Cell specific quantitative iron mapping on brain slices by immuno-µPIXE in healthy elderly and Parkinson's disease.

Iron is essential for neurons and glial cells, playing key roles in neurotransmitter synthesis, energy production and myelination. In contrast, high concentrations of free iron can be detrimental and contribute to neurodegeneration, through promotion of oxidative stress. Particularly in Parkinson's disease (PD) changes in iron concentrations in the substantia nigra (SN) was suggested to play a key role in degeneration of dopaminergic neurons in nigrosome 1. However, the cellular iron pathways and the mechanisms of the pathogenic role of iron in PD are not well understood, mainly due to the lack of quantitative analytical techniques for iron quantification with subcellular resolution. Here, we quantified cellular iron concentrations and subcellular iron distributions in dopaminergic neurons and different types of glial cells in the SN both in brains of PD patients and in non-neurodegenerative control brains (Co). To this end, we combined spatially resolved quantitative element mapping using micro particle induced X-ray emission (µPIXE) with nickel-enhanced immunocytochemical detection of cell type-specific antigens allowing to allocate element-related signals to specific cell types. Distinct patterns of iron accumulation were observed across different cell populations. In the control (Co) SNc, oligodendroglial and astroglial cells hold the highest cellular iron concentration whereas in PD, the iron concentration was increased in most cell types in the substantia nigra except for astroglial cells and ferritin-positive oligodendroglial cells. While iron levels in astroglial cells remain unchanged, ferritin in oligodendroglial cells seems to be depleted by almost half in PD. The highest cellular iron levels in neurons were located in the cytoplasm, which might increase the source of non-chelated Fe3+, implicating a critical increase in the labile iron pool. Indeed, neuromelanin is characterised by a significantly higher loading of iron including most probable the occupancy of low-affinity iron binding sites. Quantitative trace element analysis is essential to characterise iron in oxidative processes in PD. The quantification of iron provides deeper insights into changes of cellular iron levels in PD and may contribute to the research in iron-chelating disease-modifying drugs.

The emerging role of circular RNAs in transcriptome regulation.

Circular RNAs (circRNAs) are a recently discovered form of RNA that has been found to regulate mammalian transcription. CircRNAs are covalently closed, single-stranded transcripts produced from precursor mRNA. While initially circRNAs were considered to be splicing artefacts, next-generation RNA sequencing of non-polyadenylated transcriptomes has recently shown that the expression of circRNAs is widespread and over 20% of expressed genes in examined cells and tissues can produce these transcripts. Until now thousands of circRNAs have been discovered in organisms ranging from Drosophila melanogaster to Homo sapiens. Functional studies indicate that these transcripts regulate expression of protein-coding linear transcripts and thus comprise an important component of gene expression regulation. Here we provide a comprehensive overview on the biology of circRNAs, including the expression patterns and function. Moreover, we discuss current methodologies for the discovery and validation of circular transcripts. Finally, perspectives on the utilization of circRNA as molecular markers of complex diseases are presented.

Reorganization of Synaptic Connections and Perineuronal Nets in the Deep Cerebellar Nuclei of Purkinje Cell Degeneration Mutant Mice.

The perineuronal net (PN) is a subtype of extracellular matrix appearing as a net-like structure around distinct neurons throughout the whole CNS. PNs surround the soma, proximal dendrites, and the axonal initial segment embedding synaptic terminals on the neuronal surface. Different functions of the PNs are suggested which include support of synaptic stabilization, inhibition of axonal sprouting, and control of neuronal plasticity. A number of studies provide evidence that removing PNs or PN-components results in renewed neurite growth and synaptogenesis. In a mouse model for Purkinje cell degeneration, we examined the effect of deafferentation on synaptic remodeling and modulation of PNs in the deep cerebellar nuclei. We found reduced GABAergic, enhanced glutamatergic innervations at PN-associated neurons, and altered expression of the PN-components brevican and hapln4. These data refer to a direct interaction between ECM and synapses. The altered brevican expression induced by activated astrocytes could be required for an adequate regeneration by promoting neurite growth and synaptogenesis.

The neuronal extracellular matrix restricts distribution and internalization of aggregated Tau-protein.

Alzheimer's disease (AD) is a chronic degenerative disorder characterized by fibrillary aggregates of Aß and Tau-protein. Formation and progression of these pathological hallmarks throughout the brain follow a specific spatio-temporal pattern which provides the basis for neuropathological staging. Previously, we could demonstrate that cortical and subcortical neurons are less frequently affected by neurofibrillary degeneration if they are enwrapped by a specialized form of the hyaluronan-based extracellular matrix (ECM), the so called 'perineuronal net' (PN). PNs are composed of large aggregating chondroitin sulfate proteoglycans connected to a hyaluronan backbone, stabilized by link proteins and cross-linked via tenascin-R. Recently, PN-associated neurons were shown to be better protected against iron-induced neurodegeneration compared to neurons without PN, indicating a neuroprotective function. Here, we investigated the role of PNs in distribution and internalization of exogenous Tau-protein by using organotypic slice cultures of wildtype mice as well as mice lacking the ECM-components aggrecan, HAPLN1 or tenascin-R. We could demonstrate that PNs restrict both distribution and internalization of Tau. Accordingly, PN-ensheathed neurons were less frequently affected by Tau-internalization, than neurons without PN. Finally, the PNs as well as their three investigated components were shown to modulate the processes of distribution as well as internalization of Tau.

Differential effects of P2Y1 deletion on glial activation and survival of photoreceptors and amacrine cells in the ischemic mouse retina.

Gliosis of retinal Müller glial cells may have both beneficial and detrimental effects on neurons. To investigate the role of purinergic signaling in ischemia-induced reactive gliosis, transient retinal ischemia was evoked by elevation of the intraocular pressure in wild-type (Wt) mice and in mice deficient in the glia-specific nucleotide receptor P2Y1 (P2Y1 receptor-deficient (P2Y1R-KO)). While control retinae of P2Y1R-KO mice displayed reduced cell numbers in the ganglion cell and inner nuclear layers, ischemia induced apoptotic death of cells in all retinal layers in both, Wt and P2Y1R-KO mice, but the damage especially on photoreceptors was more pronounced in retinae of P2Y1R-KO mice. In contrast, gene expression profiling and histological data suggest an increased survival of amacrine cells in the postischemic retina of P2Y1R-KO mice. Interestingly, measuring the ischemia-induced downregulation of inwardly rectifying potassium channel (Kir)-mediated K(+) currents as an indicator, reactive Müller cell gliosis was found to be weaker in P2Y1R-KO (current amplitude decreased by 18%) than in Wt mice (decrease by 68%). The inner retina harbors those neurons generating action potentials, which strongly rely on an intact ion homeostasis. This may explain why especially these cells appear to benefit from the preserved Kir4.1 expression in Müller cells, which should allow them to keep up their function in the context of spatial buffering of potassium. Especially under ischemic conditions, maintenance of this Müller cell function may dampen cytotoxic neuronal hyperexcitation and subsequent neuronal cell loss. In sum, we found that purinergic signaling modulates the gliotic activation pattern of Müller glia and lack of P2Y1 has janus-faced effects. In the end, the differential effects of a disrupted P2Y1 signaling onto neuronal survival in the ischemic retina call the putative therapeutical use of P2Y1-antagonists into question.

Aggrecan, link protein and tenascin-R are essential components of the perineuronal net to protect neurons against iron-induced oxidative stress.

In Alzheimer's disease (AD), different types of neurons and different brain areas show differential patterns of vulnerability towards neurofibrillary degeneration, which provides the basis for a highly predictive profile of disease progression throughout the brain that now is widely accepted for neuropathological staging. In previous studies we could demonstrate that in AD cortical and subcortical neurons are constantly less frequently affected by neurofibrillary degeneration if they are enwrapped by a specialized form of the hyaluronan-based extracellular matrix (ECM), the so called 'perineuronal net' (PN). PNs are basically composed of large aggregating chondroitin sulphate proteoglycans connected to a hyaluronan backbone, stabilized by link proteins and cross-linked via tenascin-R (TN-R). Under experimental conditions in mice, PN-ensheathed neurons are better protected against iron-induced neurodegeneration than neurons without PN. Still, it remains unclear whether these neuroprotective effects are directly mediated by the PNs or are associated with some other mechanism in these neurons unrelated to PNs. To identify molecular components that essentially mediate the neuroprotective aspect on PN-ensheathed neurons, we comparatively analysed neuronal degeneration induced by a single injection of FeCl3 on four different mice knockout strains, each being deficient for a different component of PNs. Aggrecan, link protein and TN-R were identified to be essential for the neuroprotective properties of PN, whereas the contribution of brevican was negligible. Our findings indicate that the protection of PN-ensheathed neurons is directly mediated by the net structure and that both the high negative charge and the correct interaction of net components are essential for their neuroprotective function.

Cellular and ultra structural evidence for cytoskeletal localization of prolyl endopeptidase-like protein in neurons.

The biochemical properties and subcellular localization of prolyl endopeptidase (PREP) in brain are well characterized and its implications in the realization of cognitive processes and in the pathogenesis of neurodegenerative disorders are a matter of intensive investigation. In contrast, very little is known about its homolog, the PREP-like protein (PREPL). In order to obtain initial hints about the involvement of PREPL in physiological processes, a differential proteomic screen was performed with human skin fibroblasts from controls and patients with PREPL deficiency (hypotonia-cystinuria syndrome). The majority of affected proteins represented cytoskeletal proteins, including caldesmon, tropomyosin α3 chain, lamin A, ß-actin, γ-actin, vimentin and zyxin. Therefore, the analysis of PREPL subcellular localization by confocal laser scanning and electron microscopy in mouse neurons was focused on the cytoskeleton. The co-localization of PREPL with cytoskeletal marker proteins such as ß-actin and microtubulin-associated protein-2 was observed, in addition to the presence of PREPL within Golgi apparatus and growth cones. In the mouse brain, PREPL is neuronally expressed and highly abundant in neocortex, substantia nigra and locus coeruleus. This mirrors to some extent the distribution pattern of PREP and points toward redundant functions of both proteins. In the human neocortex, PREPL immunostaining was found in the cytoplasm and in neuropil, in particular of layer V pyramidal neurons. This staining was reduced in the neocortex of Alzheimer's disease (AD) patients. Moreover, in AD brains, PREPL immunoreactivity was observed in the nucleus and in varicose neuritic processes. Our data indicate physiological functions of PREPL associated with the cytoskeleton, which may be affected under conditions of cytoskeletal degeneration.

Perineuronal and perisynaptic extracellular matrix in the human spinal cord.

Extracellular matrix (ECM) forms an active interface around neurons of the central nervous system (CNS). Whilst the components, chemical heterogeneity and cellular recruitment of this intercellular assembly in various parts of the brain have been discussed in detail, the spinal cord received limited attention in this context. This is in sharp contrast to its clinical relevance since the overall role of ECM especially that of its chondroitin sulphate-based proteoglycan components (CSPGs) was repeatedly addressed in neuropathology, regeneration, CNS repair and therapy models. Based on two post-mortem human specimen, this study gives the first and detailed description of major ECM components of the human spinal cord. Immunohistochemical investigations were restricted to the systematic mapping of aggrecan, brevican, proteoglycan link-protein as well as tenascin-R and hyaluronan containing matrices in the whole cranio-caudal dimension of the human spinal cord. Other proteoglycans like versican, neurocan and NG2 were exemplarily investigated in restricted areas. We show the overall presence of tenascin-R and hyaluronan in both white and grey matters whereas aggrecan, proteoglycan link-protein and brevican were restricted to the grey matter. In the grey matter, the ECM formed aggrecan-based perineuronal nets in the ventral and lateral horns but established single perisynaptic assemblies, axonal coats (ACs), containing link-protein and brevican in all regions except of the Lissauer's zone. Intersegmental differences were reflected in the appearance of segment-specific nuclei but not in overall matrix distribution pattern or chemical heterogeneity. Perineuronal nets were typically associated with long-range projection neurons including cholinergic ventral horn motorneurons or dorsal spinocerebellar tract neurons of the Clarke-Stilling nuclei. Multiple immunolabelling revealed that nociceptive afferents were devoid of individual matrix assemblies unlike glycinergic or GABAergic synapses. The detailed description of ECM distribution in the human spinal cord shall support clinical approaches in injury and regenerative therapy.

Unique features of extracellular matrix in the mouse medial nucleus of trapezoid body--implications for physiological functions.

The medial nucleus of the trapezoid body (MNTB) is a vital structure of sound localization circuits in the auditory brainstem. Each principal cell of MNTB is contacted by a very large presynaptic glutamatergic terminal, the calyx of Held. The MNTB principal cells themselves are surrounded by extracellular matrix components forming prominent perineuronal nets (PNs). Throughout the CNS, PNs, which form lattice-like structures around the somata and proximal dendrites, are associated with distinct types of neurons. PNs are highly enriched in hyaluronan and chondroitin sulfate proteoglycans therefore providing a charged surface structure surrounding the cell body and proximal neurites of these neurons. The localization and composition of PNs have lead investigators to a number of hypotheses about their functions including: creating a specific extracellular ionic milieu around these neurons, stabilizing synapses, and influencing the outgrowth of axons. However, presently the precise functions of PNs are still quite unclear primarily due to the lack of an ideal experimental model system that is highly enriched in PNs and in which the synaptic transmission properties can be precisely measured. The MNTB principal cells could offer such a model, since they have been extensively characterized electrophysiologically. However, extracellular matrix (ECM) in these neurons has not yet been precisely detailed. The present study gives a detailed examination of the ECM organization and structural differences in PNs of the mouse MNTB. The different PN components and their distribution pattern are scrutinized throughout the MNTB. The data are complemented by electron microscopic investigations of the unique ultrastructural localization of PN-components and their interrelation with distinct pre- and postsynaptic MNTB cell structures. Therefore, we believe this work identifies the MNTB as an ideal system for studying PN function.

Aggrecan: Beyond cartilage and into the brain.

Aggrecan is well-studied in cartilage but its expression and function in the central nervous system has only recently begun to be appreciated. Aggrecan plays an important role in the organization of the neural extracellular space by binding and organizing hyaluronan to the cell surface through interactions with link protein and tenascins forming a large aggregated quaternary complex. While all members of the lectican family to which aggrecan belongs are thought to mediate similar roles in organizing the neural matrix, aggrecan is unique in that it is the only family member found almost exclusively in an enigmatic matrix substructure called the perineuronal net. Current work has established a critical role for perineuronal nets and aggrecan in regulating developmental neural plasticity and in the recover from injury. In this review we focus on the structure, expression and function of aggrecan in the central nervous system.

Perisynaptic aggrecan-based extracellular matrix coats in the human lateral geniculate body devoid of perineuronal nets.

The extracellular matrix surrounds different neuronal compartments in the mature nervous system. In a variety of vertebrates, most brain regions are loaded with a distinct type of extracellular matrix around the somatodendritic part of neurons, termed perineuronal nets. The present study reports that chondrotin sulfate proteoglycan-based matrix is structured differently in the human lateral geniculate body. Using various chondrotin sulfate proteoglycan-based extracellular matrix antibodies, we show that perisomatic matrix labeling is rather weak or absent, whereas dendrites are contacted by axonal coats appearing as small, oval structures. Confocal laser scanning microscopy and electron microscopy demonstrated that these typical structures are associated with synaptic loci on dendrites. Using multiple labelings, we show that different chondrotin sulfate proteoglycan components of the extracellular matrix do not associate exclusively with neuronal structures but possibly associate with glial structures as well. Finally, we confirm and extend previous findings in primates that intensity differences of various extracellular matrix markers between magno- and parvocellular layers reflect functional segregation between these layers in the human lateral geniculate body.

Effect of leukotriene inhibitors on evolution of experimental brain contusions.

AIMS: Leukotriene levels increase in cerebrospinal fluid (CSF) following controlled cortical impact (CCI) injury in rats. We investigated the impact of two different leukotriene inhibitors in the CCI model on CSF leukotriene levels, brain water content (BWC), brain swelling (BS) contusion size and cellular response. METHODS: 134 male Sprague Dawley rats were investigated at 4, 24 and 72 h after CCI for CSF leukotriene levels and BWC/BS, lesion size in T2-weighted magnetic resonance imaging and immunohistochemistry. Animals received vehicle, MK-886, an inhibitor of 5-lipoxygenase activating protein, or Boscari(®) , a mixture of boswellic acids, acting as competitive nonredox 5-lipoxygenase inhibitors before trauma and then every 8 h until sacrifice. RESULTS: The intracranial pressure (ICP) was unaffected by treatment. Boscari treatment reduced CSF leukotriene C4 increase by -45% at 4 h (P < 0.03) and increase of BWC and BS by 49% (P < 0.05) and -58% at 24 h. Treatment with both substances showed a reduction of lesion volume at 72 h by -21% (P < 0.01) in T(2) -weighted magnetic resonance imaging, which was reflected in a smaller lesion area determined from a NeuN labelled section (-17% to -20%, P < 0.05). Triple immunofluorescence and Fluoro-Jade B staining showed rarefaction of neurones, glia and vasculature in the contusion core, whereas in the pericontusional zone astro- and microglia were upregulated in the presence of dying neurones. Treatment resulted in an improved survival of NeuN labelled neurones in the pericontusional cortex (+15% to +20%, P < 0.05). CONCLUSIONS: Leukotriene inhibition should be further investigated as therapeutic option to counteract secondary growth of traumatic brain contusions and to possibly improve pericontusional neuronal survival.

Chondroitin sulphate proteoglycan-based perineuronal net establishment is largely activity-independent in chick visual system.

Extracellular matrix components consisting of large aggregating chondroitin sulphate proteoglycans accumulate around neuronal perikarya to establish perineuronal nets. These perineuronal nets surround subpopulations of neurons in many vertebrates including man. In chickens, perineuronal nets show very fast matrix maturation after hatching which is probably due to the rapid establishment of neuronal morphology and immediate functional and behavioural performance of the animals. In mammals, maturation of extracellular matrix including perineuronal nets largely depends upon specific afferent activation. The present study shows that extracellular matrix maturation in mesencephalic, diencephalic and telencephalic visual centers of chicks tectofugal system is not principally determined by light activation. Perineuronal nets show an equally developed phenotypic character on monocularly light deprived animals in all investigated brain regions. Results suggest that establishment of extracellular matrix and perineuronal nets are largely activity-independent in the investigated precocial bird.

Neurons associated with aggrecan-based perineuronal nets are protected against tau pathology in subcortical regions in Alzheimer's disease.

The biological basis for the selective vulnerability of neurons in Alzheimer's disease (AD) is elusive. Aggrecan-based perineuronal nets (PNs) of the extracellular matrix have been considered to contribute to neuroprotection in the cerebral cortex. In the present study, we investigated the organization of the aggrecan-based extracellular matrix in subcortical regions known to be preferentially affected by tau pathology in AD. Immunocytochemistry of aggrecan core protein was combined with detection of neurofibrillary degeneration. The results show that many regions affected by tau pathology in AD, such as the basal nucleus of Meynert, the dorsal thalamus, hypothalamic nuclei, raphe nuclei, and the locus coeruleus were devoid of a characteristic aggrecan-based extracellular matrix. Regions composed of nuclei with clearly different intensity of tau pathology, such as the amygdala, the thalamus and the oculomotor complex, showed largely complementary distribution patterns of neurofibrillary tangles and PNs. Quantification in the rostral interstitial nucleus of the longitudinal fascicle potentially affected by tau pathology in AD revealed that tau pathology was not accompanied by loss of aggrecan-based PNs. Neuro-fibrillary tangles in net-associated neurons extremely rarely occurred in the pontine reticular formation. We conclude that the low vulnerability of neurons ensheathed by PNs previously described for cortical areas in AD represents a more general phenomenon that also applies to subcortical regions. The aggrecan-based extracellular matrix of PNs may thus, be involved in neuroprotection.

Apolipoprotein E allele 4 is not a sufficient or a necessary predictor of the development of Mild Cognitive Impairment.

The presence of Mild Cognitive Impairment (MCI) and of an apolipoprotein E (apoE) varepsilon4 allele both predict the development of Alzheimer's disease. However, the extent to which this allele also predicts the development of MCI is unclear even though MCI is an early transitional stage in the development of Alzheimer's disease. The present study investigates the prevalence of the apoE varepsilon4 allele in incipient MCI. Participants were recruited from the population-based Leipzig Longitudinal Study of the Aged (LEILA75+). All subjects who were initially cognitively healthy, i.e. did not meet MCI criteria described by Petersen [Petersen RC. Mild cognitive impairment. J Intern Med 2004; 256(3): 183-94], and whose apoE status could be determined were followed-up. After 4.5 years, 15.5% of the cognitively healthy target population had developed MCI. The frequencies of the apoE varepsilon4 genotype did not differ between individuals with incipient MCI (12.9%) and individuals who remained cognitively healthy during the study (18.4%, p>0.5). Consequently, the apoE varepsilon4 genotype is not a necessary or sufficient risk factor for MCI. Further studies need to investigate the influence of the whole range of genetic and environmental risk factors on the course of Alzheimer's disease including the initial development of MCI and the later conversion to Alzheimer's disease.

Aggrecan-based extracellular matrix shows unique cortical features and conserved subcortical principles of mammalian brain organization in the Madagascan lesser hedgehog tenrec (Echinops telfairi Martin, 1838).

The Madagascan tenrecs (Afrotheria), an ancient mammalian clade, are characterized by unique brain anatomy. Striking features are an expanded paleocortex but a small and poorly differentiated neocortex devoid of a distinct granular layer IV. To investigate the organization of cortical areas we analyzed extracellular matrix components in perineuronal nets (PNs) using antibodies to aggrecan, lectin staining and hyaluronan-binding protein. Selected subcortical regions were studied to correlate the cortical patterns with features in evolutionary conserved systems. In the neocortex, paleocortex and hippocampus PNs were associated with nonpyramidal neurons. Quantitative analysis in the cerebral cortex revealed area-specific proportions and laminar distribution patterns of neurons ensheathed by PNs. Cortical PNs showed divergent structural phenotypes. Diffuse PNs forming a cotton wool-like perisomatic rim were characteristic of the paleocortex. These PNs were associated with a dense pericellular plexus of calretinin-immunoreactive fibres. Clearly contoured PNs were devoid of a calretinin-positive plexus and predominated in the neocortex and hippocampus. The organization of the extracellular matrix in subcortical nuclei followed the widely distributed mammalian type. We conclude that molecular properties of the aggrecan-based extracellular matrix are conserved during evolution of mammals; however, the matrix scaffold is adapted to specific wiring patterns of cortical and subcortical neuronal networks.

Enhanced Ras activity preserves dendritic size and extension as well as synaptic contacts of neurons after functional deprivation in synRas mice.

The monomeric GTP-binding protein p21Ras has been repeatedly implicated in neuronal stability and plastic changes of the adult nervous system. Recently, we have shown that expression of constitutively active Ras protein in transgenic synRas mice results in a significant increase in the dendritic size and complexity of differentiated pyramidal neurons as well as in increased synaptic connectivity. In the present study, we examined the organization of the vibrissae-barrel cortex in synRas mice and the effects of enhanced Ras activity on deprivation-induced dendritic reorganization after vibrissectomy. The results demonstrate a significant increase in vibrissae-barrel sizes and proportional spacing between barrels in synRas mice, suggesting that the neuronal target specificity of thalamocortical terminals is preserved. Accordingly, the arrangement of double bouquet cells at the borders of barrel columns ensuring functional distinctness is unchanged. Partial vibrissectomy is followed by significant dendritic regression of corresponding pyramidal neurons in the barrel cortex of wild-type mice, which, however, could not be observed in synRas mice. The results provide the first evidence for a role of Ras in preserving neuronal structure after functional deprivation in vivo.

Aggrecan-based extracellular matrix is an integral part of the human basal ganglia circuit.

The extracellular matrix is known to be involved in neuronal communication and the regulation of plastic changes, and also considered to protect neurons and synapses against damage. The goal of this study was to investigate how major extracellular matrix components (aggrecan, link protein, hyaluronan) constitute the pathways of the nigral system in the human basal ganglia circuit affected by neurodegeneration in Parkinson's disease. Here we show that aggrecan- and link protein-related components form clear regional distribution patterns, whereas hyaluronan is widely distributed in gray and white matter. Two predominant phenotypes of the aggrecan-based matrix can be discriminated: (1) perineuronal nets (PNs) and (2) axonal coats (ACs) encapsulating preterminal fibers and synaptic boutons. Clearly contoured PNs are associated with GABAergic projection neurons in the external and internal division of the globus pallidus, the lateral and reticular part of the substantia nigra, as well as subpopulations of striatal and thalamic inhibitory interneurons. Dopaminergic nigral neurons are devoid of PNs but are contacted to a different extent by matrix-coated boutons forming subnucleus-specific patterns. A very dense network of ACs is characteristic especially of the posterior lateral cell groups of the compact substantia nigra (nigrosome 1). In the subthalamic nucleus and the lateral thalamic nuclei numerous AC-associated axons were attached to principal neurons devoid of PNs. We conclude from the region-specific patterns that the aggrecan-based extracellular matrix is adapted to the fast processing of sensorimotor activities which are the therapeutic target of surgery and deep brain stimulation in the treatment of advanced stages of Parkinson's disease.

Cell cycle related signaling in Neuro2a cells proceeds via the receptor for advanced glycation end products.

Re-expression of cell cycle related genes such as cyclin-dependent kinases (cdk), cyclins, or cdk inhibitors in differentiated neurons in Alzheimer's disease (AD) is rooted in aberrant mitogenic signaling. Since microglia and astroglia proliferate in the vicinity of amyloid plaques, it is likely that plaque components or factors secreted from plaque-activated glia induce mitogenic signaling in neurons. Mitogenic compounds might be S100B, overexpressed by activated astrocytes, or advanced glycation end products (AGEs), a component of plaques. Both S100B and AGEs may interact with the multiligand receptor for AGEs (RAGE) and trigger for the activation of the p42/44 mitogen-activated protein kinase (p42/44 MAPK), whether they also count for cell cycle related signaling in neurons remains unresolved. By immunohistochemical staining, we confirmed that cyclin D(1) positive neurons are surrounded by AGE deposits, demonstrating the potential relevance in vivo. For exploring the mitogenic signal cascade, we used Neuro2a cells overexpressing human full-length RAGE (FL-RAGE) or the cytosolic deletion mutant (Delta-RAGE). In both cell lines, S100B and AGEs induced the production of reactive oxygen species but not in a RAGE-dependent manner. By contrast, in FL-RAGE cells but not in Delta-RAGE cells S100B and AGEs activate p42/44 MAPK, augment cyclin D(1)/cdk4 protein and RNA levels and the transition into the S-phase. Moreover, in FL-RAGE cells, decreased protein levels of the cdk inhibitor p16 were observed, and the p42/44 MAPK inhibitor UO126 prevented AGE and S100B stimulated cyclin D(1) expression and hindered cells to enter the S-phase. Our results demonstrate that S100B and AGE may serve as mitogenic sources for the stimulation of neurons to progress through the cell cycle whereby signaling proceeds via RAGE --> p42/44 MAPK --> cyclin D(1)/cdk4.

The significance of the cholinergic system in the brain during aging and in Alzheimer's disease.

Acetylcholine is widely distributed in the nervous system and has been implicated to play a critical role in cerebral cortical development, cortical activity, controlling cerebral blood flow and sleep-wake cycle as well as in modulating cognitive performances and learning and memory processes. Cholinergic neurons of the basal forebrain complex have been described to undergo moderate degenerative changes during aging, resulting in cholinergic hypofunction that has been related to the progressing memory deficits with aging. Basal forebrain cholinergic cell loss is also a consistent feature of Alzheimer's disease, which has been suggested to cause, at least partly, the cognitive deficits observed, and has led to the formulation of the cholinergic hypotheses of geriatric memory dysfunction. Impaired cortical cholinergic neurotransmission may also contribute to beta-amyloid plaque pathology and increase phosphorylation of tau protein the main component of neurofibrillar tangles in Alzheimer's disease. Understanding the molecular mechanisms underlying the interrelationship between cortical cholinergic dysfunction, beta-amyloid formation and deposition, and tau pathology in Alzheimer's disease, would allow to derive potential treatment strategies to pharmacologically intervene in the disease-causing signaling cascade.