Stereological estimates of number and length of capillaries in subdivisions of the human hippocampal region

Intranasal insulin attenuates hypoxia-ischemia-induced short-term sensorimotor behavioral disturbances, neuronal apoptosis, and brain damage in neonatal rats

There is a significant need for additional therapy to improve outcomes for newborns with acute Hypoxic-ischemic (HI) encephalopathy (HIE). New evidence suggests that insulin could be neuroprotective. This study aimed to investigate whether intranasal insulin attenuates HI-induced brain damage and neurobehavioral dysfunction in neonatal rats. Postnatal day 10 (P10), Sprague-Dawley rat pups were randomly divided into Sham + Vehicle, Sham + Insulin, HI + Vehicle, and HI + Insulin groups with equal male-to-female ratios. Pups either had HI by permanent ligation of the right common carotid artery followed by 90 min of hypoxia (8% O2) or sham surgery followed by room air exposure. Immediately after HI or Sham, pups were given fluorescence-tagged insulin (Alex-546-insulin)/vehicle, human insulin (25 μg), or vehicle in each nare under anesthesia. Shortly after administration, widespread Alex-546-insulin-binding cells were detected in the brain, primarily co-localized with neuronal nuclei-positive neurons on double-immunostaining. In the hippocampus, phospho-Akt was activated in a subset of Alex-546-insulin double-labeled cells, suggesting activation of the Akt/PI3K pathway in these neurons. Intranasal insulin (InInsulin) reduced HI-induced sensorimotor behavioral disturbances at P11. InInsulin prevented HI-induced increased Fluoro-Jade C+ degenerated neurons, cleaved caspase 3+ neurons, and volume loss in the ipsilateral brain at P11. There was no sex-specific response to HI or insulin. The findings confirm that intranasal insulin provides neuroprotection against HI brain injury in P10 rats associated with activation of intracellular cell survival signaling. If further pre-clinical research shows long-term benefits, intranasal insulin has the potential to be a promising non-invasive therapy to improve outcomes for newborns with HIE.

Capillary communication: the role of capillaries in sensing the tissue environment, coordinating the microvascular, and controlling blood flow

Historically, capillaries have been viewed as the microvascular site for flux of nutrients to cells and removal of waste products. Capillaries are the most numerous blood vessel segment within the tissue, whose vascular wall consists of only a single layer of endothelial cells and are situated within microns of each cell of the tissue, all of which optimizes capillaries for the exchange of nutrients between the blood compartment and the interstitial space of tissues. There is, however, a growing body of evidence to support that capillaries play an important role in sensing the tissue environment, coordinating microvascular network responses, and controlling blood flow. Much of our growing understanding of capillaries stems from work in skeletal muscle and more recent work in the brain, where capillaries can be stimulated by products released from cells of the tissue during increased activity and are able to communicate with upstream and downstream vascular segments, enabling capillaries to sense the activity levels of the tissue and send signals to the microvascular network to coordinate the blood flow response. This review will focus on the emerging role that capillaries play in communication between cells of the tissue and the vascular network required to direct blood flow to active cells in skeletal muscle and the brain. We will also highlight the emerging central role that disruptions in capillary communication may play in blood flow dysregulation, pathophysiology, and disease.

Radon-222 Brain Dosimetry

ABSTRACT

The human brain dose from radon-222 (222Rn) exposure is calculated here using 222Rn tissue solubility data. A fraction of 222Rn inhaled dissolves in blood and cellular fluids and circulates to brain and all organs. Radon-222 has a relatively high solubility in blood and body fluids based on human inhalation experiments. The brain dose uses calculated concentrations of 222Rn in blood and cellular fluids from exhaled breath measurements following human exposure in a 222Rn chamber. The annual brain dose from continuous inhalation of a concentration of 100 Bq m-3 is about 450 times less than the dose to bronchial epithelium from inhalation of the same 222Rn concentration. Based on the 222Rn dosimetry here, it is highly unlikely that brain cancer is related to even high 222Rn exposures. Any functional or neurodegenerative issues from exposure to very small doses of 222Rn alpha particles are, at present, unknown.

Chronic effects of blast injury on the microvasculature in a transgenic mouse model of Alzheimer's disease related Aβ amyloidosis

BACKGROUND

Altered cerebrovascular function and accumulation of amyloid-β (Aβ) after traumatic brain injury (TBI) can contribute to chronic neuropathology and increase the risk for Alzheimer's disease (AD). TBI due to a blast-induced shock wave (bTBI) adversely affects the neurovascular unit (NVU) during the acute period after injury. However, the chronic effects of bTBI and Aβ on cellular components of the NVU and capillary network are not well understood.

METHODS

We exposed young adult (age range: 76-106 days) female transgenic (Tg) APP/PS1 mice, a model of AD-like Aβ amyloidosis, and wild type (Wt) mice to a single bTBI (~ 138 kPa or ~ 20 psi) or to a Sham procedure. At 3-months or 12-months survival after exposure, we quantified neocortical Aβ load in Tg mice, and percent contact area between aquaporin-4 (AQP4)-immunoreactive astrocytic end-feet and brain capillaries, numbers of PDGFRβ-immunoreactive pericytes, and capillary densities in both genotypes.

RESULTS

The astroglia AQP4-capillary contact area in the Tg-bTBI group was significantly lower than in the Tg-Sham group at 3-months survival. No significant changes in the AQP4-capillary contact area were observed in the Tg-bTBI group at 12-months survival or in the Wt groups. Capillary density in the Tg-bTBI group at 12-months survival was significantly higher compared to the Tg-Sham control and to the Tg-bTBI 3-months survival group. The Wt-bTBI group had significantly lower capillary density and pericyte numbers at 12-months survival compared to 3-months survival. When pericytes were quantified relative to capillary density, no significant differences were detected among the experimental groups, for both genotypes.

CONCLUSION

In conditions of high brain concentrations of human Aβ, bTBI exposure results in reduced AQP4 expression at the astroglia-microvascular interface, and in chronic capillary proliferation like what has been reported in AD. Long term microvascular changes after bTBI may contribute to the risk for developing chronic neurodegenerative disease later in life.

Using virtual microscopy for the development of sampling strategies in quantitative histology and design-based stereology

Only a fraction of specimens under study are usually selected for quantification in histology. Multilevel sampling or tissue probes, slides and fields of view (FOVs) in the regions of interest (ROIs) are required. In general, all parts of the organs under study should be given the same probability to be taken into account; that is, the sampling should be unbiased on all levels. The objective of our study was to provide an overview of the use of virtual microscopy in the context of developing sampling strategies of FOVs for stereological quantification. We elaborated this idea on 18 examples from multiple fields of histology, including quantification of extracellular matrix and muscle tissue, quantification of organ and tumour microvessels and tumour-infiltrating lymphocytes, assessing osseointegration of bone implants, healing of intestine anastomoses and osteochondral defects, counting brain neurons, counting nuclei in vitro cell cultures and others. We provided practical implications for the most common situations, such as exhaustive sampling of ROIs, sampling ROIs of different sizes, sampling the same ROIs for multiple histological methods, sampling more ROIs with variable intensities or using various objectives, multistage sampling and virtual sampling. Recommendations were provided for pilot studies on systematic uniform random sampling of FOVs as a part of optimizing the efficiency of histological quantification to prevent over- or undersampling. We critically discussed the pros and cons of using virtual sections for sampling FOVs from whole scanned sections. Our review demonstrated that whole slide scans of histological sections facilitate the design of sampling strategies for quantitative histology.

The Chicken Chorioallantoic Membrane Tumor Assay as a Relevant In Vivo Model to Study the Impact of Hypoxia on Tumor Progression and Metastasis

Simple Summary

Hypoxia is a negative prognostic factor known to be closely associated with tumor progression and metastasis. However, existing animal models with the ability to recreate the tumor hypoxic microenvironment have disadvantages that limit our ability to understand and target this pathological condition. The chicken ChorioAllantoic Membrane (CAM) assay is increasingly used as a rapid cost-effective drug-testing model that recapitulates many aspects of human cancers. Whether this model recreates the hypoxic environment of tumors remains understudied. Here, we demonstrate that the CAM model effectively supports the development of hypoxic zones in a variety of tumor types. Treatment of tumors with angiogenesis inhibitors or inducers significantly modulated the formation of hypoxic zones as well as tumor progression and metastasis. Our findings suggest that the CAM-based tumor model is a relevant in vivo platform to further understand the pathological responses to hypoxia and test therapeutic interventions aimed at targeting hypoxic cancers.

Abstract

Hypoxia in the tumor microenvironment is a negative prognostic factor associated with tumor progression and metastasis, and therefore represents an attractive therapeutic target for anti-tumor therapy. To test the effectiveness of novel hypoxia-targeting drugs, appropriate preclinical models that recreate tumor hypoxia are essential. The chicken ChorioAllantoic Membrane (CAM) assay is increasingly used as a rapid cost-effective in vivo drug-testing platform that recapitulates many aspects of human cancers. However, it remains to be determined whether this model recreates the hypoxic microenvironment of solid tumors. To detect hypoxia in the CAM model, the hypoxic marker pimonidazole was injected into the vasculature of tumor-bearing CAM, and hypoxia-dependent gene expression was analyzed. We observed that the CAM model effectively supports the development of hypoxic zones in a variety of human tumor cell line-derived and patient’s tumor fragment-derived xenografts. The treatment of both patient and cell line-derived CAM xenografts with modulators of angiogenesis significantly altered the formation of hypoxic zones within the xenografts. Furthermore, the changes in hypoxia translated into modulated levels of chick liver metastasis as measured by Alu-based assay. These findings demonstrate that the CAM xenograft model is a valuable in vivo platform for studying hypoxia that could facilitate the identification and testing of drugs targeting this tumor microenvironment.

Basic quantitative morphological methods applied to the central nervous system

Generating numbers has become an almost inevitable task associated with studies of the morphology of the nervous system. Numbers serve a desire for clarity and objectivity in the presentation of results and are a prerequisite for the statistical evaluation of experimental outcomes. Clarity, objectivity, and statistics make demands on the quality of the numbers that are not met by many methods. This review provides a refresher of problems associated with generating numbers that describe the nervous system in terms of the volumes, surfaces, lengths, and numbers of its components. An important aim is to provide comprehensible descriptions of the methods that address these problems. Collectively known as design-based stereology, these methods share two features critical to their application. First, they are firmly based in mathematics and its proofs. Second and critically underemphasized, an understanding of their mathematical background is not necessary for their informed and productive application. Understanding and applying estimators of volume, surface, length or number does not require more of an organizational mastermind than an immunohistochemical protocol. And when it comes to calculations, square roots are the gravest challenges to overcome. Sampling strategies that are combined with stereological probes are efficient and allow a rational assessment if the numbers that have been generated are "good enough." Much may be unfamiliar, but very little is difficult. These methods can no longer be scapegoats for discrepant results but faithfully produce numbers on the material that is assessed. They also faithfully reflect problems that associated with the histological material and the anatomically informed decisions needed to generate numbers that are not only valid in theory. It is within reach to generate practically useful numbers that must integrate with qualitative knowledge to understand the function of neural systems.

Stereological Changes in Microvascular Parameters in Hippocampus of a Transgenic Rat Model of Alzheimer's Disease

BACKGROUND

Microcirculatory factors play an important role in amyloid-β (Aβ)-related neuropathology in Alzheimer's disease (AD). Transgenic (Tg) rat models of mutant Aβ deposition can enhance our understanding of this microvascular pathology.

OBJECTIVE

Here we report stereology-based quantification and comparisons (between- and within-group) of microvessel length and number and associated parameters in hippocampal subregions in Tg model of AD in Fischer 344 rats and non-Tg littermates.

METHODS

Systematic-random samples of tissue sections were processed and laminin immunostained to visualize microvessels through the entire hippocampus in Tg and non-Tg rats. A computer-assisted stereology system was used to quantify microvessel parameters including total number, total length, and associated densities in dentate gyrus (DG) and cornu ammonis (CA) subregions.

RESULTS

Thin hair-like capillaries are common near Aβ plaques in hippocampal subregions of Tg rats. There are a 53% significant increase in average length per capillary across entire hippocampus (p≤0.04) in Tg compared to non-Tg rats; 49% reduction in capillary length in DG (p≤0.02); and, higher microvessel density in principal cell layers (p≤0.03). Furthermore, within-group comparisons confirm Tg but not non-Tg rats have significant increase in number density (p≤0.01) and potential diffusion distance (p≤0.04) of microvessels in principal cell layers of hippocampal subregions.

CONCLUSION

We show the Tg deposition of human Aβ mutations in rats disrupts the wild-type microanatomy of hippocampal microvessels. Stereology-based microvascular parameters could promote the development of novel strategies for protection and the therapeutic management of AD.

Apelin Controls Angiogenesis-Dependent Glioblastoma Growth

Glioblastoma (GBM) present with an abundant and aberrant tumor neo-vasculature. While rapid growth of solid tumors depends on the initiation of tumor angiogenesis, GBM also progress by infiltrative growth and vascular co-option. The angiogenic factor apelin (APLN) and its receptor (APLNR) are upregulated in GBM patient samples as compared to normal brain tissue. Here, we studied the role of apelin/APLNR signaling in GBM angiogenesis and growth. By functional analysis of apelin in orthotopic GBM mouse models, we found that apelin/APLNR signaling is required for in vivo tumor angiogenesis. Knockdown of tumor cell-derived APLN massively reduced the tumor vasculature. Additional loss of the apelin signal in endothelial tip cells using the APLN-knockout (KO) mouse led to a further reduction of GBM angiogenesis. Direct infusion of the bioactive peptide apelin-13 rescued the vascular loss-of-function phenotype specifically. In addition, APLN depletion massively reduced angiogenesis-dependent tumor growth. Consequently, survival of GBM-bearing mice was significantly increased when APLN expression was missing in the brain tumor microenvironment. Thus, we suggest that targeting vascular apelin may serve as an alternative strategy for anti-angiogenesis in GBM.

Longitudinal trajectory of Amyloid-related hippocampal subfield atrophy in nondemented elderly

Hippocampal atrophy and abnormal β‐Amyloid (Aβ) deposition are established markers of Alzheimer's disease (AD). Nonetheless, longitudinal trajectory of Aβ‐associated hippocampal subfield atrophy prior to dementia remains unclear. We hypothesized that elevated Aβ correlated with longitudinal subfield atrophy selectively in no cognitive impairment (NCI), spreading to other subfields in mild cognitive impairment (MCI). We analyzed data from two independent longitudinal cohorts of nondemented elderly, including global PET‐Aβ in AD‐vulnerable cortical regions and longitudinal subfield volumes quantified with a novel auto‐segmentation method (FreeSurfer v.6.0). Moreover, we investigated associations of Aβ‐related progressive subfield atrophy with memory decline. Across both datasets, we found a converging pattern that higher Aβ correlated with faster CA1 volume decline in NCI. This pattern spread to other hippocampal subfields in MCI group, correlating with memory decline. Our results for the first time suggest a longitudinal focal‐to‐widespread trajectory of Aβ‐associated hippocampal subfield atrophy over disease progression in nondemented elderly.

Quantitative histomorphometry of capillary microstructure in deep white matter

White matter lesions represent a major risk factor for dementia in elderly people. Magnetic Resonance Imaging (MRI) studies have demonstrated cerebral blood flow reduction in age-related white matter lesions, indicating that vascular alterations are involved in developing white matter lesions. Hypoperfusion and changes in capillary morphology are generally linked to dementia. However, a quantitative study describing these microvascular alterations in white matter lesions is missing in the literature; most previous microvascular studies being on the cortex. The aim of this work is to identify and quantify capillary microstructural changes involved in the appearance of deep subcortical lesions (DSCL). We characterize the distribution of capillary diameter, thickness, and density in the deep white matter in a population of 75 elderly subjects, stratified into three equal groups according to DSCL: Control (subject without DSCL), Lesion (sample presenting DSCL), and Normal Appearing White Matter (NAWM, the subject presented DSCL but not at the sampled tissue location). Tissue samples were selected from the Cognitive Function and Aging Study (CFAS), a cohort representative of an aging population, from which immunohistochemically-labeled histological images were acquired. To accurately estimate capillary diameters and thicknesses from the 2D histological images, we also introduce a novel semi-automatic method robust to non-perpendicular incidence angle of capillaries into the imaging plane, and to non-circular deformations of capillary cross sections. Subjects with DSCL presented a significant increase in capillary wall thickness, a decrease in the diameter intra-subject variability (but not in the mean), and a decrease in capillary density. No significant difference was observed between controls and NAWM. Both capillary wall thickening and reduction in capillary density contribute to the reduction of cerebral blood flow previously reported for white matter lesions. The obtained distributions provide reliable statistics of capillary microstructure useful to inform the modeling of human cerebral blood flow, for instance to define microcirculation models for their estimation from MRI or to perform realistic cerebral blood flow simulations.

Isolation of Cerebral Capillaries from Fresh Human Brain Tissue

Understanding blood-brain barrier function under physiological and pathophysiological conditions is critical for the development of new therapeutic strategies that hold the promise to enhance brain drug delivery, improve brain protection, and treat brain disorders. However, studying the human blood-brain barrier function is challenging. Thus, there is a critical need for appropriate models. In this regard, brain capillaries isolated from human brain tissue represent a unique tool to study barrier function as close to the human in vivo situation as possible. Here, we describe an optimized protocol to isolate capillaries from human brain tissue at a high yield and with consistent quality and purity. Capillaries are isolated from fresh human brain tissue using mechanical homogenization, density-gradient centrifugation, and filtration. After the isolation, the human brain capillaries can be used for various applications including leakage assays, live cell imaging, and immune-based assays to study protein expression and function, enzyme activity, or intracellular signaling. Isolated human brain capillaries are a unique model to elucidate the regulation of the human blood-brain barrier function. This model can provide insights into central nervous system (CNS) pathogenesis, which will help the development of therapeutic strategies for treating CNS disorders.

Space Balls Revisited: Stereological Estimates of Length With Virtual Isotropic Surface Probes

The space ball probe was fully described in the literature 15 years ago by Mouton et al. (2002). Since then, it has been used in a number of studies in the nervous system that focus on axon, dendrite, and capillary length. The length of structural parameters in tissues reflect functional aspects of the tissues. Here, some of the various applications of this methodology will be presented, along with a review of the salient features of the methodology that has resulted in new wave of quantitative morphological studies of length in the nervous system. The validity of the method is discussed in view of its widespread use along with insights into the problems associated with its application to histological tissue and future techniques for applying space balls.

The Dynamics of Impaired Blood-Brain Barrier Restoration in a Rat Model of Co-morbid Injury

Defect in brain microperfusion is increasingly recognized as an antecedent event to Alzheimer's disease (AD) and ischemia. Nevertheless, studies on the role of impaired microperfusion as a pathological trigger to neuroinflammation, Aβ deposition as well as blood-brain barrier (BBB) disruption, and the etiological link between AD and ischemia are lacking. In this study, we employ in vivo sequential magnetic resonance imaging (MRI) and computed tomography (CT) imaging in a co-morbid rat model of β-amyloid toxicity (Aβ) and ischemia (ET1) with subsequent histopathology of striatal lesion core and penumbra at 1, 7, and 28 days post injury. Within 24 h, cerebral injury resulted in increased BBB permeability due to the dissolution of β-dystroglycan (β-DG) and basement membrane laminin by active matrix metalloproteinase9 (MMP9). As a result, net flow of circulating IgG down a hydrostatic gradient into the parenchyma led to vasogenic edema and impaired perfusion, thus increasing the apparent hyperintensity in true fast imaging with steady-state free precession (true FISP) imaging and acute hypoperfusion in CT. This was followed by a slow recruitment of reactive astroglia to the affected brain and depolarization of aquaporin4 (AQP4) expression resulting in cytotoxic edema-in an attempt to resolve vasogenic edema. On d28, functional BBB was restored in ET1 rats as observed by astrocytic MMP9 release, β-DG stabilization, and new vessel formation. This was confirmed by reduced hyperintensity on true FISP imaging and normalized cerebral blood flow in CT. While, Aβ toxicity alone was not detrimental enough, Aβ+ET1 rats showed delayed differential expression of MMP9, late recruitment of astroglial cells, protracted loss of AQP4 depolarization, and thus delayed BBB restoration and cerebral perfusion.

Sampling the Mouse Hippocampal Dentate Gyrus

Sampling is a critical step in procedures that generate quantitative morphological data in the neurosciences. Samples need to be representative to allow statistical evaluations, and samples need to deliver a precision that makes statistical evaluations not only possible but also meaningful. Sampling generated variability should, e.g., not be able to hide significant group differences from statistical detection if they are present. Estimators of the coefficient of error (CE) have been developed to provide tentative answers to the question if sampling has been “good enough” to provide meaningful statistical outcomes. We tested the performance of the commonly used Gundersen-Jensen CE estimator, using the layers of the mouse hippocampal dentate gyrus as an example (molecular layer, granule cell layer and hilus). We found that this estimator provided useful estimates of the precision that can be expected from samples of different sizes. For all layers, we found that a smoothness factor (m) of 0 generally provided better estimates than an m of 1. Only for the combined layers, i.e., the entire dentate gyrus, better CE estimates could be obtained using an m of 1. The orientation of the sections impacted on CE sizes. Frontal (coronal) sections are typically most efficient by providing the smallest CEs for a given amount of work. Applying the estimator to 3D-reconstructed layers and using very intense sampling, we observed CE size plots with m = 0 to m = 1 transitions that should also be expected but are not often observed in real section series. The data we present also allows the reader to approximate the sampling intervals in frontal, horizontal or sagittal sections that provide CEs of specified sizes for the layers of the mouse dentate gyrus.

Numerical and length densities of microvessels in the human brain: Correlation with preferential orientation of microvessels in the cerebral cortex, subcortical grey matter and white matter, pons and cerebellum

To provide basic data on the local differences in density of microvessels between various parts of the human brain, including representative grey and white matter structures of the cerebral hemispheres, the brain stem and the cerebellum, we quantified the numerical density N_V and the length density L_V of microvessels in two human brains. We aimed to correlate the density of microvessels with previously published data on their preferential orientation (anisotropy). Microvessels were identified using immunohistochemistry for laminin in 32 samples harvested from the following brain regions of two adult individuals: the cortex of the telencephalon supplied by the anterior, middle, and posterior cerebral artery; the basal ganglia (putamen and globus pallidus); the thalamus; the subcortical white matter of the telencephalon; the internal capsule; the pons; the cerebellar cortex; and the cerebellar white matter. N_V was calculated from the number of vascular branching points and their valence, which were assessed using the optical disector in 20-μm-thick sections. L_V was estimated using counting frames applied to routine sections with randomized cutting planes. After correction for shrinkage, N_V in the cerebral cortex was 1311±326mm^-3 (mean±SD) and L_V was 255±119mm^-2. Similarly, in subcortical grey matter (which included the basal ganglia and thalamus), N_V was 1350±445mm^-3 and L_V was 328±117mm^-2. The vascular networks of cortical and subcortical grey matter were comparable. Their densities were greater than in the white matter, with N_V=222±147mm^-3 and L_V=160±96mm^-2. N_V was moderately correlated with L_V. In parts of brain with greater N_V, blood vessels lacked a preferential orientation. Our data were in agreement with other studies on microvessel density focused on specific brain regions, but showed a greater variability, thus mapping the basic differences among various parts of brain. To facilitate the planning of other studies on brain vascularity and to support the development of computational models of human brain circulation based on real microvascular morphology; stereological data in form of continuous variables are made available as supplements.

Smaller Absolute Quantities but Greater Relative Densities of Microvessels Are Associated with Cerebellar Degeneration in Lurcher Mice

Degenerative affections of nerve tissues are often accompanied by changes of vascularization. In this regard, not much is known about hereditary cerebellar degeneration. In this study, we compared the vascularity of the individual cerebellar components and the mesencephalon of 3-month-old wild type mice (n = 5) and Lurcher mutant mice, which represent a model of hereditary olivocerebellar degeneration (n = 5). Paraformaldehyde-fixed brains were processed into 18-μm thick serial sections with random orientation. Microvessels were visualized using polyclonal rabbit anti-laminin antibodies. Then, the stacks comprised of three 5-μm thick optical sections were recorded using systematic uniform random sampling. Stereological assessment was conducted based on photo-documentation. We found that each of the cerebellar components has its own features of vascularity. The greatest number and length of vessels were found in the granular layer; the number of vessels was lower in the molecular layer, and the lowest number of vessels was observed in the cerebellar nuclei corresponding with their low volume. Nevertheless, the nuclei had the greatest density of blood vessels. The reduction of cerebellum volume in the Lurcher mice was accompanied by a reduction in vascularization in the individual cerebellar components, mainly in the cortex. Moreover, despite the lower density of microvessels in the Lurcher mice compared with the wild type mice, the relative density of microvessels in the cerebellar cortex and nuclei was greater in Lurcher mice. The complete primary morphometric data, in the form of continuous variables, is included as a supplement. Mapping of the cerebellar and midbrain microvessels has explanatory potential for studies using mouse models of neurodegeneration.

Microcirculation of the brain: morphological assessment in degenerative diseases and restoration processes

Brain microcirculation plays an important role in the pathogenesis of various brain diseases. Several specific features of the circulation in the brain and its functions deserve special attention. The brain is extremely sensitive to hypoxia, and brain edema is more dangerous than edema in other tissues. Brain vessels are part of the blood-brain barrier, which prevents the penetration of some of the substances in the blood into the brain tissue. Herein, we review the processes of angiogenesis and the changes that occur in the brain microcirculation in the most prevalent neurodegenerative diseases. There are no uniform vascular changes in the neurodegenerative diseases. In some cases, the vascular changes are secondary consequences of the pathological process, but they could also be involved in the pathogenesis of the primary disease and contribute to the degeneration of neurons, based on their quantitative characteristics. Additionally, we described the stereological methods that are most commonly used for generating qualitative and quantitative data to assess changes in the microvascular bed of the brain.

A zinc fixative for 3D visualization of cerebral capillaries and pericytes

BACKGROUND

A large volume of data indicates that disturbances in the morphology and function of the capillary wall may play a causal role in several types of neurodegenerative disorders. We present a highly reproducible staining method for investigating the cerebral capillary network and the pericyte cells within the basement membrane in mice - a specie specific challenging task when uniform staining in thick sections was needed for confocal microscopy or a quantitative analysis, e.g. stereological investigation using 3D probes.

NEW METHOD

We perfused C57BL6/Jbom mice and immersion fixated the brains with an aldehyde free zinc fixative, which is normally used for paraffin embedded tissues, and stained for CD31 and Collagen Type IV positive capillaries in 100μm thick sections.

RESULTS

Using the milder zinc fixative allowed complete immunohistochemical visualization of the cerebral capillary network in 100μm thick sections using CD31 or Collagen Type IV antibodies. Moreover CD31 or Collagen Type IV staining revealed the presence of pericytes, which was confirmed by a fluorescent co-localization with the NG2 pericyte marker.

COMPARISON WITH EXISTING METHODS

Compared with conventional aldehyde-based fixative, this method resulted in a homogeneous staining through the entire depth of thick sections with very limited background staining and well-preserved morphology.

CONCLUSIONS

This method is suitable for 3D stereological analysis of capillary networks and pericytes within thick brain sections using CD31 or Collagen Type IV antibodies.

Quantitative analysis of the capillary network of aged APPswe/PS1dE9 transgenic mice

A combination of immunohistochemical and stereological techniques were used to investigate the capillary network in the cerebral cortex of 18-month-old APPswe/PS1dE9 transgenic (Tg) mice and control littermates. Data regarding total capillary length, segment number, diffusion radius, and pericyte number are presented. The total length was 60 meters and there was a one-to-one relationship between the number of capillary segments and pericytes in both groups. Significant differences were not observed in the Tg and wild-type controls indicating that the Alzheimer's-like amyloidosis produced in this Tg mouse has a minimal affect on the structural integrity of the cerebral capillary network.

Interleukin-1 receptor antagonist reduces neonatal lipopolysaccharide-induced long-lasting neurobehavioral deficits and dopaminergic neuronal injury in adult rats

Our previous study showed that a single lipopolysaccharide (LPS) treatment to neonatal rats could induce a long-lasting neuroinflammatory response and dopaminergic system injury late in life. This is evidenced by a sustained activation of microglia and elevated interleukin-1β (IL-1β) levels, as well as reduced tyrosine hydroxylase (TH) expression in the substantia nigra (SN) of P70 rat brain. The object of the current study was to test whether co-administration of IL-1 receptor antagonist (IL-1ra) protects against LPS-induced neurological dysfunction later in life. LPS (1 mg/kg) with or without IL-1ra (0.1 mg/kg), or sterile saline was injected intracerebrally into postnatal day 5 (P5) Sprague-Dawley male rat pups. Motor behavioral tests were carried out from P7 to P70 with subsequent examination of brain injury. Our results showed that neonatal administration of IL-1ra significantly attenuated LPS-induced motor behavioral deficits, loss of TH immunoreactive neurons, as well as microglia activation in the SN of P70 rats. These data suggest that IL-1β may play a pivotal role in mediating a chronic neuroinflammation status by a single LPS exposure in early postnatal life, and blockading IL-1β might be a novel approach to protect the dopaminergic system against perinatal infection/inflammation exposure.

Apolipoprotein E4 produced in GABAergic interneurons causes learning and memory deficits in mice

Apolipoprotein (apo) E4 is expressed in many types of brain cells, is associated with age-dependent decline of learning and memory in humans, and is the major genetic risk factor for AD. To determine whether the detrimental effects of apoE4 depend on its cellular sources, we generated human apoE knock-in mouse models in which the human APOE gene is conditionally deleted in astrocytes, neurons, or GABAergic interneurons. Here we report that deletion of apoE4 in astrocytes does not protect aged mice from apoE4-induced GABAergic interneuron loss and learning and memory deficits. In contrast, deletion of apoE4 in neurons does protect aged mice from both deficits. Furthermore, deletion of apoE4 in GABAergic interneurons is sufficient to gain similar protection. This study demonstrates a detrimental effect of endogenously produced apoE4 on GABAergic interneurons that leads to learning and memory deficits in mice and provides a novel target for drug development for AD related to apoE4.

Matrix metalloproteinase-3 causes dopaminergic neuronal death through Nox1-regenerated oxidative stress

In the present study we investigated the interplay between matrix metalloproteinase 3 (MMP3) and NADPH oxidase 1 (Nox1) in the process of dopamine (DA) neuronal death. We found that MMP3 activation causes the induction of Nox1 via mitochondrial reactive oxygen species (ROS) production and subsequently Rac1 activation, eventually leading to Nox1-derived superoxide generation in a rat DA neuronal N27 cells exposed to 6-OHDA. While a MMP3 inhibitor, NNGH, largely attenuated mitochondrial ROS and subsequent Nox1 induction, both apocynin, a putative Nox inhibitor and GKT137831, a Nox1 selective inhibitor failed to reduce 6-OHDA-induced mitochondrial ROS. However, both inhibitors for MMP3 and Nox1 similarly attenuated 6-OHDA-induced N27 cell death. RNAi-mediated selective inhibition of MMP3 or Nox1 showed that knockdown of either MMP3 or Nox1 significantly reduced 6-OHDA-induced ROS generation in N27 cells. While 6-OHDA-induced Nox1 was abolished by MMP3 knockdown, Nox1 knockdown did not alter MMP3 expression. Direct overexpression of autoactivated MMP3 (actMMP3) in N27 cells or in rat substantia nigra (SN) increased expression of Nox1. Selective knockdown of Nox1 in the SN achieved by adeno-associated virus-mediated overexpression of Nox1-specific shRNA largely attenuated the actMMP3-mediated dopaminergic neuronal loss. Furthermore, Nox1 expression was significantly attenuated in Mmp3 null mice treated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Together we established novel molecular mechanisms underlying oxidative stress-mediated dopaminergic neuronal death in which MMP3 activation is a key upstream event that leads to mitochondrial ROS, Nox1 induction and eventual dopaminergic neuronal death. Our findings may lead to the development of novel therapeutic approach.

Quantitative assessment of angiogenesis, perfused blood vessels and endothelial tip cells in the postnatal mouse brain

During development and in various diseases of the CNS, new blood vessel formation starts with endothelial tip cell selection and vascular sprout migration, followed by the establishment of functional, perfused blood vessels. Here we describe a method that allows the assessment of these distinct angiogenic steps together with antibody-based protein detection in the postnatal mouse brain. Intravascular and perivascular markers such as Evans blue (EB), isolectin B4 (IB4) or laminin (LN) are used alongside simultaneous immunofluorescence on the same sections. By using confocal laser-scanning microscopy and stereological methods for analysis, detailed quantification of the 3D postnatal brain vasculature for perfused and nonperfused vessels (e.g., vascular volume fraction, vessel length and number, number of branch points and perfusion status of the newly formed vessels) and characterization of sprouting activity (e.g., endothelial tip cell density, filopodia number) can be obtained. The entire protocol, from mouse perfusion to vessel analysis, takes ∼10 d.

Idiopathic microscopic colitis of rhesus macaques: quantitative assessment of colonic mucosa

Idiopathic chronic diarrhea (ICD) is a common cause of morbidity and mortality among juvenile rhesus macaques. While lesions may be absent at colonoscopy, the histopathologic evaluation of the biopsy specimens is consistent with human macroscopic colitis (MC). In this study, we developed an isotropic uniform random sampling method to evaluate macroscopic and microscopic changes and applied it on proximal ascending colon in monkeys. Colonic tissue and peripheral blood specimens were collected from six MC and six control juvenile macaques at necropsy. Uniform random samples were collected from the colon using punch biopsy tools. The volume of epithelium and lamina propria were estimated in thick (25 µm) sections using point probes and normalized to the area of muscularis mucosae. Our data suggests a significant increase of the Vs of the lamina propria (1.9-fold, P = 0.02) and epithelium (1.4-fold, P = 0.05) in subjects with MC. The average colonic surface mucosa area in the MC monkeys increased 1.4-fold over the controls (P = 0.02). The volume of the proximal colon in animals with MC showed a 2.4-fold increase over the non-diarrhea control monkeys (P = 0.0001). Cytokine, chemokine, and growth factor levels in peripheral blood were found to be correlated with the volume estimate of the lamina propria and epithelium. We found that ICD in macaques has features which simulates human MC and can be used as a spontaneous animal model for human MC. Furthermore, this developed sampling method can be used for unbiased preclinical evaluation of therapeutics in this animal model.

Estimating length in biological structures

Length estimates of particular features of biological tissues can be useful in evaluating function. Such estimates have been notoriously difficult to obtain because of the requirement for an isotropic interaction between the area probes and the linear features of cells and tissues, which are most likely not isotropically oriented. For complex embedded structures, such as subdivisions of the brain, the turning of the tissue before sectioning that is needed to ensure an isotropic interaction has made it difficult to delineate many regions of interest and limited the number of unbiased stereological studies of length. The recent development of a virtual isotropic spherical probe, the spaceball, makes it relatively easy for the isotropic interaction between probe and structure to be realized. This article describes the use of the spaceball probe to estimate length, and gives an example of estimating total capillary length in CA1 stratum radiatum of the human hippocampus.

In vivo imaging of adult human hippocampal neurogenesis: progress, pitfalls and promise

New neurons are produced within the hippocampus of the mammalian brain throughout life. Evidence from animal studies has suggested that the function of these adult-born neurons is linked to cognition and emotion. Until we are able to detect and measure levels of adult neurogenesis in living human brains-a formidable challenge for now-we cannot establish its functional importance in human health, disease and new treatment development. Current non-invasive neuroimaging modalities can provide live snapshots of the brain's structure, chemistry, activity and connectivity. This review explores whether existing macroscopic imaging methods can be used to understand the microscopic dynamics of adult hippocampal neurogenesis in living individuals. We discuss recent studies that have found correlations between neuroimaging measures of human hippocampal biology and levels of pro- or anti-neurogenic stimuli, weigh whether these correlations reflect changes in adult neurogenesis, detail the conceptual and technical limitations of these studies and elaborate on what will be needed to validate in vivo neuroimaging measures of adult neurogenesis for future investigations.

Neonatal systemic exposure to lipopolysaccharide enhances susceptibility of nigrostriatal dopaminergic neurons to rotenone neurotoxicity in later life

Brain inflammation via intracerebral injection with lipopolysaccharide (LPS) in early life has been shown to increase risks for the development of neurodegenerative disorders in adult rats. To determine if neonatal systemic LPS exposure has the same effects on enhancement of adult dopaminergic neuron susceptibility to rotenone neurotoxicity as centrally injected LPS does, LPS (2 μg/g body weight) was administered intraperitoneally into postnatal day 5 (P5) rats and when grown to P70, rats were challenged with rotenone, a commonly used pesticide, through subcutaneous minipump infusion at a dose of 1.25 mg/kg/day for 14 days. Systemically administered LPS can penetrate into the neonatal rat brain and cause acute and chronic brain inflammation, as evidenced by persistent increases in IL-1β levels, cyclooxygenase-2 expression and microglial activation in the substantia nigra (SN) of P70 rats. Neonatal LPS exposure resulted in suppression of tyrosine hydroxylase (TH) expression, but not actual death of dopaminergic neurons in the SN, as indicated by the reduced number of TH+ cells and unchanged total number of neurons (NeuN+) in the SN. Neonatal LPS exposure also caused motor function deficits, which were spontaneously recoverable by P70. A small dose of rotenone at P70 induced loss of dopaminergic neurons, as indicated by reduced numbers of both TH+ and NeuN+ cells in the SN, and Parkinson's disease (PD)-like motor impairment in P98 rats that had experienced neonatal LPS exposure, but not in those without the LPS exposure. These results indicate that although neonatal systemic LPS exposure may not necessarily lead to death of dopaminergic neurons in the SN, such an exposure could cause persistent functional alterations in the dopaminergic system and indirectly predispose the nigrostriatal system in the adult brain to be damaged by environmental toxins at an ordinarily nontoxic or subtoxic dose and develop PD-like pathological features and motor dysfunction.

Cerebral neovascularization and remodeling patterns in two different models of type 2 diabetes

We previously reported intense pial cerebral collateralization and arteriogenesis in a mild and lean model of type 2 diabetes (T2D), Goto-Kakizaki (GK) rats. Increased cerebral neovascularization differed regionally and was associated with poor vessel wall maturity. Building upon these findings, the goals of this study were to determine whether a) glycemic control prevents this erratic cerebral neovascularization in the GK model, and b) this pathological neovascularization pattern occurs in Lepr(db/db) model, which is the most commonly used model of T2D for studies involving cerebral complications of diabetes. Vascular volume, surface area and structural parameters including microvessel/macrovessel ratio, non-FITC (fluorescein) perfusing vessel abundance, vessel tortuosity, and branch density were measured by 3D reconstruction of FITC stained vasculature in GK rats or Lepr(db/db) mice. GK rats exhibited an increase in all of these parameters, which were prevented by glycemic control with metformin. In Lepr(db/db) mice, microvascular density was increased but there was no change in nonFITC-perfusing vessels. Increased PA branch density was associated with reduced branch diameter. These results suggest that T2D leads to cerebral neovascularization and remodeling but some structural characteristics of newly formed vessels differ between these models of T2D. The prevention of dysfunctional cerebral neovascularization by early glucose control suggests that hyperglycemia is a mediator of this response.

Isotropy, iSectors, and vertical sections in stereology

Stereology provides meaningful quantitative descriptions of the geometry of three-dimensional (3D) structures from measurements that are made on two-dimensional (2D) images. One important consideration when designing such studies is that both length and surface features may have preferred orientations in 3D space; that is, they may not be isotropic. To fully understand the global estimators of length L and surface area S, it is essential that one understand the problems that the inherent anisotropy in the structure of most living organisms generates when designing unbiased sampling schemes for estimating length and surface. These same issues also apply to the use of local estimators of object volume v and surface s, in that they use line and surface probes. These problems and the various solutions to them, which involve sectioning and probing tissue in particular ways, are presented in this article.

Delivery of drugs to the brain via the blood brain barrier using colloidal carriers

Delivering drugs to the brain is challenging given the selective permeability of the blood brain barrier (BBB). Targeted colloidal carriers containing drug payloads offer some promise for enhanced and perhaps selective delivery to brain. This review examines the recent literature and identifies issues to be addressed if these systems are to be rationally designed. These include opsonization of nanoparticles and off-target clearance; the cerebral microvasculature, flow of nanoparticles in capillaries and binding to the capillary wall; and transcytosis. Capillary architecture, blood flow and BBB permeability are affected by disease and age and there are species differences. These complexities caution against making extravagant claims for a particular nanosystem but they also highlight the rich opportunities and need for critical research in this field.

Vasa vasorum quantification in human varicose great and small saphenous veins

Recent research regarding saphenous vasa vasorum (VV) has focused on two main topics: the VV during varicogenesis in chronic venous insufficiency and the VV in saphenous grafts used in reconstructive vascular surgery. Our aim has been (i) to establish a technique for the histological quantification of the VV in human varicose great and small saphenous veins and (ii) to describe the density and distribution of the vasa vasorum within varicose veins. Great (n=11) and small (n=5) saphenous veins (length, 15-40cm) were collected from 12 patients who were undergoing venous stripping due to chronic venous insufficiency (Clinical-Etiology-Anatomy-Pathophysiology class 2-3). The veins were divided into 5-cm long segments. In total, 92 tissue blocks were collected to trace the variability of the density and distribution of the vasa vasorum in the proximo-distal direction. The endothelium was detected by immunohistochemistry using the von Willebrand factor. We quantified the number of microvessel profiles per section area and the relative distance of the microvessels from the outer border of the adventitia. The VV did not exhibit a preferential orientation in the varicose veins. VV density profiles were highest in the middle third of the venous wall and lowest in the inner third of the venous wall. Both the density and distribution of VV were uniform along the veins, and no differences were observed between the great and small saphenous veins. The VV density was statistically independent of the relative distance from the adventitia. The usability of this technique for perioperative frozen sections remains to be tested.

Neonatal exposure to lipopolysaccharide enhances vulnerability of nigrostriatal dopaminergic neurons to rotenone neurotoxicity in later life

Brain inflammation in early life has been proposed to play important roles in the development of neurodegenerative disorders in adult life. To test this hypothesis, we used a neonatal rat model of lipopolysaccharide (LPS) exposure (1000 EU/g body weight, intracerebral injection on P5) to produce brain inflammation. By P70, when LPS-induced behavioral deficits were spontaneously recovered, animals were challenged with rotenone, a commonly used pesticide, through subcutaneous mini-pump infusion at a dose of 1.25 mg/kg per day for 14 days. This rotenone treatment regimen ordinarily does not produce toxic effects on behaviors in normal adult rats. Our results show that neonatal LPS exposure enhanced the vulnerability of nigrostriatal dopaminergic neurons to rotenone neurotoxicity in later life. Rotenone treatment resulted in motor neurobehavioral impairments in rats with the neonatal LPS exposure, but not in those without the neonatal LPS exposure. Rotenone induced losses of tyrosine hydroxylase immunoreactive neurons in the substantia nigra and decreased mitochondrial complex I activity in the striatum of rats with neonatal LPS exposure, but not in those without this exposure. Neonatal LPS exposure with later exposure to rotenone decreased retrogradely labeled nigrostriatal dopaminergic projecting neurons. The current study suggests that perinatal brain inflammation may enhance adult susceptibility to the development of neurodegenerative disorders triggered later on by environmental toxins at an ordinarily non-toxic or sub-toxic dose. Our model may be useful for studying mechanisms involved in the pathogenesis of nonfamilial Parkinson's disease and the development of potential therapeutic treatments.

Dopaminergic neuronal injury in the adult rat brain following neonatal exposure to lipopolysaccharide and the silent neurotoxicity

Our previous studies have shown that neonatal exposure to lipopolysaccharide (LPS) resulted in motor dysfunction and dopaminergic neuronal injury in the juvenile rat brain. To further examine whether neonatal LPS exposure has persisting effects in adult rats, motor behaviors were examined from postnatal day 7 (P7) to P70 and brain injury was determined in P70 rats following an intracerebral injection of LPS (1 mg/kg) in P5 Sprague-Dawley male rats. Although neonatal LPS exposure resulted in hyperactivity in locomotion and stereotyped tasks, and other disturbances of motor behaviors, the impaired motor functions were spontaneously recovered by P70. On the other hand, neonatal LPS-induced injury to the dopaminergic system such as the loss of dendrites and reduced tyrosine hydroxylase immunoreactivity in the substantia nigra persisted in P70 rats. Neonatal LPS exposure also resulted in sustained inflammatory responses in the P70 rat brain, as indicated by an increased number of activated microglia and elevation of interleukin-1β and interleukin-6 content in the rat brain. In addition, when challenged with methamphetamine (METH, 0.5 mg/kg) subcutaneously, rats with neonatal LPS exposure had significantly increased responses in METH-induced locomotion and stereotypy behaviors as compared to those without LPS exposure. These results indicate that although neonatal LPS-induced neurobehavioral impairment is spontaneously recoverable, the LPS exposure-induced persistent injury to the dopaminergic system and the chronic inflammation may represent the existence of silent neurotoxicity. Our data further suggest that the compromised dendritic mitochondrial function might contribute, at least partially, to the silent neurotoxicity.

Stereological approaches to identifying neuropathology in psychosis

The challenges involved in identifying the neuropathological substrates of the clinical syndrome recognized as schizophrenia are well known. Stereological sampling provides a means to obtain accurate and precise quantitative estimates of components of neural circuits and thus offers promise of an enhanced capacity to detect subtle alterations in brain structure associated with schizophrenia. In this review, we 1) consider the importance and rationale for robust quantitative measures of brain abnormalities in postmortem studies of schizophrenia; 2) provide a brief overview of stereological methods for obtaining such measures; 3) discuss the methodological details that should be reported to document the robustness of a stereological study; 4) given the constraints of postmortem human studies, suggest how to approach the limitations of less robust designs; and 5) present an overview of methodologically sound stereological estimates from postmortem studies of schizophrenia.

Brain aging in the oldest-old

Nonagenarians and centenarians represent a quickly growing age group worldwide. In parallel, the prevalence of dementia increases substantially, but how to define dementia in this oldest-old age segment remains unclear. Although the idea that the risk of Alzheimer's disease (AD) decreases after age 90 has now been questioned, the oldest-old still represent a population relatively resistant to degenerative brain processes. Brain aging is characterised by the formation of neurofibrillary tangles (NFTs) and senile plaques (SPs) as well as neuronal and synaptic loss in both cognitively intact individuals and patients with AD. In nondemented cases NFTs are usually restricted to the hippocampal formation, whereas the progressive involvement of the association areas in the temporal neocortex parallels the development of overt clinical signs of dementia. In contrast, there is little correlation between the quantitative distribution of SP and AD severity. The pattern of lesion distribution and neuronal loss changes in extreme aging relative to the younger-old. In contrast to younger cases where dementia is mainly related to severe NFT formation within adjacent components of the medial and inferior aspects of the temporal cortex, oldest-old individuals display a preferential involvement of the anterior part of the CA1 field of the hippocampus whereas the inferior temporal and frontal association areas are relatively spared. This pattern suggests that both the extent of NFT development in the hippocampus as well as a displacement of subregional NFT distribution within the Cornu ammonis (CA) fields may be key determinants of dementia in the very old. Cortical association areas are relatively preserved. The progression of NFT formation across increasing cognitive impairment was significantly slower in nonagenarians and centenarians compared to younger cases in the CA1 field and entorhinal cortex. The total amount of amyloid and the neuronal loss in these regions were also significantly lower than those reported in younger AD cases. Overall, there is evidence that pathological substrates of cognitive deterioration in the oldest-old are different from those observed in the younger-old. Microvascular parameters such as mean capillary diameters may be key factors to consider for the prediction of cognitive decline in the oldest-old. Neuropathological particularities of the oldest-old may be related to "longevity-enabling" genes although little or nothing is known in this promising field of future research.

Quantitative changes in hippocampal microvasculature of chronically stressed rats: no effect of fluoxetine treatment

Exposure to chronic stress alters the number and morphology of neurons and glia in the hippocampal formation; however, little is known about possible changes in vasculature. Here, we examined the effect of chronic social defeat stress on hippocampal vascular supply in rats. Recent reports document that antidepressant treatment can influence angiogenesis in the hippocampus; therefore, we also studied the effect of antidepressant drug treatment on hippocampal capillarization. Animals were subjected to 5 weeks of daily social defeat by an aggressive conspecific and received concomitant, daily, oral fluoxetine (10 mg/kg) treatment during the last 4 weeks. Rat endothelial cell antigen-1 (RECA-1)-labeling of capillaries and quantitative stereological techniques were used to evaluate the treatment effects on capillary number. Special attention was paid to analysis of the vascular supply of the subgranular zone, which is regarded as an important component of the neurogenic niche for adult hippocampal neurogenesis. Chronic stress significantly decreased the number of microvessels by 30% in all hippocampal subregions, whereas fluoxetine treatment had no influence on capillary number. Furthermore, chronic stress decreased the capillarization of the subgranular zone to a similar extent, indicating that chronic stress affects the vascular niche for adult hippocampal neurogenesis. However, fluoxetine treatment had no impact on capillarization in the subgranular zone. We also detected a decrease in hippocampal volume in the animals as a result of stress, which was mildly altered by fluoxetine treatment. These pronounced changes in vascular supply may explain why the hippocampus is more vulnerable to insults when chronic stress precedes or coincides with other harmful conditions. Reduced microvasculature may also contribute to hippocampal volume decrease in stress-related disorders.

How and when the fMRI BOLD signal relates to underlying neural activity: the danger in dissociation

Functional magnetic resonance imaging (fMRI) has become the dominant means of measuring behavior-related neural activity in the human brain. Yet the relation between the blood oxygen-level dependent (BOLD) signal and underlying neural activity remains an open and actively researched question. A widely accepted model, established for sensory neo-cortex, suggests that the BOLD signal reflects peri-synaptic activity in the form of the local field potential rather than the spiking rate of individual neurons. Several recent experimental results, however, suggest situations in which BOLD, spiking, and the local field potential dissociate. Two different models are discussed, based on the literature reviewed to account for this dissociation, a circuitry-based and vascular-based explanation. Both models are found to account for existing data under some testing situations and in certain brain regions. Because both the vascular and local circuitry-based explanations challenge the BOLD-LFP coupling model, these models provide guidance in predicting when BOLD can be expected to reflect neural processing and when the underlying relation with BOLD may be more complex than a direct correspondence.

Dissociation between vascular endothelial growth factor receptor-2 and blood vessel density in the caudate nucleus after chronic hydrocephalus

Chronic hydrocephalus (CH) is characterized by the presence of ventricular enlargement, decreased cerebral blood flow (CBF), and brain tissue oxygen delivery. Although the underlying pathophysiological role of vascular endothelial growth factor (VEGF) is not clear, ischemic-hypoxic events in CH are known to trigger its release. Previously, we have shown increased VEGF receptor-2 (VEGFR-2) and blood vessel density (BVd) in the hippocampus after CH. We investigated changes in neuronal and glial VEGFR-2 density and BVd in the caudate nucleus in an experimental model of CH. Animals with CH were divided into short term (ST, 2 to 4 weeks) and long term (LT, 12 to 16 weeks) and were compared with surgical controls (SCs, 12 to 16 weeks). The cellular and BVds were estimated using immunohistochemical and stereological counting methods. Overall, percentage (%)VEGFR-2 neurons were approximately two times greater in CH (ST, LT) than in SC. By comparison, glial cell %VEGFR-2 was greater by 10% to 17% in ST and 4% to 11% lower in LT compared with that in SC. Blood vessel density was significantly lower in CH than in SC in the superficial caudate. Changes in cerebrospinal fluid ventricular volume and pressure, as well as in CBF did not correlate with either VEGFR-2 or BVd. These observed findings suggest that destructive forces may outweigh angiogenic forces and possibly show a disassociation between VEGFR-2 and BV expressions.

Chronic hydrocephalus-induced hypoxia: increased expression of VEGFR-2+ and blood vessel density in hippocampus

Chronic hydrocephalus (CH) is a neurological disease characterized by increased cerebrospinal fluid volume and pressure that is often associated with impaired cognitive function. By and large, CH is a complex and heterogeneous cerebrospinal fluid (CSF) disorder where the exact site of brain insult is uncertain. Several mechanisms including neural compression, fiber stretch, and local or global hypoxia have been implicated in the underlying pathophysiology of CH. Specifically, the hippocampus, which plays a significant role in memory processing and is in direct contact with expanding CSF ventricles, may be involved. Using our model of chronic hydrocephalus, we quantified the density of vascular endothelial growth factor receptor 2 (VEGFR-2(+)) neurons, glial, endothelial cells, and blood vessels in hippocampal regions CA1, CA2-3, dentate gyrus and hilus using immunohistochemical and stereological methods. Density and %VEGFR-2(+) cell populations were estimated for CH animals (2-3 weeks vs. 12-16 weeks) and surgical controls (SC). Overall, we found approximately six- to eightfold increase in the cellular density of VEGFR-2(+) and more than double blood vessel density (BVd) in the hippocampus of CH compared with SC. There were no significant regional differences in VEGFR-2(+) cellular and BVd expression in the CH group. VEGFR-2(+) and BVds were significantly related to changes in CSF volume (P<or=0.05), and not intracranial pressure (ICP). The %VEGFR-2(+) was significantly greater in CH than SC (P<or=0.05), and was significantly correlated with BVd (P<or=0.05). These results showed that CH elicited a profound increase in VEGFR-2(+) in hippocampus that corresponded to increased BVd. It was unclear whether increased VEGFR-2(+) and blood vessel expression was related to focal compression alone or in combination with global ischemia/hypoxia conditions as previously described. These findings suggest that VEGFR-2 may play an adaptive role in angiogenesis after CH-induced hypoxia. Modulation of vascular endothelial growth factor/VEGFR-2(+) may be important in developing treatments for hypoxic conditions including hydrocephalus and other forms of cerebral ischemia.

Morphological substrates of cognitive decline in nonagenarians and centenarians: a new paradigm?

Brain aging is characterized by the formation of neurofibrillary tangles (NFT) and senile plaques (SP) in both cognitively intact individuals and patients with Alzheimer's disease (AD). The ubiquitous presence of these lesions and the steady increase of the prevalence of dementia up to 85 years have strongly supported a continuum between normal brain aging and AD. In this context, the study of nonagenarians and centenarians could provide key informations about the characteristics of extreme aging. We provide here a detailed review of currently available neuropathological data in very old individuals and critically discuss the patterns of NFT, SP and neuronal loss distribution as a function of age. In younger cohorts, NFTs are usually restricted to hippocampal formation, whereas clinical signs of dementia appear when temporal neocortex is involved. SPs would not be a specific marker of cognitive impairment as no correlation was found between their quantitative distribution and AD severity. The low rate of AD lesions even in severe AD as well as the weakness of clinicopathological correlations reported in the oldest-old indicate that AD pathology is not a mandatory phenomenon of increasing chronological age. Our recent stereological observations of hippocampal microvasculature in oldest-old cases challenge the traditional lesional model by revealing that mean capillary diameters is an important structural determinant of cognition in this age group.

Viral risk factor for seizures: Pathobiology of dynorphin in herpes simplex viral (HSV-1) seizures in an animal model

Up to 89% of patients with herpes simplex virus type-1 (HSV-1) encephalitis can have seizures. Possibly, viruses are environmental triggers for seizures in genetically vulnerable individuals. Inherited dynorphin promoter polymorphisms are associated with temporal lobe epilepsy and febrile seizures in man. In animals, the dynorphin system in the hippocampus regulates excitability. The hypothesis that reduced dynorphin expression in dentate gyrus of hippocampus due to HSV-1 infection leads to epileptic responses was tested in a rat model of HSV-1 encephalitis using EEG recording, histopathological and neuropharmacologic probes. HSV-1 infection causes loss of dynorphin A-like immunoreactivity in hippocampus, an effect independent of direct viral interference and cell loss. A kappa opioid receptor agonist U50488 effectively blocks ictal activity, linking absence of dynorphin to propensity for epileptic activity. These findings show a vulnerability of hippocampal dynorphin during infection, suggesting a neurochemical basis for seizures that may be generalizable to other encephalitic viruses.

Stereologic Analysis of Microvascular Morphology in the Elderly

The presence of microvascular changes has been documented both in brain aging and Alzheimer disease (AD), although the relationship between the morphometry of brain capillaries and cognitive impairment is still unknown. We performed an analysis of capillary morphometric parameters and AD-related pathology in 19 elderly individuals with variable degrees of cognitive decline. Cognitive status was assessed prospectively using the Clinical Dementia Rating (CDR) scale. Total capillary lengths and numbers as well as mean length-weighted diameter, total neurofibrillary tangle (NFT) and neuron numbers, and amyloid volume were estimated in entorhinal cortex and the CA1 field. Total capillary numbers and mean diameters explained almost 40% of the neuron number variability in both the CA1 and entorhinal cortex. Total capillary length and numbers in the CA1 and entorhinal cortex did not predict cognitive status. Mean capillary diameters in the CA1 and entorhinal cortex were significantly related to CDR scores, explaining 18.5% and 31.1% of the cognitive variability, respectively. This relationship persisted after controlling for NFT and neuron numbers in multivariate regression models. Consistent with the growing interest about microvascular pathology in brain aging, the present data indicate that changes in capillary morphometric parameters may represent independent predictors of AD-related neuronal depletion and cognitive decline.