Pericytes control key neurovascular functions and neuronal phenotype in the adult brain and during brain aging

Pericytes play a key role in the development of cerebral microcirculation. The exact role of pericytes in the neurovascular unit in the adult brain and during brain aging remains, however, elusive. Using adult viable pericyte-deficient mice, we show that pericyte loss leads to brain vascular damage by two parallel pathways: (1) reduction in brain microcirculation causing diminished brain capillary perfusion, cerebral blood flow, and cerebral blood flow responses to brain activation that ultimately mediates chronic perfusion stress and hypoxia, and (2) blood-brain barrier breakdown associated with brain accumulation of serum proteins and several vasculotoxic and/or neurotoxic macromolecules ultimately leading to secondary neuronal degenerative changes. We show that age-dependent vascular damage in pericyte-deficient mice precedes neuronal degenerative changes, learning and memory impairment, and the neuroinflammatory response. Thus, pericytes control key neurovascular functions that are necessary for proper neuronal structure and function, and pericyte loss results in a progressive age-dependent vascular-mediated neurodegeneration.

The trigeminovascular system and migraine: studies characterizing cerebrovascular and neuropeptide changes seen in humans and cats

Both clinical and physiological consideration of migraine suggests that the pathophysiology of the syndrome is intimately linked to the trigeminal innervation of the cranial vessels, the trigeminovascular system. Studies were conducted in cats and humans to examine the interaction of these systems with the effective acute antimigraine drugs dihydroergotamine and sumatriptan. In the animal studies cats were anesthetized and prepared for routine physiological monitoring as well as for blood sampling from the external jugular veins. Cerebral blood flow was monitored continuously using laser Doppler flowmetry and the effect of trigeminal ganglion stimulation on both cerebral blood flow and jugular vein peptide levels determined prior to and after administration of either sumatriptan or dihydroergotamine. Stimulation of the trigeminal ganglion led to a frequency-dependent increase in cerebral blood flow, with a mean maximum of 43 +/- 9% at a stimulus frequency of 20 per second. There was a marked reduction in these responses by some 50% after administration of either sumatriptan or dihydroergotamine. Trigeminal ganglion stimulation at a frequency of 5 per second also led to a release into the cranial circulation of calcitonin gene-related peptide (CGRP), with the level rising from 67 +/- 3 to 82 +/- 5 pmol/liter on the side of stimulation. These increases were also markedly antagonized by both sumatriptan and dihydroergotamine. Human studies were conducted as part of the overall evaluation of sumatriptan for the treatment of acute migraine. In 7 of 8 patients responding to subcutaneous sumatriptan administration, elevated CGRP levels (60 +/- 8 pmol/liter) were normalized, with the headache being relieved (40 +/- 8 pmol/liter).(ABSTRACT TRUNCATED AT 250 WORDS)

Near infrared spectroscopy (NIRS): a new tool to study hemodynamic changes during activation of brain function in human adults

In healthy human adults, cerebral concentrations of oxygenated hemoglobin ([HbO2]) and deoxygenated hemoglobin ([HbR]) were assessed during brain activation using near infrared spectroscopy (NIRS). Measurements were made either in the frontal cortex (n = 10) during performance of cognitive tasks or in the occipital cortex (n = 6) during visual stimulation (flash-light exposure, picture observation). The typical findings during brain activation were an increase in [HbO2] and a decrease in [HbR]. We demonstrate that these findings are not due to alterations in skin blood flow. NIRS is a simple bedside technique for the assessment of hemodynamic alterations accompanying brain activation.

Gender-linked brain injury in experimental stroke

BACKGROUND AND PURPOSE

Premenopausal women are at lower risk than men for stroke, but the comparative vulnerability to tissue injury once a cerebrovascular incident occurs is unknown. We hypothesized that female rats sustain less brain damage than males during experimental focal ischemia and that the gender difference in ischemic outcome can be eliminated by ovariectomy.

METHODS

Age-matched male (M), intact female (F), and ovariectomized female (O; plasma estradiol: 4.1+/-1.6 pg/mL compared with 7.4+/-1.5 in F and 4.0+/-1.1 in M) rats from two different strains, normotensive Wistar and stroke-prone spontaneously hypertensive rats, were subjected to 2 hours of intraluminal middle cerebral artery occlusion, followed by 22 hours of reperfusion. Cerebral blood flow (CBF) was monitored throughout the ischemic period by laser-Doppler flowmetry. Infarction volume in the cerebral cortex (Ctx) and caudoputamen (CP) was determined by 2,3,5-triphenyltetrazolium chloride staining. In a separate cohort of M, F, and O Wistar rats, absolute rates of regional CBF were measured at the end of the ischemic period by quantitative autoradiography using [14C]iodoantipyrine.

RESULTS

F rats of either strain had a smaller infarct size in Ctx and CP and a higher laser-Doppler flow during ischemia compared with respective M and O rats. Mean end-ischemic CBF was higher in F compared with M and O rats in CP, but not in Ctx. Cerebrocortical tissue volume with end-ischemic CBF < 10 mL/100 g/min was smaller in F than M rats, but not different from O rats.

CONCLUSIONS

We conclude that endogenous estrogen improves stroke outcome during vascular occlusion by exerting both neuroprotective and flow-preserving effects.

Enlarged infarcts in endothelial nitric oxide synthase knockout mice are attenuated by nitro-L-arginine

Infarct size and vascular hemodynamics were measured 24 h after middle cerebral artery (MCA) occlusion in mice genetically deficient in the endothelial nitric oxide synthase (eNOS) isoform. eNOS mutant mice developed larger infarcts (21%) than the wild-type strain when assessed 24 h after intraluminal filament occlusion. Moreover, regional CBF values recorded in the MCA territory by laser-Doppler flowmetry were more severely reduced after occlusion and were disproportionately reduced during controlled hemorrhagic hypotension in autoregulation experiments. Unlike the situation in wild-type mice, nitro-L-arginine superfusion (1 mM) dilated pial arterioles of eNOS knockout mice in a closed cranial window preparation. As noted previously, eNOS mutant mice were hypertensive. However, infarct size remained increased despite lowering blood pressure to normotensive levels by hydralazine treatment. Systemic administration of nitro-L-arginine decreased infarct size in eNOS mutant mice (24%) but not in the wild-type strain. This finding complements published data showing that nitro-L-arginine increases infarct size in knockout mice expressing the eNOS but not the neuronal NOS isoform (i.e., neuronal NOS knockout mice). We conclude that NO production within endothelium may protect brain tissue, perhaps by hemodynamic mechanisms, whereas neuronal NO overproduction may lead to neurotoxicity.

Estradiol protects against ischemic injury

Clinical studies demonstrate that estrogen replacement therapy in postmenopausal women may enhance cognitive function and reduce neurodegeneration associated with Alzheimer's disease and stroke. This study assesses whether physiologic levels of estradiol prevent brain injury in an in vivo model of permanent focal ischemia. Sprague-Dawley rats were ovariectomized; they then were implanted, immediately or at the onset of ischemia, with capsules that produced physiologically low or physiologically high 17beta-estradiol levels in serum (10 or 60 pg/mL, respectively). One week after ovariectomy, ischemia was induced. Estradiol pretreatment significantly reduced overall infarct volume compared with oil-pretreated controls (mean+/-SD: oil = 241+/-88; low = 139+/-91; high = 132+/-88 mm3); this protective effect was regionally specific to the cortex, since no protection was observed in the striatum. Baseline and ischemic regional CBF did not differ between oil and estradiol pretreated rats, as measured by laser Doppler flowmetry. Acute estradiol treatment did not protect against ischemic injury. Our finding that estradiol pretreatment reduces injury demonstrates that physiologic levels of estradiol can protect against neurodegeneration.

Diastolic dysfunction in normotensive men with well-controlled type 2 diabetes: importance of maneuvers in echocardiographic screening for preclinical diabetic cardiomyopathy

OBJECTIVE

Because a pseudonormal pattern of ventricular filling has never been considered in studies that reported a prevalence of left ventricular diastolic dysfunction (LVDD) between 20 and 40%, our aim was to more completely evaluate the prevalence of LVDD in subjects with diabetes.

RESEARCH DESIGN AND METHODS

We studied 46 men with type 2 diabetes who were aged 38-67 years; without evidence of diabetic complications, hypertension, coronary artery disease, congestive heart failure, or thyroid or overt renal disease; and with a maximal treadmill exercise test showing no ischemia. LVDD was evaluated by Doppler echocardiography, which included the use of the Valsalva maneuver and pulmonary venous recordings to unmask a pseudonormal pattern of left ventricular filling.

RESULTS

LVDD was found in 28 subjects (60%), of whom 13 (28%) had a pseudonormal pattern of ventricular filling and 15 (32%) had impaired relaxation. Systolic function was normal in all subjects, and there was no correlation between LVDD and indexes of metabolic control.

CONCLUSIONS

LVDD is much more common than previously reported in subjects with well-controlled type 2 diabetes who are free of clinically detectable heart disease. The high prevalence of this phenomenon in this high-risk population suggests that screening for LVDD in type 2 diabetes should include procedures such as the Valsalva maneuver and pulmonary venous recordings to unmask a pseudonormal pattern of ventricular filling.

Evidence of a cerebrovascular postarteriole windkessel with delayed compliance

A pronounced temporal mismatch was observed between the responses of relative cerebral blood volume (rCBV) measured by magnetic resonance imaging and relative cerebral blood flow measured by laser-Doppler flowmetry in rat somatosensory cortex after electrical forepaw stimulation. The increase of relative cerebral blood flow after stimulus onset and decrease after stimulus cessation were accurately described with a single exponential time constant of 2.4 +/- 0.8 seconds. In contrast, rCBV exhibited two distinct and nearly sequential processes after both onset and cessation of stimulation. A rapid change of rCBV (1.5 +/- 0.8 seconds) occurring immediately after onset and cessation was not statistically different from the time constant for relative cerebral blood flow. However, a slow phase of increase (onset) and decrease (cessation) with an exponential time constant of 14 +/- 13 seconds began approximately 8 seconds after the rapid phase of CBV change. A modified windkessel model was developed to describe the temporal evolution of rCBV as a rapid elastic response of capillaries and veins followed by slow venous relaxation of stress. Venous delayed compliance was suggested as the mechanism for the poststimulus undershoot in blood oxygen-sensitive magnetic resonance imaging signal that has been observed in this animal model and in human data.

Anesthesia induces neuronal cell death in the developing rat brain via the intrinsic and extrinsic apoptotic pathways

It was shown recently that exposure of the developing rat brain during the peak of synaptogenesis to commonly used general anesthetics can trigger widespread apoptotic neurodegeneration in many regions of the developing rat brain and persistent learning/memory deficits later on in life. To understand the mechanism by which general anesthetics induce apoptotic neuronal death we studied two common apoptotic pathways--the intrinsic and the extrinsic pathway--at different time points during synaptogenesis. We found that the intrinsic pathway is activated early on during anesthesia exposure (within two hours), as measured by the down-regulation of bcl-x(L), up-regulation of cytochrome c and the activation of caspase-9 in 7-day-old rats (the peak of synaptogenesis), but remains inactivated in 14-day-old rats (the end of synaptogenesis). The extrinsic pathway is activated later on (within six hours of anesthesia exposure), as measured by the up-regulation of Fas protein and the activation of caspase-8 in 7-day-old rats, but remains inactivated in 14-day-old rats. Anesthesia-induced apoptotic neurodegeneration is age dependent with vulnerability closely correlating with the timing of synaptogenesis, i.e. the developing brain is most sensitive at the peak of synaptogenesis (7 days old) and least sensitive at the end of synaptogenesis (14 days old).

Role of nitric oxide in the vascular effects of local warming of the skin in humans

Local warming of skin induces vasodilation by unknown mechanisms. To test whether nitric oxide (NO) is involved, we examined effects of NO synthase (NOS) inhibition with NG-nitro-L-arginine methyl ester (L-NAME) on vasodilation induced by local warming of skin in six subjects. Two adjacent sites on the forearm were instrumented with intradermal microdialysis probes for delivery of L-NAME and sodium nitroprusside. Skin blood flow was monitored by laser-Doppler flowmetry (LDF) at microdialysis sites. Local temperature (Tloc) of the skin at both sites was controlled with special LDF probe holders. Mean arterial pressure (MAP; Finapres) was measured and cutaneous vascular conductance calculated (CVC = LDF/MAP = mV/mmHg). Data collection began with a control period (Tloc at both sites = 34 degrees C). One site was then warmed to 41 degrees C while the second was maintained at 34 degrees C. Local warming increased CVC from 1.44 +/- 0.41 to 4.28 +/- 0.60 mV/mmHg (P < 0.05). Subsequent L-NAME administration reduced CVC to 2.28 +/- 0.47 mV/mmHg (P < 0.05 vs. heating), despite the continued elevation of Tloc. At a Tloc of 34 degrees C, L-NAME reduced CVC from 1.17 +/- 0.23 to 0.75 +/- 0.11 mV/mmHg (P < 0.05). Administration of sodium nitroprusside increased CVC to levels no different from those induced by local warming. Thus NOS inhibition attenuated, and sodium nitroprusside restored, the cutaneous vasodilation induced by elevation of Tloc; therefore, the mechanism of cutaneous vasodilation by local warming requires NOS generation of NO.

Retinal abnormalities in early Alzheimer's disease

PURPOSE

There is evidence suggesting that visual disturbances in patients with Alzheimer's Disease (AD) are due to pathologic changes in the retina and optic nerve, as well as to higher cortical impairment. The purpose of this study was to evaluate retinal hemodynamic parameters and to characterize patterns of retinal nerve fiber layer (RNFL) loss in patients with early AD.

METHODS

Nine patients with mild to moderate probable AD (mean Mini Mental State Examination score 24 of a possible 30 (age 74.3 +/- 3.3 years; mean +/- SD) and eight age-matched control subjects (age, 74.3 +/- 5.8 years) were included in this prospective cross-sectional study. Blood column diameter, blood velocity, and blood flow rate were measured in the major superior temporal retinal vein in each subject by using a laser Doppler instrument. Peripapillary RNFL was measured by optical coherence tomography.

RESULTS

Patients with AD showed a significant narrowing of the venous blood column diameter (131.7 +/- 10.8 microm) compared with control subjects (148.3 +/- 12.7 microm, P = 0.01), and a significantly reduced venous blood flow rate (9.7 +/- 3.1 microL/min) compared with the control subjects (15.9 +/- 3.7 microL/min, P = 0.002). A significant thinning of the RNFL was found in the superior quadrant in patients with AD (92.2 +/- 21.6 microm) compared with control subjects (113.6 +/- 10.7 microm, P = 0.02). There were no significant differences in the inferior, temporal, or nasal RNFL thicknesses between the groups.

CONCLUSIONS

Retinal abnormalities in early AD include a specific pattern of RNFL loss, narrow veins, and decreased retinal blood flow in these veins. The results show that AD produces quantifiable abnormalities in the retina.

Vascular imprints of neuronal activity: relationships between the dynamics of cortical blood flow, oxygenation, and volume changes following sensory stimulation

Modern functional neuroimaging methods, such as positron-emission tomography (PET), optical imaging of intrinsic signals, and functional MRI (fMRI) utilize activity-dependent hemodynamic changes to obtain indirect maps of the evoked electrical activity in the brain. Whereas PET and flow-sensitive MRI map cerebral blood flow (CBF) changes, optical imaging and blood oxygenation level-dependent MRI map areas with changes in the concentration of deoxygenated hemoglobin (HbR). However, the relationship between CBF and HbR during functional activation has never been tested experimentally. Therefore, we investigated this relationship by using imaging spectroscopy and laser-Doppler flowmetry techniques, simultaneously, in the visual cortex of anesthetized cats during sensory stimulation. We found that the earliest microcirculatory change was indeed an increase in HbR, whereas the CBF increase lagged by more than a second after the increase in HbR. The increased HbR was accompanied by a simultaneous increase in total hemoglobin concentration (Hbt), presumably reflecting an early blood volume increase. We found that the CBF changes lagged after Hbt changes by 1 to 2 sec throughout the response. These results support the notion of active neurovascular regulation of blood volume in the capillary bed and the existence of a delayed, passive process of capillary filling.

Rescue of diabetes-related impairment of angiogenesis by intramuscular gene therapy with adeno-VEGF

Diabetes is a major risk factor for coronary and peripheral artery diseases. Although diabetic patients often present with advanced forms of these diseases, it is not known whether the compensatory mechanisms to vascular ischemia are affected in this condition. Accordingly, we sought to determine whether diabetes could: 1) impair the development of new collateral vessel formation in response to tissue ischemia and 2) inhibit cytokine-induced therapeutic neovascularization. Hindlimb ischemia was created by femoral artery ligation in nonobese diabetic mice (NOD mice, n = 20) and in control C57 mice (n = 20). Hindlimb perfusion was evaluated by serial laser Doppler studies after the surgery. In NOD mice, measurement of the Doppler flow ratio between the ischemic and the normal limb indicated that restoration of perfusion in the ischemic hindlimb was significantly impaired. At day 14 after surgery, Doppler flow ratio in the NOD mice was 0.49+/-0.04 versus 0.73+/-0.06 for the C57 mice (P< or =0.005). This impairment in blood flow recovery persisted throughout the duration of the study with Doppler flow ratio values at day 35 of 0.50+/-0.05 versus 0.90+/-0.07 in the NOD and C57 mice, respectively (P< or =0.001). CD31 immunostaining confirmed the laser Doppler data by showing a significant reduction in capillary density in the NOD mice at 35 days after surgery (302+/-4 capillaries/mm2 versus 782+/-78 in C57 mice (P< or =0.005). The reduction in neovascularization in the NOD mice was the result of a lower level of vascular endothelial growth factor (VEGF) in the ischemic tissues, as assessed by Northern blot, Western blot and immunohistochemistry. The central role of VEGF was confirmed by showing that normal levels of neovascularization (compared with C57) could be achieved in NOD mice that had been supplemented for this growth factor via intramuscular injection of an adenoviral vector encoding for VEGF. We conclude that 1) diabetes impairs endogenous neovascularization of ischemic tissues; 2) the impairment in new blood vessel formation results from reduced expression of VEGF; and 3) cytokine supplementation achieved by intramuscular adeno-VEGF gene transfer restores neovascularization in a mouse model of diabetes.

Methodological issues in the assessment of skin microvascular endothelial function in humans

The study of microvascular function can be performed in humans using laser Doppler flowmetry of the skin. This technology lends itself to a wide range of applications for studying the endothelial function of skin blood vessels. We review the advantages and limitations of postocclusive hyperemia, local thermal hyperemia, acetylcholine iontophoresis, flowmotion and association with microdialysis as tools with which to investigate skin microvascular endothelial function in humans. Postocclusive hyperemia, thermal hyperemia and acetylcholine iontophoresis provide integrated indexes of microvascular function rather than specific endothelial markers. However, they are valuable tools and can be used as surrogate endpoints in clinical trials in which the assessment of microvascular function in humans is required.

Cortical blood flow and cerebral perfusion pressure in a new noncraniotomy model of subarachnoid hemorrhage in the rat

BACKGROUND AND PURPOSE

Acute cerebral ischemia after subarachnoid hemorrhage (SAH) is a major cause of morbidity whose precise etiology is unclear. The purpose of this study was to examine the relationships between cerebral perfusion pressure (CPP) and cortical blood flow during SAH using a new experimental model in the rat.

METHODS

CPP (mean arterial pressure minus intracranial pressure), cortical laser-Doppler flowmetry (LDF), and electroencephalogram were continuously recorded during and after SAH in 16 ventilated rats. SAH was produced by advancing an intraluminal suture from the external carotid artery through the internal carotid artery to perforate the vessel near its intracranial bifurcation.

RESULTS

Eight rats (50%) died within 24 hours of SAH. In all rats, blood was widely distributed throughout the basal, convexity, and interhemispheric subarachnoid spaces and throughout the ventricular system. CPP decreased after SAH at an initial rate of 1.1 +/- 0.2 mm Hg/s, reaching its nadir 59 +/- 9 seconds after the onset of SAH. During the same period, LDF fell at a rate of 1.4 +/- 0.3%/s (P = NS vs CPP). After reaching its nadir, CPP rose at a rate of 0.4 +/- 0.01 mm Hg/s, but LDF continued to fall at 0.2 +/- 0.03%/s (P < .05 vs CPP) reaching a nadir of 21.7 +/- 2.5% significantly later than CPP (189.5 +/- 39 s after SAH, P < .05). No correlation was found between peak changes in CPP and LDF. Electroencephalogram activity followed the changes in LDF, reaching nadir values 289 +/- 55 seconds after SAH.

CONCLUSIONS

These findings demonstrate that although reduced CPP causes the initial decrease in cortical blood flow after SAH, secondary reductions occurring after CPP has reached its nadir are caused by other factors such as acute vasoconstriction. This noncraniotomy model of SAH in the rat has several advantages over existing models.

Newly expressed SUR1-regulated NC(Ca-ATP) channel mediates cerebral edema after ischemic stroke

Pathological conditions in the central nervous system, including stroke and trauma, are often exacerbated by cerebral edema. We recently identified a nonselective cation channel, the NC(Ca-ATP) channel, in ischemic astrocytes that is regulated by sulfonylurea receptor 1 (SUR1), is opened by depletion of ATP and, when opened, causes cytotoxic edema. Here, we evaluated involvement of this channel in rodent models of stroke. SUR1 protein and mRNA were newly expressed in ischemic neurons, astrocytes and capillaries. Upregulation of SUR1 was linked to activation of the transcription factor Sp1 and was associated with expression of functional NC(Ca-ATP) but not K(ATP) channels. Block of SUR1 with low-dose glibenclamide reduced cerebral edema, infarct volume and mortality by 50%, with the reduction in infarct volume being associated with cortical sparing. Our findings indicate that the NC(Ca-ATP) channel is crucially involved in development of cerebral edema, and that targeting SUR1 may provide a new therapeutic approach to stroke.

Association between maternal anxiety in pregnancy and increased uterine artery resistance index: cohort based study

OBJECTIVE

To investigate whether maternal anxiety in the third trimester is associated with an increased uterine artery resistance index.

DESIGN

Cohort based study.

SUBJECTS

100 pregnant women, with a mean gestation of 32 weeks.

OUTCOME MEASURES

Self rating Spielberger questionnaire for state anxiety and trait anxiety, and uterine blood flow waveform patterns as assessed by colour Doppler ultrasound.

RESULTS

A significant association was found between uterine artery resistance index and scores for both Spielberger state anxiety and trait anxiety (rs=0.31, P<0.002 and 0.28 P<0.005 respectively). Women with state anxiety scores >40 (n=15) had a higher mean uterine resistance index than those with scores </= 40 (mean difference with mean resistance index 24%, 95% confidence interval 12% to 38%; P<0.0001). Similarly, women with trait anxiety scores >40 (n=32) had a higher mean resistance index than those with scores </= 40, although to a lesser extent. The presence of notches in the waveform pattern produced by uterine artery blood flow was found in 4/15 (27%) women with high state anxiety scores compared with 4/85 (5%) with low anxiety scores (P<0.02).

CONCLUSIONS

This study shows an association between maternal anxiety in pregnancy and increased uterine artery resistance index. It suggests a mechanism by which the psychological state of the mother may affect fetal development, and may explain epidemiological associations between maternal anxiety and low birth weight. The influence of maternal anxiety may be one mechanism by which the intrauterine environment contributes to later disease in offspring.

Neuroprotective effect of granulocyte colony-stimulating factor after focal cerebral ischemia

BACKGROUND AND PURPOSE

The potential neuroprotective effect of the granulocyte colony-stimulating factor (G-CSF) after glutamate-induced excitotoxicity in cell culture and after focal cerebral ischemia in rats was studied. We hypothesized the existence of the G-CSF receptor (G-CSFR) as a main G-CSF effector on neurons, and immunohistochemistry, immunoblotting, and polymerase chain reaction were performed. The G-CSFR-mediated action was studied by activation of signal transducer(s) and activator(s) of transcription-3 (STAT3) in the periphery of the infarction.

METHODS

Neuroprotection of various G-CSF concentrations on glutamate-induced excitotoxicity was studied in cell culture. In vivo, ischemia was induced by use of a suture occlusion model of the middle cerebral artery (90-minute occlusion) in the rat. Thirty minutes after the induction of ischemia, the animals (n=12 per group) received G-CSF at 60 microg/kg body wt IV for 90 minutes or vehicle (saline). Infarct volume was calculated on the basis of 2,3,5-triphenyltetrazolium chloride staining 24 hours after ischemia. Expression of the G-CSFR was studied by immunohistochemistry and verified by reverse transcription-polymerase chain reaction and immunoblotting. Expression of STAT3 was determined by immunohistochemistry.

RESULTS

In cell culture, G-CSF exhibited a significant neuroprotective effect after glutamate-induced excitotoxicity (P<0.05). A G-CSF concentration of 10 ng/mL was maximally effective, resulting in a nearly complete protection. In vivo, G-CSF reduced infarct volume to 47% (132.0+/-112.7 mm3 versus 278.9+/-91.6 mm3 [P<0.05] in the control group). Immunohistochemistry, Western blotting, and reverse transcription-polymerase chain reaction revealed the existence of G-CSFRs in neurons and glial cells. Animals treated with G-CSF significantly upregulated STAT3 in the periphery of the infarction compared with control animals (P<0.05).

CONCLUSIONS

G-CSF achieved a significant neuroprotective effect in cell culture and after intravenous administration after stroke. Increased STAT3 expression in the penumbra of G-CSF-treated rats suggests mediation by G-CSFR.

Physical inactivity rapidly induces insulin resistance and microvascular dysfunction in healthy volunteers

OBJECTIVE

Sedentary lifestyle increases the risk of cardiovascular disease and diabetes. Vascular dysfunction contributes to atherogenesis and has been linked to insulin resistance.

METHODS AND RESULTS

We measured insulin sensitivity by glucose tolerance test and vascular function by ultrasound and venous occlusion plethysmography in 20 healthy subjects (14 men, 6 women) at baseline and during 5 days of bed rest. Bed rest led to a 67% increase in the insulin response to glucose loading (P<0.001) suggesting increased insulin resistance and produced increases in total cholesterol and triglycerides. Bed rest led to decreased reactive hyperemia in the forearm (1317+/-404 to 1112+/-260 mL/min, P=0.01) and the calf (28.5+/-7.0 to 22.2+/-8.7 mL/min/dL, P=0.003) indicating impaired microvascular function. Bed rest decreased brachial artery diameter and increased systolic blood pressure suggesting increased basal arterial tone. There were no changes in circulating inflammatory markers arguing against systemic inflammation as a mechanism for vascular dysfunction in this setting.

CONCLUSIONS

Physical inactivity was associated with the development of insulin resistance, dyslipidemia, increased blood pressure, and impaired microvascular function in healthy volunteers. Our findings may provide insight into the pathogenesis of vascular disease in sedentary individuals and emphasize that even short-term physical inactivity may have adverse metabolic and vascular consequences.

The cutaneous microcirculation

The cutaneous microcirculation is organized as two horizontal plexuses. One is situated 1-1.5 mm below the skin surface and the other is at the dermal-subcutaneous junction. Ascending arterioles and descending venules are paired as they connect the two plexuses. From the upper layer, arterial capillaries rise to form the dermal papillary loops that represent the nutritive component of the skin circulation. There are sphincter-like smooth muscle cells at the point where the ascending arterioles divide to form the arteriolar component of the upper horizontal plexus. At the dermal-subcutaneous junction, there are collecting veins with two cusped valves that are oriented to prevent the retrograde flow of blood. Laser Doppler flowmetry has demonstrated vasomotion of red cell flux localized to the sites of ascending arterioles. The simultaneous recording by laser Doppler flowmetry of red cell flux and the concentration of moving red blood cells from individual sites allows one to construct topographic maps of these two values. These two maps, based on initial studies using correlative skin biopsies, can define 1 mm3 volumes of skin that are predominantly arteriolar in composition, venular in composition, or essentially devoid of all microvascular elements. The electron and light microscopic features that define the microvascular segments, when coupled with that ability of laser Doppler flowmetry to define the predominant microvascular segments under the probe, allow one to study both the mechanisms of normal physiologic states and the pathogenetic mechanisms underlying pathologic skin disorders in which the microvasculature plays a predominant role.

Abnormal coronary vasomotion as a prognostic indicator of cardiovascular events in women: results from the National Heart, Lung, and Blood Institute-Sponsored Women's Ischemia Syndrome Evaluation (WISE)

BACKGROUND

Coronary vascular dysfunction has been linked to atherosclerosis and adverse cardiovascular outcomes in men, but these relationships have not been firmly established in women.

METHODS AND RESULTS

As part of the Women's Ischemia Syndrome Evaluation (WISE) sponsored by the National Heart, Lung, and Blood Institute, 163 women referred for clinically indicated coronary angiography underwent coronary reactivity assessment with quantitative coronary angiography and intracoronary Doppler flow before and after intracoronary administration of acetylcholine, adenosine, and nitroglycerin and were then followed up for clinical outcomes. History of hypertension was present in 61%, dyslipidemia in 54%, diabetes in 26%, and current tobacco use in 21% of women enrolled. Seventy-five percent had no or only mild epicardial coronary artery disease (CAD). Over a median follow-up of 48 months, events occurred in 58 women. On bivariate analysis, women with an event had significantly less change in coronary cross-sectional area (DeltaCSA) in response to acetylcholine (P=0.0006) and nitroglycerin (P=0.04). In addition, women with abnormal coronary dilator response to acetylcholine had less time free from cardiovascular events (P=0.004). In multivariable analysis, after controlling for age, hypertension, diabetes, dyslipidemia, tobacco use, and CAD severity, %DeltaCSA with acetylcholine (P=0.001) independently predicted events. When the outcome was restricted to only death, myocardial infarction, congestive heart failure, and stroke, %DeltaCSA with acetylcholine remained a significant predictor (P=0.006).

CONCLUSIONS

In women in this study, impaired coronary vasomotor response to acetylcholine was independently linked to adverse cardiovascular outcomes regardless of CAD severity.

The role of fluid mechanics in the localization and detection of atherosclerosis

Fluid dynamics research over the past twenty years has contributed immensely to our knowledge of atherosclerosis. The ability to detect localized atherosclerotic plaques using noninvasive ultrasonic methods was advanced significantly by investigations into the nature and occurrence of velocity disturbances created by arterial stenoses, and diagnosis of carotid bifurcation disease using a combination of ultrasonic imaging and Doppler measurement of blood velocity is now quite routine. Since atherosclerotic plaques tend to be localized at sites of branching and artery curvature and since these locations would be expected to harbor complex flow patterns, investigators postulated that fluid dynamics might play an initiating role in atherogenesis. Several fluid dynamic variables were proposed as initiating factors. Investigations were undertaken during the 1980s in which fluid dynamic model experiments with physiologic geometries and flow conditions were employed to simulate arterial flows and in which morphometric mapping of intimal thickness was performed in human arteries. Correlations between fluid dynamic variables and intimal thickness revealed that atherosclerotic plaques tended to occur at sites of low and oscillating wall shear stress; and these observations were reinforced by studies in a monkey model of atherosclerosis. Concomitantly, it was realized that arteries adapt their diameters so as to maintain wall shear stress in a narrow range of values around 15 dynes/cm2, findings which were based both on observations of normal arteries and on animal studies in which flow rates were manipulated and arterial diameter adaptation was measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous time-domain analysis of cerebrovascular autoregulation using near-infrared spectroscopy

BACKGROUND AND PURPOSE

Assessment of autoregulation in the time domain is a promising monitoring method for actively optimizating cerebral perfusion pressure (CPP) in critically ill patients. The ability to detect loss of autoregulatory vasoreactivity to spontaneous fluctuations in CPP was tested with a new time-domain method that used near-infrared spectroscopic measurements of tissue oxyhemoglobin saturation in an infant animal model.

METHODS

Piglets were made progressively hypotensive over 4 to 5 hours by inflation of a balloon catheter in the inferior vena cava, and the breakpoint of autoregulation was determined using laser-Doppler flowmetry. The cerebral oximetry index (COx) was determined as a moving linear correlation coefficient between CPP and INVOS cerebral oximeter waveforms during 300-second periods. A laser-Doppler derived time-domain analysis of spontaneous autoregulation with the same parameters (LDx) was also determined.

RESULTS

An increase in the correlation coefficient between cerebral oximetry values and dynamic CPP fluctuations, indicative of a pressure-passive relationship, occurred when CPP was below the steady state autoregulatory breakpoint. This COx had 92% sensitivity (73% to 99%) and 63% specificity (48% to 76%) for detecting loss of autoregulation attributable to hypotension when COx was above a threshold of 0.36. The area under the receiver-operator characteristics curve for the COx was 0.89. COx correlated with LDx when values were sorted and averaged according to the CPP at which they were obtained (r=0.67).

CONCLUSIONS

The COx is sensitive for loss of autoregulation attributable to hypotension and is a promising monitoring tool for determining optimal CPP for patients with acute brain injury.

Altered microperfusion at the rectal stump is predictive for rectal anastomotic leak

PURPOSE

The aim of this study was to evaluate the reliability of intraoperative laser-Doppler measurements in predicting the occurrence of anastomotic leak in patients with colorectal cancer undergoing stapled straight anastomosis to the rectum.

METHODS

A prospective study was undertaken on 55 patients with rectal cancer or distal sigmoid cancer programmed for elective curative surgery. In all patients transmural colonic blood flow was measured by laser-Doppler flowmetry technique before bowel manipulation (baseline measurement) and after vascular ligation and division. Comorbidities at admission, intraoperative events, associated surgical procedures, and clinical outcome were tested for any association with anastomotic leak.

RESULTS

Postoperative mortality was 1.8 percent (1/55 patients), and the overall morbidity was 21.3 percent. Anastomotic leak occurred in eight patients (14.5 percent). After colonic division a blood flow reduction at the rectal stump was observed in 42 patients (76.3 percent) as compared with baseline measurement. The mean rectal stump flow reduction was 6.2 percent in patients without anastomotic leak, whereas in patients who developed anastomosis breakdown it was 16 percent (P < 0.001). Mean proximal stump flow reduction was 5.1 percent in the uncomplicated patients, whereas in patients who had an anastomosis breakdown it was 12.9 percent (P < 0.01). A positive linear correlation was found between decrease in blood flow and rate of anastomotic leak.

CONCLUSION

Blood flow reduction at the rectal stump is associated with an increased risk of anastomotic leak.

Contribution of arteriogenesis and angiogenesis to postocclusive hindlimb perfusion in mice

The goal of this study was to examine the mechanisms of vascular growth that lead to the restoration of perfusion in a peripheral vascular disease model in mice. We monitored blood flow recovery and measured vascular growth in inbred strains of mice following femoral artery occlusion. Acute collateral blood flow to the hindlimb was lowest in Balb/C mice, causing intense ischemia, and showed a slower recovery (more than 21 days to 50% normal) than C57Bl/6 which had a 7-fold higher acute collateral flow and a fast recovery (3 days). Collateral vessels were enlarged by proliferation of ECs and SMCs. Capillary density increased in the lower limbs of Balb/Cs (1.7-fold) and of sv129s. Tissue oxygen saturation recovered faster than flow in all strains. Morphometry of mature collaterals showed a diameter increase of 2.1-2.4 fold. The increase in total vessel wall area exceeded that of the femoral artery by 1.4-fold and the common lumenal area by 1.6-fold. Infusion of the growth factor peptide FGF-2 by osmotic minipump accelerated arteriogenesis but inhibited the angiogenic response probably because it prevented ischemia.

CONCLUSION

the speed of arteriogenesis is inversely related to the intensity of ischemia, and arteriogenesis is by far the most efficient mechanism to increase blood flow after femoral artery occlusion. De novo arteriogenesis was not observed.