Parenchymal Capillaries Research Articles

Spatiotemporal analysis of blood plasma and blood cell flow fluctuations of cerebral microcirculation in anesthetized rats

Cerebral hemodynamics fluctuates spontaneously over broad frequency ranges. However, its spatiotemporal coherence of flow oscillations in cerebral microcirculation remains incompletely understood. The objective of this study was to characterize the spatiotemporal fluctuations of red blood cells (RBCs) and plasma flow in the rat cerebral microcirculation by simultaneously imaging their dynamic behaviors. Comparisons of changes in cross-section diameters between RBC and plasma flow showed dissociations in penetrating arterioles. The results indicate that vasomotion has the least effect on the lateral movement of circulating RBCs, resulting in variable changes in plasma layer thickness. Parenchymal capillaries exhibited slow fluctuations in RBC velocity (0.1 to 0.3 Hz), regardless of capillary diameter fluctuations (<0.1 Hz). Temporal fluctuations and the velocity of RBCs decreased significantly at divergent capillary bifurcations. The results indicate that a transit of RBCs generates flow resistance in the capillaries and that slow velocity fluctuations of the RBCs are subject to a number of bifurcations. In conclusion, the high-frequency oscillation of the blood flow is filtered at the bifurcation through the capillary networks. Therefore, a number of bifurcations in the cerebral microcirculation may contribute to the power of low-frequency oscillations.

Reduced nitric oxide bioavailability mediates cerebroarterial dysfunction independent of cerebral amyloid angiopathy in a mouse model of Alzheimer’s disease

We show that vasorelaxation of the basilar artery, a large intracranial, extracerebral artery important for cerebral perfusion, is impaired independent of cerebral amyloid angiopathy in a transgenic mouse model of Alzheimer's disease. Interestingly, this dysfunction is specifically endothelium related and is mediated by impaired nitric oxide-cyclic GMP bioavailability.

Different segments of the cerebral vasculature reveal specific endothelial specifications, while tight junction proteins appear equally distributed

The identification of the "paucity of transportation vesicles" and "belt-like" tight junctions (TJs) of endothelial cells as the "morphological correlate of a blood-brain barrier" (BBB) by Reese and Karnovsky (J Cell Biol 34:207-217, 1967) has become textbook knowledge, and countless studies have helped to further define the elements, functions, and dynamics of the BBB. Most work, however, has focused on parenchymal capillaries or less clearly defined "microvessels", while a systematic study on similarities and differences between BBB architecture along the vascular tree within the brain and the meninges has been lacking. Since astrocytes induce endothelial cells to display BBB-typical characteristics by sonic hedgehog and Wnt/β-catenin signaling, we hypothesized that BBB-typical features should be most pronounced in parenchymal capillaries, where endothelium and astrocytes are separated by a basement membrane only. In contrast, this intimate contact is absent in leptomeningeal vessels, thereby potentially affecting BBB architecture. However, here, we show that claudin-3, claudin-5, zonula occludens-1, and occludin as typical constitutes of BBB TJs are comparably distributed in all segments of the parenchymal and the meningeal vascular tree of C57Bl6 mice. While electron microscopy revealed equally occluded interendothelial clefts, arterial vessels of the brain parenchyma but not within the meninges exhibited significantly longer TJ overlaps compared to capillaries. The highest density of endothelial vesicles was found in arterial vessels. Thus, endothelial expression of BBB-typical TJ proteins is not reflected by the distance to surrounding astrocytes, but electron microscopy reveals significant differences of endothelial specification along different segments of the CNS vasculature.

Evaluation of the Production and Absorption of Cerebrospinal Fluid.

The traditional hypothesis of cerebrospinal fluid (CSF) hydrodynamics presumes that CSF is primarily produced in the choroid plexus (CP), then flows from the ventricles into the subarachnoid spaces, and mainly reabsorbed in the arachnoid granulations. This hypothesis is necessary to reconsider in view of recent research and clinical observations. This literature review presents numerous evidence for a new hypothesis of CSF hydrodynamics—(1) A significantly strong relationship exists between the CSF and interstitial fluid (IF), (2) CSF and IF are mainly produced and absorbed in the parenchymal capillaries of the brain and spinal cord. A considerable amount of CSF and IF are also absorbed by the lymphatic system, and (3) CSF movement is not unidirectional flow. It is only local mixing and diffusion.

Acute Humoral Rejection of Renal Allografts in CCR5–/– Recipients

Increasing detection of acute humoral rejection (AHR) of renal allografts has generated the need for appropriate animal models to investigate underlying mechanisms. Murine recipients lacking the chemokine receptor CCR5 reject cardiac allografts with marked C3d deposition in the parenchymal capillaries and high serum donor-reactive antibody titers, features consistent with AHR. The rejection of MHC-mismatched renal allografts from A/J (H-2(a)) donors by B6.CCR5(-/-) (H-2(b)) recipients was investigated. A/J renal allografts survived longer than 100 days in wild-type C57BL/6 recipients with normal blood creatinine levels (28 +/- 7 micromol/L). All CCR5(-/-) recipients rejected renal allografts within 21 days posttransplant (mean 13.3 +/- 4 days) with elevated creatinine (90 +/- 31 micromol/L). The rejected allografts had neutrophil and macrophage margination and diffuse C3d deposition in peritubular capillaries, interstitial hemorrhage and edema, and glomerular fibrin deposition. Circulating donor-reactive antibody titers were 40-fold higher in B6.CCR5(-/-) versus wild-type recipients. Depletion of recipient CD8 T cells did not circumvent rejection of the renal allografts by CCR5-deficient recipients. In contrast, microMT(-/-)/CCR5(-/-) recipients, incapable of producing antibody, did not reject most renal allografts. Collectively, these results indicate the rapid rejection of renal allografts in CCR5(-/-) recipients with many histopathologic features observed during AHR of human renal allografts.

Co‐existence of diffuse multisystem tauopathy and cerebral amyloid angiopathy in an elderly patient with dementia

85 year old man with progressive dementia and history of stroke clinically diagnosed with Alzheimer's disease (AD) came to autopsy. There was diffuse bilateral atrophy of the frontal/temporal lobes and focal cavitations grossly consistent with remote infarcts (confirmed microscopically) were noted in parietal lobe, basal ganglia, and cerebellar hemispheres. Microscopically, numerous tau inclusions including neurofibrillary tangles, globular inclusions, grains and threads with tau immunohistochemical stain were seen. Tau deposits were present throughout the brain with increased numbers in the limbic lobe, basal telencephalon and diencephalon. Leukoencephalopathy was due to atherosclerosis and deposition of amyloid β protein predominantly in the cortical capillaries, with diffuse cortical involvement. Only rare senile plaques were noted with amyloid immunostains. The distribution of tauopathy was unusual and similar to argyrophilic grain disease (AGD), however, the morphology of tau deposits seen are inconsistent with AGD. The presence of the cerebral amyloid angiopathy is unusual due to involvement of parenchymal capillaries outside the primary visual cortex and suggests a genetic component. A low Braak stage and scattered cortical plaques were insufficient for diagnosis of AD. To our knowledge the constellation of findings seen are unique and not previously reported.

Expression and Immunolocalization of Endothelin Peptides and Its Receptors, ETA and ETB, in the Carotid Body Exposed to Chronic Intermittent Hypoxia

Increased levels of endothelin-1 (ET-1) in the carotid body (CB) contribute to the enhancement of chemosensory responses to acute hypoxia in cats exposed to chronic intermittent hypoxia (CIH). However, it is not known if the ET receptor types A (ETA-R) and B (ETB-R) are upregulated. Thus, we studied the expression and localization of ETA-R and ETB-R using Western blot and immunohistochemistry (IHC) in CBs from cats exposed to cyclic hypoxic episodes, repeated during 8 hr for 4 days. In addition, we determined if ET-1 is expressed in the chemoreceptor cells using double immunofluorescence for ET-1 and tyrosine hydroxylase (TH). We found that ET-1 expression was ubiquitous in the blood vessels and CB parenchyma, although double ET-1 and TH-positive chemoreceptor cells were mostly found in the parenchyma. ETAR was expressed in most chemoreceptor cells and blood vessels of the CB vascular pole. ETB-R was expressed in chemoreceptor cells, parenchymal capillaries, and blood vessels of the vascular pole. CIH upregulated ETB-R expression by approximately 2.1 (Western blot) and 1.6-fold (IHC) but did not change ETA-R expression. Present results suggest that ET-1,ETA-R, and ETB-R are involved in the enhanced CB chemosensory responses to acute hypoxia induced by CIH.

Ultrastructural study of the microvasculature in the cerebral bed adjacent to arteriovenous malformation nidus: a proof against endovascular embolization

Background: The pathology of cerebral arteriovenous malformations (AVMs) is still a matter of considerable debate. Endovascular embolization as a treatment modality for AVMs is not yet well established. Methods: The study was conducted on seven AVM cases that had been operated upon without preoperative endovascular embolization, three cases that had preoperative endovascular embolization, and two controls. All were examined using transmission electron microscopy. Results: The capillaries of the preoperatively embolized cases showed changes at the level of their lining endothelium and surrounding extracellular matrix. Conclusion: Preoperative endovascular embolization is proven to be harmful to the parenchymal capillaries in the bed of resected AVMs.

Expression and distribution of heme oxygenase-1 and -2 in rat brown adipose tissue: the modulatory role of the noradrenergic system

To investigate whether brown adipose tissue (BAT) expresses the inducible (HO-1) and the constitutive (HO-2) isoform of heme oxygenase, reverse transcriptase-polymerase chain reaction, Western blotting and immunohistochemistry were performed on interscapular BAT (IBAT) from rats acclimated at environmental temperature or exposed to cold. Both HO isoforms were detected in rat IBAT. They were immunolocalized in the cytoplasm and/or nuclei of brown adipocytes, in parenchymal capillaries, arteries and in some veins and nerves. Whereas cold exposure did not affect HO-2 expression, it significantly increased the expression of HO-1, both at mRNA (about 3-fold) and protein (about 2-fold) levels, reflecting the increased expression of HO-1 in the brown adipocytes and endothelial cells of parenchymal capillaries. Western blotting of cytosolic and nuclear protein extracts from cultured differentiated brown adipocytes showed that HO-1 and HO-2 are indeed localized in the cytosol and nuclei of brown adipocytes, and that noradrenaline stimulation significantly increased their amount in cytosol but not in the nuclear fraction.

The role of bradykinin in the etiology of vasogenic brain edema and perilesional brain dysfunction.

The feline infusion model of brain edema was used to evaluate the role of bradykinin in the etiology and pathophysiology of vasogenic brain edema. Bradykinin (3 or 90 ug in 600 microL saline) did not alter normocapnic regional cerebral blood flow (rCBF) nor induce specific changes in either the somatosensory (SEP) or motor (MEP) evoked potentials. The mean increases in ICP (from 4.5 to 16.1 mmHg) and peri-infusion white matter water content (from 69.4 to 79.8 ml/100 g tissue), mean decrease in lumped craniospinal compliance (from 0.040 to 0.014 ml/mmHg) and local histological changes were all similar to those after 600 microL saline infusion. The interstitial bradykinin infusion caused focal blood-brain-barrier (BBB) opening to Evans Blue dye and was chemotaxic for granulocytes. After the infusion there was a global loss of rCBF CO2 reactivity but there was no ischemia at normocapnia. These results show that bradykinin in brain edema fluid, at concentrations greater than those found in neuropathological conditions, can open the BBB of normal cerebral parenchymal capillaries and cause vascular dysregulation. In neuropathological conditions bradykinin may therefore potentiate formation of vasogenic brain edema but does not contribute to perilesional brain dysfunction.

Hydraulic regulation of brain parenchymal volume

A mechanism for the hydraulic regulation of brain parenchymal volume is hypothesized. Ventricular fluid pressure is transmitted to parenchymal capillaries and affects the pressure difference across the capillary wall, thereby influencing the rate of movement of fluid from the capillary lumen to interstitial fluid. The tendency for brain parenchyma to expand results from the resistance encountered by interstitial fluid as it slowly passes through the complex interstices of extracellular space. The tendency for the brain parenchyma to become smaller results, not from compression of tissue by ventricular fluid, but from an inherent elasticity of brain tissue. The parenchymal volume is stable only when the opposing tendencies are balanced. The critical site of action for the hydraulic control of parenchymal volume is the capillary wall, and the fundamental relationship governing this can be expressed mathematically.

Neurochemical coupled actions of transmitters in the microvasculature of the brain

The discovery that monoamine nerves end on the central microvessels of the choroid plexus, pia-arachnoid and parenchyma has prompted an intense investigation as to their physiological and neuropathological roles. The source of the monoamine fibers to the pial vessels and choroid plexus was shown to be the superior cervical ganglion. Ganglionic stimulation causes vasoconstriction or vasodilation of pial vessels, an event depending upon the functional ratio of alpha to beta adrenergic receptors. Moreover, stimulation of the superior cervical ganglion evokes an inhibition of cerebrospinal fluid formation in choroid plexus. The locus coeruleus is the site of adrenergic nerve supply to the parenchymal capillaries and stimulation of this nucleus increases capillary permeability to small molecules and water. Neurotransmitter receptors (adrenergic, histamine, adenosine, dopamine, prostacyclin, prostaglandins and specific amino acids or neuropeptides) have been identified on microvessels and in many instances these transmitter actions are coupled to cyclic AMP synthesis. Moreover, cyclic AMP has been shown to increase the rate of capillary endothelial pinocytosis and produce brain edema. In small vessels containing smooth muscle cells cyclic AMP production improves cerebral blood flow via an initiation of vasodilatory processes. The presence of receptors for serotonin and acetylcholine have likewise been demonstrated to occur on cerebral microvessels. Limited information is available as to the receptor coupled actions of these two transmitters, but cholinergic mechanisms may act to restrict catecholamine-induced formation of cyclic AMP. Altered sensitivity of microvessels to neurotransmitters has been demonstrated following conditions of stroke, hypertension, aging, diabetes and X-irradiation.

Neuropathological features of a lupus-like disorder in autoimmune mice.

Neurological syndromes are prominent in systemic lupus erythematosus, but the neuropathological and mechanisms resulting in neurological dysfunction are unknown. We report a neuropathological study of the central nervous system in female NZB/W F1 mice, an animal model of systemic lupus erythematous. NZB/W mice were studied at 3, 5, 8, 12, and 14 months of age, and 36-month-old female C57B16N/NIA mice were studied as aged controls. A lymphoproliferative process was identified in the central nervous system of 39% of 8- to 12-month-old and all 14-month-old NZB/W mice. Infiltrates of lymphocytes and plasma cells were seen in subarachnoid, choroid plexus interstitial, and Virchow-Robin spaces. Lymphoid cells occasionally infiltrated brain parenchyma or accumulated as nodular masses. Concomitant visceral lymphoid infiltration was noted in 14-month-old mice. Dense deposits were seen ultrastructurally in the basal lamina of brain parenchymal capillaries of 14-month-old NZB/W mice. These dense deposits were similar in appearance to immune complexes described in glomerular basal lamina, and appeared concomitantly with an advanced lupus-like glomerulopathy. Similar deposits were not observed in choroid plexus. The possible relevance of these neuropathological changes to human central nervous system lupus is discussed.

A histochemical and ultrastructural study of serotonin-containing nerves in cerebral blood vessels of the lamprey.

Lamprey, Entosphenus japonicus, cerebral blood vessel autonomic nerve supply was studied with fluorescence and cholinesterase histochemistry and electron microscopy. Nerve fibers emitting a yellow fluorescence characteristic of serotonin (Exc./Em. max.; 380/530 nm) were found on the major cerebral and pial arteries, but not acetylcholinesterase (AChE)-positive ones. Single ganglion cells also emitting a strong yellow fluorescence were seen in the artery adventitia. On rare occasions these cells were observed in pairs. Terminal varicosities of central catecholamine-containing nerves (Exc./Em. max.; 410/475 nm) were observed on parenchymal capillaries, but not central AChE-positive nerve terminals. In ganglion cells, dense cored vesicles (ca. 130 nm in average diameter; DCV) were abundant in the Golgi area, suggesting their formation at this site. Two types of DCV were observed; one with a homogeneous dense core and the other with a granular core. DCV were numerous in axons as well, axons in which many small clear vesicles (40--60 nm in diameter) as well as DCV were occasionally observed. The question of whether the small clear vesicles or the DCV contained serotonin could not be resolved.

A histochemical study on the innervation of the cerebral blood vessels in the carp.

Adrenergic and cholinergic innervation of the cerebral blood vessels were studied in the carp using fluorescence and cholinesterase histochemistry. Most of the major cerebral and pial arteries were densely innervated with both nerves. Moreover, both nerves, being probably of central origin, were observed frequently on the walls of parenchymal arterioles and capillaries in the sections of the inferior lobe but were only rarely found in the other brain sections.

A histochemical study on the innervation of cerebral blood vessels in the bullfrog

Specific histochemical techniques for the demonstration of catecholamine and acetylcholinesterase have been used to study the distribution of adrenergic and cholinergic nerves on the cerebral blood vessels of bullfrog, Rana catesbeiana. The adrenergic nerve meshworks on the cerebral arteries of bullfrog were less dense, had a more elongate appearance along the arterial axis as compared with those of mammals and were rather similar to those of snakes. The nerve plexuses on the cerebral carotid artery and its main branches were somewhat denser than those on the basilar artery. The most characteristic feature of innervation in the bullfrog cerebral vessels was that no acetylcholinesterase-positive fibres were observed on the extraparenchymal arteries, whereas, in all higher vertebrates investigated so far, the cerebral arteries have been found to be dually innervated although differences in the density of innervation of the two nerves may exist. This suggests that the peripheral adrenergic innervation on the cerebral blood vessels appeared earlier than the cholinergic one in the evolution of vertebrates. On the other hand, both adrenergic and acetylcholinesterase-positive fibres were observed in close contact with parenchymal arterioles and capillaries suggesting the possible existence of a dual central innervation. This feature, however, was by no means common. Thus, the central neurons have a significant influence on the cerebral circulation in the bullfrog is somewhat equivocal. Most of the pial and the parenchymal small vessels and the parenchymal capillaries exhibited a heavy acetylcholinesterase activity on the vascular walls. Although the significance of the enzyme is obscure as yet, this has to be considered in relation to the regulatory mechanism of the cerebral circulation.

Transport of 5-hydroxy-3-indoleacetic acid by spinal cord during subarachnoid perfusion

The transport of [ 14C]5-hydroxy-3-indoleacetic acid (5-HIAA) by the spinal cord was investigated with spinal subarachnoid perfusions of 20 rhesus monkeys. For spinal white matter, [ 14C]5-HIAA was found to distribute in a tissue space of 50–55% and to exchange readily between tissue and blood across parenchymal capillaries. The data were analyzed with a model of the spinal cord as a cylinder and a mean capillary transfer half-time of 20 min determined. The spinal cord cleared [ 14C]5-HIAA from 19 μl/min of CSF. Administration of probenecid yielded a somewhat lower mean tracer clearance rate (14 μl/min) but did not alter the capillary exchange half-time or the distribution volume of [ 14C]5-HIAA in the spinal cord. The data suggest that capillaries within spinal white matter transport 5-HIAA by a mechanism which is insensitive to inhibition by probenecid and that lumbar CSF concentrations reflect only a small portion of total 5-HIAA production by the central nervous system.

Effect of angiographic contrast media at the cellular level in the brain: hypertonic vs. chemical action.

EFFECT OF ANGIOGRAPHIC CONTRAST MEDIA AT THE CELLULAR LEVEL IN THE BRAIN: HYPERTONIC VS. CHEMICAL ACTIONROBERT L. WALDRON, II, M.D., RICHARD B. BRIDENBAUGH, M.D. and EDWARD W. DEMPSEY, PH.D.Audio Available | Share

Pial vessels transport of substances from cerebrospinal fluid to blood.

CEREBROSPINAL fluid (CSF) is formed in the choroid plexuses, in the ventricular cavities through ependymal walls1 and in the subarachnoid space2,3. Some authors3,4, consider that subarachnoid fluid production constitutes 40% or more of the total secreted CSF. The formation of this subarachnoid fluid can be attributed to the pial vessels or be considered as a collection of extracellular fluid produced by the parenchymal capillaries, passing to the subarachnoid space through the pial membrane. Endothelial cells of the respective vessels should possess specific transport properties if they produce a fluid which might be of similar composition to that formed by the plexus. Absorption of the fluid and selective transfer of substances from CSF to blood should also be accomplished. The aim of this investigation was to explore which of the two, pial vessels or parenchymal capillaries, was the preferential route.

Junctions between intimately apposed cell membranes in the vertebrate brain.

Certain junctions between ependymal cells, between astrocytes, and between some electrically coupled neurons have heretofore been regarded as tight, pentalaminar occlusions of the intercellular cleft. These junctions are now redefined in terms of their configuration after treatment of brain tissue in uranyl acetate before dehydration. Instead of a median dense lamina, they are bisected by a median gap 20-30 A wide which is continuous with the rest of the interspace. The patency of these "gap junctions" is further demonstrated by the penetration of horseradish peroxidase or lanthanum into the median gap, the latter tracer delineating there a polygonal substructure. However, either tracer can circumvent gap junctions because they are plaque-shaped rather than complete, circumferential belts. Tight junctions, which retain a pentalaminar appearance after uranyl acetate block treatment, are restricted primarily to the endothelium of parenchymal capillaries and the epithelium of the choroid plexus. They form rows of extensive, overlapping occlusions of the interspace and are neither circumvented nor penetrated by peroxidase and lanthanum. These junctions are morphologically distinguishable from the "labile" pentalaminar appositions which appear or disappear according to the preparative method and which do not interfere with the intercellular movement of tracers. Therefore, the interspaces of the brain are generally patent, allowing intercellular movement of colloidal materials. Endothelial and epithelial tight junctions occlude the interspaces between blood and parenchyma or cerebral ventricles, thereby constituting a structural basis for the blood-brain and blood-cerebrospinal fluid barriers.