Voronoi tessellation to study the numerical density and the spatial distribution of neurones

The conditions of regularity and isotropy, required by standard morphometric procedures, are generally not fulfilled in the central nervous system (CNS) where cells are distributed in a highly complex manner. The evaluation of the mean numerical density of neuronal or glial cells does not take into account the topographical heterogeneity and thereby misses the information that it contains. A local measurement of the density can be obtained by evaluating the 'numerical density of one cell', i.e. the ratio 1/(the volume that the cell occupies). This volume is the region of space that is closer to that cell than to any other. It has the shape of a polyhedron, called Voronoi (or Dirichlet) polyhedron. In 2-D, the Voronoi polyhedron is a polygon, the sides of which are located at mid-distance from the neighbouring cells. The Voronoi polygons are contiguous and their set fills the space without interstice or overlap, i.e. they perform a 'tessellation' that may yield a density map when the same colours are used to fill polygons of similar sizes. The use of Voronoi polygons allows computing the confidence interval of a mean numerical density that makes statistical comparisons possible. The tessellation also provides information concerning spatial distribution; the areas of the Voronoi polygons do not vary much when the cells are regularly distributed. On the contrary, small and large polygons are found when cellular clusters are present. The coefficient of variation of the polygon areas is an objective measurement of their variability and helps to define 'regular', 'clustered' and 'random' distributions. When cells are clustered, small polygons are contiguous and may be objectively identified by simple algorithms. Voronoi tessellations are easily performed in 2-D. On an average the area of a polygon times the thickness of the section equals the volume of the corresponding polyhedron. 3-D tessellations that are theoretically possible and for which algorithms have been published remain to be adapted to histological works.

Impaired brain development and hydrocephalus in a line of transgenic mice with liver-specific expression of human insulin-like growth factor binding protein-1

Insulin-like growth factors (IGFs) produced in the brain are known to participate in brain development via activation of the type 1 IGF receptor. IGF binding proteins (IGFBPs) modulate the cellular action of IGFs and some are expressed in the fetal brain. Under normal conditions IGFBP-1 is not one of these, but IGFBP-1 expression obtained via transgenesis using ubiquitous promoters affects brain development. In earlier work, we established a model of transgenic mouse in which liver-specific IGFBP-1 expression begins during fetal life. The repercussions of this IGFBP-1 over-expression include reproductive defects, ante- and perinatal mortality and post-natal growth retardation, the extent of which is related to the degree of transgene expression. Unexpectedly, during the first 2 months of postnatal life, there were some cases of head enlargement revealing hydrocephalus among homozygotes, frequently associated with motor disorders. Brain sections showed dilatation of the lateral ventricles in 10 out of 15 homozygotes examined. Histologically, dilatation was evident in four out of nine heterozygotes. Brain weight in transgenics was relatively less reduced than the weights of other organs. Hence, brain weight/body weight ratios were normal in heterozygotes and on average higher than normal in homozygotes. The width of the cerebral cortex was reduced in homozygotes, with disorganized neuronal layers. The corpus callosum was underdeveloped, particularly in homozygotes. The area of the hippocampus was reduced in homozygotes and one-third of the heterozygotes, with a short and thick dentate gyrus in the former. Similar anomalies have been reported in mice with disruption of the igf-I gene and in a model of transgenic mice over-expressing IGFBP-1 in all tissues, including the brain. Hydrocephalus was not mentioned in these reports, raising the possibility that insertional mutagenesis may have been involved in our mice. Nevertheless, our observations indicate that hepatic over-expression of IGFBP-1 may have endocrine effects on brain development.

The extent of neurofibrillary pathology in perforant pathway neurons is the key determinant of dementia in the very old

Neurofibrillary pathology as found in Alzheimer's disease (AD) is also found in the normal elderly, suggesting that these changes may be part of the aging process. In this study, we assessed the densities and distribution of structures recognized by the monoclonal antibody (mAb) to phosphorylated tau (AT8) in the hippocampal formation and medial temporal isocortex of 19 centenarians. Of these, 4 cases were demented and 15 non-demented. AT8 immunoreactivity correlated with the global deterioration scale (GDS). The density of both intraneuronal neurofibrillary tangles (I-NFTs) and neuritic clusters (NCs) significantly correlated with the GDS in the layer II of the entorhinal cortex (r = 0.66, P = 0.005 and r= 0.611, P = 0.01, respectively). Density of I-NFTs in the subiculum (r = 0.491; P = 0.034) also correlated significantly. No other area was found to be statistically significant. Importantly, no correlation was found when demented and non-demented centenarian cases were analyzed separately, suggesting that the difference marks a fundamental shift between AD and non-demented individuals. This assertion is supported by the significantly higher densities of I-NFTs and NCs in the transentorhinal (P = 0.043 and P = 0.011, respectively) and layer II of the entorhinal cortex (P = 0.02 and P = 0.007, respectively), and I-NFTs in the subiculum (P < 0.001) and CAI (P = 0.011) in the demented group when compared with the non-demented cases. Granular diffuse deposits, an early stage parameter of the neurofibrillary pathology involving accumulation of non-fibrillar abnormally phosphorylated tau protein did not correlate with the GDS or between the two groups studied. This study, combining morphometric and confocal analyses, not only provides further evidence that, in the brains of patients with AD, the perforant pathway is highly sensitive to tau pathology but also that involvement is distinct from the changes of normal aging, even of the oldest old.

Behavioral alterations associated with apoptosis and down-regulation of presenilin 1 in the brains of p53-deficient mice

Presenilin 1 (PS1) expression is repressed by the p53 tumor suppressor. As shown herein, wild-type PS1 is an effective antiapoptotic molecule capable of significantly inhibiting p53-dependent and p53-independent cell death. We analyzed, at the functional and molecular levels, the brains of p53 knockout mice. Surprisingly, we found that lack of p53 expression induces apoptotic brain lesions, accompanied by learning deficiency and behavioral alterations. p53-deficient mice show an unexpected overexpression of p21(waf1) with subsequent down-regulation of PS1 in their brains. This process is progressive and age-dependent. These data indicate that the p53 pathway, besides affecting tumor suppression, may play a major role in regulating neurobehavioral function and cell survival in the brain.

Laminar specific loss of isocortical presenilin 1 immunoreactivity in Alzheimer's disease. Correlations with the amyloid load and the density of tau-positive neurofibrillary tangles

Presenilin 1 has been shown to be mutated in a high proportion of cases of familial Alzheimer's disease. Immunoreactive epitopes of the protein have been found mainly in neurones devoid of neurofibrillary tangles - an observation that has led to the conclusion that presenilin 1 could have a protective role. In this study, the relationship between deposits of Abeta peptide (both the 40 and 42 isoforms), tau positive neurofibrillary tangles and presenilin 1-positive neuronal profiles were analysed in three cases of presenilin 1 mutation, four cases of sporadic Alzheimer's disease and five controls. Immunohistochemistry was performed in a sample from the supramarginal gyrus. The proportion of volume occupied by the Abeta1-40 and Abeta1-42 deposits (amyloid load) was evaluated by a point-counting technique. Tau-positive neurofibrillary tangles, and presenilin 1-positive neuronal profiles were directly counted. The location of the lesions in the thickness of the cortex was recorded. The density of PS1-positive neuronal profiles in Alzheimer's disease cases was lower than in the controls. The deficit was significant only in the upper layers of the cortex. The density of presenilin 1 neuronal profiles was negatively correlated with Abeta1-40 and Abeta1-42 loads, and with the density of tau-positive neurofibrillary tangles. Multivariate analysis showed that the Abeta1-42 load was the best determinant of the decrease in presenilin 1-positive neuronal profiles. Presenilin 1-positive neurones appear to be lost rather than protected in the course of Alzheimer disease.

[Research on multiple sclerosis and tissue banks]

Tissue banks are of major importance in research on human tissues, in particular as regards the furthering of our knowledge on multiple sclerosis (MS). Individuals who wish to make a 'donation of their brain' for autopsy, or pathologists in possession of biopsy specimens that have not been utilized for diagnosis provide the necessary material for investigation by research teams. In addition to their technical aspects, brain tissue banks provide information and aid in promoting research. Their functioning, usually supported by patient associations, has encountered certain difficulties. At present, it is challenged by a decrease in the number of autopsies.

[Alzheimer's disease: lesions and their progression]

Alzheimer disease appears to be a stereotyped mode of reaction of the central nervous system to various types of aggression such as different mutations involving various proteins, trisomy 21 or repeated head trauma as in dementia pugilistica. Rather than a disease, it appears to be a clinicopathological syndrome due to various causes. Lesions may be considered under 3 headings: neurofibrillary pathology, A beta peptide deposits and loss (neuronal and synaptic). Neurofibrillary pathology includes the neurofibrillary tangle, the crown of the senile plaque and the neuropil threads. All those lesions are characterized by the same ultrastructure--i.e. the accumulation of paired helical filaments--and the same immunohistochemistry: they are labelled by antibodies directed against the tau proteins. The amyloid deposits, present in the core of the senile plaque and in the vascular walls, are made of a 40 to 42 amino-acids long peptide, named A beta, derived from the amyloid precursor protein (APP). Antibodies directed against the A beta peptide also label diffuse deposits that are devoid of the tinctorial affinities and of the biochemical properties of amyloid substances. Those diffuse deposits are insufficient to cause dementia since they may be observed in high density in aged people without intellectual deterioration. Neuronal loss occurs after neurofibrillary pathology. The role of the synaptic pathology remains discussed. Besides tau proteins, A beta peptide and APP, several other proteins may play an important role: apolipoprotein E which could act as a chaperone protein, inducing or facilitating the formation of amyloid, presenilins 1 and 2, mutated in some cases of familial Alzheimer disease, alpha-synuclein which is present in the Lewy bodies found in Parkinson disease and in dementia with Lewy bodies. The A beta deposits are diffusely distributed in the cerebral cortex; the neurofibrillary changes have a hierarchical distribution. The progression of the neurofibrillary pathology in the various cortical areas follow a stereotyped sequence that may help to grade the severity of the disease. Progression may take decades. The relations between aging and Alzheimer disease are still poorly understood. Frequency of Alzheimer type lesions in old people could suggest that they are the inevitable burden of age, but this has been discussed.

Preservation of midbrain catecholaminergic neurons in very old human subjects

Parkinson's disease is characterized by a progressive degeneration of dopaminergic neurons in the midbrain, yet the cause of this neuronal loss is still unknown. It has been hypothesized that Parkinson's disease could be the consequence of accelerated ageing. In order to reveal a possible common process during ageing and Parkinson's disease neurodegeneration, catecholaminergic neurons of five anatomical regions of the brainstem (substantia nigra, central grey substance, ventral tegmental area, peri- and retrorubral area, and locus coeruleus) have been quantified using immunohistochemical staining for tyrosine hydroxylase (TH) on regularly spaced sections, between the rostral and caudal poles of the mesencephalon and in the rostral pole of the pons, in post-mortem samples of 21 control subjects who died at ages 44-110 years. No statistically significant loss of TH positive neurons was observed in the older subjects, either in the substantia nigra or in the other midbrain regions that are known to degenerate to a lesser degree in Parkinson's disease. Furthermore, in the later regions no neuronal loss was observed from age 44 to 80 years, indicating that this result is not dependent on the inclusion of 'supernormal' very old people. These results suggest that from age 44 to 110 years, ageing in control adults is not, or is scarcely, accompanied by catecholaminergic cell loss in the midbrain and hence Parkinson's disease is probably not caused by an acceleration of a degenerative process during ageing.

Microglia, amyloid and dementia in alzheimer disease. A correlative study

To elucidate the role of microglia in Alzheimer's disease, a clinicopathological study was performed involving 26 cases, the mental status of which had been studied pre mortem by the Blessed test score (BTS). We measured the volume density of CD 68 immunoreactive (IR) microglia, congophilic plaques and Abeta deposits, and the numerical density of neurofibrillary tangles (NFT) in a sample of Area 9 (middle frontal gyrus). Dementia was significantly correlated only with the volume density of Abeta deposits and the numerical density of NFT. The volume densities of microglia and congophilic plaques were strongly correlated. With the intellectual status used as a time scale, IR microglia and amyloid deposits appeared almost simultaneously at an early stage in the pathological cascade and decreased, whereas Abeta and NFT were still accumulating. The intellectual deficit seemed to be more significantly related to the latter two lesions than to the microglia-amyloid complex, that was visible at an earlier stage (around BTS = 15).

MRI description of cerebral atrophy in mouse lemur primates

We assessed cerebral atrophy in mouse lemur primates (Microcebus murinus) by estimating CSF volume in their brains from 4.7 Tesla T2-weighted magnetic resonance images. Thirty animals aged from 1 to 10.3 years were imaged, 14 of them were followed for up to 2 years. Seven of these animals were examined for neuropathology. In 12 out of 17 animals older than 3.5 years, CSF volumes were increased. A subgroup of six animals had severe atrophy of the temporal lobe. Another subgroup of five animals displayed diffuse atrophy in addition to the temporal atrophy. One animal had a dilation of the external part of the temporal horn of the lateral ventricle in addition to the temporal atrophy. The three animals with diffuse atrophy that could be studied for neuropathology had diffuse cerebral amyloid deposits detected by immunocytochemistry. The other animals did not display amyloid deposits. Relations between the different types of atrophy as well as their causes will have to be assessed in future studies.

Altered development of dopaminergic cells in the retina of weaver mice

Postnatal degeneration of dopaminergic (DA) cells is known to occur in mesencephalic nuclei of mutant weaver mice, whereas retinal DA content is reported to be unchanged in the adult animal. To determine whether morphological changes occur in the weaver retinal DA system, we compared weaver and control developing and adult retinas after tyrosine hydroxylase (TH) immunohistochemistry. The density and distribution of DA cells were analyzed using Dirichlet tessellation. Not only was no DA cell loss found in adult weaver retinas, but we even observed an increase in DA cells in weaver compared to control retinas between postnatal days 14 and 30. Furthermore, some unusual features were found during the latter period: atypical cells (representing a maximum of 12% of the whole DA cell population) were observed, and these differed from typical DA cells in terms of both location (slightly more external within the inner nuclear layer) and appearance (flat somata, round and clear nuclei, thick dendritic trunks emerging laterally and giving rise to horizontal processes). Some of the atypical cells were intermingled in a delicate network lying in a more outer focal plane than the main DA plexus. The expression of GIRK2, a G protein-related inward rectifying K(+) channel responsible for the weaver syndrome, was investigated. Although no GIRK2 labeling was demonstrated in DA cells, its possible involvement in the transient disturbances observed in the weaver DA retinal system is discussed.

1914 to 1917: the Great War years

In 1914, American and international neurology were already very well developed, but like the other scientific and societal forces of the time, they underwent numerous changes as a result of World War I. This article reviews the state of neurology between 1914 and 1917 as it can be inferred from the journals of the time, the main topics they covered, the meetings, and the neurological societies, as well as some of the actors on the neurology scene during these years. It concludes with a brief survey of the ways in which neurology was changed by the Great War. During these years, neurology was there.

[Fronto-temporal degenerative dementia. A modern neuropathologic approach]

The classification of degenerative dementias with fronto-temporal atrophy has been debated since the description of Pick's disease. The study of a clinico-pathological series of 10 cases using immunohistochemistry lead to the following conclusions: reserving the name of Pick's disease to those cases with argyrophilic inclusions, the most recognisable and characteristic marker at neuropathological examination, allows an easy and reliable diagnosis; keeping on with the splitting of these disorders into various clinico-pathologic entities seems today more useful than grouping them into a single syndrome until new data, based for example on genetic analysis, show that different phenotypes correspond to the same disease.

Nuclear inclusions in spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1 is due to a CAG repeat expansion in the gene encoding ataxin-1. In a case with an expansion of 56 repeats, intranuclear inclusions were found only in neurons, both in severely affected regions (such as the pons) and in areas where the lesions were inconspicuous (such as the cortex or the striatum). The inclusions were labelled by a monoclonal antibody directed against long polyglutamine stretches (1C2); they were also detected by the anti-ubiquitin antibody. They were faintly eosinophilic, Congo red negative and were not stained by thioflavin S or by ethidium bromide.

[Cortical lesions in progressive supranuclear palsy (Steele-Richardson-Olszewski disease)]

Histopathological changes seen in progressive supranuclear palsy (Steele-Richardson-Olszewski disease) have been thought to be located in subcortical nuclei. However, abundant neurofibrillary tangles have been found recently in several neocortical areas. Their morphology and ultrastructure, regional and laminar distributions, as well as antigenic and biochemical properties make them clearly different from the neurofibrillary tangles observed in Alzheimer's disease and aging. Tau positive fibrillary accumulation in the nevroglia has also been seen in the cortex. The topographical distribution of the lesions is rather stereotyped, but some uncommon distributions (such as pallido-luysonigral) have been identified. Factorial analysis has shown that cortical and subcortical lesions are independent; pedonculopontine nucleus could play a role in the cortical diffusion of the lesions.

Dementia following treatment of brain tumors with radiotherapy administered alone or in combination with nitrosourea-based chemotherapy: a clinical and pathological study

A retrospective clinical and pathological study of 4 patients who developed the syndrome of radiation induced dementia was performed. All patients fulfilled the following criteria: (1) a history of supratentorial irradiation; (2) no evidence of symptomatic recurrent tumor; (3) no other cause of progressive cerebral dysfunction and dementia. The clinical picture consisted of a progressive "subcortical" dementia occurring 3-12 months after a course of cerebral radiotherapy. Examination revealed early bilateral corticospinal tract involvement in all patients and dopa-resistant Parkinsonian syndrome in two. On CT scan and MRI of the brain, the main features consisted of progressive enlargement of the ventricles associated with a diffuse hypodensity/hyperintensity of the white matter best seen on T2 weighted images on MRI. The course was progressive over 8-48 months in 3 patients while one patient had stabilization of his condition for about 28 years. Treatment with corticosteroids or shunting did not produce sustained improvement and all patients eventually died. Pathological examination revealed diffuse white matter pallor with sparing of the arcuate fibers in all patients. Despite a common pattern on gross examination, microscopic studies revealed a variety of lesions that took two basic forms: (1) a diffuse axonal and myelin loss in the white matter associated with tissue necrosis, particularly multiple small foci of necrosis disseminated in the white matter which appeared different from the usual "radionecrosis"; (2) diffuse spongiosis of the white matter characterized by the presence of vacuoles that displaced the normally-stained myelin sheets and axons. Despite a rather stereotyped clinical and radiological course, the pathological substratum of radiation-induced dementia is not uniform. Whether the different types of white matter lesions represent the spectrum of a single pathological process or indicate that the pathogenesis of this syndrome is multifactorial with different target cells, remains to be seen.

[Neuropathologic markers in degenerative dementias]

The number of neuropathological markers used for the diagnosis of degenerative dementias is rapidly increasing, and this is somewhat confusing: some lesions described a long time ago, such as ballooned cells, proved to be less specific than they were supposed to be; this is also the case for Lewy bodies, that have been recognised in a larger spectrum of disorders than thought a few years ago. On the contrary, for an increasing number of neuropathologists, Pick bodies are now mandatory for the diagnosis of Pick disease, and this contrasts with the prevalent opinions of the late sixties or seventies. There are a number of reasons for the changing significance of neuropathological markers. Three of them can be easily identified: 1) the burst of immunohistochemistry into neuropathology allowed an easier recognition, a better delineation and new pathophysiological approaches to old lesions, and a dramatic increase in the description of new markers, especially in glial cells; 2) in some conditions characterized by the number and distribution of some lesions rather than by their mere presence, such as aging and Alzheimer disease, a better neuroanatomical point of view permitted new insights into the concept of disease versus age-related changes; 3) more accurate clinicopathologic correlations showed clearly the need of grouping or lumping together some entities: for example, obvious relationship aroused between progressive supranuclear palsy and corticobasal degeneration; in contrast, distinguishing different disorders in the frontal lobe dementias grouped together into "Pick disease" was felt necessary. This review summarizes the main criteria for identification, and the presumed meaning of the chief markers indicating the presence of abnormally phosphorylated tau proteins, A beta peptides, and PrP proteins. Abnormally phosphorylated tau proteins can be stored in the neurons, and participate in the constitution of many lesions (neurofibrillary tangles, neuropil threads, abnormal processes of the crown of neuritic senile plaques, Pick bodies, granulo-vacuolar degeneration, argyrophilic grains). When seen in neuroglia, they are the chief constituents of various lesions that affect mainly astrocytes (abnormal tufts of fibres, astrocytic plaques, thorn-shaped astrocytes, spiny astrocytes) and also oligodendrocytes (oligodendroglial threads and coils, glial cytoplasmic inclusions). A beta peptides, in "preamyloid" and amyloid conformations, can be seen in the extracellular space (plaques, of the neuritic or non-neuritic varieties, diffuse, focal and granular deposits) and in the vascular walls (amyloid angiopathies). Some PrP deposits are also of the amyloid variety (kuru type, multicentric or florid plaques), but immunohistochemistry, far more sensitive than conventional studies, revealed a number of other lesions (perivacuolar, neuronal, "synaptic" deposits...). Numerous markers are easily detected by ubiquitin immunohistochemistry. Lewy bodies, Pick bodies, neurofibrillary tangles had already be identified by other methods. In contrast, some ubiquitin-positive inclusions are shown, by this technique only, in amyotrophic lateral sclerosis and other conditions which were thus related to this disease. Finally, this review deals with two classic markers, ballooned cells ("Pick cells") and spongiosis seen in disorders due to non conventional agents or prions (spongiform encephalopathies).

[Memory: clinico-pathologic data]

Synaptic modifications are probably the basis of the memory processes that take place in the central nervous system. They have been studied in Aplysia or in hippocampal slices. How these minute alterations of the synaptic strength are integrated in larger neural systems is still poorly understood. In man, hippocampal lesions, when bilateral, cause a deficit in anterograde episodic memory. The loss of previously acquired memories (retrograde amnesia) is limited. Procedural memory is spared. Young patients with hippocampal lesions remain able to learn how to read or to write (abilities that belong to semantic memories). Recordings obtained with intracerebral electrodes have shown that some neurons of the hippocampus act as "place cells". They fire when the animal is in a specific place of the experimental maze, an observation that suggests that the hippocampus acts as a map that may also be viewed as a context indicator (a "cognitive map"). Computer models have been devised to test the hypothesis that the hippocampus recorded the map of the activated synapses at a particular moment in time. This pattern of activity could secondarily be transferred to the isocortex during a process known as consolidation. The frontal lobe plays a role in attention, which greatly influences the memory process. It also plays a role in the various strategies that are used to recall a memory and in the analysis of the quality of the recall (metamemory). An asymmetry has been shown by the PET-scan: the left frontal lobe is activated during acquisition, and the right one during recall. The ability to integrate one's own memories in one's own history and consciousness (self-awareness or "autonoesis") also depends on the activity of the prefrontal region. The loss of acquired memories (retrograde amnesia) is most often observed in cases of large lesions of the anterior part of the temporal lobe. Partial amnesias are difficult to separate from possibly localized deficits of a cognitive function (some types of aphasia may be considered as an amnesia of words). Subcortical amnesias are caused by diencephalic lesions; the topography of the critical structures is still discussed: mamillary bodies and mamillo-thalamic tract or dorsomedial nucleus of the thalamus. The amygdaloid nucleus, the frontal lobe and the dorsomedial nucleus of the thalamus belong to a network of connections that could be involved in emotions. It could be responsible for the emotional flavor of a memory. Basal ganglia could play a role in procedural memory, but experimental or clinicopathological confirmations are still scarce. Finally, the involvement of the cholinergic innervation in the memory processes has been discussed: it could be direct, or according to more recent data, related to its role in attention.

Transport of arginine and ornithine into isolated mitochondria of Saccharomyces cerevisiae

In this work we have characterised the transport of L-arginine and L-ornithine into mitochondria isolated from a wild-type Saccharomyces cerevisiae strain and an isogenic arg11 knock-out mutant. The Arg11 protein (Arg11p) is a mitochondrial carrier required for arginine biosynthesis [Crabeel, M., Soetens, O., De Rijcke, M., Pratiwi, R. & Pankiewicz, R. (1996) J. Biol. Chem. 271, 25011-25019]. Reconstitution experiments have confirmed that it is an L-ornithine carrier also transporting L-arginine and L-lysine by order of decreasing affinity, but not L-histidine [Palmieri, L., De Marco, V., Iacobazzi, V., Palmieri, F., Runswick, M. & Walker, J. (1997) FEBS Lett. 410, 447-451]. Evidence is presented here that the mitochondrial inner membrane contains an L-arginine and L-ornithine transporting system distinct from Arg11p, in keeping with the arginine leaky phenotype of arg11 knock-out mutants. The newly characterised carrier, which we propose to name Bac1p (basic amino acid carrier), behaves as an antiporter catalysing the electroneutral exchange of the basic amino acids L-arginine, L-lysine, L-ornithine and L-histidine and displays the highest affinity for L-arginine (Km of 30 microM). L-Arginine uptake has a pH optimum in the range of 7.5-9 and is inhibited by several sulphydryl reagents, by pyridoxal 5'-phosphate and by cations.

[Brain lesions, pathogenic and etiologic hypotheses of Alzheimer's disease]

The main lesions of Alzheimer's disease are: 1. amyloid deposits, labelled by antibodies directed against the A beta peptide (core of the senile plaques, diffuse deposits and amyloid angiopathy), 2. neurofibrillary lesions labelled by anti-tau antibodies (neurofibrillary tangles, neuropil threads, crown of the senile plaques) and 3. loss of neurons and synapses. The distribution of neurofibrillary pathology is hierarchical: they begin in the entorhinal cortex, progress along the anterograde corticocortical pathways toward the multimodal and unimodal associative cortices to reach, in the most severe cases, the primary cortices. Amyloid lesions are more diffuse, rapidly affecting all the cortical areas. The density of neurofibrillary tangles in the cerebral cortex is correlated with the severity of dementia. Neuritic plaques, synaptic and neuronal loss also contribute to the intellectual deterioration. There are various causes of Alzheimer's disease (several mutations, trisomy 21, repeated head trauma as in dementia pugilistica): it should be considered a syndrome. Its pathophysiology is complex and involves several proteins (e.g. amyloid protein precursor, tau protein, presenilins 1 and 2, and apolipoprotein E).

[125I]EGF binding in basal ganglia of patients with Parkinson's disease and progressive supranuclear palsy and in MPTP-treated monkeys

Since EGF is known to protect and stimulate the activity of dopaminergic neurons, an autoradiographic study of [125I]EGF binding sites was performed in the striatum and pallidal complex in parkinsonian syndromes. The analysis was performed on postmortem brain tissues of three control subjects, three patients with Parkinson's disease, and three patients with progressive supranuclear palsy, another parkinsonian syndrome in which dopaminergic neurons also degenerate. Since all six patients had been treated with L-Dopa, we also analyzed the effects of this drug in an animal model of Parkinson's disease. Quantitative analysis of [125I]EGF binding was performed on the brains of three control monkeys, nine monkeys rendered parkinsonian by MPTP intoxication, three of which were treated with L-Dopa. An increased density of [125I]EGF binding was observed at anterior levels in the dorsal striatum, but not in the pallidum, of patients with Parkinson's disease and progressive supranuclear palsy. [125I]EGF binding was unchanged in parkinsonian monkeys whether or not they had been treated with L-Dopa. The data suggest an increased expression of EGFRs in the striatum in chronic parkinsonian syndromes but not in acute models of the disease.

The progression of the lesions in Alzheimer disease: insights from a prospective clinicopathological study

Senile plaques and neurofibrillary tangles are the markers of Alzheimer's disease. They are also found in old patients who have been considered to be intellectually normal throughout their life, a situation referred to as "physiological aging". The neurofibrillary tangles are made of abnormally phosphorylated tau. The anti-tau antibody labels not only the neurofibrillary tangles, but also the crown of the senile plaques and the neuropil threads interspersed between the cell bodies and the plaques. The senile plaque comprises a core made of A beta peptide surrounded by a neuritic crown. The anti-A beta antibody also labels "diffuse deposits", i.e. ill limited areas of immunoreactivity which lacks the characteristics of the amyloid substance. The intellectual deficit appears to be statistically linked with the density of the tau-positive alterations-tangles, threads and plaque crowns--which usually appear simultaneously in a given cortical area. In the entorhinal area, their density increases proportionally to the intellectual deficit without threshold, suggesting that ageing and disease are a continuum. In the isocortex, the progression of the tau positive alterations is, on the contrary, stepwise--in a "all or none" fashion--from the hippocampus to the primary cortices, through the associative multimodal areas. The tau positive lesions probably progress through connections: they indeed disappear from areas, that have been disconnected by additional lesions (such as infarcts).

Striatal expression of glutamic acid decarboxylase gene in Alzheimer's disease

To examine potential alteration of GABAergic striatal neurons in Alzheimer's disease, we used quantitative in situ hybridization to analyze the messenger RNA coding for Mr 67,000 glutamic acid decarboxylase (GAD67 mRNA) in the striatum of five patients with Alzheimer's disease (AD) and nine matched control subjects. We found a 51-57% increase in the optical density of hybridization signal in the caudate nucleus and putamen, corresponding to a 30-42% increase in the number of neurons expressing a detectable amount of GAD67 mRNA. By contrast, no alteration was observed in the ventral striatum. The expression of GAD67 mRNA per neuron was similar in AD and control subjects both in the dorsal and ventral striatum. Taken together, our data indicate that, in AD, GABAergic neurotransmission is increased in the dorsal striatum but not in the ventral striatum. We suggest that this increased GABAergic neurotransmission may explain extrapyramidal signs often observed in AD.

Atypical neuronal inclusion bodies in meningioangiomatosis

A case of meningioangiomatosis not associated with neurofibromatosis 2 in a 24-year-old man is reported. Abundant neurofibrillary tangles and threads, shown by immunohistochemistry and ultrastructural analysis to be similar to those seen in Alzheimer's disease, were found in the residual neuropil. Another lesion consisting of argyrophilic globular inclusion bodies with radial fibrils was found at the periphery. Single and double immunostaining with a panel of antibodies showed similarities between these inclusions and Pick bodies.

Neuronal distribution of intranuclear inclusions in Huntington's disease with adult onset

Neuronal intranuclear inclusions were recently found in the brain of patients with inherited neurodegenerative disorders characterized by the expansion of a polyglutamine stretch in the mutated protein. These inclusions are ubiquitinated and, for some of these diseases, the presence of the mutated protein could be also identified. Using immunohistochemistry, we show here that ubiquitinated intranuclear inclusions are also observed postmortem in the brain of patients suffering from Huntington's disease characterized by small polyglutamine expansions and adult onset. We were, however, unable to detect the mutated form of huntingtin in these inclusions. These intranuclear inclusions were detected only in the affected cerebral regions, suggesting that their presence is probably linked to the neurodegenerative process.

Progression of Alzheimer histopathological changes

The clinical-pathological correlations that were prospectively obtained in a cohort of old patients (> 75 years of age) are reviewed. The pathological data were obtained in 31 cases, either normal or affected by Alzheimer disease of various degrees of severity. The density of the A beta peptide deposits was poorly linked with the intellectual status. One patient had a very high density of deposits, although she was considered intellectually normal. When present in a patient, the A beta deposits usually involved all the cortical samples; the samples devoid of deposits most often belonged to the limbic system. The distribution of the neurofibrillary tangles was highly selective: the primary areas (such as the visual cortex) were lesioned only in a few cases, invariably the most severely affected ones. Neurofibrillary tangles involved the associative cortices (sparing the primary areas) in the cases of intermediate severity. The hippocampal-parahippocampal areas contained at least a few neurofibrillary tangles in all the cases. The prevalence of the neurofibrillary lesions in that cohort of cases probably indicated the chronological (and hierarchical) order of involvement: from limbic to associative, from associative to primary areas. There was a linear relationship between the density of the neurofibrillary tangles and the intellectual deficit in the hippocampal-parahippocampal gyrus. The relationship was stepwise rather than linear in the isocortical samples, suggesting that the neurofibrillary tangles were a late phenomenon in those types of cortices. An accumulation of SNAP 25 immunoreactivity was found in some of the most severely affected cases, pointing to a deficit in axonal transport. The density and the total number of neurons were evaluated in a sample of the supramarginal gyrus. The neuronal loss was found to be severe, but only in the most affected cases, when the density of neurofibrillary tangles was higher than 5/mm2.

Dementia with Lewy bodies

The presence of a high number of Lewy bodies--the morphological marker of Parkinson's disease--in the cerebral cortex of some cases of dementia has been frequently observed in association to Alzheimer type lesions (mainly senile plaques) and changes in the substantia nigra, that may be held responsible for the frequently associated symptoms of parkinsonism. The term "dementia with Lewy body" (DLB) has recently been suggested by a consensus conference and indicates that the pathogenetic mechanism of the dementia remains poorly understood. Marked fluctuations of alertness and of the cognitive performances, moderate parkinsonism and episodes of visual hallucinations may lead to suspect this diagnosis in cases of dementia. Unexplained falls, syncopes, delirium or alterations of consciousness may also be observed, and the patients may then be admitted in departments of internal medicine or geriatrics. The Lewy body is an intraneuronal spherical inclusion, present in Parkinson's disease. It is observed in the brainstem (substantia nigra, locus coeruleus, dorsal nucleus of the Xth nerve) and in the nucleus basalis of Meynert. The cortical Lewy bodies have a different aspect, but retain their antigenic characteristics: they are, in particular, stained by the antiubiquitin antibodies. Recently, they were found to be also labeled by antisynuclein antibodies. A mutation of the synuclein gene was recently identified in cases of familial Parkinson's disease. Clinically as well as pathologically, DLB may thus be difficult to distinguish from Alzheimer's disease on the one hand, and from Parkinson's disease, on the other. That diagnosis, however, is associated with a poor prognosis and should lead to specific therapeutic measures.

Spinocerebellar ataxia type 7 (SCA7): a neurodegenerative disorder with neuronal intranuclear inclusions

Autosomal dominant cerebellar ataxia with progressive macular degeneration is caused by a CAG/glutamine repeat expansion in the SCA7 gene/protein. Neuronal intranuclear inclusions were detected in the brain of an early onset SCA7 case with the 1C2 antibody directed against an expanded polyglutamine domain. Nuclear inclusions were most frequent in the inferior olivary complex, a site of severe neuronal loss in SCA7. They were also observed in other brain regions, including the cerebral cortex, not considered to be affected in the disease. Using confocal microscopy we showed that some inclusions were ubiquitinated, but to varying degrees, ranging from <1% in the cerebral cortex to 60% in the inferior olive. In addition, we also observed cytoplasmic staining using the 1C2 antibody, particularly in the supramarginal gyrus, the hippocampus, the thalamus, the lateral geniculate body and the pontine nuclei. These data confirm that the presence of intranuclear inclusions in neurons is a common characteristic of disorders caused by CAG/polyglutamine expansions, but unlike what has been reported for Huntington's disease, SCA1 and SCA3/MJD, in SCA7 the inclusions were not restricted to the sites of severe neuronal loss.

Laminar spongiosis of the dentate gyrus: a sign of disconnection, present in cases of severe Alzheimer's disease

An extensive laminar spongiosis was found in the outer part of the dentate gyrus in an 84-year-old patient. An old cavitary infarct in the parahippocampal gyrus disconnected the dentate gyrus from the entorhinal area. This finding prompted us to seek laminar spongiosis in Alzheimer's disease, where the neuronal loss in the entorhinal cortex might be severe. The dentate gyrus was systematically examined in a series of prospectively assessed cases either intellectually normal or affected by mental impairment of graded severity. Laminar spongiosis was present in the most severely affected patients. The neuritic crown of the senile plaques seen in the laminar band of spongiosis contained only a few tau- and Bodian-positive fibers, a sign that was taken as evidence of "plaque denervation". By contrast, deposits of Abeta peptide remained abundant but lacked a dense core. These data suggest that dendritic and axonal processes are intermingled in the senile plaque and that the amyloid core is at least partially dependent on the presence of the axonal component.

Cytoarchitectonic alterations in the supramarginal gyrus of late onset Alzheimer's disease

The intellectual status of 28 women of over 75 years of age had been prospectively assessed by the Blessed test score. It ranged from nearly normal to deeply altered by dementia. After autopsy, the supramarginal gyrus was marked at the surface of the brain. Sections, 1 cm thick, were cut with a specially devised macrotome. The volume of the parietal lobe was measured by a point counting method, using Cavalieri principle. A sample from the supramarginal gyrus was taken from the previously marked area and the shrinkage due to the histological procedures was measured (it averaged 12%). More than 500 nucleolated neuronal profiles per case were mapped with a semi-automatic system. Density maps of the neuronal profiles were drawn and mean density was calculated using Dirichlet tessellation. The thickness of the cortical ribbon was standardized on the maps. The density of the neurons per unit volume was calculated, taking into account the section thickness measured for each sample with a length gauge fastened to the Z axis of the microscope. Statistical correlations were sought between the mean and laminar densities of the neurons on one hand, and Blessed test score, the densities of neurofibrillary tangles (NFT) and of senile plaques profiles, on the other hand. Finally, the total number of neurons present in the parietal lobe was estimated in each case. Neuronal loss appeared to be linked with the density of the NFT (r = -0.52; P < 0.004). The correlation was mainly due to a severe drop in neuronal number observed in the cases with more than 5 NFT/mm2. An average difference of 98 x 10(6) neurons per parietal lobe was found between the cases with less than 5 NFT/mm2 and those with more. The neuronal loss predominated in layers II and III (upper part). A multivariate analysis showed that the intellectual status was better correlated with the density of the tangles than with the neuronal loss.

[Diseases transmitted by non-conventional agents ("prions"): nosology and diagnosis]

Transmissible non conventional agents are currently called "Prions". This is not a neutral terminology: the attractive Prion hypothesis (the infectious agent being a protein able to replicate in the absence of DNA or RNA) due to Stanley Prusiner is the prevalent one, and has shown to be heuristic, but has not been formally proven and does not easily explain all the data, unless modified and expanded. No simple account has been given for the very unusual physical, chemical, and biological properties of non conventional agents. These infectious agents are associated with degenerative diseases of the nervous system that are either the consequence of a genetic mutation or develop spontaneously in apparently normal individuals, and then can be transmitted to various susceptible hosts, including man. Thus, non conventional agents cannot be considered only as fascinating biological enigmas. They constitute a challenge for public health. The changing characteristics of prion-associated diseases has led to a renewing of their clinical and neuropathological diagnostic criteria. A brief survey of the nosology and neuropathology of prions diseases, with emphasis on new data and on difficulties, is provided. A simple classification based on the familial, sporadic or infectious variety of the disease is suggested. Familial diseases can be named according to the genetic disorder. Sporadic and infectious diseases can be classified following the main clinical symptoms and signs, and the presence or absence of amyloid plaques in the brain, until new tools (analysis of the glycosylation pattern of PrP, strain recognition) allow a more precise nomenclature. The new epidemiology of Prion disorders allowed by these new approaches relies on a full study of Prion diseases affected patients, which necessarily involves their genetic study, and the analysis of brain tissue. This, for practical and ethical reasons, is better achieved by autopsy.

Cerebral T2-weighted signal decrease during aging in the mouse lemur primate reflects iron accumulation

4.7 Tesla T2-weighted magnetic resonance images showed a highly significant signal decrease in the pallidum, substantia nigra, putamen, and a less significant decrease in the thalamus and the caudate of aging mouse lemurs (Microcebus murinus). We evaluated the contribution of iron deposits to the signal decrease comparing Perls' stained histological sections of six mouse lemurs brains aged 1 to 10 years to magnetic resonance images. In young animals, none of the brain structures was stained. A large number of iron deposits were visible in the pallidum and substantia nigra of aged animals and a moderate number in the middle aged ones. In the putamen, few iron deposits were visible in aged and middle-aged animals. The thalamus and the caudate appeared unstained with Perls' technique; iron was too low to be detected. The intensification of the reaction by diaminobenzidine revealed iron deposits in the thalamus of aging animals. This study suggests that in mouse lemurs, iron deposits are responsible for T2-weighted signal decrease in the central gray nuclei.

Accumulation of SNAP-25 immunoreactive material in axons of Alzheimer's disease

Neurofibrillary tangles and neuropil threads, both made of hyperphosphorylated tau proteins, point to an alteration of microtubules in Alzheimer's disease. The aim of this study was to test the consequences of these lesions on axoplasmic flow, which is dependent on intact microtubule assembly. We assessed the transport of synaptic proteins from the neuronal cell body to axonal terminals, using SNAP-25 (synaptosomal-associated protein of 25 kD) immunohistochemistry as a marker of impaired axonal transport. A sample from the supra-marginalis gyrus was obtained from 29 individuals over 75 years of age whose cognitive function had been prospectively assessed. Accumulation of immunoreactive material in swollen axons was observed in the white matter of severely demented individuals, and their number was correlated with the density of neurofibrillary tangles (r = 0.53, p = 0.005) and of focal Abeta deposits (r = 0.61, p = 0.001). This supports the hypothesis of a dysfunction of the cytoskeleton in Alzheimer's disease. An unexpected finding was the lack of correlation between SNAP-25 immunohistochemistry in the grey matter and the intellectual status or the density of neurofibrillary tangles, focal Abeta deposits and neuronal profiles. These results which question the role of synaptic markers as correlates of dementia, should be extended to other brain areas.

Nuclear translocation of NF-kappaB in cholinergic neurons of patients with Alzheimer's disease

NF-kappaB is a nuclear transcription factor involved in the control of numerous cellular functions, particularly regulation of survival. Translocation from the cytoplasm to the nucleus, an event essential for NK-kappaB activation, could be mediated through the low-affinity nerve growth factor receptor, p75, which has recently been shown to mediate cell death. In the human brain, p75 is exclusively expressed in cholinergic neurons of the basal forebrain. This population degenerates in Alzheimer's disease (AD). To investigate whether p75 could play a role in the vulnerability of these neurons via NF-kappaB activation, we studied the cellular distribution of NF-kappaB in the nucleus basalis of Meynert of four AD patients and four control subjects. The immunostaining observed both in AD patients and control subjects was limited to large, probably cholinergic, neurons. In AD, the proportion of neurons with nuclear NF-kappaB staining was significantly increased, suggesting an association between NF-kappaB functions and the process of cholinergic degeneration in AD.

Human immunodeficiency virus type 1 DNA and RNA load in brains of demented and nondemented patients with acquired immunodeficiency syndrome

The relationship between dementia and human immunodeficiency virus type 1 (HIV-1) cerebral load is not clearly understood. We used immunohistochemistry and competitive polymerase chain reaction to evaluate the density ofgp 41 immunostained cells and the amount of HIV-1 DNA and RNA in the midfrontal gyrus of 21 HIV-1 infected patients, nine of whom were demented. The amounts of HIV-1 DNA and RNA, and the density of gp 41-positive cells were significantly linked. In this small series of cases, (1) although as a mean, there was a larger viral load in demented patients than in nondemented, this did not reach the significance level (2) discrepancies appeared in the population under study, some demented patients having low viral loads.

Phylogenetic classification of the mitochondrial carrier family of Saccharomyces cerevisiae

The screening of the open reading frames identified in the whole yeast genome has allowed us to discover 34 proteins belonging to the mitochondrial carrier family. By phylogenetic study, they can be divided into 27 subfamilies including ADP/ATP, phosphate and citrate carriers, putative oxoglutarate and GDC carriers and 22 new subfamilies. Topology predictions using the 'positive inside rule' approach have shown that the yeast carriers are similarly oriented with both extremities exposed to the cytosol. In each subfamily, a strict conservation of the charged residues in the six transmembrane alpha-helices is observed, suggesting a functional role for these residues and the existence of 27 functionally distinct carriers.

Diagnosis and staging of Alzheimer disease

Rather than determining lesions "threshold" between "normal" cases and patients, we prefer to use clinicopathological correlations, assigning a given intellectual deficit to a given amount of lesions with a chosen level of probability. Because large amounts of A beta diffuse deposits may be found in the absence of dementia, we think advisable not to take them into account for the diagnosis. The diffusion of the neurofibrillary tangles in the paralimbic, limbic and isocortical areas (described by braak and Braak stages or by the number of areas containing tangles) and the density of isocortical senile plaques (A beta focal deposits) as assessed by the CERAD protocol are both correlated with the intellectual status but give complementary information. They should thus be jointly used. We analyzed the variability of the lesions counts, their coefficients of error, and their causes, as a first step toward standardization. We have shown, however, that semiquantitative estimates are presently more reproducible than quantitative measures.

Modeling the relation between neurofibrillary tangles and intellectual status

The relationship between the neurofibrillary tangles and the intellectual deficit observed in senile dementia of the Alzheimer type was studied in 27 patients over the age of 75. The presence and density of tau positive tangles were assessed in six areas including limbic, paralimbic, and isocortical cortices. In the isocortical areas, the presence [1] or absence [0] of neurofibrillary tangles was better correlated with the Blessed test score than the density of the neurofibrillary tangles profiles. Multivariate analysis showed that the number of areas containing at least one neurofibrillary tangle was the best explanatory variable of the intellectual status. The cortical areas were ranked according to the prevalence of their involvement. The presence of tangles in an area of a given rank took place only if the areas of lower ranks were also involved. It is proposed that the presence of tangles in a given area is a more significant information than the value of their density. These data may lead to new diagnostic procedures.

Tumor necrosis factor-alpha, microglia and astrocytes in AIDS dementia complex

The pathogenesis of HIV-associated cognitive changes is poorly understood. Cytokines such as tumor necrosis factor-alpha (TNF-alpha) have been postulated to contribute to the mechanism of the neurological complications of HIV infection. One of the effects of TNF-alpha is to induce astrocyte proliferation in vitro. The purpose of this study was to look for a correlation between the expression of TNF-alpha, astrogliosis and the degree of cognitive impairment in 12 prospectively assessed AIDS cases without focal brain lesion, 8 of whom were demented. They were compared with 6 control patients without neurological disease. Neuropathological examination showed myelin pallor in 5 of the 8 demented patients. TNF-alpha expression was detected by immunohistochemistry in the midfrontal cortex, subcortical and deep white matter, and basal ganglia. Not only perivascular macrophages but also some microglial and endothelial cells were labeled. Most TNF-alpha-positive cells were in close contact with glial fibrillary acidic protein-positive astrocytes. They were more numerous than gp41-positive cells. Their density increased with increasing cognitive impairment and in parallel to the astrogliosis in the frontal cortex, basal ganglia and deep white matter. These findings further support the hypotheses that lesions of the deep white matter, driven by TNF-alpha, are associated with cognitive alteration, and that indirect effects of HIV infection in the brain participate in the development of HIV-associated dementia through a diffuse immune activation, mediated by cytokines.

Dissociation of Alzheimer type pathology in a disconnected piece of cortex

A woman with Alzheimer's disease died at the age of 85 years. A left sphenoid meningioma had been removed 27 years earlier. The tumor and the operation had severely altered the white matter of the frontal lobe and of the anterior part of the temporal lobe on the left side and massively disconnected a small piece of frontal cortex. There were numerous senile plaques and neurofibrillary tangles in the limbic and isocortical samples. The white matter lesions, on the operated (left) side, were associated with a lower density of neuritic plaques and of neuropil threads and with a higher density of beta-amyloid (A beta) deposits. The density of tau-positive neuritic plaques, neurofibrillary tangles and neuropil threads was close to zero, whereas the diffuse deposits of A beta were abundant, in the small disconnected piece of cortex. In this area, the white matter was severely damaged, as in the adjoining cortex, but the continuity of the cortical ribbon was also disrupted. These data show that neuritic and A beta pathologies may be dissociated and suggest that the neuritic alterations mainly involved cortico-cortical fibers coursing tangentially in the cortical ribbon.

Phylogenetic classification of the mitochondrial carrier family of Saccharomyces cerevisiae

The screening of the open reading frames identified in the whole yeast genome has allowed us to discover 34 proteins belonging to the mitochondrial carrier family. By phylogenetic study, they can be divided into 27 subfamilies including ADP/ATP, phosphate and citrate carriers, putative oxoglutarate and GDC carriers and 22 new subfamilies. Topology predictions using the 'positive inside rule' approach have shown that the yeast carriers are similarly oriented with both extremities exposed to the cytosol. In each subfamily, a strict conservation of the charged residues in the six transmembrane alpha-helices is observed, suggesting a functional role for these residues and the existence of 27 functionally distinct carriers.

Astrocytic adhesion molecules are increased in HIV-1-associated cognitive/motor complex

Half of AIDS dementia cases are associated with HIV-encephalitis or myelin pallor. Another half die with no HIV-related neuropathological changes. Previous observations suggest that cerebral dysfunction may result from more subtle cellular interactions. and that some of them may be mediated by cell adhesion molecules. In the present study the expression by astrocytes and endothelial cells of intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) was analysed as a function of the neuropathological diagnosis, the density of astrogliosis and of HIV-1 positive cells, and of the mental status. Twelve AIDS cases, without focal brain lesion, eight of whom were demented, were selected from a prospective study. They were compared with six control cases with multiple sclerosis, and with six control patients without neurological disease. ICAM-1 and VCAM-1 expression was localized by immunofluorescence and confocal microscopy. HIV protein gp41 was detected by immunohistochemistry on adjacent sections. Endothelial expression of ICAM-1 and VCAM-1 was significantly up-regulated in all AIDS patients. VCAM-1 only was related to myelin pallor. The density of VCAM-1 or ICAM-1 positive astrocytes increased in demented AIDS patients, independently of the neuropathological findings or the density of gp41 positive cells. Expression of cell adhesion molecules, together with other secondary mechanisms such as secretion of cytokines may play a role in the pathogenesis of white matter lesions leading to HIV-1-associated cognitive changes.

[Is the topography of Alzheimer's disease lesions a clue to their pathogenesis?]

Neurofibrillary changes, labelled by antitau antibodies and deposits, labelled by anti-A beta antibodies, were counted in 6 cortical areas in 29 prospectively studied cases (Charles Foix Longitudinal Study). The intellectual status had been assessed by the Blessed test score; 10% of the cases were found to be normal (score > 27), 10 other percents were deeply demented (score < 2) and the other cases were regularly distributed over the intermediate values. Tau positive neurofibrillary changes were present in the hippocampus and in the parahippocampal gyrus even in intellectually normal cases. They were found in a primary sensory cortex (the visual cortex) only in the most severely affected cases. Associative cortices were spared in the normal cases and in the least demented patients. They were involved only at a critical value of the Blessed Test Score. A beta deposits involved more areas than the neurofibrillary pathology and their distribution was less systematically organized. Their density was poorly correlated with the intellectual status. Neuritic plaques, made of an amyloid core and of a crown of tau positive neurites, were present only in those areas that also contained neurofibrillary tangles. Our findings support the contention that neurofibrillary pathology, involving a set of short range, "feed-backward", cortico-cortical connections, is a close correlate of dementia. The role of A beta deposits remains unclear. Although poorly connected with dementia, they could be the remote initiator of the pathological cascade that leads to the neurofibrillary pathology, immediate cause of the cortical dysfunction.

Widespread immunoreactivity of presenilin in neurons of normal and Alzheimer's disease brains: double-labeling immunohistochemical study

The immunolocalization of presenilin in human brain was studied using two antibodies raised against different portions of presenilin 1 (S182) protein. A granular staining was found in the cytoplasm of neurons in cortical layers III and V. One of the antibodies, also reactive to presenilin 2 (E5-1) protein, additionally stained dendrites and axons. This was seen in normal brains as well as in brains affected by Alzheimer's disease. Less prominent immunolabeling was noted in some senile plaques. No relationship to neurofibrillary tangles was found in double-labeling experiments combined with anti-paired helical filament-tau antibody (AT8). The widespread expression of presenilin in normal brain suggests a physiological role of the protein.