Diameter Of Myelinated Nerve Fibers Research Articles

Conventional histomorphometry and fast free of acrylamide clearing tissue (FACT) visualization of sciatic nerve in chicken (Gallus domesticus).

Histomorphometry and use of the fast free of acrylamide clearing tissue (FACT) protocol were studied on the sciatic nerve in chicken (Gallus domesticus). In the first part of the study, the sciatic nerves of 20 chickens of four age groups (7, 14, 26 and 40 days) were studied (n=5 birds per age class). Their sciatic nerve samples were stained with Hematoxylin and Eosin and Masson's trichrome and were histomorphometrically evaluated. In the second part of the study, FACT protocol was applied on the sciatic nerve of a 26 days old chicken. After clearing of 1.00 mm-thick sciatic nerve sections, they were immunolabelled using Hoechst for nuclei staining and recorded by a Z-stack motorized fluorescent microscope. In the conventional histo-morphometry, the epineurium, perineurium and endoneurium were thicker and the nerve bundle diameter was bigger in the left sciatic nerve of chicken of all age groups compared to the right sciatic nerve. On the contrary, the axon diameter and the myelinated nerve fiber diameter were bigger, the myelin sheath was thicker, the nodes of Ranvier intervals were higher and the density of myelinated nerve fibers was also higher in the right sciatic nerve compared to the left one. In conclusion, histomorphometric parameters in the left and right sciatic nerve during chicken growth were significantly different. Furthermore, the FACT protocol could be used for the 3D imaging of the chicken sciatic nerve and its immunostained evaluation.

Therapeutic efficacy of arginine-rich exenatide on diabetic neuropathy in rats

Diabetes mellitus is characterized by metabolic dysregulation associated with a number of health complications. More than 50% of patients with diabetes mellitus suffer from diabetic polyneuropathy, which involves the presence of peripheral nerve dysfunction symptoms. The aim of this study was to evaluate the potential of a new synthetic arginine-rich exendin-4 (Peptide D) in the treatment of complications caused by diabetes, including peripheral neuropathy, in rats. Diabetes was induced by administering streptozotocin (STZ). Three groups of diabetic rats were treated with Peptide D (0.1, 1, and 10 μg/kg). One group of diabetic rats was treated with Byetta® (1 μg/kg) for 80 days. Neuropathic pain development was assessed by tactile allodynia. STZ-treated rats showed an increased level of tactile allodynia unlike naïve animals. A histological study revealed that the diameter of the sciatic nerve fibers in STZ-treated rats was smaller than that of the naïve animals. An IHC study demonstrated decreased expression of myelin basic protein (MBP) in the sciatic nerve of diabetic rats compared to that in the naïve animals. Peptide D reduced the severity of tactile allodynia. This effect was more pronounced in the Peptide D treated groups than in the group treated with Byetta®. Peptide D and Byetta® treatment resulted in increased MBP expression in the sciatic nerve and increased diameter of myelinated nerve fibers. These findings suggest that poly-arginine peptides are promising agents for the treatment of peripheral polyneuropathies.

Testosterone propionate can promote effects of acellular nerve allograft‐seeded bone marrow mesenchymal stem cells on repairing canine sciatic nerve

Peripheral human nerves fail to regenerate across long tube implants (>2cm), and tissue-engineered nerve grafts represent a promising treatment alternative. The present study aims to investigate the testosterone propionate (TP) repair effect of acellular nerve allograft (ANA) seeded with allogeneic bone marrow mesenchymal stem cells (BMSCs) on 3-cm canine sciatic nerve defect. ANA cellularized with allogeneic BMSCs was implanted to the defect, and TP was injected into the lateral crus of the defected leg. The normal group, the autograft group, the ANA+BMSCs group, the ANA group, and the nongrafted group were used as control. Five months postoperatively, dogs in the TP+ANA+BMSCs group were capable of load bearing, normal walking, and skipping, the autograft group and the ANA+BMSCs group demonstrated nearly the same despite a slight limp. The compound muscle action potentials (CMAPs) on the injured side to the uninjured site in the TP+ANA+BMSCs group were significantly higher than that in the ANA+BMSCs group [CMAPs ratio at A: F(3, 20)=191.40; 0.02, CMAPs ratio at B: F(3, 20)=43.27; 0.01]. Masson trichrome staining revealed that in the TP+ANA+BMSCs group, both the diameter ratio of the myelinated nerve and the thickness ratio of regenerated myelin sheath were significantly larger than that in the other groups [the diameter of myelinated nerve fibers: F(3, 56)=13.45; P<.01, the thickness ratio of regenerated myelin sheath: F(3, 56)=51.25; P<.01]. In conclusion, TP could significantly increase the repairing effects of the ANA+BMSCs group, and their combination was able to repair 3-cm canine sciatic nerve defect. It therefore represents a promising therapeutic approach.

Effects of bone marrow mesenchymal stem cells transfected with Ang-1 gene on hyperoxia-induced optic nerve injury in neonatal mice.

Optic nerve injury triggered retinal ganglion cell (RGC) death and optic nerve atrophy lead to visual loss. Bone marrow mesenchymal stem cells (BMSCs) are stromal cells, capable of proliferating and differentiating into different types of tissues. This aims of this study is to investigate the role of BMSCs transfected with angiopoietin-1 (Ang-1) in optic nerve injury induced by hyperoxia in a neonatal mice model. Ang-1 overexpression vector was constructed and used to transfect BMSCs. Reverse transcription-quantitative polymerase chain reaction was performed to detect Ang-1 expression in BMSCs. The hyperoxia-induced optic nerve injury model was established. The optic nerves at 6-7 mm posterior to the eyeball were extracted, and were treated with luxol fast blue staining, immunohistochemistry, immunofluorescence, and transmission electron microscopy to examine the effects of Ang-1-modified BMSCs on optic nerve injury induced by hyperoxia. The mice in the Ang-1 + BMSCs and BMSCs groups showed remarkably improved myelin sheaths of nerve fibers compared to the hyperoxia saline group. The positive expression and integrated optic density of Ang-1 in the Ang-1 + BMSCs group were significantly higher compared to the air control, hyperoxia saline and BMSCs groups. The number and diameter of myelinated nerve fibers, the diameter of axons and the thickness of myelin sheath in the air control and Ang-1 + BMSCs groups were higher compared to the hyperoxia saline group. Our study provides evidence supporting that Ang-1-modified BMSCs may have preventive and therapeutic effects on hyperoxia-induced optic nerve injury in neonatal mice.

Chitosan conduit combined with hyaluronic acid prevent sciatic nerve scar in a rat model of peripheral nerve crush injury.

In the present study, the effects of hyaluronic acid (HA) combined with chitosan conduit on peripheral nerve scarring and regeneration were investigated in a rat model of peripheral nerve crush injury. A total of 60 Sprague-Dawley rats were randomly distributed into four groups (15 rats in each group), in which the nerve was either not treated (control group) or treated with chitosan conduit, hyaluronic acid, or chitosan conduit coupled with hyaluronic acid following clamp injury to the sciatic nerve. The surgical sites were evaluated by assessing the sciatic functional index, the degree of scar adhesions, the numbers of myelinated nerve fibers, the average diameter of myelinated nerve fibers and the myelin sheath thickness. Larger epineurial scar thickness was observed in the control groups compared with the treatment groups at 4, 8 and 12 weeks following surgery. There was no significant difference in scar adhesion among the four groups at 4 weeks following surgery. However, animals receiving chitosan coupled with HA demonstrated better neural recovery, as measured by reduced nerve adherence to surrounding tissues, less scar adhesion, increased number of axons, nerve fiber diameter and myelin thickness. In conclusion, the application of chitosan conduit combined with HA, to a certain extent, inhibited sciatic nerve extraneural scaring and adhesion, and promoted neural regeneration and recovery.

Neuroregenerative role of transplanted olfactory ensheathing cells in a model of sciatic nerve crush injury in rats: Histological study

Background: Olfactory ensheathing cells (OECs) are highly specialized glial cells that guide olfactory receptor axons from nasal mucosa to olfactory bulb. Olfactory ensheathing cells (OECs) are attractive candidates for transplantation-mediated repair of injured nervous system owing to their neuroregenerative properties.Aim of the work: To evaluate the neuroregenerative role of OECs in a model of sciatic nerve crush injury in rats.Materials and Methods: OECs were isolated from the olfactory mucosa of 15 male albino rats (100 gm). Thirty adult female albino rats (200-250 gm) were used and divided into three groups of 10 rats each. Group I (control group) underwent sham operation. Group II underwent crush injury of sciatic nerve. Group III underwent sciatic nerve crush injury then injected with single dose of 3×104 OECs at the lesion site. All rats were sacrificed after 3 weeks from the onset of the experiment.Results: Histological examination of sciatic nerves of group II rats showed discontinuity of nerve fibers with vacuolated axoplasm. OECs transplantation in group III revealed restoration of the normal histological architecture of the sciatic nerves. A significant decrease in the diameter of myelinated nerve fibers and myelin sheath thickness was recorded in group II compared to the control group. However, group III revealed a significant increase in the previous parameters compared to group II.Conclusions: Olfactory ensheathing cells (OECs) have neuroregenerative properties which might represent a new vision in human cell based therapy.

Reduced axonal diameter of peripheral nerve fibers in a mouse model of Rett syndrome

Rett syndrome (RTT) is a neurological disorder characterized by motor and cognitive impairment, autonomic dysfunction and a loss of purposeful hand skills. In the majority of cases, typical RTT is caused by de novo mutations in the X-linked gene, MECP2. Alterations in the structure and function of neurons within the central nervous system of RTT patients and Mecp2-null mouse models are well established. In contrast, few studies have investigated the effects of MeCP2-deficiency on peripheral nerves. In this study, we conducted detailed morphometric as well as functional analysis of the sciatic nerves of symptomatic adult female Mecp2+/− mice. We observed a significant reduction in the mean diameter of myelinated nerve fibers in Mecp2+/− mice. In myelinated fibers, mitochondrial densities per unit area of axoplasm were significantly altered in Mecp2+/− mice. However, conduction properties of the sciatic nerve of Mecp2 knockout mice were not different from control. These subtle changes in myelinated peripheral nerve fibers in heterozygous Mecp2 knockout mice could potentially explain some RTT phenotypes.

A comparative study of oculomotor, trochlear and abducens nerves in Arabian foals

We investigated the microscopic structure of transverse sections of the oculomotor, trochlear and abducens nerves of Arabian foals using stereological methods. Bilateral nerve pairs from 2-month-old female Arabian foals were analyzed. The tissues were embedded in plastic blocks, then 1 µm thick sections were cut and stained with osmium tetroxide and methylene blue-azure II. Stereology was performed using light microscopy. Morphometry showed that the right and left pairs of nerves were similar. The transverse sectional areas of the oculomotor, trochlear and abducens nerves were 1.93 ± 0.19 mm2, 0.32 ± 0.06 mm2 and 0.70 ± 0.08 mm2, respectively. The oculomotor nerve exhibited a significantly greater number of myelinated axons (16755 ± 1279) and trochlear (2656 ± 494) and the abducens nerves (4468 ± 447). The ratio of the axon diameter to myelinated nerve fiber diameter was 0.58, 0.55 and 0.55 for the oculomotor, trochlear and abducens nerves, respectively. Of the three nerves studied, the abducens nerve exhibited the greatest nerve fiber area, myelin area, nerve and axon diameters, and myelin thickness. The ratio of small myelinated nerve fibers was greatest in the oculomotor nerve.

Ursolic acid induces neural regeneration after sciatic nerve injury.

In this study, we aimed to explore the role of ursolic acid in the neural regeneration of the injured sciatic nerve. BALB/c mice were used to establish models of sciatic nerve injury through unilateral sciatic nerve complete transection and microscopic anastomosis at 0.5 cm below the ischial tube-rosity. The successfully generated model mice were treated with 10, 5, or 2.5 mg/kg ursolic acid via intraperitoneal injection. Enzyme-linked immunosorbent assay results showed that serum S100 protein expression level gradually increased at 1–4 weeks after sciatic nerve injury, and significantly decreased at 8 weeks. As such, ursolic acid has the capacity to significantly increase S100 protein expression levels. Real-time quantitative PCR showed that S100 mRNA expression in the L4–6 segments on the injury side was increased after ursolic acid treatment. In addition, the muscular mass index in the soleus muscle was also increased in mice treated with ursolic acid. Toluidine blue staining revealed that the quantity and average diameter of myelinated nerve fibers in the injured sciatic nerve were significantly increased after treatment with ursolic acid. 10 and 5 mg/kg of ursolic acid produced stronger effects than 2.5 mg/kg of ursolic acid. Our findings indicate that ursolic acid can dose-dependently increase S100 expression and promote neural regeneration in BALB/c mice following sciatic nerve injury.

The mechanism of astragaloside IV promoting sciatic nerve regeneration.

3-O-beta-D-xylopyranosyl-6-O-beta-D-glucopyranosyl-cycloastragenol (astragaloside IV), the main active component of the traditional Chinese medicine astragalus membranaceus, has been shown to be neuroprotective. This study investigated whether astragaloside IV could promote the repair of injured sciatic nerve. Denervated sciatic nerve of mice was subjected to anastomosis. The mice were intraperitoneally injected with 10, 5, 2.5 mg/kg astragaloside IV per day for 8 consecutive days. Western blot assay and real-time PCR results demonstrated that growth-associated protein-43 expression was upregulated in mouse spinal cord segments L4–6 after intervention with 10, 5, 2.5 mg/kg astragaloside IV per day in a dose-dependent manner. Luxol fast blue staining and electrophysiological detection suggested that astragaloside IV elevated the number and diameter of myelinated nerve fibers, and simultaneously increased motor nerve conduction velocity and action potential amplitude in the sciatic nerve of mice. These results indicated that astragaloside IV contributed to sciatic nerve regeneration and functional recovery in mice. The mechanism underlying this effect may be associated with the upregulation of growth-associated protein-43 expression.

Electric stimulation and decimeter wave therapy improve the recovery of injured sciatic nerves.

Drug treatment, electric stimulation and decimeter wave therapy have been shown to promote the repair and regeneration of the peripheral nerves at the injured site. This study prepared a Mackinnon's model of rat sciatic nerve compression. Electric stimulation was given immediately after neurolysis, and decimeter wave radiation was performed at 1 and 12 weeks post-operation. Histological observation revealed that intraoperative electric stimulation and decimeter wave therapy could improve the local blood circulation of repaired sites, alleviate hypoxia of compressed nerves, and lessen adhesion of compressed nerves, thereby decreasing the formation of new entrapments and enhancing compressed nerve regeneration through an improved microenvironment for regeneration. Immunohistochemical staining results revealed that intraoperative electric stimulation and decimeter wave could promote the expression of S-100 protein. Motor nerve conduction velocity and amplitude, the number and diameter of myelinated nerve fibers, and sciatic functional index were significantly increased in the treated rats. These results verified that intraoperative electric stimulation and decimeter wave therapy contributed to the regeneration and the recovery of the functions in the compressed nerves.

Simultaneous gradual lengthening of both proximal and distal nerve stumps for repair of peripheral nerve defect in rats

We investigated nerve regeneration following the repair of a segmental nerve defect induced by direct end-to-end neurorrhaphy after simultaneous gradual lengthening of both proximal and distal nerve stumps in rats. A 15-mm-long nerve segment was resected from the sciatic nerve of each rat. The proximal and distal nerve stumps, respectively, were directly lengthened at a rate of 1 mm/day using a custom-made external nerve-lengthening device. After being lengthened for 14 days, both nerve stumps were refreshed, and direct end-to-end neurorrhaphy was performed. For a control, 15-mm nerve grafting was performed immediately after nerve resection. Nerve regeneration was evaluated by motor nerve conduction velocity, muscle contraction force, and histological studies at 6, 8, and 14 weeks after initial nerve resection in both groups. As a result, at 8 and 14 weeks, the motor nerve conduction velocity was significantly higher in the nerve-lengthening group than in the autografting group. In addition, at 14 weeks, the tetanic force and wet weight of the gastrocnemius muscle were significantly higher in the nerve-lengthening group than in the autografting group. Histologically, the mean axonal diameter of myelinated nerve fibers and the total number of myelinated nerve fibers were also significantly higher in the nerve-lengthening group than in the autografting group for each evaluation period. It appears that the simultaneous gradual lengthening of both proximal and distal nerve stumps might have potential application in the repair of peripheral nerve defects.

The therapeutic effects of 4-methylcatechol, a stimulator of endogenous nerve growth factor synthesis, on experimental diabetic neuropathy in rats

We investigated therapeutic effects of 4-methylcatechol (4-MC), a non-amine catechol compound, on streptozotocin (STZ)-induced diabetic neuropathy in rats. 4-MC is one of the potent stimulators of endogenous nerve growth factor (NGF) synthesis both in vitro and in vivo. Diabetic rats showed a statistically significant reduction in motor nerve conduction velocity (MNCV), mean myelinated axon diameter, and NGF content in the sciatic nerve during the experimental period of 8 weeks. The 4-MC treatment started 4 weeks after the STZ injection resulted in significantly greater NGF content, faster MNCV, and larger mean myelinated nerve fiber diameter and axon diameter than in untreated diabetic rats. These findings suggest that a decreased NGF level in the diabetic sciatic nerves may be involved in the pathogenesis of diabetic neuropathy and that 4-MC treatment could be useful for diabetic neuropathy.

An animal model of chronic ischemic neuropathy with proliferative changes of nerve microvessel wall

In order to produce a model of ischemic neuropathy with neural microvascular alterations, sodium laurate was injected into a femoral artery and saline into the contralateral artery at the mid-thigh level in Sprague-Dawley rats aged 11 weeks. In view of the dose-related findings, 0.3 mg sodium laurate dissolved in 0.1 ml saline was used for the main experiment. The laurate-injected leg showed paresis during the experimental period. On day 1–7, various stages of Wallerian degeneration and acute microvascular changes were found. At 1 month, regenerating myelinated nerve fibers (MNFs) were found at the central or total fascicular area mainly in the distal tibial nerve. Morphometric analyses suggested that MNFs other than regenerating fibers are atrophic ones. The proliferative changes of nutrient microvascular walls were striking. The percent of closed epineurial microvessels was significantly larger on the laurate-injected sides and inversely associated with the diameter of MNFs. At 7 months, the attenuation of MNFs was more prominent and microvascular alterations were persistently observed. These pathological findings resemble those of chronic ischemic neuropathy including diabetic neuropathy, suggesting that this neuropathy model might provide some valuable and useful clues for clarifying the pathogenesis of chronic ischemic neuropathy.

Ultrastructural Changes With Age in the Human Superior Laryngeal Nerve

Electron-microscopic morphometric techniques were used to examine age-related changes in postmortem human superior laryngeal nerves obtained at autopsy (young adult, aged 20 to 30 years; old, 60 years and over). A statistically significant age-related loss of myelinated nerve fibers was detected (old, 7032 +/- 1572; young, 10,179 +/- 1969), representing a 31% decrease. Much of this loss occurred selectively in small myelinated fibers (1 to 2 microns) where there was an extensive (67%) and significant age-related fiber loss. A corresponding analysis of axonal diameter of myelinated nerve fibers similarly showed an extensive (67%) and statistically significant decrease in myelinated fibers with small axonal diameters (0 to 0.5 microns) in the old age group compared with the young adult age group. These findings may represent a significant histomorphologic correlate to the observed age-related sensorimotor dysfunction of the upper aerodigestive tract common in the elderly.

Ipsilateral and Cross-Over Elongation of the Motor Nerve by Nerve Grafting

In difficult reconstructions, ipsilateral or cross-over nerve grafting is sometimes necessary to achieve reinnervation and motor function. This experimental study in sheep was to answer the question of limitation of elongation of a motor nerve by grafting, the question of the optimal time for suturing the nerve graft to the muscle nerve, and the question of the successful application of this surgical technique in extremities. In 18 sheep, the vastus nerve was elongated by a saphenous nerve graft as long as possible up to 30 cm (step 1). In 10 animals the nerve graft was applied ipsilaterally, and in 8 animals it was used as a cross-over nerve graft to the contralateral limb. The time between nerve grafting and connection of the distal end of the nerve graft to the freshly cut rectus nerve supplying the rectus femoris muscle (step 2) was variable: 0, 3, 6, 9, and 12 months. In all animals, the final experiments (step 3) were performed 6 months after the last operation (step 2). Muscle force measurements in the rectus femoris muscle and quantitative analysis of the number and diameter of myelinated nerve fibers in cross sections of the nerve biopsies at different levels showed that elongation of a motor nerve by nerve grafting is principally not limited. The functional results were rather inhomogeneous and therefore unpredictable (ipsilateral group: maximum tetanic tension = 27 to 172 N; cross-over group: 0 to 227.5 N). Nevertheless, crossover nerve grafting is recommended for selected cases even in extremities. There was no correlation between the time interval between the two operations and the functional or morphologic results, although better functional results were obtained when the distal nerve suture (step 2) was performed some months after nerve grafting (step 1). A clear correlation was found only between the number of regenerated axons in the rectus nerve behind the second suture line and the muscle function.

Age-related reduction in 8th cervical ventral nerve root myelinated fiber diameters and numbers in man.

Reduction in the number of large myelinated nerve fibers in spinal nerve roots has been described previously. We observed a reduction in myelinated nerve fiber diameters which at least in part explains the apparent marked reduction in the number of large myelinated fibers with age.

An experimental study for analyzing nerve conduction velocity

Conduction velocities of so called A fibers in the bullfrog's sciatic-peroneal nerve were studied by means of a collision neurography in which a submaximal shock to the distal part of the nerve was used to block descending impulses from a supramaximal shock delivered to the proximal two parts of the same nerve respectively. The onset latency of the response to stimulation delivered to the proximal part was almost unchangeable within a certain range of the stimulus intensity of the distal part and fell into 3 classes, and then conduction velocities of so called A fibers were divided into 3 groups. These findings were in good agreement with those obtained by Erlanger and Gasser (1937) using monophasic recording. On the other hand, the distribution of the external diameter of myelinated nerve fibers examined was unimodal. It may depend on the change in threshold due to stimulation through fluid electrodes that the onset latency of the response of a nerve trunk was divided into 3 classes.

Peripheral nerve morphometry in stroke patients

Sural nerve biopsy specimens from affected and non-affected limbs of stroke patients were examined morphometrically. Two principle abnormalities of peripheral nerve were found in hemiparetic and hemiplegic limbs. First, the frequency of abnormal teased nerve fibers was significantly increased with abnormal internodes frequently “clustered” and showing a 50% or more reduction in myelin thickness. Second, the mean diameter of myelinated nerve fibers was reduced. These results suggest a primary atrophy of peripheral nerve fibers in the affected limbs of stroke patients with secondary demyelination. Possible aetiological factors include disuse, transynaptic degeneration, ischemia, pressure effect, and decreased axoplasmic flow. It would seem that the structural integrity of peripheral nerve is frequently compromised following a cerebral lesion.

Experimental ethambutol neuropathy in rats: Morphometric and teased-fiber studies

Eight rats were given 500 mg/kg body weight of the antituberculous drug ethambutol orally every day for 3 months (group A), and 7 took 150 mg/kg of the drug for 9 months (group B). The sciatic nerves at midthigh level and the posterior tibial nerves at ankle level were studied with morphometric examination and teased-fiber method. The number of myelinated fibers/mm 2 of fascicular area was significantly reduced in both sciatic and posterior tibial nerves of group B. The pattern of frequency distribution of myelinated nerve fiber diameters of both groups was not different from that of the controls. Teased-fiber study revealed that many fibers were undergoing axonal degeneration in both groups A and B. In addition, regenerating fibers after axonal degeneration were observed in group B. These results showed that the predominant pathologic change in ethambutol neuropathy was axonal degeneration and that regeneration was already occurring in the animals taking a small dose of the drug for a long period. The fact that the degree of pathologic change was rather more severe in the sciatic nerve than in the posterior tibial nerve indicated that this was not a “dying-back” neuropathy.