Ultrastructural changes of oligodendroglia and myelin sheaths induced by ethidium bromide

Remyelination in animal models of multiple sclerosis: finding the elusive grail of regeneration

Remyelination biology and the therapeutic potential of restoring myelin sheaths to prevent neurodegeneration and disability in multiple sclerosis (MS) has made considerable gains over the past decade with many regeneration strategies undergoing tested in MS clinical trials. Animal models used to investigate oligodendroglial responses and regeneration of myelin vary considerably in the mechanism of demyelination, involvement of inflammatory cells, neurodegeneration and capacity for remyelination. The investigation of remyelination in the context of aging and an inflammatory environment are of considerable interest for the potential translation to progressive multiple sclerosis. Here we review how remyelination is assessed in mouse models of demyelination, differences and advantages of these models, therapeutic strategies that have emerged and current pro-remyelination clinical trials.

Azetidine-2-Carboxylic Acid-Induced Oligodendrogliopathy: Relevance to the Pathogenesis of Multiple Sclerosis

The naturally occurring imino acid azetidine-2-carboxylic acid (Aze) is consumed by humans and can be misincorporated in place of proline in myelin basic protein (MBP) in vitro. To determine Aze effects on the mammalian CNS in vivo, adult CD1 mice were given Aze orally or intraperitoneally. Clinical signs reminiscent of MBP-mutant mice occurred with 600 mg/kg Aze exposure. Aze induced oligodendrocyte (OL) nucleomegaly and nucleoplasm clearing, dilated endoplasmic reticulum, cytoplasmic vacuolation, abnormal mitochondria, and Aze dose-dependent apoptosis. Immunohistochemistry demonstrated myelin blistering and nuclear translocation of unfolded protein response (UPR)/proinflammatory molecules (ATF3, ATF4, ATF6, eIF2α, GADD153, NFκB, PERK, XBP1), MHC I expression, and MBP cytoplasmic aggregation in OL. There were scattered microglial nodules in CNS white matter (WM); other CNS cells appeared unaffected. Mice given Aze in utero and postnatally showed more marked effects than their dams. These OL, myelin, and microglial alterations are found in normal-appearing WM (NAWM) in multiple sclerosis (MS) patients. Thus, Aze induces a distinct oligodendrogliopathy in mice that recapitulates MS NAWM pathology without leukocyte infiltration. Because myelin proteins are relatively stable throughout life, we hypothesize that Aze misincorporation in myelin proteins during myelinogenesis in humans results in a progressive UPR that may be a primary process in MS pathogenesis.

Remyelination promoting therapies in multiple sclerosis animal models: a systematic review and meta-analysis

An unmet but urgent medical need is the development of myelin repair promoting therapies for Multiple Sclerosis (MS). Many such therapies have been pre-clinically tested using different models of toxic demyelination such as cuprizone, ethidium bromide, or lysolecithin and some of the therapies already entered clinical trials. However, keeping track on all these possible new therapies and their efficacy has become difficult with the increasing number of studies. In this study, we aimed at summarizing the current evidence on such therapies through a systematic review and at providing an estimate of the effects of tested interventions by a meta-analysis. We show that 88 different therapies have been pre-clinically tested for remyelination. 25 of them (28%) entered clinical trials. Our meta-analysis also identifies 16 promising therapies which did not enter a clinical trial for MS so far, among them Pigment epithelium-derived factor, Plateled derived growth factor, and Tocopherol derivate TFA-12.We also show that failure in bench to bedside translation from certain therapies may in part be attributable to poor study quality. By addressing these problems, clinical translation might be smoother and possibly animal numbers could be reduced.

Inherited and acquired disorders of myelin: The underlying myelin pathology

Remyelination is a major therapeutic goal in human myelin disorders, serving to restore function to demyelinated axons and providing neuroprotection. The target disorders that might be amenable to the promotion of this repair process are diverse and increasing in number. They range primarily from those of genetic, inflammatory to toxic origin. In order to apply remyelinating strategies to these disorders, it is essential to know whether the myelin damage results from a primary attack on myelin or the oligodendrocyte or both, and whether indeed these lead to myelin breakdown and demyelination. In some disorders, myelin sheath abnormalities are prominent but demyelination does not occur. This review explores the range of human and animal disorders where myelin pathology exists and focusses on defining the myelin changes in each and their cause, to help define whether they are targets for myelin repair therapy.

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We reviewed myelin disorders of the CNS in humans and animals.

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Myelin damage results from primary attack on the oligodendrocyte or myelin sheath.

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All major categories of disease can affect CNS myelin.

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Myelin vacuolation is common, yet does not always result in demyelination.

Effects of propentofylline on CNS remyelination in the rat brainstem

Propentofylline (PPF) is a xanthine derivative with pharmacological effects distinct from those of the classical methylxanthines. It depresses activation of microglial cells and astrocytes which is associated with neuronal damage during neural inflammation and hypoxia. The aim of this study was to evaluate whether PPF had the capacity of affecting glial cells behavior during the process of demyelination and remyelination following ethidium bromide (EB) gliotoxic injury. EB injection into the CNS is commonly used as an experimental demyelinating model inducing local oligodendroglial and astrocytic death, which results in primary demyelination, blood-brain barrier and glia limitans disruption and Schwann cells invasion. Sixty Wistar rats were divided into four different groups receiving 10 microlitres of 0.1% EB or 0.9% saline solution into the cisterna pontis and treated or not with the xanthine. PPF treatment was done using 12.5 mg/kg/day by the intraperitonial route for 31 days of the experimental period. The rats were euthanized from 7 to 31 days after EB injection and brainstem sections were collected and processed for light and transmission electron microscopy studies. Results from both groups were compared by using a semi-quantitative method developed for documenting in semithin sections the extent and nature of remyelination of demyelinating lesions. Results showed that PPF administration after EB injection significantly increased both oligodendroglial and Schwann cell remyelination at 31 days (mean remyelination scores of 3.67 ± 0.5 for oligodendrocytes and 1.27 ± 0.49 for Schwann cells) compared to untreated animals (scores of 3.19 ± 0.57 and 0.90 ± 0.33, respectively).

Cyclosporine improves remyelination in diabetic rats submitted to a gliotoxic demyelinating model in the brainstem

The use of cyclosporine (CsA) has shown to induce an increase in density of oligodendrocytes near remyelinating areas following the injection of ethidium bromide (EB), a demyelinating agent, in the rat brainstem. It is also known that diabetes mellitus was capable of delaying remyelination by both oligodendrocytes and Schwann cells in this gliotoxic model. This study was designed to assess whether CsA had the capacity to improve remyelination in streptozotocin-induced (50 mg/kg, intraperitoneal route) diabetic rats. Diabetic Wistar rats were divided in different groups receiving 10 microlitres of 0.1% EB or 0.9% saline solution into the cisterna pontis and were treated or not with CsA. During 7 days and, thereafter, three times a week, 10 mg/kg/day of CsA were given by intraperitoneal route. The rats were euthanized from 7 to 31 days after EB or saline injection and brainstem sections were collected and processed for light and transmission electron microscopy studies. Results from different groups were compared by using a semi-quantitative method developed for documenting the extent and nature of remyelination in semithin sections following gliotoxic lesions. Results showed that CsA administration to diabetic rats after EB injection stimulate both oligodendroglial and Schwann cell remyelination (mean remyelination scores of 3.15 ± 0.5 for oligodendrocytes and 1.36 ± 0.58 for Schwann cells) compared to untreated animals (2.52 ± 0.71 for oligodendrocytes and 0.73 ± 0.47 for Schwann cells, respectively). CsA given to diabetic rats was capable of reversing some of the deleterial effects of diabetes on remyelination.

Semi-quantitative analysis of the effects of cyclosporine on remyelination following gliotoxic injection in the brainstem

The use of cyclosporine (CsA) has shown to induce an increase in the density of oligodendrocytes near remyelinating areas following the injection of ethidium bromide (EB), a demyelinating agent, in the rat brainstem. This study was designed in order to evaluate if CsA has the capacity of increasing remyelination. In this context, a comparison between the final balance of myelin repair in CsA treated and non-treated rats was assessed using a semi-quantitative method developed for documenting the extent and nature of remyelination in gliotoxic lesions. Wistar rats were submitted to intracisternal injection of 10 microliters of 0.1% EB. Some were treated during 31 days with CsA (group III--10 mg/kg/day by 7 days and, thereafter, 3 times a week, with a minimal interval of 48 hours) by intraperitonial route. Others were not treated with CsA (group I). A control group was planned receiving into the cisterna pontis 10 microliters of 0.9% saline solution and following after that the same CsA administration protocol (group II). Results clearly demonstrate that in vivo administration of CsA after EB-demyelinating lesions stimulated oligodendrocyte remyelination (mean remyelination scores of 3.72±0.25 for oligodendrocytes and 1.04±0.39 for Schwann cells) compared to non-treated animals (3.13±0.71 and 1.31±0.62, respectively), although the mechanisms by which this positive CsA effect occurs are unclear.

Age-related and cuprizone-induced changes in myelin and transcription factor gene expression and in oligodendrocyte cell densities in the rostral corpus callosum of mice

During aging, there is a decrease both in the stability of central nervous system (CNS) myelin once formed and in the efficiency of its repair by oligodendrocytes (OLs). To study CNS remyelination during aging, we used the cuprizone (a copper chelator) mouse model. Inclusion of cuprizone in the diet kills mature OLs and demyelinates axons in the rostral corpus callosum (CC) of mice, which enabled us to characterize age-related changes (i.e., 2-16 months of age) in glial cell response during the recruitment (i.e., demyelination) and differentiation (i.e., remyelination) phases of myelin repair. We have found that the time between 12 and 16 months of age is a critical period during which there is an age-related decrease in the number of OL lineage cells (Olig2(Nuc)+ve/GFAP-ve cells) in the rostral CC of both control mice and mice recovering from cuprizone-induced demyelination. Our results also show there was an age-related impaired recruitment of progenitor cells to replace lost OLs in spite of there being no major age-related decrease in the size of the progenitor cell pool (PDGFalphaR+ve/GFAP-ve, and Olig2(Nuc) +ve/PDGFalphaR+ve cells). However, there were cuprizone-induced increased numbers of astrocyte progenitor cells (Olig2(Cyto)+ve/PDGFalphaR+ve) in these same mice; thus PDGFalphaR+ve progenitor cells in mice as old as 16 months of age retain the ability to differentiate into astrocytes, with this fate choice occurring following cytoplasmic translocation of Olig2. These data reveal for the first time age-related differences in the differentiation of PDGFalphaR+ve progenitor cells into OLs and astrocytes and lead us to suggest that during aging there must be a transcriptional switch mechanism in the progenitor cell fate choice in favor of astrocytes. This may at least partially explain the age-related decrease in efficiency of OL myelination and remyelination.

Ultrastructural study of the effects of cyclosporine in the brainstem of Wistar rats submitted to the ethidium bromide demyelinating model

The ethidium bromide-demyelinating model (EB) was used to study remyelination in the brainstem under the use of cyclosporine (CsA). Wistar rats were submitted to intracisternal injection of 0.1% EB or 0.9% saline solution, and others were taken as histologic controls (group I). Within those injected with EB, some have not received immunosuppressive treatment (II); some were treated by intraperitonial route with CsA (III.E - 10 mg/kg/day). Rats from group III.C were injected with saline solution and treated with CsA. The animals were perfused from 15 to 31 days post-injection collecting brainstem sections for light and transmission electron microscopy studies. After EB injection it was noted the presence of macrophages and non-degraded myelin debris, demyelinated axons, oligodendrocyte or Schwann cell remyelinated axons, groups of infiltrating pial cells, hypertrophic astrocytes and few lymphocytes. Tissue repair of EB-induced lesions in group III.E was similar to that of group II, but with the presence of a higher density of oligodendrocytes near remyelinating areas.

[Evaluation of locomotor activity after a local induction of toxic demyelination in the brainstem of Wistar rats]

Ethidium-bromide (EB)-induced lesions have been used to investigate the incomplete remyelination in the central nervous system, as well as to evaluate therapeutic strategies to accelerate the reconstruction of the lost myelin sheaths. Although many electrophysiologic studies were performed in situations of experimental demyelination and remyelination, their behavioural effects have not been properly analyzed. In this study, we investigated ultrastructurally the EB - demyelinating lesions as well as the locomotor activity of rats during the beam walking test after a focal induction of demyelination using the EB model in the ventral surface of the brainstem. It was observed the occurrence of locomotor deficits until 31 days post-injection, as well as that subsequent remyelination was related to the return of the lost function.

Delayed Schwann cell and oligodendrocyte remyelination after ethidium bromide injection in the brainstem of Wistar rats submitted to streptozotocin diabetogenic treatment

Schwann cell disturbance followed by segmental demyelination in the peripheral nervous system occurs in diabetic patients. Since Schwann cell and oligodendrocyte remyelination in the central nervous system is a well-known event in the ethidium bromide (EB) demyelinating model, the aim of this investigation was to determine the behavior of both cell types after local EB injection into the brainstem of streptozotocin diabetic rats. Adult male Wistar rats received a single intravenous injection of streptozotocin (50 mg/kg) and were submitted 10 days later to a single injection of 10 microL 0.1% (w/v) EB or 0.9% saline solution into the cisterna pontis. Ten microliters of 0.1% EB was also injected into non-diabetic rats. The animals were anesthetized and perfused through the heart 7 to 31 days after EB or saline injection and brainstem sections were collected and processed for light and transmission electron microscopy. The final balance of myelin repair in diabetic and non-diabetic rats at 31 days was compared using a semi-quantitative method. Diabetic rats presented delayed macrophage activity and lesser remyelination compared to non-diabetic rats. Although oligodendrocytes were the major remyelinating cells in the brainstem, Schwann cells invaded EB-induced lesions, first appearing at 11 days in non-diabetic rats and by 15 days in diabetic rats. Results indicate that short-term streptozotocin-induced diabetes hindered both oligodendrocyte and Schwann cell remyelination (mean remyelination scores of 2.57 +/- 0.77 for oligodendrocytes and 0.67 +/- 0.5 for Schwann cells) compared to non-diabetic rats (3.27 +/- 0.85 and 1.38 +/- 0.81, respectively).

Estudo ultra-estrutural do processo remielinizante pós-injeção de brometo de etídio no tronco encefálico de ratos imunossuprimidos com dexametasona

Linfócitos estão presentes nas lesões desmielinizantes induzidas pelo brometo de etídio (BE) no sistema nervoso central (SNC) e a possibilidade de sua participação em eventuais respostas imunomediadas às bainhas de mielina desprendidas não pode ser descartada. Este estudo objetivou investigar as conseqüências da imunossupressão com dexametasona no reparo do SNC após injeção local de BE. Ratos Wistar adultos receberam 10 microlitros de solução de BE a 0,1% na cisterna pontis. Alguns destes foram tratados intraperitonealmente com dexametasona (3 mg/kg/dia, grupo I, n=15) durante o período experimental; outros não foram imunossuprimidos (grupo II, n=15). Animais de ambos os grupos foram perfundidos com solução fixadora de glutaraldeído a 4% aos 7,11,15,21 e 31 dias pós-injeção de BE. Fragmentos do tronco encefálico foram colhidos e processados para estudos de microscopia eletrônica de transmissão. Os ratos do grupo I apresentaram maiores quantidades de membranas derivadas de mielina que os não-imunossuprimidos (grupo II), sugerindo um atraso na atividade macrofágica de retirada dos restos mielínicos. Raros linfócitos foram encontrados. A atividade remielinizante oligodendroglial também mostrou um padrão retardado, com claro predomínio de axônios desmielinizados.

Estudo da imunorreatividade astrocitária para GFAP e vimentina no tronco encefálico de ratos Wistar submetidos ao modelo gliotóxico do brometo de etídio

INTRODUÇÃO: O brometo de etídio (BE) é reconhecido como um agente gliotóxico que causa desaparecimento focal astrocitário e oligodendroglial. OBJETIVO: Investigou-se a imunorreatividade astrocitária à proteína glial fibrilar ácida (GFAP) e à vimentina (VIM) após injeção do BE. MÉTODO: Ratos Wistar adultos foram tomados como controles histológicos (grupo H) ou injetados na cisterna basal com BE a 0,1% (grupo E) ou salina a 0,9% (grupo C). Fragmentos do tronco encefálico foram colhidos das 24 horas aos 31 dias pós-injeção para estudo imuno-histoquímico da GFAP e VIM pelo método da avidina-biotina. RESULTADOS: No grupo E, foram observadas extensas lesões na ponte e no mesencéfalo, com desaparecimento astrocitário da área central 24 horas pós-BE, bem como infiltração macrofágica e astrogliose periférica a partir do 3º dia. Os astrócitos marginais apresentaram imunorreatividade aumentada à GFAP e reexpressão de VIM, esta confinada às bordas imediatas do sítio lesional. No grupo C, foram visualizadas lesões pontinas discretas, com preservação astrocitária central e marcação menos intensa para GFAP nos bordos em relação ao grupo E. Nenhuma imunorreatividade para VIM foi notada em tais astrócitos. CONCLUSÃO: Os astrócitos das margens das lesões induzidas pelo BE apresentaram imunorreatividade aumentada para GFAP e reexpressão de VIM.

The reaction of glial progenitor cells in remyelination following ethidium bromide-induced demyelination in the mouse spinal cord

The present study investigated how glial progenitor cells participated in the process of remyelination following ethidium bromide (EBr)-induced demyelination in the adult mouse spinal cord. In situ hybridization techniques for detecting mRNA for platelet-derived growth factor alpha receptor (PDGFalphaR) and proteolipid protein (PLP) were employed to identify glial progenitor cells and mature oligodendrocytes, respectively. During the demyelination stage and early stage of remyelination, large cells strongly expressing PDGFalphaR mRNA were observed in the border of the demyelinating lesion, and with immunohistochemistry they exhibited positive labeling of the astrocytic marker glial fibrillary acidic protein (GFAP). Other glial progenitor cells expressing PDGFalphaR mRNA proliferated around the lesion during the demyelination stage. During the remyelination stage, some PDGFalphaR mRNA-positive cells partly expressed mRNA for PLP in the periphery of the demyelinating lesion. These results suggest that PDGFalphaR mRNA-positive glial progenitor cells may give rise to both astrocytes and oligodendrocytes, which participate in remyelination following demyelination.

Ruptura da barreira hematoencefálica após injeção de droga gliotóxica no tronco encefálico de ratos wistar

O brometo de etídio (BE) determina desaparecimento astrocitário local, com ruptura da glia limitans e suposto dano na barreira hematoencefálica (BBB). Este estudo visou avaliar a integridade da BBB após injeção de solução de BE a 0,1% (grupo E) ou de salina a 0,9% (grupo C) na cisterna pontis de ratos Wistar. Fragmentos do tronco encefálico foram coletados das 24 horas aos 31 dias pós-injeção para estudo ultra-estrutural e marcação imuno-histoquímica para a GFAP. Alguns animais receberam carvão coloidal por via intravenosa nos mesmos períodos. Nos ratos do grupo C, não houve sinal de perda astrocitária, nem extravasamento vascular de carvão no sítio da injeção. No grupo E, o desaparecimento astrocitário começou às 48 horas e algumas áreas estavam ainda destituídas de processos astrocíticos 31 dias após. Extravasamento de partículas de carvão nas lesões foi visto de 48 horas até 7 dias, não sendo detectada qualquer alteração ultra-estrutural das junções oclusivas pela falta de astrócitos perivasculares.

The effect of immunosuppressive protocols on spontaneous CNS remyelination following toxin-induced demyelination

Glial cell transplantation is a potential therapy for human demyelinating disease, though obtaining large numbers of human myelinating cells for transplantation remains a major stumbling block. Autologous transplantation is currently not possible, since the adult human CNS is not a good source of oligodendrocyte precursors, and long-term immunosuppression of engrafted allogeneic or xenogeneic cells is therefore likely to be necessary. Immunosuppressive drugs may need to be used in situations where more recent, active areas of demyelination are undergoing endogenous remyelination. It is therefore pertinent to establish the extent to which immunosuppressive protocols will suppress spontaneous remyelination. In order to investigate this issue, we created demyelinating lesions in the spinal cord of adult rats and compared the extent of remyelination in animals receiving different immunosuppressive treatments. In animals given only cyclosporin A, there was no difference in the extent of either Schwann cell or oligodendrocyte remyelination of ethidium bromide-induced demyelinating lesions. However, in animals given cyclophosphamide, either alone or in combination with cyclosporin, there was a significant reduction in the extent of oligodendrocyte-mediated remyelination. These results demonstrate that cyclophosphamide is deleterious to oligodendrocyte remyelination and for this reason should be used with caution in patients with demyelinating disease.

Uteroplacental insufficiency alters cerebral mitochondrial gene expression and DNA in fetal and juvenile rats

Uteroplacental insufficiency increases the risk of perinatal and long-term neurologic morbidity by depriving the fetus of oxidative substrate and causing intrauterine growth retardation. Skeletal muscle and liver from growth retarded fetal and juvenile rats respond to this deprivation by altering mitochondrial gene expression and function. The objective of this study was to determine whether cerebral mitochondrial mRNA is similarly altered in fetal and juvenile growth retarded rats and to correlate these alterations with mitochondrial DNA and marker protein levels. To fulfill this objective, mRNA levels of four important mitochondrial proteins were quantified using RT-PCR in growth retarded and sham-operated control fetal and juvenile rat brains; these proteins were NADH-ubiquinone oxireductase subunit 4, subunit C of the F1F0-ATPase, and the adenine nucleotide transporters 1 and 2. Mitochondrial DNA/nuclear DNA ratios and mitochondrial 60 kD marker protein levels were also quantified in growth retarded and sham-operated control fetal and juvenile rat brains using PCR and Western Blotting, respectively. Cerebral mRNA levels of all four proteins were increased in the IUGR fetuses and decreased in the IUGR juvenile animals. Cerebral mitochondrial/nuclear DNA ratios and mitochondrial marker protein levels were not significantly altered in the IUGR fetuses; however, both were significantly diminished in IUGR juvenile pups. These studies suggest that the metabolic stresses associated with uteroplacental insufficiency in the rat cause altered fetal and postnatal cerebral mitochondrial mRNA and DNA levels.

Disconnection of cerebellar Purkinje cells in Kearns-Sayre syndrome

Kearns-Sayre syndrome (KSS) is a sporadic multisystem disorder due to rearrangements in mitochondrial DNA (mtDNA). To gain further insight into the pathogenesis of cerebellar dysfunction in KSS, antibodies against synaptophysin (SY) were used to identify presynaptic terminals and antibodies to calbindin D (CB) to identify Purkinje cells in the cerebellar cortex and in the dentate nucleus from two autopsied cases of KSS. By conventional neuropathology we found marked spongiform degeneration and by immunohistochemistry a disruption of presynaptic terminals and of the terminal arborizations of Purkinje cell axons on multipolar neurons of the dentate nucleus in the KSS patients. We suggest that a disconnection of Purkinje cells at the dentate nucleus may play a role in the pathogenesis of cerebellar ataxia in KSS.

Inflammatory response of the spinal cord to multiple episodes of blood-brain barrier disruption and toxic demyelination in Wistar rats

Multiple episodes of blood-brain barrier disruption were induced by sequential intraspinal injections of ethidium bromide. In addition to the barrier disruption, there was toxic demyelination and exposure of myelin components to the immune system. Twenty-seven 3-month-old Wistar rats received 2, 3 or 4 injections of 1 microliter of either 0.1% ethidium bromide in normal saline (19 rats) or 0.9% saline (8 rats) at different levels of the spinal cord. The time intervals between the injections ranged from 28 to 42 days. Ten days after the last injection, all rats were perfused with 2.5% glutaraldehyde. The spinal sections were evaluated macroscopically and by light and transmission electron microscopy. All the lesions demonstrated a mononuclear phagocytic infiltrate apparently removing myelin. Lymphocytes were not conspicuous and were found in only 34% of the lesions. No perivascular cuffings were detected. In older lesions (38 days and older) they were found only within Virchow-Robin spaces. This result suggests that multiple blood-brain barrier disruptions with demyelination and exposure of myelin components to the immune system were not sufficient to induce an immune-mediated reaction in the central nervous system.

[Demyelination and remyelination after multiple intramedullary injections of ethidium bromide in Wistar rats]

The ethidium bromide model of demyelination has been employed to study the central nervous system response to several episodes of demyelination. Twenty-seven Wistar rats received 2 to 4 intraspinal injections of 1 microliter of either 0.1% ethidium bromide in normal saline (19 rats) or saline 0.9% (8 rats) in different anatomical locations. The intervals between the injections ranged from 28 to 42 days. Ten days after the last injection all the rats were perfused with 2.5% glutaraldehyde. The spinal sections were evaluated macroscopically and by light and transmission electron microscopy. The lesions were typical of focal primary demyelination with preserved vascular structures and followed by remyelinization and varied in size and histological aspects. After multiple sequential ethidium bromide injections, the central nervous system seems to modify its response capacity to an inflammatory challenge although there is no change in its pattern of remyelination.

Spongiform central nervous system myelinopathy in African dwarf goats

A novel spongiform myelinopathy of the central nervous system (CNS) of eleven African dwarf goats was examined by light and electron microscopy. Histological lesions consisted of extensive vacuolation predominantly of the white matter of the diencephalon, midbrain and cerebellar peduncles, as well as of spinal white matter. Ultrastructurally, vacuoles were shown to be intramyelinic, resulting from the splitting of the outer myelin lamellae at the intraperiod line. A few oligodendrocytes showed vacuolar degeneration of cell bodies and processes. Inflammatory reactions were absent. The observed lesions point to an unknown primary damage of oligodendroglia and central myelin. A hereditary background of the disorder is suspected as all investigated dwarf goats were half-brothers or -sisters and partly descended from the mating of adult females with their own sire.

Myelinolysis after correction of hyponatremia in two dogs

Two dogs developed delayed neurological deterioration after rapid correction of severe hyponatremia. Sequential magnetic resonance imaging showed the development of lesions in the thalamus. One dog was necropsied, and the lesions were characterized by myelinolysis with sparing of axons and neurons. The second dog gradually recovered with no detectable neurological deficits. The syndrome seems analogous to central pontine myelinolysis in human beings. Guidelines for correction of hyponatremia to prevent development of myelinolysis are given.

Desmielinização tóxica do sistema nervoso central: I. Ação de uma droga intercalante gliotóxica na medula espinhal de ratos Wistar

Pequenos volumes de brometo de etídio foram injetados nas colunas dorsais da medula lombar de ratos Wistar. Foi assim induzido processo desmielinizante que variou em natureza e velocidade de reparação de acordo com a dose empregada. As lesões produzidas foram classificadas em três tipos (I, rápidas; II, lentas; III, intermediárias), de acordo com as características histológicas e a extensão da remielinização. Em algumas lesões ou em áreas dentro da mesma lesão, os restos de mielina e de células gliais eram rapidamente processados por macrófagos e os axônios rapidamente remielinizados por células de Schwann, enquanto em outras lesões de duração similar, ou em áreas dentro da mesma lesão, a mielina se transformava em emaranhados de membranas que persistiam ao redor do axônio por longos períodos de tempo. Nas lesões que continham tais membranas derivadas da mielina, os macrófagos eram escassos e a remielinização, feita pelas células de Schwann, era demorada e trabalhosa. Concluiu-se que a resolução lenta de algumas lesões resultara do lapso transcorrido entre a intoxicação e o desaparecimento das células relacionadas à mielina, significando que as respostas celulares à desmielinização tiveram lugar em área livre de células gliais. Esta não podia sustentar, portanto, a movimentação celular necessária para a remoção dos restos de mielina e a posterior remielinização. Esta investigação indica que o desenvolvimento e o desfecho da desmielinização podem ser alterados pelos eventos celulares que acompanham a degeneração dos oligodendrócitos.

Demyelination in canine distemper encephalomyelitis: an ultrastructural analysis

A morphological study of selected white matter lesions was carried out in three dogs with canine distemper encephalomyelitis. Two dogs had experimental infections while the third was a spontaneous case. Two stages were identified in the process of demyelination. The earliest evidence of myelin injury was a ballooning change in myelin sheaths involving single or multiple axons. This was followed by a progressive stripping of compact sheaths by the cytoplasmic fingers of phagocytic cells which infiltrated and removed myelin lamellae. Some axonal necrosis also accompanied these changes. Where demyelination occurred, canine distemper viral nucleocapsids were found in astrocytes, macrophages, ependymal cells and infiltrating lymphocytes. In contrast, oligodendrocytes were conspicuous by their apparent lack of infection. Thus it seems that myelin loss cannot be ascribed to oligodendrocyte infection. Perturbed astrocyte function following canine distemper viral infection may cause oedema of myelin sheaths, leading to ballooning and primary demyelination. Cells which phagocytosed myelin were mainly identified as microglial cells with lesser involvement by astrocytes. Rarely, oligodendrocytes also acted as macrophages. Myelin debris was engulfed in bulk or as small droplets into coated pits. Remyelination was present in established plaques although not in great abundance, perhaps due to the diminished oligodendrocyte numbers and a relative increase in immature forms of these cells. These observations are compared to similar changes observed in other demyelinating diseases of animals and man.

Ultrastructural findings in maple syrup urine disease in Poll Hereford calves

Ultrastructural findings in the nervous systems of two Poll Hereford calves affected with maple syrup urine disease or branched chain ketoacid decarboxylase deficiency are described. The calves were affected within 2 days of birth with a severe generalised central nervous system (CNS) disorder characterised by dullness and weakness, progressing to recumbency and opisthotonus. The urine had an odour of burnt sugar. Analysis of plasma and cerebrospinal fluid demonstrated significantly elevated levels of the branched chain amino acids leucine, isoleucine and valine. Status spongiosus affecting mainly the white matter was recorded at microscopic examination of the CNS, with ultrastructural examination confirming the presence of intramyelinic vacuole formation, suggesting myelin oedema.

Cytofluorescence localization of ethidium bromide in the nervous system of the mouse. I. Ethidium bromide: its distribution in regions within and without the blood-brain barrier after intravenous injection

A direct fluorescence-microscopic technique was effected to determine in the central nervous system (CNS) of the mouse the distribution of ethidium bromide after intravenous (i.v.) injection. The compound was visualized in thin cryostat sections of the brain fixed by vascular perfusion through the heart with a 10% buffered formalin solution. Ethidium bromide emitted a bright red fluorescent light in model experiments. The compound could not be detected in the vessel walls or brain parenchyma of the cerebral gray and white matters after i.v. injection indicating the presence of a blood-brain barrier (BBB) phenomenon to this compound. Signs of extravasation of ethidium bromide were present in the choroid plexus, the postremal area, the Gasserian ganglion, and in the circumventricular organs of the brain (neurohypophysis, organum vasculosum lamina terminalis, and median eminence) 3 min after the i.v. injection. Intense fluorescence was present in the nucleus and the cytoplasm of the cells in these areas, located outside of the BBB. Fluorescence had disappeared 24 h after the injection. Unexpectedly, red fluorescent material was seen in the parenchyma of the olfactory lobes of some animals, indicating, possibly, the presence of ethidium bromide. Ethidium bromide is known to suppress RNA, DNA, and protein synthesis in mammalian cells and has been used previously in neuropathology for studies on myelin lesions after injury to oligodendroglial cells. It can now, by a simple fluorescence-microscopic method, be traced directly in fixed tissue. Correlations can therefore be made between localization of the compound and its cytotoxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytofluorescence localization of propidium iodide injected intravenously into the nervous system of the mouse

Propidium iodide, like its analogue ethidium bromide, is a compound which can be used as a marker of nucleic acids. This substance emits a red fluorescent light after exposure to UV light and has therefore been used previously as a nuclear stain in immunofluorescence studies and in flow cytometry. The present experiments were carried out to find out if propidium iodide could be traced in sections of the nervous system after i.v. injections. Due to the general toxicity of the compound detectable amounts of propidium iodide could not be obtained by a single i.v. injection. However, multiple injections of small amounts (0.1 mg) over a period from 15 min to 8 h (total dose 0.7-1.0 mg) were tolerated without any signs of adverse effects. In such experiments propidium iodide did not extravasate into the cerebral gray or white matter, i.e., areas of the brain located within the blood-brain barrier (BBB). On the other hand, the compound spread into the choroid plexus, the circumventricular organs, the Gasserian ganglion, and sciatic nerve, i.e., regions located outside the BBB. It had a strong tendency to label the nucleus and the perikaryon of the cells in each of these territories. Perifascicular injection of propidium iodide around the sciatic nerve was followed by a marked cellular uptake not only in the epineurium but also in the endoneurium. The shape and position of the labeled nuclei strongly indicated that they were the nuclei of Schwann cells. Previous studies have shown that propidium iodide can be used as a retrograde tracer in neuroanatomic research.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorescence-microscopic localization of in vivo injected ethidium bromide in the nervous system of the mouse

Ethidium bromide is a compound which can suppress DNA, RNA, and protein synthesis in mammalian cells. It is a very useful tool in experimental neuropathology for studies on myelin lesions taking place in the spinal cord after injury to oligodendroglial cells following intracisternal or intraspinal administration. By using a technique described in this short original communication we can now directly trace the distribution of the compound in various cells of the central and the peripheral nervous systems after its administration to a living experimental animal. Therefore, in the future direct correlations can be made between the cellular distribution of the compound and its cytotoxic effects.

Colchicine reduces myelin thickness and axoplasm volume

A Silastic cuff containing either colchicine (1% w/v) or no colchicine was placed around the lingual disorder tympani nerve of the Mongolian gerbil. After 3 days of exposure to colchicine, the mean period of the myelin sheaths was 23% less than the period observed in nerves treated with cuffs lacking colchicine, while the average number of lamellae was unaltered. At the same time colchicine reduced the volume of axoplasm by an average of 19%, an effect which was independent of fiber diameter.

The twitcher mouse: an ultrastructural study on the oligodendroglia

Morphological alterations of oligodendroglia were investigated in the spinal cord of the twitcher mouse, an authentic murine model of human globoid cell leukodystrophy (GLD) from day 5 to day 45 postnatal (p.n.). Typical inclusions were seen in the perikarya as well as the processes of oligodendroglia after day 10 with increasing frequency. The majority of the inclusions was non-crystalloid but rather needle-like or slender tubular in appearance. Ultrastructural features of cellular degeneration became first noticeable on days 25-30 in the oligodendroglial cytoplasm. These consisted of an increased number of microtubules and/or smooth cisterns, dispersed ribosomes, alteration of endoplasmic reticulum forming stacked lamellae or whorls, vesiculation or vacuolation of cytoplasm. The number of degenerating oligodendroglia increased in the older twitcher mice, so did the degenerating myelin sheath. However, even on day 45, when globoid cells became conspicuous in subpial and perivascular regions, many oligodendroglia and myelin sheaths were still well preserved. These observations suggested that oligodendroglial degeneration resulted in the degeneration of myelin sheaths but globoid cells appeared even before morphological evidence of myelin degeneration, presumably in response to the biochemical alterations resulted from the deficiency of galactosylceramidase.

Ethidium bromide induced demyelination in the spinal cord of the cat

Small volumes of ethidium bromide were injected into the dorsal column of the spinal cord of cats. Oligodendrocytes and astrocytes showed morphological evidence of intoxication by ethidium bromide from 2 days after injection. However, apart from around the point of injection and the needle tract, demyelination did not occur until between 8 and 14 days. Both oligodendrocytes and astrocytes were absent from the demyelinated area at 14 days and all but a small number of demyelinated axons were remyelinated by Schwann cells. These cells first appeared in the lesion at 10 days, but axon association and myelination did not occur until 16 days. This model of experimental demyelination indicates once again that Schwann cell invasion of demyelinated areas in the CNS occurs if both oligodendrocytes and astrocytes are destroyed. None of the lesions in the present investigation were in continuity with root entry zones, indicating that this location is not a prerequisite for Schwann cell invasion of the CNS.

Hexachlorophene and the central nervous system. Toxic effects in mice and baboons

A study on hexachlorophene encephalopathy in mice and baboons is reported. By light microscopy, a severe spongiform lesion of the central nervous system (CNS) was localized in the white matter, without myelin breakdown or cellular reaction. By electron microscopy, the myelin alteration was characterized by wide intralamellar spaces or "splitting" developed in the intraperiod line of compact sheaths. The acute changes described were induced by administration of the drug by the digestive or cutaneous routes at various dosage levels in an aqueous solution or in talcum powder. The toxic effects depended on the age of the animals, the survival times and the concentrations of hexachlorophene, i.e., 6%, 3%, and 0.5%. The findings are compared with previous reports on the neurotoxicity of hexachlorophene and other chemicals in human and experimental animals. Hexachlorophene cannot be recommended for use in young infants because of its neurotoxicity in very low doses as demonstrated in the present report.

Properties of bovine oligodendroglia isolated by a new procedure using physiologic conditions

A new class of procedures, previously shown to permit the isolation of pure oligodendroglia from whole rat cerebrum, has been applied with equal or greater success for the bulk isolation of this cell type from bovine white matter. Thus, the generality of this approach has been demonstrated. The bovine preparations have a purity of greater than 90% intact, phase-bright oligodendroglia and are obtained in a yield of 8 x 10(6) cells per gram of white matter. Within 1 day it is possible to obtain a preparation containing 60 mg of protein from a single cell type. These cells show a higher degree of ultrastructural preservation of all cytoplasmic constituents than previously obtained. The values for protein (33 pg/cell), DNA (5.4 pg/cell), and lipid (5-6 pg/cell) are very similar to those obtained with an earlier procedure. The cell lipids are rich in galactolipid, which comprises 20% of the total. The activity of the "myelin-specific" enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37), is 4.7 mumol/min/mg protein, similar to that obtained previously for isolated oligodendroglia and about 25-40% of that found in myelin. The activity of 5'-nucleotidase (EC 3.1.3.5) in the cells is about 10% of that in myelin or white matter.

Experimental hexachlorophene encephalopathy in mice and baboons: light and electron microscopic study

An experimental study on acute Hexachlorophene (HCP) neurotoxicity is reported in mice and baboons: - by light microscopy, a severe spongiform lesion of the central nervous system is localized in the white matter without myelin breakdown or cellular reaction; - by electron microscopy, the myelin alteration is characterized by the presence of vacuolation of "splitting" in the intralamellar spaces of compact sheaths; myelinated axons are occasionally involved. The changes described are discussed according to various reports on HCP neurotoxicity in humans and experimental animals. The effects of this chemical agent on the central nervous system is related to the percentage of HCP in talcum powder or solution for topical use. The toxicity of very low dosage level is demonstrated in baboons. Therefore HCP use cannot be recommended for young infants.

Cycloleucine encephalopathy

Cycloleucine, a non-metabolizable amino acid analogue produces status spongiosus in cerebral white matter of rats and mice as well as a distinctive lesion of astrocytes. Its mechanisms of action include competition with natural amino acids from transport across the blood-brain barrier leading to inhibition of entry of circulating amino acids into brain, interference with ribosomal RNA maturation, and blockage of transmethylation reactions, including the conversion of homocystine to methionine. Cycloleucine also affects the kidney, producing aminoaciduria. Electron microscopy of cerebral white matter reveals spongiform changes of myelin sheaths caused by separation of myelin lamellae along intraperiod lines and accumulation of whorls of filaments in astrocytes. The myelinopathy is dose related and its toxicity is cumulative due to its long half-life in animals. The findings are discussed with reference to other spongiform myelinopathies, including status spongiosus observed in homocystinuria and other aminoacidurias.