Glial activation and white matter changes in the rat brain induced by chronic cerebral hypoperfusion: an immunohistochemical study

Activation of glial cells and white matter changes (rarefaction of the white matter) induced in the rat brain by permanent bilateral occlusion of the commom carotid arteries were immunohistochemically investigated up to 90 days. One day after ligation of the arteries, expression of the major histocompatibility complex (MHC) class I antigen in microglia increased in the white matter including the optic nerve, optic tract, corpus callosum, internal capsule, anterior commissure and traversing fiber bundles of the caudoputamen. After 3 days of occlusion, MHC class I antigen was still elevated and in addition MHC class II antigen and leukocyte common antigen were up-regulated in the microglia in these same regions. Astroglia, labeled with glial fibrillary acidic protein, increased in number in these regions after 7 days of occlusion. A few lymphocytes, labeled with CD4 or CD8 antibodies, were scattered in the neural parenchyma 1 h after occlusion. Activation of glial cells and infiltration of lymphocytes persisted after 90 days of occlusion in the white matter and the retinofugal pathway. However, cellular activation and infiltration in microinfarcts of the gray matter was less extensive and was substantially diminished 30 days after occlusion. The white matter changes were most intense in the optic nerve and optic tract, moderate in the medial part of the corpus callosum, internal capsule and anterior commissure, and slight in the fiber bundles of the caudoputamen. These results indicated that chronic cerebral hypoperfusion induced glial activation preferentially in the white matter. This activation seemed to be an early indicator of the subsequent changes in the white matter.     

血管生成对慢性低灌注状态下血脑屏障及脑白质损害的影响

目的 了解脑血管生成是否参与脑白质区域慢性低灌注状态下血脑屏障的破坏机制。方法 将72只雄性Wistar大鼠随机分为3组:假手术组、脑缺血组、干预组,脑缺血组及干预组大鼠结扎双侧颈总动脉构建慢性低灌注模型,干预组给予血管生成抑制剂灌胃以抑制血管生成; 对各组大鼠在相同时间点检测脑深部白质区域微血管密度、白质纤维密度以及伊文思蓝静脉注射6 h后脑白质区域组织内伊文思蓝水平。结果 脑缺血组及干预组大鼠脑白质区域血管密度和伊文思蓝浓度均显著高于假手术组,白质纤维密度显著低于假手术组,干预组微血管密度、白质纤维密度及脑组织内伊文思蓝水平显著低于脑缺血组。结论 慢性低灌注诱导的血管生成可能导致血脑屏障通透性增加,但血管生成有助于减轻白质损伤,但这种保护作用大于血脑屏障通透性改变带来的不利影响。     

Experimental cerebral hypoperfusion induces white matter injury and microglial activation in the rat brain

Though cerebral white matter injury is a frequently described phenomenon in aging and dementia, the cause of white matter lesions has not been conclusively determined. Since the lesions are often associated with cerebrovascular risk factors, ischemia emerges as a potential condition for the development of white matter injury. In the present study, we induced experimental cerebral hypoperfusion by permanent, bilateral occlusion of the common carotid arteries of rats (n=6). A sham-operated group served as control (n=6). Thirteen weeks after the onset of occlusion, markers for astrocytes, microglia, and myelin were found to be labeled by means of immunocytochemistry in the corpus callosum, the internal capsule, and the optic tract. The ultrastructural integrity and oligodendrocyte density in the optic tract were investigated by electron microscopy. Quantitative analysis revealed that chronic cerebral hypoperfusion caused mild astrogliosis in the corpus callosum and the internal capsule, while astrocytic disintegration in the optic tract increased by 50%. Further, a ten-fold increase in microglial activation and a nearly doubled oligodendrocyte density were measured in the optic tract of the hypoperfused rats as compared with the controls. Finally, vacuolization and irregular myelin sheaths were observed at the ultrastructural level in the optic tract. In summary, the rat optic tract appears to be particularly vulnerable to ischemia, probably because of the rat brains angioarchitecture. Since the detected glial changes correspond with those reported in vascular and Alzheimer dementia, this model of cerebral hypoperfusion may serve to characterize the causal relationship between ischemia and white matter damage.     

氧化应激在慢性缺血性脑白质损伤中的作用

目的 阐明氧化应激是否参与大鼠慢性脑缺血所致的脑白质损伤.方法 健康雄性Wistar大鼠按照完全随机数字表法分为假手术组,持久性双侧颈总动脉结扎3 d组、7 d组、3周组及6周组,每组6只.应用大鼠双侧颈总动脉结扎制备慢性脑缺血模型,检测大鼠脑白质内超氧化物歧化酶(SOD)活性、过氧化氢酶(CAT)活性、谷胱甘肽(GSH)含量以及脂质过氧化产物丙二醛(MDA)和4-羟基壬烯醛(4-HNE)加合物的变化.结果 与假手术组比较,慢性脑缺血大鼠脑白质内MDA含量在手术后3周明显增加,手术后6周进一步增高,差异有统计学意义(P<0.05).手术后3d至6周,慢性脑缺血大鼠脑白质内4-HNE蛋白加合物逐渐增高,与假手术组比较有差异有统计学意K(P<0.05).SOD活性在手术后3周和6周才明显降低,与假手术组比较差异有统计学意义(P<0.05).此外,慢性脑缺血大鼠脑白质内GSH含量在手术后7d即开始降低,而在手术后3周及6周则进一步下降,与假手术组比较差异有统计学意义(P<0.05).结论 慢性脑缺血导致大鼠脑白质氧化性损伤增加,抗氧化防御能力降低:氧化性损伤的增加和抗氧化防御能力的降低与慢性脑缺血所致的脑白质损伤密切相关.     

Axonal damage and demyelination in the white matter after chronic cerebral hypoperfusion in the rat

Cerebral white matter (WM) lesions are observed frequently in human ischemic cerebrovascular disease and have been thought to contribute to cognitive impairment. This type of lesion can be experimentally induced in rat brains under chronic cerebral hypoperfusion by the permanent occlusion of both common carotid arteries. However, it remains uncertain whether chronic ischemia can damage both the gray and white matter, and whether it can induce demyelination with or without axonal damage. Therefore, we examined axonal damage using immunohistochemistry for the amyloid beta/A4 precursor protein (APP), chromogranin A (CgA) and demyelination using immunohistochemistry for the encephalitogenic peptide (EP) in this model. Severe WM lesions such as vacuolation and the loss of nerve fibers appeared in the optic nerve and optic tract after 3 days of ligation, and less intense changes were observed in the corpus callosum, internal capsule, and fiber bundles of the caudoputamen after 7 days with Klüver-Barrera and Bielschowsky staining. These WM lesions persisted even after 30 days. The APP, CgA, and EP-immunopositive fibers increased in number from 1 to 30 days after the ligation in the following WM regions: the optic nerve, optic tract, corpus callosum, internal capsule, and fiber bundles of the caudoputamen. In contrast, only a few APP, CgA, or EP-immunopositive fibers were detected in the gray matter regions, including the cerebral cortex and hippocampus. These results indicate that the WM is more susceptible to chronic cerebral hypoperfusion than the gray matter, with an involvement of both axonal and myelin components. Furthermore, immunohistochemistry for APP, CgA, and EP is far superior to routine histological staining in sensitivity and may become a useful tool to investigate WM lesions caused by various pathoetiologies.     

绞股蓝总皂甙对慢性脑缺血性白质氧化性损伤的保护作用

目的 探讨绞股蓝总皂甙对慢性脑缺血大鼠脑白质氧化性损伤的保护作用以及对脑缺血大鼠认知功能的影响.方法 将57只成年雄性SD大鼠按随机数字表法分成假手术组(n=12)、模型组(n=15)、绞股蓝总皂甙200 mg组(n=15)、绞股蓝总皂甙400 mg组(n=15),后3组采用双侧颈总动脉结扎法制备慢性脑缺血模型,且在造模后3h分别将等量生理盐水,200 mg/kg、400mg/kg绞股蓝总皂甙溶液灌胃,1次/d,持续33 d.应用Morris水迷宫实验测试各组大鼠空间学习与记忆能力的改变,酶联免疫吸附法(ELISA)测定大鼠胼胝体、视束内超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量,免疫组化染色用8-羟基脱氧鸟苷(8-OHdG)抗体测定中枢神经细胞的氧化损伤水平.结果 与模型组相比,绞股蓝总皂甙400 mg组大鼠的逃避潜伏期明显缩短及在原平台象限的游泳时间明显延长,差异有统计学意义(P＜0.05).与假手术组比较,模型组大鼠胼胝体及视束内MDA含量明显增加,SOD活性明显降低,差异有统计学意义(P＜0.05).与模型组相比,绞股蓝总皂甙400 mg组MDA含量明显降低,SOD活性明显升高,8-OHdG阳性细胞数明显减少,差异有统计学意义(P＜0.05).与模型组相比,绞股蓝总皂甙200 mg组SOD活性、MDA含量及8-OHdG阳性细胞数差异无统计学意义(P＞0.05).结论 绞股蓝总皂甙能有效改善慢性脑缺血大鼠脑白质氧化性损伤,提示其可能是一种有效的抗痴呆药物,但其作用的确切机制还有待进一步研究.     

Dose-dependent, protective effect of FK506 against white matter changes in the rat brain after chronic cerebral ischemia

Neuroprotective effects of immunosuppressive agents have been shown in cerebral ischemia. To investigate the role of immunosuppressive agents in chronic cerebral ischemia and to design a drug protocol with safe therapeutic windows, we examined the effects of FK506, a potent immunosuppressive agent, on chronic cerebral ischemia. Both common carotid arteries were ligated in 73 male Wistar rats. Fifty-eight of these rats received a chronic injection of FK506 (0.2, 0.5, 1.0 mg/kg) and the remaining 15 received a vehicle solution injection. Microglia/macrophage was investigated with immunohistochemistry for leukocyte common antigen and major histocompatibility complex, and astroglia was examined with glial fibrillary acidic protein as markers. White matter rarefaction and the number of immunopositive glial cells were assessed from 7 to 30 days after the ligation. In the vehicle-treated animals, there was persistent and extensive activation of the microglia/macrophages and astroglia in the white matter, including the optic nerve, optic tract, corpus callosum, internal capsule, anterior commissure and traversing fiber bundles of the caudoputamen. In the FK506-treated rats, the number of activated microglia/macrophages was significantly reduced in a dose-dependent manner (p<0.01) as compared to the vehicle-treated rats. Rarefaction of the white matter was also inhibited by FK506 in a dose-dependent manner (p<0.01). Thus, a clinically-relevant dosage of FK506 attenuated both glial activation and white matter changes in chronic cerebral ischemia in the rat. These results indicate a potential use for FK506 in cerebrovascular diseases.     

Chronic cerebral hypoperfusion induces white matter lesions and loss of oligodendroglia with DNA fragmentation in the rat

Cerebrovascular white matter lesions represent an age-related neurodegenerative condition that appears as a hyperintense signal on magnetic resonance images. These lesions are frequently observed in aging, hypertension and cerebrovascular disease, and are responsible for cognitive decline and gait disorders in the elderly population. In humans, cerebrovascular white matter lesions are accompanied by apoptosis of oligodendroglia, and have been thought to be caused by chronic cerebral ischemia. In the present study, we tested whether chronic cerebral hypoperfusion induces white matter lesions and apoptosis of oligodendroglia in the rat. Doppler flow meter analysis revealed an immediate reduction of cerebral blood flow ranging from 30% to 40% of that before operation; this remained at 52–64% between 7 and 30 days after operation. Transferrin-immunoreactive oligodendroglia decreased in number and the myelin became degenerated in the medial corpus callosum at 7 days and thereafter. Using the TUNEL method, the number of cells showing DNA fragmentation increased three- to eightfold between 3 and 30 days post-surgery compared to sham-operated animals. Double labeling with TUNEL and immunohistochemistry for markers of either astroglia or oligodendroglia showed that DNA fragmentation occurred in both of these glia. Messenger RNA for caspase-3 increased approximately twofold versus the sham-operated rats between 1 and 30 days post-surgery. Immunohistochemistry revealed up-regulation of caspase-3 in the oligodendroglia of the white matter, and also in the astroglia and neurons of the gray matter. Molecules involved in apoptotic signaling such as TNF- and Bax were also up-regulated in glial cells. These results indicate that chronic cerebral hypoperfusion induces white matter degeneration in association with DNA fragmentation in oligodendroglia.     

FK506 ameliorates the discrimination learning impairment due to preventing the rarefaction of white matter induced by chronic cerebral hypoperfusion in rats

We examined the effects of the immunosuppressant tacrolimus (FK506) on the discrimination learning impairment induced by chronic cerebral hypoperfusion in rats. Chronic cerebral hypoperfusion was prepared by permanent ligation of bilateral common carotid arteries for male Wistar rats aged 9 weeks. FK506 (0.05 mg/kg, s.c.) recovered the learning impairment and also prevented the rarefaction of white matter and striatal neuronal cell damage. Our findings suggest that FK506 ameliorates the learning impairment mainly due to preventing neuropathological alterations.     

Minocycline attenuates white matter damage in a rat model of chronic cerebral hypoperfusion

White matter lesions are thought to result from chronic cerebral ischemia and constitute a core pathology of subcortical vascular dementia. This rarefaction has been known to be associated with microglial activation. We investigated whether minocycline, a microglial inhibitor, attenuates the white matter damage induced by chronic cerebral hypoperfusion that is used as a model of vascular dementia. Male Wistar rats were subjected to bilateral, permanent occlusion of the common carotid arteries (BCCAO) to induce chronic cerebral hypoperfusion. Minocycline or saline was injected daily for 2 weeks after BCCAO. In the corpus callosum and the optic tract, white matter damage observed with Klüver-Barrera staining was significantly attenuated in the minocycline-treated group compared to saline-treated controls. In control rats, immunoreactivities of major basic protein (MBP), Ox-42 as a microglial marker, and matrix metalloproteinase (MMP)-2 were increased in the corpus callosum. Minocycline significantly reduced these changes. Co-expression of Ox-42 and MMP-2 was confirmed by double immunofluorescence histochemistry. Our results suggest that chronic treatment with minocycline could be protective against at least some ischemic white matter damage, and its mechanism may be related to suppressing microglial activation.     

Effects of statins on the progression of cerebral white matter lesion

Arteriosclerotic related cerebral white matter lesion (WML) is associated with increased risk of death, stroke, dementia, depression, gait disturbance, and urinary incontinence. We investigated the effects of statins on WML progression by performing a post hoc analysis on the ROCAS (Regression of Cerebral Artery Stenosis) study, which is a randomized, double-blind, placebo-controlled study evaluating the effects of statins upon asymptomatic middle cerebral artery stenosis progression among stroke-free individuals. Two hundreds and eight randomized subjects were assigned to either placebo (n = 102) or simvastatin 20 mg daily (n = 106) for 2 years. Baseline severity of WML was graded visually into none, mild, and severe. Volume (cm³) of WML was determined quantitatively at baseline and at end of study using a semi-automated method based on MRI. Primary outcome was the change in WML volume over 2 years. After 2 years of follow-up, there was no significant change in WML volume between the active and the placebo group as a whole. However, stratified analysis showed that for those with severe WML at baseline, the median volume increase in the active group (1.9 cm³) was less compared with that in the placebo group (3.0 cm³; P = 0.047). Linear multivariate regression analysis identified that baseline WML volume (β = 0.63, P < 0.001) and simvastatin treatment (β = −0.214, P = 0.043) independently predicted change in WML volume. Our findings suggest that statins may delay the progression of cerebral WML only among those who already have severe WML at baseline.     

Chronic cerebral hypoperfusion induced by right unilateral common carotid artery occlusion causes delayed white matter lesions and cognitive impairment in adult mice

Some lines of evidence have suggested that subcortical ischemic vascular dementia (SIVD) is a common form of vascular dementia (VaD), and that its pathological changes are the development of ischemic white matter (WM) lesions under chronic hypoperfusion and lacunes. Here, we have developed a novel mouse model of VaD with WM lesions, which was induced by right unilateral common carotid artery occlusion (rUCCAO). The mice subjected to rUCCAO exhibited chronic cerebral hypoperfusion in the cerebral hemisphere ipsilateral to rUCCAO monitored using a laser-Doppler flow meter (p<0.01), and significant WM damage in the corpus callosum (p<0.05) and deficits in object recognition test correlated with the damage of frontal-subcortical circuits (p<0.01). However, no differences in spontaneous alternation or spontaneous motor activity were observed. Furthermore, the levels of pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta) and interleukin-6 (IL-6), significantly increased (p<0.01), and those of anti-inflammatory cytokines, such as interleukin-4 (IL-4) and interleukin-10 (IL-10), significantly decreased in the ischemic brain (p<0.05). These results suggest that this model is a useful tool for investigating the associations among inflammatory reactions, cognitive impairment, and WM damage, which may help elucidating the pathomechanism of VaD, particularly SIVD.     

Protective effects of carnosine on white matter damage induced by chronic cerebral hypoperfusion

Carnosine is a dipeptide that scavenges free radicals,inhibits inflammation in the central nervous system,and protects against ischemic and hypoxic brain damage through its anti-oxidative and anti-apoptotic actions.Therefore,we hypothesized that carnosine would also protect against white matter damage caused by subcortical ischemic injury.White matter damage was induced by right unilateral common carotid artery occlusion in mice.The animals were treated with 200,500 or 750 mg/kg carnosine by intraperitoneal injection 30 minutes before injury and every other day after injury.Then,37 days later,Klüver-Barrera staining,toluidine blue staining and immunofluorescence staining were performed.Carnosine(200,500 mg/kg) substantially reduced damage to the white matter in the corpus callosum,internal capsule and optic tract,and it rescued expression of myelin basic protein,and alleviated the loss of oligodendrocytes.However,carnosine at the higher dose of 750 mg/kg did not have the same effects as the 200 and 500 mg/kg doses.These findings show that carnosine,at a particular dose range,protects against white matter damage caused by chronic cerebral ischemia in mice,likely by reducing oligodendroglial cell loss.     

Spinal cord injury induces widespread chronic changes in cerebral white matter

Traumatic spinal cord injuries (SCIs) lead to axonal damage at the trauma site, as well as disconnections within the central nervous system. While the exact mechanisms of the long‐term pathophysiological consequences of SCIs are not fully understood, it is known that neuronal damage and degeneration are not limited to the direct proximity of the trauma. Instead, the effects can be detected even in the cerebrum. We examined SCI‐induced chronic brain changes with a case‐control design using 32 patients and 70 control subjects. Whole‐brain white matter (WM) tracts were assessed with diffusion tensor imaging (DTI). In addition, we analysed associations between DTI metrics and several clinical SCI variables. Whole‐brain analyses were executed by tract‐based spatial statistics (TBSS), with an additional complementary atlas‐based analysis (ABA). We observed widespread, statistically significant (P ≤ 0.01) changes similar to neural degeneration in SCI patients, both in the corticospinal tract (CST) and beyond. In addition, associations between DTI metrics and time since injury were found with TBSS and ABA, implying possible long‐term post‐injury neural regeneration. Using the ABA approach, we observed a correlation between SCI severity and DTI metrics, indicating a decrease in WM integrity along with patient sensory or motor scores. Our results suggest a widespread neurodegenerative effect of SCI within the cerebrum that is not limited to the motor pathways. Furthermore, DTI‐measured WM integrity of chronic SCI patients seemed to improve as time elapsed since injury. Hum Brain Mapp 38:3637–3647, 2017. © 2017 Wiley Periodicals, Inc.     

偏头痛脑白质异常的MRI表现

目的探讨偏头痛脑白质异常(WMAs)的MRI表现。方法选取70例偏头痛患者并行MRI检查,女性51例,男性19例,年龄为18~50岁,平均年龄36.21±8.9岁。选取同期健康体检者并行MRI检查70例对照组,女性53例和男性17例,年龄为18~50岁,平均年龄35.32±8.6岁。运用SPSS13.0软件对数据进行分析。结果显示偏头痛组中有23例WMAs,表现为皮质下脑白质内等T1长T2信号影,Flair高信号;对照组中有6例WMAs。偏头痛组WMAs的比例(32.86%,23/70)明显高于对照组(8.57%,6/70)(χ2=12.57,P0.01)。偏头痛组中有先兆偏头痛患者WMAs的比例(48.39%,15/31)明显高于无先兆偏头痛患者(20.51%,8/39)(χ2=6.08,P0.05)。结论偏头痛患者WMAs的发生率较高,且有先兆偏头痛患者较无先兆偏头痛患者更高。     

Characteristics and clinical correlates of white matter changes in brain magnetic resonance of migraine females

Objective

White matter hyperintensities (WMHs) were often found in migraine patients. The aim of study was to characterize WMHs, assess their prevalence, determine relationship to clinical symptoms and homocysteine levels in migraine females.

Temporal changes in extracellular acetylcholine and CA1 pyramidal cells in gerbil hippocampus following transient cerebral ischemia

Temporal changes in cholinergic functions following transient cerebral ischemia (10 min) were studied in the hippocampus of awake unrestrained gerbils using in vivo microdialysis. These data were compared with the results for temporal change in the area of each CA1 cell soma, measured with a microcomputer imaging device. KCl-induced release of acetylcholine (ACh) tended to be lower within 1 day after recirculation, and was significantly lower on the 4th, 7th and 14th days. Atropine-induced release of ACh gradually decreased over the test period. In histological estimation, no differences were observed within the 1st day, but a significant decrease of the area of CA1 cell soma was observed from the 4th to 14th days. Moreover, ischemia over 2 min decreased KCl- and atropine-induced ACh release on the 14th day without significant changes of hippocampal CA1 pyramidal cell. From these results, it is clear that ischemia produced dysfunction of hippocampal cholinergic neurons, and that dysfunction of the hippocampal cholinergic system following transient ischemia precedes pyramidal cell damage in the hippocampal CA1 subfield.     

Age-related microvascular degeneration in the human cerebral periventricular white matter

Clinical studies have identified white matter (WM) lesions as hyperintensive regions in the MRI images of elderly patients. Since a cerebrovascular origin was attributed to such lesions, the present analysis set out to define the microvascular histopathologic changes in the periventricular WM in the aged. Post-mortem samples of the frontal, parietal, and occipital periventricular WM of 40–90-year-old subjects were prepared for quantitative light and electron microscopy. Light microscopic examination revealed microvascular fibrohyalinosis as the most common type of microvascular damage in the elderly. Ultrastructural analysis identified the microvascular thickening as collagen deposits affecting the basement membrane. The vascular density did not correlate with the age. The basement membrane pathology significantly increased, while the number of intact microvessels gradually decreased, with advancing age in the frontal and occipital WM. Finally, peripheral atherosclerosis coincided with massive microvascular fibrosis, particularly in the frontal WM. Our results demonstrate an age-related microvascular degeneration in the periventricular WM, which may contribute to the development of WM lesions by hindering a sufficient supply of nutrients to the affected WM sites. Furthermore, the data accord with previous observations identifying the frontal lobe as the site at which WM vulnerability is most pronounced. Finally, atherosclerosis in large, peripheral vessels is considered to be a predictive marker of microvascular pathology in the WM.     

Regional differences in cerebral asymmetries of human cortical white matter

The form of the structural asymmetries across the cerebral hemispheres, that support well-established functional asymmetries, are not well understood. Although, many previous studies have investigated structural differences in areas associated with strong functional asymmetries, such as language processes, regions of the brain with less well established functional laterality have received less attention. The current study aims to address this by exploring global white matter asymmetries of the healthy human brain using diffusion tensor imaging (DTI) and tractography. DTI was conducted on twenty-nine healthy right-handed males, and pathways from the four major lobes were reconstructed using probabilistic tractography. Mean FA, parallel and perpendicular diffusion values were calculated and compared across hemispheres for each pathway generated. Significant asymmetries in the parietal (rightward asymmetry) and occipital (leftward asymmetry) pathways were found in FA measures. However, asymmetric patterns in parallel and/or perpendicular diffusion were observed in all four lobes, even in pathways with symmetrical FA. For instance, significant rightward asymmetry in parallel diffusion was found in the parietal and frontal lobes, whereas significant leftward asymmetry was found in the temporal and occipital lobes. We suggest that these different patterns of diffusion asymmetry reflect differences in microanatomy that support the known patterns of differential functional asymmetry. The different directions of anatomical asymmetry support the notion that there may be a number of different lateralising influences operating in the brain.     

Multiple sclerosis and amyloid deposits in the white matter of the brain

We present the neuropathological findings in a female patient with clinically definite multiple sclerosis (MS), who at autopsy had multifocal amyloid deposits in the white matter of the brain without other signs of amyloidosis. The patient had relapsing/remitting MS between the ages of 26 and 45, and during her last 14 years she had a secondary chronic progressive form of MS. Previous reports of amyloid deposits in MS are reviewed and the possible relationship between amyloid deposits and the increased production of immunoglobulin free light chains in MS is discussed. Received: 25 March 1996 / Revised, accepted: 5 August 1996