Myelin Splitting Research Articles

Paranodal pathology in Tangier disease with remitting-relapsing multifocal neuropathy

Pathological studies of a sural nerve biopsy in a man with Tangier disease presenting as a remitting-relapsing multifocal neuropathy showed abnormalities in the paranodal regions, including lipid deposition (65%) and redundant myelin foldings, with various degrees of myelin splitting and vesiculation (43%) forming small tomacula and abnormal myelin terminal loops (4%). The internodal regions were normal in the majority of myelinated fibres. Abnormal lipid storage was also present in the Schwann cells of the majority of unmyelinated fibres (67%). The evidence suggests that the noncompacted myelin region of the paranode is a preferential site for lipid storage in the myelinated Schwann cell, and that the space-occupying effects of the cholesterol esters leads to paranodal malfunction and tomacula formation as the pathological basis for the multifocal relapsing-remitting clinical course.

Megalencephalic leukoencephalopathy with subcortical cysts: an update and extended mutation analysis ofMLC1

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is an autosomal recessive cerebral white matter disorder in children. This disease is histopathologically characterized by myelin splitting and intramyelinic vacuole formation. MLC is caused by mutations in the gene MLC1, which encodes a novel protein, MLC1. Since the first report, 50 mutations in this gene have been found. Mutations occur throughout the entire coding region and include all different types: 11 splice-site mutations; one nonsense mutation; 24 missense mutations; and 14 deletions and insertions. Until now, six polymorphisms within the coding sequence of MLC1 had been reported. In about 20% of the patients with a typical clinical and MRI picture, no mutations in the MLC1 gene are found. Several of the families, in which no mutations are found, also do not show linkage with the MLC1 locus, which suggests a second gene involved in MLC. The absence of mutations may also be the consequence of performing standard mutation analysis that can miss heterozygous deletions, mutations in the promoter, 3' and 5' untranslated regions (UTRs), and intron mutations, which may influence the amino acid composition of the end product. In this work we describe 13 novel mutations, including those found with extended mutation analysis on MLC patients. This study shows that extended mutation analysis is a valuable tool to identify at least some of the missing mutations. Therefore, we suggest extended mutation analysis for the MLC1 gene, if no mutations are found during standard analysis.

Characterization of photodamage in coherent anti-Stokes Raman scattering microscopy

We report a mechanistic analysis of photodamage in coherent anti-Stokes Raman scattering (CARS) microscopy. Photodamage to the myelin sheath in spinal tissues is induced by using the point scan mode and is featured by myelin splitting and shockwaves with broadband emission. Our measurement of photodamage rate versus the excitation power reveals that both linear and nonlinear mechanisms are involved. Moreover, we show that vibrational absorption induced by coherent Raman processes significantly contributes to the nonlinear damage at high peak powers. For CARS imaging of cultured cells, the photodamage is characterized by plasma membrane blebbing and is dominated by a second order mechanism. Our study suggests that for dense samples such as the myelin sheath, CARS imaging induced photodamage can be minimized by using laser beams with relatively long near IR wavelengths and a repetition rate of a few MHz. For less dense samples such as cultured cells, laser pulses of higher repetition rates are preferred.

Brain magnetic resonance imaging in tyrosinemia

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

MLC1: A Novel Protein in Distal Astroglial Processes

Megaloencephalic leukoencephalopathy with subcortical cysts (MLC) is a progressive cerebral white matter disease in children caused by mutations in the MLC1 gene. This disease is histopathologically characterized by myelin splitting and intramyelinic vacuole formation. MLC1 encodes a novel protein, MLC1, which is mainly expressed in the brain and leukocytes. The function is unknown, although a transport function has been suggested. In this article, we provide experimental data addressing the membrane topology and cellular localization of MLC1. We show that MLC1 contains an even number of transmembrane domains, supporting the possible transport function of MLC1. We demonstrate that MLC1 is specifically expressed in distal astroglial processes in perivascular, subependymal, and subpial regions. This localization suggests a role for MLC1 in a transport process across the blood-brain and brain-cerebrospinal fluid barriers. Astrocyte functions have long been debated. It is becoming increasingly clear that these cells are of fundamental importance in maintaining the structural and functional integrity of neural tissue. Elucidation of the function of MLC1 will contribute to a better understanding of not only the pathophysiology of the disease, but also the role of astrocytes in normal neural tissue.

Clinicopathological Features of Globoid Cell Leucodystrophy in Cats

SummaryClinical and pathological findings consistent with globoid cell leucodystrophy (GLD) were evaluated in two domestic shorthaired cats, aged 3 and 4 months. Both showed neurological signs mainly characterized by progressive pelvic limb ataxia, paraplegia with loss of deep pain perception in the pelvic limb, and intentional tremors of the thoracic limbs. Pathological changes affecting the central and peripheral nervous systems were characterised by diffuse, bilateral and symmetrical myelin loss, and marked astrogliosis. In the leucodystrophic areas there was perivascular accumulation of large PAS-positive, non-metachromatic macrophages (globoid cells), with intracytoplasmic accumulation of crystalloid tubular aggregates. Peripheral nerves showed demyelinating features with thin myelin sheaths, myelin splitting, and ballooning; the nerve fibres had bizarre shapes due to the presence of pale inclusions in the Schwann cells. GLD in cats shares clinical and pathological features with the disease described in other animals and human beings. The neurological signs differed from those of other feline inborn neurometabolic diseases and cerebellar hypoplasia.

0333 Paranodal pathology in Tangier disease with remitting-relapsing multifocal neuropathy

Pathological studies of a sural nerve biopsy in a man with Tangier disease presenting as a remitting-relapsing multifocal neuropathy showed abnormalities in the paranodal regions, including lipid deposition (65%) and redundant myelin foldings, with various degrees of myelin splitting and vesiculation (43%) forming small tomacula and abnormal myelin terminal loops (4%). The internodal regions were normal in the majority of myelinated fibres. Abnormal lipid storage was also present in the Schwann cells of the majority of unmyelinated fibres (67%). The evidence suggests that the noncompacted myelin region of the paranode is a preferential site for lipid storage in the myelinated Schwann cell, and that the space-occupying effects of the cholesterol esters leads to paranodal malfunction and tomacula formation as the pathological basis for the multifocal relapsing-remitting clinical course.

Wallerian Degeneration in the Optic Nerve of the Rabbit

Progressive anterograde axonal degeneration is known to follow after transection of the axon from the soma, which to some extent correlates with the passage of time after the lesion. However, the minimum time required for such changes to begin remains unresolved. In this study, 20 young adult rabbits of either sex underwent experimental monocular enucleation (left eye) under general anaesthesia. Left optic nerves from such animals were treated as experimental and those from either side of non-operated animals served as controls. Animals were sacrificed postoperatively at periods ranging from 12 h to 3 months. Brains were fixed with 10% formalin and Karnovsky fixatives by an intracardiac perfusion method. Light microscopy of 8-µm paraffin sections and 0.5-µm araldite sections from the optic nerves did not reveal any changes at 12 h. At 24 h, focal minute cavities appeared across the optic nerves. Those nerves from late postoperative stages revealed such cavities with increasing dimensions, disarray of fascicular organization, fragmentation, ovoid formation and finally dissolution of the myelin sheaths. There was an appreciable increase in the number, size and aggregation of glia cells. The debris of degeneration remained prominent even 3 months after enucleation. Electron microscopy revealed splitting of myelin, intramyelinic and periaxonal oedema and occurrence of amorphous and electron-dense materials in the degenerating nerve fibres. It was concluded that while the optic nerve showed degenerative changes as early as 24 h after enucleation, debris of degeneration was only partly removed even after 3 months.

"Anoikis" of oligodendrocytes induced by Wallerian degeneration: ultrastructural observations.

Oligodendrocytes undergo apoptosis in the white matter tracts remote from the experimental cord injury, although its significance is not understood. Our ultrastructural study, however, enabled us to speculate on its neurobiological implications. The spinal cords of male Wistar rats (4 week-old) were transected at Th11 level. At 4, 5, and 7 days after surgery the animals were transcardially perfusion-fixed. The removed cord was embedded in epoxy resin and examined by electron microscopy. Post-embedding terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick end labeling (TUNEL) method was also performed. In the degenerative dorsal column above the transection, profiles of apoptotic oligodendrocytes were always found, embedded in a space formed by dilated degenerative myelin lamellae. Often, the dilated space in the myelin sheath lacked any apparent background proteinaceous matrix. In the electron microscopic TUNEL method, these apoptotic cells were electron dense in accordance with nuclear heterochromatinization. In conclusion, in the process of Wallerian degeneration, we observed the apoptosis of oligodendrocytes in a space formed by the split myelin sheath. These degenerative cells, which were enclosed in an ultrafiltrate-filled space formed by split myelin lamellae, were reminiscent of "anoikis."

Parenteral N,N-diethyldithiocarbamate produces segmental demyelination in the rat that is not dependent on cysteine carbamylation

Disulfiram, a dithiocarbamate drug used in alcohol aversion therapy, produces a peripheral neuropathy characterized in rats as segmental demyelination accompanied by generation of S-(diethylaminocarbonyl)cysteine (DETC-Cys) adducts. N,N-Diethyldithiocarbamate (DEDC) is a major metabolite of disulfiram that can undergo methylation and oxidation to S-methyl- N,N-diethylthiocarbamate (MeDETC) sulfoxide and sulfone, thought to be responsible for carbamylation of sulfhydryl functions by disulfiram. To assess the role of cysteine carbamylation in disulfiram toxicity, DEDC and MeDETC were administered parenterally to male Sprague–Dawley rats for 4 and 8 weeks. The roles of the disulfide linkage in disulfiram and of carbamylated glutathione metabolites were assessed by administering S-(diethylaminodithiocarbonyl) N-acetylcysteine (DS-NAC) and S-(diethylaminocarbonyl)- N-acetylcysteine (DETC-NAC), respectively, parenterally for 12 weeks. Following exposure, spinal cord-derived neurofilament preparations and hemoglobin were isolated and analyzed by RP–HPLC and LC/MS/MS for the presence of DETC-Cys adducts. Peripheral nerve sections were also obtained and examined by light and electron microscopy for morphological lesions. RP–HPLC analysis of globin preparations from DEDC-, MeDETC-, and DS-NAC-exposed animals demonstrated a late-eluting peak, identical to that reported for disulfiram-generated DETC-Cys adducts on the β 3-globin chain. DETC-NAC exposure did not result in detectable globin modification by RP–HPLC. The quantity of DETC-Cys adducts produced on globin and neurofilament preparations determined by LC/MS/MS was twofold greater for MeDETC than DEDC following equimolar doses of each compound. Primary myelin lesions consisting of demyelinated axons and myelin splitting were observed in peripheral nerves following exposure to DEDC for 8 weeks. No lesions were detected following exposure to MeDETC, DS-NAC, or DETC-NAC at any time point or dose level. These results are consistent with DEDC, but not the other metabolites, being a demyelinating agent and thus a potential proximate toxic species for disulfiram-mediated demyelination. The production of significantly greater levels of DETC-Cys adducts by MeDETC relative to DEDC in the absence of neurotoxicity for MeDETC is consistent with cysteine carbamylation not contributing to the demyelination produced by disulfiram and DEDC.

TEMPORAL DEVELOPMENT OF 2′,3′‐DIDEOXYINOSINE (DDI)‐INDUCED PERIPHERAL MYELINOPATHY

The anti‐HIV therapeutic dideoxyinosine (ddI) has been reported to produce a painful, dose‐limiting peripheral myelinopathy in HIV‐infected patients after chronic administration. We have previously demonstrated ddI‐induced myelinopathy in a non‐HIV‐infected rat model after 20 weeks of dosing, characterized by myelin splitting and intramyelin edema. The present study examined the time course needed to produce the ddI‐induced neuropathy. Adult male Sprague‐Dawley rats were gavaged with vehicle of 415 mg/kg ddI twice daily for up to 20 weeks. Groups of treated (n = 6‐8) and control (n = 3–5) animals were killed after 5, 10, 15, and 20 weeks of dosing and the distal end of the sciatic nerve was removed. The nerve was postfixed by immersion in neutral phosphate‐buffered formalin, dehydrated in graded alcohols, and embedded in plastic embedding media. One‐micrometer‐thick sections were cut and stained with toluidine blue and basic fuchsin. Plasma levels of ddI on the day the animals were killed were greater than 10 mu g/ml within the first hour after dosing and fell rapidly to less than 1 mu g/ml (clinical range 1–2 mu g/ml) within 3 h after dosing. The abnormalities observed in the sciatic nerve were few, if any, after 5 or 10 weeks, but very prominent after 15 weeks of dosing. Four of the six ddI‐treated rats exhibited abnormal morphology as evidenced by myelin splitting and ballooned myelin sheaths. Although abnormal morphology was present at 20 weeks of dosing, the effect was not as robust as at 15 weeks. This suggests that the nerve may partially recover from the effects of ddI with time.

Temporal development of 2′,3′-dideoxyinosine (ddI)–induced peripheral myelinopathy

The anti-HIV therapeutic dideoxyinosine (ddI) has been reported to produce a painful, dose-limiting peripheral myelinopathy in HIV-infected patients after chronic administration. We have previously demonstrated ddI-induced myelinopathy in a non-HIV–infected rat model after 20 weeks of dosing, characterized by myelin splitting and intramyelin edema. The present study examined the time course needed to produce the ddI-induced neuropathy. Adult male Sprague–Dawley rats were gavaged with vehicle or 415 mg/kg ddI twice daily for up to 20 weeks. Groups of treated ( n = 6–8) and control ( n = 3–5) animals were killed after 5, 10, 15, and 20 weeks of dosing and the distal end of the sciatic nerve was removed. The nerve was postfixed by immersion in neutral phosphate-buffered formalin, dehydrated in graded alcohols, and embedded in plastic embedding media. One-micrometer-thick sections were cut and stained with toluidine blue and basic fuchsin. Plasma levels of ddI on the day the animals were killed were greater than 10 μg/ml within the first hour after dosing and fell rapidly to less than 1 μg/ml (clinical range 1–2 μg/ml) within 3 h after dosing. The abnormalities observed in the sciatic nerve were few, if any, after 5 or 10 weeks, but very prominent after 15 weeks of dosing. Four of the six ddI-treated rats exhibited abnormal morphology as evidenced by myelin splitting and ballooned myelin sheaths. Although abnormal morphology was present at 20 weeks of dosing, the effect was not as robust as at 15 weeks. This suggests that the nerve may partially recover from the effects of ddI with time. Published by Elsevier Science Inc.

Apoptotic cells associated with Wallerian degeneration after experimental spinal cord injury: a possible mechanism of oligodendroglial death.

We have investigated the temporal and spatial profiles of apoptotic cells in an experimental transection spinal cord injury by the terminal deoxynucleotidyl transferase-mediated biotin-16-2'-deoxyuridine-5'-triphosphate nick-end labeling (TUNEL) method. Twenty-four hours postinjury, a numerous TUNEL-positive cells appeared both rostrally and caudally to the transection site. Those positive cells, however, gradually diminished in number by several days postinjury. In contrast, other TUNEL-positive cells were found scattered within the white matter remote from the lesion by the third day postinjury. These cells were typically embedded in or among vacuolated fibers, where they were identified in close proximity to the vacuolated space enclosed by myelin basic protein (MBP)-positive structures confirmed by TUNEL-MBP double staining. Because of their linear arrangement, these TUNEL-positive cells were considered interfascicular oligodendrocytes, a fact that was confirmed by the finding that some TUNEL-positive cells were also stained with CCI, a cell marker for oligodendrocyte. Electron microscopic studies revealed that the cells expressing apoptotic morphology were invariably encased in a space formed by myelin splitting. Although the biological significance of apoptotic interfascicular oligodendrocytes in the process of wallerian degeneration is yet to be determined, the finding of such profiles localized within degenerating myelin structures suggests that; oligodendrocytes may be "trapped" within rapidly swollen and disintegrating myelin lamellae, which isolates and perhaps predisposes them to death.

BDNF attenuates functional and structural disorders in nerves of galactose-fed rats.

Galactose intoxication of rats was used to disrupt metabolism of Schwann cells and skeletal muscle, two sites that contain the polyol-forming enzyme aldose reductase (AR). Galactose-fed rats develop a neuropathy characterized by nerve conduction deficits and axonal atrophy. To investigate the possibility that galactose metabolism by AR influences axonal function and structure by altering production of neurotrophic factors, the impact of galactose intoxication on nerve and muscle BDNF levels and the effects of exogenous BDNF treatment on galactose neuropathy were examined using biochemical, electrophysiologic and morphometric techniques. Galactose feeding increased BDNF protein in peripheral nerve and muscle. Exogenous BDNF treatment attenuated motor nerve conduction velocity deficits in the sciatic nerve of galactose-fed animals and myelin splitting of motor axons in the ventral root. In contrast, sensory nerve conduction velocity (SNCV) deficits in the sciatic nerve and myelin splitting in the central projections of sensory neurons were not prevented by BDNF treatment. BDNF treatment did not attenuate reduced axonal caliber in the sciatic nerve, but did ameliorate the diminution of the caliber of central sensory projections in the dorsal root. These findings point to the potential use of BDNF in the treatment of peripheral neuropathies.

Neuropathology and blood flow of nerve, spinal roots and dorsal root ganglia in longstanding diabetic rats.

Vascular perfusion and neuropathologic evaluation of the lumbar spinal roots and dorsal root ganglia (DRG) were studied in rats with longstanding (duration 12-15 months) streptozotocin-induced diabetes and age- and sex-matched control rats. We also undertook nerve conduction studies including F-wave recordings and measured blood flow in sciatic nerve, DRG, and superior cervical ganglion (SCG). Light microscopically, changes of the myelin sheath in the dorsal and ventral roots and vacuolated cells in the DRG were the major findings, being significantly higher in diabetic rats than in control rats. The effects of the diabetic state on myelin splitting were greater in the dorsal than ventral roots. Electron microscopic studies revealed a gradation of changes in myelin from mild separation to severe ballooning of myelin with relative axonal sparing. DRG cells showed vacuoles of all sizes with cristae-like residues, suggestive of mitochondria. These findings suggest that diabetes mellitus has a dual effect: it accelerates the normal age-related degenerative changes in the spinal roots and DRG, and it also has a selective effect on the sensory neuron. Nerve conduction studies showed markedly reduced conduction velocities in the distal nerve segments and prolonged F-wave latency and proximal conduction time despite the shorter conduction pathway in diabetic rats. Blood flow, which was measured using iodo[14C]antipyrine autoradiography, was significantly reduced in the sciatic nerves, DRG, and SCG of diabetic rats. We suggest that the combination of hyperglycemia and ischemia results in oxidative-stress and a predominantly sensory neuropathy.

Evaluation of brain and nerve pathology in rats chronically dosed with ddI or isoniazid.

The antiviral adenosine analog, 2',3'-dideoxyinosine (ddI), and the antitubercular nicotinic acid analogue, isoniazid, have recently received widespread clinical application in the treatment of acquired immunodeficiency syndrome (AIDS). Clinical studies indicate that the primary dose limiting side effect of both drugs is neurological in nature. Most clinical studies are confounded by the fact that the observed neuropathy must be evaluated in the presence of the ongoing disease process associated with human immunodeficiency virus (HIV) infection. The purpose of this study was to develop and validate a rat model of ddI-and isoniazid-induced neuropathy in the absence of any disease-induced pathology. Myelin splitting and intramyelin edema were the most frequent abnormalities observed in the sciatic nerves of ddI-dosed animals, whereas whorls, extracellular debris, macrophages, and reduced myelinated axon number were seen following chronic isoniazid administration. Isoniazid also resulted in myelinopathy of the CNS. Thus, contrary to previous reports, the rodent is a suitable model for ddI- and isoniazid-induced neuropathies.

Metabolites of 5-fluorouracil, alpha-fluoro-beta-alanine and fluoroacetic acid, directly injure myelinated fibers in tissue culture.

The neurotoxicity of two 5-fluorouracil (5-FU) derivatives, tegafur (FT) and carmofur (HCFU), which selectively induce leukoencephalopathy involving the cerebral white matter in humans and vacuolation of myelinated fibers in dogs and cats, was examined in vitro. The common metabolites of these drugs, alpha-fluoro-beta-alanine (FBAL) and fluoroacetic acid (FA), were added to the medium of cultured murine cerebellar myelinated fibers. On day 1 of exposure to 7 microM FBAL and FA, which corresponds to their blood concentrations 2 h after oral administration of 10 mg.kg-1 HCFU to dogs that induced central nervous system vacuolation after 30 days, partial splits of the myelinic intraperiod line were observed by electron microscopy. On days 4-7, phase contrast microscopy revealed spindle-shaped swelling and granulation of myelin and electron microscopy demonstrated prominent dissociation of the myelinic intraperiod line with monolocular and multilocular vacuolation. More severe changes, such as myelin loss, were found in cultures exposed to a higher concentration (70 microM) of FBAL and FA, but no remarkable neuronal, astrocytic or oligodendrocytic changes occurred. Quantitative evaluation of myelin injury by electron microscopy revealed significant toxicity of FBAL and FA, at concentrations of 7 and 70 microM, on day 4. However, groups treated with 0.7 microM FBAL and FA, 5-FU (7 microM) and controls exposed to beta-alanine and acetic acid concentrations of 0.7, 7 and 70 microM showed no marked injury. We concluded that these anticancer drug metabolites injure myelin fibers directly, resulting in vacuolation due to myelin splitting and destruction.

Chronic relapsing experimental autoimmune encephalomyelitis with a delayed onset and an atypical clinical course, induced in PL/J mice by myelin oligodendrocyte glycoprotein (MOG)‐derived peptide: Preliminary analysis of MOG T cell epitopes

Myelin basic protein (MBP) and proteolipid protein (PLP), the most abundant proteins of central nervous system (CNS) myelin, have been extensively studied as possible primary target antigens in multiple sclerosis (MS), a primary demyelinating autoimmune disease of the CNS. However, there is increasing evidence to suggest that autoimmune reactivity against the quantitatively minor myelin component, myelin oligodendrocyte glycoprotein (MOG), can also play a role in the pathogenicity of MS. We recently demonstrated a predominant response to MOG by peripheral blood lymphocytes from patients with MS tested for their reactivity against various myelin antigens, including MBP and PLP. To ascertain whether or not T cell reactivity to MOG in MS is a potentially pathogenic response, we have tested the ability of synthetic MOG peptides (pMOG) representing potential T cell epitopes, to induce neurological disease in mice. Both strains of mice tested (SJL/J and PL/J mice) were able to mount a primary T cell response to some of the five MOG peptides synthesized, pMOG 1-21, 35-55, 67-87, 104-117 and 202-218. T cell lines could be raised in both strains to pMOG 35-55 and 67-87, but epitope definition revealed that each strain recognized a different minimal epitope within these two peptides. T cell lines to pMOG 1-21 and 202-218 could also be raised in SJL/J and PL/J mice, respectively. T cell reactivity to pMOG 104-117 was not observed in either mouse strain. None of the peptides tested induced detectable clinical signs in SJL/J mice. In contrast, an MS-like chronic relapsing-remitting disease could be induced in PL/J mice with pMOG 35-55. The disease presented with a delayed onset and with clinical signs which differed significantly in their progression and expression from the typical ascending paralysis of experimental autoimmune encephalomyelitis induced with other myelin components, such as MBP and PLP. Histological examination of CNS tissue from mice injected with pMOG 35-55 revealed only mild neuropathological signs with few inflammatory foci in brain and spinal cord. Some myelin splitting and edema were detected upon electron microscopic examination in the spinal cord and cerebellum. Transfer of pMOG 35-55 reactive T cells into naive PL/J mice resulted in pathological changes characterized by inflammatory foci in the brain and spinal cord. This passively induced disease was clinically silent, as was also reported for Lewis rats injected with T cells specific for the same MOG peptide.(ABSTRACT TRUNCATED AT 400 WORDS)

Severe radicular pathology in rats with longstanding diabetes

There few pathological abnormalities in nerves from animals with diabetes. Reported changes consist of mild distal axonal atrophy, axoglial disjunction and minimal segmental demyelination and remyelination. These changes are seen in distal nerves but no studies of radicular pathology in diabetic animals have been reported. We therefore studied peripheral nerve and radicular pathology in rats with longstanding, severe, chemically-induced diabetes. We found marked interstitial edema and severe changes of myelin in the roots of diabetic rats, particularly in the dorsal root. The earliest changes consist of myelin splitting, occurring at the intraperiod line. This progresses to myelin ballooning, accompanied by both tubulovescicular myelin degeneration and macrophage stripping, all of which tend to predominate in large myelinated fibers. There is minimal axonal degeneration. Despite these severe changes in nerve roots, the distal peripheral nerves show no discernible edema and only minimal myelin splitting without demyelination or axonal degeneration. The radicular changes are almost identical to those seen in much older nondiabetic animals. This suggests that they may represent an acceleration of the normal aging process, perhaps related to increased glycation of myelin proteins induced by accumulation of glucose rich interstitial endoneurial edema.

Dose-dependent alterations in nerve polyols and (Na +,K +)-ATPase activity in galactose intoxication

Nerve polyol content and (Na +,K +)-adenosine triphosphatase (ATPase) activity of nerve homogenates were studied in a colony of rats fed diets containing either 0%, 10%, 20%, or 40% galactose for 4 months. Nerve water and dulcitol content exhibited dose-dependent increases, whereas nerve myo-inositol content declined with increasing dietary galactose. Homogenate (Na +,K +)-ATPase activity increased with increasing galactose consumption of up to 20% dietary intake and thereafter remained consistently elevated at twice the activity of 0% galactose-fed values. Nerves of rats fed 40% galactose were also examined at the light microscope level and showed evidence of both edema and myelin splitting. These data demonstrate that increased nerve water content, dulcitol accumulation, and myo-inositol depletion parallel the previously reported dose-related increase of endoneurial fluid sodium and chloride in nerves of galactose-fed rats and suggest that elevated nerve homogenate (Na +,K +)-ATPase activity may be related to one or more of these consequences of exaggerated polyol pathway flux.