Mean Myelin Research Articles

The potential protective effects of melatonin and omega-3 on the male rat optic nerve exposed to 900 MHz electromagnetic radiation during the prenatal period

Background Due to children and adolescents’ widespread use of electronic devices, researchers have focused on pre-and early postnatal electromagnetic field (EMF) exposure. However, little is known about the effects of EMF exposure on the optic nerve. The aim of study was to investigate the changes occurring in the optic nerve and the protective effects of melatonin (mel) and omega 3 (ω-3) in rats. Methods Thirty-five pregnant rats were divided into seven groups, Cont, Sham, EMF, EMF + melatonin (EMF + Mel), EMF + ω3, Mel, and ω3. The EMF groups were exposed to 900 megahertz (MHz) EMF daily for two hours during pregnancy. After the experiment, the right optic nerve of each offspring rat was removed and fixed in glutaraldehyde. Thin and semi-thin sections were taken for electron microscopic and stereological analyses. Myelinated axon numbers, myelin sheath thicknesses, and axonal areas were estimated using stereological methods. Results The groups had no significant differences regarding mean numbers of axons, mean axonal areas, or mean myelin sheath thicknesses (p > 0.05). Histological observations revealed impaired lamellae in the myelin sheath of most axons, and vacuolization was frequently observed between the myelin sheath and axon in the EMF-exposed group. The Mel and ω-3-treated EMF groups exhibited well-preserved myelinated nerve fibers and intact astrocytes and oligodendrocytes. Conclusions At the ultrastructural level, Mel and ω3 exhibits a neuroprotective effect on the optic nerve exposed to prenatal EMF. The protective effects of these antioxidants on oligodendrocytes, which play an essential role in myelin formation in the central nervous system, now require detailed investigation.

Estimation of white matter hyperintensities with synthetic MRI myelin volume fraction in patients with multiple sclerosis and non-multiple-sclerosis white matter hyperintensities: A pilot study among the Indian population

<abstract><sec> <title>AIM</title> <p>Synthetic MRI (SyMRI) works on the MDME sequence, which acquires the relaxation properties of the brain and helps to measure the accurate tissue properties in 6 minutes. The aim of this study was to evaluate the synthetic MRI (SyMRI)-generated myelin (MyC) to white matter (WM) ratio, the WM fraction (WMF), MyC partial maps performing normative brain volumetry to investigate MyC loss in multiple sclerosis (MS) patients with white-matter hyperintensites (WMHs) and non-MS patients with WMHs in a clinical setting.</p> </sec><sec> <title>MATERIALS and METHODS</title> <p>Synthetic MRI images were acquired from 15 patients with MS, and from 15 non-MS patients on a 3T MRI scanner (Discovery MR750w; GE Healthcare; Milwaukee, USA) using MAGiC, a customized version of SyntheticMR's SyMRI® IMAGE software marketed by GE Healthcare under a license agreement. Fast multi-delay multi-echo acquisition was performed with a 2D axial pulse sequence with different combinations of echo time (TEs) and saturation delay times. The total image acquisition time was 6 minutes. SyMRI image analysis was done using SyMRI software (SyMRI Version: 11.3.6; Synthetic MR, Linköping, Sweden). SyMRI data were used to generate the MyC partial maps and WMFs to quantify the signal intensities of test group and control group, andcontrol group , and their mean values were recorded. All patients also underwent conventional diffusion-weighted imaging, i.e., T1w and T2w imaging.</p> </sec><sec> <title>RESULTS</title> <p>The results showed that the WMF was significantly lower in the test group than in the control group (38.8% vs 33.2%, p < 0.001). The Mann-Whitney U nonparametric t-test revealed a significant difference in the mean myelin volume between the test group and the control group (158.66 ± 32.31 vs. 138.29 ± 29.28, p = 0.044). Also, there were no significant differences in the gray matter fraction and intracranial volume between the test group and the control group.</p> </sec><sec> <title>CONCLUSIONS</title> <p>We observed MyC loss in test group using quantitative SyMRI. Thus, myelin loss in MS patients can be quantitatively evaluated using SyMRI.</p> </sec></abstract>

Quantification of individual remyelination during short-term disease course by synthetic magnetic resonance imaging.

MRI is an important diagnostic tool for evaluation of myelin content in multiple sclerosis and other CNS diseases, being especially relevant for studies investigating remyelinating pharmacotherapies. In this study, we evaluated a new synthetic MRI–based myelin estimation in methylenetetrahydrofolate reductase deficiency as a treatable primary demyelinating disorder and compared this method with established diffusion tensor imaging in both methylenetetrahydrofolate reductase deficiency patients and healthy controls. This is the first synthetic MRI–based in vivo evaluation of treatment-associated remyelination. 1.5 T synthetic MRI and 3 T diffusion MRI were obtained from three methylenetetrahydrofolate reductase deficiency patients at baseline and 6 months after therapy initiation, as well as from age-matched healthy controls (diffusion tensor imaging: n = 14, synthetic MRI: n = 9). Global and regional synthetic MRI parameters (myelin volume fraction, proton density, and relaxation rates) were compared with diffusion metrics (fractional anisotropy, mean/radial/axial diffusivity) and related to healthy controls by calculating z-scores and z-deviation maps. Whole-brain myelin (% of intracranial volume) of the index patient was reduced to 6 versus 10% in healthy controls, which recovered to a nonetheless subnormal level of 6.6% following initiation of high-dosage betaine. Radial diffusivity was higher at baseline compared with healthy controls (1.34 versus 0.79 × 10−3 mm2/s), recovering at follow-up (1.19 × 10−3 mm2/s). The index patient’s lesion volume diminished by 58% under treatment. Regional analysis within lesion area and atlas-based regions revealed lower mean myelin volume fraction (12.7Baseline/14.71Follow-up%) and relaxation rates, higher proton density, as well as lower fractional anisotropy and higher radial diffusivity (1.08 × 10−3Baseline/0.94 × 10−3Follow-up) compared with healthy controls. The highest z-scores were observed for myelin volume fraction in the posterior thalamic radiation, with greater deviation from controls at baseline and reduced deviation at follow-up. Z-deviations of diffusion metrics were less pronounced for radial and mean diffusivity than for myelin volume fraction. Z-maps for myelin volume fraction of the index patient demonstrated high deviation within and beyond lesion areas, among others in the precentral and postcentral gyrus, as well as in the cerebellum, and partial remission of these alterations at follow-up, while radial diffusivity demonstrated more widespread deviations in supra- and infratentorial regions. Concordant changes of myelin volume fraction and radial diffusivity after treatment initiation, accompanied by dramatic clinical and paraclinical improvement, indicate the consistency of the methods, while myelin volume fraction seems to characterize remyelinated regions more specifically. Synthetic MRI–based myelin volume fraction provides myelin estimation consistent with changes of diffusion metrics to monitor short-term myelin changes on individual patient level.

Histological and Morphometric Changes in the Femoral Nerve During Lateral Interbody Fusion of the Lumbar Spine: Experimental Study

Background. Neuropathies of the lumbar plexus trunks, in particular those of the femoral nerve, are the most common complications of lateral interbody fusion of the lumbar spine. Modeling of this surgical intervention in normal animals experimentally makes it possible to assess the degree of its trauma to the nervous structures, and to understand what is the reason for the persistence or aggravation of neurological symptoms iatrogenic injuries or the existing pathology progression. Purpose to study histological and morphometric changes in the femoral nerve in the long-term periods after the lateral interbody fusion modeling of the canine lumbar spine. Study design an experimental prospective continuous uncontrolled study. Materials and Methods. Discectomy via lateral approach was performed in 18 mongrel dogs (aged 2-3 years, mass 13.2-17.6 kg) at the level of L4-5 и L5-6, interbody titanium implants were mounted, the lumbar spine was stabilized with a wire device for external fixation within 30 days. Clinical and neurological evaluation was performed, as well as histological investigation of the femoral nerves from the side of surgical approach. Results. In the early postoperative period a temporary decrease in the femoral nerve function was observed, which was manifested by the disorder of the support function and muscle weakness of the pelvic limbs, decrease in the knee reflex, the foot support shift to the metatarsal pad. Later, until the end of the study (18 months), the general condition of all animals was satisfactory, there were no disorders of the limb support function and motor reflexes. After six months, in the femoral nerve there was 4-fold decrease in the proportion of large fast-conducting myelin fibers D10 m and 3-fold increase in that of the small ones. The mean axon diameter and myelin thickness were 62% and 53% of the norm. After 12-18 months, the dimensional characteristics of myelin fibers were restored. During the entire experiment, 4-6% of myelin fibers were reactively and destructively altered. Conclusions. The modeling of the lateral interbody fusion of the lumbar spine in normal animals experimentally demonstrated the absence of neurological symptoms after 6-18 months, which indicated low invasiveness of the surgical intervention. Nevertheless, the subclinical reactive and destructive changes in the myelin fibers of the femoral nerve revealed 6 months after the surgery indicated the need for preventive anti-neurotic therapy.

An atlas for human brain myelin content throughout the adult life span

Myelin water imaging is a quantitative neuroimaging technique that provides the myelin water fraction (MWF), a metric highly specific to myelin content, and the intra-/extra-cellular T2 (IET2), which is related to water and iron content. We coupled high-resolution data from 100 adults with gold-standard methodology to create an optimized anatomical brain template and accompanying MWF and IET2 atlases. We then used the MWF atlas to characterize how myelin content relates to demographic factors. In most brain regions, myelin content followed a quadratic pattern of increase during the third decade of life, plateau at a maximum around the fifth decade, then decrease during later decades. The ranking of mean myelin content between brain regions remained consistent across age groups. These openly available normative atlases can facilitate evaluation of myelin imaging results on an individual basis and elucidate the distribution of myelin content between brain regions and in the context of aging.

Axonal myelin decrease in the splenium in major depressive disorder

The corpus callosum has become a key area of interest for researchers in severe mental illness. Disruptions in fractional anisotropy in the callosum have been reported in schizophrenia and major depressive disorder. No change has been reported in oligodendrocyte density and overall size of the callosum in either illness, suggesting that gross morphology is unchanged, but subtler organisational disruption may exist within this structure. Using high-resolution oil immersion microscopy, we examined the cross-sectional area of the nerve fibre and the axonal myelin sheath; and using standard high-resolution light microscopy, we measured the density of myelinated axons. These measurements were made in the splenium of the corpus callosum. Measures were taken in the sagittal plane in the callosal splenium to contrast with the previous similar examination of the callosal genu. Cases of major depressive disorder had significantly decreased mean myelin cross-sectional area (p = 0.014) per axon in the splenium than in controls or schizophrenia groups. There was no significant change in the density of myelinated axons. The results suggest a clear decrease of myelin in the axons of the callosal splenium in MDD, although this type of neuropathological study is unable to clarify whether this is caused by changes during life or has a developmental origin. In contrast with increased myelin in the callosal genu, this result suggests a longitudinal change in callosal myelination in major depressive disorder not present in normal or schizophrenic brains.

Deep learning of joint myelin and T1w MRI features in normal-appearing brain tissue to distinguish between multiplesclerosispatients and healthy controls.

Myelin imaging is a form of quantitative magnetic resonance imaging (MRI) that measures myelin content and can potentially allow demyelinating diseases such as multiple sclerosis (MS) to be detected earlier. Although focal lesions are the most visible signs of MS pathology on conventional MRI, it has been shown that even tissues that appear normal may exhibit decreased myelin content as revealed by myelin-specific images (i.e., myelin maps). Current methods for analyzing myelin maps typically use global or regional mean myelin measurements to detect abnormalities, but ignore finer spatial patterns that may be characteristic of MS. In this paper, we present a machine learning method to automatically learn, from multimodal MR images, latent spatial features that can potentially improve the detection of MS pathology at early stage. More specifically, 3D image patches are extracted from myelin maps and the corresponding T1-weighted (T1w) MRIs, and are used to learn a latent joint myelin-T1w feature representation via unsupervised deep learning. Using a data set of images from MS patients and healthy controls, a common set of patches are selected via a voxel-wise t-test performed between the two groups. In each MS image, any patches overlapping with focal lesions are excluded, and a feature imputation method is used to fill in the missing values. A feature selection process (LASSO) is then utilized to construct a sparse representation. The resulting normal-appearing features are used to train a random forest classifier. Using the myelin and T1w images of 55 relapse-remitting MS patients and 44 healthy controls in an 11-fold cross-validation experiment, the proposed method achieved an average classification accuracy of 87.9% (SD = 8.4%), which is higher and more consistent across folds than those attained by regional mean myelin (73.7%, SD = 13.7%) and T1w measurements (66.7%, SD = 10.6%), or deep-learned features in either the myelin (83.8%, SD = 11.0%) or T1w (70.1%, SD = 13.6%) images alone, suggesting that the proposed method has strong potential for identifying image features that are more sensitive and specific to MS pathology in normal-appearing brain tissues.

Effects of decompression on behavioral, electrophysiologic, and histomorphologic recovery in a chronic sciatic nerve compression model of streptozotocin-induced diabetic rats.

PurposeTo determine susceptibility to decompression surgery in diabetic and nondiabetic peripheral neuropathy using a chronic compression neuropathy model.Materials and methodsTwenty-four streptozotocin-induced diabetic rats were randomly divided into three groups: group I, chronic compression of the left sciatic nerve for 4 weeks with decompression; group II, similar without decompression; and group III, sham exposing the sciatic nerve only. The other 24 nondiabetic rats were assigned to groups IV–VI, which received compression–decompression, compression, and the sham operation, respectively. Mixed-nerve-elicited somatosensory evoked potentials (M-SSEPs) and compound muscle action potentials (CMAPs) were measured to verify the compression neuropathy in the posttreatment follow-up. Behavioral observations in thermal hyperalgesia tests were quantified before electrophysiologic examinations. Treated and contralateral nerves were harvested for histomorphologic analysis.ResultsChronic compression of sciatic nerve induced significant reduction of amplitude and increment of latency of M-SSEP and CMAP in both diabetic and nondiabetic rats. Diabetic group changes were more susceptible. Decompression surgery significantly improved both sensory and motor conduction, thermal hyperalgesia, and the mean myelin diameter of the rat sciatic nerve in both diabetic and nondiabetic groups. Near full recovery of motor and sensory function occurred in the nondiabetic rats, but not in the diabetic rats 8 weeks postdecompression.ConclusionBehavioral, electrophysiologic, and histomorphologic findings indicate that decompression surgery is effective in both diabetic and nondiabetic peripheral neuropathy.

Manganese-enhanced MRI Offers Correlation with Severity of Spinal Cord Injury in Experimental Models.

Background:Spinal cord injuries (SCI) are clinically challenging, because neural regeneration after cord damage is unknown. In SCI animal models, regeneration is evaluated histologically, requiring animal sacrifice. Noninvasive techniques are needed to detect longitudinal SCI changes.Objective:To compare manganese-enhanced magnetic resonance imaging (MRI [MEMRI]) in hemisection and transection of SCI rat models with diffusion tensor imaging (DTI) and histology.Methods:Rats underwent T9 spinal cord transection (n=6), hemisection (n=6), or laminectomy without SCI (controls, n=6). One-half of each group received lateral ventricle MnCl2 injections 24 hours later. Conventional DTI or T1-weighted MRI was performed 84 hours post-surgery. MEMRI signal intensity ratio above and below the SCI level was calculated. Fractional anisotropy (FA) measurements were taken 1 cm rostral to the SCI. The percentage of FA change was calculated 10 mm rostral to the SCI epicenter, between FA at the dorsal column lesion normalized to a lateral area without FA change. Myelin load (percentage difference) among groups was analyzed by histology.Results:In transection and hemisection groups, mean MEMRI ratios were 0.62 and 0.87, respectively, versus 0.99 in controls (P<0.001 and P<0.001, respectively); mean FA decreases were 67.5% and 40.1%, respectively, compared with a 6.1% increase in controls (P=0.002 and P=0.019, respectively). Mean myelin load decreased by 38.8% (transection) and 51.8% (hemisection) compared to controls (99.1%) (P<0.001 and P<0.001, respectively). Pearson’s correlation coefficients were -0.94 for MEMRI ratio and FA changes and 0.87 for MEMRI and myelin load.Conclusion:MEMERI results correlated to SCI severity measured by FA and myelin load. MEMRI is a useful noninvasive tool to assess neuronal damage after SCI.

Quantifying visual pathway axonal and myelin loss in multiple sclerosis and neuromyelitis optica.

BackgroundThe optic nerve is frequently injured in multiple sclerosis and neuromyelitis optica, resulting in visual dysfunction, which may be reflected by measures distant from the site of injury.ObjectiveTo determine how retinal nerve fiber layer as a measure of axonal health, and macular volume as a measure of neuronal health are related to changes in myelin water fraction in the optic radiations of multiple sclerosis and neuromyelitis optica participants with and without optic neuritis and compared to healthy controls.Methods12 healthy controls, 42 multiple sclerosis (16 with optic neuritis), and 10 neuromyelitis optica participants (8 with optic neuritis) were included in this study. Optical coherence tomography assessment involved measurements of the segmented macular layers (total macular, ganglion cell layer, inner plexiform layer, and inner nuclear layer volume) and paripapillary retinal nerve fiber layer thickness. The MRI protocol included a 32-echo T2-relaxation GRASE sequence. Average myelin water fraction values were calculated within the optic radiations as a measure of myelin density.ResultsMultiple sclerosis and neuromyelitis optica eyes with optic neuritis history had lower retinal nerve fiber layer thickness, total macular, ganglion cell and inner plexiform layer volumes compared to eyes without optic neuritis history and controls. Inner nuclear layer volume increased in multiple sclerosis with optic neuritis history (mean = 0.99 mm3, SD = 0.06) compared to those without (mean = 0.97 mm3, SD = 0.06; p = 0.003). Mean myelin water fraction in the optic radiations was significantly lower in demyelinating diseases (neuromyelitis optica: mean = 0.098, SD = 0.01, multiple sclerosis with optic neuritis history: mean = 0.096, SD = 0.01, multiple sclerosis without optic neuritis history: mean = 0.098, SD = 0.02; F3,55 = 3.35, p = 0.03) compared to controls. Positive correlations between MRI and optical coherence tomography measures were also apparent (retinal nerve fiber layer thickness and ganglion cell layer thickness: r = 0.25, p = 0.05, total macular volume and inner plexiform layer volume: r = 0.27, p = 0.04).ConclusionsThe relationship between reductions in OCT measures of neuro-axonal health in the anterior visual pathway and MRI-based measures of myelin health in the posterior visual pathway suggests that these measures may be linked through bidirectional axonal degeneration.

Effects of different dosage of dexamethasone on behavioral, electrophysiological, and histomorphological recovery in a chronic sciatic nerve compression model.

To investigate the effects of different doses of topical dexamethasone (Dex) on sciatic nerves with simulated compressive neuropathy. Thirty-two Wistar rats were divided into four groups of 8: Sham group: no compression of the sciatic nerve + no treatment; Saline: chronic compression of the left sciatic nerve for 4 weeks + saline; 0.8% Dex: chronic compression + 0.8 mg of Dex; 3.2% Dex: chronic compression + 3.2 mg of Dex. Two sponge strips soaked with saline or Dex were placed under and over the nerve for 30 min in both Dex groups. Mixed-nerve-elicited somatosensory evoked potentials (M-SSEPs) and compound muscle action potentials (CMAPs) were measured to verify the compressive neuropathy in post-treatment follow-up. Behavioral observations of thermal hyperalgesia tests were quantified before electrophysiological examinations. Treated and contralateral nerves were harvested for histomorphological analysis. M-SSEP and CMAP amplitudes significantly decreased and latencies were significantly prolonged on postcompression thermal hyperalgesia tests. Rats in both Dex groups showed significant improvement in both sensory and motor conductive values and in neurological function, as well as increased mean myelin diameter on the final histomorphological examination. For rats in the saline group, these parameters showed incomplete recovery compared with the Sham group and the precompression baseline. Moreover, the changes after Dex treatment were not dose-dependent. Topical Dex reversed electrophysiological, behavioral, and structural changes in chronically compressed sciatic nerves. Differences between the beneficial effects of high-dose and low-dose Dex were nonsignificant.

Protective effects of mineralocorticoid receptor blockade against neuropathy in experimental diabetic rats

Mineralocorticoid receptor (MR) blockade is an effective treatment for hypertension and diabetic nephropathy. There are no data on the effects of MR blockade on diabetic peripheral neuropathy (DPN). The aim of this study was to determine whether MRs are present in the peripheral nerves and to investigate the effectiveness of MR blockade on DPN in streptozotocin (STZ)-induced diabetic rats. Expression of MR protein and messenger RNA (mRNA) was examined in the peripheral nerves using Western blot analysis and RT-PCR. We next studied the effects of the selective MR antagonist eplerenone and the angiotensin II receptor blocker candesartan on motor and sensory nerve conduction velocity (NCV), morphometric changes and cyclooxygenase-2 (COX-2) gene and NF-κB protein expression in the peripheral nerves of STZ-induced diabetic rats. Expression of MR protein and mRNA in peripheral nerves was equal to that in the kidney. Motor NCV was significantly improved by 8 weeks of treatment with either eplerenone (39.1 ± 1.2 m/s) or candesartan (46.4 ± 6.8 m/s) compared with control diabetic rats (33.7 ± 2.0 m/s) (p < 0.05). Sensory NCV was also improved by treatment with candesartan or eplerenone in diabetic rats. Eplerenone and candesartan caused significant improvement in mean myelin fibre area and mean myelin area compared with control diabetic rats (p < 0.05). COX-2 mRNA and NF-κB protein were significantly elevated in the peripheral nerves of diabetic rats compared with control rats, and treatment with eplerenone or candesartan reduced these changes in gene expression (p < 0.05). MR blockade may have neuroprotective effects on DPN.

Concentration-Dependent Neurotoxicity of Articaine

We performed this study to quantify the detrimental effect of intraneural injection of 50 μL of saline, articaine 2%, or articaine 4% in the rat sciatic nerve. Lumbar-evoked electrospinograms from stimulation of the sciatic nerve were recorded before and immediately after injection and again after 3 weeks. Test substance was injected into the right sciatic nerve, and the untreated left sciatic nerve served as control. The animals were killed after the 3-week follow-up, and cross-sections of the sciatic nerve were examined stereologically. The evoked spinal cord field potential in the articaine groups faded away immediately after injection and was concentration-dependently, significantly more reduced at the 3-week follow-up in comparison with the saline group. The response from the control sides was unaffected in all groups. The number of myelinated axons was unaffected by the treatment. The mean cross-sectional axon area and the mean myelin sheath thickness were significantly reduced in animals injected with articaine 4%. These observations indicate concentration-dependent neurotoxic injuries after injection of articaine with a significant difference between 2% and 4% formulations. The mechanical injury of needle penetration with saline injection had no significant effect on nerve conduction or histomorphology.

Acetyl- l-carnitine increases nerve regeneration and target organ reinnervation – a morphological study

Peripheral nerve injury frequently results in functional morbidity since standard management fails to adequately address many of the neurobiological hurdles to optimal regeneration. Neuronal survival and regeneration are neurotrophin dependent and require increased aerobic capacity. Acetyl-l-carnitine (ALCAR) facilitates this need and prevents neuronal loss. ALCAR is clinically safe and is shown here to significantly improve nerve regeneration and target organ reinnervation. Two groups of five rats underwent sciatic nerve division followed by immediate repair. One group received parenteral ALCAR (50mg/kg/day) from time of operation until termination at 12 weeks. A 'sham treatment' group received normal saline. A third group was left unoperated and did not receive any treatment. A segment of nerve was harvested between 5mm proximal and 10mm distal to the repair in operated groups, and at the corresponding level in the unoperated group. Mean axonal count in normal, non-axotomised nerve was 14,720 (SD 2378). That of the saline group (17,217 SD 1808) was not significantly different from normal nerve (P=0.0985). Mean number of myelinated axons in the ALCAR group (24,460 SD 3750) was significantly greater than both sham group (P<0.01) and normal nerve (P=0.0012). Mean myelin thickness in the saline treated group (0.408 microm SD 0.067 microm) was less than normal nerve (0.770 microm SD 0.143 microm) (P<0.001). Mean myelin thickness in the ALCAR group (0.627 microm SD 0.052 microm) was greater than the sham (saline) group (P<0.01) and not statistically different from normal nerve (P=0.07). ALCAR increased dermal PGP9.5 staining by 210% compared to sham treatment (P<0.0001) and significantly reduced the mean percentage weight loss in gastrocnemius muscle (ALCAR group 0.203% vs. 0.312% in sham group P=0.015). ALCAR not only increases the number of regenerating nerve fibres but also morphologically improves the quality of regeneration and target organ reinnervation. Adjuvant ALCAR treatment may improve both sensory and motor outcomes and merits further investigation.

Effect of Donor Nerve Injury Distal to an End-to-Side Neurorrhaphy Model

In end-to-side neurorrhaphy, "noninjury" models of the donor nerve do not seem to offer worthwhile functional outcomes. The role of donor nerve injury distal to the coaptation site remains unclear. End-to-side neurorrhaphy was studied in a rat model in which the proximal stump of the transected musculocutaneous nerve was sutured to the median nerve by end-to-side coaptation. Twenty Sprague-Dawley rats were randomized to four groups of five animals each, in which three different types of donor injury (crush, ligation, or transection injury) distal to the coaptation site were executed; findings were compared with a similar end-to-side model without donor nerve injury (control). Behavioral analysis, electrophysiological studies, muscle morphometric studies, and nerve fibers counts showed no significant differences among groups. However, there was a significant difference regarding mean myelin area (P = 0.0362) and mean fiber diameter (P = 0.0159) for the crush injury group as compared with the control group. No significant differences were found among the other groups. These data suggest that donor crush injury distal to the coaptation site may increase the rate of myelin formation in regenerating axons across an end-to-side model; however, at 4 weeks of follow-up, there was no significant behavioral or functional significance in this treatment group.

Costimulation blockade in transplantation of nerve allografts: long‐term effects

Costimulation blockade can prevent rejection of nerve allografts in short-term studies. We tested if costimulation blockade also prevented rejection of nerve allografts in long-term experiments, thereby improving functional recovery. A 7-mm sciatic nerve defect in C57/BL6 mice was bridged either by nerve allografts from Balb/C mice or by isogenic nerve grafts (isografts) from C57/BL6 mice. Costimulation blockade in the form of a triple treatment with anti-LFA-1, anti-CD40L, and CTLA4Ig was given at post-operative days 0, 2, 4, and 6 (intraperitoneal). Control mice (placebo; allografts) with nerve grafts were treated with isotype antibodies during the same time period. After 49 days, tetanic muscle force, wet weight of gastrocnemius muscle, histology, and morphometry in the tibial nerve were evaluated. Costimulation blockade diminished rejection of the nerve allografts. Axons bridged the graft. Treatment increased wet weight of the gastrocnemius muscle and resulted in a higher mean myelin area/nerve fiber in the tibial nerve distal to the nerve grafts. Tetanic muscle force and number of axons in tibial nerve showed no differences between groups. We conclude that rejection is suppressed by costimulation blockade. Treatment improves recovery of target muscle and myelination after nerve allografting.

The influence of continuous exposure to 50 Hz electric field on nerve regeneration in a rat peroneal nerve crush injury model

The effect of power frequency electric field (EF) on nerve regeneration was investigated on a rat peroneal nerve crush injury model. The animals were assigned to three groups: 50 Hz EF and Static EF groups were exposed at 10 kV/m. The sham group was kept in the same setting without any EF applications. EF was uninterruptedly applied for 21 days postoperatively. Repeated measures analysis of daily walking tracks during EF exposure demonstrated lower toe spread recovery (TSR) in the 50 Hz EF group. Significant difference across the groups was found only at days 7, 8, 12, 16, 17, 20, and 21 when TSR was analyzed for each measurement time. Print length recovery and peroneal function index did not differ across the groups. Walking track parameters were found to recover to their baseline values by day 28 in all groups. Day 14 but not day 21 measurements revealed smaller nerve cross-sectional area, lower total regenerating axon area, and higher mean myelin debris area in 50 Hz EF group. Both day 14 and 21 measurements revealed higher total myelin debris area, lower EDL muscle weight, and lack of significant enlargement in nerve cross-section distal to the injury, compared to the normal counterpart in 50 Hz EF group. All differences were in keeping with lower rates of Wallerian degeneration and nerve regeneration in 50 Hz EF group. When walking track, histomorphometry and muscle weight are considered individually, their differences across the groups may appear to be subtle to derive a conclusion for a 50 Hz EF effect. However, their concordance with each other in direction of effect suggests that continuous 50 Hz EF exposure has a weak effect that is detrimental mostly to the rate of early nerve regeneration in this axonotmetic injury model. Recovery of walking tracks was not different between Static EF and Sham groups. This suggests that the surface charges that may indirectly affect walking behaviors of the rats, do not account for the lower recovery of TSR in 50 Hz EF group. Differences in nerve regeneration between 50 Hz EF and Static EF groups suggests that electric induction may be required for pure EF effects even though the estimated density of induced fields is not above the endogenous background level for the 50 Hz EF exposure in this study.

Local effects on triiodothyronine-treated polyglactin sutures on regeneration across peripheral nerve defects.

We have previously described a new and simple method for nerve repair in which continuous longitudinal polyglactin sutures alone are used to bridge limited nerve defects in rats. Here we examined whether such sutures could be used to deliver a growth-promoting substance, triiodothyronine (T(3)), and enhance regeneration of the rat sciatic nerve. Sutures were pretreated in highly concentrated solutions of T(3) for 24 h. In vitro measurements showed that such sutures released T(3) with an initial rapid phase followed by a slow-release phase lasting at least 3 weeks. Bilateral sciatic nerve defects (7 mm) in rats were bridged by either T(3)- or saline-incubated sutures. Immunocytochemistry for Schwann cells and axons at 2 weeks showed no differences in Schwann cell distribution or axonal outgrowth length. Morphometric analysis 4 and 12 weeks after the repair revealed a slight but significant (p < 0.05) increase in the mean myelin area in T(3)-treated nerves. No differences were seen in the number of axons or return of force in the gastrocnemius muscle at 12 weeks. The results show that sutures can be used both for the bridging of defects in peripheral nerves and for the delivery of a growth-promoting substance to regenerating nerve structures.

Computer-assisted morphometric study on the postnatal growth of axon size and myelin thickness in the ventral and dorsal roots of the rabbit

The morphometric analysis of the myelinated fibers is of great value in developmental, experimental, and pathological studies. The present study was performed on the ventral and dorsal spinal roots (L7) of new-born, 10-, 15-, 20-, 30-, 60-, 120- and 240-day-old rabbits. Semi-thin cross-sections were investigated by OLYMPUS Video image analyser. The average axonal diameter was measured as an average length of Feret's diameters and the specific width of the myelin sheaths as a total width of the myelin sheath. In the ventral roots, the increase of the axon size is more intensive than the increase of the myelin thickness. In adult rabbits, the mean axonal diameter for the ventral root is approximately 15% greater than the mean axonal diameter for the dorsal root, whereas the mean myelin thickness values are practically equal for both roots. For the period newborn-adult (240-day-old) rabbits, a full correlation was found in respect to the increase of the dorsal root mean axonal diameter and mean myelin thickness (380% and 380%). In the ventral roots, the mean axonal diameter increased 420% whereas the mean myelin thickness increased 350%. It is intriguing whether the greater axonal size of the ventral roots might compensate their relatively thin myelin sheaths in comparison to the dorsal roots. Our findings of essential increase (16%) of the mean myelin thickness in the last (120-240 days) period in both, ventral and dorsal roots, points to a protracted period of myelinization in the rabbit.

Regenerative axonal sprouting in the cat trochlear nerve.

Following peripheral trochlear nerve axotomy in the cat, the normal number of myelinated axons is restored despite significant motor neuron death, suggesting regulation of the number of myelinated axons in the regenerated nerve. In this study we used light and electron microscopy to examine the production and maintenance of axonal sprouts at different locations in the nerve and at different postoperative intervals. Despite proliferative sprouting and an overproduction of nonmyelinated axons in the regenerating trochlear nerve, the number of myelinated axons was strictly regulated. Only approximately 1,000 regenerated axons were eventually remyelinated, but many nonmyelinated axons were still present 6-8 months postaxotomy. Regenerated axons were remyelinated in a proximal-to-distal direction between 3 and 4 weeks postaxotomy. We also examined the maturation of regenerated myelinated axons by measuring axon diameter and myelin index (an expression of myelin thickness). Mean myelinated axon diameter remained significantly below normal in long-term regenerated nerves. Mean myelin index was not different from normal at 4 weeks postaxotomy but was significantly decreased at long postoperative intervals, reflecting a slightly thicker myelin sheath relative to the axon diameter. This relative increase in mean myelin thickness could serve to restore normal conduction velocity despite the decrease in mean axon diameter. We suggest that the regulation of the number of myelinated axons at the normal number despite cell death and the increase in mean myelin thickness may both be compensatory mechanisms that function to restore preoperative conditions and maximize functional recovery.