Stages Of Wallerian Degeneration Research Articles

Stressed axons craving for glial sugar: links to regeneration?

Stressed axons craving for glial sugar: links to regeneration?

O-29 CMAP scan and MScanFit MUNE during Wallerian degeneration after nerve transactions

Background Wallerian degeneration (WD) includes complex physiological changes in the distal portion of the axon which follow a severe injury. The aim of this study was to advance our earlier observations with MUNE studies during early stages of WD by evaluating the CMAP Scan curve and MScanFit MUNE in the same period. Materials and methods Twelve patients with acute nerve transections at the forearm (7 median, 5 ulnar) were recruited. First electrophysiological studies, performed at 9–72 h after the insult, were followed by serial studies at 1–2 day intervals until CMAP amplitudes reached at zero. At each session, CMAP Scan curves were recorded, their quantitative parameters and the new MUNE method, MScanFit, were calculated. The results were grouped according to the recording time after injury (before and after the 48th hour). They were compared with those of healthy controls and amyotrophic lateral sclerosis (ALS) patients. Results Excitability of axons was reduced in patients with transected nerves, as compared controls and ALS patients, irrespective of the recording time. In most of the patients, MUNE values decreased during the follow-up as a result of relatively more pronounced reduction of CMAP amplitudes as compared to mean unit sizes. While steps occurred in 8 patients, D50 remained unchanged during the follow-up. Conclusions These suggest higher ability of MScanFit, as compared to other MUNE methods, in discriminating the changes caused by functional instability of neuromuscular junction. Occasional steps in the early WD deserve some arguments on their possible mechanisms.

Diffusion-Weighted Imaging of the Early Phase of Wallerian Degeneration

Wallerian degeneration (WD) affects axons and their myelin sheaths distally from the site of injury of the axon and/or body of the neuron. There is limited knowledge about brain injuries in newborns, mostly because non-invasive imaging sensitive enough to detect subtle changes was not available. Diffusion-weighted magnetic resonance (MR) imaging (DWI) is sensitive in the detection of early injury to the corticospinal tracts (CST) before the occurrence of WD in distal segments. We describe the cases of 14- and seven-day-old newborns in whom MR imaging revealed vascular injury in the territory supplied by the middle cerebral artery, and early development of WD. We performed DWI and faced an unexpected finding because DWI hyperintensities were at the same time hyperintense on T2-weighted images. Hyperintense structures on DWI are supposed to reflect pre-Wallerian injured tissue, which should not be visible on standard MR sequences, while their T2- signal indicated the third, late subacute phase of WD. It seems that time-related stages of WD observed in adults do not necessarily apply to the immature brain of newborns/infants as reflected by differences in signal intensity in various MR sequences. DWI hyperintensity in CST below infarct should not be mistaken for new ischemic foci.

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.

Granulocyte macrophage colony stimulating factor (GM-CSF) activity is regulated by a GM-CSF binding molecule in Wallerian degeneration following injury to peripheral nerve axons

The hematopoietic factor and inflammatory cytokine GM-CSF is involved in PNS and CNS injury and disease, and in macrophage and microglia function regulation. We presently document that injury to PNS axons induces in vivo production of GM-CSF-inhibitor and GM-CSF-augmenter activities. GM-CSF-inhibitor activity was detected in extract and conditioned medium (CM) of injured PNS but not in extract of intact PNS, and was removed from CM by GM-CSF affinity chromatography, suggesting it is carried by a secreted GM-CSF binding molecule. CM further displayed GM-CSF-augmenter activity along with GM-CSF-inhibitor activity but at contrasting concentrations; augmentation at lowest and inhibition at highest. GM-CSF activity is thus regulated during Wallerian degeneration (WD); augmenter activity characterizes the onset and inhibitor activity the later stages of WD.

Diffusion-weighted imaging in Wallerian degeneration

We report two patients displaying hyperintensities on diffusion-weighted imaging (DWI) in the area of Wallerian degeneration (WD) at 12 days after stroke. High signal intensities were more conspicuous on DWI than on T2-weighted images. Both patients showed decreased diffusion anisotropy resulting in elevated apparent diffusion coefficient in the area of WD. These patients illustrate that DWI may be useful in the detection of the early stage of WD.

230 Electrodermal activity and neural regeneration

Axon injury rapidly activates microglial and astroglial cells close to the axotomized neurons. Following motor axon injury, astrocytes upregulate within hour(s) the gap junction protein connexin-43, and within one day glial fibrillary acidic protein (GFAP). Concomitantly, microglial cells proliferate and migrate towards the axotomized neuron perikarya. Analogous responses occur in central termination territories of peripherally injured sensory ganglion cells. The activated microglia express a number of inflammatory and immune mediators. When neuron degeneration occurs, microglia act as phagocytes. This is uncommon after peripheral nerve injury in the adult mammal, however, and the functional implications of the glial cell responses in this situation are unclear. When central axons are injured, the glial cell responses around the affected neuron perikarya appears to be minimal or absent, unless neuron degeneration occurs.Microglia proliferate, and astrocytes upregulate GFAP along central axons undergoing anterograde, Wallerian, degeneration. Although microglia develop into phagocytes, they eliminate the disintegrating myelin very slowly, presumably because they fail to release molecules which facilitate phagocytosis. During later stages of Wallerian degeneration, oligodendrocytes express clusterin, a glycoprotein implicated in several conditions of cell degeneration.A hypothetical scheme for glial cell activation following axon injury is discussed, implying the injured neurons initially interact with adjacent astrocytes. Subsequently, neighbouring resting microglia are activated. These glial reactions are amplified by paracrine and autocrine mechanisms, in which cytokines appear to be important mediators. The specific functional properties of the activated glial cells will determine their influence on neuronal survival, axon regeneration, and synaptic plasticity. The control of the induction and progression of these responses are therefore likely to be critical for the outcome of, for example, neurotrauma, brain ischemia and chronic neurodegenerative diseases.

Central neuron–glial and glial–glial interactions following axon injury

Axon injury rapidly activates microglial and astroglial cells close to the axotomized neurons. Following motor axon injury, astrocytes upregulate within hour(s) the gap junction protein connexin-43, and within one day glial fibrillary acidic protein (GFAP). Concomitantly, microglial cells proliferate and migrate towards the axotomized neuron perikarya. Analogous responses occur in central termination territories of peripherally injured sensory ganglion cells. The activated microglia express a number of inflammatory and immune mediators. When neuron degeneration occurs, microglia act as phagocytes. This is uncommon after peripheral nerve injury in the adult mammal, however, and the functional implications of the glial cell responses in this situation are unclear. When central axons are injured, the glial cell responses around the affected neuron perikarya appears to be minimal or absent, unless neuron degeneration occurs. Microglia proliferate, and astrocytes upregulate GFAP along central axons undergoing anterograde, Wallerian, degeneration. Although microglia develop into phagocytes, they eliminate the disintegrating myelin very slowly, presumably because they fail to release molecules which facilitate phagocytosis. During later stages of Wallerian degeneration, oligodendrocytes express clusterin, a glycoprotein implicated in several conditions of cell degeneration. A hypothetical scheme for glial cell activation following axon injury is discussed, implying the injured neurons initially interact with adjacent astrocytes. Subsequently, neighbouring resting microglia are activated. These glial reactions are amplified by paracrine and autocrine mechanisms, in which cytokines appear to be important mediators. The specific functional properties of the activated glial cells will determine their influence on neuronal survival, axon regeneration, and synaptic plasticity. The control of the induction and progression of these responses are therefore likely to be critical for the outcome of, for example, neurotrauma, brain ischemia and chronic neurodegenerative diseases.

Expression of Neuregulins and their Putative Receptors, ErbB2 and ErbB3, Is Induced during Wallerian Degeneration

Schwann cell dedifferentiation and proliferation is a prerequisite to axonal regeneration in the injured peripheral nervous system. The neuregulin (NRG) family of growth and differentiation factors may play a particularly important role in this process, because these axon-associated molecules are potent Schwann cell mitogens and differentiation factors in vitro. We have examined Schwann cell DNA synthesis and the expression of NRGs and their receptors, the erbB membrane tyrosine kinases, in rat sciatic nerve, sensory ganglia, and spinal cord 0-30 d postaxotomy. Analysis of NRG cDNAs from these tissues revealed several novel splice variants and showed that cells endogenous to injured nerve express NRG mRNAs. A selective induction of mRNAs encoding the glial growth factor (GGF) subfamily of NRGs occurs in nerve beginning 3 d postaxotomy and thus coincides with the onset of Schwann cell DNA synthesis. In later stages of Wallerian degeneration, however, Schwann cell mitogenesis markedly decreases, whereas elevated GGF expression persists. Of the four known erbB kinases, Schwann cells express both erbB2 and erbB3 receptors over the entire interval studied. Expression of erbB2 and erbB3 is coordinately induced in response to axotomy, indicating that Schwann cell responses to NRGs may be modulated by changes in receptor density. Neuregulin (including transmembrane precursors) and erbB protein are associated with Schwann cells postaxotomy. Thus, in contrast to the concept of NRGs as axon-associated mitogens, our findings suggest that NRGs produced by Schwann cells themselves may be partially responsible for Schwann cell proliferation during Wallerian degeneration, probably acting via autocrine or paracrine mechanisms.

Inhibitory effects of thalidomide on cellular proliferation, endoneurial edema and myelin phagocytosis during early wallerian degeneration.

In addition to the well-known teratogenic effect of thalidomide, previous studies have revealed mild immunosuppressive properties and, more recently, an anti-angiogenic activity. To find out more about the specificity of these effects we studied the influence of orally administered thalidomide on Wallerian degeneration in rats. Wallerian degeneration is a potent experimental model for studying reproducible cell proliferation in vivo. Examination of distal nerve segments of transected sciatic nerves from rats that had been treated with thalidomide (2 x 250 mg/kg per day) revealed a significant reduction of endoneurial cell counts at 10-15 days after surgery compared to that seen in controls. This effect was not statistically significant, at a very early stage of Wallerian degeneration, i.e., at 5 days after transection of the nerve. Subperineurial edema and phagocytosis was also reduced, although this was not statistically significant. This apparently nonspecific inhibitory effect of thalidomide during early Wallerian degeneration shown in the present study should be investigated further for its possible relationship to other previously established inhibitory activities of thalidomide, especially its immunosuppressive effect in man.

Radiation‐induced Reductions in Macrophage Recruitment Have Only Slight Effects on Myelin Degeneration in Sectioned Peripheral Nerves of Mice

Macrophage recruitment into the distal nerve stump of the cut or crushed sciatic or saphenous nerves of C57BL/6J mice was reduced by prior whole body irradiation. This procedure was successful in keeping the numbers of cells stained with the mouse macrophage-specific antibody F4/80 to the levels found in unsectioned nerves. Quantitative image analysis of immunostained sections showed that the rate of loss of myelin basic protein was identical in nerves from irradiated and unirradiated mice up to 5 days but thereafter was slower in macrophage-deprived nerves. Similar analysis of semithin sections stained with toluidine blue detected more undegenerated myelin in the nerves from irradiated mice 10 days after operation. Quantitative counts made from electron micrographs of the sectioned nerves at 7 days also showed slightly less extensive myelin breakdown in the nerves from irradiated mice. Complete removal of myelin from some Schwann cells can occur without macrophages, but macrophages accelerate the removal of myelin in the later stages of Wallerian degeneration. It is concluded that there are two phases to the breakdown of myelin in peripheral nerves undergoing Wallerian degeneration: an initial stage entirely dependent on the activity of Schwann cells and a later stage dependent on both Schwann cells and the presence of macrophages.

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

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

Nodal and paranodal structural changes in frog optic nerve during early Wallerian degeneration.

Ultrastructural changes in the nodal and paranodal regions of myelinated nerve fibres of frog optic nerves were studied during early stages of Wallerian degeneration. The earliest changes seen include retraction of paranodal loops of myelin from the axolemma and disconnection of paranodal myelin loops from myelin lamellae. These paranodal changes are asymmetric around the node and may be more advanced on either the proximal or distal side. Axoplasmic changes, including segregation of microtubules from neurofilaments, disorientation of microtubules and accumulation of abnormal organelles at nodes, appear shortly. In some axons the 'undercoating' along the widened nodal surfaces becomes patchy, and blebs appear in the nodal axolemma. In freeze-fracture replicas a mixture of particle clusters and particle-free areas appears in both E- and P-faces of the nodal axolemma. Blebs remain particle free. Initially, E-face particles remain segregated to the node and are present only at much lower concentrations in the demyelinated paranodal axolemma, suggesting that they are not freely mobile at this stage. Nodal E-face particles begin to decrease on day 5 associated with an increase in particles at the adjacent demyelinated paranode, and by day 11 the particle distribution is uniformly low over the entire extent of the nodal and demyelinated paranodal axolemma. If nodal E-face particles represent sodium channels, as has been proposed, the sequence of changes in Wallerian degeneration would be compatible with a gradual redistribution of nodal sodium channels into the demyelinated paranode.

Effect of Wallerian degeneration on histamine concentration of the peripheral nerve.

One sciatic nerve of a White Leghorn hen was severed and the distal portion was allowed to undergo Wallerian degeneration. The change in histamine and DNA concentration and mast cell number was measured at different times following nerve sectioning in the proximal regenerating, distal degenerating, and intact, contralateral nerves. The experimental results revealed a significant accumulation of histamine in the proximal desheathed segment and in the contralateral "functional nerve," whereas the biogenic amine in the distal desheathed nerve significantly decreased. The pattern of change of histamine in the distal and proximal nerve sheaths was different: it dropped at 2 h and then rose in the later stages of Wallerian degeneration. In the distal desheathed nerves and in both the proximal and distal nerve sheaths DNA increased significantly by 14 days. The number of mast cells appeared to be highest in the 14-day distal nerve and in the 7-day proximal nerve sheaths. These results support a dual localization of histamine in the peripheral nerve, and are consistent with the interpretation that the amine has either some role in neurotransmission or in the process of growth and regeneration.

Wallerian degeneration of the optic nerve in light of histological and biochemical studies.

Wallerian degeneration of the rabbit optic nerve was produced by enucleation. The ultrastructure, enzyme histochemistry, myelin output as well as the lipid composition of degenerated nerve were studied. The obtained results lead to following conclusions: 1. Esterified cholesterol appeared in the lipid spectrum of myelin membranes undergoing Wallerian degeneration preceding a significant drop of myelin mass, without an involvement of lipomacrophages and without notable changes in the structure of myelin. 2. Esterification of cholesterol could function as a primary factor injuring the myelin membrane in central Wallerian degeneration, similarly as in other demyelinating processes. 3. Lipomacrophages occurring in the later stage of Wallerian degeneration of the optic nerve are of astroglial origin. 4. The slow progress of phagocytosis in the degenerating optic nerve might explain the almost unaffected pattern of myelin lipids in the course of Wallerian degeneration of this structure. 5. Lysocompounds play an important role in the pathomechanism of demyelination in the central nervous system including the optic nerve during further steps of myelin decay.

Ionic shifts in myelinated nerve fibers during early stages of Wallerian degeneration.

The distribution and relative mass fraction of the diffusible ions Na, K, Cl and Ca were determined by X-ray microanalysis in the axons of rat sciatic nerve 18 h and 36 h after crush and in control nerves. The investigations were performed in freeze-dried ultrathin cryosections after shock freezing of the nerves in liquified propane. 18 h after crush, no definite alteration of the ions were found compared to the control nerves. In electron micrographs of routinely processed nerves, no ultrastructural changes were seen. 36 h after crush, two types of ionic imbalance were found, the first characterized by decreased K and slightly increased Na in the axon, the second by concurrently increasing axonal Na and Cl, accompanied, in some fibers, by accumulating Ca. These types of ionic imbalance presumably represent two stages of axolemmal permeability alteration corresponding to early structural changes of axoplasm in electron micrographs of routinely processed nerves at that time.

Histochemistry of myelin. XI. Loss of basic protein in early myelin breakdown and multiple sclerosis plaques.

the early stages of Wallerian degeneration in peripheral nerves are accompanied by loss of a trypanophilic, trypsin-digestible basic protein from myelin. This loss of basic protein is ascribed to the activity of proteolytic enzymes. The reduced trypanophilia in degenerating nerves could not be attributed to loss of lipid. Likewise, the tryptophan-rich trypsin-resistant neurokeratin component of peripheral nerve myelin showed no change in the first week of degeneration. Loss of basic protein has been observed in and surrounding plaques of multiple sclerosis. We infer that digestion of basic protein would lead to the release of the encephalitogenic antigen contained therein.

Struktur und Funktion peripherer Warmblüter-nervenfasern im Frühstadium der Wallerschen Degeneration

1. Morphologisches und physiologisches Verhalten des N. saphenus vom Kaninchen wahrend der Fruhphase der Wallerschen Degeneration wurden untersucht. 2. Von den morphologischen Zeichen der Degeneration weist die granulare Desintegration des Achsenzylinders die beste, wenn auch keine vollstandige zeitliche Ubereinstimmung mit dem Aufhoren der Leitungsfahigkeit auf. Das gilt sowohl fur die Gruppen Aα und Aβ als auch fur die Gruppen B und C. 3. Entgegen der Vermutung anderer Autoren findet sich kein engerer zeitlicher Zusammenhang der Kontinuitatstrennung von Markscheide und Achsenzylinder mit dem Erloschen der Leitungsfunktion. Die Kontinuitatstrennungen folgen der granularen Desintegration und dem Erliegen der Leitungsfahigkeit in groserem zeitlichem Abstand nach. 4. Die quantitative Analyse zeigt, das zunachst die dickeren markhaltigen Fasern, welche den Gruppen Aα und Aβ des physiologischen Schrifttums entsprechen, dann die feineren markhaltigen Fasern mit einem Gesamtkaliber unter 3μ, welche in unserem Material uberwiegend mit den B-Fasern des physiologischen Schrifttums identisch sind, und schlieslich die markarmen C-Fasern von der granular-vakuoligen Desintegration betroffen werden. 5. Dementsprechend werden zunachst die Aα- und Aβ-Fasern, dann die B- und schlieslich die C-Fasern leitunfahig. Die Amplitudenverminderung der Aα-Fasern geht jener der Aβ-Fasern ein wenig voran. 6. Wenige Stunden vor Aufhoren der Leitungsfahigkeit ist eine Verminderung der Zeiterregbarkeit durch Veranderungen in der Reizzeitspannungskurve und durch die Vergroserung der Nutzzeit bei 1,3facher Rheobase nachzuweisen. Die Verminderung der Erregbarkeit betrifft die Gruppen Aα und Aβ fruher als die Gruppe B. 7. Die Leitungsgeschwindigkeit erscheint in den Gruppen Aα und Aβ eher als in der Gruppe B reduziert. 8. Vor Einsetzen der Leitunfahigkeit kommt es in den Gruppen Aα und B zu einem anfanglichen Abfall, spater zu einem leichten Anstieg der Refraktarzeit uber den Ausgangswert des undegenerierten Nerven. Entsprechende Veranderungen bestehen in den Aβ-Fasern, konnen an dem weniger umfangreichen Material jedoch nicht statistisch gesichert werden. 9. Die morphologischen und physiologischen Ergebnisse zeigen, das funktionelle Veranderungen und granular-vakuolige Desintegration des Achsenzylinders nicht in zentrifugaler Richtung im degenerierenden peripheren Nervenstumpf ablaufen. Auch fur die Annahme eines zentripetalen Ablaufes ergibt sich aus dem vorliegenden Material kein ausreichender Anhalt. 10. Die Desintegration des Achsenzylinders betrifft jedoch nicht sofort eine ganze Faser, sondern setzt an mehreren Stellen gleichzeitig ein. Zwischen den desintegrierten Abschnitten finden sich kurzere oder langere Stucke, die lichtmikroskopisch sichere Degenerationszeichen vermissen lassen. Entsprechend lassen die physiologischen Befunde die Moglichkeit offen, das die Leitungsfahigkeit in einer Faser nicht uberall gleichzeitig, sondern zunachst abschnittsweise erlischt.