Cortical Extracellular Space Research Articles

Reply: the early pathological process in sporadic Alzheimer’s disease

[7] was designated NFT stage I [8]. Gallyas-negative AT8immunopositive pretangles, described by Bancher et al. [5] and Braak et al. [6], were included in a revised staging protocol for AD [13], but subcortical and cortical “pretangle stages” (a–c, 1a, 1b) as such have been proposed only recently [10, 11, 14]. The LC is not routinely examined at autopsy for the presence of aggregated tau or other proteinopathies in children or young and middle-aged persons. We performed such a study on 42 cases under the age of 30 using AT8 immunohistochemistry and found tau aggregates in LC neurons of 38/42 (90 %) individuals [10]. The tau pathology was located only in dorsal portions of the LC that contain cortically projecting neurons [27, 43]. 41 out of 42 (98 %) cases lacked cortical Aβ deposition [10]. In a larger autopsy-based study, elobeid et al. [23] reported AT8-immunopositive tau in the LC of 25/83 (30 %) young and middle-aged cases, all without concomitant cortical Aβ deposits and all without aggregated tau in the transentorhinal region. If, as Mann and Hardy [41] speculate, the LC lesions in some of the young subjects were driven by acute lethal head injury [10], we also should have encountered at least some Aβ deposition in the brains of these individuals, inasmuch as head trauma studies performed in humans have reported the presence of transient Aβ deposits [26, 54]. Yet, this was not the case. performance of 3r and 4r immunohistochemistry can allay (or confirm) the reservations expressed by Mann and Hardy [41] regarding the absence of evidence for the different isoforms of phospho-tau in such cases. However, the presence of AT8-immunopositive tau aggregates in the LC of both relatively young cohorts makes it unlikely that all or most of the lesions seen there represent prodromal (“incidental”) pathology associated with rare non-AD tauopathies, such as corticobasal degeneration (CBD) or We are inclined to think that the riddle of the chicken or the egg (i.e., the chicken egg or simply an egg?) is too problematic to help illustrate the problem of tau and amyloid-β (Aβ). However, one can summarize our respective viewpoints in the form of “either/or” propositions: Either Aβ is present in the extracellular space at cortical predilection sites and, from there, causes tau to aggregate within coeruleus neurons, as postulated by Mann and Hardy [41]— the authors do not mention how extracellular cortical Aβ reaches the locus coeruleus (LC) to influence nerve cells there (e.g., by means of retrograde axonal transport)—“the undiscerning ‘locus chicken’ eagerly pecks at” the “bad egg (Aβ deposition).” Or involved projection cells (i.e., nerve cells containing aggregated tau) in the LC and in other nonthalamic nuclei with diffuse cortical projections [10, 29, 31, 50] cause via anterograde axonal transport the release of Aβ into the cortical extracellular space [46], where it can aggregate at local diffusion zones into diffuse amyloid plaques, as we have recently postulated [12]. In our view, the pathological process underlying sporadic Alzheimer’s disease (AD) develops over the course of a lifetime [11, 14]. The original staging protocol was based on the topographical distribution patterns of (1) Gallyasstained neurofibrillary changes (tangles, neuropil threads, dystrophic neurites of neuritic plaques) across six stages (NFT I–VI) and (2) Campbell–switzer-stained Aβ plaque deposition (stages A–C) in the cerebral cortex [8]. The earliest stage of cortical neurofibrillary pathology in the superficial entorhinal layer pre-α of the transentorhinal region

Boosting slow oscillations during sleep potentiates memory

There is compelling evidence that sleep contributes to the long-term consolidation of new memories. This function of sleep has been linked to slow (<1 Hz) potential oscillations, which predominantly arise from the prefrontal neocortex and characterize slow wave sleep. However, oscillations in brain potentials are commonly considered to be mere epiphenomena that reflect synchronized activity arising from neuronal networks, which links the membrane and synaptic processes of these neurons in time. Whether brain potentials and their extracellular equivalent have any physiological meaning per se is unclear, but can easily be investigated by inducing the extracellular oscillating potential fields of interest. Here we show that inducing slow oscillation-like potential fields by transcranial application of oscillating potentials (0.75 Hz) during early nocturnal non-rapid-eye-movement sleep, that is, a period of emerging slow wave sleep, enhances the retention of hippocampus-dependent declarative memories in healthy humans. The slowly oscillating potential stimulation induced an immediate increase in slow wave sleep, endogenous cortical slow oscillations and slow spindle activity in the frontal cortex. Brain stimulation with oscillations at 5 Hz--another frequency band that normally predominates during rapid-eye-movement sleep--decreased slow oscillations and left declarative memory unchanged. Our findings indicate that endogenous slow potential oscillations have a causal role in the sleep-associated consolidation of memory, and that this role is enhanced by field effects in cortical extracellular space.

Apolipoprotein E, smooth muscle cells and the pathogenesis of cerebral amyloid angiopathy: the potential role of impaired cerebrovascular A beta clearance.

Cerebral amyloid angiopathy (CAA) is caused by the deposition of beta-amyloid (A beta) in Alzheimer disease brains. It also occurs isolated, representing a major cause for cerebral hemorrhage in the elderly. The E4 genotype of apolipoprotein E (ApoE) is a risk factor for CAA; however, the molecular mechanism underlying this genetic association is unknown. Various findings suggest that cerebrovascular A beta is derived from the soluble A beta contained in the cortical extracellular space or the cerebrospinal fluid (CSF) that communicates and surrounds small cortical or leptomeningeal vessels. CAA deposits are always intimately associated with smooth muscle cells (SMCs) or SMC-derived pericytes. As we have previously reported, SMCs internalize A beta in vitro via a lipoprotein pathway involving ApoE and the low-density lipoprotein receptor family. Internalized A beta is subsequently located to lysosomes, suggesting its intracellular degradation. We show that A beta is internalized via multiple pathways, because class A and class B scavenger receptors are also colocalized to A beta-containing endosomes in SMCs, and A beta uptake is inhibited by various scavenger receptor antagonists. It has been recently shown for different cell types that the cellular uptake of ApoE is more efficient for the ApoE3 isoform when compared to ApoE4 and that this isoform-specific difference depends on the presence of heparan sulfate proteoglycan (HSPG). HSPG is produced by SMCs and promotes A beta fibrillogenesis. We propose a pathogenetic model of CAA, in which the ApoE- and HSPG-mediated clearance of CSF-derived A beta peptides by SMCs protects the vascular extracellular matrix against critical A beta concentrations. Impairment of this pathway or its reduced efficiency in carriers of the ApoE4 genotype may increase the risk of developing CAA.

Detection of single amyloid beta-protein aggregates in the cerebrospinal fluid of Alzheimer's patients by fluorescence correlation spectroscopy.

Alzheimer's disease is associated with the intraparenchymal growth of plaque-like amyloid deposits. Amyloid plaques are formed by the progressive deposition and transformation of soluble amyloid beta-protein monomers into insoluble and fibrillar aggregates that contain amyloid beta-protein in a beta-pleated sheet conformation. This process is described as 'seeded polymerization' of the monomers with slow-nucleation and fast-growth kinetics. Soluble amyloid beta-protein monomers are present in the cortical extracellular space and in the cerebrospinal fluid, whereas insoluble aggregates so far can be found only by the examination of brain tissue by biopsy or autopsy. Here we present a biophysical method that uses the principle of seeded polymerization in combination with fluorescence correlation spectroscopy, which allowed us to detect single amyloid beta-peptide aggregates in the cerebrospinal fluid samples from Alzheimer's patients. All of 15 Alzheimer's samples but none of the 19 age-matched control samples produced large peaks with fluorescence correlation spectroscopy indicating the rapid aggregation of the fluorescent labelled synthetic amyloid beta-protein probe onto the amyloid beta-protein 'seeds' present in the cerebrospinal fluid. Our method could enable easy in vivo detection of the cerebral amyloid beta-protein pathology of Alzheimer's disease and might be of potential value to facilitate its routine diagnosis.

Developmental changes in NMDA-induced cell swelling and its transition to necrosis measured with 1H magnetic resonance imaging, impedance and histology

The vulnerability of the rat brain to intracerebrally injected N-methyl- d-aspartate (NMDA) drastically changes with age. We evaluated the developmental changes in the early and late responses to NMDA using 1H magnetic resonance imaging (MRI), cortical impedance and histology. NMDA, injected in the striatum of rats at postnatal days (P) 4, 7, 10, 14 and 21, induced a significant age-dependent reduction in the apparent diffusion coefficient (ADC) of tissue water in the striatum and the cerebral cortex monitored 1 h later using diffusion-weighted MRI. The reduction in ADC amounted 65% at P4 with lower values thereafter and was about 30% at P21. NMDA similarly induced a reduction in the cortical extracellular space (by 50% at P7 and 10% at P16) as measured with impedance recordings. The progressive decrease in the effect of NMDA with brain development was also indicated by a decrease in the volume of tissue in which the changes in ADC occurred (50 mm 3 at P4 and 8 mm 3 at P21). The diffusion of extracellular tracer molecules Mn 2+ or [ 3]H-( R)-α-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) injected in the striatum and monitored with T 1-weighted MRI and autoradiography respectively showed a similar age dependence with the diffusion volume being twofold larger in P7 than in P21 brain. Thus restriction in diffusion during brain development may contribute to the decrease in NMDA-induced injury with age. The volume of tissue necrosis and gliosis, measured with T 2-weighted MRI and histology 5 days after NMDA injection, was similar to that outlined by the ADC reduction detected soon after the insult at P4, P7 and P21. However, at P10 and P14 only 50% of the tissue showing a hyperintense signal in DW images displayed necrosis and gliosis 5 days later. This study shows that during development the early response to NMDA in terms of cytotoxic cell swelling (indicated both with impedance recordings and diffusion-weighted MRI) decreases with age. In addition, with maturation only part of the brain tissue acutely affected by NMDA does proceed into necrosis and gliosis, indicating an increased capacity of cells in the developing rat brain to survive NMDA-induced cell swelling.

Extracellular release of acetylcholine, noradrenaline and serotonin increases in the cerebral cortex during walking in conscious rats

The effect of walking on the extracellular release of acetylcholine (ACh), noradrenaline (NA) and serotonin (5-HT) in the parietal lobe of the cerebral cortex was examined in conscious rats using the microdialysis technique. Walking at the speed of 2.3 m/min for 5 min produced significant increases in ACh, NA and 5-HT release in the cerebral cortical extracellular space. The increase in ACh release was the most prominent among the transmitters examined. It is suggested that the increased release of ACh in the cerebral cortex may contribute at least partly to the increases in the cerebral cortical blood flow during walking.

Blood-brain barrier permeability and the brain extracellular space in acute cerebral inflammation

The diffusion properties of the brain cortical extracellular space have never been examined in models of inflammation, even though inflammation can cause increased blood-brain barrier permeability. Uptake of intravascular 125I-labelled albumin and the diffusion of the tetramethylammonium ion within the brain extracellular space was measured in an experimental brain abscess to determine the effect of acute inflammation upon blood-brain barrier permeability and diffusion properties of the cortical extracellular space. The blood-brain transfer constant for albumin was increased in the abscess region, indicating that an increase in blood-brain barrier permeability occurred in animals inoculated with a weakly pathogenic strain of Staphylococcus aureus. The volume fraction of the extracellular space, as measured by the diffusion of tetramethylammonium ion, ranged from 0.19 to 0.23 in bacteria inoculated subjects and from 0.21 to 0.22 in controls. The tortuosity of the extracellular space ranged from 1.40 to 1.42 in bacteria inoculated subjects and was 1.39 in controls. These results showed that the volume fraction and tortuosity of the cortical extracellular space were not affected by inflammation even though vascular permeability was increased. This result was supported by the finding that brain water content, measured in the same animals, was increased to a non-significant extent in the bacteria inoculated subjects. These findings lead to the conclusion that acute inflammation induced by a weak pathogen can cause increased blood-brain barrier permeability without a significant change in the diffusion properties of the brain cortical space.

Clearance of brain edema and macromolecules through the cortical extracellular space.

The transit routes of fluid and particulate matter through brain tissue remain unclear. The object of this study was to examine the movement of macromolecules through brain tissue to further clarify the clearance pathways of edema proteins as they migrate toward the cortex. For this purpose, albumin solution (20 microliters rat albumin diluted to 65 mg/ml with mock cerebrospinal fluid (CSF)) was intracerebrally infused into the caudate putamen, and the migration through brain tissue as well as through the ultrastructure of the cortical surfaces was explored using an immunocytochemical technique. The authors observed immunoreactive product on the glial limitans and pial lining as well as in the extracellular space of the cortical neuropil at 24 hours postinfusion, confirming that the protein had reached the cortical surface. To confirm the efflux of macromolecules into the subarachnoid CSF, 71,200 D fluorescein isothiocyanate-dextran (FITC-dextran 71,200) was infused; cortical surfaces of brains removed en bloc as well as coronal sections were macroscopically observed under ultraviolet illumination at 15 minutes and 24 hours postinfusion. It was observed that infused FITC-dextran 71,200 mainly localized in the cortical white matter and caudate putamen of the infusion site at 15 minutes postinfusion and by 24 hours was distributed in the entire cortex of the infused hemisphere. However, the dynamics of lower-molecular-weight substances was completely different. The spatial distribution of FITC-dextran 4400 diverged upward toward the cortical surface and spread more extensively than FITC-dextran 71,200. These observations were consistent with a diffusion process as the spread of the tracer was dependent upon molecular size. These studies provide compelling evidence that a process other than bulk flow was involved in the spread of macromolecules through the extracellular space of the normal cortical neuropil to sink into the subarachnoid space. It was concluded that the CSF pathway via the extracellular space of the cortical neuropil is a primary route for clearance of extracellular edema proteins to the subarachnoid space and that diffusion is involved in this process.

The effect of hyperglycemia on extracellular levels of adenosine in the hypoxic rat cerebral cortex

The levels of adenosine in rat cerebral cortical superfusates were studied in rats prior to, and after, the administration of saline or d-glucose (3 g/kg). Hypoxia-evoked increases in purine release were significantly attenuated after glucose administration. After glucose administration, the falls in arterial blood pressure, which normally accompany systemic hypoxia, were reduced. To ensure that this was not the reason for the decrease in adenosine release, blood was withdrawn from a second group of hyperglycemic rats so that the post-glucose hypoxia was equivalent to the original control. Adenosine release was still significantly attenuated. This decrease in the levels of adenosine, a cerebroprotective agent, in the cerebral cortical extracellular space, may be a contributing factor to the detrimental effects of hyperglycemia on recovery from cerebral ischemia.

Lanthanum and Procion yellow as extracellular markers in the crystalline lens of the rat

When rat lenses are incubated in La(NO 3) 3 or Procion yellow containing salt solutions at 37°C, the markers enter the lens extracellular space as determined by electron microscopy and fluorescence microscopy respectively. Nearly continuous tracks of either marker can be found between each epithelial cell whether the incubations are done by totally immersing the lenses in solution in a single chamber or by isolating the anterior and posterior lens surfaces so that only a small portion of the anterior surface contacts the marker containing solution. Counting of specialized junctions associated with lens epithelial cells in thin sections, shows that less than 20% of these cells have junctions associated with their lateral borders, either near the anterior pole of the lens or near the equator. Junctions between epithelial cells and lens fibers occur more frequently near the equator than anteriorly. It is concluded that the extracellular space between rat lens epithelial cells is not sealed off by zonulae occludentes and that morphologic markers are free to move in the channels between these cells. It is further suggested that the well known physiologic barrier at the anterior side of the lens is not associated directly with the lens epithelium. Procion yellow does not enter the nuclear extracellular space even after eight hours of incubation although it is ubiquitously distributed throughout the cortical extracellular space.

Kinetics of horseradish peroxidase migration through cerebral cortex

This study provides a semiquantitative description of the migration of the extracellular space marker, horseradish peroxidase (HRP), through the cerebral cortex. Following a continuous subarachnoid infusion of HRP, this marker was fixed rapidly within the cortical extracellular space (ECS) by intravascular aldehyde perfusion fixation. Microscopic measurements of the maximum depth of penetration of HRP into the cortex perpendicular to the pial surface were taken from coronal whole brain sections of rabbits that had been exposed to HRP for varying periods of time. The depth of penetration plotted as a function of time of exposure to HRP produced a ‘diffusion profile’. The failure of experimental points to conform to an ideal diffusion curve indicates that simple diffusion alone is an inadequate explanation of the rate of movement of large molecules solutes from the subarachnoid space through the cerebral cortical ECS. The complex pattern of migration velocity of HRP through cortex may be due to alterations of flux of this solute which result from variations in the volume of ECS in different cortical laminae and to the presence of bulk flow of extracellular fluid in the deeper cortical regions.

The contribution of local blood flow to the rapid clearance of potassium from the cortical extracellular space

The transport of potassium to the blood stream following stimulation of the cortex in cats is evaluated by means of a potassium sensitive microelectrode technique. Potassium levels are measured in cortical veins, the sagittal sinus and the extracellular space during and after both pharmacological and electrical stimulation of the cortex. It is concluded that the potassium transport to the blood stream is not a significant factor in the rapid clearance of potassium from the extracellular space following stimulation.

The extracellular space in the developing rat brain: Its variation with changes in osmolarity of the fixative, method of fixation and maturation

Considerable extracellular space was demonstrated in the newborn rat cerebral cortex. The extent of this space could be easily modified by changes in the osmolarity of the glutaraldehyde fixative. With maturation this space became progressively less, generally from the deeper layers outward, and attained adult dimensions by the end of the second week. However, in the white matter, between subpial astrocytes, between ependymal cells and between the cells of the choroid plexus, much narrower spaces were present at all ages. These results compare well with the morphologic findings reported by others following primary glutaraldehyde fixation or freeze-substitution, as well as with the physiologic measurements of the cerebral extracellular spaces in the immature brain also reported by other investigators. Following immersion fixation, the extracellular space was somewhat narrower. The most marked decrease in the extracellular space was noted after immersion fixation in isotonic fixative. All these observations of a relatively large extracellular space in the immature brain contrast with the narrow space seen following primary osmium tetroxide fixation reported by other investigators. It is concluded that the cerebral cortical extracellular space in the immature brain is quite large, but that its true in vivo extent cannot be definitely demonstrated because of the sensitivity of the immature brain to the processes of fixation and embedding.

Changes in cortical extracellular space during spreading depression investigated with the electron microscope.

Changes in cortical extracellular space during spreading depression investigated with the electron microscope.A Van Harreveld, and F I KhattabA Van Harreveld, and F I KhattabPublished Online:01 Jul 1967https://doi.org/10.1152/jn.1967.30.4.911MoreSectionsPDF (4 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Download PDF FiguresReferencesRelatedInformation Cited BySpreading depolarization is not an epiphenomenon but the principal mechanism of the cytotoxic edema in various gray matter structures of the brain during strokeNeuropharmacology, Vol. 134Simulation of spreading depolarization trajectories in cerebral cortex: Correlation of velocity and susceptibility in patients with aneurysmal subarachnoid hemorrhageNeuroImage: Clinical, Vol. 16Spreading Depression, Spreading Depolarizations, and the Cerebral VasculatureCenk Ayata and Martin Lauritzen1 July 2015 | Physiological Reviews, Vol. 95, No. 3Activity-Dependent Layer-Specific Changes in the Extracellular Chloride Concentration and Chloride Driving Force in the Rat HippocampusD. 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High sodium content of cortical astrocytes.

FOR MORE than a decade, an unexplained disparity has existed between the values for extracellular space in the cerebral cortex obtained by different methods. Electron microscopy of thin sections has revealed, with rare exceptions, a space between cells or cell processes measuring only 150 to 200 Angstrom wide. 1-5 More recently, localized obliterations of even this small gap by the formation of so-called tight junctions 6-8 has been described. Calculations based on measurement of the cortical extracellular space in electron micrographs 9 yield a maximum value of 5% for this compartment as a fraction of total cortical volume. Not only has a consistent average value of 200 A for the width of the intercellular gap been measured in electron micrographs of normal cerebral cortex fixed and embedded in various ways, but brain slices incubated in vitro 10,11 show astrocytic swelling without change in the dimensions of the extracellular space. A