Minocycline reduces microgliosis and improves subcortical white matter function in a model of cerebral vascular disease

Chronic cerebral hypoperfusion is a key mechanism associated with white matter disruption in cerebral vascular disease and dementia. In a mouse model relevant to studying cerebral vascular disease, we have previously shown that cerebral hypoperfusion disrupts axon‐glial integrity and the distribution of key paranodal and internodal proteins in subcortical myelinated axons. This disruption of myelinated axons is accompanied by increased microglia and cognitive decline. The aim of the present study was to investigate whether hypoperfusion impairs the functional integrity of white matter, its relation with axon‐glial integrity and microglial number, and whether by targeting microglia these effects can be improved. We show that in response to increasing durations of hypoperfusion, the conduction velocity of myelinated fibres in the corpus callosum is progressively reduced and that paranodal and internodal axon‐glial integrity is disrupted. The number of microglial cells increases in response to hypoperfusion and correlates with disrupted paranodal and internodal integrity and reduced conduction velocities. Further minocycline, a proposed anti‐inflammatory and microglia inhibitor, restores white matter function related to a reduction in the number of microglia. The study suggests that microglial activation contributes to the structural and functional alterations of myelinated axons induced by cerebral hypoperfusion and that dampening microglia numbers/proliferation should be further investigated as potential therapeutic benefit in cerebral vascular disease.     

Disproportionate atrophy of cerebral white matter in chronic alcoholics

Morphometric analysis of postmortem brains from chronic ethyl alcohol abusers and controls was performed to determine the regional distribution and extent of atrophy in the cerebral hemispheres of alcoholics. This study was performed by digitizing photographs of coronal slices of the brains to compute the cross-sectional area of the cerebrum, cerebral cortex, subcortical nuclei, cerebral white matter, and the ventricular system at five standardized levels. Although the alcoholics and controls had similar demographic features and mean brain weights, brains from the alcoholic group showed mild but consistent atrophy of the cerebral cortex (2.5% to 4.2% reductions in cross-sectional area at all five levels), moderate atrophy of cerebral white matter (6.1% to 17.5% reductions), and enlargement of the ventricular system (31.8% to 71.9% increases). There were no differences in the sizes of subcortical nuclei. The absolute increase in the size of the ventricles in the alcoholic group was roughly equal to the amount of tissue lost in cerebral white matter, thereby representing hydrocephalus ex vacuo. The disproportionate loss of cerebral white matter relative to cerebral cortex suggests that a major neurotoxic effect of chronic alcohol intoxication in the central nervous system is axonal degeneration.     

Light and electron microscopic assessment of progressive atrophy following moderate traumatic brain injury in the rat

The presence of progressive white matter atrophy following traumatic brain injury (TBI) has been reported in humans as well as in animal models. However, a quantitative analysis of progressive alterations in myelinated axons and other cellular responses to trauma has not been conducted. This study examined quantitative differences in myelinated axons from several white and gray matter structures between non-traumatized and traumatized areas at several time points up to 1 year. We hypothesize that axonal numbers decrease over time within the structures analyzed, based on our previous work demonstrating shrinkage of tissue in these vulnerable areas. Intubated, anesthetized male Sprague-Dawley rats were subjected to moderate (1.8–2.2 atm) parasagittal fluid-percussion brain injury, and perfused at various intervals after surgery. Sections from the fimbria, external capsule, thalamus and cerebral cortex from the ipsilateral hemisphere of traumatized and sham-operated animals were prepared and. estimated total numbers of myelinated axons were determined by systematic random sampling. Electron micrographs were obtained for ultrastructural analysis. A significant (P<0.05) reduction in the number of myelinated axons in the traumatized hemisphere compared to control in all structures was observed. In addition, thalamic and cortical axonal counts decreased significantly (P<0.05) over time. Swollen axons and macrophage/microglia infiltration were present as late as 6 months post-TBI in various structures. This study is the first to describe quantitatively chronic axonal changes in vulnerable brains regions after injury. Based on these data, a time-dependent decrease in the number of myelinated axons is seen to occur in vulnerable gray matter regions including the cerebral cortex and thalamus along with distinct morphological changes within white matter tracts after TBI. Although this progressive axonal response to TBI may include Wallerian degeneration, other potential mechanisms underlying this progressive pathological response within the white matter are discussed.     

The myelinated fiber changes in the white matter of aged female Long‐Evans rats

Age‐related changes of the white matter and the myelinated fibers in white matter of female Long‐Evans rats were investigated by the use of design‐based stereological methods. The white matter volume in middle‐aged rats was not significantly different from that in young rats, but the white matter volume in aged rats was significantly decreased by 42.7% and 37.7%, respectively, when compared with young and middle‐aged rats. When compared with young rats, the total volumes of the myelinated fibers and myelin sheaths in white matter of aged rats were significantly decreased by 26.7% and 30.7%, respectively. When compared with young and middle‐aged rats, the total length of the myelinated fibers in white matter of aged rats was significantly decreased by 52.5% and 48.6%, respectively. The mean diameter of the myelinated fibers in white matter of aged rats was significantly increased by 37.5% when compared with young rats. The absolute diameter distributions of the myelinated fiber length in the white matter of young, middle‐aged, and aged rats indicated that the age‐related loss of the myelinated fiber length in the white matter of aged rats was mainly as a result of the marked loss of the myelinated fibers with smaller diameter. The age‐related changes of the white matter and the myelinated fibers in white matter may have important implications for age‐related cognitive impairments. © 2009 Wiley‐Liss, Inc.     

The myelinated fiber loss in the corpus callosum of mouse model of schizophrenia induced by MK-801

Previous magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) investigations have shown that the white matter volume and fractional anisotropy (FA) were decreased in schizophrenia (SZ), which indicated impaired white matter integrity in SZ. However, the mechanism underlying these abnormalities has been less studied. The current study was designed to investigate the possible reasons for white matter abnormalities in the mouse model of SZ induced by NMDA receptor antagonist using the unbiased stereological methods and transmission electron microscope technique. We found that the mice treated with MK-801 demonstrated a series of schizophrenia-like behaviors including hyperlocomotor activity and more anxiety. The myelinated fibers in the corpus callosum (CC) of the mice treated with MK-801 were impaired with splitting lamellae of myelin sheaths and segmental demyelination. The CC volume and the total length of the myelinated fibers in the CC of the mice treated with MK-801 were significantly decreased by 9.4% and 16.8% when compared to those of the mice treated with saline. We further found that the loss of the myelinated fibers length was mainly due to the marked loss of the myelinated nerve fibers with the diameter of 0.4–0.5 μm. These results indicated that the splitting myelin sheaths, demyelination and the loss of myelinated fibers with small diameter might provide one of the structural bases for impaired white matter integrity of CC in the mouse model of SZ. These results might also provide a baseline for further studies searching for the treatment of SZ through targeting white matter.     

Progressive centripetal degeneration in polyneuropathies (author's transl)

This is a clinicopathologic report on three patients with sensory polyneuropathies of different origin. Sensory loss involved all four limbs reaching the upper third of the thighs and the elbow level or higher, in all three patients. In addition to the limbs the central region of the anterior aspect of the trunk, from lower abdomen up to level T2, and on the top of the scalp were involved. There was minimal weakness. This pattern of sensory deficit can best be explained by a length dependent degeneration of fibers. Familial amyloidosis, Portugese type, was responsible for the neuropathy in the first patient, diabetes mellitus in the second and alcoholism in the third one. On teased nerve fiber study, single regenerating fibers were isolated on sural nerve biopsy specimens from patients 1 and 2. Segmental demyelination and/or remyelination occurred in 11 per cent of the fibres in patient 1, in 36 per cent in patient 2 and in 4 of the 19 fibres isolated in patient 3. On cross sections of nerve specimens embedded in Epon there was a striking loss of myelinated fibres which was less important and predominated on smaller fibres in patients 1 and 2. On electron microscopic examination loss of unmyelinated fibres was conspicuous in all three patients. On single fiber studies as well as on sections of embedded specimens, myelinated fibres occasionally showed demyelination in contact to amyloid deposits. The present study demonstrates that in this pattern of neuropathy degeneration of myelinated fibers begins in the distal part of longest axons and may be associated with axonal sprouting in more proximal parts of degenerating axons. As the neuropathy progresses axons of shorter and shorter length become involved.     

Hereditary diffuse leukoencephalopathy with spheroids: clinical, pathologic and genetic studies of a new kindred

Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is a rare autosomal dominant disorder characterized by cerebral white matter degeneration with axonal spheroids leading to progressive cognitive and motor dysfunction. We report clinical and pathological features, as well as molecular genetic analysis, of a family with HDLS. A pedigree consisting of 27 persons in 5 generations contained 6 affected individuals. Dementia and depression were common; two individuals presented with a syndrome resembling corticobasal degeneration (CBD). Postmortem neuropathologic evaluation of three affected individuals revealed enlargement of the lateral ventricles and marked attenuation of cerebral white matter, but preservation of white matter in brainstem and cerebellum, except for the corticospinal tract. Histopathologic studies showed a loss of myelinated fibers, lipid-laden macrophages and bizarre astrocytes, as well as abundant axonal spheroids that were immunoreactive for phosphorylated neurofilament protein and amyloid precursor protein (APP), but not αB-crystallin and variably with ubiquitin. By electron microscopy, axonal spheroids contained aggregates of intermediate filaments or of organelles that were predominantly vesicular and lamellar. The cerebral cortex had focal neuronal degeneration with αB-crystallin-immunoreactive ballooned neurons. In summary, the present report describes a previously unreported kindred with HDLS with individuals presenting as CBD. Immunohistochemistry for APP and αB-crystallin demonstrates distinctive neurodegeneration in cerebral axons and perikarya.     

Calcitonin gene-related peptide immunostained axons provide evidence for fine primary afferent fibers in the dorsal and dorsolateral funiculi of the rat spinal cord

The hypothesis being tested in the present paper is that there are large numbers of fine primary afferent axons in the dorsal and dorsolateral funiculi of the lumbar spinal cord of the rat. The data show numerous calcitonin gene-related peptide labeled fine myelinated and unmyelinated axons in these funiculi. Approximately 95% of the labeled axons disappear after dorsal rhizotomy. Accordingly, the hypothesis is confirmed. Thus it is becoming apparent that fine primary afferent fibers are more widely distributed in spinal white matter than had been previously recognized. Implications are that it is not possible to find areas in the spinal white matter that contain only large myelinated sensory axons and that significant numbers of fine primary afferent fibers will be lost even if lesions are restricted to the dorsal funiculus. The sizable population of fine myelinated primary afferent axons in the dorsal funiculus is emphasized. An obvious question, suggested by significant differences in average diameters of the axons in the different pathways, is whether there are differences in the types of information carried by the fine afferent fibers in their different locations in the white matter of the lumbar cord.     

Myelinated fibres in the human paravertebral sympathetic chain; quantitative studies on white rami communicantes

Myelinated fibres in the human sympathetic paravertebral chain were examined histologically and in single teased fibre preparations in various age groups in subjects dying from disorders not affecting primarily the autonomic nervous system. An increase in fibre density predominantly due to an increase in the number of small fibres was found in older subjects. A correlation between internodal length and fibre diameter was found but the internodes of sympathetic myelinated fibres are shorter for any given diameter than those found on fibres of comparable size in the sural nerve. A reduction in internodal lengths with advancing years was demonstrated. These observations are interpreted to show that Wallerian degeneration and segmental demyelination occur with increasing frequency in old age and that regeneration does not keep pace with successive degenerative events. The deterioration in function of the autonomic nervous system with advancing years may be attributed in part to the changes found in myelinated fibres in the paravertebral sympathetic chain.     

Unmyelinated nerve fiber degeneration in chronic inflammatory demyelinating polyneuropathy

To determine whether unmyelinated nerve fibers escape degeneration as one might expect in an immune response exclusively directed at myelin, we performed a morphometric examination of unmyelinated axons and myelinated nerve fibers in sural nerve biopsy specimens of 14 patients with a chronic inflammatory demyelinating polyneuropathy (CIDP) and of 12 age-matched normal controls. The numbers of unmyelinated axons, myelinated nerve fibers, denervated Schwann cell units and collagen pockets were quantified and related to the clinical and electrophysiological data of the patients with CIDP. In 4 patients with a rapid onset of the neuropathy and a highly elevated CSF protein, the numbers of both unmyelinated axons and myelinated nerve fibers were decreased equally. In 8 patients we found that the unmyelinated axons were relatively spared compared with the loss of myelinated nerve fibers. In these patients, however, the presence of denervated Schwann cell units and of collagen pockets was increased. We conclude that unmyelinated nerve fibers are affected in patients with CIDP.     

Axonal attenuation and secondary segmental demyelination in myeloma neuropathies

The sural nerves of 5 patients with osteosclerotic myeloma and polyneuropathy, of 3 patients with multiple myeloma and polyneuropathy, and of 6 healthy subjects were studied by neuropathological, morphometric, and teased-fiber approaches to assess cellular (Schwann cell or axon) vulnerability and to explore the mechanism of segmental demyelination. As compared with controls, the nerves of both types of myeloma neuropathy demonstrated a statistically significant and marked loss of myelinated fibers and increased frequencies of axonal degeneration among teased fibers at statistically significant levels. The peaks of diameter histograms of myelinated fibers of osteosclerotic myeloma/polyneuropathy nerves were displaced to smaller diameter categories, suggesting fiber atrophy. Segmental demyelination and remyelination was clustered, as found in secondary demyelination. Large- and intermediate-diameter myelinated fibers of osteosclerotic myeloma/polyneuropathy nerves had significantly smaller axon calibers relative to myelin spiral length seen in electron micrographs. The loss of myelinated fiber axons, the shift of the peaks of diameter histograms to smaller sizes, the lack of noticeable increased numbers of demyelinated axons, the clustered distribution of segmental demyelination, and the axonal attenuation suggest a special axonal or neuronal vulnerability and appear to provide an explanation for the observed segmental demyelination. Whether axonal attenuation has a perikaryeal or proximal axonal genesis now needs to be determined.     

Development of the pyramidal tract in the hamster. II. An electron microscopic study

We undertook a qualitative and quantitative electron microscopic study of the growth and development of the pyramidal tract in the hamster to investigate the mode of growth of the axons, the possibility of fiber degeneration during development, and the process of myelination. By calculating the total fiber number as the product of axon density and tract area for several postnatal ages, we found that the pyramidal tract grows through the medulla as a compact bundle containing nearly twice the number of fibers as the mature tract. During the second postnatal week there is a substantial loss of axons followed in the third and fourth weeks by a more gradual loss such that by 34 days after birth the total number of axons reaches the adult value. Myelination in the hamster pyramidal tract begins at 7 days and continues at a very slow rate until the third postnatal week, when a dramatic increase in myelin formation occurs. By 34 days after birth the number of myelinated axons is approximately 80% that of the adult. As has been reported for other CNS tracts, there does not seem to be a “critical diameter” of an axon that absolutely determines the presence or absence of myelin on a fiber. However, all axons above 0.5 μm in diameter are myelinated at approximately the same rate, while those under this diameter are myelinated much more slowly and even in the adult make up only a small percentage of the total myelinated fibers.     

Thalamic retrograde degeneration in the congenitally hydrocephalic rat is attributable to apoptotic cell death

Congenitally hydrocephalic HTX rats develop ventricular dilatation with extensive damage of the cerebral white matter. Recently, we have reported that neuronal cell death also occurs in the thalamus of HTX rats. To investigate the mechanism underlying this thalamic degeneration in these animals, we carried out a histopathological study of the brain at different phases of postnatal development. Eosinophilic neurons with condensed chromatin or fragmented nuclei were observed in the thalamus from postnatal day 17 onward. The incidence of cell death in the thalamus increased with the progression of hydrocephalus. Ultrastructurally, thalamic neurons occasionally had apoptotic features including nuclear chromatin condensation and marginalization. Immunohistochemically, single‐stranded DNA‐positive neuronal nuclei were found in the thalamus. They were also positively stained with the TUNEL method. Marked loss of myelin and axons with many TUNEL‐positive oligodendrocytes were found in the cerebral white matter. These findings suggest that the neuronal cell death observed in the thalamus in hydrocephalic HTX rats is retrograde degeneration due to extensive damage of axons in the cerebral white matter and that the thalamic retrograde degeneration is attributable to apoptotic cell death.     

Loss of large myelinated nerve fibres of the recurrent laryngeal nerve in patients with multiple system atrophy and vocal cord palsy.

OBJECTIVES: Vocal cord palsy seen in some patients with multiple system atrophy may result from neuronopathy of the recurrent laryngeal nerve. METHODS: Six controls and six patients with multiple system atrophy, four with and two without vocal cord palsy were studied. The number of myelinated nerve fibres were counted and fibre diameter histograms were established for the motor and sensory divisions of the laryngeal branch of the recurrent laryngeal nerve. RESULTS: Although both groups of patients with multiple system atrophy showed selective loss of the myelinated fibres in the motor branch, the change was greater in those with vocal cord palsy than in those without. The small myelinated nerve fibres (diameter < 7 microm) were decreased in number in both multiple system atrophy groups, whereas the large myelinated nerve fibres (diameter < 8 microm) were decreased only in those with vocal cord palsy, and preserved in those without the symptom. CONCLUSION: In multiple system atrophy, the small myelinated fibres innervating the vocal cord are affected first, without obvious clinical signs. The patient develops vocal cord palsy only after the loss of the large myelinated fibres, which mostly comprise the alpha motor axons that innervate the intrinsic laryngeal muscles.     

The topographic distribution of brain atrophy in Alzheimer's disease

Summary The extent of regional atrophy in ten patients, aged 52–74 years, dying with Alzheimer's disease uncomplicated pathologically by the effects of advanced old age or cerebrovascular disease, was quantified by image analysis of fixed coronal brain slices. Atrophy of the cerebral cortex was globally distributed, although the temporal lobe was most severely affected. Grey and white matter was in general affected equally. Atrophy was also present within the basal ganglia, particularly the caudate nucleaus and putamen. Cerebral cortical atrophy is probably due mostly to neurofibrillary degeneration and loss of intrinsic pyramidal cells and their processes (grey matter) and axons (white matter) although loss of ascending subcortical fibres from regions such as nucleus basalis and locus caeruleus will contribute. Atrophy of the basal ganglia may relate to loss of descending cortical projections.     

Marked loss of myelinated nerve fibers in the human brain with age

The white matter is the structure of the brain that declines most with age-almost 30%, but little is known about the age-effect on the fibers that constitute the white matter. In the present study, the total length of myelinated fibers was measured with a newly developed stereologic method. Specimens came from 36 normal Danes (18 males and 18 females) with an age ranging between 18 and 93 years. Samples were taken systematically and randomly from the white matter, and the biopsy specimens were randomly rotated before sectioning to avoid bias due to the anisotropic nature of nerve fibers. The fibers were counted at light microscopic level at approximately 10,000x magnification, and the diameter of each counted fiber was measured to get the diameter distribution. Males were found to have a total myelinated fiber length of 176,000 km at the age of 20 and 97,200 km at the age of 80, whereas the total length in females was 149,000 km at the age of 20 and 82,000 km at the age of 80. This finding corresponds to a 10% decrease per decade or a total decrease of 45% from the age of 20 to 80 years, and a sex difference of 16%. The fiber diameter distribution showed that primarily the thinner fibers were lost with a relative preservation of the thicker ones. The marked loss of myelinated nerve fibers with age could explain some of the cognitive decline seen in the elderly.     

Total length of nerve fibers in prefrontal and global white matter of chronic schizophrenics

It has been suggested that the dysfunction of the prefrontal cortex in schizophrenics is due to dysfunctional connections between the prefrontal cortex and more posterior structures. The present study uses a recent stereological method that allows quantitation of the myelinated nerve fibers in the brain white matter. As especially the prefrontal region is of interest in schizophrenics, the prefrontal white matter was quantitated separately. The total length of nerve fibers in post-mortem brains was estimated from eight male chronic schizophrenics and nine male controls (age-range: 40–81 years). Samples were taken systematically and randomly from both the entire white matter and selectively from the prefrontal white matter. The biopsies were rotated randomly before sectioning to avoid bias due to the anisotropic nature of nerve fibers. The fibers were counted at light microscopic level at about 10,000× magnification and the fiber diameter of each counted fiber was measured to get the size distribution of the fibers. The schizophrenics had a total of 129,000 km myelinated fibers in the white matter and 25,700 km in the prefrontal white matter, which was non-significantly different from a total of 137,000 km in the entire white matter and 27,600 km in the prefrontal white matter in controls. The size distribution of the fibers in schizophrenics was within normal limits compared to controls. Our results do not show a larger loss of nerve fibers in neither the white matter globally or in the prefrontal white matter of schizophrenics.     

Adult polyglucosan body disease (APBD)

Three patients aged 63, 63 and 74 years had various combinations of progressive lower and upper motor neuron dysfunction, sensory loss, urinary incontinence and dementia. Postmortem examinations in two cases showed moderate cerebral and spinal atrophy, ill-defined areas of incomplete myelin loss in white matter and small necrotic foci in the white matter of gyri, around the basal ganglia and near the dentate nuclei. The main microscopic abnormality was a massive accumulation of PAS-positive polyglucosan bodies (PB) of various sizes and shapes in the cerebral hemispheres, brainstem, cerebellum, spinal cord, nerve roots and nerves. These PB were found in the processes of nerve cells and astrocytes, but not in their perikarya. Similar PB were present in peripheral nerves and in the lungs, heart, liver and kidneys. In the third case, a nerve biopsy revealed several, unusually large, PB in the axons of myelinated fibers. These clinicopathologic features are consistent with adult polyglucosan body disease (APBD) and are distinctive from other conditions in which PB may accumulate. Twelve similar cases have been reported previously. The diagnosis can be made by nerve biopsy. The pathogenesis of APBD is not known, but it may be a polysaccharide storage disease.     

Pathological changes in the vagus nerves in chronic alcoholism

A systematic morphometric examination of the vagus nerves at different levels obtained at autopsy in 4 control subjects and 6 alcoholic patients. Morphometric studies on myelinated fibres were performed on the nerve at the mid-cervical, lung hilum and diaphragmatic levels. In the patients with alcoholic neuropathy there was a significant reduction in density of myelinated fibers in the distal part of the vagus nerves when compared with controls. The more severe distal degeneration in the nerves and the pathological changes of axonal degeneration distally are consistent with the dying back neuropathy. The relation between the secondary segmental demyelination and degeneration of the involved nerves were discussed.     

Distribution of mitochondria along small-diameter myelinated central nervous system axons

Small-diameter myelinated CNS axons are preferentially affected in multiple sclerosis (MS) and in the hereditary spastic paraplegias (HSP), in which the distal axon degenerates. Mitochondrial dysfunction has been implicated in the pathogenesis of these and other disorders involving axonal degeneration. The aim of this study was to determine whether the frequency of axonal mitochondria changes along the length of small-diameter fibers and whether there is a preferential localization to the region of the node of Ranvier. We find that mitochondrial numbers do not change along the length of a myelinated small-diameter fiber, and, in contrast to the peripheral nervous system, there is no tendency for mitochondrial numbers to increase at the node.