COVID-19 Vaccine-Related Thrombosis: A Systematic Review and Exploratory Analysis

Introduction

The World Health Organization declared the coronavirus disease 2019 (COVID-19) pandemic on March 11, 2020. Two vaccine types were developed using two different technologies: viral vectors and mRNA. Thrombosis is one of the most severe and atypical adverse effects of vaccines. This study aimed to analyze published cases of thrombosis after COVID-19 vaccinations to identify patients' features, potential pathophysiological mechanisms, timing of appearance of the adverse events, and other critical issues.

Materials and Methods

We performed a systematic electronic search of scientific articles regarding COVID-19 vaccine-related thrombosis and its complications on the PubMed (MEDLINE) database and through manual searches. We selected 10 out of 50 articles from February 1 to May 5, 2021 and performed a descriptive analysis of the adverse events caused by the mRNA-based Pfizer and Moderna vaccines and the adenovirus-based AstraZeneca vaccine.

Results

In the articles on the Pfizer and Moderna vaccines, the sample consisted of three male patients with age heterogeneity. The time from vaccination to admission was ≤3 days in all cases; all patients presented signs of petechiae/purpura at admission, with a low platelet count. In the studies on the AstraZeneca vaccine, the sample consisted of 58 individuals with a high age heterogeneity and a high female prevalence. Symptoms appeared around the ninth day, and headache was the most common symptom. The platelet count was below the lower limit of the normal range. All patients except one were positive for PF4 antibodies. The cerebral venous sinus was the most affected site. Death was the most prevalent outcome in all studies, except for one study in which most of the patients remained alive.

Discussion

Vaccine-induced thrombotic thrombocytopenia (VITT) is an unknown nosological phenomenon secondary to inoculation with the COVID-19 vaccine. Several hypotheses have been formulated regarding its physiopathological mechanism. Recent studies have assumed a mechanism that is assimilable to heparin-induced thrombocytopenia, with protagonist antibodies against the PF4-polyanion complex. Viral DNA has a negative charge and can bind to PF4, causing VITT. New experimental studies have assumed that thrombosis is related to a soluble adenoviral protein spike variant, originating from splicing events, which cause important endothelial inflammatory events, and binding to endothelial cells expressing ACE2.

Conclusion

Further studies are needed to better identify VITT's pathophysiological mechanisms and genetic, demographic, or clinical predisposition of high-risk patients, to investigate the correlation of VITT with the different vaccine types, and to test the significance of the findings.

Dilation of Brain Veins and Perivascular Infiltration by Glioblastoma Cells in an In Vivo Assay of Early Tumor Angiogenesis

The cranial window (CW) technique provides a simple and low-cost method to assess tumor angiogenesis in the brain. The CW combined with histology using selective markers for tumor and endothelial cells can allow a sensitive monitoring of novel antiangiogenesis therapies in preclinical models. The CW was established in cyclosporine immunosuppressed rats that were stereotactically grafted with fluorescent U87MG glioblastoma cells. One to 3 weeks after grafting, brain vasculature was visualized in vivo and assessed by immunofluorescence microscopy using antibodies against endothelial and smooth-muscle cells and blood brain barrier. At 1-2 weeks after grafting, the CW reliably detected the hypertrophy of venous-venous anastomoses and cortical veins. These structures increased highly significantly their pregrafting diameter. Arterialized veins and hemorrhages were seen by three weeks after grafting. Immunofluorescence microscopy showed significant branching and dilation of microvessels, particularly those surrounded by tumor cells. Mechanistically, these changes lead to loss of vascular resistance, increased venous outflow, and opening of venous-venous anastomoses on the cortical surface. Data from the present study, namely, the hypertrophy of cortical venous-venous anastomoses, microvessel branching, and dilation of the microvessels surrounded by tumor cells, indicate the power of this in vivo model for the sensitive monitoring of early tumor angiogenesis.

Characterization of Endothelial Cilia Distribution During Cerebral-Vascular Development in Zebrafish ( Danio rerio)

Objective- Endothelial cells (ECs) sense and respond to flow-induced mechanical stress, in part, via microtubule-based projections called primary cilia. However, many critical steps during vascular morphogenesis occur independent of flow. The involvement of cilia in regulating these stages of cranial vascular morphogenesis is poorly understood because cilia have not been visualized in primary head vessels. The objective of this study was to investigate involvement of cilia in regulating the early stages of cranial vascular morphogenesis. Approach and Results- Using high-resolution imaging of the Tg(kdrl:mCherry-CAAX) y171 ;(bactin::Arl13b:GFP) zebrafish line, we showed that cilia are enriched in the earliest formed cranial vessels that assemble via vasculogenesis and in angiogenic hindbrain capillaries. Cilia were more prevalent around the boundaries of putative intravascular spaces in primary and angiogenic vessels. Loss of cardiac contractility and blood flow, because of knockdown of cardiac troponin T type 2a ( tnnt2a) expression, did not affect the distribution of cilia in primary head vasculature. In later stages of development, cilia were detected in retinal vasculature, areas of high curvature, vessel bifurcation points, and during vessel anastomosis. Loss of genes crucial for cilia biogenesis ( ift172 and ift81) induced intracerebral hemorrhages in an EC-autonomous manner. Exposure to high shear stress induced premature cilia disassembly in brain ECs and was associated with intracerebral hemorrhages. Conclusions- Our study suggests a functional role for cilia in brain ECs, which is associated with the emergence and remodeling of the primary cranial vasculature. This cilia function is flow-independent, and cilia in ECs are required for cerebral-vascular stability.

Gene expression analysis of nidus of cerebral arteriovenous malformations reveals vascular structures with deficient differentiation and maturation

Objective

Arteriovenous malformations (AVMs) are characterised by tangles of dysplastic blood vessels which shunt blood from arteries to veins with no intervening capillary bed. It is not known at what stage of development and differentiation, AVM vessels became aberrant. To address this, we have analysed the expression of vascular differentiation, vascular maturation and brain capillary specific genes in AVM nidus.

Methodology

We performed immunohistochemistry and western blot analysis of vascular differentiation (HEY2, DLL4, EFNB2, and COUP-TFII), vascular maturation (ENG and KLF2) and brain capillary specific genes (GGTP and GLUT1) on ten surgically excised human brain AVMs and ten normal human brain tissues.

Results

Immunohistochemical analysis revealed that AVM vessels co-express both artery and vein differentiation genes. H-score analysis revealed that there is statistically significant (P < 0.0001) increase in expression of these proteins in AVM vessels compared to control vessels. These findings were further confirmed by western blot analysis and found to be statistically significant (P < 0.0001 and P < 0.001) for all proteins except Hey2. Both immunostaining and western blot analysis revealed that AVM vessels express GGTP and GLUT1, markers specific to brain capillaries. Immunofluorescent staining demonstrated that expression of KLF2, a vascular maturation marker is significantly (P <0.001) decreased in AVM vessels and was further confirmed by western blot analysis (P < 0.001). Immunohistochemical and western blot analysis demonstrated that another vascular maturation protein Endoglin had high expression in AVM vessels compared to control vessels. The results were found to be statistically significant (P < 0.0001).

Summary

Our findings suggest that vascular structures of AVMs co-express markers specific for arteries, veins and capillaries. We conclude that AVM nidus constitutes of aberrant vessels which are not terminally differentiated and inadequately matured.

Reduced deep regional cerebral venous oxygen saturation in hemodialysis patients using quantitative susceptibility mapping

Cerebral venous oxygen saturation (SvO₂) is an important indicator of brain function. There was debate about lower cerebral oxygen metabolism in hemodialysis patients and there were no reports about the changes of deep regional cerebral SvO₂ in hemodialysis patients. In this study, we aim to explore the deep regional cerebral SvO₂ from straight sinus using quantitative susceptibility mapping (QSM) and the correlation with clinical risk factors and neuropsychiatric testing_. 52 hemodialysis patients and 54 age-and gender-matched healthy controls were enrolled. QSM reconstructed from original phase data of 3.0 T susceptibility-weighted imaging was used to measure the susceptibility of straight sinus. The susceptibility was used to calculate the deep regional cerebral SvO₂ and compare with healthy individuals. Correlation analysis was performed to investigate the correlation between deep regional cerebral SvO₂, clinical risk factors and neuropsychiatric testing. The deep regional cerebral SvO₂ of hemodialysis patients (72.5 ± 3.7%) was significantly lower than healthy controls (76.0 ± 2.1%) (P < 0.001). There was no significant difference in the measured volume of interests of straight sinus between hemodialysis patients (250.92 ± 46.65) and healthy controls (249.68 ± 49.68) (P = 0.859). There were no significant correlations between the measured susceptibility and volume of interests in hemodialysis patients (P = 0.204) and healthy controls (P = 0.562), respectively. Hematocrit (r = 0.480, P < 0.001, FDR corrected), hemoglobin (r = 0.440, P < 0.001, FDR corrected), red blood cell (r = 0.446, P = 0.003, FDR corrected), dialysis duration (r = 0.505, P = 0.002, FDR corrected) and parathyroid hormone (r = -0.451, P = 0.007, FDR corrected) were risk factors for decreased deep regional cerebral SvO₂ in patients. The Mini-Mental State Examination (MMSE) scores of hemodialysis patients were significantly lower than healthy controls (P < 0.001). However, the deep regional cerebral SvO₂ did not correlate with MMSE scores (P = 0.630). In summary, the decreased deep regional cerebral SvO₂ occurred in hemodialysis patients and dialysis duration, parathyroid hormone, hematocrit, hemoglobin and red blood cell may be clinical risk factors.

Cerebral Vein Malformations Result from Loss of Twist1 Expression and BMP Signaling from Skull Progenitor Cells and Dura

Dural cerebral veins (CV) are required for cerebrospinal fluid reabsorption and brain homeostasis, but mechanisms that regulate their growth and remodeling are unknown. We report molecular and cellular processes that regulate dural CV development in mammals and describe venous malformations in humans with craniosynostosis and TWIST1 mutations that are recapitulated in mouse models. Surprisingly, Twist1 is dispensable in endothelial cells but required for specification of osteoprogenitor cells that differentiate into preosteoblasts that produce bone morphogenetic proteins (BMPs). Inactivation of Bmp2 and Bmp4 in preosteoblasts and periosteal dura causes skull and CV malformations, similar to humans harboring TWIST1 mutations. Notably, arterial development appears normal, suggesting that morphogens from the skull and dura establish optimal venous networks independent from arterial influences. Collectively, our work establishes a paradigm whereby CV malformations result from primary or secondary loss of paracrine BMP signaling from preosteoblasts and dura, highlighting unique cellular interactions that influence tissue-specific angiogenesis in mammals.

[THE INFLUENCE OF SHORT-TIME CEREBRAL ISCHEMIA ON PIAL VESSELS ADRENOREACTIVITY IN RATS]

Reactivity of pial vessels in response to a brain surface irrigation by norepinephrine solution in rats, subjected to transient global cerebral ischemia (2VO+hypo model), was investigated. Four different groups of rats at 2, 7, 14 or 21 days after ischemia were subjected to microvascular studies using in vivo video microscopy method. The diameter changes of pial arteries and veins in response to norepinephrine were measured. It was established that cerebral ischemia led to increase the number of the constrictions to norepinephrine mainly at the vessels to relating to a group of small pial arteries and arterioles and pial veins of the 3rd generation. Reactivity changes were observed in all time points studied. These changes probably is connected with caused by ischemia the increase in reactivity and sensitivity of pial vessels adrenoceptors. The greatest changes are noted in 14 days after ischemia.

Prevalence and Geographical Variation of Prothrombin G20210A Mutation in Patients with Cerebral Vein Thrombosis: A Systematic Review and Meta-Analysis

Objectives

To compare the prevalence of prothrombin G20210A in patients with objectively confirmed cerebral vein or cortical vein thrombosis against healthy controls, and evaluate geographical variations.

Design

Systematic review and meta-analysis of case control studies.

Methods

We conducted a systematic review of electronic databases including MEDLINE and EMBASE. The main outcome was the prevalence of prothrombin G20210A in patients with objectively confirmed cerebral vein or cortical vein thrombosis; we also analyzed individual country variations in the prevalence. The random-effects model OR was used as the primary outcome measure.

Results

In total 19 studies evaluated 868 cases of cerebral venous thrombosis and 3981 controls. Prothrombin G20210A was found in 103/868 of the patients with cerebral venous thrombosis and 105/3999 of the healthy controls [random effects pooled OR 5.838, 95% CI 3.96 to 8.58; I²17.9%]. The prevalence of prothrombin G20210A was significantly elevated in Italian studies (OR 9.69), in Brazilian studies (OR 7.02), and in German studies (OR 3.77), but not in Iranian studies (OR 0.98).

Conclusion

Prothrombin G20210A is significantly associated with cerebral venous thrombosis when compared to healthy controls, although this association is highly dependent on the country of origin.

Ablation of matrix metalloproteinase-9 gene decreases cerebrovascular permeability and fibrinogen deposition post traumatic brain injury in mice

Traumatic brain injury (TBI) is accompanied with enhanced matrix metalloproteinase-9 (MMP-9) activity and elevated levels of plasma fibrinogen (Fg), which is a known inflammatory agent. Activation of MMP-9 and increase in blood content of Fg (i.e. hyperfibrinogenemia, HFg) both contribute to cerebrovascular disorders leading to blood brain barrier disruption. It is well-known that activation of MMP-9 contributes to vascular permeability. It has been shown that at an elevated level (i.e. HFg) Fg disrupts blood brain barrier. However, mechanisms of their actions during TBI are not known. Mild TBI was induced in wild type (WT, C57BL/6 J) and MMP-9 gene knockout (Mmp9(-/-)) homozygous, mice. Pial venular permeability to fluorescein isothiocyanate-conjugated bovine serum albumin in pericontusional area was observed 14 days after injury. Mice memory was tested with a novel object recognition test. Increased expression of Fg endothelial receptor intercellular adhesion protein-1 and formation of caveolae were associated with enhanced activity of MMP-9 causing an increase in pial venular permeability. As a result, an enhanced deposition of Fg and cellular prion protein (PrP(C)) were found in pericontusional area. These changes were attenuated in Mmp9(-/-) mice and were associated with lesser loss of short-term memory in these mice than in WT mice. Our data suggest that mild TBI-induced increased cerebrovascular permeability enhances deposition of Fg-PrP(C) and loss of memory, which is ameliorated in the absence of MMP-9 activity. Thus, targeting MMP-9 activity and blood level of Fg can be a possible therapeutic remedy to diminish vasculo-neuronal damage after TBI.

Venous oxygenation mapping using velocity-selective excitation and arterial nulling

A new MRI technique to map the oxygenation of venous blood is presented. The method uses velocity-selective excitation and arterial nulling pulses, combined with phase sensitive signal detection to isolate the venous blood signal. T₂ of this signal along with a T₂-Y calibration curve yields estimates of venous oxygenation in situ. Results from phantoms and healthy human subjects under normoxic and hypoxic conditions are shown, and venous saturation levels estimated from both sagittal sinus and gray matter-based regions of interest are compared with the related techniques TRUST and QUIXOTIC. In addition, combined with an additional scan without arterial nulling pulses, the oxygen saturation level on arterial side can also be estimated.

Cerebralcare Granule, a Chinese herb compound preparation, improves cerebral microcirculatory disorder and hippocampal CA1 neuron injury in gerbils after ischemia-reperfusion

AIM OF THE STUDY

Cerebralcare Granule (CG) is a Chinese herb compound preparation that has been used for treatment of cerebrovascular related diseases. However, the effect of post-treatment with CG on ischemia and reperfusion (I/R) induced cerebral injury is so far unclear.

MATERIALS AND METHODS

In present study, cerebral global I/R was induced in Mongolian gerbils by clamping bilateral carotid arteries for 30 min followed by reperfusion for 5 days, and CG (0.4 g/kg or 0.8 g/kg) was administrated 3h after the initiation of reperfusion.

RESULTS

Post-treatment with CG for 5 days attenuated the I/R-induced production of hydrogen peroxide in, leukocyte adhesion to, and albumin leakage from cerebral microvessels, and, meanwhile, protected neuron from death, reduced the number of caspase-3- and Bax-positive cells, and increased Bcl-2-positive cells in hippocampal CA1 region.

CONCLUSION

The results suggest that CG given after initiation of reperfusion is able to ameliorate cerebral microvascular dysfunction and hippocampal CA1 neuron damage caused by I/R.

Developmental changes of leptin receptors in cerebral microvessels: unexpected relation to leptin transport

The adipokine leptin participates not only in the regulation of feeding and obesity in adults but also in neonatal development. It crosses the blood-brain barrier (BBB) by receptor-mediated transport. Leptin concentrations in blood differ between neonates and adults. We determined the developmental changes of leptin receptor subtypes in the cerebral microvessels composing the BBB and examined their expected correlation with leptin transport across the BBB. Total RNA was extracted from enriched cerebral microvessels of mice 1, 7, 14, and 60 d of age for real-time RT-PCR analysis of leptin receptor subtypes. In cerebral microvessels from neonates, ObRa, ObRb, ObRc, and ObRe mRNA were all higher than in adults, but ObRd was not detectable. Hypothalamus showed similar age-related changes except for ObRb, which was higher in adults. The homologous receptor gp130 did not show significant age-related changes in either region. Despite the increase of leptin receptors, leptin permeation across the BBB after iv injection was less in the neonates. In situ brain perfusion with blood-free buffer showed no significant difference in the brain uptake of leptin between neonates and adults, indicating an antagonistic role of leptin-binding proteins in the circulation, especially the soluble receptor ObRe. The results are consistent with our previous finding that ObRe antagonizes leptin endocytosis in cultured endothelia and transport from blood to brain in mice. Overall, the developmental changes observed for leptin receptors unexpectedly failed to correlate with the entry of leptin into brain, and this may indicate different functions of the receptors in neonates and adults.

Increased expression of ephrin A1 in brain arteriovenous malformation: DNA microarray analysis

A number of previous studies have revealed the abnormal expression of various angiogenesis-related genes or products in brain arteriovenous malformation (AVM). To understand the molecular process of this disease, we analyzed gene expression profiles in brain AVM. Using a DNA microarray consisting of 17,086 genes, we identified differentially expressed genes in 5 brain AVMs from their draining veins, vessels retaining basic venous architecture. Not many genes were differentially expressed between the AVM nidus and the draining vein. When we applied an absolute cut-off value for normalized log2 (cy5/cy3 ratio) of 0.4, 19 genes were selected. Genes such as SOX8, TRIM2, FENA1 (ephrin A1), and AQP4 were upregulated, and genes such as I_1000105, KRT18, IGFBP7, EMILIN-2, and KRT14 were downregulated. Genes relating to angiogenesis, such as vascular endothelial growth factor and angiopoietin and other members of the ephrin family, were not differentiated. Among differentially expressed genes detected in this analysis, we focused on ephrin A1, a gene related to embryogenesis and angiogenesis. The expression of ephrin A1 was two and three to nine times higher than that of the draining vein and normal brain, respectively, using real-time reverse transcription-polymerase chain reaction. For the first time, here we report the increased expression of ephrin A1 in brain AVM, which may play an important role in the pathogenesis of AVM.

Matrix metalloproteinase-mediated disruption of tight junction proteins in cerebral vessels is reversed by synthetic matrix metalloproteinase inhibitor in focal ischemia in rat

Matrix metalloproteinases (MMPs) disrupt the blood-brain barrier (BBB) during reperfusion. Occludin and claudins are recently described tight junction proteins (TJPs) that form the BBB. We hypothesized that the opening of the BBB was because of the degradation of TJPs by the MMPs. Spontaneously hypertensive rats had a 90 mins middle cerebral artery occlusion with reperfusion for 2, 3, or 24 h. Matrix metalloproteinases were measured by immunohistochemistry and in situ and gel zymography. Real-time polymerase chain reaction (PCR) measured mRNAs of MMP-2 and -9, furin, membrane-type MMP (MT1-MMP), occludin, and claudin-5. There was opening of the BBB in the piriform cortex after 3 h of reperfusion, and an MMP inhibitor, BB-1101 (30 mg/kg), prevented the opening. At 3 h, in situ zymograms showed gelatinase activity. Zymography and PCR showed greater increases in MMP-2 than in MMP-9. There were increased mRNA and immunohistochemistry for MT1-MMP and furin, which activate MMP-2. Claudin-5 and occludin mRNA expression decreased at 2 h in both hemispheres with fragments of both proteins seen on Western blot by 3 h on the ischemic side; treatment with BB-1101 reversed the degradation of the TJPs. Immunohistochemistry at 3 h showed fragmented TJPs within the endothelial cell clefts. By 24 h, in situ zymography showed gelatinase activity and gel zymography showed elevated levels of MMP-9. Disrupted TJPs previously seen in endothelial cells appeared in the surrounding astrocytes. Our results provide direct evidence that MMPs open the BBB by degrading TJPs and that an MMP inhibitor prevents degradation of the TJPs by MMPs.

Component structure of event-related fMRI responses in the different neurovascular compartments

In most functional magnetic resonance imaging (fMRI) studies, brain activity is localized by observing changes in the blood oxygenation level-dependent (BOLD) signal that are believed to arise from capillaries, venules and veins in and around the active neuronal population. However, the contribution from veins can be relatively far downstream from active neurons, thereby limiting the ability of BOLD imaging methods to precisely pinpoint neural generators. Hemodynamic measures based on apparent diffusion coefficients (ADCs) have recently been used to identify more upstream functional blood flow changes in the capillaries, arterioles and arteries. In particular, we recently showed that, due to the complementary vascular sensitivities of ADC and BOLD signals, the voxels conjointly activated by both measures may identify the capillary networks of the active neuronal areas. In this study, we first used simultaneously acquired ADC and BOLD functional imaging signals to identify brain voxels activated by ADC only, by both ADC and BOLD and by BOLD only, thereby delineating voxels relatively dominated by the arterial, capillary, and draining venous neurovascular compartments, respectively. We then examined the event-related fMRI BOLD responses in each of these delineated neurovascular compartments, hypothesizing that their event-related responses would show different temporal componentries. In the regions activated by both the BOLD and ADC contrasts, but not in the BOLD-only areas, we observed an initial transient signal reduction (an initial dip), consistent with the local production of deoxyhemoglobin by the active neuronal population. In addition, the BOLD-ADC overlap areas and the BOLD-only areas showed a clear poststimulus undershoot, whereas the compartment activated by only ADC did not show this component. These results indicate that using ADC contrast in conjunction with BOLD imaging can help delineate the various neurovascular compartments, improve the localization of active neural populations, and provide insight into the physiological mechanisms underlying the hemodynamic signals.

Multiwavelength optoacoustic system for noninvasive monitoring of cerebral venous oxygenation: a pilot clinical test in the internal jugular vein

A noninvasive, high-resolution optoacoustic technique is a promising alternative to currently used invasive methods of brain oxygenation monitoring. We present the results of our pilot clinical test of this technique in healthy volunteers. Multiwavelength optoacoustic measurements (with nanosecond optical parametric oscillator as a source of radiation) were performed on the area of the neck overlying the internal jugular vein, a deeply located large vein that drains blood from the brain and from extracranial tissues. Optoacoustic signals induced in venous blood were measured with high resolution and signal-to-noise ratio despite the presence of a thick layer of overlying tissue (up to 10 mm). The characteristic parameters of the signal at different wavelengths correlated well with the spectrum of the effective attenuation coefficient of blood.

Collagen XVIII: a novel heparan sulfate proteoglycan associated with vascular amyloid depositions and senile plaques in Alzheimer's disease brains

Heparan sulfate proteoglycans (HSPGs) may play a role in the formation and persistence of senile plaques and neurofibrillary tangles in Alzheimer's disease brains. Recently, it has been demonstrated that the human extracellular matrix-associated molecule collagen XVIII is the first collagen carrying heparan sulfate side-chains. Two variants of collagen XVIII with both different signal peptides and N-terminal domains have been described and are referred to as the short and long form. To investigate the distribution of these variants we performed an immunohistochemical analysis by using specific well-characterized polyclonal antibodies. Anti-long huXVIII, a polyclonal antibody directed against the long variant of collagen XVIII, weakly stained large cortical and leptomeningeal vessels, whereas small cortical vessels remained unstained. Interestingly, all amyloid-laden vessels and classic senile plaques were strongly stained. Anti-all huXVIII, a polyclonal antibody directed against an epitope common to both collagen XVIII variants, intensely stained all types of cerebral blood vessels, cerebral amyloid angiopathy-affected vessels and classic senile plaques. Collagen XVIII expression was absent in neurofibrillary tangles. We conclude that collagen XVIII is a novel heparan sulfate proteoglycan associated with vascular A beta and classic senile plaques and that at least the long form of collagen XVIII accumulates in amyloid-laden vessels and classic senile plaques.

Effects of adenosine receptor antagonists on pial arteriolar dilation during carbon dioxide inhalation

The role of adenosine in the cerebrovascular response to carbon dioxide inhalation was evaluated in two sets of experiments. The pial circulation was recorded by a Laser-Doppler flow probe placed over a closed cranial window in methoxyflurane anesthetized rats. Topical application of the nonselective adenosine receptor antagonist caffeine (1 mM), the selective A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX,1 microM), or the selective A2A receptor antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a]triazin-5-yl amino]ethyl) phenol (ZM 241385, 1 microM) all failed to affect mean arterial blood pressure, basal cerebral blood flow, or the carbon dioxide-evoked hyperemia. Systemically administered caffeine (20 mg/kg) also had no significant effects. However, following the systemic administration of the nonselective nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME, 20 mg/kg), the topical application of both caffeine and ZM 241385 (but not DPCPX) significantly reduced the carbon dioxide-evoked hyperemia. L-NAME (20 mg/kg) administered intravenously, evoked a significant increase in mean arterial blood pressure, a slow progressive decline in cerebral blood flow and, during brief (60-90 s) periods of 7.5% carbon dioxide inhalation, a significant decrease in arterial blood pressure. L-NAME failed to reduce the carbon dioxide-evoked increase in cerebral blood flow as measured by the area under the curve (AUC), although it did reduce the peak flow response. Topically applied L-NAME (1 mM) failed to alter mean arterial blood pressure, basal cerebral blood flow, or the carbon dioxide-evoked increases in cerebral blood flow. In a second series of experiments, we evaluated the ability of 10% carbon dioxide inhalation for 8 min to elicit a release of adenosine from the cerebral cortex. Adenosine levels in the cortical superfusates rose significantly during periods of carbon dioxide inhalation. The data suggest that following the removal of the confounding effects of nitric oxide, which are unlikely to be mediated locally, a significant contribution by adenosine A2A receptor activation to the carbon dioxide-evoked cortical hyperemia was evident.

Oxidation of bilirubin produces compounds that cause prolonged vasospasm of rat cerebral vessels: a contributor to subarachnoid hemorrhage-induced vasospasm

The authors have previously shown that bilirubin-oxidation products (BOXes) are present in CSF of subarachnoid hemorrhage patients with vasospasm, and that BOXes cause vasoconstriction in vitro. This study determined whether BOXes cause vasospasm in vivo. Identical volumes of either lysed blood or standardized amounts of BOXes were injected into the cisterna magna of adult rats. BOX injections caused 6 of 10 rats to die within 10 minutes, whereas 12 of 12 rats survived for 24 hours after blood injections. The mechanism for this significant (P < or = 0.01) increase in mortality was unclear. To directly test whether BOXes produced vasospasm, a cranial window technique was used. Application of 20 microL of 10-micromol/L bilirubin had little effect on the vessels. However, application of BOXes produced marked, dose-dependent small artery and arteriole vasospasm that approached a 90% decrease in diameter by 40 minutes after application in some vessels, and persisted for at least 24 hours. To determine if BOX-mediated vasospasm led to cortical injury, histology and immunocytochemistry were performed on animals that survived for 24 hours. There was a BOX-related stress protein response for HSP25 and HSP32 (HO-1) without evidence of infarction. The finding that the BOXes produce vasospasm of cerebral vessels in vivo, in conjunction with BOXes being found in CSF of vasospasm patients, supports our hypothesis that BOXes contribute to or cause cerebral vasospasm after subarachnoid hemorrhage.

5-HT1B-receptors and vascular reactivity in human isolated blood vessels: assessment of the potential craniovascular selectivity of sumatriptan

AIMS

5-HT1B-receptor mediated vasoconstriction of cranial arteries is a potential mechanism by which 5-HT1B/1D-receptor agonists such as sumatriptan produce their antimigraine effects. 5-HT1B-receptors exist in other blood vessels which may give rise to unwanted vascular effects. Therefore we examined the distribution of 5-HT1B-receptor immunoreactivity (i.r.) in human blood vessels (including target and nontarget vessels) and confirmed the functionality of this receptor protein, by comparing the vasoconstrictor effects of sumatriptan and 5-HT (the endogenous ligand) in isolated vessels.

METHODS

Blood vessels (middle meningeal, pial, temporal and uterine arteries and saphenous veins) were obtained from surgical patients (with consent). Sections of the vessels were prepared for routine immunohistochemical studies using specific 5-HT1B- and 5-HT1D-receptor antibodies. For functional studies, ring segments of the vessels were mounted in organ baths for isometric tension recording.

RESULTS

5-HT1B-receptor i.r. was detected on the smooth muscle layer in middle meningeal, pial and uterine arteries and in saphenous vein and sumatriptan produced contractions in these vessels with potency values (mean pEC50) of 7.00, 7.08, 6.44 and 6.61, respectively, the magnitude of contraction was greatest in the cranial arteries with Emax values of 100.7, 60.3, 23.0 and 35.9%, respectively (expressed as a percentage of the reference agonist 45 mm KCl). 5-HT1B-receptor i.r. was not detected in temporal artery and sumatriptan had no effect in this artery. 5-HT1D-receptor i.r. was not detected in any of the vessels studied.

CONCLUSIONS

Sumatriptan can evoke vasoconstriction in antimigraine target vessels and also in nontarget vessels through an action at 5-HT1B-rcceptors. Sumatriptan acts preferentially to cause contraction in human cranial arteries compared with the other blood vessels we examined and this effect is likely to be shared by other drugs of this class.

Expression of smooth muscle proteins in cavernous and arteriovenous malformations

Cavernous malformations (CVMs) and arteriovenous malformations (AVMs) were immunostained for three smooth muscle cell (SMC)-specific protein markers (smooth muscle alpha-actin, SM1 and SM2). Smooth muscle alpha-actin, a widely used marker of SMCs, is reportedly one of the earliest proteins expressed during differentiation of SMCs and expressed in some kinds of mesoderm-derived cells. In contrast, SM1, an isoform of myosin heavy chain (MHC), is detected only in SMCs. SM2 is another MHC isoform and expressed in the contractile phenotype of SMC. All 14 intraaxial CVMs were positive for smooth muscle alpha-actin, but SM1 was detected in only three of them and SM2 was not found. Their staining pattern resembled that of normal intraparenchymal and pial veins. All 15 cerebral AVMs and 5 out of 6 extraaxial CVMs from the cavernous sinus, orbit and scalp were positive for all three markers, as were the normal cerebral arteries. The venous components of AVMs, as well as the arterial components, expressed SM2, and were different from normal veins in the brain and intraaxial CVMs. This study shows that the histological analysis using the three markers for SMC is useful to differentiate intraaxial CVM from AVM and extraaxial CVMs.

The peptidergic innervation of human coronary and cerebral vessels

It is now well established that in addition to nerves containing classical transmitters, the mammalian vascular system is also supplied by nerve fibre subpopulations containing several vasoactive peptides. The precise function of these peptides (neuropeptide Y, calcitonin gene-related peptide, vasoactive intestinal polypeptide, somatostatin and the tachykinins) is still unknown, however, their widespread occurrence in perivascular nerves indicates that they are likely candidates for a role in the neurogenic regulation of the vascular system. It has been suggested that they may exert a direct vasomotor action via their own receptors and/or modulate the release and action of other vascular transmitters. Recently, several studies have focused on the supply of nerve fibres storing neuropeptides in the coronary and cerebral vasculature of laboratory animals, however, little is known on the distribution of these putative transmitters in human coronary and cerebral vessels. In this paper, the immunocytochemical evidence that several neuropeptides are localized in subpopulations of afferent and efferent nerve fibres supplying the human coronary and cerebral vasculature is focused.

Analysis of endoglin expression in normal brain tissue and in cerebral arteriovenous malformations

BACKGROUND AND PURPOSE

A high incidence of arteriovenous malformations (AVMs) is associated with hereditary hemorrhagic telangiectasia type 1. Endoglin, the gene mutated in this disorder, is expressed at reduced levels on blood vessels of these patients. Since endoglin is a component of the transforming growth factor-beta receptor complex critical for vascular development and homeostasis, we determined its expression in sporadic cerebral AVMs and in normal brain vessels.

METHODS

Twenty cerebral AVMs and 10 normal brain samples were analyzed for endoglin, platelet endothelial cell adhesion molecule 1 (PECAM-1), alpha-smooth muscle cell actin, vimentin, and desmin by immunohistochemistry.

RESULTS

In normal brain, endoglin was found not only on the endothelium of all vessels but also on the adventitial layer of arteries and arterioles. In cerebral AVMs, the numerous vessels present expressed endoglin on both endothelium and adventitia. Arterialized veins, identified by lack of elastin and uneven thickness of smooth muscle cells, revealed endoglin-positive mesenchymal cells in the adventitia and perivascular connective tissue. These cells were fibroblasts since they expressed vimentin but not actin and/or desmin.

CONCLUSIONS

This is the first report of endoglin expression on adventitia of normal brain arteries and on arterialized veins in cerebral AVMs. Increasing numbers of endoglin-positive endothelial and adventitial cells were seen in sporadic cerebral AVMs, but endoglin density was normal. Thus, it is not involved in the generation of these lesions. However, the presence of endoglin on fibroblasts in the perivascular stroma suggests an active role for this protein in vascular remodeling in response to increased blood flow and shear stress.

Measurement of arterial, venous, and interstitial pO2 during acute hypoxia in rat brain using a time-resolved luminescence-based oxygen sensor

This is the first publication using a fiber optic "optode" and a luminescence based pO2 detection method for assessing neural tissue oxygenation. The system was used to simultaneously monitor pO2 in tissue (PtO2) and venous blood (PvO2) during normoxia, hyperoxia and hypoxia. PaO2 was varied by changing inspired oxygen (FiO2) from 0.3 to 0.13. Tissue and arterial pO2 were measured in 5 rats while the simultaneous venous measurements were undertaken in 3 animals. The PtO2 was 29 +/- 10 at an arterial pO2 of 116 +/- 10 (mean +/- SE, n = 5). The PvO2 was consistently higher than PtO2 although PvO2 approached PtO2 as PaO2 declined to 50 mmHg and was lower than tissue pO2 during the complete hypoxic period in one animal. These data indicate that brain venous pO2 is not representative of brain tissue pO2 and support published models predicting that in brain PvO2 is higher than PtO2.

The effects of propranolol on heterogeneity of rat cerebral small vein oxygen saturation

beta-Adrenergic receptors are involved in altering cerebral metabolism and blood flow. This study was performed to determine whether propranolol would alter the microregional O2 balance in the brain. Rats were anesthetized with 1.4% isoflurane. Isotonic sodium chloride solution (control group), propranolol 2 mg/kg (low propranolol group) or propranolol 20 mg/kg (high propranolol group) was administered IV to the rats. Twenty minutes later, regional cerebral blood flow (rCBF) was measured using the 14C-iodoantipyrine autoradiographic technique. Small (diameter <70 microm) arterial and venous oxygen saturation (SaO2 and SvO2, respectively) was determined using microspectrophotometry in the alternate slices of the tissue sections used to measure rCBF. In both the low and high propranolol groups, average cortical rCBF was 35% lower than that in the control group. The average O2 consumption of the cortex of the propranolol groups was significantly lower than control (low propranolol: -41%, high propranolol: -49%). In all groups, SaO2 was almost identi-cal. The heterogeneity of the microregional SvO2 expressed as the coefficient of variation (CV = 100 x sD/mean) was significantly lower in the propranolol groups (low propranolol: 8.0+/-2.3, high propranolol: 7.3 +/- 2.9) than in the control group (13.4 +/- 3.5). The proportion of cortical veins with Svo2 <55% was significantly smaller in the low and high propranolol groups (4 of 60 and 3 of 60, respectively) than that in the control group (15 of 60). In the other brain regions, the data followed a similar pattern. Our data demonstrated that propranolol is effective in decreasing O2 consumption, improving microregional O2 balance, and reducing its heterogeneity in the brain.

IMPLICATIONS

Our data suggest that the linkage of O2 supply and consumption is not tightly coupled under isoflurane anesthesia. beta-Adrenergic blockers may tighten this linkage and reduce the number of low O2-saturated microregions.

Muscarinic acetylcholine receptors in the hippocampus, neocortex and amygdala: a review of immunocytochemical localization in relation to learning and memory

Immunocytochemical mapping studies employing the extensively used monoclonal anti-muscarinic acetylcholine receptor (mAChR) antibody M35 are reviewed. We focus on three neuronal muscarinic cholinoceptive substrates, which are target regions of the cholinergic basal forebrain system intimately involved in cognitive functions: the hippocampus; neocortex; and amygdala. The distribution and neurochemistry of mAChR-immunoreactive cells as well as behaviorally induced alterations in mAChR-immunoreactivity (ir) are described in detail. M35+ neurons are viewed as cells actively engaged in neuronal functions in which the cholinergic system is typically involved. Phosphorylation and subsequent internalization of muscarinic receptors determine the immunocytochemical outcome, and hence M35 as a tool to visualize muscarinic receptors is less suitable for detection of the entire pool of mAChRs in the central nervous system (CNS). Instead, M35 is sensitive to and capable of detecting alterations in the physiological condition of muscarinic receptors. Therefore, M35 is an excellent tool to localize alterations in cellular cholinoceptivity in the CNS. M35-ir is not only determined by acetylcholine (ACh), but by any substance that changes the phosphorylation/internalization state of the mAChR. An important consequence of this proposition is that other neurotransmitters than ACh (especially glutamate) can regulate M35-ir and the cholinoceptive state of a neuron, and hence the functional properties of a neuron. One of the primary objectives of this review is to provide a synthesis of our data and literature data on mAChR-ir. We propose a hypothesis for the role of muscarinic receptors in learning and memory in terms of modulation between learning and recall states of brain areas at the postsynaptic level as studied by way of immunocytochemistry employing the monoclonal antibody M35.

Arachidonic acid increases cerebral microvascular permeability by free radicals in single pial microvessels of the anaesthetized rat

1. We have investigated the permeability-increasing effect of arachidonic acid on pial venular capillaries in vivo using the single microvessel occlusion technique. 2. Permeability to Lucifer Yellow dye (476 Da) increased dose dependently when arachidonic acid was applied focally to the abluminal surface of the vessels. This was completely reversible at all but the highest dose. The permeability increase was 1.65 x 10(-6) +/- 0.247 x 10(-6) cm s-1 (mean +/- S.E.M.) at 0.25 mM, 3.53 x 10(-6) +/- 0.872 x 10(-6) cm s-1 at 0.5 mM, 12.61 x 10(-6) +/- 3.44 x 10(-6) cm s-1 at 1 mM and 18.46 x 10(-6) +/- 5.90 x 10(-6) cm s-1 at 2 mM arachidonic acid. There was a similar reversible dose-dependent permeability increase to eicosapentaenoic acid. 3. These permeability increases could be prevented by co-application of a mixture of the antioxidants superoxide dismutase and catalase (30 and 100 U ml-1), or by the iron chelator desferrioxamine (100 microM). 4. The permeability increases were also prevented by the cyclooxygenase and 5-lipoxygenase blockers indomethacin (100 microM) and nordihydroguariaretic acid (100 microM), respectively, when applied together, but not singly. 5. It was concluded that the permeability response to arachidonic acid depends on the formation of free radicals and subsequent lipid peroxidation.

Nicotine induces leukocyte rolling and adhesion in the cerebral microcirculation of the mouse

Nicotine and several related metabolites were examined for their ability to induce leukocyte rolling and adhesion in the cerebral microcirculation of the mouse. A cranial window was surgically prepared for the visualization of the pial microcirculation using an intra-vital microscopy imaging system. Using this technique rhodamine-labeled leukocytes could be visualized and video-recorded as they traveled within the microvessels, and the quantitation of their rolling and adhesion along the pial venule walls was assessed during an off-line video playback analysis. Nicotine was found to produce significant dose-related increases in leukocyte rolling and adhesion. Cotinine, a major nicotine metabolite, did not induce the same degree of leukocyte rolling and adhesion. Mecamylamine, a nicotine antagonist, was found to inhibit the nicotine-induced leukocyte rolling and adhesion. Anti-P-selectin antibody blocked nicotine-induced leukocyte rolling, while anti-CD18 antibody effectively inhibited leukocyte adhesion, but not rolling in similar experiments. Nicotine-induced leukocyte rolling and adhesion were also inhibited by superoxide dismutase and catalase. These data suggest that nicotine, the principle pharmacological agent in cigarette smoke and related tobacco products, acts via a ganglionic-type nicotinic receptor to enhance leukocyte rolling via P-selectin and reactive oxygen radical-dependent mechanisms in cerebral microcirculation of the mouse.

The brain uses mostly dissolved oxygen during profoundly hypothermic cardiopulmonary bypass

BACKGROUND

During profoundly hypothermic cardiopulmonary bypass, cerebral venous oxygen saturation increases (eg, to 98% at 15 degrees C). We reanalyzed results of clinical studies to learn why.

METHODS

One hundred sixty-eight cerebral oxygen transport measurements were available from 96 infants and children undergoing profoundly hypothermic cardiopulmonary bypass during repair of congenital heart defects.

RESULTS

Dissolved oxygen accounted for 2% to 17% of arterial oxygen content, depending on the arterial oxygen partial pressure and hemoglobin concentration. The fraction of the cerebral metabolic rate for oxygen obtained from dissolved oxygen depended on pump flow, temperature, hemoglobin concentration, and arterial oxygen partial pressure (all p < 10(-3)). For "full-flow" cardiopulmonary bypass, temperatures less than 18 degrees C, and arterial oxygen partial pressure measurements more than 180 mm Hg, the mean +/- standard deviation of the fraction of cerebral metabolic rate for oxygen obtained from dissolved oxygen equaled 77% +/- 19%.

CONCLUSIONS

Dissolved oxygen satisfies most of the brain's oxygen requirements during profound hypothermic cardiopulmonary bypass. This result reflects four properties of profound hypothermic cardiopulmonary bypass: (1) increases in hemoglobin's oxygen affinity due to profound hypothermia (which impairs oxygen transfer from hemoglobin to cerebral tissue), (2) use of hemodilution, (3) use of high arterial oxygen partial pressure, and (4) low cerebral metabolic rate of oxygen.

Role of nitric oxide synthase inhibition in leukocyte-endothelium interaction in the rat pial microvasculature

We investigated the role of nitric oxide (NO) in leukocyte-endothelium interaction, blood-brain barrier (BBB) function and oxygen free-radical production in the rat pial microcirculation. In a closed cranial window preparation (dura removed) over the parietal cortex of pentobarbital-anesthetized Wistar rats, NO synthase (NOS) was inhibited by systemic and/or topical application of N omega-nitro-L-arginine (L-NNA) under physiological conditions and during leukotriene B4 (LTB4) activation. Circulating leukocytes were labeled by intravenous injection of rhodamine 6G. We used a confocal laser scanning microscope (CLSM) and studied leukocyte rolling and sticking in pial veins and arteries before and after NOS inhibition. At the end of the experiments, sodium-fluorescein was injected intravenously to test BBB integrity. Brain cortex oxygen free-radical production was investigated in the cranial window preparation using lucigenin-enhanced chemiluminescence (CL). L-NNA application did not lead to significant changes in leukocyte-endothelium interaction, BBB function, and oxygen free-radical production under physiological conditions [leukocyte-endothelium interaction: control (n = 5), L-NNA systemically (n = 5), L-NNA topically (n = 5): at baseline rollers/100 microns: 0.76 +/- 0.55, 0.64 +/- 0.94, 0.44 +/- 0.55 and stickers/100 microns: 0.90 +/- 0.28, 0.76 +/- 0.24, 0.84 +/- 0.42; at 60 min rollers/100 microns: 1.49 +/- 0.66, 1.21 +/- 0.99, 0.67 +/- 0.66 and stickers/100 microns: 1.04 +/- 0.20, 1.19 +/- 0.23, 1.21 +/- 0.54; oxygen free-radical production (n = 4): CL count before L-NNA application 35 +/- 17 cps, after 1 h of topical superfusion of L-NNA 38 +/- 14 cps; p < 0.05]. In contrast to the results achieved under physiological conditions, a significant further increase of rolling leukocytes and BBB permeability occurred due to NOS inhibition under LTB4-activated conditions [76 +/- 47% significant (p < or = 0.01, n = 7) further increase of rollers/100 microns due to 60 min L-NNA application following the activation period of 120 min LTB4 superfusion]. Our results support a modulatory role for NO in leukocyte-endothelium interaction and BBB permeability in the pial microcirculation when this interaction is increased.

Brain tissue response to CO2 in patients with arteriovenous malformation

We tested whether cerebral arteriovenous malformations (AVM) alter brain tissue oxygen pressure, PO2, carbon dioxide pressure PCO2, and pH before, during, and after hypercapnia. A craniotomy was performed and a sensor inserted into normal brain tissue (control) (n = 7) or into tissue adjacent to an AVM (n = 9). Under baseline conditions, tissue PO2 was 80% lower in AVM compared to control patients, but PCO2 and pH were normal. During a 10 mm Hg increase in PaCO2, tissue PO2 increased only in AVM patients, PCO2 increased in both groups, and pH decreased only in controls. When hypercapnia was reversed, tissue PCO2 decreased below baseline and pH increased in AVM patients. Results suggest that tissue CO2 washout and elevated pH result from increases in blood flow during hypercapnia. This response may be related to symptoms of hyperperfusion during AVM resection.

Norepinephrine attenuates serotonin inhibition of pial venous tone

Serotonin (5-hydroxytryptamine, 5-HT) has been shown to inhibit the rhythmic constrictions, accompanied by an increase in cAMP synthesis, in porcine pial veins. Since porcine pial veins contain predominant postsynaptic alpha 2-adrenoceptors which are coupled to Gi-protein, the possibility that the inhibitory effect of 5-HT is antagonized by norepinephrine was examined pharmacologically, using tissue bath techniques. The results indicated that norepinephrine (0.1-1 microM) attenuated 5-HT-induced inhibition of rhythmic constriction. This effect of norepinephrine was mimicked by clonidine (an alpha 2-adrenoceptor agonist), but not by methoxamine (an alpha 1-adrenoceptor agonist). Furthermore, the effect of norepinephrine was prevented by yohimbine (an alpha 2-adrenoceptor antagonist) and pertussis toxin, but was not prevented by prazosin (an alpha 1-adrenoceptor antagonist). In parallel studies, the basal concentration of cAMP and that induced by 5-HT in the pial veins were inhibited by norepinephrine (0.3 microM). These results are consistent with the previous findings that 5-HT-induced inhibition of rhythmic constriction in the porcine pial veins is associated with an increase in vascular cAMP synthesis and suggest that norepinephrine attenuates 5-HT-induced inhibition of rhythmic constriction in part by negatively coupling to adenylate cyclase via alpha 2-adrenoceptors.

Loss of nitric oxide synthase immunoreactivity in cerebral vasospasm

To determine the distribution of nitric oxide synthase (NOS) in the primate cerebral artery nervi vasorum and to examine the potential role of NOS in cerebral vasospasm after subarachnoid hemorrhage (SAH) in primates, the distribution of NOS immunoreactivity (NOS-IR) in the major cerebral arteries was examined immunohistochemically in cynomolgus monkeys by the use of whole, mounted preparations of the circle of Willis. In four normal monkeys, NOS-IR was localized to the endothelial and adventitial layers of the large cerebral arteries. On the abluminal side, NOS-IR staining was densely concentrated in perivascular nerve fibers (nervi vasorum) of the anterior circulation. Staining was less prominent in the posterior circulation. In six monkeys with vasospasm on Day 7 after placement of preclotted arterial blood to form an SAH around the right middle cerebral artery (MCA) (42% +/- 8.3% decrease of MCA area, mean +/- standard deviation), NOS-IR was virtually absent in nerve fibers around the spastic right MCA but was normal on the contralateral side. In five monkeys in which vasospasm resolved by Day 14 after SAH (36% +/- 14% decrease of right MCA area on Day 7, and 5% +/- 14% decrease on Day 14), NOS-IR was also absent in the right MCA adventitial nerve fibers and remained normal in the left MCA. Adventitial NOS-IR was also normal in cerebral vessels of a sham-operated, nonspastic monkey. These findings provide further evidence that nitric oxide (NO) functions as a neuronal transmitter to mediate vasodilation in primates and indicate a role for adventitial NO in the pathogenesis of cerebral vasospasm after SAH in humans.

Amyloid beta-protein induces the cerebrovascular cellular pathology of Alzheimer's disease and related disorders

One of the hallmark pathologic characteristics of Alzheimer's disease (AD) and related disorders is deposition of the 39-42 amino acid amyloid beta-protein (A beta) in the walls of cerebral blood vessels. The cerebrovascular A beta deposits in these disorders are associated with degenerating smooth muscle cells in the vessel wall which have been implicated in the expression of the amyloid beta-protein precursor (A beta PP) and formation of A beta. We have established primary cultures of human cerebrovascular smooth muscle cells as a model for investigating the cellular pathologic processes involved in the cerebral amyloid angiopathy of AD and related disorders. Recently, we have shown that A beta 1-42, the predominant pathologic cerebrovascular form of A beta, causes extensive cellular degeneration that is accompanied by a striking increase in the levels of cellular A beta PP, potentially amyloidogenic carboxyl terminal A beta PP fragments, and soluble A beta peptide in the cultured human cerebrovascular smooth muscle cells. Together, these studies provide evidence that A beta contributes to the onset and progression of the cerebrovascular pathology associated with AD and related disorders and suggests the mechanism involves a molecular cascade with a novel product-precursor relationship that results in the adverse production and accumulation of A beta.

Relation between cyclic GMP generation and cerebrovascular reactivity: modulation by NPY and alpha-trinositol

It is considered that cyclic guanosine monophosphate (cGMP) plays a pivotal role in mediating the relaxation of vascular and nonvascular smooth muscles. cGMP steady state levels are regulated by guanylyl cyclase, cGMP phosphodiesterases and its flux from cells. The present study examines the possible relation between cerebrovascular vasodilator agents and generation of cGMP in guinea pig cerebral vessels. Acetylcholine, substance P, nitroglycerine and sodium nitroprusside significantly increased the generation of cGMP. The application of acetylcholine, substance P, nitroglycerine and sodium nitroprusside elicited concentration-dependent relaxation of basilar artery segments. Neuropeptide Y increased the generation of cGMP by 2%-46% of control levels (at 10(-7)-10(-6)M of neuropeptide Y; *P < 0.05). In addition, neuropeptide Y (10(-6)M) induced a transient relaxation of the precontracted guinea pig basilar arteries with endothelium. This transient relaxation was blocked by nitro-L-arginine (10(-4)M). alpha-Trinositol does not alter the formation of cGMP nor the neuropeptide Y-induced relaxation. In the presence of alpha-trinositol neuropeptide Y (10(-7)-10(-6)M) did not significantly elevate the production of cGMP as compared with controls. The rise in cGMP induced by acetylcholine, substance P and nitroglycerine was slightly increased by the addition of neuropeptide Y (3 x 10(-7) M). Acetylcholine and substance P induced an endothelium-dependent relaxation of the precontracted guinea pig basilar arteries, while sodium nitroprusside and nitroglycerine induced an endothelium-independent relaxation. Acetylcholine, substance P and nitroglycerine induced concentration-dependent relaxations of basilar artery, respectively. The relaxation elicited by acetylcholine or substance P, but not nitroglycerine, was markedly attenuated by neuropeptide Y (3 x 10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)

A novel 5-HT1-like receptor subtype mediates cAMP synthesis in porcine pial vein

The 5-hydroxytryptamine (5-HT) receptor subtype mediating 5-HT inhibition of spontaneous rhythmic contractions (SRC) in the porcine pial vein was characterized. Results from pharmacological studies using in vitro tissue bath techniques indicated that the inhibitory effects of 5-HT on SRC were qualitatively and quantitatively mimicked by 5-HT1-like agonists 5-methoxytryptamine (5-MT) and 5-carboxamidotryptamine (5-CT). 5-HT-, 5-MT-, and 5-CT-induced inhibitions of SRC were attenuated in a concentration-dependent manner by methysergide, which yielded similar pA2 values against these three agonists, suggesting that 5-HT, 5-MT, and 5-CT act on the same 5-HT1-like receptors. 5-MT inhibition of SRC was not affected by blocking 5-HT2 (with ketanserin and spiperone), 5-HT3 (with MDL-72222 and ICS-205-930), or 5-HT4 (with ICS-205-930) receptors. Neither was 5-MT inhibition of SRC affected by blocking 5-HT1A (with propranolol and spiperone), 5-HT1B (with propranolol), or 5-HT1C (with ketanserin) receptors. Furthermore, 5-HT and 5-MT inhibitions of SRC were enhanced by cilostazol [a selective adenosine 3',5'-cyclic monophosphate (cAMP) phosphodiesterase inhibitor] and were diminished by KT-5720 (a cAMP-dependent protein kinase inhibitor) but were not affected by M&B-22948 [a selective guanosine 3',5'-cyclic monophosphate (cGMP) phosphodiesterase inhibitor] or KT-5823 (a cGMP-dependent protein kinase inhibitor). Biochemical studies further demonstrated that 5-HT inhibition of SRC in porcine pial veins was accompanied by an increase in cAMP, but not cGMP, synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Periventricular venous collagenosis: association with leukoaraiosis

PURPOSE

To investigate the association between an age-related degenerative disease of subependymal veins and leukoaraiosis.

MATERIALS AND METHODS

Brains obtained at autopsy from 22 patients (average age, 73.2 years; range, 25-95 years) were examined with magnetic resonance (MR) imaging and neuropathologic methods with alkaline phosphatase microvascular staining. The degrees of leukoaraiosis shown on MR images and of deep venous occlusion were scored independently and results compared with logistic regression analysis.

RESULTS

Noninflammatory collagenous thickening of venous walls resulting in severe periventricular venous stenosis was found in 13 (65%) of 20 patients over 60 years old. Advanced leukoaraiosis was found in 10 (77%) of these 13 patients. Greater venous disease was associated with more severe leukoaraiosis.

CONCLUSION

Periventricular venous collagenosis, a commonly observed and previously ignored degenerative disease of elderly humans, is strongly associated with leukoaraiosis. Stenosis or occlusion of deep cerebral veins may promote development of leukoaraiosis.

Metabolism-dependent binding of the heterocyclic amine Trp-P-1 in endothelial cells of choroid plexus and in large cerebral veins of cytochrome P450-induced mice

Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole) is known to be metabolized by cytochrome P4501A (P4501A) to reactive intermediates which may bind irreversibly to tissue macromolecules. The irreversible binding of [3H]Trp-P-1 in the brain of NMRI-mice was studied by microautoradiography. There was a selective irreversible binding of radioactivity in endothelial cells following an i.v. or i.p. injection of [3H]Trp-P-1 (100 micrograms/kg or 1.5 mg/kg) in mice treated with the P4501A-inducing agent beta-naphthoflavone (BNF). The binding of radioactivity was highest in capillary loops of the choroid plexus, less marked in large cerebral veins and in arachnoidal veins whereas no binding was observed in cerebral capillaries, arteries, neurons or in other brain cells. In endothelial cells of vehicle-treated control mice injected with [3H]Trp-P-1 no binding of radioactivity was observed. At incubation of brain slices with [3H]Trp-P-1, there was a marked irreversible binding of radioactivity in endothelial cells in the choroid plexus of BNF-treated mice but not in vehicle-treated control mice. The P4501A inhibitor ellipticine abolished the BNF-induced endothelial binding of [3H]Trp-P-1-derived radioactivity in vivo and in vitro. The marked binding of Trp-P-1-derived radioactivity in endothelial cells of the choroid plexus of BNF-treated mice demonstrate that a BNF-responsive enzyme activity, possibly P4501A, may be induced at this site and suggests that a P450-dependent enzyme activity be part of the blood-cerebrospinal fluid barrier regulating the transendothelial passage of compounds.

[Peptide modulation in vascular headache]

This article reviews recent developments in the field of vasoactive peptides in relation to certain types of headache. The equilibrium existing in the brain between contraction and dilatation of blood vessels is controlled by, among other factors, vasoactive peptides. Several of these have been discovered only recently and constitute a rapidly expanding field of research with exciting perspectives. Cranial blood vessels are innervated by sympathetic, parasympathetic and sensory nerve fibres, all of which contain certain vasoactive peptides as co-transmitters. Others, like endothelin, can be produced by the endothelium. There is evidence to suggest that vasoactive peptides of the trigeminovascular system are liberated in response to abnormal constriction of cranial blood vessels and contribute to headache. New drug therapies based on the activity of such substances are now being developed.

A prospective, randomized comparison of cerebral venous oxygen saturation during normothermic and hypothermic cardiopulmonary bypass

Recent reports have described cerebral venous oxygen desaturation during and after rewarming from hypothermic cardiopulmonary bypass. Additionally, patients undergoing normothermic cardiopulmonary bypass may be at higher risk for neurologic injury. This study was designed to determine whether patients undergoing normothermic cardiopulmonary bypass are at increased risk for sustained cerebral desaturation. Fifty-two patients undergoing first-time coronary artery bypass grafting were randomized to receive normothermic (37 degrees C, n = 26) or hypothermic (27 degrees C, n = 26) cardiopulmonary bypass. The anesthetic was standardized and alpha-stat pH management was used. A 4F oximetric catheter was placed in the jugular bulb and cerebral venous and radial arterial blood were sampled. Oxygen partial pressure and saturation were measured at six intervals from cerebral venous blood and from radial arterial blood. Patients receiving normothermic cardiopulmonary bypass had lesser values of oxygen partial pressure and saturation in cerebral venous blood than patients subjected to hypothermia during the first 40 minutes of bypass. Cerebral venous desaturation (oxygen saturation in cerebral venous blood of 50% or less) was observed in 54% of patients in the normothermic group and 12% of patients in the hypothermic group during cardiopulmonary bypass. In the normothermic group, cerebral desaturation occurred primarily in early bypass (14 of 26). The three episodes of desaturation in the hypothermic group occurred during rewarming. During cardiopulmonary bypass, the arteriovenous oxygen content difference was greater in the normothermic group than in that in the hypothermic group, suggesting higher oxygen consumption. Differences in glucose utilization during early cardiopulmonary bypass between the groups was also detected. One patient in the hypothermic group had an embolic stroke and subsequently died. There were no other perioperative strokes or deaths in the study population. The present study demonstrates that patients undergoing normothermic cardiopulmonary bypass are at greater risk for cerebral desaturation. Because it is a global assessment, cerebral venous oxygen saturation may be insensitive to focal ischemic events. It remains to be seen whether these differences in cerebral physiologic states translate into differences in clinical outcome.

Effect of cervical sympathectomy and hypoxia on the heterogeneity of O2 saturation of small cerebrocortical veins

This study evaluated the hypothesis that the sympathetic nervous system was one of the factors increasing the heterogeneity of cerebrocortical venous O2 saturation and this heterogeneity would be greater during hypoxia when cervical sympathetic activity was elevated. Thirty-two male Long-Evans rats were either sham operated (n = 16) or received bilateral cervical sympathectomy (n = 16). One-half of the animals (n = 8) in each treatment were challenged by hypoxia (8% O2 in N2). Cerebral blood flow was determined in five brain regions with [14C]iodoantipyrine. Oxygen saturation was measured microspectrophotometrically in small cerebrocortical arteries and veins. The degree of hypoxic hyperemia was not significantly different between sham-operated and sympathectomized rats. Cortical venous O2 saturations, indicating the balance between O2 supply and consumption, were significantly more heterogeneous in the sham-operated group under both normoxic and hypoxic conditions. The coefficient of variation (CV = 100 x SD/mean) for the normoxic sham-operated animals was 24.9% and the average venous O2 saturation was 53.8%. During hypoxia, venous O2 saturation was significantly decreased to 43.1% without a change in CV (24.5%). Sympathectomy significantly reduced this heterogeneity through a reduction in the number of low O2 saturation veins (CV = 13.2%) under normoxic conditions and the effect was similar under hypoxic conditions (CV = 15.3%). In both sham-operated and sympathectomized groups, hypoxia elicited a significantly higher cerebrocortical O2 consumption. Thus, bilateral cervical sympathectomy improved the O2 supply in selective cerebrocortical regions with high O2 extraction. However, the effect of sympathetic innervation on the heterogeneity of cerebrocortical venous O2 saturation was not potentiated by hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

The identification of adrenergic receptors in human pial membranes

Recent experimental work has suggested that the adrenergic nervous system is important in regulating cerebral blood flow under conditions of hypoxia and systemic arterial hypertension. Although previous investigations have demonstrated the presence of adrenergic neurons adjacent to human cerebral vessels, the nature of adrenergic receptors on human cerebral blood vessels remains poorly defined. The present study was performed to characterize adrenergic reception on membranes prepared from human pia, a rich source of small blood vessels, using radioligand binding techniques. Adrenergic membrane receptors were characterized using the binding of [3H]dihydroalprenolol for the beta subtypes and [3H]prazosin and [3H]yohimbine for the alpha subtypes. Displaceable binding was demonstrated with each agent. A small series of adrenergic agents competed for the [3H]dihydroalprenolol, [3H]yohimbine, and [3H]praz binding sites in a fashion suggesting the presence of alpha 1-, alpha 2-, beta 1-, and beta 2-receptors on the vessels within human pia.

Increased cerebral lactate output to cerebral venous blood after forebrain ischemia in rats

Increased cerebral lactate levels are a well-known aspect of the sequelae of the metabolic derangements that follow cerebral ischemia. A new technique has recently become available to sample cerebral venous blood from the superior sagittal sinus on a long-term basis in conscious rats. We report the applicability of this method to assess serial biochemical responses to brain injury. Serum samples were obtained from the superior sagittal sinus, the common carotid artery, and the external jugular vein of nine anesthetized rats before and up to 7 days after 10 minutes of forebrain ischemia was produced by carotid occlusion and hypovolemic hypotension (mean arterial blood pressure 50 +/- 4 mm Hg). The cerebral venous-arterial difference in serum lactate concentration was increased for up to 3 hours after ischemia, while there was no significant change in the difference in serum lactate concentrations in the common carotid artery and the external jugular vein. This indicates an elevated output of lactate from brain tissue to blood, detectable only in the superior sagittal sinus, which underlines the usefulness of the technique. We observed a persistent elevation in brain lactate production after virtually complete recovery from the acute insult.

[The early decrease in the endothelial cells of the cerebral vessels of rats after local irradiation]

Possible causes of diminution of endothelial cells of rat brain vessels immediately after local irradiation have been investigated. It has been shown that the diminution occurs during the first 24 h following irradiation, its value (-15%) being independent of radiation dose within a wide range (from 5 to 100 Gy), and the cellularity is not restored during the subsequent two weeks of observation. Interphase death of part of cells distinguished by high radiosensitivity seems to be the most probable reason for the population heterogeneity observed.

The dihydropyridine niguldipine modulates calcium and potassium currents in vascular smooth muscle cells

1. Vascular smooth muscle cells were isolated from the portal vein and from pial vessels of the cow. They were voltage-clamped with a single patch electrode technique (whole cell recording) in order to analyse the effects of niguldipine on ionic membrane currents. Due to adsorption of niguldipine to plastic and glass, the effective concentrations are lower than the nominal concentrations by a factor of about 3. 2. Niguldipine reduced Ca-currents (ICa of the L-type, voltage operated) at nominal concentrations greater than 0.1 microM up to a complete block at 1 microM (50% block at 0.4 microM). Nominal concentrations between 50 and 200 nM facilitated ICa ('Ca-agonistic effect'). The Ca-agonistic effects of niguldipine showed modest use- but strong voltage-dependence. 3. Niguldipine increased the outward currents at nominal concentrations greater than 10 nM. The extra outward currents reversed at -85 mV, the result suggesting that niguldipine had increased potassium currents, IK. Maximal facilitation of IK by niguldipine was about 400% and was obtained at 1 microM, half-maximal facilitation was obtained with a nominal concentration of 20 nM. 4. Both reduction of ICa and facilitation of IK may contribute to vasodilatation by niguldipine. Due to its greater sensitivity, the effects on IK may dominate.

Are muscarinic receptors present in rat pial or intracerebral vessels?

Experiments were performed to determine whether muscarinic receptors were present within rat pial or intracerebral vessels. Localization of muscarinic receptors was determined by autoradiography using [3H]-quinuclidinyl benzilate ([3H]-QNB) as a ligand on brain sections of the frontoparietal and the temporal cortex, the neostriatum and the hippocampus. [3H]-QNB was bound specifically to sections of rat brain in a manner consistent with the labelling of muscarinic receptors. A high density of muscarinic receptors was found primarily in the neostriatum, followed, in descending order, by the cerebral cortex and the hippocampus. However, no specific [3H]-QNB binding was observed at the level of either the pial or intraparenchymal vessels. On the basis of the present data, the existence of muscarinic receptors within rat pial arteries and arterioles, as well as within intracerebral vessels, seems to be highly questionable.