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Peripheral nerve injury is a common, important problem that lacks a definitive, effective treatment. It can cause neurologic deficits ranging from paresthesia to paralysis. This study evaluated the effect of ozone therapy on sciatic nerve crush injury in rats.Twenty-four male rats were divided into control sham surgery, sciatic nerve injury, and sciatic nerve injury with ozone groups (each n = 8). The sciatic nerve injury was inflicted via De Koning's crush-force method. The sciatic nerve injury group received medical air and the sciatic nerve injury ozone group received 0.7 mg/kg ozone. Sciatic nerve samples were obtained 4 weeks after injury. Vascular congestion, vacuolization, edema formation, S100 expression, and the thicknesses of the perineurium and endoneurium and diameter of the injured sciatic nerves were evaluated.The diameter of the sciatic nerve and thicknesses of the perineurium and epineurium were significantly greater in the sciatic nerve injury group (P 0.05) and significantly less in the sciatic nerve injury with ozone group (P0.001). High S100 immunoreactivity was seen in the sciatic nerve injury group compared with the other 2 groups (P0.05). The distributions of vascular congestion and vacuolization were significantly less in the sciatic nerve injury with ozone group (P 0.05).Ozone therapy improved sciatic nerve injury recovery without causing an increase in fibrotic tissue. Ozone reduced fibrosis, vascular congestion, vacuolization, and edema in rodents. Ozone treatment might be used to assist in sciatic nerve injury.

We report a new transthyretin (ATTR) gene c.272C>G mutation and variant protein, p.Leu32Val, in a kindred of Bolivian origin with a rapid progressive peripheral neuropathy and cardiomyopathy. Three individuals from a kindred with peripheral nerve and cardiac amyloidosis were examined. Analysis of the TTR gene was performed by Sanger direct sequencing. Neuropathologic examination was obtained on the index patient with mass spectrometry study of the ATTR deposition. Direct DNA sequence analysis of exons 2, 3, and 4 of the TTR gene demonstrated a c.272 C>G mutation in exon 2 (p.L32V). Sural nerve biopsy revealed massive amyloid deposition in the perineurium, endoneurium and vasa nervorum. Mass spectrometric analyses of ATTR immunoprecipitated from nerve biopsy showed the presence of both wild-type and variant proteins. The observed mass results for the wild-type and variant proteins were consistent with the predicted values calculated from the genetic analysis data. The ATTR L32V is associated with a severe course. This has implications for treatment of affected individuals and counseling of family members.

The molecular determinants of pathogenic leukocyte migration across the blood-nerve barrier (BNB) in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) are unknown. Specific disease modifying therapies for CIDP are also lacking. Fibronectin connecting segment-1 (FNCS1), an alternatively spliced fibronectin variant expressed by microvascular endothelial cells at sites of inflammation in vitro and in situ, is a counterligand for leukocyte α4 integrin (also known as CD49d) implicated in pathogenic leukocyte trafficking in multiple sclerosis and inflammatory bowel disease. We sought to determine the role of FNCS1 in CIDP patient leukocyte trafficking across the BNB in vitro and in severe chronic demyelinating neuritis in vivo using a representative spontaneous murine CIDP model. Peripheral blood mononuclear leukocytes from 7 untreated CIDP patients were independently infused into a cytokine-treated, flow-dependent in vitro BNB model system. Time-lapse digital video microscopy was performed to visualize and quantify leukocyte trafficking, comparing FNCS1 peptide blockade to relevant controls. Fifty 24-week old female B7-2 deficient non-obese diabetic mice with spontaneous autoimmune peripheral polyneuropathy (SAPP) were treated daily with 2 mg/kg FNCS1 peptide for 5 days via intraperitoneal injection with appropriate controls. Neurobehavioral measures of disease severity, motor nerve electrophysiology assessments and histopathological quantification of inflammation and morphometric assessment of demyelination were performed to determine in vivo efficacy. The biological relevance of FNCS1 and CD49d in CIDP was evaluated by immunohistochemical detection in affected patient sural nerve biopsies. 25 μM FNCS1 peptide maximally inhibited CIDP leukocyte trafficking at the human BNB in vitro. FNCS1 peptide treatment resulted in significant improvements in disease severity, motor electrophysiological parameters of demyelination and histological measures of inflammatory demyelination. Microvessels demonstrating FNCS1 expression and CD49d+ leukocytes were seen within the endoneurium of patient nerve biopsies. Taken together, these results imply a role for FNCS1 in pathogenic leukocyte trafficking in CIDP, providing a potential target for therapeutic modulation.

BACKGROUND: Autograft is still the gold standard technique for the repair of long peripheral nerve injuries. The addition of biologically active scaffolds into the lumen of conduits to mimic the endoneurium of peripheral nerves may increase the final outcome of artificial nerve devices. Furthermore, the control of the orientation of the collagen fibers may provide some longitudinal guidance architecture providing a higher level of mesoscale tissue structure. OBJECTIVE: To evaluate the regenerative capabilities of chitosan conduits enriched with extracellular matrix-based scaffolds to bridge a critical gap of 15 mm in the rat sciatic nerve. METHODS: The right sciatic nerve of female Wistar Hannover rats was repaired with chitosan tubes functionalized with extracellular matrix-based scaffolds fully hydrated or stabilized and rolled to bridge a 15 mm nerve gap. Recovery was evaluated by means of electrophysiology and algesimetry tests and histological analysis 4 months after injury. RESULTS: Stabilized constructs enhanced the success of regeneration compared with fully hydrated scaffolds. Moreover, fibronectin-enriched scaffolds increased muscle reinnervation and number of myelinated fibers compared with laminin-enriched constructs. CONCLUSION: A mixed combination of collagen and fibronectin may be a promising internal filler for neural conduits for the repair of peripheral nerve injuries, and their stabilization may increase the quality of regeneration over long gaps.

Studies presented here, using a murine model of bone morphogenetic protein type 2 (BMP2)-induced heterotopic ossification (HO) show that the protein initiates HO by signaling through progenitors in the endoneurium of peripheral nerves. In the mouse, these cells were identified in the endoneurium one day after BMP2 induction using antibody against phosphoSMAD (PS) 1, 5, and 8. Studies conducted in a tracking mouse that contains a tamoxifen-regulated Wnt1-Cre recombinase crossed with a td Tomato red (TR) reporter (Wnt1CreErt:Ai9Tm) confirmed their neural origin. In this model both BMP2 induction and tamoxifen are absolutely required to induce TR. SP7+(osterix+)TR+ cells were found in the endoneurium on day 1 and associated with bone on day 7. Quantification of TR+ and TR− cells isolated by fluorescence-activated cell sorting showed that all SP7+ cells were found in the TR+ population, whereas only about 80% of the TR+ cells expressed SP7. Pre-chondrocytes (Sox 9+) and transient brown fat (tBAT, UCP1+) also coexpressed TR, suggesting that the progenitor in nerves is multi-potential. The endoneurium of human nerves near the site of HO contained many PS+ cells, and SP7+ cells were found in nerves and on bone in tissue from patients with HO. Control tissues and nerves did not contain these PS+ and SP7+ cells. Some osteoblasts on bone from patients with HO were positive for PS, suggesting the continued presence of BMP during bone formation. The data suggests that the progenitors for HO are derived from the endoneurium in both the mouse model of HO and in humans with HO.

We herein report the findings of a 67-year-old woman with steroid-responsive multiple mononeuropathy associated with chronic natural killer (NK) cell lymphocytosis. The patient developed progressive, asymmetric weakness and numbness in all four extremities in the course of a three-month period. Nerve conduction studies revealed asymmetric demyelination in both the motor and sensory nerves, and a biopsy specimen of the sural nerve showed a conspicuous difference in the demyelination between the neighboring fascicles and the infiltration of NK cells in the endoneurium. We considered the multiple mononeuropathy in this patient to have been caused by NK cell infiltration in the endoneurium, and the observed asymmetry might have been due to differences in the NK cell intrusion among the fascicles. Corticosteroid administration resulted in a rapid neurological, electrophysiological and hematological improvement. The rapid clinical amelioration that was observed after corticosteroid therapy suggested that the neuropathy in this case had been mainly caused by the mechanical compression of the endoneurial NK cells or the inflammatory cytokines that had been released by them.

Meissner corpuscles are cutaneous mechanoreceptors that are usually located in the dermal papillae of human glabrous skin. Structurally, these sensory corpuscles consist of a mechanoreceptive sensory neuron surrounded by non-myelinating lamellar Schwann-like cells. Some authors have described a partially developed fibroblastic capsule of endoneurial or perineurial origin around Meissner corpuscles; however, others have noted that these structures are non-encapsulated. As there is continuity between the periaxonic cells forming the sensory corpuscles and the cells of the nerve trunks, we used immunohistochemistry to examine the expression of endoneurial (CD34 antigen) or perineurial [Glucose transporter 1 (Glut1)] markers in human cutaneous Meissner corpuscles. We also investigated the immunohistochemical patterns of nestin and vimentin (the main intermediate filaments of the cytoskeleton of endoneurial and perineurial cells, respectively) in Meissner corpuscles. The most important finding from this study was that CD34-positive cells formed a partial/complete capsule of endoneurial origin around most Meissner corpuscles, without signs of other perineurial Glut1-positive elements. However, the cytoskeletal proteins of the capsular CD34-positive cells did not include either nestin or vimentin, so the cytoskeletal composition of these cells remains to be established. Finally, the intensity of the immunoreactivity for CD34 in the capsule decreased with ageing, sometimes becoming completely absent in the oldest individuals. In conclusion, we report the first immunohistochemical evidence of the capsule of Meissner corpuscles in humans and demonstrate the endoneurial origin of the capsule.

Tarlov Cyst (TC) is defined as a cystic dilatation between the perineurium and endoneurium of spinal nerve roots, located at level of the spinal ganglion and filled with Cerebrospinal Fluid..

It has generally been accepted that intrafascicular spread of local anesthetic solution is the major cause of severe and devastating neurological complications after intraneural local anesthetic injection.1 Furthermore, the validity of the human extrapolation of animal experiment conclusions has been recently disputed.2 After performing deliberate intraneural injections using StimuPlex D, 22-guage (15° bevel) needles with a new marker (heparinized erythrocytes)3 under ultrasound guidance mimicking clinical practice, and creating the worst possible conditions for regional block, we microscopically analyzed the longitudinal and circumferential spread in the extrafascicular and intrafascicular compartments in human sciatic and median nerves. This was also done in sciatic nerves of dogs, pigs and sheep. Swelling of the nerves confirmed intraneural injection. Extrafascicular spread was seen in all human and animal samples outside the perineurium, intermingled between the interfascicular adipocytes except in extrafascicular compartments where adipocytes were absent. Intrafascicular spread was absent in almost all samples. the marker was also observed filling the entire thickness of perineurium between the perineurium cellular layers. Erythrocytes were not found inside the endoneurium of most of the fascicles examined. Intrafascicular intraneural injection has been entertained as possible option in a few cases, but we were surprises to find no evidence of intrafascicular spreading in the vast majority of fascicles. the compact endoneural structure and the absence of endoneural spaces4–5 probably explain our findings and may help to understand the relatively low number of neurological complications caused by peripheral regional anesthesia considering the high number of blocks that are performed and the high number of intraneural injections that may be done intentionally or unintentionally. References Brull R, Hadzic A, Reina MA, Barrington MJ: Pathophysiology and etiology of nerve injury following peripheral nerve blockade. Reg Anesth Pain Med 2015;40:479–90. Server A, Reina MA, Boezaart AP, Prats-Galino A, Esteves Coelho M, Sala-Blanch X. Microanatomical nerve architecture of six mammalian species: Is trans-species translational anatomic extrapolation valid?Reg Anesth Pain Med 2018;43:496–501. Reina MA, Boezaart AP, Sala-Blanch X, Monzo E, Tubbs S, Server A, Bigeleisen P. A novel marker for studying nerves. Clin Anat 2018; In Press. doi:10.1002/ca.23253 Reina MA, Maches F, De Diego-Isasa P, Del Olmo C. Ultrastructure of endoneurium, Atlas of Functional Anatomy of Regional Anesthesia and Pain Medicine. Edited by Reina MA. New York, Springer, 2015, pp 37–58. Reina MA, Sala Blanch X, Arriazu R, Maches F. Microscopic morphology and ultrastructure of human peripheral nerves, Nerves and Nerve Injuries, Vol. 1: History, Embryology, Anatomy, Imaging, and Diagnostics. Edited by Tubbs RS, Rizk E, Shoja M, Loukas M. Cambridge, MA, Elsevier, 2015, pp. 91–106.

Peripheral nerves consist of bundles of nerve fibers organized into several nerve fasciculi. Peripheral nerves consist of bundles of nerve fibers surrounded by connective tissue. The bundles of nerve fibers can be both myelinated and unmyelinated. Unmyelinated fibers, termed fibers of Remak, consist of axons directly enveloped by the Schwann cell sheath that is not unlike the same sheath in myelinated fibers. Each fasciculus is composed of myelinated and unmyelinated fibers surrounded by additional sheaths of connective tissue: the endoneurium and the perineurium. Peripheral nerves are supplied by small blood vessels, the vasa nervorum, that penetrate the perineurium and run parallel to the nerve fibers. The divisions and anastomosis of these vessels form a continuous vascular network inside the nerve. The vascular network is functionally important in peripheral nerve blocks, especially when the block recedes, as there is a greater uptake in the central part of the nerves than in the periphery.

Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background There is confusion regarding the spread of intraneurally injected local anesthetic agents during regional anesthesia. The aim of this research was to deliberately inject a marker that does not leave the neural compartment into which it is injected, and then to study the longitudinal and circumferential spread and possible pathways of intraneural spread. Methods After institutional review board approval, we intraneurally injected 20 and 5 ml of heparinized blood solution under ultrasound guidance into 12 sciatic nerves in the popliteal fossa and 10 median nerves, respectively, of eight fresh, unembalmed cadavers using standard 22-gauge “D” needles, mimicking the blocks in clinical conditions. Ultrasound evidence of nerve swelling confirmed intraneural injection. Samples of the nerves were then examined under light and scanning electron microscopy. Results Extrafascicular spread was observed in all the adipocyte-containing neural compartments of the 664 cross-section samples we examined, but intrafascicular spread was seen in only 6 cross-sections of two nerves. None of the epineurium, perineurium, or neural components were disrupted in any of the samples. Spread between the layers of the perineurium was a route of spread that included the perineurium surrounding the fascicles and the perineurium that formed incomplete septa in the fascicles. Similar to the endoneurium proper, subepineural compartments that did not contain any fat cells did not reveal any spread of heparinized blood solution cells. No “perineural” spaces were observed within the endoneurium. We also did not observe any true intrafascicular spread. Conclusions After deliberate intraneural injection, longitudinal and circumferential extrafascicular spread occurred in all instances in the neural compartments that contained adipocytes, but not in the relatively solid endoneurium of the fascicles.

Peripheral nerves and nerve roots comprise of three structural compartments: the outer epineurium consisting of longitudinal arrays of collagen fibers responsible for structural integrity and the inner perineurium consisting of multiple concentric layers of specialized epithelioid myofibroblasts that surround the innermost endoneurium which consists of myelinated and unmyelinated axons embedded in a looser mesh of collagen fibers. Axons are responsible for signal transduction to and from the central nervous system required for normal physiological processes and are targeted by the immune system in autoimmune disorders. A highly regulated endoneurial microenvironment is required for normal axonal function. This is achieved by tight junction-forming endoneurial microvessels that control ion, solute, water, nutrient, macromolecule and leukocyte influx and efflux between the bloodstream and endoneurium, and the innermost layers of the perineurium that control interstitial fluid component flux between the epineurium and endoneurium. Endoneurial microvascular endothelium is considered the blood-nerve barrier (BNB) due to direct communication with circulating blood. The mammalian BNB is considered the second most restrictive vascular system after the blood-brain barrier (BBB). Guided by human in vitro studies using primary and immortalized endoneurial endothelial cells that form the BNB, in situ studies in normal and pathologic human peripheral nerves, and representative animal models of peripheral nerve autoimmune disorders, knowledge is emerging on human BNB molecular and functional characteristics, including its array of cytokines/cytokine receptors, selectins, and cellular adhesion and junctional complex molecules that may be employed during normal immune surveillance and altered in autoimmune diseases, providing potential targets of efficacious immunotherapy.

The separate nerve fibers are loosely bound by a fine meshwork of collagen, called the endoneurium. The nerve fibers of each are enclosed by the perineurium, which is epithelial in nature. This perineurium is continuous proximally with the arachnoid mater and distally with sarcolemmal sheath of a muscle or the capsule of a sensory end organ. The fascicles of a nerve are in turn bound together by a coarsely structured fibrous sheath known as the epineurium, which run next to the blood vessels supplying the nerve.

To understand traumas to the nervous system, the relation between mechanical load and functional impairment needs to be explained. Cellular-level computational models are being used to capture the mechanism behind mechanically-induced injuries and possibly predict these events. However, uncertainties in the material properties used in computational models undermine the validity of their predictions. For this reason, in this study the squid giant axon was used as a model to provide a description of the axonal mechanical behavior in a large strain and high strain rate regime $$({\boldsymbol{\varepsilon }}={\bf{10}}{\boldsymbol{ \% }},\,\mathop{{\boldsymbol{\varepsilon }}}\limits^{\cdot }={\bf{1}}{{\boldsymbol{s}}}^{-{\bf{1}}})$$ ( ε = 10 % , ε ⋅ = 1 s − 1 ) , which is relevant for injury investigations. More importantly, squid giant axon membrane sheaths were isolated and tested under dynamic uniaxial tension and relaxation. From the lumen outward, the membrane sheath presents: an axolemma, a layer of Schwann cells followed by the basement membrane and a prominent layer of loose connective tissue consisting of fibroblasts and collagen. Our results highlight the load-bearing role of this enwrapping structure and provide a constitutive description that could in turn be used in computational models. Furthermore, tests performed on collagen-depleted membrane sheaths reveal both the substantial contribution of the endoneurium to the total sheath’s response and an interesting increase in material nonlinearity when the collagen in this connective layer is digested. All in all, our results provide useful insights for modelling the axonal mechanical response and in turn will lead to a better understanding of the relationship between mechanical insult and electrophysiological outcome.

OBJECTIVE. Computational modeling is an important tool for developing and optimizing implantable neural stimulation devices, but requires accurate electrical and geometrical parameter values to improve predictive value. We quantified the effects of perineurial (resistive sheath around each fascicle) and endoneurial (within each fascicle) parameter values for modeling peripheral nerve stimulation. APPROACH. We implemented three-dimensional finite element models of compound peripheral nerves and cuff electrodes to quantify activation and block thresholds of model axons. We also implemented a two-dimensional finite element model of a bundle of axons to estimate the bulk transverse endoneurial resistivity; we compared numerical estimates to an analytical solution. MAIN RESULTS. Since the perineurium is highly resistive, potentials were approximately constant over the cross section of a fascicle, and the perineurium resistivity, longitudinal endoneurial resistivity, and fascicle diameter had important effects on thresholds. Activation thresholds increased up to ~130% for higher perineurium resistivity (~400 vs. 2200 Ω-m) and by ~35–250% for lower longitudinal endoneurial resistivity (3.5 vs. 0.75 Ω-m), with larger increases for smaller diameter axons and for axons in larger fascicles. Further, thresholds increased by ~30–180% for larger fascicle radii, yielding a larger increase with higher perineurium resistivity. Thresholds were largely insensitive to the transverse endoneurial resistivity, but estimates of the bulk resistivity increased with extracellular resistivity and axonal area fraction; the numerical and analytical estimates were in strong agreement except at high axonal area fractions, where structured axon placements that achieved tighter packing produced electric field inhomogeneities. SIGNIFICANCE. We performed a systematic investigation of the effects of values and methods for modeling the perineurium and endoneurium on thresholds for neural stimulation and block. These results provide guidance for future modeling studies, including parameter selection, data interpretation, and comparison to experimental results.

Whereas neurovascular interactions in spinal neuropathic pain models have been well characterized, little attention has been given to such neurovascular interactions in orofacial neuropathic pain models. This study investigated in male Sprague-Dawley rats the vascular changes following chronic constriction injury (CCI) of the infraorbital nerve (IoN), a broadly validated preclinical model of orofacial neuropathic pain. Following IoN-CCI, an early downregulation of tight junction proteins Claudin-1 and Claudin-5 was observed within the endoneurium and perineurium, associated with increased local accumulation of sodium fluorescein (NaFlu) within the IoN parenchyma, as compared with sham animals. These events were evidence of local blood-nerve barrier disruption and increased vascular permeability. A significant upregulation of immunocytes (CD3, CD11b) and innate immunity (TLR2, TLR4) mRNA markers was also observed, suggestive of increased local inflammation. Finally, a significant downregulation of Hedgehog pathway readouts Patched-1 and Gli-1 was observed within the IoN after CCI and local injections of cyclopamine, a Hedgehog pathway inhibitor, replicated in naïve rats the molecular, vascular, and behavioral changes observed following IoN-CCI. These results suggest a major role of Hedgehog pathway inhibition in mediating local increased endoneurial and perineurial vascular permeability following trigeminal nerve injury, thus facilitating immunocytes infiltration, neuroinflammation development, and neuropathic pain-like aversive behavior.

Renaut corpuscles are cylindrical hyaline structures that arise from the peripheral nerve perineurium and project into the endoneurium. Despite their earlier accurate description in the French and German literature, Kernohan and Woltman (1938) reported very similar structures as “nerve infarcts” in a case series of vasculitic neuropathy. Krücke (1955) deserves credit for discovering this error and further explaining how peripheral nerves react differently (from brain parenchyma) to ischemia. We tried to elucidate the reason why Kernohan and Woltman, and others, made this scientific error by describing the historical evolution of our understanding of the structure and function of Renaut corpuscles.

A sustained decrease in the M-response amplitudes of m. gastrocnemius and m. tibialis anterior was revealed during experimental orthopedic shin lengthening in dogs using Ilizarov external fixator with an automated drive (distraction 3 mm/day in 120 steps). Transverse contraction of intrafascicular content (by 13.2%), endoneural hypervascularization (by 28-95%), axonal degeneration and myelin decompactization, and destructive changes of no more than 5% fibers were detected in the tibial nerve. In the peroneal nerve, the contraction reached 17.3%. Endoneurium hypovascularization (by 12%), axonal degeneration and demyelinization, and destructive changes of more than 20% fibers were detected in 6 of 9 experiments.

Introduction Adult polyglucosan body disease (APBD) usually presents with progressive spastic paraparesis, neurogenic bladder, and distal lower limb sensory abnormalities. It is caused by mutations in the glycogen branching enzyme gene (GBE1). Methods We describe a woman with an unusual phenotype manifesting as progressive left brachial more than lumbosacral plexopathies, with central sensory and corticospinal tract involvement. Results Magnetic resonance imaging of the brain and cervical spine showed abnormal T2 signal within the ventral pons and medulla bilaterally, involving the pyramidal tracts and the medial leminisci. There was also medullary and cervical spine atrophy. On nerve biopsy, large polyglucosan bodies were noted in the endoneurium. The patient was found to be compound heterozygous for 2 novel mutations in GBE1. Peripheral blood leukocyte GBE activity was markedly reduced to 7% of normal, confirming the diagnosis of APBD. Conclusions In this report we describe a new phenotype of APBD associated with 2 novel mutations. Muscle Nerve 53: 976-981, 2016.

A nerve block is an effective tool for diagnostic and therapeutic methods. If a diagnostic nerve block is successful for pain relief and the subsequent therapeutic nerve block is effective for only a limited duration, the next step that should be considered is a nerve ablation or modulation. The nerve ablation causes iatrogenic neural degeneration aiming only for sensory or sympathetic denervation without motor deficits. Nerve ablation produces the interruption of axonal continuity, degeneration of nerve fibers distal to the lesion (Wallerian degeneration), and the eventual death of axotomized neurons. The nerve ablation methods currently available for resection/removal of innervation are performed by either chemical or thermal ablation. Meanwhile, the nerve modulation method for interruption of innervation is performed using an electromagnetic field of pulsed radiofrequency. According to Sunderland's classification, it is first and foremost suggested that current neural ablations produce third degree peripheral nerve injury (PNI) to the myelin, axon, and endoneurium without any disruption of the fascicular arrangement, perineurium, and epineurium. The merit of Sunderland's third degree PNI is to produce a reversible injury. However, its shortcoming is the recurrence of pain and the necessity of repeated ablative procedures. The molecular mechanisms related to axonal regeneration after injury include cross-talk between axons and glial cells, neurotrophic factors, extracellular matrix molecules, and their receptors. It is essential to establish a safe, long-standing denervation method without any complications in future practices based on the mechanisms of nerve degeneration as well as following regeneration.

Few studies in the literature have reported recovery data for different types of recurrent laryngeal nerve injuries (RLNIs). This study is the first attempt to classify RLNIs and rank them by severity. This prospective clinical study analyzed 281 RLNIs in which a true loss of signal was identified by intraoperative neuromonitoring (IONM), and vocal cord palsy (VCP) was confirmed by a postoperative laryngoscope. For each injury type, the prevalence of VCP, the time of VCP recovery, and physical changes on nerves were analyzed. Additionally, different RLNI types were experimentally induced in a porcine model to compare morphological change. The overall VCP rate in at-risk patients/nerves was 8.9/4.6 %, respectively. The distribution of RLNI types, in order of frequency, was traction (71 %), thermal (17 %), compression (4.2 %), clamping (3.4 %), ligature entrapment (1.6 %), suction (1.4 %), and nerve transection (1.4 %). Complete recovery from VCP was documented in 91 % of RLNIs. Recovery time was significantly faster in the traction group compared to the other groups (p

Iatrogenic nerve injuries are always a matter for concern. This article will address the common causes, diagnosis and management of iatrogenic peripheral nerve injuries. The most widely used classification of peripheral nerve injury is that described by Seddon in 1943.1 He divided nerve injuries into three types: neurapraxia, axonotmesis and neurotmesis. Neurapraxia (inactivity of the nerve) is a non-degenerative lesion of a nerve characterised by a complete or partial failure to propagate an action, potentially resulting in motor and/or sensory loss. It is usually caused by compression or ischaemia, resulting in ischaemia of the myelin sheath. The nerve remains intact and Wallerian degeneration does not occur. It is reversible if the injurious agent is removed. If the distal segment of the nerve is stimulated, there is a motor response. The lesion recovers by remyelination of the distal segment and takes between two and 12 weeks, depending on the age of the patient and the site of the injury. In practice, it is unwise to assume that a lesion is a neurapraxia rather than a more severe injury because this will lead to delay in diagnosis and a poorer outcome. The presence of persistent pain suggests that the injurious agent is continuing to act. The diagnosis should not be made in the presence of a strong Tinel test which indicates that axons have been ruptured. An axonotmesis (cutting of the axon) is the result of disruption of the axon and its myelin sheath. The supporting structures, Schwann cells, endoneurium, perineurium and epineurium remain intact. It is usually the result of severe compression or a crush injury. Wallerian degeneration occurs distally, and proximally to the closest node of Ranvier. Repair is by a combination of collateral sprouting in lesser injuries and axonal regeneration in more severe injuries. The latter occurs at …

Tarlov (perineural) cysts are meningeal dilations of the posterior spinal nerve root sheath located in between the peri- and endoneurium. We present a patient with a symptomatic sacral Tarlov cyst and the technical challenges faced by surgically treating the lesion by disconnection of the cyst from the subarachnoid space.

The aim of this research is to perform an analysis of the epineurial and endoneurial blood vessels in relation to aging. The research is conducted on samples of the human sciatic nerve of 12 case (age from 27 to 89). The histological sections are stained by streptavidin-biotin method of detecting the presence of Type IV collagen. After morphometric analysis the following stereological parameters have been calculated: the number of blood vessels per unit of area, the volume density of the blood vessels and the surface density of the blood vessels of the epineurium and endoneurium. An additional diameter measurement is performed for the endoneural blood vessels. In order to perform a more detailed analysis, the cases were classified into three age groups, the first (27–48 years), the second (49–70 years) and, the third (over 70 years). The bivariate correlation analysis showed that the number of blood vessels of the endoneurium, their volume and surface densities in relation to age produced a statistically significant positive correlation. One Way ANOVA test demonstrated a statistically significant increase in the number of endoneurial blood vessels in the age group III when compared the age group I and, in addition, it showed a significant decrease in the diameter of the age group II when compared to the age group I. Paired t – test shows a statistically significant higher number of endoneurial blood vessels in relation to the epineurial, namely, in the age group III. The volume and surface density of the epineurial blood vessels is significantly higher than the endoneurial in both the I and II age group. Age brings about significant changes of the endoneurial vascular network of the sciatic nerve due to the increase in density of the endoneurial blood vessels, their volume and surface densities. Consequently, in the cases older than 70 years, the number of endoneurial blood vessels significantly exceeds the number of epineurial blood vessels.

We report the pathological findings of hourglass-like fascicular constriction (HLFC) under optical and electron microscopy. A 24-year-old man with spontaneous posterior interosseous nerve palsy was treated by interfascicular neurolysis at 29 weeks after onset. One fascicle in the radial nerve presented severe HLFC with torsion at 5 cm proximal to the elbow. Functional recovery was achieved by resection of the enlarged fascicle including HLFC and sural nerve grafting. Proximal to the HLFC, the endoneurium was filled with clusters of regenerating nerve fibers. At the level of the HLFC, a complete loss of myelinated nerve fibers and vascular occlusion of endo- and perineurial vessels were found. Few regenerating nerve fibers were observed. Distal to the HLFC, severe endoneurial edema, a complete loss of myelinated and unmyelinated nerve fibers, and bands of Bungner were noted. These electron microscopic findings demonstrated a detailed pathology of the nerve around the HLFC.

Rationale: Perineural cysts, commonly referred to as Tarlov cysts, are cerebrospinal fluid-filled dilations between the perineurium and endoneurium typically arising at the junction of posterior and dorsal root ganglia in the neural foramina. This anatomical location is in close proximity to usual needle trajectory during performing transforaminal epidural injection, and therefore presents a potential risk of dural puncture and associated complications. Patient concerns: Severe lower extremity pain interfering with activities of daily living. Diagnoses: Lumbar radiculopathy secondary to left-sided L4-5 disc herniation in the presence of multilevel Tarlov cysts in the neural foramina. Interventions: Posterior interlaminar epidural steroid injection technique was preferred, as opposed to transforaminal approach, to avoid potential risk of dural puncture and associated complications in the presence of multilevel Tarlov cysts in the neural foramina. Outcomes: The patient responded favorably to epidural steroid injection via interlaminar approach with complete resolution of pain, symptoms, and signs. There were no complications. The patient was able to tolerate physical therapy, wean pain medications, and achieve normal activities of daily living without any significant limitations. Lessons: In patients presenting with an MRI report of “Tarlov cysts”, meticulous evaluation of diagnostic images should be an essential first step before considering invasive spinal procedures. Should there be any presence of Tarlov cyst in close proximity to planned needle trajectory, we recommend appropriate modification of spinal intervention to avoid potential complications.

Hybrid transplantation of skeletal muscle-derived multipotent stem cells (Sk-MSCs) and bioabsorbable polyglyconate (PGA) felt was studied as a novel regeneration therapy for the transected recurrent laryngeal nerve (RLN). Sk-MSCs were isolated from green fluorescence protein transgenic mice and then expanded and transplanted with PGA felt for the hybrid transplantation (HY group) into the RLN transected mouse model. Transplantation of culture medium (M group) and PGA + medium (PGA group) were examined as controls. After eight weeks, trans-oral video laryngoscopy demonstrated 80% recovery of spontaneous vocal-fold movement during breathing in the HY group, whereas the M and PGA groups showed wholly no recoveries. The Sk-MSCs showed active engraftment confined to the damaged RLN portion, representing favorable prevention of cell diffusion on PGA, with an enhanced expression of nerve growth factor mRNAs. Axonal re-connection in the HY group was confirmed by histological serial sections. Immunohistochemical analysis revealed the differentiation of Sk-MSCs into Schwann cells and perineurial/endoneurial cells and axonal growth supportive of perineurium/endoneurium. The number of axons recovered was over 86%. These results showed that the stem cell and cytokine delivery system using hybrid transplantation of Sk-MSCs/PGA-felt is a potentially practical and useful approach for the recovery of transected RLN.

Peripheral innervation plays an important role in regulating tissue repair and regeneration. Here we provide evidence that injured peripheral nerves provide a reservoir of mesenchymal precursor cells that can directly contribute to murine digit tip regeneration and skin repair. In particular, using single-cell RNA sequencing and lineage tracing, we identify transcriptionally distinct mesenchymal cell populations within the control and injured adult nerve, including neural crest-derived cells in the endoneurium with characteristics of mesenchymal precursor cells. Culture and transplantation studies show that these nerve-derived mesenchymal cells have the potential to differentiate into non-nerve lineages. Moreover, following digit tip amputation, neural crest-derived nerve mesenchymal cells contribute to the regenerative blastema and, ultimately, to the regenerated bone. Similarly, neural crest-derived nerve mesenchymal cells contribute to the dermis during skin wound healing. These findings support a model where peripheral nerves directly contribute mesenchymal precursor cells to promote repair and regeneration of injured mammalian tissues.

Author(s): Sung, Jaemyoung | Advisor(s): Shah, Sameer B; Bloodgood, Brenda L | Abstract: Peripheral nerves span one or more articulating joints, and must accommodate mechanical loads during day-to-day activities. Axons are protected in part by their undulation within the nerve, implied by the Bands of Fontana. In addition, previous studies have identified regions of increased epineurial strain and compliance, particularly near joints. Most of these studies have focused on regional differences in epineurial strain; however, how internal nerve compartments, including the axons, perceive this increased deformation is less understood. Using transgenic mice expressing a fluorescent reporter within their neurons, we tested 1) whether mesoneurial tissue contributes to regional variability in epineurial strain, and 2) whether nerves increase their local axonal undulation in regions of high epineurial strain, as a strategy to protect nerve fibers from strain-induced damage.In our results, we observed a decoupling between regions of high epineurial strain and high axonal tortuosity. Consistent with previous studies, decompression resulted in significant differences in regional strain, confirming strong mesoneurial influences on epineurial strain. However, regional differences in axonal tortuosity were largely unchanged by decompression or excision, signaling that epineurial measurements may not fully represent the response of the inner nerve. Based on our findings and previous literatures, we propose a neuromechanical model that permits axons to unravel along their length due to looser coupling between the peri/endoneurium. This capability may result in enhanced axonal protection to injury than suspected. These findings have implications for our understanding of nerve biomechanics as well as the progression of nerve dysfunction due to injury, disease, or surgery.

Peripheral nerves are composed of complex layered anatomical structures, including epineurium, perineurium, and endoneurium. Perineurium and endoneurium contain many physical barriers, including the blood-nerve barrier at endoneurial vessels and the perineurial barrier. These physical barriers help to eliminate flux penetration and thus contribute to the establishment of a stable microenvironment. In the current review, we introduce the anatomical compartments and physical barriers of peripheral nerves and then describe the cellular and molecular basis of peripheral physical barriers. We also specifically explore peripheral nerve injury-induced changes of peripheral physical barriers, including elevated endoneurial fluid pressure, increased leakage of tracer, decreased barrier-type endothelial cell ratio, and altered distributions and expressions of cellular junctional proteins. The understanding of the pathophysiological changes of physical barriers following peripheral nerve injury may provide a clue for the treatment of peripheral nerve injury.

To understand the pathology and molecular signatures of microangiopathy in diabetic neuropathy, we systemically and quantitatively examined the morphometry of microvascular and nerve pathologies of sural nerves. In the endoneurium of diabetic nerves, prominent microangiopathy was observed, as evidenced by reduced capillary luminal area, increased capillary basement membrane thickness and increased proportion of fibrin(+) blood vessels. Furthermore, capillary basement membrane thickness and the proportion of fibrin(+) blood vessels were correlated with small myelinated fiber density in diabetic nerves. In diabetic nerves, there was also significant macrophage and T cell infiltration, and cluster of differentiation 40 (CD40) expression was increased. The molecular alterations observed were upregulation of hypoxia-inducible factor-1α (HIF-1α), mitogen-activated protein kinase-activated protein kinase 2 (MK2; MAPKAPK2) and phosphatase and tensin homolog (PTEN). In addition, HIF-1α was correlated with small myelinated fiber density and capillary luminal area, while both MK2 and PTEN were correlated with capillary basement membrane thickness. The molecular cascades were further demonstrated and replicated in a cell model of microangiopathy on human umbilical vein endothelial cells (HUVECs) exposed to high-glucose medium by silencing of CD40, PTEN and HIF-1α in HUVECs using shRNA. These data clarified the hierarchy of the molecular cascades, i.e. upregulation of CD40 leading to HIF-1α expression in endothelium and nerve fibers. In conclusion, this study revealed the association of microangiopathy, thrombosis and inflammatory infiltrates with nerve degeneration in diabetic nerves, demonstrating that CD40 is a key molecule for the upregulation of HIF-1α and PTEN underlying the severity of microangiopathy., Summary: This study provides a new therapeutic strategy for diabetic neuropathy, by demonstrating CD40 as a key mediator of microangiopathy leading to HIF-1α expression in endothelial cells.

Gran variedad de lesiones atingen a los nervios perifericos, derivadas de enfermedades adquiridas o degenerativas congenitas que afectan la parte central del sistema nervioso y que ocasionan perdida de funciones sensoriomotoras. El objetivo de ese trabajo fue realizar un estudio experimental estereologico axonal post neurorrafias termino-lateral o latero-lateral para comparar densidad de volumen de axones, endoneuro y vaina de mielina (asi como masa muscular) en nervios fibular y tibial, con union de contacto entre 0,25 cm y 0,50 cm. Tras la aprobacion del comite de etica, fueran utilizados 20 ratones machos de la raza Wistar divididos en cuatro grupos de 5 ratones cada uno (G1= Neurorrafia termino lateral; G2= Neurorrafia latero lateral de 0,25 cm; G3= Neurorrafia latero lateral de 0,50 cm y G4= Control). Posteriormente, fragmentos de los nervios tibiales y fibulares fueron procesados para estudios histologicos y estereologicos. En el estudio experimental estereologico comparativo entre neurorrafias termino-lateral y latero-lateral, la densidad de volumen de axones, endoneuro y vaina de mielina de nervios tibial y fibular y tambien la masa muscular post quirurgica se mantuvo equitativa, independientemente del area de union de contacto. Podemos inferir como opciones de reparacion quirurgica, que el tratamiento de la neurorrafia termino-lateral y latero-lateral previnen la atrofia de placa motora, independiente de la distancia entre los munones nerviosos.

Heterotopic ossification (HO) is the process of bone formation at a nonskeletal site. Recently, we showed that the earliest steps occur in sensory nerves. We now extend these studies by identifying unique osteogenic progenitors within the endoneurial compartment of sensory nerves. We asked: (1) What is the nature of the osteoprogenitor in the endoneurium of peripheral nerves? (2) How do osteoprogenitors travel from the nerve to the site of new bone formation? HO was induced by intramuscular injection of Ad5BMP-2-transduced cells in mice. Osteoprogenitors were identified through immunohistochemistry and then quantified and further characterized by fluorescence-activated cell sorting and immunocytochemistry. The kinetics of the appearance of markers of extravasation was determined by quantitative reverse transcription-polymerase chain reaction. In each experiment mice were injected with bone morphogenetic protein-2 (BMP-2)-producing cells (experimental) or with cells transduced with empty vector or, in some cases, a group receiving no injection (control). Induction of HO leads to the expression, within 24 hours, of osteoblast-specific transcription factors in cells in the endoneurium followed by their coordinate disappearance from the nerve at 48 hours. They reappear in blood also at 48 hours after induction. During vessel entrance they begin to express the tight junction molecule, claudin 5. The cells expressing both the osteoblast-specific transcription factor, osterix, as well as claudin 5, then disappear from circulation at approximately 3 to 4 days by extravasation into the site of new bone formation. These endoneurial osteoprogenitors express neural markers PDGFRα, musashi-1, and the low-affinity nerve growth factor receptor p75(NTR) as well as the endothelial marker Tie-2. In a key experiment, cells that were obtained from mice that were injected with cells transduced with an empty vector, at 2 days after injection, contained 0.83% (SD, 0.07; 95% confidence interval [CI], 0.59–1.05) cells expressing claudin 5. However, cells that were obtained from mice 2 days after injection of BMP-2-producing cells contained 4.5% cells expressing claudin 5 (SD, 0.72%; 95% CI, 2.01–6.94; p

Inflammatory neuropathies encompass groups of heterogeneous disorders characterized by pathogenic immune-mediated hematogenous leukocyte infiltration of peripheral nerves, nerve roots or both, with resultant demyelination or axonal degeneration or both. Inflammatory neuropathies may be divided into three major disease categories: Guillain-Barré syndrome (particularly the acute inflammatory demyelinating polyradiculoneuropathy variant), Chronic inflammatory demyelinating polyradiculoneuropathy and nonsystemic vasculitic neuropathy (or peripheral nerve vasculitis). Despite major advances in molecular biology, pathology and genetics, the pathogenesis of these disorders remains elusive. There is insufficient knowledge on the mechanisms of hematogenous leukocyte trafficking into the peripheral nervous system to guide the development of specific molecular therapies for immune-mediated inflammatory neuropathies compared to disorders such as psoriasis, inflammatory bowel disease, rheumatoid arthritis or multiple sclerosis. The recent isolation and characterization of human endoneurial endothelial cells that form the blood-nerve barrier provides an opportunity to elucidate leukocyte-endothelial cell interactions critical to the pathogenesis of inflammatory neuropathies at the interface between the systemic circulation and peripheral nerve endoneurium. This review discusses our current knowledge of the classic pathological features of inflammatory neuropathies, attempts at molecular classification and genetic determinants, the utilization of in vitro and in vivo animal models to determine pathogenic mechanisms at the interface between the systemic circulation and the peripheral nervous system relevant to these disorders and prospects for future potential molecular pathology biomarkers and targets for specific therapeutic intervention.

The mechanical characteristics of ultrastructures of rat sciatic nerves were investigated through animal experiments and finite element analyses. A custom-designed dynamic testing apparatus was used to conduct in vitro transverse compression experiments on the nerves. The optical coherence tomography (OCT) was utilized to record the cross-sectional images of nerve during the dynamic testing. Two-dimensional finite element models of the nerves were built based on their OCT images. A hyper-viscoelastic model was employed to describe the elastic and stress relaxation response of each ultrastructure of the nerve, namely the endoneurium, the perineurium and the epineurium. The first-order Ogden model was employed to describe the elasticity of each ultrastructure and a generalized Maxwell model for the relaxation. The inverse finite element analysis was used to estimate the material parameters of the ultrastructures. The results show the instantaneous shear modulus of the ultrastructures in decreasing order is perineurium, endoneurium, and epineurium. The FE model combined with the first-order Ogden model and the second-order Prony series is good enough for describing the compress-and-hold response of the nerve ultrastructures. The integration of OCT and the nonlinear finite element modeling may be applicable to study the viscoelasticity of peripheral nerve down to the ultrastructural level.

We studied the effect of transplantation of neural crest-derived multipotent stem cells (NC-MSCs) obtained from vibrissa germs on regeneration of the injured (transected) sciatic nerve in adult mice (strain FVB). After transplantation of the cells into the injured region, regeneration of the severed nerve was intensified, as compared with that in mice with no implantation. The intensity of vascularization and renewal of the endoneurium also increased. The density of nerve fibers in the distal part of the injured nerve in mice after transplantation of NC-MSCs (10522.8 ± 1044.0 mm–2) was significantly higher than that in mice with nerve injury but without transplantation (8409.5 ± 739.5 mm–2). Possible mechanisms of acceleration of regeneration of the injured peripheral nerve under conditions of transplantation of stem cells are discussed.

Key points Conduction in myelinated axons involves substantial ion movements that must be reversed to restore homeostasis. The pathway taken by sodium ions returning to their original location and the potential osmotic consequences are currently unknown. We report striking morphological changes in axons following sustained impulse conduction that appear to result from osmosis and to indicate accumulation of ions in the periaxonal space followed by their release at the paranode. We conclude that the morphological changes illustrate a hitherto unrecognized part of normal axonal physiology that may also indicate the return pathway for the sodium ions involved in impulse formation. Abstract Myelinated axons can conduct sustained trains of impulses at high frequency, but this involves substantial ion movements that must be reversed to restore homeostasis. Little attention has been paid to the potential osmotic consequences of the ion movements or to the pathway taken by sodium ions returning to their original endoneurial location, given that the axolemmal Na+–K+-ATPase extrudes these ions into the periaxonal space beneath the myelin rather than into the endoneurium. Serial confocal imaging of fluorescent axons conducting at sustained physiological frequencies in vivo has revealed surprising morphological changes that may illuminate these problems. Saphenous nerves and spinal roots of anaesthetized transgenic mice expressing axoplasmic yellow fluorescent protein were stimulated electrically or pharmacologically (veratridine). Within 2 h, the axon herniated on one or both sides of the nodal membrane, displacing the paranodal myelin and widening the nodal gap. The herniated axoplasm became directed back towards the internode, forming a ‘cap’ up to 30 μm long. Concurrently, the fluid in the expanded periaxonal space accumulated into droplets that appeared to travel to the paranode, where they escaped. No such alterations occurred in axons treated with sodium channel or Na+–K+-ATPase inhibitors. Remarkably, impulse conduction continued throughout, and all these changes reversed spontaneously over hours or days. The morphological changes were verified ultrastructurally, and occurred in virtually all myelinated axons. The findings appear to reveal an overlooked part of the physiological repertoire of nerve fibres, and here they are interpreted in terms of osmotic changes that may illuminate the pathway by which sodium ions return to the endoneurial space after they have entered the axon during impulse conduction.

Severe edema in the endoneurium can occur after non-freezing cold injury to the peripheral nerve, which suggests damage to the blood-nerve barrier. To determine the effects of cold injury on the blood-nerve barrier, the sciatic nerve on one side of Wistar rats was treated with low temperatures (3-5°C) for 2 hours. The contralateral sciatic nerve was used as a control. We assessed changes in the nerves using Evans blue as a fluid tracer and morphological methods. Excess fluid was found in the endoneurium 1 day after cold injury, though the tight junctions between cells remained closed. From 3 to 5 days after the cold injury, the fluid was still present, but the tight junctions were open. Less tracer leakage was found from 3 to 5 days after the cold injury compared with 1 day after injury. The cold injury resulted in a breakdown of the blood-nerve barrier function, which caused endoneurial edema. However, during the early period, the breakdown of the blood-nerve barrier did not include the opening of tight junctions, but was due to other factors. Excessive fluid volume produced a large increase in the endoneurial fluid pressure, prevented liquid penetration into the endoneurium from the microvasculature. These results suggest that drug treatment to patients with cold injuries should be administered during the early period after injury because it may be more difficult for the drug to reach the injury site through the microcirculation after the tissue fluid pressure becomes elevated.

In 1882, von Recklinghausen described a group of patients with multiple tumors arising from the ‘endoneurium' of peripheral nerves, and called them ‘neurofibromas'. The term von Recklinghausen disease was used up to the end of the 20th century, when the gene of neurofibromatosis (NF1) was cloned on chromosome 17q11.2. The gene product is a cytoplasmic protein termed neurofibromin, regulating proliferation and maturation of both glial and neuronal progenitors during embryogenesis. Loss of neurofibromin function determines the hyperactivation of the proto-oncogene RAS, leading to an increased risk of tumor formation, predominantly affecting the skin, bone and the nervous system. NF1 is clinically and genetically distinct from neurofibromatosis type 2, characterized by bilateral vestibular schwannomas and other nervous system tumors. An increased incidence of central precocious puberty, diencephalic syndrome, GH deficiency and GH hypersecretion has been described in NF1 children. These conditions are commonly complications of optic pathway gliomas (OPG) involving the hypothalamic and sellar region. Nevertheless, these endocrine disorders have been observed also in children without evidence of OPG at magnetic resonance imaging. Clinical and laboratory follow-up is crucial in all children with NF1, particularly in those with an OPG, aiming at the early identification of signs suggestive of secondary endocrine alterations.

Peripheral nerve research as well as nerve repair simulation has relied heavily on the rat animal model, more specifically on the rat sciatic nerve.1 As the use of animals in experiments and training has received much criticism from animal rights activists and society at large, the field of surgical simulation is currently emerging. In microsurgery, high-fidelity Silastic models, animal parts such as chicken thighs or wings, and cadaveric specimens have been used. Based on the available experience with Thiel embalmed cadaveric tissue in simulation,2–4 we experimented with Thiel embalmed peripheral nerves for the purpose of microsurgical skill training. We used median, ulnar, and tibial nerves from cadavers that had been used for anatomic and surgical training and had not touched the peripheral nerve tissue. The donors had previously consented to tissue utilization in postmortem research. The tissues originated from cadavers prepared with the embalming method described by Thiel.5 This technique preserves texture, volume, color, and shape of the body as perfect as possible, with the advantage of avoiding decay observed with fresh cadaveric specimens. There is no shrinking or soaking of the soft tissues. Thirteen nerve sections measuring 5 cm eachwere prepared on a foam board. Needles (25 G) are used to fix the nerves to the foam board. A blue background was used for the exercise, as it improves contrast. An operating microscope (Opmi Pico, Carl Zeiss, Oberkochen, German) at 10 magnification was used for all microneurorrhaphies. Under magnification, the nerves were crushed in the midsection to simulate an injured nerve. The participants transected the nerve using a 15-blade scalpel, and trimmed the damagednerve tissue. The two endswere inspected for the fascicular architecture and oriented appropriately for the repair. The epineurium was then gently reflected back and the proud fascicles trimmed. Nylon 8–0 sutures were used to perform a simple epineural repair, starting with the 0and 180-degree orientation sutures and then filling in the required sutures to obtain a well-oriented microneurorrhaphy. Under magnification of the operative microscope, we found the Thiel nerve tissue to show a slight gray-brown discoloration with an epineural layer that was hydrophilic, giving the impression of edematous tissue (►Fig. 1). This thicker-than-normal epineural layer, however, offers adequate support for manipulation. Unfortunately, the cadaveric nature of themodel precludes the use of the vasa nervorum,which are not visible, for adequate orientation of the nerve. Upon transection of the nerve, it can be observed that the fascicles arewell preserved and bound byfirm endoneurium and perineurium which have not undergone the same edema as the epineurium (►Fig. 1). Despite therebeing no immediate herniation of nerve fascicles upon transection, the fascicles have a tendency to bemorehygroscopic, and by the end of the neurorrhaphy, one can observe some protrusion of fascicles in between suture. The fascicular pattern is easily identifiable and permits good alignment of the nerve before suturing. Thirteen volunteer plastic surgery, otolaryngology, and orthopedics residents utilized themodel once each, andfilled out a postsimulation survey. The results were graded on a five-point Likert scale (strongly agree, disagree, neither agree nor disagree, agree, strongly agree). A question regarding the frequency participants would use the laboratory with answers graded in five categories was also asked. The contents of the postsimulation survey are presented in ►Table 1. Descriptive statistics are presented for the results of the survey questions. All participants (100.0%) agreed that they would use themodule at least twice a year,with 53.9% (seven residents) stating theywoulduse itmore than once amonth, 38.5% (five residents) once amonth, and7.7% (one resident) twice a year. The rapid development of microsurgery over the last three decades has been echoed by the development of several simulation models for the teaching and honing of microsurgical skills. Free flaps are routine procedures in most plastic surgery centers, and residents have ample opportunity to participate and perform in these procedures. As a

In PNAS, Kagiava et al. (1) report their rescue of the X-linked form of Charcot–Marie–Tooth disease (CMT1X) in mice, through the use of a single intrathecal injection with a lentiviral vector. The vector expresses the gap junction beta 1 ( GJB1 ) gene and its encoded protein connexin32 (Cx32), expressed from a myelin-specific promoter from the myelin protein zero (MPZ) gene. The mice are Cx32-null animals (2), and therefore lack Cx32. Injecting the vector into the subarachnoid space permitted the virus access to the endoneurium of multiple spinal nerves because the dura mater surrounding the spinal cord directly merges with epineurial connective tissue layers from the proximal end of peripheral nerves. Therefore, there is continuity between the subarachnoid space and endoneurial space. The MPZ promoter is only expressed by myelinating Schwann cells, providing tissue specificity to the study. Lentiviruses are incorporated into target cell genomes, where they can provide prolonged expression of the transduced gene. Taken together, these features certainly contribute to the encouraging results reported by Kagiava et al. (1). Specifically, the authors demonstrated robust expression of the vector in Schwann cells with improvement of the neuropathy at all levels in the mice and with little evidence of toxicity or inflammation. Using a similar vector expressing the reporter EGFP, they demonstrated transduction of over 50% of all Schwann cells in sciatic nerve and similar levels in other sites, including the femoral nerve, dorsal root ganglia (DRG), and ventral roots. Transduced Schwann cells were detected as far away as the trigeminal nerve. Moreover, expression rates increased significantly between 2 and 16 wk postinjection. Results with the GJB1 vector were just as impressive. Cx32 was correctly targeted to noncompact areas of myelin, such as paranodes and Schmidt–Lanterman incisures. Treated mice improved by behavioral and physiological … [↵][1]1Email: michael-shy{at}uiowa.edu. [1]: #xref-corresp-1-1