Prediction of Motor Recovery after Stroke by Assessment of Corticospinal Tract Wallerian Degeneration Using Diffusion Tensor Imaging

Aim of the Study To predict motor recovery after stroke by detection of diffusion tensor imaging (DTI) fractional anisotropy (FA) changes of corticospinal tract (CST) and correlate findings with clinical scores to provide more effective treatment and rehabilitation.

Subjects and Methods Thirty patients with cerebral stroke were enrolled and underwent conventional magnetic resonance imaging and DTI at admission and 1 month after stroke. Mean diffusivity (MD), FA, FA ratio (rFA), and fiber number (FN) values of CST were calculated at the pons at admission and after 1 month of stroke. Three-dimensional reconstruction of bilateral CST and the structural changes of fibrous bands were observed. Severity of limb weakness was assessed by using the motor sub-index scores of the National Institutes of Health Stroke Scale (NIHSS) at admission, and after 1, 6, and 9 months for severity of limb weakness.

Results The mean age of our patients was 61.32 ± 4.34 years, 17/30 (56.6%) were females, and 13/30 (43.4%) were males. In our study, 18/30 (60%) were hypertensive, 19/30 (63.3%) were diabetic, and 12/30 (40%) were smokers. A significant negative correlation was found between rFA and FN in the ipsilateral CST of the cerebral infarction at the rostral part of pons after 1 month of infarction and NIHSS score at 6 months ( r = 0.377, p = 0.04 and r = 0.237, p = 0.02, respectively). However, a positive insignificant correlation was found between MD and NIHSS ( r = 0.345, p = 0.635). The initial NIHSS score at the time of injury was 19.2 ± 4.3, which changed to 7.9 ± 2.4, 4.6 ± 1.9, and 3.3 ± 1.4 at 1, 6, and 9 months, respectively.

Conclusion DTI is a sensitive tool for early detection of Wallerian degeneration in the CST after stroke, and can predict motor performance to provide effective treatment and rehabilitation to improve quality of life.

Passenger Mutations Confound Phenotypes of SARM1-Deficient Mice

The Toll/IL-1R-domain-containing adaptor protein SARM1 is expressed primarily in the brain, where it mediates axonal degeneration. Roles for SARM1 in TLR signaling, viral infection, inflammasome activation, and chemokine and Xaf1 expression have also been described. Much of the evidence for SARM1 function relies on SARM1-deficient mice generated in 129 ESCs and backcrossed to B6. The Sarm1 gene lies in a gene-rich region encompassing Xaf1 and chemokine loci, which remain 129 in sequence. We therefore generated additional knockout strains on the B6 background, confirming the role of SARM1 in axonal degeneration and WNV infection, but not in VSV or LACV infection, or in chemokine or Xaf1 expression. Sequence variation in proapoptotic Xaf1 between B6 and 129 results in coding changes and distinct splice variants, which may account for phenotypes previously attributed to SARM1. Reevaluation of phenotypes in these strains will be critical for understanding the function of SARM1.

Spermatic Cord Block Series as a Minimally Invasive Therapy for Chronic Scrotal Content Pain

PURPOSE

The primary aim of our study was to evaluate relief of chronic scrotal content pain after a series of spermatic cord blocks with a combination of local anesthetic and a steroid. Secondary aims were to assess factors associated with a positive response and complications.

MATERIALS AND METHODS

We performed a retrospective chart review of patients who underwent spermatic cord block series for chronic scrotal content pain at our practice between 2012 and 2019. Pain scores were compared before and after treatment using an 11-point numerical pain rating scale. We performed univariate analysis to assess differences between responders and nonresponders, and the relationship between symptom duration and response was analyzed by rank-order correlation.

RESULTS

We included 44 men with chronic scrotal content pain present for a median duration of 24 months who underwent a spermatic cord block series. At a median followup of 16 months, 31 patients (70.5%) experienced sustained relief, including 9 patients (20.5%) with complete resolution of pain. There were no differences between responders and nonresponders in terms of symptom duration, perceived etiology, or previous treatments, and there was no association between response and duration of pain. Minor complications occurred in 5 cases (11.4%).

CONCLUSIONS

Spermatic cord block series is a safe, minimally invasive treatment for men with refractory chronic scrotal content pain. Response to cord block series appears to be independent of symptom duration, perceived etiology or prior medical and surgical treatments. Future studies should be conducted to evaluate long-term durability and predictors of success.

MGMT-Methylation in Non-Neoplastic Diseases of the Central Nervous System

Quantifying O⁶-methylguanine-DNA methyltransferase (MGMT) promoter methylation plays an essential role in assessing the potential efficacy of alkylating agents in the chemotherapy of malignant gliomas. MGMT promoter methylation is considered to be a characteristic of subgroups of certain malignancies but has also been described in various peripheral inflammatory diseases. However, MGMT promoter methylation levels have not yet been investigated in non-neoplastic brain diseases. This study demonstrates for the first time that one can indeed detect slightly enhanced MGMT promoter methylation in individual cases of inflammatory demyelinating CNS diseases such as multiple sclerosis and progressive multifocal leucencephalopathy (PML), as well as in other demyelinating diseases such as central pontine and exptrapontine myelinolysis, and diseases with myelin damage such as Wallerian degeneration. In this context, we identified a reduction in the expression of the demethylase TET1 as a possible cause for the enhanced MGMT promoter methylation. Hence, we show for the first time that MGMT hypermethylation occurs in chronic diseases that are not strictly associated to distinct pathogens, oncogenic viruses or neoplasms but that lead to damage of the myelin sheath in various ways. While this gives new insights into epigenetic and pathophysiological processes involved in de- and remyelination, which might offer new therapeutic opportunities for demyelinating diseases in the future, it also reduces the specificity of MGMT hypermethylation as a tumor biomarker.

Neuron-Oligodendrocyte Interactions in the Structure and Integrity of Axons

The myelination of axons by oligodendrocytes is a highly complex cell-to-cell interaction. Oligodendrocytes and axons have a reciprocal signaling relationship in which oligodendrocytes receive cues from axons that direct their myelination, and oligodendrocytes subsequently shape axonal structure and conduction. Oligodendrocytes are necessary for the maturation of excitatory domains on the axon including nodes of Ranvier, help buffer potassium, and support neuronal energy metabolism. Disruption of the oligodendrocyte-axon unit in traumatic injuries, Alzheimer's disease and demyelinating diseases such as multiple sclerosis results in axonal dysfunction and can culminate in neurodegeneration. In this review, we discuss the mechanisms by which demyelination and loss of oligodendrocytes compromise axons. We highlight the intra-axonal cascades initiated by demyelination that can result in irreversible axonal damage. Both the restoration of oligodendrocyte myelination or neuroprotective therapies targeting these intra-axonal cascades are likely to have therapeutic potential in disorders in which oligodendrocyte support of axons is disrupted.

Injury-Induced Inhibition of Bystander Neurons Requires dSarm and Signaling from Glia

Nervous system injury and disease have broad effects on the functional connectivity of the nervous system, but how injury signals are spread across neural circuits remains unclear. We explored how axotomy changes the physiology of severed axons and adjacent uninjured "bystander" neurons in a simple in vivo nerve preparation. Within hours after injury, we observed suppression of axon transport in all axons, whether injured or not, and decreased mechano- and chemosensory signal transduction in uninjured bystander neurons. Unexpectedly, we found the axon death molecule dSarm, but not its NAD+ hydrolase activity, was required cell autonomously for these early changes in neuronal cell biology in bystander neurons, as were the voltage-gated calcium channel Cacophony (Cac) and the mitogen-activated protein kinase (MAPK) signaling cascade. Bystander neurons functionally recovered at later time points, while severed axons degenerated via α/Armadillo/Toll-interleukin receptor homology domain (dSarm)/Axundead signaling, and independently of Cac/MAPK. Interestingly, suppression of bystander neuron function required Draper/MEGF10 signaling in glia, indicating glial cells spread injury signals and actively suppress bystander neuron function. Our work identifies a new role for dSarm and glia in suppression of bystander neuron function after injury and defines two genetically and temporally separable phases of dSarm signaling in the injured nervous system.

Quantitative birefringence microscopy for imaging the structural integrity of CNS myelin following circumscribed cortical injury in the rhesus monkey

Significance: Myelin breakdown is likely a key factor in the loss of cognitive and motor function associated with many neurodegenerative diseases. Aim: New methods for imaging myelin structure are needed to characterize and quantify the degradation of myelin in standard whole-brain sections of nonhuman primates and in human brain. Approach: Quantitative birefringence microscopy (qBRM) is a label-free technique for rapid histopathological assessment of myelin structural breakdown following cortical injury in rhesus monkeys. Results: We validate birefringence microscopy for structural imaging of myelin in rhesus monkey brain sections, and we demonstrate the power of qBRM by characterizing the breakdown of myelin following cortical injury, as a model of stroke, in the motor cortex. Conclusions: Birefringence microscopy is a valuable tool for histopathology of myelin and for quantitative assessment of myelin structure. Compared to conventional methods, this label-free technique is sensitive to subtle changes in myelin structure, is fast, and enables more quantitative assessment, without the variability inherent in labeling procedures such as immunohistochemistry.

Ascorbic acid accelerates Wallerian degeneration after peripheral nerve injury

Wallerian degeneration occurs after peripheral nerve injury and provides a beneficial microenvironment for nerve regeneration. Our previous study demonstrated that ascorbic acid promotes peripheral nerve regeneration, possibly through promoting Schwann cell proliferation and phagocytosis and enhancing macrophage proliferation, migration, and phagocytosis. Because Schwann cells and macrophages are the main cells involved in Wallerian degeneration, we speculated that ascorbic acid may accelerate this degenerative process. To test this hypothesis, 400 mg/kg ascorbic acid was administered intragastrically immediately after sciatic nerve transection, and 200 mg/kg ascorbic acid was then administered intragastrically every day. In addition, rat sciatic nerve explants were treated with 200 μM ascorbic acid. Ascorbic acid significantly accelerated the degradation of myelin basic protein-positive myelin and neurofilament 200-positive axons in both the transected nerves and nerve explants. Furthermore, ascorbic acid inhibited myelin-associated glycoprotein expression, increased c-Jun expression in Schwann cells, and increased both the number of macrophages and the amount of myelin fragments in the macrophages. These findings suggest that ascorbic acid accelerates Wallerian degeneration by accelerating the degeneration of axons and myelin in the injured nerve, promoting the dedifferentiation of Schwann cells, and enhancing macrophage recruitment and phagocytosis. The study was approved by the Southern Medical University Animal Care and Use Committee (approval No. SMU-L2015081) on October 15, 2015.

Changes in proteins related to early nerve repair in a rat model of sciatic nerve injury

Peripheral nerves have a limited capacity for self-repair and those that are severely damaged or have significant defects are challenging to repair. Investigating the pathophysiology of peripheral nerve repair is important for the clinical treatment of peripheral nerve repair and regeneration. In this study, rat models of right sciatic nerve injury were established by a clamping method. Protein chip assay was performed to quantify the levels of neurotrophic, inflammation-related, chemotaxis-related and cell generation-related factors in the sciatic nerve within 7 days after injury. The results revealed that the expression levels of neurotrophic factors (ciliary neurotrophic factor) and inflammation-related factors (intercellular cell adhesion molecule-1, interferon γ, interleukin-1α, interleukin-2, interleukin-4, interleukin-6, monocyte chemoattractant protein-1, prolactin R, receptor of advanced glycation end products and tumor necrosis factor-α), chemotaxis-related factors (cytokine-induced neutrophil chemoattractant-1, L-selectin and platelet-derived growth factor-AA) and cell generation-related factors (granulocyte-macrophage colony-stimulating factor) followed different trajectories. These findings will help clarify the pathophysiology of sciatic nerve injury repair and develop clinical treatments of peripheral nerve injury. This study was approved by the Ethics Committee of Peking University People’s Hospital of China (approval No. 2015-50) on December 9, 2015.

Heat shock protein is a key therapeutic target for nerve repair in autoimmune peripheral neuropathy and severe peripheral nerve injury

Guillain-Barré syndrome (GBS) is an autoimmune peripheral neuropathy and a common cause of neuromuscular paralysis. Preceding infection induces the production of anti-ganglioside (GD) antibodies attacking its own peripheral nerves. In severe proximal peripheral nerve injuries that require long-distance axon regeneration, motor functional recovery is virtually nonexistent. Damaged axons fail to regrow and reinnervate target muscles. In mice, regenerating axons must reach the target muscle within 35 days (critical period) to reform functional neuromuscular junctions and regain motor function. Successful functional recovery depends on the rate of axon regeneration and debris removal (Wallerian degeneration) after nerve injury. The innate-immune response of the peripheral nervous system to nerve injury such as timing and magnitude of cytokine production is crucial for Wallerian degeneration. In the current study, forced expression of human heat shock protein (hHsp) 27 completely reversed anti-GD-induced inhibitory effects on nerve repair assessed by animal behavioral assays, electrophysiology and histology studies, and the beneficial effect was validated in a second mouse line of hHsp27. The protective effect of hHsp27 on prolonged muscle denervation was examined by performing repeated sciatic nerve crushes to delay regenerating axons from reaching distal muscle from 37 days up to 55 days. Strikingly, hHsp27 was able to extend the critical period of motor functional recovery for up to 55 days and preserve the integrity of axons and mitochondria in distal nerves. Cytokine array analysis demonstrated that a number of key cytokines which are heavily involved in the early phase of innate-immune response of Wallerian degeneration, were found to be upregulated in the sciatic nerve lysates of hHsp27 Tg mice at 1 day postinjury. However, persistent hyperinflammatory mediator changes were found after chronic denervation in sciatic nerves of littermate mice, but remained unchanged in hHsp27 Tg mice. Taken together, the current study provides insight into the development of therapeutic strategies to enhance muscle receptiveness (reinnervation) by accelerating axon regeneration and Wallerian degeneration.

N-Formylated Peptide Induces Increased Expression of Both Formyl Peptide Receptor 2 (Fpr2) and Toll-Like Receptor 9 (TLR9) in Schwannoma Cells-An In Vitro Model for Early Inflammatory Profiling of Schwann Cells

Following nerve injury, disintegrated axonal mitochondria distal to the injury site release mitochondrial formylated peptides and DNA that can induce activation and inflammatory profiling of Schwann cells via formyl peptide receptor 2 (Fpr2) and toll-like receptor 9 (TLR9), respectively. We studied RT4 schwannoma cells to investigate the regulation of Fpr2 and TLR9 after stimulation with fMLF as a prototypical formylated peptide. RT4 cells were treated with fMLF at various concentrations and times with and without pretreatment with inhibitors (chloroquine for activated TLR9, PBP10 for Fpr2). Western blots of Fpr2, TLR9, p-p38, p-NFκB, and IL-6 were compared in relation to inflammatory profiling of RT4 cells and chemokine receptors (CCR2, CXCR4) as potential co-receptors of Fpr2. fMLF stimulation upregulated Fpr2 in RT4 cells at low concentrations (10 nM and 100 nM) but higher concentrations were required (10 µM and 50 µM) when the cells were pretreated with an activated TLR9 inhibitor. Moreover, the higher concentrations of fMLF could modulate TLR9 and inflammatory markers. Upregulation of Fpr2 triggered by 10 nM and 100 nM fMLF coincided with higher levels of chemokine receptors (CCR2, CXCR4) and PKCβ. Treating RT4 cells with fMLF, as an in vitro model of Schwann cells, uncovered Schwann cells’ complex responses to molecular patterns of release from injured axonal mitochondria.

Clinical Features, Risk Factors, and Early Prognosis for Wallerian Degeneration in the Descending Pyramidal Tract after Acute Cerebral Infarction

BACKGROUND

Wallerian degeneration(WD) occurs in the descending pyramidal tract(DPT) after cerebral infarction commonly, but studies of its degree evaluation, influencing factors and effects on nervous function are still limited.

OBJECTIVES

The purpose of this study was to describe these findings and estimate their clinical significance.

METHODS

In total, 133 patients confirmed acute cerebral infarction and restricted diffusion in the DPT of the cerebral peduncle by MRI scans. These cases were retrospectively reviewed. We describe their clinical characteristics and analyze influence factors of WD, including the timespan from symptom onset to MRI and TOAST classification. Their NIHSS scores at admission and first 7 days NIHSS improvement rate after admission were also analyzed.

RESULTS

These patients were divided into three groups by timespan ≤7 days(n = 45),7-14 days(n = 70) and >14 days(n = 18). The mean WD degree (%)of these three groups was 44.41 ± 22.51,52.35 ± 22.61and 44.31 ± 19.35,respectively(p = 0.122).According to the TOAST classification, the mean WD degree(%) of the cardioembolism group(n = 28, 62.80 ± 25.12) was significantly different from both the large-artery atherosclerosis group(n = 73,45.08 ± 20.03,p = 0.000) and the small-vessel occlusion group(n = 23,39.68 ± 16.95,p = 0.000). The mean NIHSS score upon admission of the WD degree≤50% group(n = 82,8.17 ± 5.87) was different from that of the >50% group(n = 51,11.31 ± 7.00)(p = 0.006). However, the mean 7 days NIHSS improvement rate(%) of the WD degree≤50% group(n = 79,11.83 ± 23.76)and >50% group(n = 50,13.40 ± 27.88) was not significantly different(p = 0.733).

CONCLUSIONS

Early WD in ischemic stroke patients has a correlation with serious baseline functional defects. Therefore, we should give close attention to imaging change, especially in those with cardioembolism .

In vivo imaging of injured cortical axons reveals a rapid onset form of Wallerian degeneration

Background

Despite the widespread occurrence of axon and synaptic loss in the injured and diseased nervous system, the cellular and molecular mechanisms of these key degenerative processes remain incompletely understood. Wallerian degeneration (WD) is a tightly regulated form of axon loss after injury, which has been intensively studied in large myelinated fibre tracts of the spinal cord, optic nerve and peripheral nervous system (PNS). Fewer studies, however, have focused on WD in the complex neuronal circuits of the mammalian brain, and these were mainly based on conventional endpoint histological methods. Post-mortem analysis, however, cannot capture the exact sequence of events nor can it evaluate the influence of elaborated arborisation and synaptic architecture on the degeneration process, due to the non-synchronous and variable nature of WD across individual axons.

Results

To gain a comprehensive picture of the spatiotemporal dynamics and synaptic mechanisms of WD in the nervous system, we identify the factors that regulate WD within the mouse cerebral cortex. We combined single-axon-resolution multiphoton imaging with laser microsurgery through a cranial window and a fluorescent membrane reporter. Longitudinal imaging of > 150 individually injured excitatory cortical axons revealed a threshold length below which injured axons consistently underwent a rapid-onset form of WD (roWD). roWD started on average 20 times earlier and was executed 3 times slower than WD described in other regions of the nervous system. Cortical axon WD and roWD were dependent on synaptic density, but independent of axon complexity. Finally, pharmacological and genetic manipulations showed that a nicotinamide adenine dinucleotide (NAD⁺)-dependent pathway could delay cortical roWD independent of transcription in the damaged neurons, demonstrating further conservation of the molecular mechanisms controlling WD in different areas of the mammalian nervous system.

Conclusions

Our data illustrate how in vivo time-lapse imaging can provide new insights into the spatiotemporal dynamics and synaptic mechanisms of axon loss and assess therapeutic interventions in the injured mammalian brain.

Hypertrophic olivary degeneration concomitant with bilateral middle cerebellar peduncles Wallerian degeneration following unilateral pontine infarction

Background

Wallerian degeneration (WD) can occur in different projecting systems, such as corticospinal tract, dentate-rubro-olivary pathway, and corticopontocerebellar tract. However, the co-occurrence of hypertrophic olivary degeneration (HOD) and middle cerebellar peduncles (MCPs) degeneration secondary to unilateral pontine infarction in a single patient is extremely rare.

Case presentation

A 71-year-old man presented with acute onset of dizzness, slurred speech, and right-sided weakness. On the next day, his previous neurologic deficits deteriorated. Brain magnetic resonance imaging (MRI) revealed acute ischemic stroke of the left pons. After treatment with thrombolysis, antiplatelets, and rehabilitation training, his speaking and motor function improved moderately. At the 3-month follow-up, the MRI showed hyperintensity in the left medulla oblongata and bilateral MCPs on T2-weighted and FLAIR images, suggesting HOD as well as MCPs degeneration.

Conclusions

It is of great importance for us to know the anatomic knowledge of dentate-rubro-olivary and corticopontocerebellar pathways.

Wallerian degeneration in cervical spinal cord tracts is commonly seen in routine T2-weighted MRI after traumatic spinal cord injury and is associated with impairment in a retrospective study

Objectives

Wallerian degeneration (WD) is a well-known process after nerve injury. In this study, occurrence of remote intramedullary signal changes, consistent with WD, and its correlation with clinical and neurophysiological impairment were assessed after traumatic spinal cord injury (tSCI).

Methods

In 35 patients with tSCI, WD was evaluated by two radiologists on T2-weighted images of serial routine MRI examinations of the cervical spine. Dorsal column (DC), lateral corticospinal tract (CS), and lateral spinothalamic tract (ST) were the analyzed anatomical regions. Impairment scoring according to the American Spinal Injury Association Impairment Scale (AIS, A–D) as well as a scoring system (0–4 points) for motor evoked potential (MEP) and sensory evoked potential (SEP) was included. Mann-Whitney U test was used to test for differences.

Results

WD in the DC occurred in 71.4% (n = 25), in the CS in 57.1% (n = 20), and in 37.1% (n = 13) in the ST. With WD present, AIS grades were worse for all tracts. DC: median AIS B vs D, p < 0.001; CS: B vs D, p = 0.016; and ST: B vs D, p = 0.015. More pathological MEP scores correlated with WD in the DC (median score 0 vs 3, p < 0.001) and in the CS (0 vs 2, p = 0.032). SEP scores were lower with WD in the DC only (1 vs 2, p = 0.031).

Conclusions

WD can be detected on T2-weighted scans in the majority of cervical spinal cord injury patients and should be considered as a direct effect of the trauma. When observed, it is associated with higher degree of impairment.

Key Points

• Wallerian degeneration is commonly seen in routine MRI after traumatic spinal cord injury.

• Wallerian degeneration is visible in the anatomical regions of the dorsal column, the lateral corticospinal tract, and the lateral spinothalamic tract.

• Presence of Wallerian degeneration is associated with higher degree of impairment.

Coding transcriptome analyses reveal altered functions underlying immunotolerance of PEG-fused rat sciatic nerve allografts

BACKGROUND

Current methods to repair ablation-type peripheral nerve injuries (PNIs) using peripheral nerve allografts (PNAs) often result in poor functional recovery due to immunological rejection as well as to slow and inaccurate outgrowth of regenerating axonal sprouts. In contrast, ablation-type PNIs repaired by PNAs, using a multistep protocol in which one step employs the membrane fusogen polyethylene glycol (PEG), permanently restore sciatic-mediated behaviors within weeks. Axons and cells within PEG-fused PNAs remain viable, even though outbred host and donor tissues are neither immunosuppressed nor tissue matched. PEG-fused PNAs exhibit significantly reduced T cell and macrophage infiltration, expression of major histocompatibility complex I/II and consistently low apoptosis. In this study, we analyzed the coding transcriptome of PEG-fused PNAs to examine possible mechanisms underlying immunosuppression.

METHODS

Ablation-type sciatic PNIs in adult Sprague-Dawley rats were repaired using PNAs and a PEG-fusion protocol combined with neurorrhaphy. Electrophysiological and behavioral tests confirmed successful PEG-fusion of PNAs. RNA sequencing analyzed differential expression profiles of protein-coding genes between PEG-fused PNAs and negative control PNAs (not treated with PEG) at 14 days PO, along with unoperated control nerves. Sequencing results were validated by quantitative reverse transcription PCR (RT-qPCR), and in some cases, immunohistochemistry.

RESULTS

PEG-fused PNAs display significant downregulation of many gene transcripts associated with innate and adaptive allorejection responses. Schwann cell-associated transcripts are often upregulated, and cellular processes such as extracellular matrix remodeling and cell/tissue development are particularly enriched. Transcripts encoding several potentially immunosuppressive proteins (e.g., thrombospondins 1 and 2) also are upregulated in PEG-fused PNAs.

CONCLUSIONS

This study is the first to characterize the coding transcriptome of PEG-fused PNAs and to identify possible links between alterations of the extracellular matrix and suppression of the allorejection response. The results establish an initial molecular basis to understand mechanisms underlying PEG-mediated immunosuppression.

Bilateral middle cerebellar peduncle lesions: Neuroimaging features and differential diagnoses

OBJECTIVES

Lesions limited to the bilateral middle cerebellar peduncles (MCPs) are uncommon. This retrospective study investigated diseases with a proclivity for the bilateral MCPs and explored the associations between their neuroimaging features and clinical findings for the differential diagnosis of such lesions.

METHODS

We enrolled 26 patients who were admitted to our department between January 2016 and March 2019 with bilateral MCP abnormalities on magnetic resonance imaging (MRI). The demographic, clinical, and neuroimaging characteristics, and the biomarkers and diagnoses were evaluated.

RESULTS

Although all patients exhibited symmetrical bilateral MCP hypointensities on T1-weighted imaging and hyperintensities on T2-weighted and fluid-attenuated inversion recovery imaging, they were diagnosed with different conditions. Diagnoses included acute cerebral infarction (ACI) (n = 9, 34.62%), Wallerian degeneration (WD) (n = 8, 30.77%), multiple system atrophy (MSA) (n = 6, 23.08%), neuromyelitis optica (NMO) (n = 1, 3.85%), heroin-induced leukoencephalopathy (n = 1, 3.85%), and primary central nervous system lymphoma (PCNSL) (n = 1, 3.85%). Patients with ACI exhibited bilateral MCP-restricted diffusion hyperintensities on diffusion-weighted imaging and corresponding stenosis or occlusion of the vertebrobasilar system. The initial MRI of patients with WD depicted pontine infarctions, while symmetrical MCP lesions were observed on follow-up MRI. Symmetrical MCP lesions, cruciform hyperintensity, and marked atrophy in the posterior fossa were characteristic manifestations of MSA. Longitudinally extensive myelitis affecting more than three vertebral segments on cervical MRI and positive serum AQP4-IgG may be indicative of NMO. Heroin-induced leukoencephalopathy was characterized by extra-symmetrical lesions in the posterior limbs of the internal capsules, while the anterior limbs were spared. PCNSL was indicated by a significant and characteristic "fist" sign on contrast-enhanced MRI.

CONCLUSIONS

Bilateral MCP lesions were most frequently observed in cerebrovascular diseases, followed by neurodegenerative diseases, inflammatory diseases, toxic encephalopathies, and lymphomas. Our findings demonstrate that bilateral MCP signal abnormalities are more common in patients with ACI and WD, with fewer degenerative processes than previously believed. The high frequency of WD may be attributed to the specific awareness of this pathology. WD can also present with stage-related restricted diffusion and should not be mistaken for a new infarction. The symmetrical bilateral MCP hypointensities on T1-weighted imaging and hyperintensities on T2-weighted imaging often raise concern regarding a demyelinating process. Our findings emphasize that neurologists should consider the aforementioned conditions and correlate the specific neuroimaging characteristics and medical history before arriving at the final diagnosis.

Polyethylene glycol-fusion repair of sciatic allografts in female rats achieves immunotolerance via attenuated innate and adaptive responses

Ablation/segmental loss peripheral nerve injuries (PNIs) exhibit poor functional recovery due to slow and inaccurate outgrowth of regenerating axons. Viable peripheral nerve allografts (PNAs) as growth-guide conduits are immunologically rejected and all anucleated donor/host axonal segments undergo Wallerian degeneration. In contrast, we report that ablation-type sciatic PNIs repaired by neurorrhaphy of viable sciatic PNAs and a polyethylene glycol (PEG)-fusion protocol using PEG immediately restored axonal continuity for many axons, reinnervated/maintained their neuromuscular junctions, and prevented much Wallerian degeneration. PEG-fused PNAs permanently restored many sciatic-mediated behaviors within 2-6 weeks. PEG-fused PNAs were not rejected even though host/donors were neither immunosuppressed nor tissue-matched in outbred female Sprague Dawley rats. Innate and adaptive immune responses to PEG-fused sciatic PNAs were analyzed using electron microscopy, immunohistochemistry, and quantitative reverse transcription polymerase chain reaction for morphological features, T cell and macrophage infiltration, major histocompatibility complex (MHC) expression, apoptosis, expression of cytokines, chemokines, and cytotoxic effectors. PEG-fused PNAs exhibited attenuated innate and adaptive immune responses by 14-21 days postoperatively, as evidenced by (a) many axons and cells remaining viable, (b) significantly reduced infiltration of cytotoxic and total T cells and macrophages, (c) significantly reduced expression of inflammatory cytokines, chemokines, and MHC proteins, (d) consistently low apoptotic response. Morphologically and/or biochemically, PEG-fused sciatic PNAs often resembled sciatic autografts or intact sciatic nerves. In brief, PEG-fused PNAs are an unstudied, perhaps unique, example of immune tolerance of viable allograft tissue in a nonimmune-privileged environment and could greatly improve the clinical outcomes for PNIs relative to current protocols.

Corticospinal Wallerian Degeneration Before Myelination: A Case Report

Wallerian degeneration is defined as axonal fiber and myelin sheath degeneration that affects myelinated axons within the peripheral or central nervous system. Wallerian degeneration or anterograde axonal degeneration before myelination is rarely reported. Involvement of both corticospinal tracts (CSTs) is rarely documented in the literature. We present the postmortem neuropathologic findings of a 1-week-old male neonate born at 23 weeks of gestation with bilateral CST degeneration extending from the posterior limb of the internal capsule through the brainstem into the lumbar spinal cord. Abundant CD68- and CD163-positive macrophages were the prominent histopathology in both CSTs. The cerebrum, brainstem, and spinal cord were unmyelinated, as expected. In contrast, the spinal nerve roots demonstrated early myelination. This case illustrates that Wallerian degeneration occurs in unmyelinated axis cylinders.

Closing the Gap Between Mammalian and Invertebrate Peripheral Nerve Injury: Protocol for a Novel Nerve Repair

BACKGROUND

Outcomes after peripheral nerve injuries are poor despite current nerve repair techniques. Currently, there is no conclusive evidence that mammalian axons are capable of spontaneous fusion after transection. Notably, certain invertebrate species are able to auto-fuse after transection. Although mammalian axonal auto-fusion has not been observed experimentally, no mammalian study to date has demonstrated regenerating axolemmal membranes contacting intact distal segment axolemmal membranes to determine whether mammalian peripheral nerve axons have the intrinsic mechanisms necessary to auto-fuse after transection.

OBJECTIVE

This study aims to assess fusion competence between regenerating axons and intact distal segment axons by enhancing axon regeneration, delaying Wallerian degeneration, limiting the immune response, and preventing myelin obstruction.

METHODS

This study will use a rat sciatic nerve model to evaluate the effects of a novel peripheral nerve repair protocol on behavioral, electrophysiologic, and morphologic parameters. This protocol consists of a variety of preoperative, intraoperative, and postoperative interventions. Fusion will be assessed with electrophysiological conduction of action potentials across the repaired transection site. Axon-axon contact will be assessed with transmission electron microscopy. Behavioral recovery will be analyzed with the sciatic functional index. A total of 36 rats will be used for this study. The experimental group will use 24 rats and the negative control group will use 12 rats. For both the experimental and negative control groups, there will be both a behavior group and another group that will undergo electrophysiological and morphological analysis. The primary end point will be the presence or absence of action potentials across the lesion site. Secondary end points will include behavioral recovery with the sciatic functional index and morphological analysis of axon-axon contact between regenerating axons and intact distal segment axons.

RESULTS

The author is in the process of grant funding and institutional review board approval as of March 2020. The final follow-up will be completed by December 2021.

CONCLUSIONS

In this study, the efficacy of the proposed novel peripheral nerve repair protocol will be evaluated using behavioral and electrophysiologic parameters. The author believes this study will provide information regarding whether spontaneous axon fusion is possible in mammals under the proper conditions. This information could potentially be translated to clinical trials if successful to improve outcomes after peripheral nerve injury.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/18706.

Development and Characterisation of an in vitro Model of Wallerian Degeneration

Following peripheral nerve injury, a sequence of events termed Wallerian degeneration (WD) takes place at the distal stump in order to allow the regenerating axons to grow back toward the target organs. Schwann cells (SCs) play a lead role in this by initiating the inflammatory response attracting macrophages and immune cells, as well as producing neurotrophic signals that are essential for nerve regeneration. The majority of existing research has focused on tools to improve regeneration, overlooking the critical degeneration phase. This is also due to the lack of in vitro models recapitulating the features of in vivo WD. In particular, to understand the initial SC response following injury, and to investigate potential interventions, a model that isolates the nerve from other systemic influences is required. Stem cell intervention has been extensively studied as a potential therapeutic intervention to augment regeneration; however, data regarding their role in WD is lacking. Thus, in this study we describe an in vitro model using rat sciatic nerve explants degenerating up to 14 days. Characterisation of this model was performed by gene and protein expression for key markers of WD, in addition to immunohistochemical analysis and electron microscopy. We found changes in keeping with WD in vivo: upregulation of repair program protein CJUN, downregulation of myelin protein genes and subsequent disorganisation and breakdown of myelin structure. As a means of testing the effects of stem cell intervention on WD we established indirect co-cultures of human adipose-derived mesenchymal stem cells (AD-MSC) with the degenerating nerve explants. The stem cell intervention potentiated neurotrophic factors and Cjun expression. We conclude that our in vitro model shares the main features of in vivo WD, and we provide proof of principle on its effectiveness to study experimental approaches for nerve regeneration focused on the events happening during WD.

Inhibition of transient receptor potential melastatin 7 (TRPM7) protects against Schwann cell trans-dedifferentiation and proliferation during Wallerian degeneration

Irreversible peripheral neurodegenerative diseases such as diabetic peripheral neuropathy are becoming increasingly common due to rising rates of diabetes mellitus; however, no effective therapeutic treatments have been developed. One of main causes of irreversible peripheral neurodegenerative diseases is dysfunction in Schwann cells, which are neuroglia unique to the peripheral nervous system (PNS). Because homeostasis of calcium (Ca²⁺) and magnesium (Mg²⁺) is essential for Schwann cell dynamics, the regulation of these cations is important for controlling peripheral nerve degeneration and regeneration. Transient receptor potential melastatin 7 (TRPM7) is a non-selective ion (Ca²⁺ and Mg²⁺) channel that is expressed in Schwann cells. In the present study, we demonstrated in an ex vivo culture system that inhibition of TRPM7 during peripheral nerve degeneration (Wallerian degeneration) suppressed dedifferentiable or degenerative features (trans-dedifferentiation and proliferation) and conserved a differentiable feature of Schwann cells. Our results indicate that TRPM7 could be very useful as a molecular target for irreversible peripheral neurodegenerative diseases, facilitating discovery of new therapeutic methods for improving human health.

Direct and specific assessment of axonal injury and spinal cord microenvironments using diffusion correlation imaging

We describe a practical two-dimensional (2D) diffusion MRI framework to deliver specificity and improve sensitivity to axonal injury in the spinal cord. This approach provides intravoxel distributions of correlations of water mobilities in orthogonal directions, revealing sub-voxel diffusion components. Here we use it to investigate water diffusivities along axial and radial orientations within spinal cord specimens with confirmed, tract-specific axonal injury. First, we show using transmission electron microscopy and immunohistochemistry that tract-specific axonal beading occurs following Wallerian degeneration in the cortico-spinal tract as direct sequelae to closed head injury. We demonstrate that although some voxel-averaged diffusion tensor imaging (DTI) metrics are sensitive to this axonal injury, they are non-specific, i.e., they do not reveal an underlying biophysical mechanism of injury. Then we employ 2D diffusion correlation imaging (DCI) to improve discrimination of different water microenvironments by measuring and mapping the joint water mobility distributions perpendicular and parallel to the spinal cord axis. We determine six distinct diffusion spectral components that differ according to their microscopic anisotropy and mobility. We show that at the injury site a highly anisotropic diffusion component completely disappears and instead becomes more isotropic. Based on these findings, an injury-specific MR image of the spinal cord was generated, and a radiological-pathological correlation with histological silver staining % area was performed. The resulting strong and significant correlation (r = 0.70, p < 0.0001) indicates the high specificity with which DCI detects injury-induced tissue alterations. We predict that the ability to selectively image microstructural changes following axonal injury in the spinal cord can be useful in clinical and research applications by enabling specific detection and increased sensitivity to injury-induced microstructural alterations. These results also encourage us to translate DCI to higher spatial dimensions to enable assessment of traumatic axonal injury, and possibly other diseases and disorders in the brain.

Early exposure to environmental enrichment protects male rats against neuropathic pain development after nerve injury

Because environmental elements modify chronic pain development and endogenous mechanisms of pain control are still a great therapeutic source, we investigated the effects of an early exposure to environmental enrichment (EE) in a translational model of neuropathic pain. Young male rats born and bred in an enriched environment, which did not count on running wheel, underwent chronic constriction injury (CCI) of sciatic nerve. EE abolished neuropathic pain behavior 14 days after CCI. Opioid receptors' antagonism reversed EE-analgesic effect. β-endorphin and met-enkephalin serum levels were increased only in EE-CCI group. Blockade of glucocorticoid receptors did not alter EE-analgesic effect, although corticosterone circulating levels were increased in EE animals. In the spinal cord, EE controlled CCI-induced serotonin increase. In DRG, EE blunted the expression of ATF-3 after CCI. Surprisingly, EE-CCI group showed a remarkable preservation of sciatic nerve fibers compared to NE-CCI group. This work demonstrated global effects induced by an EE protocol that explain, in part, the protective role of EE upon chronic noxious stimulation, reinforcing the importance of endogenous mechanisms in the prevention of chronic pain development.

Axon Degeneration Assays in Superior Cervical Ganglion Explant Cultures

The ability of peripheral nervous system neurons to extend long, axon-like neurites in vitro makes them ideally suited for studies on mechanisms of axon survival and degeneration. In this chapter, we describe how to prepare explant cultures of sympathetic neurons of the superior cervical ganglion (SCG). We also describe how to induce and assess axon degeneration with an injury or a chemical insult.