Progressive transformation of the cytoskeleton associated with normal aging and Alzheimer's disease

SMI-32 labeling in Cajal-Retzius cells of feline primary visual cortex

Cajal-Retzius cells are one of the transient elements of the developing cerebral cortex. These cells express some characteristic molecules. One of them, heavy-chain neurofilaments, participating in the construction of the mature cerebral networks, are believed to be a specific feature of the human's Cajal-Retzius cells. Using histochemical stain for SMI-32 antibody to the non-phosphorylated heavy-chain neurofilaments, large neurons having horizontally oriented soma and bipolar processes were labeled in the molecular layer of the primary visual cortex of cats aged 0-2 postnatal days. Using DiI technique, similar neurons having a well-developed system of parallel vertical branches coming from the two horizontal processes were visualized in these areas. The location and general morphology of these neurons were similar to the Cajal-Retzius cells allowing to suppose for the carnivores to share similar with primates developmental mechanisms of the corticogenesis.

Cerebellar Calcium-Binding Protein and Neurotrophin Receptor Defects in Down Syndrome and Alzheimer's Disease

Cerebellar hypoplasia is a major characteristic of the Down syndrome (DS) brain. However, the consequences of trisomy upon cerebellar Purkinje cells (PC) and interneurons in DS are unclear. The present study performed a quantitative and qualitative analysis of cerebellar neurons immunostained with antibodies against calbindin D-28k (Calb), parvalbumin (Parv), and calretinin (Calr), phosphorylated and non-phosphorylated intermediate neurofilaments (SMI-34 and SMI-32), and high (TrkA) and low (p75NTR) affinity nerve growth factor (NGF) receptors as well as tau and amyloid in DS (n = 12), Alzheimer's disease (AD) (n = 10), and healthy non-dementia control (HC) (n = 8) cases. Our findings revealed higher Aβ42 plaque load in DS compared to AD and HC but no differences in APP/Aβ plaque load between HC, AD, and DS. The cerebellar cortex neither displayed Aβ40 containing plaques nor pathologic phosphorylated tau in any of the cases examined. The number and optical density (OD) measurements of Calb immunoreactive (-ir) PC soma and dendrites were similar between groups, while the number of PCs positive for Parv and SMI-32 were significantly reduced in AD and DS compared to HC. By contrast, the number of SMI-34-ir PC dystrophic axonal swellings, termed torpedoes, was significantly greater in AD compared to DS. No differences in SMI-32- and Parv-ir PC OD measurements were observed between groups. Conversely, total number of Parv- (stellate/basket) and Calr (Lugaro, brush, and Golgi)-positive interneurons were significantly reduced in DS compared to AD and HC. A strong negative correlation was found between counts for Parv-ir interneurons, Calr-ir Golgi and brush cells, and Aβ42 plaque load. Number of TrkA and p75NTR positive PCs were reduced in AD compared to HC. These findings suggest that disturbances in calcium binding proteins play a critical role in cerebellar neuronal dysfunction in adults with DS.

Young Coconut Juice Reduces Some Histopathological Changes Associated with Alzheimer's Disease through the Modulation of Estrogen Receptors in Orchidectomized Rat Brains

Propose. This study aimed to evaluate the protective role of young coconut juice (YCJ) against the pathological changes in Alzheimer's disease (AD) in orchidectomized (orx) rats. Methods and Results. Animals were divided into 7 groups including: baseline normal control group, sham control, orx rat group, orx rat group injected with 2.5 μg/kg b.w. estradiol benzoate (EB) 3 days a week for 10 weeks, and the orx rat groups treated orally with 10, 20, and 40 ml/kg b.w. of YCJ for 10 weeks. At the end of treatment period, animals were sacrificed and the brain of each rat was removed, fixed in 10% neutral formalin, and stained by specific antibodies against NF200, parvalbumin (PV), β-amyloid (Aβ), and estrogen receptors (ERα and ERβ). The results showed that the number of NF200- and PV-reactive neurons in the hippocampus and cerebral cortex was significantly reduced in orx rats. However, it restored to normal in orx rats injected with EB or those administrated with YCJ in a dose-related manner. Neurons containing β-amyloid (Aβ), a hallmark of Alzheimer's disease (AD), were found to be increased in the orx rats; however; they were reduced by EB injection or YCJ administration. These results suggested the binding of the YCJ active ingredient(s) with estrogen receptors (ERs) in the brain as indicated by the detection of ERα and ERβ in neurons since a significant correlation was detected between NF200-/PV-reactive neurons vs ERα-/ERβ-reactive neurons.Conclusion. It could be concluded that YCJ is effective as EB in reducing AD pathology, probably by being selective estrogen receptor modulators.

Combination treatment with leptin and pioglitazone in a mouse model of Alzheimer's disease

INTRODUCTION

Combination therapy approaches may be necessary to address the many facets of pathologic change in the brain in Alzheimer's disease (AD). The drugs leptin and pioglitazone have previously been shown individually to have neuroprotective and anti-inflammatory actions, respectively, in animal models.

METHODS

We studied the impact of combined leptin and pioglitazone treatment in 6-month-old APP/PS1 (APPswe/PSEN1dE9) transgenic AD mouse model.

RESULTS

We report that an acute 2-week treatment with combined leptin and pioglitazone resulted in a reduction of spatial memory deficits (Y maze) and brain β-amyloid levels (soluble β-amyloid and amyloid plaque burden) relative to vehicle-treated animals. Combination treatment was also associated with amelioration in plaque-associated neuritic pathology and synapse loss, and also a significantly reduced neocortical glial response.

DISCUSSION

Combination therapy with leptin and pioglitazone ameliorates pathologic changes in APP/PS1 mice and may represent a potential treatment approach for AD.

Defining the earliest pathological changes of Alzheimer's disease

The prospects for effectively treating well-established dementia, such as Alzheimer's disease (AD), are slim, due to the destruction of key brain pathways that underlie higher cognitive function. There has been a substantial shift in the field towards detecting conditions such as AD in their earliest stages, which would allow preventative or therapeutic approaches to substantially reduce risk and/or slow the progression of disease. AD is characterized by hallmark pathological changes such as extracellular Aβ plaques and intracellular neurofibrillary pathology, which selectively affect specific subclasses of neurons and brain circuits. Current evidence indicates that Aβ plaques begin to form many years before overt dementia, a gradual and progressive pathology which offers a potential target for early intervention. Early Aβ changes in the brain result in localized damage to dendrites, axonal processes and synapses, to which excitatory synapses and the processes of projection neurons are highly vulnerable. Aβ pathology is replicated in a range of transgenic models overexpressing mutant human familial AD genes (e.g. APP and presenilin 1). Studying the development of aberrant regenerative and degenerative changes in neuritic processes associated with Aβ plaques may represent the best opportunity to understand the relationship between the pathological hallmarks of AD and neuronal damage, and to develop early interventions to prevent, slow down or mitigate against Aβ pathology and/or the neuronal alterations that leads to cognitive impairment.

The influence of aging on the number of neurons and levels of non-phosporylated neurofilament proteins in the central auditory system of rats

In the present study, an unbiased stereological method was used to determine the number of all neurons in Nissl stained sections of the inferior colliculus (IC), medial geniculate body (MGB), and auditory cortex (AC) in rats (strains Long Evans and Fischer 344) and their changes with aging. In addition, using the optical fractionator and western blot technique, we also evaluated the number of SMI-32-immunoreactive (-ir) neurons and levels of non-phosphorylated neurofilament proteins in the IC, MGB, AC, and visual cortex of young and old rats of the two strains. The SMI-32 positive neuronal population comprises about 10% of all neurons in the rat IC, MGB, and AC and represents a prevalent population of large neurons with highly myelinated and projecting processes. In both Long Evans and Fischer 344 rats, the total number of neurons in the IC was roughly similar to that in the AC. With aging, we found a rather mild and statistically non-significant decline in the total number of neurons in all three analyzed auditory regions in both rat strains. In contrast to this, the absolute number of SMI-32-ir neurons in both Long Evans and Fischer 344 rats significantly decreased with aging in all the examined structures. The western blot technique also revealed a significant age-related decline in the levels of non-phosphorylated neurofilaments in the auditory brain structures, 30–35%. Our results demonstrate that presbycusis in rats is not likely to be primarily associated with changes in the total number of neurons. On the other hand, the pronounced age-related decline in the number of neurons containing non-phosphorylated neurofilaments as well as their protein levels in the central auditory system may contribute to age-related deterioration of hearing function.

Neurites containing the neurofilament-triplet proteins are selectively vulnerable to cytoskeletal pathology in Alzheimer's disease and transgenic mouse models

Amyloid-β plaque accumulation in Alzheimer’s disease (AD) is associated with dystrophic neurite (DN) formation and synapse loss in principal neurons, but interneuron pathology is less clearly characterized. We compared the responses of neuronal processes immunoreactive for either neurofilament triplet (NF⁺) or calretinin (CR⁺) to fibrillar amyloid (Aβ) plaques in human end-stage and preclinical AD, as well as in APP/PS1 and Tg2576 transgenic mouse AD models. Neurites traversing the Aβ plaque core, edge, or periphery, defined as 50, 100, and 150% of the plaque diameter, respectively, in human AD and transgenic mouse tissue were compared to age-matched human and wild-type mouse controls. The proportion of NF⁺ neurites exhibiting dystrophic morphology (DN) was significantly larger than the proportion of dystrophic CR⁺ neurites in both human AD and transgenic mice (p < 0.01). Additionally, the number of NF⁺, but not CR⁺, DNs, correlated with Aβ plaque size. We conclude that CR⁺ interneurons appear to be more resistant than NF⁺ neurons to AD-mediated cytoskeletal pathology.

Distribution of SMI-32-immunoreactive neurons in the central auditory system of the rat

SMI-32 antibody recognizes a non-phosphorylated epitope of neurofilament proteins, which are thought to be necessary for the maintenance of large neurons with highly myelinated processes. We investigated the distribution and quantity of SMI-32-immunoreactive(-ir) neurons in individual parts of the rat auditory system. SMI-32-ir neurons were present in all auditory structures; however, in most regions they constituted only a minority of all neurons (10-30%). In the cochlear nuclei, a higher occurrence of SMI-32-ir neurons was found in the ventral cochlear nucleus. Within the superior olivary complex, SMI-32-ir cells were particularly abundant in the medial nucleus of the trapezoid body (MNTB), the only auditory region where SMI-32-ir neurons constituted an absolute majority of all neurons. In the inferior colliculus, a region with the highest total number of neurons among the rat auditory subcortical structures, the percentage of SMI-32-ir cells was, in contrast to the MNTB, very low. In the medial geniculate body, SMI-32-ir neurons were prevalent in the ventral division. At the cortical level, SMI-32-ir neurons were found mainly in layers III, V and VI. Within the auditory cortex, it was possible to distinguish the Te1, Te2 and Te3 areas on the basis of the variable numerical density and volumes of SMI-32-ir neurons, especially when the pyramidal cells of layer V were taken into account. SMI-32-ir neurons apparently form a representative subpopulation of neurons in all parts of the rat central auditory system and may belong to both the inhibitory and excitatory systems, depending on the particular brain region.

Autophagy, organelles and ageing

As a result of insufficient digestion of oxidatively damaged macromolecules and organelles by autophagy and other degradative systems, long-lived postmitotic cells, such as cardiac myocytes, neurons and retinal pigment epithelial cells, progressively accumulate biological 'garbage' ('waste' materials). The latter include lipofuscin (a non-degradable intralysosomal polymeric substance), defective mitochondria and other organelles, and aberrant proteins, often forming aggregates (aggresomes). An interaction between senescent lipofuscin-loaded lysosomes and mitochondria seems to play a pivotal role in the progress of cellular ageing. Lipofuscin deposition hampers autophagic mitochondrial turnover, promoting the accumulation of senescent mitochondria, which are deficient in ATP production but produce increased amounts of reactive oxygen species. Increased oxidative stress, in turn, further enhances damage to both mitochondria and lysosomes, thus diminishing adaptability, triggering mitochondrial and lysosomal pro-apoptotic pathways, and culminating in cell death.

Life and death of neurons in the aging cerebral cortex

The transition from age-associated memory impairment (AAMI) to the dramatic loss of cognitive abilities accompanying Alzheimer's disease (AD) requires progressive development of neocortical pathology that results in neuron death. The selective vulnerability of this neuron death is reflected in the characteristics of cortical pyramidal neurons that are prone to form neurofibrillary tangles. Loss of the neurons that form long corticocortical projections in the association neocortex emerges as the pathological outcome most directly related to the dementia observed in AD. AAMI likely involves alterations of neuronal spines and synapses without neuron death. Interestingly, the same circuits that are vulnerable to degeneration in AD are vulnerable to synaptic alterations short of neuron death. These synaptic alterations likely impact cognitive function in normal aging in a manner consistent with the more modest cognitive decline typically seen in aging. Estrogen levels affect spine density on pyramidal neurons in the prefrontal cortex; these neurons may provide many of the same circuits implicated in AAMI. This association demonstrates an important interface between reproductive and neural senescence and suggests that the synaptic alterations prevalent in normal aging may be responsive to therapy.

The nature and effects of cortical microvascular pathology in aging and Alzheimer's disease

Age-related and amyloid-induced pathology of the cerebral microvasculature have been implicated as potential contributing factors to the pathogenesis of Alzheimer's disease (AD). The microvasculature plays a crucial role in maintaining brain homeostasis and deterioration of its integrity may have deleterious effects on brain function in AD, possibly leading to neurofibrillary degeneration, plaque formation, and cell loss. Brain vessels possess peculiar anatomical and physiological properties owing to their role in the exchange processes of various substances between blood and brain, which are highly regulated for the maintenance of ionic homeostasis of the neuronal environment. Here we review neuropathological aspects of cortical microvessels in aging and AD in relationship to known cardiovascular risk factors and their possible impact on the cognitive decline seen in late-onset dementia.

Progressive degeneration of nonphosphorylated neurofilament protein-enriched pyramidal neurons predicts cognitive impairment in Alzheimer's disease: stereologic analysis of prefrontal cortex area 9

We performed a stereologic analysis of a subset of pyramidal neurons known to be vulnerable in Alzheimer's disease (AD) and characterized by particularly high somatodendritic levels of nonphosphorylated neurofilament protein. In the neocortex, these large pyramidal neurons reside in the deep part of layer III (layer IIIc) and the superficial part of layer V (layer Va). We focused on prefrontal cortex area 9 in elderly control cases in comparison to cases with different degrees of cognitive dysfunction. The results confirmed that these neurons are preferentially vulnerable in AD, as their numbers decrease dramatically in cases with definite dementia, correlating strongly with the severity of the disease, to a nearly complete loss (>90%) in the endstages of AD. Furthermore, a triple-labeling experimental paradigm revealed that these particular neurons are far more likely to develop neurofibrillary tangles (NFT) and do so at a faster rate than other pyramidal cells. Nonphosphorylated neurofilament protein-rich neurons also shrink considerably during formation of NFT and the largest among them are preferentially affected. Laminar differences in the severity of these effects were observed, layer Va being more severely affected, possibly correlating with the involvement of specific cortical projections. These data reveal that different populations of neurons prone to NFT formation are lost at different rates in AD, and that nonphosphorylated neurofilament protein-enriched neurons emerge as a strikingly vulnerable subpopulation of neurons. Their preferential involvement suggests that neurons providing specific corticocortical connections between association areas are at high risk for degeneration in AD.

Stereologic analysis of neurofibrillary tangle formation in prefrontal cortex area 9 in aging and Alzheimer's disease

Alzheimer's disease (AD) is characterized neuropathologically by several features including extensive neuronal death in the cerebral cortex. In fact, while neuropathological changes restricted to the hippocampal formation are a consistent reflection of age-related memory impairment, overt dementia is present only in cases with neocortical involvement. Several quantitative studies have reported a substantial loss of neurons from these regions and a parallel increase in the number of neurofibrillary tangles (NFT). However, accurate quantitative data on the dynamics of NFT formation are lacking. In the present study, we performed a stereologic analysis of the proportions of intracellular and extracellular (ghost) NFT, and unaffected neurons in the deep part of layer III (layer IIIc) and the superficial part of layer V (layer Va) of Brodmann's prefrontal cortex area 9. Elderly cognitively unimpaired cases were compared with cases with different degrees of cognitive dysfunction. The data revealed differential rates of formation of intracellular and extracellular NFT between the two layers, and confirmed the presence of a severe disease-associated, but not age-related, neuronal loss. It was also shown that a susbtantial number of pyramidal cells may persist either unaffected or in a transitional stage of NFT formation in both neocortical layers. These results suggest that a considerable number of neurons containing an intracellular NFT exists in the neocortex until late in the course of AD. Whereas it is not possible to assess whether such transitional neurons are fully functional, these affected neurons might respond positively to therapeutic strategies aimed at protecting the cells that are prone to neurofibrillary degeneration in AD.

Direct determination of the proportion of intra- and extra-cellular neocortical neurofibrillary tangles in Alzheimer's disease

We investigated the cellular localisation of neurofibrillary tangles in Alzheimer's disease. All tau-positive tangles were stained for thioflavine S, while approximately 84% of thioflavine S-stained tangles were tau-immunolabelled. Approximately 58-62% and 73-76% of thioflavine S- and tau-labelled tangles, respectively, were present within cortical neurons labelled for microtubule-associated protein-2. Thus, most neocortical tangles in Alzheimer's disease are intracellular and may not be the principal cause of neocortical cell loss.

Stereologic evidence for persistence of viable neurons in layer II of the entorhinal cortex and the CA1 field in Alzheimer disease

The entorhinal cortex and hippocampus are the first cortical regions to be affected by the degenerative cellular process that leads to Alzheimer disease (AD) and display a limited degree of neuronal alterations in normal aging. Several quantitative studies have reported a substantial loss of neurons in these regions and a parallel increase in the number of neurofibrillary tangles (NFTs). However, accurate quantitative data on the dynamics of NFT formation are lacking. Here, we performed a stereologic assessment of the proportions of intracellular and extracellular (ghost) NFTs (iNFTs and eNFTs, respectively) and unaffected neurons in layer II of the entorhinal cortex and in the pyramidal cell layer of the CA1 field of the hippocampus in elderly control cases compared to cases with varying degrees of cognitive dysfunction. The data revealed differential rates of formation of iNFTs and eNFTs between the 2 regions and confirmed the presence of a severe disease-associated, but not age-related, neuronal loss. They also revealed that large numbers of neurons may persist either unaffected or in a transitional stage of NFT formation until the late stages of AD progression. These neurons with viability potential constitute 73% of the total numbers of profiles in layer II of the entorhinal cortex and 77% in the CA1 field in cases with a Clinical Dementia Rating score of 3. Whereas it is not possible in the present study to assess how functional such neurons with altered physiology might be, it is nonetheless likely that these transitional neurons open new options for potential therapeutic interventions aimed at protecting neurons vulnerable to neurofibrillary degeneration.

Selective vulnerability of corticocortical and hippocampal circuits in aging and Alzheimer's disease

Alzheimer's disease (AD), a classic neurodegenerative disorder, is characterized by extensive yet selective neuron death in the neocortex and hippocampus that leads to dramatic decline in cognitive abilities and memory. Crucial subsets of pyramidal cells and their projections are particularly vulnerable. A more modest disruption of memory occurs often in normal aging, yet such functional decline does not appear to be accompanied by significant neuron death. However, the same circuits that are devastated through degeneration in AD are vulnerable to sublethal age-related biochemical and morphologic shifts that alter synaptic transmission, and thereby impair function. For example, in the monkey neocortex, pyramidal cells that are homologous to those that degenerate in AD do not degenerate with aging, yet they lose spines, suggesting that an age-related synaptic disruption has occurred. Such age-related synaptic alterations have also been reported in hippocampus. For example, NMDA receptors are decreased in certain hippocampal circuits with aging. NMDA receptors are also responsive to circulating estrogen levels, thus interactions between reproductive senescence and brain aging may also affect excitatory synaptic transmission in the hippocampus. Thus, the aging synapse may be the key to age-related memory decline, whereas neuron death is the more prominent and problematic culprit in AD.

Age-related changes in GluR2 and NMDAR1 glutamate receptor subunit protein immunoreactivity in corticocortically projecting neurons in macaque and patas monkeys

A distinct subpopulation of neurons forming long corticocortical projections in the association neocortex is highly vulnerable to the degenerative process in Alzheimer's disease. However, the degree to which age-related molecular and morphologic alterations of identifiable neuronal populations reflects early cellular degeneration leading to functional deficits has not yet been fully investigated in the aging brain. We performed an immunohistochemical analysis of neurons forming short and long corticocortical projections in young and old monkeys using antibodies to the GluR2 and NMDAR1 glutamate receptor subunit proteins. Projection neurons differed in their expression of these receptor subunits, as GluR2 was less prevalent than NMDAR1 among retrogradely labeled neurons. Long and short corticocortical pathways in old animals demonstrated a considerable decrease in the proportions of projection neurons containing GluR2 and NMDAR1, an observation that was particularly consistent in the case of GluR2. No age-related differences were observed in distribution of neurofilament protein in either type of projection neurons. These data suggest that cortical neurons furnishing long and short corticocortical projections display consistent neurochemical changes during aging and that a differential decrease in cellular expression of glutamate receptor subunit proteins occurs. The fact that in aging these neurons have lower levels of GluR2 than in young individuals, but comparatively higher levels of NMDAR1 than GluR2, may render them prone to calcium-mediated excitotoxicity, which in humans may be related to the selective vulnerability of such neurons during the course of Alzheimer's disease. Also, it is apparent that age-related neuronal changes are quite subtle and involve subcellular components of the cortical circuits rather than major morphologic alterations.

Garbage catastrophe theory of aging: imperfect removal of oxidative damage?

Increasing evidence suggests an important role of oxidant-induced damage in the progress of senescent changes, providing support for the free radical theory of aging proposed by Harman in 1956. However, considering that biological organisms continuously renew their structures, it is not clear why oxidative damage should accumulate with age. No strong evidence has been provided in favor of the concept of aging as an accumulation of synthetic errors (e.g. Orgel's 'error-catastrophe' theory and the somatic mutation theory). Rather, we believe that the process of aging may derive from imperfect clearance of oxidatively damaged, relatively indigestible material, the accumulation of which further hinders cellular catabolic and anabolic functions. From this perspective, it might be predicted that: (i) suppression of oxidative damage would enhance longevity; (ii) accumulation of incompletely digested material (e.g. lipofuscin pigment) would interfere with cellular functions and increase probability of death; (iii) rejuvenation during reproduction is mainly provided by dilution of undigested material associated with intensive growth of the developing organism; and (iv) age-related damage starts to accumulate substantially when development is complete, and mainly affects postmitotic, cells and extracellular matrix, not proliferating cells. There is abundant support for all these predictions.

Neurofilament-immunoreactive neurons are not selectively vulnerable in Alzheimer's disease

Abnormal neurofilament protein distribution and phosphorylation contributes to the cytoskeletal pathology of Alzheimer's disease. Anatomical studies suggest that cortical neurons immunoreactive for nonphosphorylated 200-kDa neurofilament are most vulnerable. We repeated these studies in formalin-fixed temporal lobe tissue from five Alzheimer's disease cases with tissue volume loss compared to five controls without tissue loss. Immunohistochemistry for nonphosphorylated and phosphorylated forms of the neurofilament protein was counterstained for Nissl substance and immuno-positive and -negative pyramidal neurons quantified using areal fraction counts. Compared with controls, cases with Alzheimer's disease had similar numbers of neurons expressing the nonphosphorylated neurofilament protein, suggesting these neurons are largely spared by the disease process. In Alzheimer's disease there was a significant increase in neurons containing phosphorylated neurofilament and tau proteins and a decrease in neurons devoid of neurofilament protein. Our results challenge the theory that neurons containing 200 kDa neurofilament are selectively vulnerable in Alzheimer's disease.

Early and selective pathology of light chain neurofilament in the spinal cord and sciatic nerve of G86R mutant superoxide dismutase transgenic mice

Pathologic accumulation of neurofilament protein (NF), both within spheroids of the proximal axon and within inclusions of motor neuron somata, is a hallmark of neurodegeneration in amyotrophic lateral sclerosis (ALS). Transgenic mice that express mutations in superoxide dismutase (SOD-1), which were genetically linked to familial ALS, develop symptomatology and pathology that strongly resemble ALS and therefore provide a useful model for studying the disease. Examining NF in the G86R mutant SOD-1 transgenic mice, we previously demonstrated that phosphorylated NF accumulates in motor neuron somata of symptomatic transgenic mice. In the present study, we expand these results by examining the immunocytochemical distribution of the three subunits of NF (i.e., light, medium, and heavy chains) as well as tubulin in presymptomatic and symptomatic SOD-1 transgenic mice. Although all NF subunits, but not tubulin, accumulate along with phosphorylated NF in the spinal cord inclusions of symptomatic mice, numerous inclusions containing only light chain NF are found in the spinal cord of presymptomatic SOD-1 transgenic mice. In addition to these results in the spinal cord, intensely immunoreactive aggregates of NF-L, but not the other NF subunits or tubulin, were observed in the sciatic nerve of both symptomatic and presymptomatic mutant SOD-1 transgenic mice. These results suggest that the mechanism of NF alteration in SOD-1 transgenic mice, and also perhaps in ALS patients, originates with the disruption of NF-L, only later involving the other subunits.

Neuropathology of mitral valve prolapse in man and cardiopulmonary bypass (CPB) surgery in adolescent Yorkshire pigs

We investigated the brains of non-demented individuals with mitral valve prolapse (MVP) and found evidence of Alzheimer-like lesions. This neuropathology consisted of premature presence of beta-amyloid-containing senile plaques (SP) without increased prevalence of neurofibrillary tangles. Low levels of SP occurred in 20 to 45- year-old subjects with MVP, and much greater densities were observed in subjects between 45 and 62 years of age. We also investigated the brains of adolescent Yorkshire pigs undergoing cardiopulmonary bypass surgery and likewise found evidence of Alzheimer-like neuropathology. This took the form of intraneuronal accumulation of beta-amyloid immunoreactivity and increasing numbers of Alz-50 immunoreactive neurons with reduced recovery of cardiac efficiency after the surgery. Based on prevailing concepts in Alzheimer's disease, it is feasible to hypothesize that cognitive dysfunction occurring after cardiopulmonary bypass surgery with coronary artery grafting or valve repair/replacement is a functional sequela of AD-like neuropathology. This postulate is based on the premise that an individual seeking such surgery would have pre-existing, elevated AD-like neuropathology to start with. It is further coupled with the probability that these forms of cardiovascular surgery exacerbate the extent and progression of AD-like neuropathology.

Increased density of metallothionein I/II-immunopositive cortical glial cells in the early stages of Alzheimer's disease

We have examined the possible role of metallothionein I/II (MT I/II) in Alzheimer's disease (AD), with a focus on the cellular localization of MT I/II relative to the astrocyte marker, glial fibrillary acidic protein (GFAP). In AD and preclinical AD cases, MT I/II immunolabeling was present in glial cells and did not show a spatial relationship with beta-amyloid plaques or neurofibrillary pathology. There was a six- to sevenfold increase in both MT I/II- and GFAP-labeled cells in the gray matter of AD cases, relative to non-AD cases. However, there was a threefold increase in MT I/II-immunoreactive cells, but not GFAP-labeled cells, in the gray matter of preclinical AD cases compared to non-AD cases. Therefore, the specific increase in MT I/II is associated with the initial stages of the disease process, perhaps due to oxidative stress or the mismetabolism of heavy metals.

Selective vulnerability of neocortical association areas in Alzheimer's disease

This article reviews the possible relationships between the localization of cellular pathologic changes in Alzheimer's disease (AD), and the distribution of neuronal components of the neocortical circuitry that are affected by these alterations. In particular, evidence from the study of large autopsy series supporting the role of the inferior temporal cortex as a key area in the progression of the dementing process is presented. The notion of selective vulnerability in AD at the level of affected neocortical association areas, layers, and specific cell populations is discussed to provide insight into the molecular background of the development of neurofibrillary tangles within the cerebral cortex. Moreover, recent data on pathological correlates of apraxia in AD are examined in the light of the hypothesis of global corticocortical disconnection in this disorder.

Neurofilament proteins in Y-cells of the cat lateral geniculate nucleus: normal expression and alteration with visual deprivation

We examined neurofilament staining in the normal and visually deprived lateral geniculate nucleus (LGN), using the SMI-32 antibody. This antibody preferentially stains LGN cells that display the morphological characteristics of Y-cells. The soma sizes of SMI-32-stained cells were consistent with those of the overall population of Y-cells, and the Golgi-like staining of their dendrites revealed a radial distribution that often crossed laminar boundaries. Labeled cells were distributed within the A laminae (primarily near laminar borders), the magnocellular portion of the C laminae, and the medial intralaminar nucleus, but they were absent in the parvocellular C laminae. Electron microscopic examination of SMI-32-stained tissue revealed that staining was confined to somata, dendrites, and large myelinated axons. Retinal synapses on SMI-32-labeled dendrites were primarily simple axodendritic contacts; few triadic arrangements were observed. In the LGN of cats reared with monocular lid suture, SMI-32 staining was decreased significantly in the A laminae that received input from the deprived eye. Dephosphorylation of the tissue did not alter the cellular SMI-32 staining patterns. Analysis of staining patterns in the C laminae and monocular zone of the A laminae suggests that changes in the cytoskeleton after lid suture reflect cell class and not binocular competition. Taken together, the results from normal and lid-sutured animals suggest that the cat LGN offers a unique model system in which the cytoskeleton of one class of cells can be manipulated by altering neuronal activity.

Regulation of neurofilament interactions in vitro by natural and synthetic polypeptides sharing Lys-Ser-Pro sequences with the heavy neurofilament subunit NF-H: neurofilament crossbridging by antiparallel sidearm overlapping

Neurofilaments are organised into parallel bundles in axons through crossbridges formed by lateral projections of neurofilament subunits. Pure neurofilaments form gels in vitro, consisting of interconnected parallel arrays of filaments regulated by the phosphorylation level of neurofilament subunits. Neurofilament-associated polypeptides sharing phosphorylated epitopes with the repetitive lysine-serine-proline (Lys-Ser-Pro) motifs of the neurofilament heavy subunit sidearm are characterised: they regulate in vitro the neurofilament gelation kinetics in a concentration- and phosphorylation-dependent manner. Studies with synthetic peptides show that interactions between neurofilaments involve both acid and base amino acid residues of neurofilament sidearms and demonstrate the opposite effects of peptides containing either one (inhibition) or two (activation) Lys-Ser-Pro motifs. Electron microscopy reveals an organised network of native neurofilament sidearms, regulated by the phosphorylation level of neurofilament subunits, suggesting a structural transition between intra- and inter-neurofilament sidearm interactions. These results favour the hypothesis of a mechanism of neurofilament crossbridging through the variable antiparallel overlapping of the phosphorylable Lys-Ser-Pro domains of neurofilament sidearms from adjacent filaments, following an equilibrium regulated by neurofilament-associated proteins, bivalent cations and the phosphorylation level of Lys-Ser-Pro motifs from both neurofilament sidearms and neurofilament-associated proteins.

Cortical distribution of neurofibrillary tangles in Alzheimer's disease matches the pattern of neurons that retain their capacity of plastic remodelling in the adult brain

The formation of neurofibrillary tangles in Alzheimer's disease shows a preferential involvement of certain cytoarchitecturally defined cortical areas suggesting systematic differences in regional neuronal vulnerability. The cellular and molecular nature of this selective neuronal vulnerability that follows a certain hierarchy of structural brain organization is largely unknown. In the present study, we compared the regional pattern of tangle density in Alzheimer's disease with systematic regional differences in neuronal plasticity that can be observed both during ageing and in Alzheimer's disease. Changes in dendritic length and arborization of Golgi-impregnated pyramidal neurons were analysed after three-dimensional reconstruction in 12 cortical areas. The intensity of dendritic remodelling that was observed during ageing as well as in Alzheimer's disease was regionally different and decreased in the following order: transentorhinal region > limbic areas (entorhinal region, hippocampus) > non-primary association areas (37, 40, 46) > primary sensory association areas (7, 18, 22) > primary sensory and motor cortex (17, 41, 4). These regional differences of neuronal plasticity follow the same pattern as the regional vulnerability to tangle formation in Alzheimer's disease. The results of the present study provide evidence that a high degree of structural neuronal plasticity might predispose neurons to tangle formation.

Relationship between apolipoprotein E and the amyloid deposits and dystrophic neurites of Alzheimer's disease

Although the inheritance of certain apolipoprotein E (ApoE) alleles has been recognized as a genetic risk factor for Alzheimer's disease, the role of ApoE in the pathology underlying this disease is unclear. Several reports have emphasized the association of ApoE with either beta-amyloid plaque formation or the development of neurofibrillary pathology. Utilization of multiple label immunohistochemical methods enabled us to examine directly the localization of ApoE immunoreactivity relative to beta-amyloid plaques, dystrophic neurites and neurofibrillary tangles. In Alzheimer's disease cases, beta-amyloid plaques showing high ApoE immunoreactivity were localized to layers II, III and V of the neocortex. In layer I, beta-amyloid plaques were unlabelled for ApoE relative to beta-amyloid. Dense core plaques labelled for beta-amyloid often had only the central portions labelled for ApoE. Conversely, ApoE labelled spherical structures within some plaques were not immunoreactive for beta-amyloid or dystrophic neurite markers. Unlike beta-amyloid labelled plaques, all ApoE immunoreactive plaques were associated with dystrophic neurites. In preclinical Alzheimer's disease cases, most plaques were double labelled for beta-amyloid and ApoE. ApoE did not label dystrophic neurites or the early stages of neurofibrillary tangle formation, indicating that ApoE may not be directly involved in neurofibrillary pathology. The specific presence of ApoE in plaques associated with dystrophic neurites in demented patients suggests that ApoE may contribute toward a higher degree of beta-amyloid fibrillogenesis, enhancing the ability of certain plaques to cause damage to surrounding axons.

Life and death of neurons in the aging brain

Neurodegenerative disorders are characterized by extensive neuron death that leads to functional decline, but the neurobiological correlates of functional decline in normal aging are less well defined. For decades, it has been a commonly held notion that widespread neuron death in the neocortex and hippocampus is an inevitable concomitant of brain aging, but recent quantitative studies suggest that neuron death is restricted in normal aging and unlikely to account for age-related impairment of neocortical and hippocampal functions. In this article, the qualitative and quantitative differences between aging and Alzheimer's disease with respect to neuron loss are discussed, and age-related changes in functional and biochemical attributes of hippocampal circuits that might mediate functional decline in the absence of neuron death are explored. When these data are viewed comprehensively, it appears that the primary neurobiological substrates for functional impairment in aging differ in important ways from those in neurodegenerative disorders such as Alzheimer's disease.

Cerebral cortex pathology in aging and Alzheimer's disease: a quantitative survey of large hospital-based geriatric and psychiatric cohorts

In order to explore the relationships between the involvement of specific neuronal populations and cognitive deterioration, and to compare the hierarchical patterns of cortical involvement in normal brain aging and Alzheimer's disease, over 1200 brains from elderly subjects without cognitive deficits, as well as from patients with age-associated memory impairment and Alzheimer's disease, were examined. Our results suggest that the neuropathological changes associated with normal brain aging and Alzheimer's disease affect select cortical circuits at different points in time. Extensive hippocampal alterations are correlated with age-associated memory impairment, whereas substantial neurofibrillary tangle formation in neocortical association areas of the temporal lobe is a prerequisite for the development of Alzheimer's disease. Despite several lines of evidence involving amyloid deposit in the pathogenesis of Alzheimer's disease and Down's syndrome, our observations indicate that there is no correlation between senile plaque densities and degree of dementia in both disorders. In contrast to younger elderly cases, in the ninth and tenth decades of life, there is a differential cortical involvement in that parietal and cingulate areas are early affected in the course of Alzheimer's disease, and neocortical senile plaques densities are strongly correlated with the severity of dementia. Moreover, Alzheimer's disease symptomatology is characterized in these very old patients by high neurofibrillary tangle densities in the anterior CA1 field, but not in the entorhinal cortex and inferior temporal cortex. These observations are discussed in the light of the hypothesis of global corticocortical disconnection and with respect to the notion of selective neuronal vulnerability in Alzheimer's disease.

Age-dependent changes in the immunoreactivity for neurofilaments in rabbit hippocampus

The distribution of the three subunits of neurofilaments was examined in the hippocampus of young adult rabbits (three months of age), employing a panel of six monoclonal antibodies. Thereafter, age-dependent and subunit-selective changes in neurofilament immunoreactivity in the ageing rabbit hippocampus were studied, using animals of one, three, six, 12, 24, 30, 36, 48, and 60 months. Principal cells, interneurons, axons, and various fibre systems were immunoreactive for all three subunits, although the localization and staining intensity of neurofilament immunoreactivity depended on the antibody used. Small cells immunopositive for the low subunit of neurofilament (presumably glial cells) were found abundantly in the hippocampal formation at one month, and (occasionally) at 30-36 months. Young rabbits (one to three months of age) had high numbers of interneurons stained for the high subunit of neurofilament in the stratum oriens/pyramidale. The number declined and plateaued to approximately 78% at six to 30 months, and further declined and plateaued to approximately 56% at 36-60 months. The first decline may reflect a process of maturation, while the latter decline most likely relates to ageing. Ageing pyramidal cells in 48-60 months animals revealed a slight increase for the low subunit of neurofilament, but no changes for the other subunits. Transient changes in neurofilament immunoreactivity were a striking observation in dentate gyrus granule cells during ageing. The staining intensity for the low subunit of neurofilament decreased gradually from one to 24-30 months until it was no longer detectable in these cells. The immunoreactivity then reappeared, most notably in granule cells lining the hilus, at the age of 36-48 months. By 60 months all granule cells were nearly immunonegative for this subunit. Axonal aberrations, immunoreactive for all three subunits, were found throughout the hippocampal formation. These aberrations first appeared in 24-month-old animals and increased in number and maximal size in older rabbits. The alterations in neurofilament immunoreactivity in the ageing hippocampus correlated with age-associated learning disabilities in the acquisition of a hippocampally-dependent learning task. The potential relevance of changes in the cytoskeletal profile of hippocampal neurons to age-associated learning and memory disabilities is discussed.

The cellular mechanism underlying neuronal degeneration in glaucoma: parallels with Alzheimer's disease

Evidence is presented that the characteristic pattern of neuronal degeneration associated with glaucoma is due to a combination of the persistent physical damage to axons at the level of the lamina cribrosa and the associated neuronal reaction to this kind of trauma. The class of neuronal cytoskeletal proteins known as the neurofilament triplet are crucially involved in the reaction to physical damage and the selective localization of these proteins to larger retinal ganglion cells may underlie their susceptibility to eventual degeneration. The appearance of glaucoma-like neuronal pathology in Alzheimer's disease may follow the reaction of neurofilament-containing retinal ganglion neurons to persistent damage to their axons by beta-amyloid plaque formation in subcortical visual centers.

The cellular basis for the relative resistance of parvalbumin and calretinin immunoreactive neocortical neurons to the pathology of Alzheimer's disease

The vulnerability of nerve cells to the neurofibrillary pathology of Alzheimer's disease (AD) may be determined by the presence within them of certain cytoskeletal proteins. Fluorescence multiple labeling was used to assess the vulnerability of two separate subpopulations of nonpyramidal neurons in the superior frontal gyrus, distinguished by their content of the calcium-binding proteins parvalbumin (PV) and calretinin (CR), to the neuropathology of AD. In AD, counterstaining PV- and CR-labeled sections with thioflavine S demonstrated that the great majority of these cells did not contain neurofibrillary tangles, except for the large CR-immunoreactive neurons in layer I. This latter group of cells was also characterized as containing neurofilament (NF) triplet proteins, whereas other CR-labeled cortical neurons were not immunoreactive for NF. There was also a small AD-related increase in the proportion of PV-labeled cells showing NF protein immunoreactivity (1-9% of the total population in AD cases compared to 0-0.4% in non-AD cases), which likewise may be linked to the susceptibility of a minute proportion (0-0.7%) of these neurons to form neurofibrillary tangles in AD. These data are further evidence that the presence of NF in cortical nerve cells is linked to their vulnerability to the pathological process underlying AD.

Neurofilament protein is differentially distributed in subpopulations of corticocortical projection neurons in the macaque monkey visual pathways

Previous studies of the primate cerebral cortex have shown that neurofilament protein is present in pyramidal neuron subpopulations displaying specific regional and laminar distribution patterns. In order to characterize further the neurochemical phenotype of the neurons furnishing feedforward and feedback pathways in the visual cortex of the macaque monkey, we performed an analysis of the distribution of neurofilament protein in corticocortical projection neurons in areas V1, V2, V3, V3A, V4, and MT. Injections of the retrogradely transported dyes Fast Blue and Diamidino Yellow were placed within areas V4 and MT, or in areas V1 and V2, in 14 adult rhesus monkeys, and the brains of these animals were processed for immunohistochemistry with an antibody to nonphosphorylated epitopes of the medium and heavy molecular weight subunits of the neurofilament protein. Overall, there was a higher proportion of neurons projecting from areas V1, V2, V3, and V3A to area MT that were neurofilament protein-immunoreactive (57-100%), than to area V4 (25-36%). In contrast, feedback projections from areas MT, V4, and V3 exhibited a more consistent proportion of neurofilament protein-containing neurons (70-80%), regardless of their target areas (V1 or V2). In addition, the vast majority of feedback neurons projecting to areas V1 and V2 were located in layers V and VI in areas V4 and MT, while they were observed in both supragranular and infragranular layers in area V3. The laminar distribution of feedforward projecting neurons was heterogeneous. In area V1, Meynert and layer IVB cells were found to project to area MT, while neurons projecting to area V4 were particularly dense in layer III within the foveal representation. In area V2, almost all neurons projecting to areas MT or V4 were located in layer III, whereas they were found in both layers II-III and V-VI in areas V3 and V3A. These results suggest that neurofilament protein identifies particular subpopulations of corticocortically projecting neurons with distinct regional and laminar distribution in the monkey visual system. It is possible that the preferential distribution of neurofilament protein within feedforward connections to area MT and all feedback projections is related to other distinctive properties of these corticocortical projection neurons.

Plaque biogenesis in brain aging and Alzheimer's disease. I. Progressive changes in phosphorylation states of paired helical filaments and neurofilaments

Paired helical filament (PHF)/tau immunoreactive dystrophic neurites are a common pathological feature in the brain of patients with Alzheimer's disease. Recent studies suggest that swollen neurofilament-immunoreactive neurites are also present in senile plaques. In the present study, we investigated whether PHF/tau-positive dystrophic neurites are located in all subtypes of plaques and whether swollen neurofilament-immunoreactive neurites are hyper-phosphorylated, using a battery of antibodies to PHF/tau, neurofilament, and beta-amyloid protein. PHF/tau-positive dystrophic neurites were present in and around nearly all subtypes of plaques, including small amyloid deposits, diffuse plaques, and perivascular plaques in the hippocampal formation of Alzheimer brain. The earlier changes were detectable with AT8 antibody and later changes with PHF-1 antibody. Plaque-associated PHF/tau-positive dystrophic neurites were rare or absent in the hippocampal formation of normal aged brain. Swollen neurofilament-positive neurites appeared to be hyper-phosphorylated in Alzheimer's disease and to a lesser degree in aged control brains. Neurites that contained hyper-phosphorylated tau as well as neurofilament were strongly argentophilic because both populations of dystrophic neurites stained with silver stains. Swollen neurofilament-positive plaque-associated neurites were often present in the absence of PHF/tau-positive plaque-associated dystrophic neurites. These data suggest that PHF/tau-positive dystrophic neurites are a common component of all subtypes of plaques in Alzheimer brain and neurofilament protein in swollen neurites, like tau protein, is hyper-phosphorylated. Hyper-phosphorylated neurofilaments in plaque-associated neurites may represent one of the earliest cytoskeletal changes in vulnerable neurons in Alzheimer's disease and aged control brains.

Neuronal activity and early neurofibrillary tangles in Alzheimer's disease

We studied neuronal activity and its relation to the accumulation of neurofibrillary tangles in Alzheimer's disease (AD) neurons by in situ hybridization to cytochrome oxidase subunit III messenger RNA, a marker of mitochondrial energy metabolism. In AD midtemporal cortex, levels of cytochrome oxidase subunit III messenger RNA were decreased by 26% in neurons bearing early-stage neurofibrillary tangles as compared to tangle-free neurons (p < 0.01). However, levels of 12S ribosomal RNA, also encoded by mitochondrial DNA, and of total messenger RNA were decreased only in later stages of tangle development. Comparing tangle-free neurons of 4 AD brains to tangle-free neurons of 3 control brains, levels of cytochrome oxidase subunit III messenger RNA were found to be 25% lower (p < 0.001) in AD tangle-free neurons. Because energy metabolic needs of neurons are mainly determined by synaptic input, the observed decreases in cytochrome oxidase subunit III messenger RNA likely reflect downregulation due to impaired synaptic function in AD. Thus, a failure in synaptic transmission may precede tangle formation. A further decline in neuronal activity is seen as tangle formation progresses. However, these results can also be viewed as showing the viability and continuing activity, albeit at a lower level, of neurons in the early stages of neurofibrillary pathology.

Increased ALZ-50 immunoreactivity in sudden infant death syndrome

Neuronal expression of the ALZ-50 epitope was investigated in hippocampus and medulla from infants dying of sudden infant death syndrome or known causes (controls). Hippocampal studies include data from 31 infants dying of known causes between 32 weeks' gestation and 16 months postpartum and 46 infants who died of sudden infant death syndrome. The medulla at the level of the mid olivary protuberance was investigated in 22 infants with sudden infant death syndrome and 11 controls matched for age and postmortem interval. Medullary sections were also examined using immunohistochemical methods to demonstrate reactivity to glial fibrillary acidic protein antibody. The density of ALZ-50-immunodecorated neurons in control hippocampus rises from the level observable in utero to a maximum between 1 and 4 months of age and declines thereafter. The density of ALZ-50-immunoreactive neurons in hippocampus is significantly increased in infants with sudden infant death syndrome at all ages. Significant regionally specific increases in the number of ALZ-50-immunoreactive neurons, and glial fibrillary acidic protein-reactive cells were found in sudden infant death syndrome medulla; coincidental increases were observed in only the solitary nucleus. Neurons exhibiting the ALZ-50 epitope may reflect apoptotic neuron death of normal development, and increased numbers of immunoreactive neurons may suggest enhanced neurodegeneration in sudden infant death syndrome.

Neurochemical phenotype of corticocortical connections in the macaque monkey: quantitative analysis of a subset of neurofilament protein-immunoreactive projection neurons in frontal, parietal, temporal, and cingulate cortices

The neurochemical characteristics of the neuronal subsets that furnish different types of corticocortical connections have been only partially determined. In recent years, several cytoskeletal proteins have emerged as reliable markers to distinguish subsets of pyramidal neurons in the cerebral cortex of primates. In particular, previous studies using an antibody to nonphosphorylated neurofilament protein (SMI-32) have revealed a consistent degree of regional and laminar specificity in the distribution of a subpopulation of pyramidal cells in the primate cerebral cortex. The density of neurofilament protein-immunoreactive neurons was shown to vary across corticocortical pathways in macaque monkeys. In the present study, we have used the antibody SMI-32 to examine further and to quantify the distribution of a subset of corticocortically projecting neurons in a series of long ipsilateral corticocortical pathways in comparison to short corticocortical, commissural, and limbic connections. The results demonstrate that the long association pathways interconnecting the frontal, parietal, and temporal neocortex have a high representation of neurofilament protein-enriched pyramidal neurons (45-90%), whereas short corticocortical, callosal, and limbic pathways are characterized by much lower numbers of such neurons (4-35%). These data suggest that different types of corticocortical connections have differential representation of highly specific neuronal subsets that share common neurochemical characteristics, thereby determining regional and laminar cortical patterns of morphological and molecular heterogeneity. These differences in neuronal neurochemical phenotype among corticocortical circuits may have considerable influence on cortical processing and may be directly related to the type of integrative function subserved by each cortical pathway. Finally, it is worth noting that neurofilament protein-immunoreactive neurons are dramatically affected in the course of Alzheimer's disease. The present results support the hypothesis that neurofilament protein may be crucially linked to the development of selective neuronal vulnerability and subsequent disruption of corticocortical pathways that lead to the severe impairment of cognitive function commonly observed in age-related dementing disorders.

Increased incidence of neurofibrillary tangles (NFT) in non-demented individuals with hypertension

The incidence rates and numerical densities of argryophilic neurofibrillary tangles (NFT) and senile plaques (SP) were determined in non-demented individuals and subjects with Alzheimer's disease (AD). The non-AD subjects were grouped according to cardiac status; those individuals with critical coronary artery disease (cCAD), those hypertensive individuals without cCAD (HyperT), and those without heart disease (non-HD). The incidence and densities of SP and NFT were significantly greater in AD than any of the non-demented groups. The prevalence of SP was increased in both HyperT and cCAD compared to non-HD controls, while NFT occurrence was accentuated in non-demented HyperT subjects only. The densities of SP and NFT in HyperT were elevated compared to cCAD or both cCAD and non-HD controls; NFT densities were similar in cCAD and non-HD. NFT density increased with increasing age in only the non-HD and cCAD groups, suggesting a possible relationship between disease process and NFT formation in the AD and HyperT populations.

Ubiquitin-positive achromatic neurons in corticobasal degeneration

A 66-year-old woman presented with an alien limb syndrome without dementia. The course of her illness was unremitting and at autopsy 6 years later her diagnosis was confirmed as corticobasal degeneration without Alzheimer-type pathology. Although the presence of ballooned achromatic cortical neurons and cell loss from the substantia nigra distinguishes such patients, the site and density of achromatic neurons has not previously been quantified. We show that immunohistochemistry for the cell stress protein ubiquitin selectively stains these achromatic neurons, whereas they do not stain for abnormally phosphorylated tau protein. Phosphorylated neurofilament antibodies recognise both ballooned and non-ballooned neurons. In this case, high densities of ubiquitin-positive ballooned neurons were found in frontal cortical regions with the highest densities in layers V and VI of the anterior cingulate cortex. In addition, high densities of ubiquitin-positive ballooned neurons were found in the insular cortex, claustrum and amygdala. These results confirm past reports of frontal pathology, but show that there is also considerable pathology in insular and parahippocampal cortical regions and some subcortical regions. Our findings suggest that the distribution and staining characteristics of ballooned neurons in corticobasal degeneration may help to differentiate these cases pathologically, while the absence of dementia appears to be an important clinical criterion.