Myelin Deficiency Research Articles

Anatomical and physiological measures of auditory system in mice with peripheral myelin deficiency

Animal models with genetic abnormalities have been increasingly used in auditory research. Both Tr J mice and P o-DT-A mice are animals with peripheral myelin deficiency. In Tr J mice, the defect is due to a mutated PMP-22 gene. In P o-DT-A mice, the defect is produced by a transgene using the rat P o promotor to direct the expression of gene encoding for the bacterial diphtherial toxin A chain (DT-A). This study evaluates the auditory system both physiologically and histologically in these two strains of mice. Histological examination revealed that there was myelin deficiency of the auditory nerve fibers, accompanied by a loss of dendrites and a loss of spiral ganglion cell bodies in both strains of mice. In general, histological deficits in Tr J mice were greater than those in P o-DT-A mice. There was a strong correlation between the degree of myelin deficiency and the survival of spiral ganglion neurons. ABR measurements exhibited differences in threshold, latency and slope of the ABR growth function between myelin-deficient mice and their respective controls. These results suggest that the integrity of the myelin in the auditory nerve is important both for neural survival and for normal electrophysiological function of spiral ganglion neurons.

Electrically evoked auditory brainstem response in peripherally myelin-deficient mice

The integrity of the myelin sheath is important for normal electrophysiological function and survival of neurons that make up the auditory nerve. It is hypothesized that myelin deficiency of the auditory nerve may change the electrophysiologic characteristics of the auditory system, especially the temporal properties. In this study, the electrically evoked auditory brainstem response (EABR) was systematically evaluated in Tr J and P o-DT-A mice. Both of these mice have a deficit of their peripheral myelin. Correlation between the EABR and degree of myelin deficiency was also evaluated. The EABR in both strains of poorly myelinated mice exhibited prolonged latency, decreased amplitude, elevated threshold of wave I evoked by short-duration stimuli (20 μs/phase). A 2-pulse stimulation paradigm was used to evaluate refractory properties. Myelin-deficient mice exhibited slower recovery from the refractory state than controls. Long-duration stimuli (4 ms/phase) were used to assess integration properties. Myelin-deficient mice demonstrated prolonged wave I latency and more gradual latency changes with current level. Myelin thickness showed a strong correlation with EABR threshold for short-duration stimulation ( r = −0.784), maximum wave I latency ( r = −0.778) and the time constant of the wave I latency-current level function ( r = −0.736) for long-duration stimulation and normalized wave I recovery functions ( r = −0.718). These findings suggest that EABR measurement may be a promising tool to assess the electrically stimulated properties of auditory neurons, particularly related to the status of myelin sheath.

Neuropathology and Genetics of Pelizaeus‐Merzbacher Disease

The recent history of Pelizaeus-Merzbacher Disease (PMD) demonstrates paradigmatically the impact of basic biological research on clinical neurology and brain pathology: this rare and peculiar hereditary disease has become one of the best known disorders of its kind, through a cooperative research effort in neuropathology, human genetics, neurochemistry and molecular biology. PMD, a genetic dysmyelination restricted to the CNS, has been identified as a disease that involves the X chromosome-linked gene for myelin proteolipid protein (PLP), a major structural myelin component. Today more than 30 different mutations in this gene have been defined and associated with PMD or the clinically distinct form X-linked spastic paraplegia type-2 (SPG-2). Improved scanning techniques, specifically the non-invasive magnetic resonance imaging (MRI), allow its early diagnosis in the heterogeneous group of CNS myelin deficiencies. These remarkable achievements have, at the same time, caused a problem for disease classification. Myelin disorders have been grouped in the past on the basis of clinical and neuropathological criteria, creating a system that has now to be reconciled with molecular-genetic data.

Chapter 3 Molecular genetic analyses of myelin deficiency and cerebellar ataxia

Publisher Summary Mutation of the mouse gene causes various types of abnormality in the development and functions of the nervous system. Many mutant animals show abnormal morphogenesis and behavior. The analysis of these mutants compared with those of the control mice yields much information about the development and differentiation of the nervous system. This chapter presents two examples of the results of such analyses: (1) mutations showing deficiencies in myelination and (2) mutant mice showing the deficiencies of P400 protein, a protein enriched in Purkinje cell, which was identified recently as an inositol 1,4,5-trisphosphate (InsP3)receptor. InsP3 receptor is a calcium-releasing channel located on the endoplasmic reticulum and is now a very important molecule for signal transduction cascade in the cell. The chapter provides an example of myelin-deficient mutation, shiverer, mld, and jimpy. Analysis of the mutation by producing chimera animals is very important because it enables to analyze the events occurring among cells. Analysis of jimpy has provided a new finding that myelin protein has another functional role such as factors important for differentiation.

Cerebral myelin deficiency in teenage girls with the 18q- syndrome

Cerebral myelin deficiency in teenage girls with the 18q- syndrome

Effects of cerebellar lesions on tonic seizures, tremor and lifespan in myelin-deficient rats

In common with other dysmyelinating mutants, the myelin-deficient rat displays an action tremor and tonic seizures culminating in the death of the animals at ∼ 23−26 days. We find that deep lesions of the cerebellar vermis alleviate the manifestations of the myelin deficiency significantly. Such lesions introduced at 20 days or later eliminate both tremor and seizures for periods up to 10 days. Lifespan is prolonged to nearly 30 days, on average, and to 35 days in some cases. Shallow lesions of the vermis or lateral lobe lesions have relatively little effect. Based on these observations we suggest that the cerebellum ccontributes not only to the action tremor but also to the tonic seizures characteristic of central myelin deficiency. Spontaneous activity originating in myelin-deficient fiber tracts may be carried to the cerebellum and processed there to produce a highly amplified and/or synchronized output to broad areas of the neuraxis. Deep lesions of the vermis presumably interfere with cerebellar output and compromise the cerebellar contribution to the seizures. Tonic seizures and other ‘paroxysmal attacks’ also occur commonly in human demyelinating diseases including multiple sclerosis [11]. Manipulation of cerebellar output offers a potential approach to the control of such spontaneous activity.

Interhemispheric transfer in children with early-treated phenylketonuria

Phenylketonuria (PKU) is a genetic disorder of amino acid metabolism that is associated with brain catecholamine depletion and deficient myelination. Although neuropsychological deficits have been documented in children with early-treated PKU (ETPKU), no study to date has examined possible effects of impaired myelination in this population. In the present study, interhemispheric transfer time was assessed for 14 children with ETPKU, 22 children with attention deficit-hyperactivity disorder, and 48 normal children, using a manual reaction time paradigm previously validated with callosal agenesis patients (Milner, 1982). Children with ETPKU demonstrated slowed interhemispheric transfer from the left to the right hemisphere as compared with the two other groups. The magnitude of slowing was correlated with age and phenylalanine levels at birth. Results support the hypothesis that abnormal myelination disrupts the development of interhemispheric connections in ETPKU, and suggest that left hemisphere projections may be particularly susceptible to such disruption.

Premature arrest of myelin formation in transgenic mice with increased proteolipid protein gene dosage

Proteolipid protein (PLP) is an integral membrane protein of CNS myelin. Mutations of the X chromosome-linked PLP gene cause glial cell death and myelin deficiency in jimpy mice and other neurological mutants. As part of an attempt to rescue these mutants by transgenic complementation, we generated normal mouse lines expressing autosomal copies of the entire wild-type PLP gene. Surprisingly, increase of the PLP gene dosage in nonmutant mice with only 2-fold transcriptional overexpression results in a novel phenotype characterized by severe hypomyelination and astrocytosis, seizures, and premature death. This demonstrates that precise control of the PLP gene is a critical determinant of terminal oligodendrocyte differentiation. Dysmyelination of PLP transgenic mice provides experimental evidence that Pelizaeus-Merzbacher disease, previously associated with a partial duplication of the human X chromosome, can be caused by doubling of the PLP gene dosage.

Optic nerve hypoplasia in an acute exposure model of the fetal alcohol syndrome

The effects of acute prenatal exposure to ethanol on the postnatal optic nerve have been examined in a C57B1/6J mouse model. Pregnant mice were exposed by intraperitoneal injection to ethanol (25% ethanol, each dose at 0.015 ml/g separated by 4 h), or to saline on the 8th gestational day and the optic nerve examined at P15. There was a significant difference in the cross-sectional areas of optic nerves from ethanol-exposed mice (Mean ± SD: 32,800 ± 11,000 μm 2) compared to control nerves (Mean ± SD: 52,100 ± 8,900 μm 2). T difference was mainly the result of a reduction in the number of optic nerve axons (ethanol group, Mean ± SD: 30,655 ± 4,795; control group, Mean ± SD: 45,791 ± 5,215) but there was also deficient myelination (ethanol group, mean of 15% myelinated axons compared to 34% for controls) in the ethanol-exposed optic nerves. There were no significant differences between experimental and control animals in the neuronal populations of the dorsal lateral geniculate nucleus and superior colliculus. This suggests that the axonal deficit is due to direct retinal damage, rather than increased postnatal axon loss arising from retinorecipient nuclei damage.

The ontogeny of ultrasonic vocalizations and other behaviors in male jimpy (jp/Y) mice and their normal male littermates.

Jimpy (jp/Y) male mice have a sex-linked mutation which results in dysmyelination throughout the CNS, causing tremors and behavioral abnormalities. These mice rarely live past 30 days of age. Due to the sex-linked nature of this mutation, both jimpy and normal male pups occur within the same litter. We examined the early behavioral development of these mice by recording their motor behaviors, including slight movement, locomotion and grooming, and their ultrasonic vocalizations (UVs) at 2-day intervals from 2-20 days of age. Jimpy males weighed less than their normal littermates and reached developmental milestones at a later age. They produced fewer UVs than their normal male littermates from 2-8 days of age, after which UVs ceased almost completely in both groups of mice. Jimpy mice spent less time engaged in coordinated motor activities (locomotion and grooming) than normal littermates, and more time engaged in slight movement or remaining inactive. On three of the behavioral measures used (UV production, slight movement, and inactivity) differences were evident early in development (Day 2 postpartum), whereas differences on the other measures (locomotion, grooming) were not evident until later in the developmental period. Our results indicate the importance of using multiple behavioral measures when examining the functional effects of myelin deficiency.

Myelin-associated glycoprotein (MAG) in myelin deficiency of caprine β-mannosidosis

Caprine β-mannosidosis is an inherited lysosomal storage disorder due to a deficiency of β-mannosidase which cleaves β-linked mannose residues from the ends of N-asparagine linked oligosaccharides of glycoproteins. Histological and chemical examination has revealed a deficiency of compact myelin in the brains and spinal cords of affected goats. Since myelin-associated glycoprotein (MAG) is glycosylated and its metabolism could be directly affected in this disease, we investigated the possibility of a differential treatment of MAG in caprine β-mannosidosis in comparison to non-glycosylated myelin proteins. MAG, myelin basic protein (MBP), 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNP), proteolipid protein (PLP) and glial fibrillary acidic protein (GFAP) were quantified by western blot analysis in whole homogenates of spinal cords and hemispheres from affected goats at 1,4 and days of age and from normal controls. The yields of isolated myelin from the spinal cords of affected goats varied from 37 to 63% of normal and were 7% or less of normal from the hemispheres. In mutant spinal cords, the deficits of MAG, CNP and PLP measured in whole homogenates corresponded reasonably well with the decreased myelin yields, but the levels of MBP were consistently much closer to control levels than those of the other myelin proteins. A greater deficiency of PLP than MBP was also apparent in the myelin fractions purified from the affected spinal cords. In homogenates of mutant hemispheres, MAG, MBP, PLP and CNP were undetectable or at trace levels in comparison to controls. There was no indication of preferential involvement of MAG in this disorder, since the MAG deficiency was comparable to that of other unglycosylated myelin proteins, and its apparent molecular weight was the same as that of controls on SDS gels suggesting normal glycosylation. GFAP was increased (115–150% of the control level) in most tissue samples from the affected goats indicative of astrocytosis.

The attenuation of GABA sensitivity in the maturing myelin-deficient rat optic nerve

GABA (γ-aminobutyric acid) can modulate axonal excitability by activating GABA A receptors on some central nervous system axons. The effects of GABA on optic nerve axons decrease significantly during the course of myelination, suggesting that myelination may influence changes in GABA sensitivity. To test this hypothesis, we compared the depolarizing effect of GABA and the GABA A-receptor agonist, muscimol, on optic nerves of myelin-deficient (MD) rats and their unaffected siblings using a modified sucrose-gap technique. Optic nerves from both control and MD rats displayed relatively large GABA-induced depolarizations when studied at an early postnatal period. In both the control and MD rats, the GABA uptake inhibitor nipecotic acid led to a distinct depolarization suggesting endogenous release of GABA. Although the GABA-induced depolarization in the MD rat was significantly greater than that in the control rat at the third postnatal week, the response in the MD rat attenuated with maturation. These results demonstrate that the attenuation of the depolarization induced by GABA and nipecotic acid seen in the normal optic nerve also occurs in the MD rat optic nerve. This suggests that the attenuation of optic nerve sensitivity to GABA is not the result of myelination or interaction with myelin-associated proteins.

Spinal dysmyelination in new-born brown Swiss x Braunvieh calves.

In four new-born Braunvieh calves suffering from connate recumbency and body tremor, a hitherto not described myelination disorder of the spinal cord was examined. Bilateral symmetric hypo- as well as demyelination in several spinal tracts were the most conspicuous findings, affecting the ascending gracile funiculus, the ascending dorsolateral spinocerebellar tract, and the mainly descending sulcomarginal tract. Deficient myelin production, loss of myelin, consecutive axonal degenerations, and prominent astrogliosis within these tracts were the histological hallmarks of the disease. This possibly inherited primary myelination disorder of the spinal cord differs markedly from known hereditary neurological diseases in Brown Swiss and Braunvieh cattle, respectively, i.e. the weaver-syndrome and the spinal muscular atrophy.

Acute ozone-induced lung injury in rats: Structural-functional relationships of developing alveolar edema

As part of a study on the effects of acute ozone stress on the lung surfactant system, we correlated morphometric, biochemical, and functional indices of lung injury using male rats exposed to 3 ppm ozone for 1, 2, 4, and 8 hr. Evaluation of lung mechanics, using the Pulmonary Evaluation and Diagnostic Laboratory System, revealed a significant decrease in dynamic lung compliance (ml/cmH 2O/kg) from a control value of 0.84 ± 0.02 (SEM) to 0.72 ± 0.04 and 0.57 ± 0.06 at 4 and 8 hr, respectively. At 2 hr there was a transient increase in PaO 2 to 116 torr (control = 92 torr) followed by a decrease at 4 hr (65 torr) and 8 hr (55 torr). Morphometry of lung tissue, fixed by perfusion of fixative via the pulmonary artery at 12 cm H 2O airway distending pressure, demonstrated an increase in the area of the intravascular compartment at 8 hr, in association with a 65 and 39% replacement of the alveolar area by fluid in ventral and dorsal lung regions, respectively. There was a positive correlation ( r = 0.966) between alveolar edema and transudated proteins in lavage fluid. A stepwise multiple regression model, with edema as the dependent variable, suggested that pulmonary vasodilatation, hypoxemia, and depletion of surfactant tubular myelin in lavage fluid were indices for predicting alveolar edema. In a second model, with lavage protein concentration as the dependent variable, decreasing dynamic compliance and hypoxemia were predictors of progressive, intraalveolar transudation of plasma proteins. The above structural-functional relationships support the concept that ozone-induced high-protein alveolar edema is pathogenetically linked to pulmonary hyperemia, deficiency of surfactant tubular myelin, and associated lung dysfunctions.

Myelin deficiency in female rats due to a mutation in the PLP gene

Myelin deficiency ( md) in female rats due to a mutation in the X-linked proteolipid protein (PLP) gene is caused by X-chromosome monosomy. Cytogenetic analysis revealed a single X karyotype [41,X(md/0)]. An immunocytochemical, electron microscopic, and biochemical study was performed on male and female md rats. The central nervous system (CNS) of the female md rat [41,X(md/0)] revealed the same total lack of PLP as the CNS of the affected male littermate [42,XY(md/Y)]. Immunocytochemistry for myelin basic protein (MBP), myelin-associated glycoprotein (MAG), and 2′,3′-cyclic nucleotide-3′-phosphodiesterase (CNP) revealed “islands” of myelin sheath-like reaction product in both. Electron microscopy showed great paucity of compact myelin sheaths in 41,X(md/0) and 42,XY(md/Y). Reduced levels of MPB, MAG, and CNP were confirmed for both sexes but MAG and CNP were substantially higher in 41,X(md/0). Sexual differentiation of the brain may account for the observed differences since normal female reproductive organs are present in the md female rat.

A neuropathological study of early onset cockayne syndrome with chromosomal anomaly 47XXX

We present the clinical and neuropathological findings in a female patient with early onset Cockayne syndrome and a chromosomal anomaly (47XXX). The girl was the only child of healthy, unrelated parents. She was born with a birth weight of 1,930 gm. She had progeroid facial features with bilateral cataracts. A diagnosis of 47XXX was made on the basis of a chromosomal study. Physical shortness became increasingly prominent while her weight remained stationary. Psychomotor retardation was noted, and she could never sit alone. A brain CT scan showed cerebral atrophy and calcification of the basal ganglia. Cultured skin fibroblast exhibited significant sensitivity to the ultraviolet light. She died from a chest infection at the age of 7 years and 4 months. Microscopically, the renal glomeruli showed diffuse sclerotic changes with thick capillary basement membranes. A neuropathological examination revealed a very small brain (295 gm), extensive myelin deficiency, gliosis in the white matter, and calcifications in the basal ganglia, and cerebral and cerebellar cortices. The loss of both Purkinje and granular cells was noticed in the cerebellar cortex. This is the first report of a case with the Cockayne syndrome and 47XXX, and the 47XXX in this patient seems to be coincidental.

Neuropathology of Bovine β-Mannosidosis

beta-Mannosidosis, an inherited defect of glycoprotein catabolism previously identified in goats and humans, has been recently diagnosed in Salers cattle. This disorder is associated with deficiency of lysosomal beta-mannosidase and accumulation of oligosaccharides. Analysis of bovine beta-mannosidosis neuropathology was initiated to determine whether independently arising gene defects in cattle and goats result in expression of similar lesions. Brain, spinal cord, and selected peripheral nerves from seven affected newborn Salers calves and three normal newborn calves were available for gross, light microscopic, and electron microscopic analysis. Gross examination revealed hydrocephalus of variable severity and myelin deficiency in the cerebral hemispheres, cerebellum, and brainstem. Microscopic examination revealed cytoplasmic vacuolation, myelin deficiency, and axonal spheroids of similar type and distribution to that reported in affected goats. Cytoplasmic vacuolation resulting from lysosomal storage showed consistent variation among cell types. Myelin deficits were more severe in the cerebral hemispheres and cerebellum than in the spinal cord. Axonal spheroids occurred in the cerebrum, brainstem, cerebellum, and trigeminal nerve endings. The presence of similar lesions in bovine and caprine beta-mannosidosis supports a direct relationship with the gene defect.

Immunocytochemical analysis of glial cells in the hypomyelinated optic nerve of the BW mutant rat

The Browman-Wyse (BW) rat is a mutant with structural defects of the visual system, including a failure of the proximal (retinal) end of the optic nerve to myelinate. This latter abnormality is correlated with an absence of CAII+ oligodendrocytes, but we have previously shown that astrocytes are normally distributed, as judged by morphological characteristics of GFAP+ cells in vivo. We have further examined in vitro the immunohistochemical characteristics of macroglia isolated from the BW optic nerve, either as cell suspensions or after 4 days in culture. Cell cultures derived from the hypomyelinated proximal segment of BW optic nerves contained very few 0-2A progenitor cells (from which oligodendrocytes and cells with the GFAP+/A2B5+ phenotype develop), whereas over 90% of the glia were Schwann cells. A proportion of these few 0-2A progenitor cells differentiated normally after 4 days in vitro into both progeny phenotypes in appropriate media. Accordingly, we conclude that the myelination deficiency in the BW optic nerve could be explained as a failure of 0-2A progenitor cells to populate fully the proximal extremity of the nerve during development. Since most glia isolated from adult optic nerves did not adhere to the culture substrate, we analysed the phenotypes of freshly isolated cells in suspension. Comparing optic nerves of normal adult rats with those of BW mutants, a significantly higher fraction of the GFAP+ cells reacted with A2B5 in cell suspensions of the latter. The double-labelled cells which are present in abnormally high numbers may be the differentiated progeny of 0-2A progenitors in the hypomyelinated segment of nerve. One explanation for these findings is that Schwann cells within the BW nerve induce the differentiation of 0-2A progenitor cells to the GFAP+/A2B5+ phenotype. We investigated this possibility using conditioned medium from cultured Schwann cells which increased tenfold the frequency of GFAP+/A2B5+ cells in normal neonatal rat optic nerve cultures. Oligodendrocyte numbers showed a concomitant decline with increasing concentration of Schwann cell conditioned medium. Hypomyelination in the BW rat optic nerve may therefore arise because Schwann cells, present in the proximal segment of the nerve, not only impede the migration of 0-2A progenitor cells but also release a factor which induces those 0-2A progenitor cells which arrive in the proximal segment of the nerve to differentiate into GFAP+ cells at a critical stage in oligodendrocyte development.

Regional Central Nervous System Oligosaccharide Storage in Caprine β‐Mannosidosis

Goats affected with beta-mannosidosis, an autosomal recessive disease of glycoprotein metabolism, have deficient activity of the lysosomal enzyme beta-mannosidase along with tissue storage of oligosaccharides, including a trisaccharide [Man(beta 1-4)GlcNAc(beta 1-4)GlcNAc] and a disaccharide [Man(beta 1-4)GlcNAc]. CNS myelin deficiency, with regional variation in severity, is a major pathological characteristic of affected goats. This study was designed to investigate regional CNS differences in oligosaccharide accumulation to assess the extent of correlation between oligosaccharide accumulation and severity of myelin deficits. The concentrations of accumulated disaccharide and trisaccharide and the activity of beta-mannosidase were determined in cerebral hemisphere gray and white matter and in spinal cord from three affected and two control neonatal goats. In affected goats, the content of trisaccharide and disaccharide in spinal cord (moderate myelin deficiency) was similar to or greater than that in cerebral hemispheres (severe myelin deficiency). Thus, greater oligosaccharide accumulation was not associated with more severe myelin deficiency. Regional beta-mannosidase activity levels in control goats were consistent with the affected goat oligosaccharide accumulation pattern. The similarity of trisaccharide and disaccharide content in cerebral hemisphere gray and white matter suggested that lysosomal storage vacuoles, more numerous in gray matter, may not be the only location of stored CNS oligosaccharides.

Spongy Degeneration of White Matter in the Central Nervous System of Silver Foxes (Vulpes vulpes)

A disorder of central nervous white matter in Norwegian-bred silver foxes is described from the case histories of 21 clinically affected foxes. The main presenting sign of this disorder was caudal limb ataxia, which appeared between 2 1/2 and 4 months of age and progressed over the next 4-8 weeks. Only four affected foxes were allowed to live beyond this period, but they showed moderate to marked improvement. Light microscopic examination of specimens from 16 affected foxes necropsied between 3 1/2 and 6 1/2 months of age revealed lesions that were restricted to the white matter of brain and spinal cord. The lesions were characterized by a symmetrical spongy change with vacuoles of varying sizes and included significant myelin deficiency. There was a relative preservation of axons and nerve cells and no significant inflammation or vascular reaction. An astrocytic hypertrophy was usually associated with the spongy change. Ultrastructural examination of central nervous tissue from two, perfusion-fixed, 6-month-old foxes showed intramyelin vacuoles resulting from splitting of the myelin lamellae at the intraperiod line and was interpreted as indicating myelin edema. Expanded extracellular spaces and watery astrocytic processes also contributed to the vacuolar appearance. Astrocytic processes in affected areas were hypertrophic and contained abundant filaments. Although the 16 silver foxes had severe clinical signs, their lesions had features in common with the juvenile form of Canavan's disease in children and a spongy degeneration reported in Labrador Retrievers; however, the clinical course in the foxes was not uniformly progressive.