Neuropathy associated with mitochondrial disorders

Myelin protein zero mutation-related hereditary neuropathies: Neuropathological insight from a new nerve biopsy cohort

Myelin protein zero (MPZ/P0) is a major structural protein of peripheral nerve myelin. Disease-associated variants in the MPZ gene cause a wide phenotypic spectrum of inherited peripheral neuropathies. Previous nerve biopsy studies showed evidence for subtype-specific morphological features. Here, we aimed at enhancing the understanding of these subtype-specific features and pathophysiological aspects of MPZ neuropathies. We examined archival material from two Central European centers and systematically determined genetic, clinical, and neuropathological features of 21 patients with MPZ mutations compared to 16 controls. Cases were grouped based on nerve conduction data into congenital hypomyelinating neuropathy (CHN; n = 2), demyelinating Charcot-Marie-Tooth (CMT type 1; n = 11), intermediate (CMTi; n = 3), and axonal CMT (type 2; n = 5). Six cases had combined muscle and nerve biopsies and one underwent autopsy. We detected four MPZ gene variants not previously described in patients with neuropathy. Light and electron microscopy of nerve biopsies confirmed fewer myelinated fibers, more onion bulbs and reduced regeneration in demyelinating CMT1 compared to CMT2/CMTi. In addition, we observed significantly more denervated Schwann cells, more collagen pockets, fewer unmyelinated axons per Schwann cell unit and a higher density of Schwann cell nuclei in CMT1 compared to CMT2/CMTi. CHN was characterized by basal lamina onion bulb formation, a further increase in Schwann cell density and hypomyelination. Most late onset axonal neuropathy patients showed microangiopathy. In the autopsy case, we observed prominent neuromatous hyperinnervation of the spinal meninges. In four of the six muscle biopsies, we found marked structural mitochondrial abnormalities. These results show that MPZ alterations not only affect myelinated nerve fibers, leading to either primarily demyelinating or axonal changes, but also affect non-myelinated nerve fibers. The autopsy case offers insight into spinal nerve root pathology in MPZ neuropathy. Finally, our data suggest a peculiar association of MPZ mutations with mitochondrial alterations in muscle.

Ablation of Argonaute 2 in Schwann cells accelerates the progression of diabetic peripheral neuropathy

Schwann cells (SCs) form myelin and provide metabolic support for axons, and are essential for normal nerve function. Identification of key molecules specific to SCs and nerve fibers may provide new therapeutic targets for diabetic peripheral neuropathy (DPN). Argonaute2 (Ago2) is a key molecular player that mediates the activity of miRNA-guided mRNA cleavage and miRNA stability. Our study found that Ago2 knockout (Ago2-KO) in proteolipid protein (PLP) lineage SCs in mice resulted in a significant reduction of nerve conduction velocities and impairments of thermal and mechanical sensitivities. Histopathological data revealed that Ago2-KO significantly induced demyelination and neurodegeneration. When DPN was induced in both wild-type and Ago2-KO mice, Ago2-KO mice exhibited further decreased myelin thickness and exacerbated neurological outcomes compared with wild-type mice. Deep sequencing analysis of Ago2 immunoprecipitated complexes showed that deregulated miR-206 in Ago2-KO mice is highly related to mitochondrial function. In vitro data showed that knockdown of miR-200 induced mitochondrial dysfunction and apoptosis in SCs. Together, our data suggest that Ago2 in SCs is essential to maintain peripheral nerve function while ablation of Ago2 in SCs exacerbates SC dysfunction and neuronal degeneration in DPN. These findings provide new insight into the molecular mechanisms of DPN.

Peripheral neuropathy in mitochondrial disease

Mitochondria are essential for the health and viability of both motor and sensory neurons and their axons. Processes that disrupt their normal distribution and transport along axons will likely cause peripheral neuropathies. Similarly, mutations in mtDNA or nuclear encoded genes result in neuropathies that either stand alone or are part of multisystem disorders. This chapter focuses on the more common genetic forms and characteristic clinical phenotypes of "mitochondrial" peripheral neuropathies. We also explain how these various mitochondrial abnormalities cause peripheral neuropathy. In a patient with a neuropathy either due to a mutation in a nuclear or an mtDNA gene, clinical investigations aim to characterize the neuropathy and make an accurate diagnosis. In some patients, this may be relatively straightforward, where a clinical assessment and nerve conduction studies followed by genetic testing is all that is needed. In others, multiple investigations including a muscle biopsy, CNS imaging, CSF analysis, and a wide range of metabolic and genetic tests in blood and muscle may be needed to establish diagnosis.

Strategy for genetic analysis in hereditary neuropathy

Inherited neuropathies are a heterogeneous group of slowly progressive disorders affecting either motor, sensory, and/or autonomic nerves. Peripheral neuropathy may be the major component of a disease such as Charcot-Marie-Tooth disease or a feature of a more complex multisystemic disease involving the central nervous system and other organs. The goal of this review is to provide the clinical clues orientating the genetic diagnosis in a patient with inherited peripheral neuropathy. This review focuses on primary inherited neuropathies, amyloidosis, inherited metabolic diseases, while detailing clinical, neurophysiological and potential treatment of these diseases.

Prohibitin 1 is essential to preserve mitochondria and myelin integrity in Schwann cells

In peripheral nerves, Schwann cells form myelin and provide trophic support to axons. We previously showed that the mitochondrial protein prohibitin 2 can localize to the axon-Schwann-cell interface and is required for developmental myelination. Whether the homologous protein prohibitin 1 has a similar role, and whether prohibitins also play important roles in Schwann cell mitochondria is unknown. Here, we show that deletion of prohibitin 1 in Schwann cells minimally perturbs development, but later triggers a severe demyelinating peripheral neuropathy. Moreover, mitochondria are heavily affected by ablation of prohibitin 1 and demyelination occurs preferentially in cells with apparent mitochondrial loss. Furthermore, in response to mitochondrial damage, Schwann cells trigger the integrated stress response, but, contrary to what was previously suggested, this response is not detrimental in this context. These results identify a role for prohibitin 1 in myelin integrity and advance our understanding about the Schwann cell response to mitochondrial damage.

Mitochondrial neuropathy and neurogenic features in mitochondrial myopathy

Mitochondrial diseases (MIDs) involve multiple organs including peripheral nerves and skeletal muscle. Mitochondrial neuropathy (MN) and mitochondrial myopathy (MM) are commonly associated and linked at the neuromuscular junction (NMJ). Herein we review MN in connection with neurogenic features of MM, and pathological evidence for the involvement of the peripheral nerve and NMJ in MID patients traditionally assumed to have predominantly MM. MN is not uncommon, but still likely under-reported, and muscle biopsies of MM commonly exhibit neurogenic features. Pathological examination remains the gold standard to assess the nerve and muscle changes in patients with MIDs. Ultrastructural studies by electron microscopy are often necessary to fully characterize the pathology of mitochondrial cytopathy in MN and MM.

Mitochondrial disorders and the eye

Mitochondria are cellular organelles that play a key role in energy metabolism and oxidative phosphorylation. Malfunctioning of mitochondria has been implicated as the cause of many disorders with variable inheritance, heterogeneity of systems involved, and varied phenotype. Metabolically active tissues are more likely to be affected, causing an anatomic and physiologic disconnect in the treating physicians' mind between presentation and underlying pathophysiology. We shall focus on disorders of mitochondrial metabolism relevant to an ophthalmologist. These disorders can affect all parts of the visual pathway (crystalline lens, extraocular muscles, retina, optic nerve, and retrochiasm). After the introduction reviewing mitochondrial structure and function, each disorder is reviewed in detail, including approaches to its diagnosis and most current management guidelines.

Novel genetic and neuropathological insights in neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP)

INTRODUCTION

Neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP) is caused by m.8993T>G/C mutations in the mitochondrial adenosine triphosphate synthase subunit 6 gene (MT-ATP6). Traditionally, heteroplasmy levels between 70% and 90% lead to NARP, and >90% result in Leigh syndrome.

METHODS

In this study we report a 30-year-old man with NARP and m.8993T>G in MT-ATP6.

RESULTS

Although the patient carried the mutation in homoplasmic state in blood with similarly high levels in urine (94%) and buccal swab (92%), he presented with NARP and not the expected, more severe Leigh phenotype. The mutation could not be detected in any of the 3 analyzed tissues of the mother, indicating a large genetic shift between mother and offspring. Nerve biopsy revealed peculiar endoneurial Schwann cell nuclear accumulations, clusters of concentrically arranged Schwann cells devoid of myelinated axons, and degenerated mitochondria.

CONCLUSIONS

We emphasize the phenotypic variability of the m.8993T>G MT-ATP6 mutation and the need for caution in predictive counseling in such patients. Muscle Nerve 54: 328-333, 2016.

Nerve excitability changes related to muscle weakness in chronic progressive external ophthalmoplegia

OBJECTIVE

To explore potential spreading to peripheral nerves of the mitochondrial dysfunction in chronic progressive external ophthalmoplegia (CPEO) by assessing axonal excitability.

METHODS

CPEO patients (n=13) with large size deletion of mitochondrial DNA and matching healthy controls (n=22) were included in a case-control study. Muscle strength was quantified using MRC sum-score and used to define two groups of patients: CPEO-weak and CPEO-normal (normal strength). Nerve excitability properties of median motor axons were assessed with the TROND protocol and changes interpreted with the aid of a model.

RESULTS

Alterations of nerve excitability strongly correlated with scores of muscle strength. CPEO-weak displayed abnormal nerve excitability compared to CPEO-normal and healthy controls, with increased superexcitability and responses to hyperpolarizing current. Modeling indicated that the CPEO-weak recordings were best explained by an increase in the 'Barrett-Barrett' conductance across the myelin sheath.

CONCLUSION

CPEO patients with skeletal weakness presented sub-clinical nerve excitability changes, which were not consistent with axonal membrane depolarization, but suggested Schwann cell involvement.

SIGNIFICANCE

This study provides new insights into the spreading of large size deletion of mitochondrial DNA to Schwann cells in CPEO patients.

Schwann cell mitochondria as key regulators in the development and maintenance of peripheral nerve axons

Formation of myelin sheaths by Schwann cells (SCs) enables rapid and efficient transmission of action potentials in peripheral axons, and disruption of myelination results in disorders that involve decreased sensory and motor functions. Given that construction of SC myelin requires high levels of lipid and protein synthesis, mitochondria, which are pivotal in cellular metabolism, may be potential regulators of the formation and maintenance of SC myelin. Supporting this notion, abnormal mitochondria are found in SCs of neuropathic peripheral nerves in both human patients and the relevant animal models. However, evidence for the importance of SC mitochondria in myelination has been limited, until recently. Several studies have recently used genetic approaches that allow SC-specific ablation of mitochondrial metabolic activity in living animals to show the critical roles of SC mitochondria in the development and maintenance of peripheral nerve axons. Here, we review current knowledge about the involvement of SC mitochondria in the formation and dysfunction of myelinated axons in the peripheral nervous system.

Neuronal Regulation of Schwann Cell Mitochondrial Ca(2+) Signaling during Myelination

Schwann cells (SCs) myelinate peripheral neurons to promote the rapid conduction of action potentials, and the process of myelination is known to be regulated by signals from axons to SCs. Given that SC mitochondria are one of the potential regulators of myelination, we investigated whether SC mitochondria are regulated by axonal signaling. Here, we show a purinergic mechanism that sends information from neurons to SC mitochondria during myelination. Our results show that electrical stimulation of rat sciatic nerve increases extracellular ATP levels enough to activate purinergic receptors. Indeed, electrical stimulation of sciatic nerves induces Ca(2+) increases in the cytosol and the mitochondrial matrix of surrounding SCs via purinergic receptor activation. Chronic suppression of this pathway during active myelination suppressed the longitudinal and radial development of myelinating SCs and caused hypomyelination. These results demonstrate a neuron-to-SC mitochondria signaling, which is likely to have an important role in proper myelination.

In vivo time-lapse imaging of mitochondria in healthy and diseased peripheral myelin sheath

The myelin sheath that covers a large amount of neurons is critical for their homeostasis, and myelinating glia mitochondria have recently been shown to be essential for neuron survival. However morphological and physiological properties of these organelles remain elusive. Here we report a method to analyze mitochondrial dynamics and morphology in myelinating Schwann cells of living mice using viral transduction and time-lapse multiphoton microscopy. We describe the distribution, shape, size and dynamics of mitochondria in live cells. We also report mitochondrial alterations in Opa1(delTTAG) mutant mice cells at presymptomatic stages, suggesting that mitochondrial defects in myelin contribute to OPA1 related neuropathy and represent a biomarker for the disease.

The tumour suppressor LKB1 regulates myelination through mitochondrial metabolism

A prerequisite to myelination of peripheral axons by Schwann cells (SCs) is SC differentiation, and recent evidence indicates that reprogramming from a glycolytic to oxidative metabolism occurs during cellular differentiation. Whether this reprogramming is essential for SC differentiation, and the genes that regulate this critical metabolic transition are unknown. Here we show that the tumour suppressor Lkb1 is essential for this metabolic transition and myelination of peripheral axons. Hypomyelination in the Lkb1-mutant nerves and muscle atrophy lead to hindlimb dysfunction and peripheral neuropathy. Lkb1-null SCs failed to optimally activate mitochondrial oxidative metabolism during differentiation. This deficit was caused by Lkb1-regulated diminished production of the mitochondrial Krebs cycle substrate citrate, a precursor to cellular lipids. Consequently, myelin lipids were reduced in Lkb1-mutant mice. Restoring citrate partially rescued Lkb1-mutant SC defects. Thus, Lkb1-mediated metabolic shift during SC differentiation increases mitochondrial metabolism and lipogenesis, necessary for normal myelination.

Aberrant Schwann cell lipid metabolism linked to mitochondrial deficits leads to axon degeneration and neuropathy

Mitochondrial dysfunction is a common cause of peripheral neuropathy. Much effort has been devoted to examining the role played by neuronal/axonal mitochondria, but how mitochondrial deficits in peripheral nerve glia (Schwann cells [SCs]) contribute to peripheral nerve diseases remains unclear. Here, we investigate a mouse model of peripheral neuropathy secondary to SC mitochondrial dysfunction (Tfam-SCKOs). We show that disruption of SC mitochondria activates a maladaptive integrated stress response (ISR) through the actions of heme-regulated inhibitor (HRI) kinase, and causes a shift in lipid metabolism away from fatty acid synthesis toward oxidation. These alterations in SC lipid metabolism result in depletion of important myelin lipid components as well as in accumulation of acylcarnitines (ACs), an intermediate of fatty acid β-oxidation. Importantly, we show that ACs are released from SCs and induce axonal degeneration. A maladaptive ISR as well as altered SC lipid metabolism are thus underlying pathological mechanisms in mitochondria-related peripheral neuropathies.

Peripheral neuropathy associated with mitochondrial disease in children

Mitochondrial diseases in children are often associated with a peripheral neuropathy but the presence of the neuropathy is under-recognized because of the overwhelming involvement of the central nervous system (CNS). These mitochondrial neuropathies are heterogeneous in their clinical, neurophysiological, and histopathological characteristics. In this article, we provide a comprehensive review of childhood mitochondrial neuropathy. Early recognition of neuropathy may help with the identification of the mitochondrial syndrome. While it is not definite that the characteristics of the neuropathy would help in directing genetic testing without the requirement for invasive skin, muscle or liver biopsies, there appears to be some evidence for this hypothesis in Leigh syndrome, in which nuclear SURF1 mutations cause a demyelinating neuropathy and mitochondrial DNA MTATP6 mutations cause an axonal neuropathy. POLG1 mutations, especially when associated with late-onset phenotypes, appear to cause a predominantly sensory neuropathy with prominent ataxia. The identification of the peripheral neuropathy also helps to target genetic testing in the mitochondrial optic neuropathies. Although often subclinical, the peripheral neuropathy may occasionally be symptomatic and cause significant disability. Where it is symptomatic, recognition of the neuropathy will help the early institution of rehabilitative therapy. We therefore suggest that nerve conduction studies should be a part of the early evaluation of children with suspected mitochondrial disease.

Endothelial ultrastructural alterations of intramuscular capillaries in infantile mitochondrial cytopathies: "mitochondrial angiopathy"

Electron microscopy (EM) is a reliable method for diagnosing mitochondrial diseases in striated muscle biopsy in infancy. Ultrastructural alterations in mitochondria of myofibers are well documented, but there are few studies of endothelial involvement in intramuscular capillaries. Quadriceps femoris biopsies of five representative infants and toddlers, ages neonate to 3.5 years, were performed because of clinical and laboratory data consistent with mitochondrial disease without mitochondrial DNA (mtDNA) mutations and likely with nuclear DNA mutations. Pathological studies included histochemistry, EM, respiratory chain enzymatic assay and mtDNA sequencing and deletion/duplication analysis. EM demonstrated frequent and severe alterations of mitochondria in capillary endothelium. The most constant changes included: either too few or fragmented cristae; stacked and whorled cristae; paracrystallin structures that often were large and spheroid with stress fractures; closely apposed membranes of granular endoplasmic reticulum surrounding mitochondria with loss of the normal intervening layer of cytoplasm; long narrow, thin looped microvilli extending into the lumen; and thick microvilli containing large, abnormal mitochondria. We conclude that mitochondrial cytopathies in early life exhibit more severe ultrastructural alterations in the endothelium than in myofibers and that paracrystallin body structure differs, perhaps due to less rigid surrounding structures. This distribution may explain the frequent lack of prominent histochemical and biochemical abnormalities in muscle biopsies of young patients. Endothelial changes do not distinguish the genetic defects. Vascular involvement in brain contributes to cerebral lesions and neuronal death by impairment of molecular and nutrient transport and ischemia; endothelium in muscle may reflect similar changes.

Schwann cell mitochondrial metabolism supports long-term axonal survival and peripheral nerve function

Mitochondrial dysfunction is a common cause of peripheral neuropathies. While the role of neuron and axonal mitochondria in peripheral nerve disease is well appreciated, whether Schwann cell (SC) mitochondrial deficits contribute to peripheral neuropathies is unclear. Here, we examine how SC mitochondrial dysfunction affects axonal survival and contributes to the decline of peripheral nerve function by generating mice with SC-specific mitochondrial deficits. These mice (Tfam-SCKOs) were produced through the tissue-specific deletion of the mitochondrial transcription factor A gene (Tfam), which is essential for mitochondrial DNA (mtDNA) transcription and maintenance. Tfam-SCKOs were viable, but as they aged, they developed a progressive peripheral neuropathy characterized by nerve conduction abnormalities as well as extensive muscle denervation. Morphological examination of Tfam-SCKO nerves revealed early preferential loss of small unmyelinated fibers followed by prominent demyelination and degeneration of larger-caliber axons. Tfam-SCKOs displayed sensory and motor deficits consistent with this pathology. Remarkably, the severe mtDNA depletion and respiratory chain abnormalities in Tfam-SCKO mice did not affect SC proliferation or survival. Mitochondrial function in SCs is therefore essential for maintenance of axonal survival and normal peripheral nerve function, suggesting that SC mitochondrial dysfunction contributes to human peripheral neuropathies.

Retrospective chart review of duloxetine and pregabalin in the treatment of painful neuropathy

The primary aims of our study were to compare pregabalin and duloxetine in a neuromuscular clinic for diabetic neuropathic pain (DPN) and to study the effect of these medications in cryptogenic sensory polyneuropathy. We performed a retrospective chart review of 143 patients who were started on pregabalin or duloxetine during a 10-month period in a tertiary neuromuscular outpatient center for neuropathic pain. Duloxetine and pregabalin were started in 103 and 91 patients, respectively. Ninety-two patients tried only one of the two medications while both medications were used at different time periods in 51 patients. Follow-up was available for 87 patients on pregabalin and 89 patients on duloxetine. More patients with neuropathic pain reported an improvement with pregabalin (33%) than duloxetine (21%). Duloxetine (38%) had a higher frequency of side effects compared to pregabalin (30%). However, these differences between pregabalin and duloxetine were not statistically significant. Despite the study's limitations of retrospective design, these findings suggest that both pregabalin and duloxetine are probably effective for neuropathic pain, secondary to diabetes or cryptogenic sensory peripheral neuropathy in a tertiary care academic neuromuscular center. Prospective randomized controlled comparative effectiveness studies are required for both drugs in the treatment of neuropathic pain.

Inherited mitochondrial neuropathies

Mitochondrial disorders (MIDs) occasionally manifest as polyneuropathy either as the dominant feature or as one of many other manifestations (inherited mitochondrial neuropathy). MIDs in which polyneuropathy is the dominant feature, include NARP syndrome due to the transition m.8993T>, CMT2A due to MFN2 mutations, CMT2K and CMT4A due to GDAP1 mutations, and axonal/demyelinating neuropathy with external ophthalmoplegia due to POLG1 mutations. MIDs in which polyneuropathy is an inconstant feature among others is the MELAS syndrome, MERRF syndrome, LHON, Mendelian PEO, KSS, Leigh syndrome, MNGIE, SANDO; MIRAS, MEMSA, AHS, MDS (hepato-cerebral form), IOSCA, and ADOA syndrome. In the majority of the cases polyneuropathy presents in a multiplex neuropathy distribution. Nerve conduction studies may reveal either axonal or demyelinated or mixed types of neuropathies. If a hereditary neuropathy is due to mitochondrial dysfunction, the management of these patients is at variance from non-mitochondrial hereditary neuropathies. Patients with mitochondrial hereditary neuropathy need to be carefully investigated for clinical or subclinical involvement of other organs or systems. Supportive treatment with co-factors, antioxidants, alternative energy sources, or lactate lowering agents can be tried. Involvement of other organs may require specific treatment. Mitochondrial neuropathies should be included in the differential diagnosis of hereditary neuropathies.

Congenital type IV glycogenosis: the spectrum of pleomorphic polyglucosan bodies in muscle, nerve, and spinal cord with two novel mutations in the GBE1 gene

A diagnosis of GSD-IV was established in three premature, floppy infants based on characteristic, however unusually pleomorphic polyglucosan bodies at the electron microscopic level, glycogen branching enzyme deficiency in two cases, and the identification of GBE1 mutations in two cases. Pleomorphic polyglucosan bodies in muscle fibers and macrophages, and less severe in Schwann cells and microglial cells were noted. Most of the inclusions were granular and membrane-bound; others had an irregular contour, were more electron dense and were not membrane bound, or homogenous ('hyaline'). A paracrystalline pattern of granules was repeatedly noted showing a periodicity of about 10 nm with an angle of about 60 degrees or 120 degrees at sites of changing linear orientation. Malteser crosses were noted under polarized light in the larger inclusions. Some inclusions were PAS positive and others were not. Severely atrophic muscle fibers without inclusions, but with depletion of myofibrils in the plane of section studied indicated the devastating myopathic nature of the disease. Schwann cells and peripheral axons were less severely affected as was the spinal cord. Two novel protein-truncating mutations (c.1077insT, p.V359fsX16; g.101517_127067del25550insCAGTACTAA, DelExon4-7) were identified in these families. The present findings extend previous studies indicating that truncating GBE1 mutations cause a spectrum of severe diseases ranging from generalized intrauterine hydrops to fatal perinatal hypotonia and fatal cardiomyopathy in the first months of life.

Pediatric autonomic disorders

The scope of pediatric autonomic disorders is not well recognized. The goal of this review is to increase awareness of the expanding spectrum of pediatric autonomic disorders by providing an overview of the autonomic nervous system, including the roles of its various components and its pervasive influence, as well as its intimate relationship with sensory function. To illustrate further the breadth and complexities of autonomic dysfunction, some pediatric disorders are described, concentrating on those that present at birth or appear in early childhood.

Neuropathology of Charcot-Marie-Tooth and related disorders

The peripheral nervous system (PNS), with all its branches and connections, is so complex that it is impossible to study all components at the light or electron microscopic level in any individual case; nevertheless, in certain diseases a simple nerve biopsy may suffice to arrive at a precise diagnosis. Structural changes of the PNS in neuropathies of the Charcot-Marie-Tooth (CMT) type and related disorders comprise various components of the PNS. These include peripheral motor, sensory, and autonomous neurons with their axons, Schwann cells, and myelin sheaths in the radicular and peripheral nerves as well as satellite cells in spinal and autonomous ganglia. Astrocytes, oligodendroglial cells, and microglial cells around motor neurons in the anterior horn and around sensory neurons in other areas of the spinal cord are also involved. In addition, connective tissue elements such as endoneurial, perineurial, and epineurial components including blood and lymph vessels play an important role. This review focuses on the cellular components and organelles involved, that is, myelin sheaths, axons with their micro-tubules and neurofilaments; nuclei, mitochondria, endoplasmic reticulum, and connective tissue including the perineurium and blood vessels. A major role is attributed to recent progress in the pathomorphology of various types of CMT1, 2,4, CMTX, and HMNSL, based on light and electron microscopic findings, morphometry, teased fiber studies, and new immunohisto-chemical results such as staining of certain periaxin domains in CMT4F.

Peripheral neuropathy in genetic mitochondrial diseases

Peripheral neuropathy is an underrecognized but common occurrence in genetic mitochondrial disorders. To gain insight into the frequency and clinical presentation of this complication, nerve conduction studies were performed on 43 subjects with congenital lactic acidosis enrolled in a controlled clinical trial of oral dichloroacetate. Median and peroneal motor conduction studies and median and sural sensory conduction studies were performed on each patient. The mean amplitude of the peroneal motor nerve (P < 0.001) and the conduction velocities of the median (P < 0.001) and peroneal (P < 0.001) motor nerves were uniformly lower in our subjects than in healthy literature control subjects. There were no significant differences in sensory nerve conduction studies. A generalized reduction in motor nerve conduction velocity was the dominant electrophysiological abnormality in the patients in this study and was independent of age, sex, or congenital mitochondrial disorder. We postulate that cellular energy failure is the most likely common cause of peripheral neuropathy in patients with genetic mitochondrial diseases, owing to the high demand for adenosine triphosphate via aerobic carbohydrate metabolism by nerve tissue.

Peripheral nerve and skeletal muscle involvement in CADASIL

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is characterized by degeneration of vascular smooth muscle cells (VSMC) of nearly all tissues studied so far. The clinical phenotype of CADASIL shows great variability. The disease is caused by mutations of the Notch3 gene encoding the transmembrane receptor Notch3, which is expressed predominantly in VSMC. In some patients, neuromuscular symptoms have been described. To investigate the fine structural features of peripheral nerve and muscle biopsy specimens in more cases and greater detail, seven electron microscopically confirmed CADASIL patients showing a variable amount of granular osmiophilic material on the surface of VSMC were included in this study. Pathogenic mutations within the cluster region (exon 3 and 4) of the Notch3 gene were identified in six cases. Degeneration and regeneration of nerve fibers in the sural nerves, studied in four cases, was present, although moderate, in all nerve biopsy specimens, whereas an intramuscular nerve fascicle showed more severe changes. Enlarged mitochondria with needle-like calcium precipitates were repeatedly seen. In muscle biopsy specimens, some degree of neurogenic atrophy was apparent in addition to myopathic changes, including occasional ragged red fibers with abnormally large mitochondria, focal tubular aggregates, abnormal terminal cisternae, and myofibrillary abnormalities. Automated sequence analysis of the whole mitochondrial DNA performed in one patient revealed several nucleotide polymorphisms, which were not considered pathogenic. The findings suggest that in CADASIL degeneration of small blood vessels is initiated by defects of the surface membrane of VSMC. Dysfunction of these blood vessels may cause low-grade chronic ischemia with secondary hypoxidosis and a large variety of structural changes noted in skeletal muscle and peripheral nerves, although a primary influence of the underlying genetic defect can not be excluded.

Multiple Symmetric Lipomatosis (Madelung's Disease) Caused by the MERRF (A8344G) Mutation: A Report of Two Cases and Review of the Literature

Multiple symmetric lipomatosis (MSL) was first described by Brodie in 1846 and is characterized by accumulation of non-encapsulated lipomas in the cervical-cranial-thoracic region. Alcohol consumption is regarded as essential in lipoma development by some. Mitochondrial dysfunction was first reported in 1991. Since then, there has been controversy regarding etiology of MSL, with a number of studies supporting and some refuting the role of mitochondrial dysfunction. We report on 2 cases of MSL with pathologic (ragged-red fibers) and molecular (A8344G mutation) features of mitochondrial dysfunction. A literature review revealed that mitochondrial gene dysfunction was evident in 28% of MSL cases. Furthermore, the MERRF mutation (A8344G) was detected in 16% and mitochondrial gene deletions in 12% of MSL cases. Therefore, clinicians need to be vigilant of the fact that a significant proportion of the MSL phenotype results from mitochondrial gene mutations and/or deletions.

3-nitropropionic acid inhibition of succinate dehydrogenase (complex II) activity in cultured Chinese hamster ovary cells: antagonism by L-carnitine

3-Nitropropionic acid (3-NPA) is an inhibitor of the mitochondrial enzyme succinate dehydrogenase (SDH, a part of complex II) that links the tricarboxylic acid (TCA) cycle to the respiratory electron transport chain. 3-NPA inactivates SDH by covalently and irreversibly binding to its active site. We previously examined the effects of 3-NPA on the histochemical activity of SDH in vivo, by using the reduction of a yellow tetrazolium dye (nitro blue tetrazolium) to a blue formazan as an indicator. In studies of cultured cells, the related dye methylthiazoletetrazolium (MTT) has commonly been used as an indicator of the presence and number of viable cells; that is cells that are capable of producing energy via the TCA cycle. Here we observed that doses of 3-NPA as low as 10(-8) M inhibited formazan production in an in vitro model system using CHO cells. This effect was antagonized by l-carnitine, which greatly increased the production of formazan, indicating a considerable improvement in energy production by the cultured cells. CHO cells appear to be a convenient model for the evaluation of therapeutic compounds that may modulate cellular bioenergetics.

Mitochondrial encephalomyopathies

Mitochondrial encephalomyopathies are diseases caused by defective oxidative phosphorylation (OXPHOS), and affect the nervous system and/or skeletal muscle. They have emerged as a major entity among the neurometabolic diseases of childhood with an incidence of 1 in 11,000 children, and also have a high prevalence in adults. The first pathogenic mutation of human mitochondrial DNA (mtDNA) was discovered in 1988. Since then more than 100 mutations of mtDNA have been reported, including point mutations of genes encoding transfer RNA, ribosomal RNA, and proteins, as well as large-scale deletions. The first nuclear-DNA gene mutation causing OXPHOS disease was described in 1995. Mutations in nuclear genes may affect the respiratory chain by various mechanisms. Pathogenic mutations of nuclear-DNA-encoded subunits of complex I and II have been demonstrated as have mutations of respiratory chain assembly proteins. Several nuclear genes associated with mtDNA maintenance have been found to be associated with mitochondrial disorders since mutations in these genes predispose to multiple mtDNA deletions and/or reduced copy number of mtDNA. The genotype-phenotype correlation is not yet entirely clear, but new animal models will enhance our ability to study the pathophysiology of OXPHOS disorders.

Creatine kinase B-driven energy transfer in the brain is important for habituation and spatial learning behaviour, mossy fibre field size and determination of seizure susceptibility

Creatine kinases are important in maintaining cellular-energy homeostasis, and neuroprotective effects have been attributed to the administration of creatine and creatine-like compounds. Herein we examine whether ablation of the cytosolic brain-type creatine kinase (B-CK) in mice has detrimental effects on brain development, physiological integrity or task performance. Mice deficient in B-CK (B-CK-/-) showed no gross abnormalities in brain anatomy or mitochondrial ultrastructure, but had a larger intra- and infrapyramidal mossy fibre area. Nuclear magnetic resonance spectroscopy revealed that adenosine triphosphate (ATP) and phosphocreatine (PCr) levels were unaffected, but demonstrated an apparent reduction of the PCr left arrow over right arrow ATP phosphorus exchange capacity in these mice. When assessing behavioural characteristics B-CK-/- animals showed diminished open-field habituation. In the water maze, adult B-CK-/- mice were slower to learn, but acquired the spatial task. This task performance deficit persisted in 24-month-old, aged B-CK-/- mice, on top of the age-related memory decline normally seen in old animals. Finally, a delayed development of pentylenetetrazole-induced seizures (creating a high-energy demand) was observed in B-CK-/- mice. It is suggested that the persistent expression of the mitochondrial isoform ubiquitous mitochondrial CK (UbCKmit) in the creatine/phospho-creatine shuttle provides compensation for the loss of B-CK in the brain. Our studies indicate a role for the creatine-phosphocreatine/CK circuit in the formation or maintenance of hippocampal mossy fibre connections, and processes that involve habituation, spatial learning and seizure susceptibility. However, for fuelling of basic physiological activities the role of B-CK can be compensated for by other systems in the versatile and robust metabolic-energy network of the brain.

A painful peripheral neuropathy in the rat produced by the chemotherapeutic drug, paclitaxel

Paclitaxel, an effective anti-neoplastic agent in the treatment of solid tumors, produces a dose-limiting painful peripheral neuropathy in a clinically significant number of cancer patients. Prior work has demonstrated paclitaxel-induced neurodegeneration and sensory loss in laboratory rodents. We describe here an experimental paclitaxel-induced painful peripheral neuropathy. Adult male rats were given four intraperitoneal injections on alternate days of vehicle or 0.5, 1.0, or 2.0 mg/kg of paclitaxel (Taxol). Behavioral tests for pain using mechanical and thermal stimuli applied to the tail and hind paws, and tests for motor performance, were taken before, during and after dosing for 22-35 days. All three doses of paclitaxel caused heat-hyperalgesia, mechano-allodynia, mechano-hyperalgesia, and cold-allodynia, but had no effect on motor performance. Neuropathic pain began within days and lasted for several weeks. We did not detect any dose-response relationship. Tests at the distal, mid, and proximal tail failed to show evidence of a length-dependent neuropathy. Vehicle control injections had no effect on any measure. No significant systemic toxicities were noted in the paclitaxel-treated animals. Light-microscopic inspection of the sciatic nerve (mid-thigh level), L4-L5 dorsal root ganglia, and dorsal and ventral roots, and the gray and white matter of the L4-L5 spinal cord, showed no structural abnormalities. Electron microscopic examination of the sciatic nerve (mid-thigh level) and the L4-L5 dorsal root ganglia and dorsal horns demonstrated no degeneration of myelinated and unmyelinated axons in the sciatic nerve and roots, but revealed endoneurial edema. This model may be useful in understanding a significant source of pain in cancer patients, and in finding ways to avoid the neurotoxicity that limits paclitaxel therapy.

Mitochondrial toxicity and HIV therapy

Nucleoside reverse transcriptase inhibitors (NRTIs) remain the cornerstone of highly active antiretroviral therapy (HAART) combination regimens. However, it has been known for some time that these agents have the potential to cause varied side effects, many of which are thought to be due to their effects on mitochondria. Mitochondria, the key energy generating organelles in the cell, are unique in having their own DNA, a double stranded circular genome of about 16 000 bases. There is a separate enzyme present inside the cell that replicates mitochondrial DNA, polymerase gamma. NRTIs can affect the function of this enzyme and this may lead to depletion of mitochondrial DNA or qualitative changes. The study of inherited mitochondrial diseases has led to further understanding of the consequences of mutations or depletion in mitochondrial DNA. Key among these is the realisation that there may be substantial heteroplasmy among mitochondria within a given cell, and among cells in a particular tissue. The unpredictable nature of mitochondrial segregation during cellular replication makes it difficult to predict the likelihood of dysfunction in a given tissue. In addition, there is a threshold effect for the expression of mitochondrial dysfunction, both at the mitochondrial and cellular level. Various clinical and in vitro studies have suggested that NRTIs are associated with mitochondrial dysfunction in different tissues, although the weight of evidence is limited in many cases. The heterogeneity in the tissues affected by the different drugs raises interesting questions, and possible explanations include differential distribution or activation of these agents. This article reviews the major recognised toxicities associated with NRTI therapy and evidence for mitochondrial dysfunction in these complications. Data were identified through searching of online databases including Medline and Current Contents for relevant articles, along with abstracts and posters from recent conferences in the HIV and mitochondrial fields.

Biomarkers of 3-nitropropionic acid (3-NPA)-induced mitochondrial dysfunction as indicators of neuroprotection

In humans or animals, symptoms of mitochondrial energy dysfunction may be produced by mutations or inborn errors of the necessary enzymes, as well as by enzyme inhibitors or uncouplers of the oxidative phosphorylation process. 3-Nitropropionic acid (3-NPA) is a toxin that is sometimes produced on moldy crops (sugarcane, peanuts, etc.) in amounts sufficient to cause severe neuromuscular disorders when consumed by humans. In vitro, 3-NPA irreversibly inactivates SDH, a Complex II respiratory enzyme important for mitochondrial energy production. We have been studying biomarkers of 3-NPA exposure in the expectation that such markers may be useful in the screening process to identify neuroprotective agents against neurotoxicity produced by mitochondrial energy dysfunction. Animals were sacrificed at various times after 3-NPA exposure for histochemical visualization of SDH activity and measurement of immediate postmortem rectal temperature. 3-NPA-treated rats experienced progressive hypothermia that reached a loss of 3 degrees C or more in core body temperature by three hours after dosing. The optical density of the SDH stain in brain was reduced, following a similar time course, most prominently in the cerebellum and least sharply in the thalamus. Some rats were given injections of L-carnitine (an enhancer of fatty acid transport) either alone, or as a pretreatment prior to a dose of 3-NPA. Although L-carnitine deficiency by itself can produce mitochondrial dysfunction, pretreatment with L-carnitine was of limited efficacy at overcoming the effects of 3-NPA on either body temperature or quantitative SDH histochemistry. Body temperature and SDH histochemistry may be useful biomarkers for evaluating the efficacy of neuroprotective agents against lower doses of 3-NPA, against other pharmacological models of mitochondrial dysfunction, or even against genetic mitochondrial diseases.

Mitochondrial dysfunction and neuromuscular disease

Mitochondrial diseases are a heterogeneous group of disorders with widely varying clinical features, due to defects in mitochondrial function. Involvement of both muscle and nerve is common in mitochondrial disease. In some cases, this involvement is subclinical or a minor part of a multisystem disorder, but myopathy and neuropathy are a major, often presenting, feature of a number of mitochondrial syndromes. In addition, mitochondrial dysfunction may play a role in a number of classic neuromuscular diseases. This article reviews the role of mitochondrial dysfunction in neuromuscular disease and discusses a rational approach to diagnosis and treatment of patients presenting with a neuromuscular syndrome due to mitochondrial disease.

The oxen gene of Drosophila encodes a homolog of subunit 9 of yeast ubiquinol-cytochrome c oxidoreductase complex: evidence for modulation of gene expression in response to mitochondrial activity

A P-element insertion in the oxen gene, ox(1), has been isolated in a search for modifiers of white gene expression. The mutation preferentially exerts a negative dosage effect upon the expression of three genes encoding ABC transporters involved in pigment precursor transport, white, brown, and scarlet. A precise excision of the P element reverts the mutant phenotype. Five different transcription units were identified around the insertion site. To distinguish a transcript responsible for the mutant phenotype, a set of deletions within the oxen region was generated. Analysis of gene expression within the oxen region in the case of deletions as well as generation of transgenic flies allowed us to identify the transcript responsible for oxen function. It encodes a 6.6-kD homolog of mitochondrial ubiquinol cytochrome c oxidoreductase (QCR9), subunit 9 of the bc(1) complex in yeast. In addition to white, brown, and scarlet, oxen regulates the expression of three of seven tested genes. Thus, our data provide additional evidence for a cellular response to changes in mitochondrial function. The oxen mutation provides a model for the genetic analysis in multicellular organisms of the effect of mitochondrial activity on nuclear gene expression.

Peripheral neuropathy associated with hereditary and sporadic inclusion body myositis: confirmation by electron microscopy and morphometry

Inclusion body myositis (IBM) is a disabling myopathy affecting proximal and distal muscle groups. The involvement of peripheral nerves in IBM is still a controversial matter. In a previous morphometric study at the light microscopic level only, we described a peripheral neuropathy in sural nerve biopsies of eight patients with sporadic IBM (s-IBM). Here we present a larger series of 14 cases in which a combined muscle and nerve biopsy was available for additional electron microscopic investigation. In two of the new cases, the IBM had a hereditary background (h-IBM). The presence of neuropathy was confirmed in all 14 cases studied. Morphometry using an optic-electronic, digital evaluation system showed large variation of severity presumably due to age and coincidal factors such as diabetes mellitus or lymphoma. Ultrastructural analysis revealed a variety of changes considered to be non-specific. Signs of axonal damage predominated. In addition, there were numerous changes in Schwann cells and myelin sheaths. Neither inflammatory changes nor tubulofilamentous inclusions were detectable in the sural nerves. Peripheral neuropathy, although occasionally without apparent clinical manifestation, appears to be a common and aggravating feature in IBM; its pathogenesis, however, remains elusive.

Review: model peptides and the physicochemical approach to beta-amyloids

beta-Amyloid peptides are the main protein components of neuritic plaques and may be important in the pathogenesis of Alzheimer's Disease. The determination of the structure of beta-amyloid fibrils poses a challenge because of the limited solubility of beta-amyloid peptides and the noncrystalline nature of fibrils formed from these peptides. In this paper, we describe several physicochemical approaches which have been used to examine fibrils and the fibrillogenesis of peptide models of beta-amyloid. Recent advances in solid state NMR, such as the DRAWS pulse sequence, have made this approach a particularly attractive one for peptides such as beta-amyloid, which are not yet amenable to high-resolution solution phase NMR and crystallography. The application of solid state NMR techniques has yielded information on a model peptide comprising residues 10-35 of human beta-amyloid and indicates that in fibrils, this peptide assumes a parallel beta-strand conformation, with all residues in exact register. In addition, we discuss the use of block copolymers of Abeta peptides and polyethylene glycol as probes for the pathways of fibrillogenesis. These methods can be combined with other new methods, such as high-resolution synchrotron X-ray diffraction and small angle neutron and X-ray scattering, to yield structural data of relevance not only to disease, but to the broader question of protein folding and self-assembly.

Tissue mosaicism in the skeletal muscle and sural nerve biopsies in the MELAS syndrome

We describe a clinically full-blown MELAS patient, who had an A3243G point mutation of mitochondrial DNA (mtDNA) in muscle and blood cells, and his family members. From the proband two muscle biopsies from the vastus lateralis muscle were analysed; one had typical ragged red fibers and focal cytochrome c oxidase deficiency and the other was completely normal. He also had a peripheral neuropathy confirmed by nerve conduction velocity and sural nerve biopsy studies. Axonal degeneration, relative loss of large myelinated fibers and paracrystalline inclusion bodies in the Schwann cells were noted. Intriguingly, the A3243G mutation of mtDNA was not found in the sural nerve biopsy. Therefore, we conclude that tissue mosaicism is present in the muscle fibers and that the mtDNA mutation may not be detected in the nerve involved as proved by pathology. We also suggest that the involvement of specific tissues in patients with mitochondrial diseases should be further determined by single fiber mtDNA analysis.

Congenital insensitivity to pain and anhidrosis with mitochondrial and axonal abnormalities

Hereditary sensory and autonomic neuropathy type IV, or congenital insensitivity to pain with anhidrosis (CIPA), is a rare clinical disorder with only 32 cases reported in the literature. There has been no consistent pathophysiologic defect of the sensory nerve detected by light microscopic examination, but a frequent finding of decreased small myelinated fibers and a uniform finding of decreased unmyelinated fibers by ultrastructural analysis has been reported. Muscle biopsy in a 2-year-old boy with congenital insensitivity to pain with anhidrosis indicated lipid droplet accumulation and reduced cytochrome C oxidase histochemically on light microscopy. Electron microscopic study showed almost absent small unmyelinated nerve axons within the muscle, increased microfilaments, and decreased microtubules in axons, some abnormally enlarged mitochondria, and normal-appearing motor endplates. Biochemical analysis of muscle mitochondrial enzyme function revealed cytochrome c oxidase function to be reduced to 35% of normal, with normal function of the other mitochondrial enzymes.

Mitochondrial dysfunction with myoclonus epilepsy and ragged-red fibers point mutation in nerve, muscle, and adipose tissue of a patient with multiple symmetric lipomatosis

We report a 64-year-old man presenting with multiple symmetric lipomatosis (MSL) and mitochondrial encephalomyoneuropathy. The diagnosis of a mitochondrial cytopathy was based on the typical clinical symptoms and signs, including chronic progressive external ophthalmoplegia, hearing impairment, cerebellar ataxia, proximal myopathy, and polyneuropathy, and on molecular genetic and histological examinations. As a unique finding, the A-->G(8344) myoclonus epilepsy and ragged-red fibers point mutation was found in peripheral nerve, muscle, and adipose tissue. Muscle biopsy revealed multiple ragged-red fibers and other morphological signs of a mitochondrial myopathy. Sural nerve biopsy demonstrated a mixed axonal and demyelinating neuropathy with extensive loss of myelinated fibers and conspicuous onion bulb formations, as well as structural mitochondrial abnormalities on electron microscopy. These findings clearly demonstrate mitochondrial dysfunction in muscle, adipose tissue, and for the first time also in nervous tissue of an MSL patient, and strongly support the concept of mitochondrial cytopathy as one of the possible causes of multiple symmetric lipomatosis.

Impairment of central and peripheral myelin in mitochondrial diseases

Clinical or sub-clinical impairment of central and peripheral myelin is often part of the overlapping multisystem disorders associated with a variety of mitochondrial (mt)DNA abnormalities. Suboptimal energy metabolism of the oligodendrocytes and Schwann cells carrying mitochondrial defects may cause insufficient production of myelin. Further, edema, vascular and toxic factors may directly damage myelin. The recognition that certain mtDNA point mutations are associated with inflammatory demyelination of the central nervous system suggests that additional mechanisms besides degeneration need to be considered in the development of some forms of myelin damage.

Mitochondrial encephalomyopathies presenting with features of autonomic and visceral dysfunction

Three children are reported with mitochondrial encephalomyopathy who presented with autonomic dysfunction. Autonomic dysfunction included gastrointestinal dysmotility, apnea, cardiac arrhythmias, decreased lacrimation, supersensitivity to metacholine, altered sweating, and postural hypotension. These patients illustrate that in some mitochondrial encephalomyopathies autonomic features may be prominent and can mimic the clinical features associated with hereditary sensory and autonomic neuropathies.

Increase of mitochondria in vasa nervorum of cases with mitochondrial myopathy, Kearns-Sayre syndrome, progressive external ophthalmoplegia and MELAS

Previous studies on patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) revealed accumulations of mitochondria in endothelial cells, smooth muscle cells of pial arterioles, and small intracerebral arteries up to 250 microns in diameter; in pericytes of capillaries, endothelial cells, and smooth muscle cells of small blood vessels in skeletal muscle; and according to preliminary results also in endothelial and smooth muscle cells of capillaries and arterioles in sural nerves. These mitochondria do not show the prominent paracrystalline inclusions which are seen in striated muscle fibres and led to the identification of this group of disorders. To corroborate our preliminary findings in peripheral nerves, additional cases have been evaluated morphometrically by electron microscopy including cases in which mitochondrial DNA (mtDNA) mutations have been identified. In fact, an increase of the mean number and an enlargement of the mean cross-sectional area of mitochondria was noted in endothelial and smooth muscle cells of endoneurial and epineurial arterioles, and in endothelial cells and in pericytes of capillaries in sural nerves of the 20 cases with mitochondrial disorders studied. This increase was statistically significant compared to the control group. However, due to heteroplasmia, which is a common feature in mitochondrial disorders, and because of the limited number of measurable blood vessels and cases, no significant differences could be detected between the various types of mitochondrial diseases which were characterized by different point mutations or deletions of mtDNA. Our findings suggest that the mitochondria play a significant role in the pathogenesis not only of myopathic and encephalopathic symptoms, but also in the pathogenesis of peripheral neuropathy which appears to be regularly associated with mitochondrial disorders.

Ultrastructural pathology of an inherited lower motor neuron disease of pigs

The ultrastructural features of a recently described inherited lower motor neuron disease were studied in 5 affected pigs. Clinical signs comprised progressive ataxia and paresis of variable severity. Affected pigs, 6, 7, 15, 15, and 19 weeks of age, and 2 unrelated healthy pigs, 9 and 15 weeks of age, were anesthetized and their tissues were fixed by whole body perfusion with mixed aldehydes. From 1 or more affected pigs, samples of cervical and lumbar spinal ventral horn, lateral and ventral spinal columns, dorsal and ventral lumbar spinal nerve roots, 2 peripheral nerves (Nn. phrenicus and fibularis communis), and 2 skeletal muscles (Mm. diaphragma and tibialis cranialis) were examined ultrastructurally. There was widespread degeneration of myelinated axons in peripheral nerves and in lateral and ventral columns of lumbar and cervical segments of spinal cord. Axonal degeneration was present in ventral spinal nerve roots and was absent in dorsal spinal nerve roots sampled at the same lumbar levels. Unmyelinated axons in peripheral nerves and spinal nerve roots were unaffected. In 4 of 5 affected pigs, there were atrophic alpha motor neurons in cervical spinal cord that contained dense, round osmiophilic perikaryal inclusions up to 4 microns in diameter and round swollen mitochondria. Axonal regeneration was present in N. phrenicus of the 19-week-old affected pig that had clinical signs of longest duration (10 weeks). There was no morphologic evidence of axonal degeneration or spinal neuronal atrophy in either control pig. The ultrastructural features of this motor neuron disease distinguish it from other reported progressive spinal neuropathies of pigs.

Experimental germanium dioxide-induced neuropathy in rats

We report an experimental model of germanium dioxide (GeO2)-induced neuropathy in rats. More than 6 months administration of GeO2 to young rats produced neuropathy characterized by segmental demyelination/remyelination and nerve edema. Electron microscopic studies demonstrated that changes in Schwann cells, such as an increased cytoplasmic volume or disintegration of the cytoplasm, were the earliest pathological findings. Schwann cell mitochondria contained high electron-dense materials. Subsequent removal of necrotic Schwann cell debris and myelin by invading macrophages was evident. These findings suggested that the Schwann cells themselves are the primary target of the toxin. The deposition of electron-dense granules in the intra-axonal vesicles, which was suggestive of glycogen granules in mitochondria, was observed in the advanced stage of the neuropathy. The findings of endoneurial edema with splitting of myelin lamellae were noted at the early stage of demyelination. Nerve edema may be the result of GeO2-induced endothelial cell injury.