Structure and barrier functions of the perineurium and its relationship with associated sensory corpuscles: A review.

Peripheral nerves are provided with a blood-nerve barrier which prevents the invasion of harmful substances and pathogens, and also regulates metabolic and ionic homeostasis within nerve fascicles. The barrier functions are attributed to both the concentric layer of flattened cells in the perineurium and blood vessels running in the endoneurium. The perineurial cells develop continuous tight junctions as a diffusion barrier. In order to take up a predominant nutrient, glucose, the perineurium as well as endoneurial capillaries expresses GLUT1, a glucose transporter. An axon-Schwann cell complex within peripheral nerves utilizes glucose as a major energy source via the GLUT1, as does the brain. Under conditions of a reduced utilization of glucose, only the perineurial cells can transfer other nutrients, namely monocarboxylates such as ketone bodies and lactate via MCT1. Thus, MCT1 colocalizes with GLUT1 in the perineurium but not in endoneurial capillaries. To identify the cellular origins of the nerve sheath, marker proteins such as glial specific S100 protein, GLUT1, endoneurial CD34, and EMA (epithelial membrane antigen) are useful. Immunohistochemical findings for these markers are reviewed in this paper, focusing on the perineurium and endoneurium and their derivatives, Pacinian and Meissner corpuscles. Growing evidence throws light on the critical involvement of the nerve sheaths in the development, maintenance, and diseases of peripheral nerves.

Flow-Through Arterialized Posterior Interosseous Nerve Grafts for Digital Neurovascular Bundle Defects: Anatomical Study.

BACKGROUND: Digital neurovascular bundle defects are often encountered during crush or avulsion injuries and require complex reconstruction. Use of an arterialized nerve graft (neurovascular graft) serving both as an interpositional arterial conduit and as a nerve graft could be a reconstructive option in these cases. In this anatomical study, the authors aimed to describe a neurovascular graft of the posterior interosseous nerve and a branch of the anterior interosseous artery for neurovascular bundle reconstruction of the fingers. METHODS: Eighteen forearms were injected with red latex in order to collect the anatomical characteristics of the posterior interosseous nerve and the artery running near it. RESULTS: In all cases, the posterior interosseous nerve was followed by a branch of the anterior interosseous artery: the distal dorsal branch of the anterior interosseous nerve. The origin of this artery was proximal to the radiocarpal joint, at an average of 56.5 ± 11.1 mm. The proximal and distal diameters of the branch of the anterior interosseous artery were 1.6 ± 0.2 and 1.1 ± 0.2 mm, respectively. The proximal and distal diameters of the posterior interosseous nerve were 1.2 ± 0.3 mm and 1.1 ± 0.3 mm, respectively. CONCLUSIONS: These results show that a potential free neurovascular graft using the posterior interosseous nerve as nerve graft and the anterior interosseous artery as an arterial bypass to reconstruct both the nerve and arterial tree of the finger could be a useful approach. The authors speculate that this graft could be used to reconstruct the neurovascular bundle of amputated or devascularized digits.

Blood-Nerve Barrier (BNB) Pathology in Diabetic Peripheral Neuropathy and In Vitro Human BNB Model.

In diabetic peripheral neuropathy (DPN), metabolic disorder by hyperglycemia progresses in peripheral nerves. In addition to the direct damage to peripheral neural axons, the homeostatic mechanism of peripheral nerves is disrupted by dysfunction of the blood-nerve barrier (BNB) and Schwann cells. The disruption of the BNB, which is a crucial factor in DPN development and exacerbation, causes axonal degeneration via various pathways. Although many reports revealed that hyperglycemia and other important factors, such as dyslipidemia-induced dysfunction of Schwann cells, contributed to DPN, the molecular mechanisms underlying BNB disruption have not been sufficiently elucidated, mainly because of the lack of in vitro studies owing to difficulties in establishing human cell lines from vascular endothelial cells and pericytes that form the BNB. We have developed, for the first time, temperature-sensitive immortalized cell lines of vascular endothelial cells and pericytes originating from the BNB of human sciatic nerves, and we have elucidated the disruption to the BNB mainly in response to advanced glycation end products in DPN. Recently, we succeeded in developing an in vitro BNB model to reflect the anatomical characteristics of the BNB using cell sheet engineering, and we established immortalized cell lines originating from the human BNB. In this article, we review the pathologic evidence of the pathology of DPN in terms of BNB disruption, and we introduce the current in vitro BNB models.

A rapid, nondestructive method for vascular network visualization.

The quantitative analysis of blood vessel networks is an important component in many animal models of disease. We describe a nondestructive technique for blood vessel imaging that visualizes in situ vasculature in harvested tissues. The method allows for further analysis of the same tissues with histology and other methods that can be performed on fixed tissue. Consequently, it can easily be incorporated upstream to analysis methods to augment these with a three-dimensional reconstruction of the vascular network in the tissues to be analyzed. The method combines iodine-enhanced micro-computed tomography with a deep learning algorithm to segment vasculature within tissues. The procedure is relatively simple and can provide insight into complex changes in the vascular structure in the tissues.

Differential clinicopathologic features of EGPA-associated neuropathy with and without ANCA.

OBJECTIVE: To investigate the clinicopathologic features of eosinophilic granulomatosis with polyangiitis (EGPA)-associated neuropathy with a focus on the presence or absence of anti-neutrophil cytoplasmic antibodies (ANCAs). METHODS: We examined the clinical features and pathologic findings of sural nerve biopsy specimens from 82 patients with EGPA-associated neuropathy. Of these patients, 32.9% were myeloperoxidase (MPO)-ANCA positive, and 67.1% were MPO-ANCA negative. PR3-ANCA was negative in all of 78 examined patients. RESULTS: Upper limb symptoms were more frequently reported as initial neuropathic manifestations in the MPO-ANCA-positive group than in the MPO-ANCA-negative group (44.4% vs 14.6%, p < 0.01). The serum levels of C-reactive protein were significantly higher in the MPO-ANCA-positive group than in the MPO-ANCA-negative group (p < 0.05). Sural nerve biopsy specimens showed findings suggestive of vasculitis (i.e., destruction of vascular structures) in epineurial vessels; these results were seen more frequently in the MPO-ANCA-positive group than in the MPO-ANCA-negative group (p < 0.0001). Conversely, the numbers of eosinophils in the lumen of the epineurial vessels (p < 0.01) and epineurial vessels occluded by intraluminal eosinophils (p < 0.05) were higher in the MPO-ANCA-negative group than in the MPO-ANCA-positive group. Furthermore, the incidence of eosinophil infiltration in the endoneurium was higher in the MPO-ANCA-negative group than in the MPO-ANCA-positive group (p < 0.01). CONCLUSIONS: This study suggests that the pathogenesis of EGPA comprises at least 2 distinct mechanisms: ANCA-associated vasculitis resulting in ischemic effects and inflammation, which is prominent in MPO-ANCA-positive patients, and eosinophil-associated vascular occlusion leading to ischemia and eosinophil-associated tissue damage, which is conspicuous in MPO-ANCA-negative patients.

The mouse olfactory peduncle 4: Development of synapses, perineuronal nets, and capillaries.

Olfaction is critical for survival in neonatal mammals. However, little is known about the neural substrate for this ability as few studies of synaptic development in several olfactory processing regions have been reported. Odor information detected in the nasal cavity is first processed by the olfactory bulb and then sent via the lateral olfactory tract to a series of olfactory cortical areas. The first of these, the anterior olfactory nucleus pars principalis (AONpP), is a simple, two layered cortex with an outer plexiform and inner cell zone (Layers 1 and 2, respectively). Five sets of studies examined age-related changes in the AONpP. First, immunocytochemistry for glutamatergic (VGlut1 and VGlut2) and GABAergic (VGAT) synapses demonstrated that overall synaptic patterns remained uniform with age. The second set quantified synaptic development with electron microscopy and found different developmental patterns between Layers 1 and 2. As many of the interhemispheric connections in the olfactory system arise from AONpP, the third set examined the development of crossed projections using anterograde tracers and electron microscopy to explore the maturation of this pathway. A fourth study examined ontogenetic changes in immunostaining for the proteoglycans aggrecan and brevican, markers of mesh-like extracellular structures known as perineuronal nets whose maturation is associated with the end of early critical periods of synaptogenesis. A final study found no age-related changes in the density of vasculature in the peduncle from P5 to P30. This work is among the first to examine early postnatal changes in this initial cortical region of the olfactory system.

Synergistic effects of dual-presenting VEGF- and BDNF-mimetic peptide epitopes from self-assembling peptide hydrogels on peripheral nerve regeneration.

The crosstalk between vascularization and nerve regeneration in the peripheral nervous system has recently been suggested to play an important role in the treatment of peripheral nerve injury. Regenerative strategies via synergistic delivery of multiple biochemical cues have received growing attention, especially the combination of pro-angiogenic factors and neurotrophic factors. Here we developed a self-assembling peptide nanofiber hydrogel dual-functionalized with vascular endothelial growth factor (VEGF)- and brain-derived neurotrophic factor (BDNF)-mimetic peptide epitopes for peripheral nerve reconstruction. It could simultaneously present VEGF- and BDNF-mimetic peptide epitopes and provides a three-dimensional (3D) neurovascular microenvironment for endothelial cell and neural cell growth. In vitro cellular experiments showed that the functionalized peptide hydrogel scaffold effectively promoted the pro-myelination of Schwann cell, as well as the adhesion and proliferation of endothelial cell compared with scaffolds presenting VEGF- or BDNF-mimetic peptide epitope alone. When implanted in a rat model to bridge a critical-size sciatic nerve gap in vivo, the functionalized peptide hydrogel significantly improved the number of newly formed blood vessels, the density of regenerating axons, the morphometric analysis of the regenerated muscles and the electrophysiological findings, indicating the synergistic effect of the two bioactive motifs on peripheral nerve regeneration. Collectively, constructing an artificial neurovascular microenvironment in the lesion area by using the functionalized self-assembling peptide nanofiber hydrogel may have a great potential for promoting nerve tissue engineering and regeneration in other tissues.

3D-printed nerve conduit with vascular networks to promote peripheral nerve regeneration.

Peripheral nerve regeneration remains a challenge in tissue engineering and regenerative medicine. However, the existing approaches have limited regenerative capability. 3D-printed nerve conduits with well-defined properties are potent tools to facilitate peripheral nerve regeneration after injuries. Meanwhile, the vascular networks within the constructs can promote the exchange of oxygen, neurotrophic factors, and removal of waste products, thereby providing an advantageous microenvironment for tissue regeneration. It will be an interesting approach to integrate 3D-printed nerve conduit with vascular networks for the guidance of regenerated nerves. We hypothesize that 3D-printed vascularized nerve conduit will be an effective platform to promote nerve regeneration and functional restoration.

Three-dimensional reconstruction of internal fascicles and microvascular structures of human peripheral nerves.

Biofabricated nanostructured and microstructured scaffolds have exhibited great potential for nerve tissue regeneration and functional restoration, and prevascularization and biotransportation within 3D fascicle structures are critical. Unfortunately, an ideal internal fascicle and microvascular model of human peripheral nerves is lacking. In this study, we used microcomputed tomography (microCT) to acquire high-resolution images of the human sciatic nerve. We propose a novel deep-learning network technique, called ResNetH3D-Unet, to segment fascicles and microvascular structures. We reconstructed 3D intraneural fascicles and microvascular topography to quantify the fascicle volume ratio (FVR), microvascular volume ratio (MVR), microvascular to fascicle volume ratio (MFVR), fascicle surface area to volume ratio (FSAVR), and microvascular surface area to volume ratio (MSAVR) of human samples. The frequency distributions of the fascicle diameter, microvascular diameter, and fascicle-to-microvasculature distance were analyzed. The obtained microCT analysis and reconstruction provided high-resolution microstructures of human peripheral nerves. Our proposed ResNetH3D-Unet method for fascicle and microvasculature segmentation yielded a mean intersection over union (IOU) of 92.1% (approximately 5% higher than the U-net IOU). The 3D reconstructed model showed that the internal microvasculature runs longitudinally within the internal epineurium and connects to the external vasculature at some points. Analysis of the 3D data indicated a 48.2 ± 3% FVR, 23.7 ± 1.8% MVR, 4.9 ± 0.5% MFVR, 7.26 ± 2.58 mm-1 FSAVR, and 1.52 ± 0.52 mm-1 MSAVR. A fascicle diameter of 0.98 mm, microvascular diameter of 0.125 mm, and microvasculature-to-fascicle distance of 0.196 mm were most frequent. This study provides fundamental data and structural references for designing bionic scaffolding constructs with 3D microvascular and fascicle distributions.

Imaging of Microhemodynamics in Peripheral Nerves by Contact Endoscope.

BACKGROUND: Entrapment neuropathies include a wide field of locations. In most cases, the microsurgical decompression is still the therapy of choice. However, the role of venous stasis and ischemia is still discussed controversially. Here the authors evaluated the visualization of microvessels and the microperfusion at peripheral nerves with a contact endoscope during the surgical decompression for the first time. METHODS: Eight patients were subjected to endoscopic or endoscopically assisted peripheral nerve decompression. In 3 patients with nerve tumors, the tumor carrying nerve was inspected endoscopically proximal and distal to the tumor site before and after resection. Microcirculation was assessed by a contact endoscope, allowing a 150-fold magnification, at superficial areas proximal and distal to the compression site. The electronically stored records were analyzed retrospectively using image processing software. Vessel diameter, red blood cell velocity, and blood flow, before and after decompression, were extracted. RESULTS: The contact endoscope was easy to handle intraoperatively without problems. All minimally invasive procedures were performed without complications. In the offline computer-assisted analysis, single arterioles and veins were visualized showing decreased red blood cell velocity prior to decompression. After surgical treatment, a statistically significant increase of blood flow was observed. CONCLUSIONS: Basically, the application of a contact endoscope for visualization of peripheral nerves' microcirculation is feasible. The observed effect of increased blood flow after decompression should be compared with the clinical outcome in a further prospective randomized study.

Local blood flow in peripheral nerves and their ganglia: Resurrecting key ideas around its measurement and significance.

Over 3 decades ago, seminal work by Phillip Low and colleagues established exquisite physiology around the measurement of nerve blood flow (NBF). Although not widely explored recently, its connection to the clinic has awaited human methodology. While human studies have not achieved a convincing level of rigour, newer imaging technologies are offering early information. The peripheral nerve trunk has parallel blood flow compartments that include epineurial flow dominated by arteriovenous shunts and downstream endoneurial blood flow (EBF). NBF and EBF have lower values than central nervous system blood flow, lack autoregulation yet have sympathetic and peptidergic neurovascular control. Contrary to expectation, injury to nerves is often associated with rises in NBF rather than ischemia, a finding of biological interest corroborated by human studies. Despite its potential importance, quantitative human measurements of EBF and NBF are not yet available. However, with development, careful NBF analysis may present new insights into nerve disorders. Muscle Nerve 57: 884-895, 2018.

Isoliquiritigenin reduces oxidative damage and alleviates mitochondrial impairment by SIRT1 activation in experimental diabetic neuropathy.

Sirtuin (SIRT1) inactivation underlies the pathogenesis of insulin resistance and hyperglycaemia-associated vascular complications, but its role in diabetic neuropathy (DN) has not been yet explored. We have evaluated hyperglycaemia-induced alteration of SIRT1 signalling and the effect of isoliquiritigenin (ILQ) on SIRT1-directed AMP kinase (AMPK) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) signalling in peripheral nerves of streptozotocin (STZ) (55 mg/kg, ip)-induced diabetic rats and in high glucose (30 mM)-exposed neuro2a (N2A) cells. Diabetic rats and high glucose-exposed N2A cells showed reduction in SIRT1 expression with consequent decline in mitochondrial biogenesis and autophagy. ILQ (10 & 20 mg/kg, po) administration to diabetic rats for 2 weeks and exposure to glucose-insulted N2A cells resulted in significant SIRT1 activation with concurrent increase in mitochondrial biogenesis and autophagy. ILQ administration also enhanced NAD+/NADH ratio in peripheral sciatic nerves which explains its possible SIRT1 modulatory effect. Functional and behavioural studies show beneficial effect of ILQ as it alleviated nerve conduction and nerve blood flow deficits in diabetic rats along with improvement in behavioural parameters (hyperalgesia and allodynia). ILQ treatment to N2A cells reduced high glucose-driven ROS production and mitochondrial membrane depolarization. Further, ILQ-mediated SIRT1 activation facilitated the Nrf2-directed antioxidant signalling. Overall, results from this study suggest that SIRT1 activation by ILQ mimic effects of calorie restriction, that is, PGC-1α-mediated mitochondrial biogenesis, FOXO3a mediated stress resistance and AMPK mediated autophagy effects to counteract the multiple manifestations in experimental DN.

Age-related morphological regression of myelinated fibers and capillary architecture of distal peripheral nerves in rats.

BACKGROUND: Regression of myelinated peripheral nerve fibers in the lower extremities contributes to sarcopenia and balance dysfunction in normal aging. This subclinical regression of myelinated fibers (MFs) is heavily influenced by alterations in microvasculature, though the mechanism underlying these age-related degenerative phenomena remains unclear. The aim of the present study was to examine age-related regressions in myelinated distal peripheral nerve fibers as well as capillary architecture in rats using both morphological and histochemical methods. RESULTS: MFs were categorized into tertiles of 'large', 'medium', and 'small' sizes based on the distribution of MF diameters. A two-way ANOVA was used to assess effects of fiber size (large/medium/small) and group (young/elderly) on myelin thickness, axon diameter, myelin perimeter, axon perimeter, and G-ratio (axon diameter/fiber diameter). Significant main effects were observed for both MF size and group with respect to all dimensions except for G-ratio. Values for fiber diameter (P < 0.01), myelin thickness (P < 0.01), axon diameter (P < 0.01), myelin perimeter (P < 0.01), and axon perimeter (P < 0.01) were significantly lower than those in the young group. Additionally, mean capillary diameter and number of microvascular branch points were significantly lower in the elderly group than in the young group. CONCLUSIONS: The present study demonstrated that spontaneous age-related regression predominantly occurs for all fiber sizes in the distal peripheral nerves and the capillary architecture. The results of the present study further suggest that both the distal MFs and capillaries in the peripheral nerve may simultaneously regress with aging.

Recent Strategies in Tissue Engineering for Guided Peripheral Nerve Regeneration.

The repair of large crushed or sectioned segments of peripheral nerves remains a challenge in regenerative medicine due to the complexity of the biological environment and the lack of proper biomaterials and architecture to foster reconstruction. Traditionally such reconstruction is only achieved by using fresh human tissue as a surrogate for the absence of the nerve. However, recent focus in the field has been on new polymer structures and specific biofunctionalization to achieve the goal of peripheral nerve regeneration by developing artificial nerve prostheses. This review presents various tested approaches as well their effectiveness for nerve regrowth and functional recovery.

Investigation of venous drainage patterns of rabbit peripheral nerves.

In this study, the venous drainage patterns of white New Zealand rabbits' peripheral nerves were examined in an effort to provide an animal model for studies focusing on the venous drainage of the healing nerves. Extremities of rabbits sacrificed via intraarterial lead oxide-gelatin solution, and thus had their peripheral bloods pushed out of the arteries and into the veins were dissected for the venous drainage of radial, median, ulnar, femoral, sciatic, tibial and fibular nerves. The observations revealed that white New Zealand rabbit was a feasible model due to its consistent venous anatomy draining the major nerves and accessibility and workability of them. Of those dissected, the most suitable set of nerves suitable for such studies seem to be the Median nerve of the anterior extremity, and Sciatic nerve of the posterior extremity (Fig. 12, Ref. 16). Text in PDF www.elis.sk. Text in PDF www.elis.sk.

Vastus lateralis vascularized nerve graft in facial nerve reconstruction: an anatomical cadaveric study and clinical implications.

BACKGROUND: The present study investigates the vascular anatomy of the vastus lateralis motor nerve (VLMN) to be used as a vascularized nerve graft in facial nerve reconstruction. We evaluated the maximum length of the nerve that can be included in the flap and its vascular pedicle. In addition, we discuss its adequacy for use in early reconstruction of the facial nerve both as ipsilateral facial nerve reconstruction and as cross-facial nerve graft. METHODS: Five fresh cadavers were used in this study. In all specimens, the VLMN and its vascular pedicle were dissected, photodocumented and measured using calipers. In addition, two vascularized VLMN were injected with a radiopaque contrast and underwent CT angiography and three dimensional reconstructions were scanned to illustrate the vascular supply of the nerve using OsiriX Software. RESULTS: The VLMN was divided into two divisions, an oblique proximal and a descending distal, in 70% of the dissections with a mean maximal length of 8.4 ± 4.5 cm for the oblique division and 15.03 ± 3.87 cm for the descending division. The length of the oblique division, when present, was shorter than the length of the descending branch in all specimens. The mean length of the pedicle was 2.93 ± 1.69 cm, and 3.27 ± 1.49 cm until crossing the oblique and the descending division of the nerve respectively. The mean caliber of the nerve was 2.4 ± 0.62 mm. Three-dimensional computed tomography angiography demonstrated perfusion throughout the entire VLMN by branches from the descending branch of the lateral femoral circumflex artery which ran parallel to the descending division of the VLMN. Additionally, we observed that technically it was possible to preserve the oblique branch of the VLMN. CONCLUSION: This study confirms that VLMN presents adequate anatomic features to be used as a vascularized nerve graft for facial nerve reconstruction in terms of length, pedicle, and caliber.