Axon damage and repair in multiple sclerosis

Diffusion-derived parameters in lesions, peri-lesion and normal-appearing white matter in multiple sclerosis using tensor, kurtosis and fixel-based analysis

Neuronal damage is the primary cause of long-term disability of multiple sclerosis (MS) patients. Assessment of axonal integrity from diffusion MRI parameters might enable better disease characterisation. 16 diffusion derived measurements from diffusion tensor imaging (DTI), diffusion kurtosis imaging (DKI), and fixel-based analysis (FBA) in lesions, peri-lesion and normal appearing white matter were investigated. Diffusion MRI scans of 11 MS patients were processed to generate DTI, DKI, and FBA images. Fractional anisotropy (FA) and fibre density (FD) were used to assess axonal integrity across brain regions. Subsequently, 359 lesions were identified, and lesion and peri-lesion segmentation was performed using structural T₁w, T₂w, T₂w-FLAIR, and T₁w post-contrast MRI. The segmentations were then used to extract 16 diffusion MRI parameters from lesion, peri-lesion, and contralateral normal appearing white matter (NAWM). The measurements for axonal integrity, DTI-FA, DKI-FA, FBA-FD, produced similar results. All diffusion MRI parameters were affected in lesions as compared to NAWM (p < 0.001), confirming loss of axonal integrity in lesions. In peri-lesions, most parameters, except FBA-FD, were also significantly different from NAWM, although the effect size was smaller than in lesions. The reduction in axonal integrity in peri-lesions, despite unaffected fibre density estimates, suggests an effect of Wallerian degeneration.

Demyelination-Remyelination of the Rat Caudal Cerebellar Peduncle Evaluated with Magnetic Resonance Imaging

Remyelination is common under physiological conditions and usually occurs as a response to a pathological demyelinating event. Its potentiation is an important goal for the development of therapies against pathologies such as multiple sclerosis and white matter injury. Visualization and quantification in vivo of demyelination and remyelination processes are essential for longitudinal studies that will allow the testing and development of pro-myelinating strategies. In this study, ethidium bromide (EB) was stereotaxically injected into the caudal cerebellar peduncle (c.c.p.) in rats to produce demyelination; the resulting lesion was characterized (i) transversally through histology using Black-Gold II (BGII) staining, and (ii) longitudinally through diffusion-weighted magnetic resonance imaging (dMRI), by computing fractional anisotropy (FA) and diffusivity parameters to detect microstructural changes. Using this characterization, we evaluated, in the lesioned c.c.p., the effect of N-butyl-β-carboline-3-carboxylate (β-CCB), a potentiator of GABAergic signaling in oligodendrocytes. The dMRI analysis revealed significant changes in the anisotropic and diffusivity properties of the c.c.p. A decreased FA and increased radial diffusivity (λ_⊥) were evident following c.c.p. lesioning. These changes correlated strongly with an apparent decrease in myelin content as evidenced by BGII. Daily systemic β-CCB administration for 2 weeks in lesioned animals increased FA and decreased λ_⊥, suggesting an improvement in myelination, which was supported by histological analysis. This study shows that structural changes in the demyelination-remyelination of the caudal cerebellar peduncle (DRCCP) model can be monitored longitudinally by MRI, and it suggests that remyelination is enhanced by β-CCB treatment. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

Understanding the Physiopathology Behind Axial and Radial Diffusivity Changes-What Do We Know?

The use of the diffusion tensor imaging (DTI) is rapidly growing in the neuroimaging field. Nevertheless, rigorously performed quantitative validation of DTI pathologic metrics remains very limited owing to the difficulty in co-registering quantitative histology findings with magnetic resonance imaging. The aim of this review is to summarize the existing state-of-the-art knowledge with respect to axial (λ_║) and radial (λ_┴) diffusivity as DTI markers of axonal and myelin damage, respectively. First, we provide technical background for DTI and briefly discuss the specific organization of white matter in bundles of axonal fibers running in parallel; this is the natural target for imaging based on diffusion anisotropy. Second, we discuss the four seminal studies that paved the way for considering axial (λ_║) and radial (λ_┴) diffusivity as potential in vivo surrogate markers of axonal and myelin damage, respectively. Then, we present difficulties in interpreting axial (λ_║) and radial (λ_┴) diffusivity in clinical conditions associated with inflammation, edema, and white matter fiber crossing. Finally, future directions are highlighted. In summary, DTI can reveal strategic information with respect to white matter tracts, disconnection mechanisms, and related symptoms. Axial (λ_║) and radial (λ_┴) diffusivity seem to provide quite consistent information in healthy subjects, and in pathological conditions with limited edema and inflammatory changes. DTI remains one of the most promising non-invasive diagnostic tools in medicine.

Increased white matter radial diffusivity is associated with prefrontal cortical folding deficits in schizophrenia

The neuronal underpinnings of cortical folding alterations in schizophrenia remain unclear. Theories on the physiological development of cortical folds stress the importance of white matter fibers for this process and disturbances of fiber tracts might be relevant for cortical folding alterations in schizophrenia. Nine-teen patients with schizophrenia and 19 healthy subjects underwent T1-weighted MRI and DTI. Cortical folding was computed using a surface based approach. DTI was analyzed using FSL and SPM 5. Radial diffusivity and cortical folding were correlated covering the entire cortex in schizophrenia. Significantly increased radial diffusivity of the superior longitudinal fasciculus (SLF) in the left superior temporal region was negatively correlated with cortical folding of the left dorsolateral prefrontal cortex (DLPFC) in patients, i.e. higher radial diffusivity, as an indicator for disturbed white matter fiber myelination, was associated with lower cortical folding of the left DLPFC. Patients with pronounced alterations of the SLF showed significantly reduced cortical folding in the left DLPFC. Our study provides novel evidence for a linkage between prefrontal cortical folding alterations and deficits in connecting white matter fiber tracts in schizophrenia and supports the notion that the integrity of white matter tracts is crucial for intact morphogenesis of the cortical folds.

Utility of a Multiparametric Quantitative MRI Model That Assesses Myelin and Edema for Evaluating Plaques, Periplaque White Matter, and Normal-Appearing White Matter in Patients with Multiple Sclerosis: A Feasibility Study

BACKGROUND AND PURPOSE

T1 and T2 values and proton density can now be quantified on the basis of a single MR acquisition. The myelin and edema in a voxel can also be estimated from these values. The purpose of this study was to evaluate a multiparametric quantitative MR imaging model that assesses myelin and edema for characterizing plaques, periplaque white matter, and normal-appearing white matter in patients with MS.

MATERIALS AND METHODS

We examined 3T quantitative MR imaging data from 21 patients with MS. The myelin partial volume, excess parenchymal water partial volume, the inverse of T1 and transverse T2 relaxation times (R1, R2), and proton density were compared among plaques, periplaque white matter, and normal-appearing white matter.

RESULTS

All metrics differed significantly across the 3 groups (P < .001). Those in plaques differed most from those in normal-appearing white matter. The percentage changes of the metrics in plaques and periplaque white matter relative to normal-appearing white matter were significantly more different from zero for myelin partial volume (mean, -61.59 ± 20.28% [plaque relative to normal-appearing white matter], and mean, -10.51 ± 11.41% [periplaque white matter relative to normal-appearing white matter]), and excess parenchymal water partial volume (13.82 × 10³ ± 49.47 × 10³% and 51.33 × 10² ± 155.31 × 10²%) than for R1 (-35.23 ± 13.93% and -6.08 ± 8.66%), R2 (-21.06 ± 11.39% and -4.79 ± 6.79%), and proton density (23.37 ± 10.30% and 3.37 ± 4.24%).

CONCLUSIONS

Multiparametric quantitative MR imaging captures white matter damage in MS. Myelin partial volume and excess parenchymal water partial volume are more sensitive to the MS disease process than R1, R2, and proton density.

Expression of brain-derived neurotrophic factor in astrocytes - Beneficial effects of glatiramer acetate in the R6/2 and YAC128 mouse models of Huntington's disease

Glatiramer acetate (GA) is a FDA-approved drug which is licensed for the treatment of relapsing-remitting multiple sclerosis and which may exert neuroprotective effects via brain-derived neurotrophic factor (BDNF). In this study, we investigate effects of GA on BDNF expression especially in astrocytes in vitro and in vivo in brains of R6/2 and YAC128 transgenic mouse models of Huntington's disease (HD) where a pathogenic role of astroglial cells has recently been shown. We show that GA increases the expression of functionally active BDNF in astrocyte culture and in astrocytes of GA treated HD mice. In the brains of these mice, GA decreases neurodegeneration and restores BDNF levels. The beneficial effect of GA in R6/2 mice also comprises reduced weight loss and prolonged life span and, for both models, also improved motor performance. Further studies with this safe and effective drug in HD are warranted.

T1 relaxation maps allow differentiation between pathologic tissue subsets in relapsing-remitting and secondary progressive multiple sclerosis

In an attempt to clarify whether T1 relaxation time mapping may assist in characterizing the pathological brain tissue substrate of multiple sclerosis (MS), we compared the T1 relaxation times of lesions, areas of normal-appearing white matter (NAWM) located proximal to lesions, and areas of NAWM located distant from lesions in 12 patients with the relapsing-remitting and 12 with the secondary progressive (SP) subtype of disease. Nine healthy volunteers served as controls. Calculated mean T1 values were averaged across all patients within each clinical group, and comparisons were made by means of the Mann-Whitney U-test. Significant differences were found between all investigated brain regions within each clinical subgroup. Significant differences were also detected for each investigated brain region among clinical subgroups. While T1 values of NAWM were significantly higher in patients with SP disease than in normal white matter (NWM) of controls, no differences were detected when corresponding brain areas of patients with RR MS were compared with NWM of controls. T1 maps identify areas of the brain that are damaged to a different extent in patients with MS, and may be of help in monitoring disease progression.

Associations of white matter integrity and cortical thickness in patients with schizophrenia and healthy controls

Typical brain development includes coordinated changes in both white matter (WM) integrity and cortical thickness (CT). These processes have been shown to be disrupted in schizophrenia, which is characterized by abnormalities in WM microstructure and by reduced CT. The aim of this study was to identify patterns of association between WM markers and cortex-wide CT in healthy controls (HCs) and patients with schizophrenia (SCZ). Using diffusion tensor imaging and structural magnetic resonance imaging data of the Mind Clinical Imaging Consortium study (130 HC and 111 SCZ), we tested for associations between (a) fractional anisotropy in selected manually labeled WM pathways (corpus callosum, anterior thalamic radiation, and superior longitudinal fasciculus) and CT, and (b) the number of lesion-like WM regions ("potholes") and CT. In HC, but not SCZ, we found highly significant negative associations between WM integrity and CT in several pathways, including frontal, temporal, and occipital brain regions. Conversely, in SCZ the number of WM potholes correlated with reduced CT in the left lateral temporal gyrus, left fusiform, and left lateral occipital brain area. Taken together, we found differential patterns of association between WM integrity and CT in HC and SCZ. Although the pattern in HC can be explained from a developmental perspective, the reduced gray matter CT in SCZ patients might be the result of focal but spatially heterogeneous disruptions of WM integrity.

IL7Rα contributes to experimental autoimmune encephalomyelitis through altered T cell responses and nonhematopoietic cell lineages

A mutation in the IL7Rα locus has been identified as a risk factor for multiple sclerosis (MS), a neurodegenerative autoimmune disease characterized by inflammation, demyelination, and axonal damage. IL7Rα has well documented roles in lymphocyte development and homeostasis, but its involvement in disease is largely understudied. In this study, we use the experimental autoimmune encephalomyelitis (EAE) model of MS to show that a less severe form of the disease results when IL7Rα expression is largely restricted to thymic tissue in IL7RTg(IL7R-/-) mice. Compared with wild-type (WT) mice, IL7RTg(IL7R-/-) mice exhibited reduced paralysis and myelin damage that correlated with dampened effector responses, namely decreased TNF production. Furthermore, treatment of diseased WT mice with neutralizing anti-IL7Rα Ab also resulted in significant improvement of EAE. In addition, chimeric mice were generated by bone marrow transplant to limit expression of IL7Rα to cells of either hematopoietic or nonhematopoietic origin. Mice lacking IL7Rα only on hematopoietic cells develop severe EAE, suggesting that IL7Rα expression in the nonhematopoietic compartment contributes to disease. Moreover, novel IL7Rα expression was identified on astrocytes and oligodendrocytes endogenous to the CNS. Chimeric mice that lack IL7Rα only on nonhematopoietic cells also develop severe EAE, which further supports the role of IL7Rα in T cell effector function. Conversely, mice that lack IL7Rα throughout both compartments are dramatically protected from disease. Taken together, these data indicate that multiple cell types use IL7Rα signaling in the development of EAE, and inhibition of this pathway should be considered as a new therapeutic avenue for MS.

Increased axonal expression of nectin-1 in multiple sclerosis plaques

Nectin-1 is a cell adhesion molecule that plays a role in interneuronal synapse formation, in axonal guidance during development and possibly in neuron-glia interactions. To better understand axonal changes in MS, nectin-1 expression was determined by immunohistochemistry in normal adult human cerebral white matter (n = 4) and in six MS plaques (three active and three inactive). The intensity of axonal nectin-1 expression was scored on a scale of 0 to 4+. In normal adult cerebral white matter, axons showed weak nectin-1 expression with a score of 1.25 ± 0.50. Axonal nectin-1 expression was significantly stronger within both active (score = 3.33 ± 0.289, p = 0.001) and inactive (score = 2.16 ± 0.29, p = 0.038) MS plaques than in normal white matter. Axons in white matter adjacent to MS plaques showed nectin-1 expression (score = 1.5 ± 0.50) that was not statistically different from normal controls (p = 0.542). These findings raise the possibility that increased expression of nectin-1 in MS lesions plays a role in the pathogenesis of MS through participation in axonal responses to injury and mediation of altered neuron-glia interactions relevant to myelination.

Simulation of spread and control of lesions in brain

A simulation model for the spread and control of lesions in the brain is constructed using a planar network (graph) representation for the central nervous system (CNS). The model is inspired by the lesion structures observed in the case of multiple sclerosis (MS), a chronic disease of the CNS. The initial lesion site is at the center of a unit square and spreads outwards based on the success rate in damaging edges (axons) of the network. The damaged edges send out alarm signals which, at appropriate intensity levels, generate programmed cell death. Depending on the extent and timing of the programmed cell death, the lesion may get controlled or aggravated akin to the control of wild fires by burning of peripheral vegetation. The parameter phase space of the model shows smooth transition from uncontrolled situation to controlled situation. The simulations show that the model is capable of generating a wide variety of lesion growth and arrest scenarios.

Disrupted white matter connectivity is associated with reduced cortical thickness in the cingulate cortex in schizophrenia

INTRODUCTION

Both impaired white matter connectivity and alterations in gray matter morphometry have repeatedly been reported in schizophrenia. Neurodevelopmental models propose a close linkage between gray matter alterations and white matter deficits. However, there are no studies investigating alterations in cortical thickness in relation to white matter connectivity changes.

METHODS

This combined diffusion tensor imaging (DTI) - surface based morphometry study examined a potential linkage between disruption in white matter connectivity and alterations in cortical thickness. Cortical thickness was analyzed using the FreeSurfer software package (version 4.0.5, http://surfer.nmr.harvard.edu) in a sample of 19 patients with schizophrenia and 20 healthy controls.

RESULTS

Whole brain node-by-node correlational analysis revealed a highly significant association ( r= -.8, p < .0001) between disturbed white matter connectivity in the superior temporal cortex and diminished cortical thickness in the posterior part of the cingulate cortex (Brodmann area 23/31).

CONCLUSIONS

This result indicates a significant linkage between disturbed white matter connectivity and reduced cortical thickness in a relevant node of the default mode network that is held to be of high pathophysiological relevance in schizophrenia. The result moreover provides support for the assumption of a neurodevelopmental pathogenesis of the disorder.

Delayed axonal degeneration in slow Wallerian degeneration mutant mice detected using diffusion tensor imaging

Previous studies have shown the feasibility of using diffusion tensor imaging (DTI) as a noninvasive imaging modality to evaluate neurodegeneration in humans and animals. The axial and radial diffusivities derived from DTI were demonstrated to be sensitive markers for axonal and myelin damage, respectively. This study used DTI to evaluate optic nerve degeneration in wild-type and slow Wallerian degeneration (Wld(S)) mutant mice. Longitudinal DTI was performed on optic nerves following high intraocular pressure-induced transient retinal ischemia. The axial diffusivity of wild-type nerves decreased 30% (P<0.05) at 3 days and 40% (P<0.05) at 5-30 days after transient elevation of intraocular pressure. In contrast, the axial diffusivity of Wld(S) nerves did not change at 3 days; decreased by 20% (P<0.05) at 5 days, and continued to decrease by 30% (P<0.05) at 15 days and 40% (P<0.05) at 30 days after transient intraocular pressure elevation, suggesting delayed axonal damage in Wld(S) mice. Radial diffusivity increased 200% (P<0.05) at 15-30 days in the wild-type mice and 100% (P<0.05) at 30 days in the Wld(S) mice after transient intraocular pressure elevation, suggesting delayed myelin damage in Wld(S) mice. DTI detected damage was confirmed with immunohistochemistry using phosphorylated neurofilament and myelin basic protein for assessing axonal and myelin integrity, respectively. These findings support the use of DTI not only to evaluate the progression of neurodegeneration but also to noninvasively demonstrate Wld(S) mutation to delay the Wallerian degeneration.

Spatiotemporal distribution pattern of white matter lesion volumes and their association with regional grey matter volume reductions in relapsing-remitting multiple sclerosis

The association of white matter (WM) lesions and grey matter (GM) atrophy is a feature in relapsing-remitting multiple sclerosis (RRMS). The spatiotemporal distribution pattern of WM lesions, their relations to regional GM changes and the underlying dynamics are unclear. Here we combined parametric and non-parametric voxel-based morphometry (VBM) to clarify these issues. MRI data from RRMS patients with progressive (PLV, n = 45) and non-progressive WM lesion volumes (NPLV, n = 44) followed up for 12 months were analysed. Cross-sectionally, the spatial WM lesion distribution was compared using lesion probability maps (LPMs). Longitudinally, WM lesions and GM volumes were studied using FSL-VBM and SPM5-VBM, respectively. WM lesions clustered around the lateral ventricles and in the centrum semiovale with a more widespread pattern in the PLV than in the NPLV group. The maximum local probabilities were similar in both groups and higher for T2 lesions (PLV: 27%, NPLV: 25%) than for T1 lesions (PLV: 15%, NPLV 14%). Significant WM lesion changes accompanied by cortical GM volume reductions occurred in the corpus callosum and optic radiations (P = 0.01 corrected), and more liberally tested (uncorrected P < 0.01) in the inferior fronto-occipital and longitudinal fasciculi, and corona radiata in the PLV group. Not any WM or GM changes were found in the NPLV group. In the PLV group, WM lesion distribution and development in fibres, was associated with regional GM volume loss. The different spatiotemporal distribution patterns of patients with progressive compared to patients with non-progressive WM lesions suggest differences in the dynamics of pathogenesis.

Gray- and white-matter changes 1 year after first clinical episode of multiple sclerosis: MR imaging

PURPOSE

To assess, by means of magnetic resonance (MR) imaging, the longitudinal changes in white matter (WM) and gray matter (GM) in a cohort of patients with clinically isolated syndrome (CIS) who were followed up for 1 year.

MATERIALS AND METHODS

This prospective, HIPAA-compliant study was approved by the institutional review board. Written informed consent was obtained from all the participants. Changes in GM and WM integrity were respectively investigated by using three-dimensional T1-weighted and diffusion-tensor (DT) imaging sequences and by applying voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) analyses. Thirty-four consecutive patients (21 women, 13 men; mean age, 32.8 years ± 7.7 [standard deviation]) who had CIS were recruited. All the patients underwent a neurologic and an MR examination at baseline and 12 months later; the MR examination consisted of three-dimensional T1-weighted dual-echo turbo spin-echo DT imaging. VBM and TBSS were used to analyze GM volume and WM fractional anisotropy, respectively.

RESULTS

After 1 year, multiple sclerosis (MS) was diagnosed in 33 (97%) of 34 patients with CIS. Longitudinal volumetric analysis revealed a significant (P < .001) reduction in global GM volume. The VBM analysis showed the development of regional GM atrophy involving several cortical and subcortical regions in both hemispheres (P < .05). No significant longitudinal change in global or regional WM fractional anisotropy was otherwise observed.

CONCLUSION

WM damage was detectable early and involved most fiber tracts in patients with MS, but it did not worsen significantly during the 1st year after clinical onset. In contrast, GM damage was not detectable at the time of clinical onset, but a significant decrease in cortical and deep GM volume was observed at 1 year.

Understanding the roles of the kynurenine pathway in multiple sclerosis progression

The kynurenine pathway (KP) is a major degradative pathway of tryptophan ultimately leading to the production of nicotinamide adenine dinucleotide (NAD⁺) and is also one of the major regulatory mechanisms of the immune response. The KP is known to be involved in several neuroinflammatory disorders including Alzheimer’s disease, amyotrophic lateral sclerosis, AIDS dementia complex, Parkinson’s disease, schizophrenia, Huntington’s disease and brain tumours. However, the KP remains a relatively new topic for the field of multiple sclerosis (MS). Over the last 2–3 years, some evidence has progressively emerged suggesting that the KP is likely to be involved in the pathogenesis of autoimmune diseases especially MS. Some KP modulators are already in clinical trials for other inflammatory diseases and would potentially provide a new and important therapeutic strategy for MS patients. This review summarizes the known relationships between the KP and MS.

Major histocompatibility complex class I expression and glial reaction influence spinal motoneuron synaptic plasticity during the course of experimental autoimmune encephalomyelitis

Recent studies have shown that major histocompatibility complex class I (MHC I) expression directly influences the stability of nerve terminals. Also, the acute phase of experimental autoimmune encephalomyelitis (EAE) has shown a significant impact on inputs within the spinal cord. Therefore, the present work investigated the synaptic covering of motoneurons during the induction phase of disease and progressive remissions of EAE. EAE was induced in C57BL/6J mice, which were divided into four groups: normal, peak disease, first remission, and second remission. The animals were killed and their lumbar spinal cords processed for in situ hybridization (IH), immunohistochemistry, and transmission electron microscopy (TEM). The results indicated an increase in glial reaction during the peak disease. During this period, the TEM analysis showed a reduction in the synaptic covering of the motoneurons, corresponding to a reduction in synaptophysin immunolabeling and an increase in the MHC I expression. The IH analysis reinforced the immunolabeling results, revealing an increased expression of MHC I mRNA by motoneurons and nonneuronal cells during the peak disease and first remission. The results observed in both remission groups indicated a return of the terminals to make contact with the motoneuron surface. The ratio between excitatory and inhibitory inputs increased, indicating the potential for development of an excitotoxic process. In conclusion, the results presented here indicate that MHC I up-regulation during the course of EAE correlates with the periods of synaptic plasticity induced by the infiltration of autoreactive immune cells and that synaptic plasticity decreases after recurrent peaks of inflammation.

Clinically isolated syndrome suggestive of multiple sclerosis: voxelwise regional investigation of white and gray matter

PURPOSE

To quantify white matter (WM) and gray matter (GM) damage in patients who presented with clinically isolated syndrome (CIS), which is suggestive of multiple sclerosis (MS), by combining volume-based morphometry (VBM) and tract-based spatial statistics (TBSS).

MATERIALS AND METHODS

This prospective HIPAA-compliant study was approved by the institutional review board. Written informed consent was obtained from all participants. In this study, 34 consecutive patients (21 women, 13 men; mean age, 31.7 years +/- 7.7 [standard deviation]) who presented with CIS were recruited. The magnetic resonance (MR) examination included dual-echo fast spin-echo, three-dimensional T1, and diffusion-tensor imaging. Sixteen matched healthy volunteers served as control subjects. T2 lesion volumes were assessed with a semiautomatic technique. VBM and TBSS were used for the GM and WM analyses, respectively, to compare regional GM volumes and fractional anisotropy (FA) values in the two groups.

RESULTS

TBSS analysis revealed a pattern of diffuse FA reductions in patients with CIS at the cluster level (P < .05). Regions of decreased FA involved most of the WM pathways, including the corticospinal tracts, corpus callosum, and superior and inferior longitudinal fasciculi. There were no significant differences between the two groups in terms of global GM, WM, or cerebrospinal fluid volume or in terms of regional GM volume.

CONCLUSION

Diffuse WM damage not accompanied by any change in GM or WM volume is observed in patients with CIS. This suggests that WM involvement plays a relevant role in the early phases of MS. Subsequently detected GM damage may be secondary to WM alterations.

Loss of translation elongation factor (eEF1A2) expression in vivo differentiates between Wallerian degeneration and dying-back neuronal pathology

Wallerian degeneration and dying-back pathology are two well-known cellular pathways capable of regulating the breakdown and loss of axonal and synaptic compartments of neurons in vivo. However, the underlying mechanisms and molecular triggers of these pathways remain elusive. Here, we show that loss of translation elongation factor eEF1A2 expression in lower motor neurons and skeletal muscle fibres in homozygous Wasted mice triggered a dying-back neuropathy. Synaptic loss at the neuromuscular junction occurred in advance of axonal pathology and by a mechanism morphologically distinct from Wallerian degeneration. Dying-back pathology in Wasted mice was accompanied by reduced expression levels of the zinc finger protein ZPR1, as found in other dying-back neuropathies such as spinal muscular atrophy. Surprisingly, experimental nerve lesion revealed that Wallerian degeneration was significantly delayed in homozygous Wasted mice; morphological assessment revealed that approximately 80% of neuromuscular junctions in deep lumbrical muscles at 24 h and approximately 50% at 48 h had retained motor nerve terminals following tibial nerve lesion. This was in contrast to wild-type and heterozygous Wasted mice where < 5% of neuromuscular junctions had retained motor nerve terminals at 24 h post-lesion. These data show that eEF1A2 expression is required to prevent the initiation of dying-back pathology at the neuromuscular junction in vivo. In contrast, loss of eEF1A2 expression significantly inhibited the initiation and progression of Wallerian degeneration in vivo. We conclude that loss of eEF1A2 expression distinguishes mechanisms underlying dying-back pathology from those responsible for Wallerian degeneration in vivo and suggest that eEF1A2-dependent cascades may provide novel molecular targets to manipulate neurodegenerative pathways in lower motor neurons.

Medulla oblongata volume: a biomarker of spinal cord damage and disability in multiple sclerosis

BACKGROUND AND PURPOSE

While brain MR imaging is routinely performed, the MR imaging assessment of spinal cord pathology in multiple sclerosis (MS) is less frequent in clinical practice. The purpose of this study was to determine whether measurements of medulla oblongata volume (MOV) on routine brain MR imaging could serve as a biomarker of spinal cord damage and disability in MS.

MATERIALS AND METHODS

We identified 45 patients with MS with both head and cervical spinal cord MR imaging and 29 age-matched and sex-matched healthy control subjects with head MR imaging. Disability was assessed by the expanded disability status scale (EDSS) and ambulation index (AI). MOV and upper cervical cord volume (UCCV) were manually segmented; semiautomated segmentation was used for brain parenchymal fraction (BPF). These measures were compared between groups, and linear regression models were built to predict disability.

RESULTS

In the patients, MOV correlated significantly with UCCV (r = 0.67), BPF (r = 0.45), disease duration (r = -0.64), age (r = -0.47), EDSS score (r = -0.49) and AI (r = -0.52). Volume loss of the medulla oblongata was -0.008 cm(3)/year of age in patients with MS, but no significant linear relationship with age was found for healthy control subjects. The patients had a smaller MOV (mean +/- SD, 1.02 +/- 0.17 cm(3)) than healthy control subjects (1.15 +/- 0.15 cm(3)), though BPF was unable to distinguish between these 2 groups. MOV was smaller in patients with progressive MS (secondary- progressive MS, 0.88 +/- 0.19 cm(3) and primary-progressive MS, 0.95 +/- 0.30 cm(3)) than in patients with relapsing-remitting MS (1.08 +/- 0.15 cm(3)). A model including both MOV and BPF better predicted AI than BPF alone (P = .04). Good reproducibility in MOV measurements was demonstrated for intrarater (intraclass correlation coefficient, 0.97), interrater (0.79), and scan rescan data (0.81).

CONCLUSION

MOV is associated with disability in MS and can serve as a biomarker of spinal cord damage.

Evaluation of white matter in patients with multiple sclerosis through diffusion tensor magnetic resonance imaging

OBJECTIVE: To study the white matter of patients with multiple sclerosis (MS) with diffusion tensor magnetic resonance (MR) imaging (DTI). METHOD: Forty patients with clinical-laboratorial diagnosis of relapsing-remitting MS and 40 age- and sex-matched controls, who underwent conventional and functional (DTI) MR imaging, were included in the study. The DTI sequences resulted in maps of fractional anisotropy (FA) and regions of interest were placed on the plaques, peri-plaque regions, normal-appearing white matter (NAWM) around the plaques, contralateral normal white matter (CNWM) and normal white matter of the controls (WMC). The FA values were compared and the statistical treatment was performed with the Mann-Whitney U test. RESULTS: The mean FA in plaques was 0.268, in peri-plaque regions 0.365, in NAWM 0.509, in CNWM 0.552 and in WMC 0.573. Statistical significant differences in FA values were observed in plaques, peri-plaque regions and in NAWM around the plaques when compared to the white matter in the control group. There was no significant difference between the FA values of the CNWM of patients with MS and normal white matter of controls. CONCLUSION: Patients with MS show difference in the FA values of the plaques, peri-plaques and NAWM around the plaques when compared to the normal white matter of controls. As a result, DTI may be considered more efficient than conventional MR imaging for the study of patients with MS.

Brain atrophy in multiple sclerosis: what we know and would like to know

Brain and spinal cord atrophy measures are becoming standard in multiple sclerosis (MS) clinical trials, yet we know little about the underlying mechanisms resulting in atrophy, or the factors accounting for variable rates of atrophy in individuals and across the MS phenotype. We do not understand, as yet, why apparently effective treatment does or does not affect atrophy. Some limitations of this measure may be accounted for by complex structural and temporal factors that become active at the initiation of injury, but are not immediately expressed. Additional limitations include differential effects related to the focal versus diffuse pathology in MS, and variable expression of the pathology underlying atrophy, depending on location in central nervous system (CNS) tissue.

Glatiramer Acetate: Mechanisms of Action in Multiple Sclerosis

Glatiramer acetate (GA), formerly known as copolymer 1, is a mixture of synthetic polypeptides composed of four amino acids resembling the myelin basic protein (MSP). GA has been shown to be highly effective in preventing and suppressing experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). Therefore, it was tested in several clinical studies and so approved for the immunomodulatory treatment of relapsing-type MS. In contrast to other immunomodulatory MS therapies, GA has a distinct mechanism of action: GA demonstrates an initial strong promiscuous binding to major histocompatibility complex molecules and consequent competition with various (myelin) antigens for their presentation to T cells. In addition, antigen-based therapy generating a GA-specific immune response seems to be the prerequisite for GA therapy. GA treatment induces an in vivo change of the frequency, cytokine secretion pattern and the effector function of GA-specific CD4+ and CD8+ T cells, probably by affecting the properties of antigen-presenting cells such as monocytes and dendritic cells. As demonstrated extensively in animal experiments, GA-specific, mostly, T helper 2 cells migrate to the brain and lead to in situ bystander suppression of the inflammatory process in the brain. Furthermore, GA-specific cells in the brain express neurotrophic factors like the brain-derived neurotrophic factor (BDNF) in addition to anti-inflammatory T helper 2-like cytokines. This might help tip the balance in favor of more beneficial influences because there is a complex interplay between detrimental and beneficial factors and mediators in the inflammatory milieu of MS lesions.

Anatomical changes in the emerging adult brain: a voxel-based morphometry study

Research has consistently confirmed changes occur in brain morphometry between adolescence and adulthood. The purpose of the present study was to explore anatomical change during a specific environmental transition. High-resolution T1-weighted structural magnetic resonance imaging (MRI) scans were acquired from 19 participants (mean age at initial scan = 18.6 years) during their freshman year. Scans were completed during the fall term and 6 months later before the conclusion of the school year. Voxel-based morphometry was used to assess within-subject change. Significant intensity increases were observed along the right midcingulate, inferior anterior cingulate gyrus, right caudate head, right posterior insula, and bilateral claustrum. Regional changes were not observed in two control groups; one controlling for method and another controlling for age-specific change over time. The results suggest that significant age-related changes in brain structure continue after the age of 18 and may represent dynamic changes related to new environmental challenges. Findings from the regions of change are discussed in the context of specific environmental demands during a period of normative maturation.

Neuroprotection by ovarian hormones in animal models of neurological disease

Ovarian hormones can protect against brain injury, neurodegeneration, and cognitive decline. Most attention has focused on estrogens and accumulating data demonstrate that estrogen seems to specifically protect cortical and hippocampal neurons from ischemic injury and from damage due to severe seizures. Although multiple studies demonstrate protection by estrogen, in only a few instances is the issue of how the steroid confers protection known. Here, we first review data evaluating the neuroprotective effects of estrogens, a selective estrogen receptor modulator (SERM), and estrogen receptor alpha- and beta-selective ligands in animal models of focal and global ischemia. Using focal ischemia in ovariectomized ERalphaKO, ERbetaKO, and wild-type mice, we clearly established that the ERalpha subtype is the critical ER mediating neuroprotection in mouse focal ischemia. In rats and mice, the middle cerebral artery occlusion (MCAO) model was used to represent cerebrovascular stroke, while in gerbils the two-vessel occlusion model, representing global ischemia, was used. The gerbil global ischemia model was used to evaluate the neuroprotective effects of estrogen, SERMs, and ERalpha- and ERbeta-selective compounds in the hippocampus. Analysis of neurogranin mRNA, a marker of viability of hippocampal neurons, with in situ hybridization, revealed that estrogen treatment protected the dorsal CA1 regions not only when administered before, but also when given 1 h after occlusion. Estrogen rarely is secreted alone and studies of neuroprotection have been less extensive for a second key ovarian hormone progesterone. In the second half of this review, we present data on neuroprotection by estrogen and progesterone in animal model of epilepsy followed by exploration into ovarian steroid effects on neuronal damage in models of multiple sclerosis and traumatic brain injury.

Noninvasive detection of cuprizone induced axonal damage and demyelination in the mouse corpus callosum

Previously, we tested the prediction that axonal damage results in decreased axial diffusivity (lambda(parallel)) while demyelination leads to increased radial diffusivity (lambda(perpendicular)). Cuprizone treatment of C57BL/6 mice was a highly reproducible model of CNS white matter demyelination and remyelination affecting the corpus callosum (CC). In the present study, six C57BL/6 male mice were fed 0.2% cuprizone for 12 weeks followed by 12 weeks of recovery on normal chow. The control mice were fed normal chow and imaged in parallel. Biweekly in vivo DTI examinations showed transient decrease of lambda(parallel) in CC at 2-6 weeks of cuprizone treatment. Immunostaining for nonphosphorylated neurofilaments demonstrated corresponding axonal damage at 4 weeks of treatment. Significant demyelination was evident from loss of Luxol fast blue staining at 6-12 weeks of cuprizone ingestion and was paralleled by increased lambda(perpendicular) values, followed by partial normalization during the remyelination phase. The sensitivity of lambda(perpendicular) to detect demyelination may be modulated in the presence of axonal damage during the early stage of demyelination at 4 weeks of cuprizone treatment. Our results suggest that lambda(parallel) and lambda(perpendicular) may be useful in vivo surrogate markers of axonal and myelin damage in mouse CNS white matter.

Axon loss is responsible for chronic neurological deficit following inflammatory demyelination in the rat

Axonal loss is now considered a consistent feature of MS pathology and evidence suggests that its accumulation may be the pathological correlate for the development of irreversible disability. In this study, we investigated the features of axonal loss in myelin autoimmunity and tested the hypothesis that loss of axons determines permanent neurological impairment in a model of inflammatory demyelination that closely mimics the pathology and course of MS. EAE was induced in DA rats by injection of recombinant mouse MOG with IFA. Animals that developed progressive EAE were killed at several time points after disease onset and animals that followed a chronic relapsing-remitting course of EAE were killed at approximately 4 months, exhibiting varying degrees of residual disability. Toluidine blue staining of semithin sections and immunohistochemistry for OX-42 were used to quantify demyelination, remyelination, inflammation and axonal loss in the spinal cord of MOG-EAE rats. In progressive EAE, the degree of axon loss, demyelination and inflammation all correlated significantly with clinical severity scores and a causative role for macrophages in the pathogenesis of axonal injury is suggested. However, in the chronic stage of relapsing-remitting EAE, in rats having suffered a variable number of relapses, only axonal loss correlated significantly with clinical severity scores. In addition, both axonal loss and clinical severity scores correlated with the number of relapses. These findings imply that secondary, or 'bystander', axonal loss is the main determinant of irreversible neurological disability in MOG-EAE and make the model a useful tool for the investigation of mechanisms of axonal loss and the evaluation of the benefits of neuroprotective therapies under conditions of antibody-mediated inflammatory demyelination.

Demyelination increases radial diffusivity in corpus callosum of mouse brain

Myelin damage, as seen in multiple sclerosis (MS) and other demyelinating diseases, impairs axonal conduction and can also be associated with axonal degeneration. Accurate assessments of these conditions may be highly beneficial in evaluating and selecting therapeutic strategies for patient management. Recently, an analytical approach examining diffusion tensor imaging (DTI) derived parameters has been proposed to assess the extent of axonal damage, demyelination, or both. The current study uses the well-characterized cuprizone model of experimental demyelination and remyelination of corpus callosum in mouse brain to evaluate the ability of DTI parameters to detect the progression of myelin degeneration and regeneration. Our results demonstrate that the extent of increased radial diffusivity reflects the severity of demyelination in corpus callosum of mouse brain affected by cuprizone treatment. Subsequently, radial diffusivity decreases with the progression of remyelination. Furthermore, radial diffusivity changes were specific to the time course of changes in myelin integrity as distinct from axonal injury, which was detected by betaAPP immunostaining and shown to be most extensive prior to demyelination. Radial diffusivity offers a specific assessment of demyelination and remyelination, as distinct from acute axonal damage.

Motor neuron pathology in experimental autoimmune encephalomyelitis: studies in THY1-YFP transgenic mice

Using adult male C57BL/6 mice that express a yellow fluorescent protein transgene in their motor neurons, we induced experimental autoimmune encephalomyelitis (EAE) by immunization with myelin oligodendrocyte glycoprotein peptide 35-55 (MOG peptide) in complete Freund's adjuvant (CFA). Control mice of the same transgenic strain received CFA without MOG peptide. Early in the course of their illness, the EAE mice showed lumbosacral spinal cord inflammation, demyelination and axonal fragmentation. By 14 weeks post-MOG peptide, these abnormalities were much less prominent, but the mice remained weak and, as in patients with progressive multiple sclerosis, spinal cord atrophy had developed. There was no significant loss of lumbar spinal cord motor neurons in the MOG peptide-EAE mice. However, early in the course of the illness, motor neuron dendrites were disrupted and motor neuron expression of hypophosphorylated neurofilament-H (hypoP-NF-H) immunoreactivity was diminished. By 14 weeks post-MOG peptide, hypoP-NF-H expression had returned to normal, but motor neuron dendritic abnormalities persisted and motor neuron perikaryal atrophy had appeared. We hypothesize that these motor neuron abnormalities contribute to weakness in this form of EAE and speculate that similar motor neuron abnormalities are present in patients with progressive multiple sclerosis.

Diffusion tensor imaging detects and differentiates axon and myelin degeneration in mouse optic nerve after retinal ischemia

Both axon and myelin degeneration have significant impact on the long-term disability of patients with white matter disorder. However, the clinical manifestations of the neurological dysfunction caused by white matter disorders are not sufficient to determine the origin of neurological deficits. A noninvasive biological marker capable of detecting and differentiating axon and myelin degeneration would be a significant addition to currently available tools. Directional diffusivities derived from diffusion tensor imaging (DTI) have been previously proposed by this group as potential biological markers to detect and differentiate axon and myelin degeneration. To further test the hypothesis that axial (lambdaparallel) and radial (lambdaperpendicular) diffusivities reflect axon and myelin pathologies, respectively, the optic nerve was examined serially using DTI in a mouse model of retinal ischemia. A significant decrease of lambdaparallel, the putative DTI axonal marker, was observed 3 days after ischemia without concurrently detectable changes in lambdaperpendicular, the putative myelin marker. This result is consistent with histological findings of significant axonal degeneration with no detectable demyelination at 3 days after ischemia. The elevation of lambdaperpendicular observed 5 days after ischemia is consistent with histological findings of myelin degeneration at this time. These results support the hypothesis that lambdaparallel and lambdaperpendicular hold promise as specific markers of axonal and myelin injury, respectively, and, further, that the coexistence of axonal and myelin degeneration does not confound this utility.

Regulation of cytokine-induced neuron death by ovarian hormones: involvement of antiapoptotic protein expression and c-JUN N-terminal kinase-mediated proapoptotic signaling

Mechanisms underlying the divergent effects of ovarian hormones on neuron death induced by TNFalpha were investigated in differentiated PC12 cells (dPC12). dPC12 cells were exposed to 17beta-estradiol (E, 1.0 nm), progesterone (P, 100 nm), or a combination of both hormones for 0-72 h before treatment with TNFalpha (0-150 ng) to induce cell death. Cells undergoing apoptosis were identified by a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling assay and fluorescence-activated cell sorting after 18 h. Cell death induced by TNFalpha was decreased 89% after E treatment and increased 2-fold after P treatment compared with cells treated with TNFalpha alone. Treatment with E for 24 h before TNFalpha exposure was required for maximum neuroprotection, whereas P-enhanced death was maximal after a 30-min P treatment. TNFalpha induced a 3-fold increased activity of c-JUN-N-terminal kinase (JNK) 1 in d PC12 cells within 20 min that could be increased 5- to 8-fold by P together with TNFalpha. A peptide inhibitor of JNK1 abrogated P enhancement of TNFalpha-mediated dPC12 death but had only a minimal effect on cell death by TNFalpha alone. Inhibition of caspase-8 activation reduced death induced by TNFalpha alone but was much less effective for P+TNF. P alone did not activate caspase-8. E increased estrogen receptor alpha (ERalpha) and Bcl-xL expression and all but abolished TNFalpha receptor 1 (TNFR1) expression. P decreased ERalpha and Bcl-xL expression and doubled TNFR1 expression. These data suggest that P regulates apoptosis or survival through augmentation of JNK signaling and altered TNFR1 expression, whereas E mainly affects the expression of BCL-xL, TNFR1, and ERalpha.

Neurites undergoing Wallerian degeneration show an apoptotic-like process with Annexin V positive staining and loss of mitochondrial membrane potential

Wallerian degeneration, the disintegration of the distal part of an injured axon, is an important event in many neurodegenerative diseases. We studied Wallerian degeneration in dorsal root ganglion (DRG) explants in culture by separating neurites from their cell bodies with a scalpel. The severed neurites showed Annexin V positive staining, that spreads distally with a rate comparable to that of slow axonal transport in intact neurons in vivo. Moreover, the injured neurites showed loss of mitochondrial membrane potential. These features resemble those seen when cells undergo apoptosis. These data contribute to a new understanding of the mechanism of axonal degeneration, have implications for the response of stromal cells in central nervous system (CNS) and raise the prospect of new pharmacological treatments for those neurodegenerative pathologies where the protection of the cell body alone does not alleviate the disease.

Axonal injury heralds virus-induced demyelination

Axonal pathology has been highlighted as a cause of neurological disability in multiple sclerosis. The Daniels (DA) strain of Theiler's murine encephalomyelitis virus infects the gray matter of the central nervous system of mice during the acute phase and persistently infects the white matter of the spinal cord during the chronic phase, leading to demyelination. This experimental infection has been used as an animal model for multiple sclerosis. The GDVII strain causes an acute fatal polioencephalomyelitis without demyelination. Injured axons were detected in normal appearing white matter at 1 week after infection with DA virus by immunohistochemistry using antibodies specific for neurofilament protein. The number of damaged axons increased throughout time. By 2 and 3 weeks after infection, injured axons were accompanied by parenchymal infiltration of Ricinus communis agglutinin I(+) microglia/macrophages, but never associated with perivascular T-cell infiltration or obvious demyelination until the chronic phase. GDVII virus infection resulted in severe axonal injury in normal appearing white matter at 1 week after infection, without the presence of macrophages, T cells, or viral antigen-positive cells. The distribution of axonal injury observed during the early phase corresponded to regions where subsequent demyelination occurs during the chronic phase. The results suggest that axonal injury might herald or trigger demyelination.

Autoimmunity as a special case of immunity: removing threats from within

The function of the adaptive immune response against exogenous (non-self) agents is to help the innate arm of the immune system (represented by phagocytic cells) to fight and eliminate these agents. We suggest that the body also protects itself against potentially harmful self components using mechanisms similar to those used for fighting and eliminating non-self agents, and that the protective immune activity against self-components competes with the activity of self-destructive compounds. Tolerance to self is thus not a lack of response to self, but the ability to tolerate an active defense response to self without developing an autoimmune disease.

Early nuclear exclusion of the transcription factor max is associated with retinal ganglion cell death independent of caspase activity

We examined the behavior of the transcription factor Max during retrograde neuronal degeneration of retinal ganglion cells. Using immunohistochemistry, we found a progressive redistribution of full-length Max from the nucleus to the cytoplasm and dendrites of the ganglion cells following axon damage. Then, the axotomized cells lose all their content of Max, while undergoing nuclear pyknosis and apoptotic cell death. After treatment of retinal explants with either anisomycin or thapsigargin, the rate of nuclear exclusion of Max accompanied the rate of cell death as modulated by either drug. Treatment with a pan-caspase inhibitor abolished both TUNEL staining and immunoreactivity for activated caspase-3, but did not affect the subcellular redistribution of Max immunoreactivity after axotomy. The data show that nuclear exclusion of the transcription factor Max is an early event, which precedes and is independent of the activation of caspases, during apoptotic cell death in the central nervous system.

Autoimmunity as the body's defense mechanism against the enemy within: Development of therapeutic vaccines for neurodegenerative disorders

Insults to the central nervous system (CNS), whether of microbial or microbe-free origin, result in tissue damage. Until recently, it was generally believed that only microbe-related damage elicits an adaptive immune response, the purpose of which is to eliminate the offending microorganisms. Recent studies in the author's laboratory suggest, however, that the body exhibits an adaptive immune response to microbe-free injuries as well. The immune response in this case is directed against dominant self-antigens residing in the damaged site, where such an adaptive anti-self immune response reinforces the protective activity of local resident cells by providing them with factors that can augment and regulate their capacity for buffering troublemakers such as destructive self-compounds emerging from the injured neural tissue. Because the specificity of this autoimmune response apparently depends not on the type but on the site of lesion, the response can be boosted by therapeutic vaccination for acute and chronic neurodegenerative conditions irrespective of their primary etiology. The results have far-reaching implications, both for microbial infections and for neurodegenerative diseases of the CNS.

Dysmyelination revealed through MRI as increased radial (but unchanged axial) diffusion of water

Myelin loss and axonal damage are both observed in white matter injuries. Each may have significant impact on the long-term disability of patients. Currently, there does not exist a noninvasive biological marker that enables differentiation between myelin and axonal injury. We describe herein the use of magnetic resonance diffusion tensor imaging (DTI) to quantify the effect of dysmyelination on water directional diffusivities in brains of shiverer mice in vivo. The principal diffusion eigenvalues of eight axonal fiber tracts that can be identified with certainty on DTI maps were measured. The water diffusivity perpendicular to axonal fiber tracts, lambda(perpendicular), was significantly higher in shiverer mice compared with age-matched controls, reflecting the lack of myelin and the increased freedom of cross-fiber diffusion in white matter. The water diffusivity parallel to axonal fiber tracts, lambda(parallel), was not different, which is consistent with the presence of intact axons. It is clear that dysmyelination alone does not impact lambda(parallel). The presence of intact axons in the setting of incomplete myelination was confirmed by electron microscopy. Although further validation is still needed, our finding suggests that changes in lambda(perpendicular) and lambda(parallel) may potentially be used to differentiate myelin loss versus axonal injury.

Dual action of glatiramer acetate (Cop-1) in the treatment of CNS autoimmune and neurodegenerative disorders

Protective autoimmunity is the body's defense mechanism against destructive self-compounds such as those commonly associated with neurodegenerative disorders. Autoimmune disease and neurodegenerative disorders can thus be viewed as two extreme manifestations of the same process. Therefore, when designing therapy, it is important to avoid an approach that will cure the one by invoking the other. One way to stop, or at least slow down, the progression of neurodegeneration without risking development of an autoimmune disease is by boosting protective autoimmunity in a well-controlled way. Copolymer 1 (Cop-1), an approved drug for the treatment of multiple sclerosis, can be used as a treatment for autoimmune diseases and as a therapeutic vaccine for neurodegenerative diseases. We propose that the protective effect of Cop-1 vaccination is obtained through a well-controlled inflammatory reaction, and that the activity of Cop-1 in driving this reaction derives from its ability to serve as a 'universal antigen' by weakly activating a wide spectrum of self-reactive T cells.

Multiple sclerosis: diffusion tensor MR imaging for evaluation of normal-appearing white matter

PURPOSE

To determine whether the normal-appearing white matter (NAWM) regions surrounding and remote from multiple sclerosis (MS) plaques have abnormal diffusional anisotropy and to compare anisotropy maps with apparent diffusion coefficient (ADC) maps for sensitivity in the detection of white matter (WM) abnormalities.

MATERIALS AND METHODS

Conventional and diffusion tensor magnetic resonance (MR) imaging examinations were performed in 26 patients with MS and in 26 age-matched control subjects. Fractional anisotropy (FA) and ADC maps were generated and coregistered with T2-weighted MR images. Uniform regions of interest were placed on plaques, periplaque white matter (PWM) regions, NAWM regions in the contralateral side of the brain, and WM regions in control subjects to obtain FA and ADC values, which were compared across the WM regions.

RESULTS

The mean FA was 0.280 for plaques, 0.383 for PWM, 0.493 for NAWM, and 0.537 for control subject WM. The mean ADC was 1.025 x 10(-3) mm(2)/sec for plaques, 0.786 x 10(-3) mm(2)/sec for PWM, 0.739 x 10(-3) mm(2)/sec for NAWM, and 0.726 x 10(-3) mm(2)/sec for control subject WM. Significant differences in anisotropy and ADC values were observed among all WM regions (P <.001 for all comparisons, except ADC in NAWM vs control subject WM [P =.018]).

CONCLUSION

The anisotropy and ADC values were abnormal in all WM regions in the patients with MS and were worse in the periplaque regions than in the distant regions. Diffusion tensor MR imaging may be more accurate than T2-weighted MR imaging for assessment of disease burden.

Regulation of microglia - potential new drug targets in the CNS

Microglia respond to any disturbance in the CNS which poses a threat to physiological homeostasis. Although these responses are secondary, mainly to neuronal alterations, the way the microglial response evolves in many situations promotes further damage to the CNS. The list of clinical conditions in which this situation is a major problem is continuously growing and includes neurodegenerative diseases, stroke, trauma, demyelinating disorders and neuropathic pain. The significance of microglia for the pathogenesis of neurological and neuropsychiatric conditions has led to a rapidly expanding search for therapeutic possibilities to regulate microglial activity. As will be clear from this review, treatments which are currently available appear to offer some positive effects but are still far from satisfactory. A major challenge is to understand the mechanisms that determine whether activated microglia will develop into a cytotoxic or a cytoprotective component.

Wallerian degeneration of injured axons and synapses is delayed by a Ube4b/Nmnat chimeric gene

Axons and their synapses distal to an injury undergo rapid Wallerian degeneration, but axons in the C57BL/WldS mouse are protected. The degenerative and protective mechanisms are unknown. We identified the protective gene, which encodes an N-terminal fragment of ubiquitination factor E4B (Ube4b) fused to nicotinamide mononucleotide adenylyltransferase (Nmnat), and showed that it confers a dose-dependent block of Wallerian degeneration. Transected distal axons survived for two weeks, and neuromuscular junctions were also protected. Surprisingly, the Wld protein was located predominantly in the nucleus, indicating an indirect protective mechanism. Nmnat enzyme activity, but not NAD+ content, was increased fourfold in WldS tissues. Thus, axon protection is likely to be mediated by altered ubiquitination or pyridine nucleotide metabolism.

Divergent effects of ovarian steroids on neuronal survival during experimental allergic encephalitis in Lewis rats

Experimental allergic encephalitis, (EAE) a Th1-cell-dependent autoimmune disease of the central nervous system (CNS) used to study immune responses relevant to multiple sclerosis (MS) displays gender susceptibility. The underlying basis of the sexual dimorphism may reflect multiple factors including gender-specific hormones. To study the relationship between ovarian hormones and CNS inflammation, we induced EAE in susceptible female Lewis rats ovariectomized (OVX) 7 days earlier and implanted with blank capsules or capsules containing estradiol (E), progesterone (P), or both (EP). Rats were immunized with complete Freunds' adjuvant alone or combined with guinea pig myelin basic protein. Motor function was scored 0-5 on standard criteria (days 7-11 postimmunization). On day 11, the rats were euthanized and the lumbar spinal cord was analyzed for Nissl, neuron nuclear antigen, and DNA fragmentation with a TUNEL assay. Inflammation was judged qualitatively on a scale of 0-4. Our immunization protocol induced limited sensorimotor deficits in OVX rats (2.3 +/- 0.6, mean +/- SEM) with moderate inflammation (2.5 +/- 0.4). E limited both behavioral impairments (1.0 +/- 0.4) and inflammation (0.5 +/- 0.2). P-treated rats had more severe sensorimotor deficits (3.1 +/- 0.5) with increased inflammatory infiltrates (3.6 +/- 0.4) and markedly increased numbers of TUNEL(+) neurons. Neuron counts of the outer two Rexed lamina (L3-L5) showed a 20% neuron loss (P < 0.02) in P-treated rats with EAE in comparison to other groups. Coadministration of E with P prevented the consequences of P, including neuronal apoptosis (behavioral score, 0.6 +/- 0.6; inflammation, 1.4 +/- 0.5). Our results suggest a potential and novel function of P that increases the vulnerability of neurons to apoptotic injury in EAE and may have pathophysiologic implications in the progression of disability in women with MS.