Long-term effects of a lumbosacral ventral root avulsion injury on axotomized motor neurons and avulsed ventral roots in a non-human primate model of cauda equina injury

Here, we have translated from the rat to the non-human primate a unilateral lumbosacral injury as a model for cauda equina injury. In this morphological study, we have investigated retrograde effects of a unilateral L6-S2 ventral root avulsion (VRA) injury as well as the long-term effects of Wallerian degeneration on avulsed ventral roots at 6-10 months post-operatively in four adult male rhesus monkeys. Immunohistochemistry for choline acetyl transferase and glial fibrillary acidic protein demonstrated a significant loss of the majority of the axotomized motoneurons in the affected L6-S2 segments and signs of an associated astrocytic glial response within the ventral horn of the L6 and S1 spinal cord segments. Quantitative analysis of the avulsed ventral roots showed that they exhibited normal size and were populated by a normal number of myelinated axons. However, the myelinated axons in the avulsed ventral roots were markedly smaller in caliber compared to the fibers of the intact contralateral ventral roots, which served as controls. Ultrastructural studies confirmed the presence of small myelinated axons and a population of unmyelinated axons within the avulsed roots. In addition, collagen fibers were readily identified within the endoneurium of the avulsed roots. In summary, a lumbosacral VRA injury resulted in retrograde motoneuron loss and astrocytic glial activation in the ventral horn. Surprisingly, the Wallerian degeneration of motor axons in the avulsed ventral roots was followed by a repopulation of the avulsed roots by small myelinated and unmyelinated fibers. We speculate that the small axons may represent sprouting or axonal regeneration by primary afferents or autonomic fibers.

Longitudinal assessment of white matter pathology in the injured mouse spinal cord through ultra-high field (16.4 T) in vivo diffusion tensor imaging

This study examined the sensitivity of ultra-high field (16.4 T) diffusion tensor imaging (DTI; 70 μm in-plane resolution, 1mm slice thickness) to evaluate the spatiotemporal development of severe mid-thoracic contusive spinal cord injury (SCI) in mice. In vivo imaging was performed prior to SCI, then again at 2h, 1 day, 3 days, 7 days, and 30 days post-SCI using a Bruker 16.4 T small animal nuclear magnetic resonance spectrometer. Cross-sectional spinal cord areas were measured in axial slices and various DTI parameters, i.e. fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ||) and radial diffusivity (λ⊥), were calculated for the total spared white matter (WM), ventral funiculi (VF), lateral funiculi (LF) and dorsal columns (DCs) and then correlated with histopathology. Cross-sectional area measurements revealed significant atrophy (32% reduction) of the injured spinal cord at the lesion epicentre in the chronic phase of injury. Analysis of diffusion tensor parameters further showed that tissue integrity was most severely affected in the DCs, i.e. the site of immediate impact, which demonstrated a rapid and permanent decrease in FA and λ||. In contrast, DTI parameters for the ventrolateral white matter changed more gradually with time, suggesting that these regions are undergoing more delayed degeneration in a manner that may be amenable to therapeutic intervention. Of all the DTI parameters, λ⊥ was most closely correlated to myelin content whereas changes in FA and λ|| appeared more indicative of axonal integrity, Wallerian degeneration and associated presence of macrophages. We conclude that longitudinal DTI at 16.4T provides a clinically relevant, objective measure for assessing white matter pathology following contusive SCI in mice that may aid the translation of putative neuroprotective strategies into the clinic.

Rapidly progressive amyotrophic lateral sclerosis initially masquerading as a demyelinating neuropathy

Rare cases of demyelinating neuropathy have been described in association with amyotrophic lateral sclerosis (ALS). We report two patients with typical ALS whose initial electroneuromyographic (ENMG) presentation could suggest the existence of a process of motor nerve fiber demyelination. However, subsequent ENMG examinations and the fatal course of the disease in a few months rather supported severe ongoing axonal degeneration at the origin of motor nerve conduction abnormalities. Repeated examinations could be required to distinguish between ENMG features of concomitant demyelinating neuropathy and rapidly progressive motor neuron loss in ALS.

The Corpus Callosum Wallerian Degeneration in the Unilateral Brain Tumors: Evaluation with Diffusion Tensor Imaging (DTI)

PURPOSE

The purpose of this study was to evaluate whether DTI could demonstrate the water diffusivity changes in the corpus callosum (CC), which were not visible on the morphologic imaging in patients with glioblastoma multiforme (GBM) and brain metastases with no midline CC infiltration.

MATERIALS AND METHODS

Twenty-seven patients with treatment naïve unilateral GBM and eleven patients with a solitary brain metastasis with no midline CC infiltration underwent DTI. Ten controls with normal brain MRI were also included. Based on the tensors, the principal diffusion directions, the anisotropy values, and the prior information about the diffusivity pattern in CC, a similarity measure was proposed. Subsequently, the CC was automatically divided into the Witelson subdivisions.

RESULTS

We observed significantly decreased fractional anisotropy values in all the regions of CC in the patients with GBM and metastases as compared to those in the controls. The mean diffusivity values showed a significant increase in all the regions of CC, except the splenium in patients with GBM and the isthmus in the patients with metastases, as compared to that in the controls respectively.

CONCLUSION

In conclusion, DTI is more sensitive than the morphologic MR imaging in the evaluation of changes within the CC, in brain tumours which do not infiltrate the CC. However, these changes of the DTI metrics in the CC are due to a Wallerian degeneration rather than a tumour infiltration, as was shown by our results, as similar changes were seen in the GBM as well as the non-infiltrating metastases patients.

Role of inflammation and cytokines in peripheral nerve regeneration

This chapter provides a review of immune reactions involved in classic as well as alternative methods of peripheral nerve regeneration, and mainly with a view to understanding their beneficial effects. Axonal degeneration distal to nerve damage triggers a cascade of inflammatory events alongside injured nerve fibers known as Wallerian degeneration (WD). The early inflammatory reactions of WD comprise the complement system, arachidonic acid metabolites, and inflammatory mediators that are related to myelin fragmentation and activation of Schwann cells. Fine-tuned upregulation of the cytokine/chemokine network by Schwann cells activates resident and hematogenous macrophages to complete the clearance of axonal and myelin debris and stimulate regrowth of axonal sprouts. In addition to local effects, immune reactions of neuronal bodies and glial cells are also implicated in the survival and conditioning of neurons to regenerate severed nerves. Understanding of the cellular and molecular interactions between the immune system and peripheral nerve injury opens new possibilities for targeting inflammatory mediators to improve functional reinnervation.

Gene expression profiling of the rat sciatic nerve in early Wallerian degeneration after injury

Wallerian degeneration is an important area of research in modern neuroscience. A large number of genes are differentially regulated in the various stages of Wallerian degeneration, especially during the early response. In this study, we analyzed gene expression in early Wallerian degeneration of the distal nerve stump at 0, 0.5, 1, 6, 12 and 24 hours after rat sciatic nerve injury using gene chip microarrays. We screened for differentially-expressed genes and gene expression patterns. We examined the data for Gene Ontology, and explored the Kyoto Encyclopedia of Genes and Genomes Pathway. This allowed us to identify key regulatory factors and recurrent network motifs. We identified 1 546 differentially-expressed genes and 21 distinct patterns of gene expression in early Wallerian degeneration, and an enrichment of genes associated with the immune response, acute inflammation, apoptosis, cell adhesion, ion transport and the extracellular matrix. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed components involved in the Jak-STAT, ErbB, transforming growth factor-β, T cell receptor and calcium signaling pathways. Key factors included interleukin-6, interleukin-1, integrin, c-sarcoma, carcinoembryonic antigen-related cell adhesion molecules, chemokine (C-C motif) ligand, matrix metalloproteinase, BH3 interacting domain death agonist, baculoviral IAP repeat-containing 3 and Rac. The data were validated with real-time quantitative PCR. This study provides a global view of gene expression profiles in early Wallerian degeneration of the rat sciatic nerve. Our findings provide insight into the molecular mechanisms underlying early Wallerian degeneration, and the regulation of nerve degeneration and regeneration.

Transient lysosomal activation is essential for p75 nerve growth factor receptor expression in myelinated Schwann cells during Wallerian degeneration

Myelinated Schwann cells in the peripheral nervous system express the p75 nerve growth factor receptor (p75NGFR) as a consequence of Schwann cell dedifferentiation during Wallerian degeneration. p75NGFR has been implicated in the remyelination of regenerating nerves. Although many studies have shown various mechanisms underlying Schwann cell dedifferentiation, the molecular mechanism contributing to the re-expression of p75NGFR in differentiated Schwann cells is largely unknown. In the present study, we found that lysosomes were transiently activated in Schwann cells after nerve injury and that the inhibition of lysosomal activation by chloroquine or lysosomal acidification inhibitors prevented p75NGFR expression at the mRNA transcriptional level in an ex vivo Wallerian degeneration model. Lysosomal acidification inhibitors suppressed demyelination, but not axonal degeneration, thereby suggesting that demyelination mediated by lysosomes may be an important signal for inducing p75NGFR expression. Tumor necrosis factor-α (TNF-α) has been suggested to be involved in regulating p75NGFR expression in Schwann cells. In this study, we found that removing TNF-α in vivo did not significantly suppress the induction of both lysosomes and p75NGFR. Thus, these findings suggest that lysosomal activation is tightly correlated with the induction of p75NGFR in demyelinating Schwann cells during Wallerian degeneration.

The role of axonopathy in Parkinson's disease

New genetic and environmental studies of Parkinson's disease have revealed early problems in synaptic function and connectivity indicating that axonal impairment may be an important hallmark in this disorder. Since many studies suggest that axonal dysfunction precedes cell body loss, it is critical to target axons with treatments aimed at preserving "connectivity" as well as to develop and verify "biomarkers" with which to assess disease progression and drug efficacy.

Restricted diffusion in Wallerian degeneration of the middle cerebellar peduncles following pontine infarction

BACKGROUND

Acute Wallerian degeneration following infarction has been show to result in areas of restricted diffusion within the brain. Very few reports describe this appearance in middle cerebellar peduncles.

CASE REPORT

A 37 year old woman was admitted to hospital following sudden collapse and was subsequently found to have a pontine infarct. The complex clinical course resulted in MR imaging including DWI at day 4, 9 and 23 after the initial presentation. The cerebellar peduncles were normal when imaged on day 4 and 9. At day 23, symmetrical high T2 signal was seen in both cerebellar peduncles. The DWI illustrated high signal with corresponding low signal on the ADC map consistent with restricted diffusion. We discuss why this appearance is in keeping with Wallerian degeneration and also describe the fibre pathways involved.

CONCLUSIONS

Symmetrical high signal with restricted diffusion in the middle cerebellar peduncles following a pontine lesion is almost certainly attributable to Wallerian degeneration and should not be mistaken for a new ischaemia.