five branches in the extratemporal trunk of the rat facial nerve (ETFN). Fifteen adult Sprague-Dawley albino rats were divided randomly into five groups corresponding to the five facial...
Contexts in source publication
Context 1
... w/v). The animals were randomized to five groups. FG was applied to one branch in each group. The facial nerve branches were dissected carefully under an operating microscope. A 10-µl Hamilton syringe was used to inject 5 µl 2% FG to the proximal end of the nerve under manual pressure. The nerve was clearly transected 10 mm distal to the trunk (Fig. 2). A pipette containing 5 µl FG was then kept in position at the cut end of the trunk for the next 10 min to allow the tracer to penetrate into the tissue. Particular care was taken to achieve complete immersion of the nerve stump in the FG solution. A single 4-0 silk suture (Ethicon) was used to close each wound. The operation was ...
Context 2
... were cut serially into 10 µm-thick cross-sections on a Leica 1900CM microtome. Care was taken to maintain the serial order of the sections so that the location of the labeled nerve fibers would be apparent. The specimens were examined on three different levels [proximal, medial, and distal parts of the extratemporal trunk of the facial nerve ( Fig. 2)], using a Zeiss Axiophot fluorescence microscope and H365 filters (band-pass 365 nm, long pass 397 nm). The study was approved by the PLA Postgraduate Medical School ethics board All animal experiments were carried out in accordance with the guidelines of the Animal Care and Use Committee of PLA Postgraduate Medical ...
Citations
... Optimal single-photon excitation of FG is achieved using ultraviolet light. Imaging of FG-labeled specimens is typically performed using widefield fluorescence microscopy, with standard DAPI/Hoechst filter sets yielding narrow-band 365 nm excitation and long-pass filters providing broadband detection 1,9,13,14,26,27 . However, widefield imaging lacks depth discrimination, preventing optical sectioning and high-resolution three-dimensional (3D) imaging. ...
Fluoro-Gold is a fluorescent neuronal tracer suitable for targeted deep imaging of the nervous system. Widefield fluorescence microscopy enables visualization of Fluoro-Gold, but lacks depth discrimination. Though scanning laser confocal microscopy yields volumetric data, imaging depth is limited, and optimal single-photon excitation of Fluoro-Gold requires an unconventional ultraviolet excitation line. Two-photon excitation microscopy employs ultrafast pulsed infrared lasers to image fluorophores at high-resolution at unparalleled depths in opaque tissue. Deep imaging of Fluoro-Gold-labeled neurons carries potential to advance understanding of the central and peripheral nervous systems, yet its two-photon spectral and temporal properties remain uncharacterized. Herein, we report the two-photon excitation spectrum of Fluoro-Gold between 720 and 990 nm, and its fluorescence decay rate in aqueous solution and murine brainstem tissue. We demonstrate unprecedented imaging depth of whole-mounted murine brainstem via two-photon excitation microscopy of Fluoro-Gold labeled facial motor nuclei. Optimal two-photon excitation of Fluoro-Gold within microscope tuning range occurred at 720 nm, while maximum lifetime contrast was observed at 760 nm with mean fluorescence lifetime of 1.4 ns. Whole-mount brainstem explants were readily imaged to depths in excess of 450 µm via immersion in refractive-index matching solution.
... Optimal single-photon excitation of FG is achieved using ultraviolet light. Imaging of FG-labeled specimens is typically performed using wide eld uorescence microscopy, with standard DAPI/Hoechst lter sets yielding narrow-band 365 nm excitation and long-pass lters providing broadband detection [1,9,13,14,24,25]. However, wide eld imaging lacks depth discrimination, preventing optical sectioning and high-resolution three-dimensional (3D) imaging. ...
Fluoro-Gold is a uorescent neuronal tracer suitable for targeted deep imaging of the nervous system. Wide eld uorescence microscopy enables visualization of uoro-gold, but lacks depth discrimination. Though scanning laser confocal microscopy yields volumetric data, imaging depth is limited, and optimal single-photon excitation of uoro-gold requires an unconventional ultraviolet excitation line. Two-photon excitation microscopy employs ultrafast pulsed infrared lasers to image uorophores at high-resolution at unparalleled depths in opaque tissue. Deep imaging of uoro-gold-labeled neurons carries potential to advance understanding of the central and peripheral nervous systems, yet its two-photon spectral and temporal properties remain uncharacterized. Herein, we report the relative two-photon excitation spectrum of uoro-gold between 720 nm and 1100 nm, and its uorescence decay rate in aqueous solution and murine brainstem tissue. We demonstrate unprecedented imaging depth of whole-mounted murine brainstem via two-photon excitation microscopy of uoro-gold-labeled facial motor nuclei. Optimal two-photon excitation of uoro-gold occurred at 730 nm, while maximum lifetime contrast was observed at 760 nm with mean uorescence lifetime of 1.4 ns. Whole-mount brainstem explants were readily imaged to depths in excess of 450 µm via immersion in refractive-index matching solution.
... Five months after surgery, the fluorescence retrograde axon tracer Fluoro-Gold (Sigma, St. Louis, MO, USA) was used to demonstrate axonal growth after end-to-side neurorrhaphy (McBride et al., 1990;Byers and Lin, 2003;Chiu et al., 2008;Chen et al., 2012). As described above, the animals were re-anesthetized, and 1 µL 3% Fluoro-Gold dyes were injected into the cutaneous antebrachii medialis nerve (end-to-side and sham groups, n = 6) using a Hamilton syringe. ...
End-to-side neurorrhaphy is an option in the treatment of the long segment defects of a nerve. It involves suturing the distal stump of the disconnected nerve (recipient nerve) to the side of the intimate adjacent nerve (donor nerve). However, the motor-sensory specificity after end-to-side neurorrhaphy remains unclear. This study sought to evaluate whether cutaneous sensory nerve regeneration induces motor nerves after end-to-side neurorrhaphy. Thirty rats were randomized into three groups: (1) end-to-side neurorrhaphy using the ulnar nerve (mixed sensory and motor) as the donor nerve and the cutaneous antebrachii medialis nerve as the recipient nerve; (2) the sham group: ulnar nerve and cutaneous antebrachii medialis nerve were just exposed; and (3) the transected nerve group: cutaneous antebrachii medialis nerve was transected and the stumps were turned over and tied. At 5 months, acetylcholinesterase staining results showed that 34% ± 16% of the myelinated axons were stained in the end-to-side group, and none of the myelinated axons were stained in either the sham or transected nerve groups. Retrograde fluorescent tracing of spinal motor neurons and dorsal root ganglion showed the proportion of motor neurons from the cutaneous antebrachii medialis nerve of the end-to-side group was 21% ± 5%. In contrast, no motor neurons from the cutaneous antebrachii medialis nerve of the sham group and transected nerve group were found in the spinal cord segment. These results confirmed that motor neuron regeneration occurred after cutaneous nerve end-to-side neurorrhaphy.
Background The intricacies of nerve regeneration following injury have prompted increased research efforts in recent years, with a primary focus on elucidating regeneration mechanisms and exploring various surgical techniques. While many experimental animals have been used for these investigations, the rat continues to remain the most widely used model due to its cost-effectiveness, accessibility, and resilience against diseases and surgical/anesthetic complications. A comprehensive evaluation of all the experimental rat models available in this context is currently lacking.
Methods We summarize rat models of cranial nerves while furnishing descriptions of the intricacies of achieving optimal exposure.
Results This review article provides an examination of the technical exposure, potential applications, and the advantages and disadvantages inherent to each cranial nerve model.
Conclusion Specifically in the context of cranial nerve injury, numerous studies have utilized different surgical techniques to expose and investigate the cranial nerves in the rat.
Injury to the facial nerve can occur after different etiologies and range from simple transection of the branches to varying degrees of segmental loss. Management depends on the extent of the injury and options include primary repair for simple transections and using autografts, allografts or conduits for larger gaps. Tissue engineering plays an important role to create artificial materials that are able to mimic the nerve itself without extra morbidity in the patients. The use of neurotrophic factors or stem cells inside the conduits or around the repair site are being increasingly studied to enhance neural recovery to a greater extent. Pre-clinical studies remain as the hallmark for development of these novel approaches and translation into the clinical practice. This review will focus on pre-clinical models of repair after facial nerve injury to help researchers establish an appropriate model to quantify recovery and analyze functional outcomes. Different bioengineered materials, including conduits and nerve grafts, will be discussed based on the experimental animals that were used and the defects introduced. Future directions to extend the applications of processed nerve allografts, bioengineered conduits and cues inside the conduits to induce neural recovery after facial nerve injury will be highlighted.
Background and objectives:
Early persistent facial paralysis is characterized by intact muscles of facial expression through maintained perfusion but lacking nerve supply. In facial reanimation procedures aiming at restoration of facial tone and dynamics, neurotization through a donor nerve is performed. Critical for reanimating target muscles is axonal capacity of both donor and recipient nerves. In cases of complete paralysis, the proximal stump of the extratemporal facial nerve trunk may be selected as a recipient site for coaptation. To further clarify the histological basis of this facial reanimation procedure we conducted a human cadaver study examining macro and micro anatomical features of the facial nerve trunk including its axonal capacity in human cadavers. Axonal loads, morphology and morbidity of different donor nerves are discussed reviewing literature in context of nerve transfers.
Methods:
From 6/2015 to 9/2016 in a group of 53 fresh frozen cadavers a total of 106 facial halves were dissected. Biopsies of the extratemporal facial nerve trunk (FN) were obtained at 1 cm distal to the stylomastoid foramen. After histological processing and digitalization of 99 specimens available, 75 were selected eligible for fascicle counts and 64 fulfilled quality criteria for a semi-automated computer-based axon quantification software using ImageJ/Fiji.
Results:
An average of 3,89 fascicles (1- 9) were noted (n = 75). 5904±1819 axons (2655- 11352) were counted for the entire group (n = 64). Right facial halves showed 5645±1975 axons (n = 29). Left facial halves demonstrated 6119±1357 axons (n = 35) with a significant difference (p = 0.043). Female cadavers featured 5757±1851 (n = 24), male showed 6099±1631 axons (n = 34). No statistical difference was seen between genders (p = 0.59). A comparison with different studies in literature is made. The nerve diameter in 81 of our specimens could be measured at 1933±430μm (975- 3012).
Conclusions:
No donor nerve has been described to match axonal load or fascicle number of the extratemporal facial nerve main trunk. However, the masseteric nerve may be coapted for neurotization of facial muscles with a low complication rate and good clinical outcomes. Nerve transfer is indicated from 6 months after onset of facial paralysis if no recovery of facial nerve function is seen.
