Interferon-gamma inhibits central nervous system remyelination through a process modulated by endoplasmic reticulum stress

Interferon-gamma (IFN-gamma) is believed to play a deleterious role in the immune-mediated demyelinating disorder multiple sclerosis. Here we have exploited transgenic mice that ectopically express IFN-gamma in a temporally controlled manner in the CNS to specifically study its effects on remyelination in the cuprizone-induced demyelination model and in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. CNS delivery of IFN-gamma severely suppressed remyelination in both models and impaired the clinical recovery of the mice experiencing EAE. These observations correlated with a dramatic reduction of oligodendroglial repopulation in the demyelinated lesions. Moreover, we found that in cuprizone-treated mice the detrimental actions of IFN-gamma were associated with endoplasmic reticulum (ER) stress in remyelinating oligodendrocytes. Compared with a wild-type genetic background, the presence of IFN-gamma in mice heterozygous for a loss of function mutation in the pancreatic ER kinase (PERK), a kinase that responds specifically to ER stress, further reduced the percentage of remyelinated axons and oligodendrocyte numbers in cuprizone-induced demyelinated lesions. Thus, these data suggest that IFN-gamma is capable of inhibiting remyelination in demyelinated lesions and that ER stress modulates the response of remyelinating oligodendrocytes to this cytokine.

p75NTR independent oligodendrocyte death in cuprizone-induced demyelination in C57BL/6 mice

Feeding C57Bl/6 J mice the copper chelator cuprizone leads to selective apoptosis of mature oligodendrocytes and concomitant demyelination predominantly in the corpus callosum. The process of oligodendrocyte apoptosis in this animal model for multiple sclerosis (MS) involves early microglial activation, but no infiltration of T-lymphocytes. Therefore, this model could mimic early stages of oligodendrocyte degeneration Affected oligodendrocytes express the common neurotrophin receptor, p75(NTR), a 'stress-receptor' which under certain circumstances can induce apoptosis. Only affected oligodendrocytes in MS lesions and MS animal models express this receptor. In order to study the significance of p75(NTR) in the fate of oligodendrocytes, we have exposed wild-type as well as p75(NTR)-knockout mice to a 0.2% (w/w) cuprizone diet and performed a comparative immunohistochemical analysis of the corpus callosum at various time points. Surprisingly, our results show that the absence of p75(NTR) did not alter cuprizone-induced oligodendrocyte death (and subsequent de- or remyelination). Apparently, intracellular apoptosis pathways in adult oligodendrocytes do not require p75(NTR) activated signal transduction in the absence of T-lymphocytes and T-lymphocyte derived cytokines.

Multicontrast MRI of remyelination in the central nervous system

Although magnetic resonance imaging (MRI) represents the most sensitive tool for the detection of white matter abnormalities in patients with multiple sclerosis (MS), the heterogeneity of MS placques severely hampers the elucidation of specific pathophysiological processes. In order to identify putative MRI markers for de- and remyelination, we employed the cuprizone mouse model which leads to a selective and reversible demyelination of the corpus callosum with little or no axonal damage. Apart from histopathology, animals were studied with high-resolution three-dimensional MRI in vivo using multiple contrasts. While individual MRI findings significantly correlated with electron microscopy, the differentiation of regions with normal, demyelinated or remyelinated white matter by one contrast alone was less specific than by histology or electron microscopy. However, an accurate MRI prediction of the in vivo myelin status was achieved by a discriminant function analysis using a combination of T1, T2 and magnetization transfer contrast. With a correct assignment of 95% of all animals examined, the procedure will allow for the survey of new therapeutic approaches aiming at improved remyelination.

Demyelination increases radial diffusivity in corpus callosum of mouse brain

Myelin damage, as seen in multiple sclerosis (MS) and other demyelinating diseases, impairs axonal conduction and can also be associated with axonal degeneration. Accurate assessments of these conditions may be highly beneficial in evaluating and selecting therapeutic strategies for patient management. Recently, an analytical approach examining diffusion tensor imaging (DTI) derived parameters has been proposed to assess the extent of axonal damage, demyelination, or both. The current study uses the well-characterized cuprizone model of experimental demyelination and remyelination of corpus callosum in mouse brain to evaluate the ability of DTI parameters to detect the progression of myelin degeneration and regeneration. Our results demonstrate that the extent of increased radial diffusivity reflects the severity of demyelination in corpus callosum of mouse brain affected by cuprizone treatment. Subsequently, radial diffusivity decreases with the progression of remyelination. Furthermore, radial diffusivity changes were specific to the time course of changes in myelin integrity as distinct from axonal injury, which was detected by betaAPP immunostaining and shown to be most extensive prior to demyelination. Radial diffusivity offers a specific assessment of demyelination and remyelination, as distinct from acute axonal damage.

K+ channel blockade impairs remyelination in the cuprizone model

The adult CNS has the capacity to remyelinate following metabolic, toxic and autoimmune demyelinating insults. In cuprizone-induced demyelination, spontaneous remyelination occurs after the cessation of cuprizone diet. We used the cuprizone model to investigate the role of glial K(+) channels in oligodendroglial (OLG) regeneration and remyelination in vivo. We found that treatment with 4-aminopyridine (4-AP), a broad-spectrum K(+) channel antagonist, results in: (1) decreased number of oligodendroglial progenitors (OP) and OLGs; (2) diminished astrogliosis; and (3) decreased remyelination in the corpus callosum based on the immunoreactivity to myelin basic protein (MBP), Rip monoclonal antibody, and by electron microscopy. Our findings support the concept that glial K(+) channels play an important role during OLG regeneration and remyelination, a crucial factor to be considered during the development of therapeutic strategies to facilitate recovery in demyelinating diseases and spinal cord injury.

Experimental demyelination caused by primary oligodendrocyte dystrophy. Regional distribution of the lesions in the nervous system of mice [corrected]

BACKGROUND AND PURPOSE

Heterogeneity of multiple sclerosis lesions has been recently indicated: In addition to T-cell-mediated or T-cell plus antibody-mediated autoimmune mechanisms (patterns I-II) two other patterns (IIl-IV) were described. Patterns Ill-IV are characterized by primary oligodendrocyte dystrophy, reminiscent of virus- or toxin-induced demyelination rather than autoimmunity. It was described more than 30 years ago that dietary application of a copper-chelating agent called cuprizone results in primary oligodendrocyte degeneration which is followed by demyelination. The aim of the present study was to examine the regional distribution of cuprizone induced oligodendrocyte dystrophy and demyelination in the nervous system of mice. MATERIAL A METHODS: Demyelination was induced in male weanling Swiss-Webster mice by feeding them on a diet containing 0.6% (W/W) cuprizone bis(cyclohexanone)-oxalyldihydrazone (G. F. Smith Chemical, Columbus OH) for 8 weeks. Animals were sacrificed after 3, 7, 14, 27, 35, 56 days of cuprizone administration. Samples were taken from corpus callosum, anterior commissure, optic nerve, cervical spinal cord and sciatic nerve. Samples were examined by immunohistochemistry, in situ hybridization for myelin proteins and myelin protein mRNA-s, respectively. Conventional neuropathological stainings and electron microscopy was also performed.

RESULTS

Oligodendrocyte degeneration and demyelination followed a particular standard pattern in the central nervous system. Profound myelin loss developed in the superior cerebellar peduncle, anterior commissure and corpus callosum, whereas the optic nerves, velum medullare anterior and spinal cord showed little or no demyelination. Sciatic nerves were unaffected. No infiltration by lymphocytes or blood-brain barrier damage was observed during cuprizone treatment.

CONCLUSION

Cuprizone induced oligodendrocyte damage and demyelination follows a particular standard pattern in the central nervous system of mice. Cuprizone induced demyelination might be considered as a model for human demyelinating disorders with primary oligodendrocyte dystrophy and apoptosis.

Remyelination assessment by MRI texture analysis in a cuprizone mouse model

The purpose of this study was to perform serial texture analysis of brain MRI of cuprizone-treated mice for the assessment of regional demyelination and remyelination. Cuprizone-fed mice undergo a brain demyelination process. This process was followed over 56 days by MRI in the olfactory bulbs, cerebellum, putamen and brain stem. The texture of T2-weighted images has been analyzed at two levels: (1) with the average intensity as first order parameter and (2) with several higher order parameters for the best differentiation between myelinated (controls) and demyelinated brains. The most pertinent of these parameters, called horizontal gray level nonuniformity (HGLNU), has been selected by stepwise discriminant analysis. The time evolution of the average value of HGLNU not only confirmed the overall demyelination tendency followed by the average intensity, but also more precisely characterized a transitory remyelination on day 41 in the olfactory bulbs and cerebellum, in agreement with already published immunohistochemical destructive studies.

Platelet-derived growth factor regulates oligodendrocyte progenitor numbers in adult CNS and their response following CNS demyelination

To design therapies for demyelinating diseases such as multiple sclerosis, it will be important to understand the mechanisms that control oligodendrocyte progenitor cell (OPC) numbers in the adult central nervous system (CNS). During development, OPC numbers are limited by the supply of platelet-derived growth factor-A (PDGF-A). Here, we examine the role of PDGF-A in regulating OPC numbers in normal and demyelinated adult CNS using transgenic mice that overexpress PDGF-A in astrocytes under the control of the glial fibrillary acidic protein (GFAP) gene promoter (GFAP-PDGF-A mice). In adult GFAP-PDGF-A mice, there was a marked increase in OPC density, particularly in white matter tracts, indicating that the PDGF-A supply controls OPC numbers in the adult CNS as well as during development. To discover whether increasing PDGF expression increases the number of OPCs following demyelination and whether this enhances the efficiency of remyelination, we induced demyelination in GFAP-PDGF-A transgenic mice by intraspinal injection of lysolecithin or dietary administration of cuprizone. In both demyelinating models, OPC density within lesions was significantly increased compared to wild-type mice. However, morphological analysis of lysolecithin lesions did not reveal any difference in the time course or extent of remyelination between GFAP-PDGF-A and wild-type mice. We conclude that the availability of OPCs is not rate limiting for remyelination of focal demyelinated lesions in the mouse. Nevertheless, our experiments show that it is possible to increase OPC population density in demyelinated areas by artificially increasing the supply of PDGF.

Peripheral benzodiazepine receptor imaging in CNS demyelination: functional implications of anatomical and cellular localization

The peripheral benzodiazepine receptor (PBR) has been used as a sensitive marker to visualize and measure glial cell activation associated with various forms of brain injury and inflammation. Previous studies have shown that increased PBR levels following brain injury are specific to areas expressing activated glial cells. However, the contribution of glial cell types responsible for the increases in PBR levels following brain injury is not well defined. In the present study, we used a murine model of cuprizone-induced demyelination to broaden the application of PBR as a marker of brain injury and to validate the relationship between PBR levels and glial cell types. C57BL/6J mice were maintained on a cuprizone-containing or control diet and sacrificed at specific time points after initiation of treatment. Quantitative autoradiography of the PBR-selective ligand [(3)H]-(R)-PK11195 and [(125)I]-(R)-PK11195 showed that increased PBR levels were associated with the degree of demyelination assessed by Black-Gold histochemistry and activation of glial cells assessed by glial fibrillary acidic protein (GFAP) immunohistochemistry for astrocytes and CD11b (Mac-1) for microglia. Our findings indicate that brain PBR levels increased as a function of dose and duration of cuprizone treatment and it was detectable prior to observable demyelination. Increased PBR levels were associated with the degree of demyelination and temporal activation of glial cell types in different anatomical regions. In the corpus striatum, we found a close anatomical correlation between microglial activation and increased PBR levels in demyelinating fibre tracts. In the deep cerebellar nuclei, the temporal increases in PBR paralleled demyelination and microglia and astrocyte activation. On the other hand, in the corpus callosum there was an apparent temporal shift in the increase in PBR levels by different glial cell types from an early and predominantly microglial contribution to a late microglial and astrocytic response. High-resolution emulsion autoradiography of [(3)H]-(R)-PK11195 binding to PBR coupled with GFAP or Mac-1 immunohistochemistry showed that demyelination-induced increases in PBR levels were co-localized to both microglia and astrocytes. These findings support the notion that PBR is a sensitive and specific marker for the in vitro and in vivo visualization and quantification of neuropathological changes in the brain.

Osteopontin is upregulated during in vivo demyelination and remyelination and enhances myelin formation in vitro

We have used in vitro oligodendrocyte differentiation and the in vivo remyelination model, the cuprizone model, to identify genes regulating oligodendrocyte function and remyelination. One of the genes we identified, osteopontin (opn), is a secreted glycoprotein with cytokine-like, chemotactic, and anti-apoptotic properties that contains an Arg-Gly-Asp (RGD) cell adhesion motif-mediating interactions with several integrins. Both microglia and astrocytes in demyelinating brain regions of cuprizone-fed mice expressed OPN protein. Recombinant OPN protein produced in a baculovirus expression system induced proliferation of both the rat CG-4 and the mouse Oli-neu oligodendrocyte precursor (OLP)-like cell lines in a dose-dependent manner. In addition, recombinant OPN treatment stimulated both myelin basic protein (MBP) synthesis and myelin sheath formation in mixed cortical cultures from embryonic mouse brain, an in vitro primary culture model of myelination. Interestingly, myelinating mixed cultures prepared from OPN(-/-) mice contained significantly less MBP compared to wild-type cultures after 17 days in culture. We propose that in the central nervous system, OPN may act as a novel regulator of myelination and remyelination.

Astroglial-derived lymphotoxin-? exacerbates inflammation and demyelination, but not remyelination

Tumor necrosis factoralpha (TNFalpha) and lymphotoxin-alpha (Ltalpha) are upregulated in and around multiple sclerosis plaques and are proposed to play a role during chronic inflammation in demyelinating disease. Despite the perceived detrimental role of these cytokines, human clinical trials inhibiting TNFalpha signaling has led to worsening of symptoms in multiple sclerosis (MS) patients. Our laboratory has verified a role for TNFalpha in the exacerbation of demyelination but, more importantly, has demonstrated a novel role for TNFalpha in reparative remyelination in a cuprizone-induced demyelination model. This may explain the worsening of symptoms experienced by MS patients. In view of the cross-talk in TNF family signaling, the aim of this study is to understand the role of Ltalpha in demyelination and remyelination in hopes of improving therapeutic strategies for MS. Using the same model, we show that mice lacking Ltalpha exhibit a delay in demyelination that is greater than that exhibited by TNFalpha null mice. In this model, Ltalpha is expressed primarily by astroglia. The delay in demyelination is accompanied by a delay in the loss of mature GSTpi-positive oligodendrocytes in Ltalpha-/- mice compared with wild-type mice. Ltalpha-/- mice have decreased numbers of microglia at the site of insult during demyelination, although the number of astrocytes present is similar between strains. In contrast to TNFalpha the lack of Ltalpha did not alter the time course of remyelination, or the number of mature oligodendrocytes during the remyelination phase. Since Ltalpha is detrimental in inflammation and demyelination, but not necessary for remyelination and repair, inhibiting Ltalpha signaling may represent a promising strategy to treat MS.

Functional genomic analysis of remyelination reveals importance of inflammation in oligodendrocyte regeneration

Tumor necrosis factor alpha (TNFalpha), a proinflammatory cytokine, was shown previously to promote remyelination and oligodendrocyte precursor proliferation in a murine model for demyelination and remyelination. We used Affymetrix microarrays in this study to identify (1) changes in gene expression that accompany demyelination versus remyelination and (2) changes in gene expression during the successful remyelination of wild-type mice versus the unsuccessful attempts in mice lacking TNFalpha. Alterations in inflammatory genes represented the most prominent changes, with major histocompatibility complex (MHC) genes dramatically enhanced in microglia and astrocytes during demyelination, remyelination, and as a consequence of TNFalpha stimulation. Studies to examine the roles of these genes in remyelination were then performed using mice lacking specific genes identified by the microarray. Analysis of MHC-II-null mice showed delayed remyelination and regeneration of oligodendrocytes, whereas removal of MHC-I had little effect. These data point to the induction of MHC-II by TNFalpha as an important regulatory event in remyelination and emphasize the active inflammatory response in regeneration after pathology in the brain.

Absence of fibroblast growth factor 2 promotes oligodendroglial repopulation of demyelinated white matter

This study takes advantage of fibroblast growth factor 2 (FGF2) knock-out mice to determine the contribution of FGF2 to the regeneration of oligodendrocytes in the adult CNS. The role of FGF2 during spontaneous remyelination was examined using two complementary mouse models of experimental demyelination. The murine hepatitis virus strain A59 (MHV-A59) model produces focal areas of spinal cord demyelination with inflammation. The cuprizone neurotoxicant model causes extensive corpus callosum demyelination without a lymphocytic cell response. In both models, FGF2 expression is upregulated in areas of demyelination in wild-type mice. Surprisingly, in both models, oligodendrocyte repopulation of demyelinated white matter was significantly increased in FGF2 -/- mice compared with wild-type mice and even surpassed the oligodendrocyte density of nonlesioned mice. This dramatic result indicated that the absence of FGF2 promoted oligodendrocyte regeneration, possibly by enhancing oligodendrocyte progenitor proliferation and/or differentiation. FGF2 -/- and +/+ mice had similar oligodendrocyte progenitor densities in normal adult CNS, as well as similar progenitor proliferation and accumulation during demyelination. To directly analyze progenitor differentiation, glial cultures from spinal cords of wild-type mice undergoing remyelination after MHV-A59 demyelination were treated for 3 d with either exogenous FGF2 or an FGF2 neutralizing antibody. Elevating FGF2 favored progenitor proliferation, whereas attenuating endogenous FGF2 activity promoted the differentiation of progenitors into oligodendrocytes. These in vitro results are consistent with enhanced progenitor differentiation in FGF2 -/- mice. These studies demonstrate that the FGF2 genotype regulates oligodendrocyte regeneration and that FGF2 appears to inhibit oligodendrocyte lineage differentiation during remyelination.

Alterations in metabolism and gene expression in brain regions during cuprizone-induced demyelination and remyelination

Exposure of mice to the copper chelator, cuprizone, results in CNS demyelination. There is remyelination after removal of the metabolic insult. We present brain regional studies identifying corpus callosum as particularly severely affected; 65% of cerebroside is lost after 6 weeks of exposure. We examined recovery of cerebroside and ability to synthesize cerebroside and cholesterol following removal of the toxicant. The temporal pattern for concentration of myelin basic protein resembled that of cerebroside. We applied Affymetrix GeneChip technology to corpus callosum to identify temporal changes in levels of mRNAs during demyelination and remyelination. Genes coding for myelin structural components were greatly down-regulated during demyelination and up-regulated during remyelination. Genes related to microglia/macrophages appeared in a time-course (peaking at 6 weeks) correlating with phagocytosis of myelin and repair of lesions. mRNAs coding for many cytokines had peak expression at 4 weeks, compatible with intercellular signaling roles. Of interest were other genes with temporal patterns correlating with one of the three above patterns, but of function not obviously related to demyelination/remyelination. The ability to correlate gene expression with known pathophysiological events should help in elucidating further function of such genes as related to demyelination/remyelination.

The protective role of nitric oxide in a neurotoxicant-induced demyelinating model

Demyelination is often associated with acute inflammatory events involving the recruitment-activation of microglia/macrophage, astrocytes, and leukocytes. The ultimate role of inflammatory products in demyelinating disease and in the survival of oligodendrocytes, the myelin forming cells, is unresolved. The current study examines the role of inducible NO synthase (iNOS)-derived NO in a neurotoxicant-induced model of demyelination. NO levels were greatly elevated in the midline corpus callosum during demyelination in genetically intact C57BL/6 mice, and this NO was due solely to the induction of iNOS, as the correlates of NO were not found in mice lacking iNOS. C57BL/6 mice lacking iNOS exhibited more demyelination, but did not display an increased overall cellularity in the corpus callosum, attributable to an unimpeded microglia/macrophage presence. An enhanced course of pathology was noted in mice lacking iNOS. This was associated with a greater depletion of mature oligodendrocytes, most likely due to apoptosis of oligodendrocytes. Microglia and astrocytes did not undergo apoptosis during treatment. Our results suggest a moderately protective role for NO during acute inflammation-association demyelination.

Interleukin-1beta promotes repair of the CNS

Interleukin-1beta (IL-1beta) is a proinflammatory cytokine associated with the pathophysiology of demyelinating disorders such as multiple sclerosis and viral infections of the CNS. However, we demonstrate here that IL-1beta appears to promote remyelination in the adult CNS. In IL-1beta(-/-) mice, acute demyelination progressed similarly to wild-type mice and showed parallel mature oligodendrocyte depletion, microglia-macrophage accumulation, and the appearance of oligodendrocyte precursors. In contrast, IL-1beta(-/-) mice failed to remyelinate properly, and this appeared to correlate with a lack of insulin-like growth factor-1 (IGF-1) production by microglia-macrophages and astrocytes and to a profound delay of precursors to differentiate into mature oligodendrocytes. Thus, IL-1beta may be crucial to the repair of the CNS, presumably through the induction of astrocyte and microglia-macrophage-derived IGF-1.

Episodic demyelination and subsequent remyelination within the murine central nervous system: changes in axonal calibre

Exposure of young adult C57BL/6 mice to cuprizone in the diet initiated profound and synchronous demyelination of the corpus callosum, which was virtually complete by 4 weeks of exposure. Interestingly, even in the face of a continued exposure to cuprizone, there was spontaneous remyelination 2 weeks later. This remyelination preferentially involved smaller calibre axons. There was a suggestion of yet another cycle of demyelination (at 10 weeks) and remyelination (at 12 weeks), but by 16 weeks of exposure, the regenerative capacity was exhausted and the animals were near death. The relapsing-remitting pattern suggests this may be a useful model for certain human demyelinating disorders. In contrast to the above chronic model, the corpus callosum from mice exposed to cuprizone for only 6 weeks continued to remyelinate, with 67% of the axons being myelinated or remyelinated at 10 weeks. Interestingly, a significant reduction in the mean value for axonal diameter was observed during acute demyelination. Upon remyelination, however, the axonal calibre distribution returned to near-normal. In contrast, when mice were maintained on a cuprizone diet for 16 weeks, the mean value for axonal diameter was reduced to 60% of normal. These results provide further evidence that the interactions between oligodendrocytes and axons alter axonal calibre.

Interferon-gamma protects against cuprizone-induced demyelination

Evidence suggests that interferon-gamma (IFN-gamma), a proinflammatory cytokine secreted by activated T lymphocytes, contributes a deleterious effect to immune-mediated demyelinating disorders such as multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). Nevertheless, mouse strains that are normally resistant to EAE induction become susceptible when the gene encoding either IFN-gamma or its receptor is mutated, demonstrating that the role that this cytokine plays in demyelinating disorders is complex. We have examined the effect of IFN-gamma in a chemically induced model of CNS demyelination. Mice that receive through their diet the copper chelator cuprizone display extensive demyelination of the corpus callosum. Remarkably, transgenic mice that ectopically express low levels of IFN-gamma in the CNS did not display evidence of demyelination when treated with cuprizone, nor did they shows signs of oligodendroglial death, astrogliosis, or microgliosis, which are typically seen in treated animals. Myelin protein gene expression was, however, dramatically reduced in both the treated control and the transgenic animals, indicating that demyelination is not an obligatory consequence of a large diminution of myelin protein synthesis. Interestingly, the CNS of the IFN-gamma-expressing mice contained elevated levels of insulin-like growth factor I, which has been demonstrated to have a protective effect against the demyelinating action of cuprizone.

Mature oligodendrocyte apoptosis precedes IGF-1 production and oligodendrocyte progenitor accumulation and differentiation during demyelination/remyelination

We have documented changes in the oligodendrocyte population during demyelinating insult to the adult CNS. Feeding of cuprizone to adult mice led to apoptotic death of mature oligodendrocytes followed by profound demyelination of the corpus callosum. A regenerative response was initiated even during active demyelination. Oligodendrocyte progenitors have begun to proliferate and then accumulate within the lesion. Many of these cells may have migrated from the sub-ventricular zone and fornix before their accumulation in the demyelinating corpus callosum. The accumulation of differentiating oligodendrocyte progenitors was followed closely by the reappearance of mature oligodendrocytes and remyelination. Interestingly, an increase in IGF-1 mRNA was detected at Week 3 through Week 7, suggesting potential involvement in remyelination. Other factors, however, such as PDGF, NT3, FGF, jagged, and notch remained unchanged. These results suggest that the mature oligodendroglial population depleted by apoptosis is replaced by a newly formed oligodendroglial population derived from progenitors; these accumulate and seem to differentiate during remyelination.

Decrease in oligodendrocyte carbonic anhydrase activity preceding myelin degeneration in cuprizone induced demyelination

Both immunohistochemical and biochemical evidence is presented to show for the first time that carbonic anhydrase II (CA II) activity falls in the brain of mice in cuprizone (bis(cyclohexanone)oxalyldihydrazone) induced demyelination well before demyelination develops. This fall began during the first week, whereas the first signs of myelin degeneration induced by cuprizone did not appear until 3 weeks and demyelination in the superior cerebellar peduncle in the mouse took 6-8 weeks to develop. The findings suggest that oligodendrocyte CA II activity is essential either for the survival of oligodendrocytes or for the maintenance of central myelin.

Biochemical changes in Cuprizone-induced spongiform encephalopathy. I. Changes in the activities of 2',3'-cyclic nucleotide 3'-phosphohydrolase, oligodendroglial ceramide galactosyl transferase, and the hydrolysis of the alkenyl group of alkenyl, acyl-glycerophospholipids by plasmalogenase in different regions of the brain

Cuprizone (biscyclohexanone oxaldihydrazone) which is known to produce a status spongiosus and demyelination in the CNS was administered in the diet of weanling male mice at a concentration of 0.4% by weight for a period of six weeks before returning animals to a normal diet. Changes in body weight but not brain weight were reversible. Based on the decline in CNP'ase activity and the concentration of galactocerebroside, the loss of myelin was around 70% in those sections of the cerebrum with a high content of white matter while the cerebellum was less affected. The activity of oligodendroglial HFA-ceramide galactosyl transferase was also reduced. These biochemical parameters of myelination were increased after withdrawal of Cuprizone. Remyelination in the cerebrum but not the cerebellum was incomplete. The activity of plasmalogenase hydrolysing the alkenyl group of alkenyl, acyl-phospholipids increased 2-fold in those sections in which myelin loss was most severe. The increase preceded the greatest loss of myelin components (3 to 6 weeks on Cuprizone). The origin of the increased phospholipase activity in demyelinating tissue is discussed. Following myelination, there was a deficit in plasmalogenase activity particularly in the frontal cortex of the cerebrum, where the plasmalogen concentration was higher than in controls.

Retinal degeneration during clinical scrapie encephalopathy in hamsters

Weanling hamsters were inoculated intracerebrally with brain suspensions from normal or scrapie-infected hamsters. A third group of uninoculated animal was fed cuprizone. Histologic and electron microscopic examination of the neural retinas and retinal pigment epithelium was done. At 50 days postinoculation, when scrapie-infected animals began to show clinical signs of encephalopathy, there was a variable degree of photoreceptor degeneration. By the time animals were moribund, at 74 days postinoculation, photoreceptor degeneration was severe, as demonstrated by loss of most outer and inner segments and cell bodies. The outer plexiform, inner nuclear, and inner plexiform layers were reduced in thickness. Some retinal pigment epithelial cells contained lipoidal inclusions. The neural retinas and retinal pigment epithelium of noninfected and cuprizone-treated animals were normal. We have previously shown that the scrapie agent accumulates in the retina; that together with our present work, we conclude that the scrapie agent is the cause of photoreceptor degeneration in experimentally inoculated hamsters.

Chronic demyelination inhibits remyelination in the central nervous system. An analysis of contributing factors

The remyelinative capacity of the central nervous system was investigated in the superior cerebellar peduncles of mice chronically demyelinated for 6 to 7 months by the administration of Cuprizone. It was found that, although the axons retained their capacity for remyelination, this capacity was greatly reduced compared to acutely demyelinated animals. The possible causes for this reduction were examined, and it was concluded that the limiting factor was the decreased availability of oligodendrocytes for remyelination, rather than inherent factors in the axons, or changes in the surrounding glial environment. The implications for both experimental and clinical disease are discussed.