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).