Myelin Vacuolation Research Articles

Genetic and Physiological Evidence That Oligodendrocyte Gap Junctions Contribute to Spatial Buffering of Potassium Released during Neuronal Activity

Mice lacking the K+ channel Kir4.1 or both connexin32 (Cx32) and Cx47 exhibit myelin-associated vacuoles, raising the possibility that oligodendrocytes, and the connexins they express, contribute to recycling the K+ evolved during neuronal activity. To study this possibility, we first examined the effect of neuronal activity on the appearance of vacuoles in mice lacking both Cx32 and Cx47. The size and number of myelin vacuoles was dramatically increased when axonal activity was increased, by either a natural stimulus (eye opening) or pharmacological treatment. Conversely, myelin vacuoles were dramatically reduced when axonal activity was suppressed. Second, we used genetic complementation to test for a relationship between the function of Kir4.1 and oligodendrocyte connexins. In a Cx32-null background, haploinsufficiency of either Cx47 or Kir4.1 did not affect myelin, but double heterozygotes developed vacuoles, consistent with the idea that oligodendrocyte connexins and Kir4.1 function in a common pathway. Together, these results implicate oligodendrocytes and their connexins as having critical roles in the buffering of K+ released during neuronal activity.

Progressive white matter pathology in the spinal cord of transgenic mice expressing mutant (P301L) human tau

Transgenic mice expressing mutant (P301L) tau develop paresis, neurofibrillary tangles and neuronal loss in spinal motor neurons beginning at 4 to 6 months of age. Astrocytes and oligodendrocytes acquire filamentous tau inclusions at later ages. Here we report pathology in the spinal white matter of these animals. Progressive white matter pathology, detected as early as 2 months of age, was most marked in lateral and anterior columns, with sparing of posterior columns until late in the disease. Early changes in Luxol fast blue/periodic acid Schiff (LFB/PAS) and toluidine blue stained sections were vacuolation of myelin followed by accumulation of myelin figures within previous axonal tubes and finally influx of PAS-positive macrophages. Myelin debris and vacuoles were found in macrophages. At the ultrastructural level, myelinated axons showed extensive vacuolation of myelin sheaths formed by splitting of myelin lamellae at the intra-period line, while axons were atrophic and contained densely packed neurofilaments. Other axons were lost completely, resulting in collapse and phagocytosis of myelin sheaths. Also present were spheroids derived from swollen axons with thin myelin sheaths containing neurofilaments, tau filaments and degenerating organelles. Many oligodendrocytes had membrane-bound cytoplasmic bodies composed of tightly stacked lamellae capped by dense material. The vacuolar myelopathy in this model to some extent resembles that reported in acquired immune deficiency syndrome and vitamin B12 deficiency. The progressive axonal pathology is most consistent with a dying-back process caused by abnormal accumulation of tau in upstream neurons, while vacuolar myelinopathy may be a secondary manifestation of neuroinflammation.

Systematic analysis of axonal damage and inflammatory response in different white matter tracts of acutely injured rat spinal cord

The mechanisms of white matter (WM) damage during secondary degeneration are a fundamental issue in the pathophysiology of central nervous system (CNS) diseases. Our main goal was to describe the pattern of an acute inflammatory response and secondary damage to axons in different WM tracts of acutely injured rat spinal cord. Adult rats were deeply anesthetized and injected with 20 nmol of NMDA into the spinal cord ventral horn on T7. Animals were perfused after survival times of 1 day, 3 days and 7 days. Ten micrometer sections were submitted to immunocytochemical analysis for activated macrophages/microglia, neutrophils and damaged axons. There were inflammatory response and progressive tissue destruction of ventral WM (VWM) with formation of microcysts in both VWM and lateral WM (LWM). In the VWM, the number of β-amyloid precursor protein (β-APP) end-bulbs increased from 1 day with a peak at 3 days, decreasing by 7 days following the injection. APP end-bulbs were present in the dorsal WM (DWM) at 3 days survival time but were not in the LWM. Electron microscopic analysis revealed different degrees of myelin disruption and axonal pathology in the vacuolated WM up to 14 mm along the rostrocaudal axis. Quantitative analysis revealed a significant loss of medium and large axons ( P < 0.05), but not of small axons ( P > 0.05). Our results suggest that bystander axonal damage and myelin vacuolation are important secondary component of the pathology of WM tracts following rat SCI. Further studies are needed to understand the mechanisms of these pathological events.

The Effects of Vigabatrin on Rat Liver Antioxidant Status

The anti-epileptic drug vigabatrin was developed as an inhibitor of gamma-aminobutyric acid transaminase, and its ability to increase inhibition in the central nervous system led to its testing in an animal model. In animal models chronic use of vigabatrin is associated with irreversible myelin vacuolation. Antioxidant drugs change the antioxidant capacity of the body. Oxidative stress of the body increased when valproic acid and carbamazepine were used chronically. To assess whether vigabatrin may affect protein oxidation and lipid peroxidation, glutathione, glutathione peroxidase (GPx), and glutathione-S-transferase (GST) levels were studied in the livers of 57 rat fetuses after administration of vigabatrin to the mothers (19 in the first week of pregnancy, 20 in the second week, and 18 in the third week) and in 19 control rat fetuses without vigabatrin. We compared the results of administration of vigabatrin in each group with the controls. Rat fetus protein oxidation in group I (0.686 nmol/mg protein) and group II (0.723 nmol/mg protein) was higher than in the control group (0.388 nmol/mg protein). Lipid peroxidation (0.209, 0.224, 0.253 nmol/mg protein, respectively) and GPx levels (345.4, 329.0, 283.2 nmol/mg protein, respectively) of groups I, II, and III were higher than in the control group (0.104, 167.2 nmol/mg protein, respectively). GST in group II (79.2 nmol/mg protein) and group III (77.8 nmol/mg protein) were not different from that in the control group (78 nmol/mg protein). It was found that vigabatrin affected all the parameters that were studied, especially in group I, which was given the drug in the first week of pregnancy.

Brain magnetic resonance imaging in tyrosinemia

A 3.5-year-old girl with tyrosinemia is reported. A computed tomography scan of the abdomen revealed multiple hepatic nodules. Brain magnetic resonance imaging revealed bilateral high-signal changes confined to the globus pallidus on T2-weighted images. Globus pallidus lesions likely represented neuropathologic changes such as astocytosis, delayed myelination, and status spongiosus (myelin splitting and vacuolation).

Renal (Uremic) Encephalopathy in a Goat

Renal encephalopathy was diagnosed in a 2-year-old male boar goat with a history of chronic weight loss and ataxia. Histopathological examination of the brain revealed a striking myelin vacuolation distributed mainly in two patterns: (i) along the junction of the neocortex and corona radiata, and (ii) in the bundles of the internal capsule as it dissects through the basal nuclei. The kidneys had diffuse severe tubular and glomerular necrosis and degeneration. The neural lesions are consistent with renal (uremic) encephalopathy. To the authors' knowledge, this is the first report of renal encephalopathy in a goat.

Brain Apparent Diffusion Coefficient Evaluation in Pediatric Patients With Neurofibromatosis Type 1

The most frequent intracranial appearance in children with neurofibromatosis type 1 (NF1) is represented by the presence of hyperintense lesions on T2-weighted images, the so-called "unidentified bright objects" (UBOs). Di Paolo demonstrated that these lesions represent foci of myelin vacuolization with increased water content. The aim of this study was to investigate the isotropic apparent diffusion coefficient (ADC) values within the UBOs and normal-appearing brain and at the regressed UBO sites. Fifteen consecutive children with NF1 underwent magnetic resonance diffusion evaluation of the brain. Fifteen healthy age- and sex-matched children constituted the control group. Apparent diffusion coefficient maps were obtained, and regions of interest were placed bilaterally in 8 different areas. Two cortical areas were evaluated using single-pixel analysis. Apparent diffusion coefficient values within the UBOs were calculated by using irregular regions of interest. Regressed UBO sites were investigated by using circular regions of interest. Apparent diffusion coefficient values within the different areas were compared using a t test. Compared with the controls, NF1 patients showed higher ADC values (P < 0.001) in all locations. In the NF1 group, the mean ADC value in the UBOs was higher than in other locations (P < 0.001). The mean ADC value within the regressed UBO sites was higher than in the normal-appearing locations (P < 0.001). The higher ADC values in children with NF1 suggest an increase in water content of the normal-appearing brain. The UBOs are the areas with the highest water content. The regressed UBOs sites show higher water content than the normal-appearing areas.

Effects of AAV-2-mediated aspartoacylase gene transfer in the tremor rat model of Canavan disease

The tremor rat is a spontaneous epilepsy model with a seizure phenotype caused by a deletion in the aspartoacylase ( ASPA) gene. The absence of ASPA expression in these animals results in undetectable levels of enzyme activity and the accumulation of the substrate N-acetyl-aspartate (NAA) in brain, leading to generalized myelin vacuolation and severe motor and cognitive impairment. In support of human gene therapy for CD, recombinant adeno-associated viral vector (AAV-2) expressing ASPA was stereotactically delivered to the tremor rat brain and effects on the mutant phenotype were measured. AAV– ASPA gene transfer resulted in elevated aspartoacylase bioactivity compared to untreated mutant animals and elicited a significant decrease in the pathologically elevated whole-brain NAA levels. Assessment of motor function via quantitative rotorod testing demonstrated that rats injected with AAV– ASPA significantly improved on tests of balance and coordinated locomotion compared to animals receiving control vectors. This study provides evidence that AAV-2-mediated aspartoacylase gene transfer to the brain improves biochemical and behavioral deficits in tremor rat mutants ( tm/ tm) and supports the rationale of human gene transfer for Canavan disease.

Pediatric brain MRI in neurofibromatosis type I.

Neurofibromatosis (NF) is the most common of the phakomatoses, with a prevalence of 1 in 3-4,000. Many organ systems can be affected. In addition to multiple peripheral neurofibromas, NF I predisposed to CNS tumors including optic glioma, astrocytoma and plexiform neurofibroma. The purpose of this pictorial review is to illustrate characteristic brain MR imaging lesions in children with NF I and to give some recommendations about diagnostic imaging procedures in children suffering from NF I. Typical findings in brain MRI are hyperintense lesion on T2-weighted images, so-called unknown bright objects, which may be useful as an additional imaging criterion for NF I. Contrast administration is necessary in MR studies to maximize tumor detection and characterization, to add confidence to the diagnosis of benign probable myelin vacuolization, and to document stability of neoplasm on follow-up examinations. We recommend to perform serial MR imaging in children every 12 months. The frequency of follow-up in children with known brain tumors will vary with the tumor grade, biological activity and treatment.

PCR-Based Genotyping of the Rat Atrnmv Mutation

Rat myelin vacuolation mutation at the Attractin locus (Atrn(mv)) is a genomic deletion including the whole exon 1 of the Atrn gene. The precise size and location of the deleted region has not yet been identified because of poor information on genomic organization of the rat Atrn gene. Here, we identified the breakpoints of the Atrn(mv) mutation, using a draft sequence of the rat genome. In the Atrn(mv/mv) rat, a 6,914-bp genomic region was deleted. Primers flanked 5'- and 3'- breakpoints amplified the Atrn(mv) allele but not the wild-type allele. This primer set enables us to distinguish Atrn(mv/+) heterozygous rats from Atrn(+/+) rats, and will contribute to the efficient production of Atrn(mv/mv) rats.

Longitudinal evaluation of apparent diffusion coefficient in children with neurofibromatosis type 1.

Foci of T2-prolongation in both supra- and infratentorial brain in neurofibromatosis type-1 (NF1) patients have been called hamartoma-like NF1 lesions (HLL); however, their behavior is not consistent with this definition. Diffusion-weighted imaging has been used to study structure and cellularity of intracranial lesions. We applied this technique to characterize HLL as they change with time in pediatric patients. We retrospectively studied 12 children (ages 2-20 years) with proven NF1. Forty lesions were studied longitudinally on multiple exams for a total of 166 measurements. Apparent diffusion coefficients (ADCs) were also obtained from a comparison group comprising 14 normal children (ages 2-16 years). The ADC for the lesions was generally greater than normal brain. Both supra- and infratentorial lesions had increasing ADC with patient age. This is contrasted to our comparison group of normal subjects who showed decreasing ADC with age. Linear regression analysis of infratentorial lesions yielded a slope of 2.70 x 10(-6) mm2 x s(-1) x year(-1) versus a slope of 17.57 x 10(-6) mm2 x s(-1) x year(-1) for supratentorial lesions. Our observed increase in ADC of lesions in pediatric patients with NF1 suggests increasing water in the extracellular space and/or decreasing cellularity with patient age. This change may be due to increased number or size of myelin vacuoles in NF1 lesions. Supratentorial lesions had a statistically significant increase in the rate of change of ADC compared with infratentorial lesions which may reflect an intrinsic difference in the lesion or similar lesions expressed in different environments.

Prominent myelin vacuolization in neurofibromatosis type 2

Myelin vacuolization has previously been documented by MRI with histopathologic correlation in patients with neurofibromatosis type 1. This paper presents a patient with neurofibromatosis type 2 with MRI findings consistent with a prominent form of myelin vacuolization, unilaterally involving the right thalamus, globus pallidus and substantia nigra. On MRI, they appeared as multiple nodular-ovoid structures with a layered configuration. They were hypointense on T1-weighted, and FLAIR images, and hyperintense on T2-weighted images. On the apparent diffusion coefficient (ADC) map of an echo-planar diffusion imaging sequence, their ADC value ranged between 1.98 and 2.27×10 −3 mm 2/s, a value higher than that of normal cerebral parenchyma, less than that of CSF.

The Myelin Vacuolation (mv) Rat with a Null Mutation in the Attractin Gene

We recently found a spontaneous tremor mutant in an outbred colony of Sprague-Dawley rats. The tremor behavior was exhibited from around 3 weeks of age and inherited as an autosomal recessive trait. The mutant rats had variously sized vacuoles in the neuropil and white matter throughout the central nervous system, especially in the brain stem, cerebellum, and spinal cord. Ultrastructurally these vacuoles mainly consisted of splitting of myelin lamella both in the periaxonal and intermyelinic spaces. Linkage analysis using intercross progeny between the myelin vacuolation (mv) rat, named after the pathologic characteristics, and normal control rat strains showed that the mv phenotypes were cosegregated with polymorphic markers adjacent to the Atrn (Attractin, formerly zi [zitter]) locus on rat chromosome 3. A test for allelism suggested that the mv mutation was a new allele in Atrn. In comparison with a marked decrease of Atrnzi/Arnzi, Northern blot analysis revealed no expression of Atrn mRNA in the brain of the mv rats. Finally, a genomic deletion including exon 1 of the mv rats was detected by genomic and sequence analyses. Discovery of the rat null mutation Atrnmv, different from Atrnzi, provides a new animal model for studying the functions of the attractin protein.

The central nervous system in systemic lupus erythematosus. Part 2. Pathogenetic mechanisms of clinical syndromes: a literature investigation.

To identify the pathogenetic mechanisms of central nervous system (CNS) syndromes of systemic lupus erythematosus (SLE) as described in the literature. Using PUBMED, we performed a systematic search of publications from 1980 onwards. Studies were eligible if they had been performed on patients or material from patients with CNS manifestations and definite SLE and when the CNS manifestations were not secondary. Criteria were formulated for the identification of pathogenetic mechanisms. The single most important cause of the CNS syndromes of SLE is ischaemia due to narrowing or occlusion of small vessels, arteries and veins. Antiphospholipid antibodies and premature atherosclerosis play roles in these processes, but they have not been delineated definitely. Intracranial and intraspinal haemorrhages are much less frequent than ischaemia and are presumably in part due directly to SLE. Vasculitis may cause ischaemia or haemorrhage in the CNS and is involved occasionally, as shown by imaging and histological findings. White matter damage is heterogeneous and ill-understood. It includes white matter degeneration and myelin vacuolation of the spinal cord, and reversible leucoencephalopathy due to oedema. Antibody-induced neuronal dysfunction in the CNS is a realistic hypothesis and may involve anti-ribosomal P antibodies and several other antibodies. Deficiency of psychological reactions forms a separate and entirely different category of mechanisms. Causes have been identified or possible causes have been suggested for most of the CNS syndromes of SLE, thus offering rationales for different forms of prevention and therapy.

Paclitaxel (Taxol) attenuates clinical disease in a spontaneously demyelinating transgenic mouse and induces remyelination.

Treatment with paclitaxel by four intraperitoneal injections (20 mg/kg) 1 week apart attenuated clinical signs in a spontaneously demyelinating model, if given with onset of clinical signs. If given at 2 months of age (1 month prior to clinical signs), disease was almost completely prevented The astrogliosis, prominent in our model, was reversed by paditaxel as determined by astrocyte counts and quantitation of GFAP. Electron microscopic examination of affected regions at 2.5 months demonstrated that the myelin was generally normal. By 4 months of age, demyelination was common in the superior cerebellar peduncle, maximal at 6 months, but continued to 8 months. In addition to myelin vacuolation and nude axons, the presence of many thin myelin sheaths suggested remyelination or partial demyelination. Although no evidence of oligodendrocyte loss was seen, nuclear changes were observed. To substantiate that remyelination was occurring, we measured MBP (18.5 kDa), MBP-exon II, Golli-MBP, TP8, Golli-MBP-J37, platelet-derived growth factor alpha (PDGFR alpha) and sonic hedgehog (SHH). Of these TP8, PDGFR alpha and SHH were up-regulated in the untreated transgenic. After paditaxel treatment, MBP-Exon II, TP8, PDGFR alpha and SHH were further up-regulated. We concluded that some of the effects of paditaxel were to stimulate proteins involved in early myelinating events possibly via a signal transduction mechanism.

Diffusion MRI in neurofibromatosis type 1: ADC evaluations of the optic pathways, and a comparison with normal individuals

In a control group of 12 normal children (ages ranging from 9 months to 3 years; mean=1.6 years ) the mean apparent diffusion coefficient (ADC) value of the normal white matter, obtained from automatically generated ADC maps, was 0.84±0.14×10 −3 mm 2/ s. A patient with neurofibromatosis type 1 with bilateral optic gliomas, and extensive optic pathway involvement was evaluated by diffusion MRI. Multiple measurements of ADC values throughout the involved optic radiations revealed a higher mean value: 1.16±0.06×10 −3 mm 2/ s than that of the normal white matter, suggesting relatively high molecular motion in these regions, probably representing myelin vacuolization. ADC evaluation of a thalamic hamartoma revealed a lower value (=1.06×10 −3 mm 2/ s) than this. The mean ADC value obtained from multiple measurements of the enlarged optic chiasm, and intraorbital portions of the nerve was similar (=0.81±0.09×10 −3 mm 2/ s) to that of the normal cerebral white matter of the control cases. It appears that diffusion imaging can be useful in evaluation of optic pathway involvement in NF1, and might contribute to differentiating optic gliomas from hamartomas, and myelin vacuolization, however, further studies will be required for assessing the role of diffusion imaging in such lesions.

In vivo damage of CNS myelin and axons induced by peroxynitrite

In multiple sclerosis (MS) the mechanisms of injury caused by peroxynitrite remain uncertain. To study histological, ultra structural and molecular alterations caused by peroxynitrite in brain, the peroxynitrite donor 3-morpholinosydnonimine was injected in rat corpus callosum. Peroxynitrite induces strong primary axonal damage with characteristics of primary acute axonopathy, together with severe myelin alteration, myelin vacuolation and demyelination, and nitrotyrosine formation as confirmed by detection of nitrosated target proteins. Administration of the peroxynitrite scavenger uric acid inhibited these effects. In vivo, peroxynitrite leads to a disorganisation of myelin and to axonal damage presenting some similarities to the formation of MS lesions. Understanding the action of peroxynitrite in this process will open new therapeutic strategies by specific inhibition of peroxynitrite formation and action.

Beneficial effects of nitric oxide synthase inhibition on the recovery of neurological function after spinal cord injury in rats.

We have demonstrated recently that treatment with N(G)-monomethyl-L-arginine (L-NMMA) accelerates electrophysiological recovery after transient spinal cord ischaemia in anaesthetized cats. To determine whether nitric oxide synthase (NOS) inhibition in the acute phase of spinal cord injury results in better functional recovery in the chronic phase, we evaluated the influence of L-NMMA on the time course of changes of neurological function and the histopathological changes after spinal cord compression in rats. Experimental spinal cord injury was produced in anaesthetized rats by short-term (5 min) compression with a thread placed around the spinal cord at T13. The recovery of motor function was assessed by a treadmill test 10, 20 and 30 days after spinal cord compression. The latency of potentials evoked by hindlimb stimulation was measured at the funiculus posterior at C1 10 days after the spinal cord injury in anaesthetized rats. Histological examinations were also performed at the same time. The compression-induced spinal cord injury resulted in motor dysfunction of hindlimbs, an increase in the latency of the evoked potentials and neuronal degeneration in funiculus posterior at T13. Repeated administration of L-NMMA for 1 day significantly accelerated the recovery of the motor function, shortened the latency of the evoked potentials and attenuated the myelin vacuolization in the spinal cord. These beneficial effects of L-NMMA on neurological function and histopathological changes were abolished by coadministration of L- but not D-arginine. These results suggest that NOS inhibition during the early stage of spinal cord injury has beneficial effects on the recovery of neurological function and the histopathological changes in the chronic stage.

Oligodendrocyte Apoptosis and Primary Demyelination Induced by Local TNF/p55TNF Receptor Signaling in the Central Nervous System of Transgenic Mice: Models for Multiple Sclerosis with Primary Oligodendrogliopathy

The scientific dogma that multiple sclerosis (MS) is a disease caused by a single pathogenic mechanism has been challenged recently by the heterogeneity observed in MS lesions and the realization that not all patterns of demyelination can be modeled by autoimmune-triggered mechanisms. To evaluate the contribution of local tumor necrosis factor (TNF) ligand/receptor signaling pathways to MS immunopathogenesis we have analyzed disease pathology in central nervous system-expressing TNF transgenic mice, with or without p55 or p75TNF receptors, using combined in situ terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling and cell identification techniques. We demonstrate that local production of TNF by central nervous system glia potently and selectively induces oligodendrocyte apoptosis and myelin vacuolation in the context of an intact blood-brain barrier and absence of immune cell infiltration into the central nervous system parenchyma. Interestingly, primary demyelination then develops in a classical manner in the presence of large numbers of recruited phagocytic macrophages, possibly the result of concomitant pro-inflammatory effects of TNF in the central nervous system, and lesions progress into acute or chronic MS-type plaques with axonal damage, focal blood-brain barrier disruption, and considerable oligodendrocyte loss. Both the cytotoxic and inflammatory effects of TNF were abrogated in mice genetically deficient for the p55TNF receptor demonstrating a dominant role for p55TNF receptor-signaling pathways in TNF-mediated pathology. These results demonstrate that aberrant local TNF/p55TNF receptor signaling in the central nervous system can have a potentially major role in the aetiopathogenesis of MS demyelination, particularly in MS subtypes in which oligodendrocyte death is a primary pathological feature, and provide new models for studying the basic mechanisms underlying oligodendrocyte and myelin loss.

Actin modifications and calcium homoeostasis in neurotoxicity. The case of organotin salts

The cytoskeleton is a major constituent of the neuronal cytoplasm; it controls cell shape and plays important roles in regulating various physiological processes. In neurons, actin filaments are involved in the growth of the neurite and the neurotransmitter release. Recent findings suggest that actin filaments play a role in modulating [Ca 2+] i responses to neurotoxic insults. The physiological functioning of the neural cell is critically dependent on the intracellular distribution of calcium. An increase of cytosolic free calcium can activate a number of intracellular reactions, including neurotransmitter release, protein phosphorylation, protease activity, and, eventually, cell death. Many neurotoxic agents with diverse mechanisms have been reported to affect mechanisms associated with calcium. Among these are organotin compounds: they can both raise the cytosolic and synaptosomal [Ca 2+] i concentrations and interfere with the [Ca 2+] i response evoked by different agonists. Furthermore, some of these compounds cause actin depolymerization. The interference of triethyltin (TET)—a compound inducing myelin vacuolization and brain oedema—with Ca 2+ homoeostasis and actin polymerization results in an adverse effect on neurotransmitter release in different neural cell lines. However, another neurotoxic organotin compound (trimethyltin, TMT) induces apoptosis in neural cells through the activation of a Ca 2+-dependent pathway. In conclusion, the identification of the key changes in actin and Ca 2+ homoeostasis could give early information on neural cell perturbation resulting in altered functionality or even cell death.