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Calcium-mediated degeneration of the axonal cytoskeleton in the Ola mouse.

The C57BL/Ola (Ola) mouse is a mutant substrain in which transected axons undergo very slow Wallerian degeneration. Because axonal degradation during Wallerian degeneration is calcium dependent, we tested whether Ola axons are susceptible to calcium-mediated axonal degeneration by comparing neurofilament degradation between Ola and C57BL/6 mice in sciatic nerve explants. Using immunoblot analysis of neurofilament degradation and electron microscopy we found that as in normal axons, axonal degeneration in the Ola is calcium dependent. However, when compared with normal animals, higher levels of calcium were required for complete degradation of neurofilaments in Ola nerve, suggesting a relative insensitivity to calcium-mediated degeneration in the Ola. We conclude that calcium-activated proteases are present and active in Ola axons but that higher levels of calcium are required to accomplish complete axonal degradation. These results suggest a possible mechanism for prolonged survival of transected Ola axons and provide potential insight into the pathophysiology of axonal degeneration in injury and disease.

Animals↗

Wallerian degeneration involves Rho/Rho-kinase signaling.

Local axon degeneration is a common pathological feature of many neurodegenerative diseases, whereas the underlying molecular mechanisms are largely unknown. In this study, we used the degeneration of transected axons, termed "Wallerian degeneration," as a model to examine the possible involvement of Rho. Nogo-66, a myelin-derived inhibitor of axon regeneration, significantly accelerated axon degeneration of the dorsal root ganglion explant in vitro, whereas inhibiting Rho-kinase activity abolished the effect. Rho activation was observed in the distal part of the injured axons after spinal cord injury. We demonstrate that degeneration of the injured cortico-spinal axons was significantly retarded by a Rho-kinase inhibitor in vivo. Our findings suggest that inhibiting the signaling pathway may retard axon degeneration in pathological conditions.

Amides↗

Expression of multiple forms of clusterin during light-induced retinal degeneration.

PURPOSE: Clusterin has been associated with active cell death in several different model systems, including animal models of retinal degeneration. Clusterin is also expressed in normal tissues, a finding that leads to the question of how it could then play a cell death-specific role during tissue regression. To address this paradox, we have examined clusterin expression during light-induced retinal damage in rats. METHODS: Normal albino rats were reared in darkness and then exposed to intense visible light to induce retinal degeneration. Clusterin expression was then examined at various times after light treatment. Standard molecular techniques including Northern analysis, immunohistochemistry, and Western analysis were employed. RESULTS: Northern analysis established that the largest increase in clusterin expression occurs after a decrease in interphotoreceptor retinoid binding protein, IRBP, expression (an indication of a photoreceptor cell dysfunction) and after an increase in heme oxygenase 1, HO-1, expression (an oxidative stress inducible gene), suggesting that induction of clusterin expression is an oxidative stress response. Immuno-histochemical analysis with two different clusterin-specific antibodies, anti(SGP-2) and anti(301), localized distinct forms of clusterin to Müller cells and degenerating photo-receptor cells. Western analysis demonstrated degeneration associated isoforms of clusterin in light treated retina that are not present in normal retina. CONCLUSION: Clusterin over-expression is characteristic of a retinal degeneration phenotype and we propose that clusterin action may be defined by the nature in which it is modified. We hypothesize that alternate processing leads to retinal degeneration-specific forms of the protein (65, 61, and 50 kDa) that are not present in normal retina.

Animals↗

Myelin sheath survival after guanethidine-induced axonal degeneration.

Membrane-membrane interactions between axons and Schwann cells are required for initial myelin formation in the peripheral nervous system. However, recent studies of double myelination in sympathetic nerve have indicated that myelin sheaths continue to exist after complete loss of axonal contact (Kidd, G. J., and J. W. Heath. 1988. J. Neurocytol. 17:245-261). This suggests that myelin maintenance may be regulated either by diffusible axonal factors or by nonaxonal mechanisms. To test these hypotheses, axons involved in double myelination in the rat superior cervical ganglion were destroyed by chronic guanethidine treatment. Guanethidine-induced sympathectomy resulted in a Wallerian-like pattern of myelin degeneration within 10 d. In doubly myelinated configurations the axon, inner myelin sheath (which lies in contact with the axon), and approximately 75% of outer myelin sheaths broke down by this time. Degenerating outer sheaths were not found at later periods. It is probably that outer sheaths that degenerated were only partially displaced from the axon at the commencement of guanethidine treatment. In contrast, analysis of serial sections showed that completely displaced outer internodes remained ultrastructurally intact. These internodes survived degeneration of the axon and inner sheath, and during the later time points (2-6 wk) they enclosed only connective tissue elements and reorganized Schwann cells/processes. Axonal regeneration was not observed within surviving outer internodes. We therefore conclude that myelin maintenance in the superior cervical ganglion is not dependent on direct axonal contact or diffusible axonal factors. In addition, physical association of Schwann cells with the degenerating axon may be an important factor in precipitating myelin breakdown during Wallerian degeneration.

Animals↗

Fine structural localization of cholesterol-1,2- 3 H in degenerating and regenerating mouse sciatic nerve.

The localization of (3)H-labeled cholesterol in nerves undergoing degeneration and regeneration was studied by radioautography at the electron microscope level. Two types of experiments were carried out: (a) Cholesterol-1,2-(3)H was injected intraperitoneally into suckling mice. 5 wk later, Wallerian degeneration was induced in the middle branch of the sciatic nerve, carefully preserving the collateral branches. The animals were then sacrificed at various times after the operation. During degeneration, radioactivity was found over myelin debris and fat droplets. In early stages of regeneration, radioactivity was found in myelin debris and regenerating myelin sheaths. Afterwards, radioactivity was found predominantly over the regenerated myelin sheaths. Radioactivity was also associated with the myelin sheaths of the unaltered fibers, (b) Wallerian degeneration was induced in the middle branch of the sciatic nerves of an adult mouse, preserving the collateral branches. Cholesterol-1,2-(3)H was injected 24 and 48 hr after the operation and the animal was sacrificed 6 wk later. Radioactivity was found in the myelin sheaths of the regenerated and unaltered fibers. The results from these experiments indicate that: (a) exogenous cholesterol incorporated into peripheral nerve during myelination remains within the nerve when it undergoes degeneration. Such cholesterol is kept in the myelin debris as an exchangeable pool from which it is reutilized for the formation of the newly regenerating fibers, especially myelin. (b) exogenous cholesterol incorporated into the nerves at the time that degeneration is beginning is also used in the formation of new myelin sheaths during regeneration, (c) mature myelin maintains its ability to incorporate cholesterol.

Animals↗

Proximodistal degeneration of C-fibers detached from their perikarya.

Degeneration was followed in the garfish olfactory nerve after removal of the mucosa containing the cell bodies. Degeneration, as measured by a decrease in the weight of consecutive 3-mm nerve segments, spreads at constant velocity from the site of injury toward the synaptic area. The proximodistal degeneration is temperature dependent and progresses from 0.3 mm/d at 10 degrees C to 13.0 mm/d at 35 degrees C. Between 14 and 35 degrees C, the velocity increases linearly with temperature. At all the temperatures investigated, these proximodistal degeneration velocities are identical to the rates of slow intraaxonal flow measured in axons detached from their cell bodies, or to the rates measured in regenerating fibers, and, except at 10 degrees C, are 3.3 times faster than the rate of slow flow in intact nerves. These results were confirmed by light and electron microscopy. We hypothesize that the collapse and subsequent degeneration of the axons is the result of a proximodistal depletion of cytoskeletal elements no longer provided by the cell body to the axon by slow intraaxonal flow. A significant number of axons disappeared rapidly from the nerve before the arrival of the slow degenerative wave. From studies by other groups, this rapid degeneration may be the result of a lack of rapidly transported, mainly membranous components.

Animals↗

NMDA-receptor antagonist protects neurons from secondary degeneration after partial optic nerve crush.

Damage resulting from a partial acute lesion of white matter in the central nervous system (CNS) gradually spreads also to neurons that escaped the primary injury, resulting in their degeneration. Such spreading has been referred to as secondary degeneration. In order to demonstrate that this degeneration is indeed secondary to that caused by the acute insult, as well as to investigate the mechanism underlying the spread of damage and ways in which to protect neurons from such damage, we have proposed the use of partial lesion of the rodent optic nerve as a model. In this model we examined whether an antagonist of a receptor-mediated channel, shown to be beneficial in gray matter lesions, can protect neurons from undergoing secondary degeneration following white matter lesion. A well-calibrated partial crush lesion inflicted on the optic nerve of adult rats was immediately followed by a single intraperitoneal injection of the N-methyl-D-aspartate receptor antagonist, MK-801 (1 mg/kg). Protection of neurons from secondary degeneration was assessed by retrograde labeling and by measurement of the visual evoked potential (VEP) response to light. Two weeks after the injury, the mean number of neurons that were still intact was about threefold higher in the MK-801-treated group than in the saline-treated control group, indicating a treatment-induced protection of neurons that had escaped primary injury. A positive VEP response to light was obtained in 90% of the MK-801 treated animals and in only 50% of injured controls. The questions regarding whether the secondary degeneration of initially spared neurons starts in their cell bodies or in their axons, and consequently the identity of the primary site of their protection by MK-801, are discussed in relation to the absence of N-methyl-D-aspartate receptors on nerve fibers. The present findings may have implications for both acute and chronic injuries of the CNS.

Analysis of Variance↗

Retinal degeneration and other eye disorders in wives of farmer pesticide applicators enrolled in the agricultural health study.

Retinal degeneration is the leading cause of visual impairment in older adults. An association between retinal degeneration and fungicide use was observed previously among farmer pesticide applicators in the Agricultural Health Study, a large study of farm families from Iowa and North Carolina. The objective of this investigation was to determine whether wives of these farmer pesticide applicators were at increased risk of retinal degeneration. Self-reported cross-sectional data obtained via questionnaire between 1993 and 1997 from 31,173 wives were used. Associations of specific pesticides and groups of pesticides based on function (fungicides, herbicides, insecticides, and fumigants) or chemical structure (organophosphates, organochlorines, and carbamates) with eye disorders were evaluated using logistic and hierarchical logistic regression analyses. Self-reported retinal degeneration was associated with the wife's fungicide use (odds ratio = 1.9, 95% confidence interval: 1.2, 3.1) after adjustment for age and state of residence. Specific fungicides that appeared to drive this association were maneb or mancozeb and ziram. No associations between pesticide use and other eye disorders were found. Although these findings for retinal degeneration are based solely on self-reported disease, they are consistent with those reported for farmer pesticide applicators. These findings suggest that exposure to some fungicides and other pesticides may increase the risk of retinal degeneration and warrant further investigation.

Adult↗

The slow Wallerian degeneration gene, WldS, inhibits axonal spheroid pathology in gracile axonal dystrophy mice.

Axonal dystrophy is the hallmark of axon pathology in many neurodegenerative disorders of the CNS, including Alzheimer's disease, Parkinson's disease and stroke. Axons can also form larger swellings, or spheroids, as in multiple sclerosis and traumatic brain injury. Some spheroids are terminal endbulbs of axon stumps, but swellings may also occur on unbroken axons and their role in axon loss remains uncertain. Similarly, it is not known whether spheroids and axonal dystrophy in so many different CNS disorders arise by a common mechanism. These surprising gaps in current knowledge result largely from the lack of experimental methods to manipulate axon pathology. The slow Wallerian degeneration gene, Wld(S), delays Wallerian degeneration after injury, and also delays 'dying-back' in peripheral nervous system disorders, revealing a mechanistic link between two forms of axon degeneration traditionally considered distinct. We now report that Wld(S) also inhibits axonal spheroid pathology in gracile axonal dystrophy (gad) mice. Both gracile nucleus (P < 0.001) and cervical gracile fascicle (P = 0.001) contained significantly fewer spheroids in gad/Wld(S) mice, and secondary signs of axon pathology such as myelin loss were also reduced. Motor nerve terminals at neuromuscular junctions continued to degenerate in gad/Wld(S) mice, consistent with previous observations that Wld(S) has a weaker effect on synapses than on axons, and probably contributing to the fact that Wld(S) did not alleviate gad symptoms. Wld(S) acts downstream of the initial pathogenic events to block gad pathology, suggesting that its effect on axonal swelling need not be specific to this disease. We conclude that axon degeneration mechanisms are more closely related than previously thought and that a link exists in gad between spheroid pathology and Wallerian degeneration that could hold for other disorders.

Animals↗

Involvement of monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha and interleukin-1beta in Wallerian degeneration.

Wallerian degeneration in the CNS and PNS consists of degradation and phagocytosis of axons and their myelin sheath distal to the site of injury. This process of degeneration, which requires an effective macrophage response, occurs rapidly in peripheral nerves but is slow in the CNS. Rapid Wallerian degeneration in peripheral nerves may contribute to subsequent axonal regeneration. We show that there is a marked increase in mRNA expression of three pro-inflammatory molecules, the chemokines monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1alpha (MIP-1alpha), and the cytokine interleukin-1beta (IL-1beta), in the mouse sciatic nerve but not in the spinal cord undergoing Wallerian degeneration. Neutralizing MCP-1, MIP-1alpha and IL-1beta in the lesioned sciatic nerve with function-blocking antibodies suppressed macrophage responses and myelin clearance. Injecting recombinant MCP-1, MIP-1alpha or IL-1beta into the normal, uninjured spinal cord triggered the expression of a number of chemokines and cytokines. Furthermore, injecting recombinant MCP-1/MIP-1alpha or IL-1beta into the dorsal column of the spinal cord undergoing Wallerian degeneration triggered rapid macrophage/microglial activation and myelin clearance. These findings provide direct evidence that MCP-1, MIP-1alpha and IL-1beta are important regulators of macrophage responses that lead to rapid myelin breakdown and clearance in Wallerian degeneration.

Animals↗

Age-related macular degeneration is associated with atherosclerosis. The Rotterdam Study.

Age-related macular degeneration is the most frequent cause of blindness in the elderly. A vascular basis of the disease has been suggested, but not confirmed. The association between atherosclerosis and this type of macular degeneration was investigated in 104 subjects with and 1,324 subjects without macular degeneration as part of the population-based Rotterdam Study. The study was performed between March 1990 and July 1993 in a suburb of Rotterdam, the Netherlands. Macular degeneration was assessed on fundus photographs. Carotid atherosclerosis was ultrasonographically evaluated by measurement of the common carotid intima-media thickness and by assessment of the presence of atherosclerotic plaques. Atherosclerosis in arteries of the lower extremities was studied by determination of the ankle-arm systolic blood pressure ratio. In subjects younger than age 85 years, plaques in the carotid bifurcation were associated with a 4.7 times increased prevalence odds of macular degeneration (95% confidence interval (CI) 1.8-12.2); those with plaques in the common carotid artery showed an increased prevalence odds of 2.5 (95% CI 1.4-4.5). The intima-media thickness of the common carotid arteries was not significantly different. Lower extremity arterial disease (ankle-arm index less than 0.90 on at least one side) was associated with a 2.5 times increased prevalence odds (95% CI 1.4-4.5). These findings suggest that atherosclerosis may be involved in the etiology of age-related macular degeneration.

Aged↗

The human lumbar endplate. Evidence of changes in biosynthesis and denaturation of the extracellular matrix with growth, maturation, aging, and degeneration.

STUDY DESIGN: The authors measured concentrations of specific molecules reflecting matrix synthesis and degradation in 121 human endplates and correlated them with aging and grade of degeneration. OBJECTIVES: Abnormal endplate development has been implicated in many spinal abnormalities, yet little is known about endplate matrix component turnover. SUMMARY OF BACKGROUND DATA: Techniques are available to perform an in situ investigation of matrix component turnover with aging and degeneration. METHODS: Newly synthesized aggrecan and Type I and Type II procollagens were measured with recently developed immunoassays. Percentage of denatured Type II collagen was assessed with a new enzyme-linked immunosorbent inhibition assay. RESULTS: Synthesis in endplates, measured by content of an aggrecan marker (846) and content of Types I and II procollagen markers (CPI and CPII), is highest in the neonatal and 2- to 5-year age groups and steadily diminishes with increasing age. However, in the oldest age group and in highly degenerated discs, the CPI epitope level increased significantly. Percentage of denatured Type II collagen, assessed by the presence of an epitope exposed with the cleavage of Type II collagen, increased from the neonatal to the 2- to 5-year age groups. The percentage progressively decreased with increasing age. However, it significantly increased in endplates from highly degenerated discs. CONCLUSIONS: The authors identified three matrix turnover phases, related to age and grade of degeneration. Phase I (growth) is characterized by active synthesis of matrix molecules and active denaturation of Type II collagen. Phase II (aging and maturation) is distinguished by a drop in synthetic activity and a reduction in denaturation of Type II collagen. Phase III (degenerative) is illustrated by an increase in Type II collagen denaturation and Type I procollagen synthesis, both related to grade of tissue degeneration.

Adolescent↗

Nutritional supplement use and age-related macular degeneration.

Age-related macular degeneration is one of the leading causes of visual loss among people aged 65 years or older. The causes and factors associated with the progression of age-related macular degeneration are unknown presently. Basic research and epidemiologic data support the hypotheses that higher levels of antioxidant vitamins and minerals may protect the eye from the development of age-related macular degeneration. For this reason and also because of the lack of effective treatment for most cases of age-related macular degeneration, nutritional supplements with antioxidants have emerged as possible therapy for age-related macular degeneration. Nutritional supplements are not proven therapy for age-related macular degeneration. The potential beneficial effects and adverse side effects of the nutritional supplements have not yet been fully evaluated in carefully conducted clinical trials. Several randomized placebo-controlled clinical trials are presently underway. Results of these studies will provide important data to clarify the potential beneficial and adverse effects of such treatment. Until these results are available, it would be premature to make recommendations in favor of vitamin or mineral supplements.

Aged↗

Pathological study of corticospinal-tract degeneration in Friedreich's ataxia.

The pattern of fibre degeneration in the lateral corticospinal tract (LCST) was studied in a case of Friedreich's ataxia (FA). There was preferential involvement of the lateral area of the LCST in the cervical spinal cord. More caudally, the degeneration involved the entire area of the LCST and did not reveal a medial to lateral gradient of involvement. We suggest that this distinctive pattern of tract degeneration is a consequence of the somatotopic organization of the LCST, with the dying-back degeneration preferentially affecting those LCST fibers that extend to the lumbo-sacral spinal cord. This pattern of tract degeneration may be a useful morphological marker of dying-back degeneration in corticospinal tracts.

Adult↗

Dying back type axonal degeneration of sensory nerve terminals in muscle spindles of the gracile axonal dystrophy (GAD) mutant mouse.

A disorder of the gracile axonal dystrophy (GAD) mutant mouse is characterized by a neuromuscular disease with sensory ataxia (detectable 30 days after birth) and paresis of the hindlimbs (detectable at 80 days). In the sensory ataxia stage, histological study of the primary sensory system shows that, in addition to the lesions in the central nervous system, peripherally projecting axons have also started to degenerate at their distal ends in muscle spindles. Although the structure of Ia fibre endings appear normal until 15 days after birth, initial changes in the annulo-spiral structure are detected around the 20th day by a degeneration of the terminal axons. Degeneration then progressed proximally and the secondary endings also start to degenerate. Neuron cell bodies located in the dorsal root ganglia are morphologically intact until the later stages. Chronological studies indicate that, although axonal degeneration progresses throughout life, it is accentuated during the rapid somatic growth period. Around 50 days of age, transient regeneration takes place at axonal endings when somatic growth has attained a plateau. Such primary sensory endings tend to be restored by fine, multiple axons which gain access to the intrafusal fibres through the original endoneurial tubes. Ultrastructural observations at the fully affected stage show intrafusal muscle fibres lying scattered within spindles due to loss of the fine network of inner capsule layers and an almost complete loss of sensory endings from the surface of intrafusal muscle fibres. These results indicate that this mutant mouse is a useful model for naturally occurring 'dying back' type axonal degeneration or 'central and peripheral distal axonopathies', and would provide significant information about the complete evolution of the pathological processes involved.

Animals↗

Progressive degeneration of motor nerve terminals in GAD mutant mouse with hereditary sensory axonopathy.

The evolution of motor nerve degeneration was examined in gracile axonal dystrophy (GAD) mutant mice, which develop initial sensory ataxia and subsequent motor paresis. Using the anterior gracilis (AG) muscle, which is innervated at two discrete and well-separated endplate zones, we demonstrated that axonal degeneration occurred first at motor nerve terminals in the distal endplate zone, and then extended gradually from the distal to the more proximal parts of affected axons in the intra-muscular nerve trunk. In contrast to the degeneration in the distal zone, active degeneration was less marked in the proximal endplate zone and, furthermore, most terminal axons had begun to produce regenerating sprouts. Ventral horn cells were histologically normal, even at advanced stages. These results indicate that, as previously observed in sensory nerves, dying back degeneration progresses later in the lower motor neuron system, even within one muscle. The mechanism(s) influencing the activation of axonal regeneration are discussed. This mutant mouse will be a useful model for the study of regenerating phenomena in dying back degeneration of genetically compromised motor neurons, as well as for the study of the pathogenesis of hereditary sensory and motor neuropathies in man.

Acetylcholinesterase↗

Partial reversal of aluminium-induced neurofibrillary degeneration by desferrioxamine in adult male rabbits.

Desferrioxamine, a chelating agent with a high affinity for aluminium, has been reported to slow the clinical progression of dementia associated with Alzheimer's disease [4]. We report here the effects of desferrioxamine treatment on aluminium-induced neurofibrillary degeneration in rabbits. Adult male New Zealand white rabbits received a single injection of aluminium-maltolate into the lateral cerebral ventricle. Three days later, one group of rabbits was treated with intramuscular injections of desferrioxamine twice daily; a second group received saline instead of desferrioxamine. Both groups were sacrificed 4 or 5 days following initiation of desferrioxamine or saline treatment. Minimal neurofibrillary degeneration was found in two of six desferrioxamine-treated rabbits, while all six rabbits treated with saline showed extensive neurofibrillary degeneration, particularly in the ventral horn of the lower spinal cord. Quantitation of the neurofibrillary degeneration in ventral horn neurons of lumbar cord revealed 30% to be affected in saline-treated animals compared to zero-affected neurons following desferrioxamine treatment. When sacrificed just 3 days after aluminium treatment, 50% of the rabbits already revealed neurofibrillary degeneration, corresponding to the time-point when desferrioxamine treatment was begun in the above animals; on quantitation, 7.5% of ventral lumbar cord neurons were involved. These findings indicate a partial reversal of aluminium-induced neurodegeneration by desferrioxamine. Delaying desferrioxamine treatment to 6 days after aluminium administration prevented any reversal of the aluminium effect; all animals had abundant neurofibrillary degeneration as well as a striking basophilic spicular deposit of calcium and argyrophilic material in the leptomeninges, lateral ventricles and brain parenchyma adjacent to these areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Compounds↗

Vision testing in atrophic macular degeneration.

PURPOSE: To determine the correlation between a group of vision tests in atrophic macular degeneration (AMD) in an office setting. METHODS: Patients with documented vision loss from atrophic macular degeneration in one eye were invited to attend an eye clinic every three months for a series of six vision tests for their good eye followed by fundus photography. Modified contrast sensitivity, blue/yellow anomaloscopy, flicker fusion frequency, Amsler grid, and photostress recovery time were correlated with Snellen acuity using the Pearson correlation coefficient. The regression of the Snellen acuity on sex, age and the presence of disciform macular degeneration in the other eye was obtained using a general linear model. RESULTS: The correlation with Snellen acuity result was low for all tests. It was highest for Amsler grid abnormality (r = -0.33345) and blue/yellow anomaloscopy matching range (r = -0.20742), where r denotes the correlation coefficient. Patient age was strongly correlated with Snellen results (P = 0.0001), but it was not significantly related to sex (P = 0.1187) or the presence of disciform macular degeneration in the other eye (P = 0.9989). The photostress recovery time showed enormous inter-visit variations and poor correlation with Snellen acuity (P = 0.0526). CONCLUSIONS: The course of AMD is routinely assessed by Snellen acuity and any of several additional tests. When employing a test battery in an office setting, a clinician needs to know the relative utility and correlation between the tests at his disposal. Of the tests used in this study, the Amsler grid was the most useful addition to the Snellen acuity at all stages of atrophic macular degeneration, and blue/yellow anomaloscopy was useful only in mild macular degeneration where Snellen acuity was 6/12 or better.

Aged↗