The effect of acute arterial hypertension on the blood-brain barrier to protein tracers

Intracranial Pressure During the Development of Renovascular Hypertension

[Figure: see text].

Grape Seed Extract Polyphenols Improve Resistance Artery Function in Pregnant eNOS-/- Mice

Hypertension during pregnancy is a leading cause of maternal and fetal morbidity and mortality worldwide, increasing the risk of complications including preeclampsia, intracerebral hemorrhage and fetal growth restriction. Increased oxidative stress is known to contribute to poor vascular function; however, trials of antioxidant supplementation have raised concerns about fetal outcomes, including risk of low birthweight. Grape seed extract polyphenols (GSEP) have been suggested to promote cardiovascular protection, at least in part through antioxidant actions. We tested the hypothesis that administration of GSEP during pregnancy would reduce oxidative stress and improve resistance artery function with no detrimental effects on fetal growth, in an established model of maternal hypertension associated with vascular dysfunction, the endothelial NO synthase knockout (eNOS^-/-) mouse. Pregnant C57BL/6J (WT) and eNOS^-/- mice received either GSEP (200 mg/kg/day) or drinking water, between gestational (GD) day 10.5 and GD18.5. At GD17.5, maternal systolic blood pressure (SBP) was measured; at GD18.5, maternal malondialdehyde (MDA) concentrations, vascular function of aortic, mesenteric, uterine and posterior cerebral arteries was assessed, and fetal outcome evaluated. GSEP reduced maternal SBP (P < 0.01) and plasma MDA concentrations (P < 0.01) in eNOS^-/- mice. Whilst there was no effect of GSEP on vascular reactivity of aortas, GSEP improved endothelial-dependent relaxation in mesenteric and uterine arteries of eNOS^-/- mice (P < 0.05 and P < 0.001, respectively) and normalized lumen diameters of pressurized posterior cerebral arteries in eNOS^-/- mice (P < 0.001). Supplementation with GSEP had no effect in WT mice and did not affect fetal outcomes in either genotype. Our data suggest that GSEP improve resistance artery function, potentially through antioxidant actions, and provide a basis to further investigate these beneficial effects including in the prevention of intracerebral hemorrhage. Maternal supplementation with GSEP may be a safe intervention to improve outcomes in pregnancies associated with hypertension and vascular dysfunction.

Blood-cerebrospinal fluid barrier: another site disrupted during experimental cerebral malaria caused by Plasmodium berghei ANKA

Cerebral malaria is one of the most severe pathologies of malaria; it induces neuro-cognitive sequelae and has a high mortality rate. Although many factors involved in the development of cerebral malaria have been discovered, its pathogenic mechanisms are still not completely understood. Most studies on cerebral malaria have focused on the blood-brain barrier, despite the importance of the blood-cerebrospinal fluid barrier, which protects the brain from peripheral inflammation. Consequently, the pathological role of the blood-cerebrospinal fluid barrier in cerebral malaria is currently unknown. To examine the status of the blood-cerebrospinal fluid barrier in cerebral malaria and malaria without this pathology (non-cerebral malaria), we developed a new method for evaluating the permeabilization of the blood-cerebrospinal fluid barrier during cerebral malaria in mice, using Evans blue dye and a software-assisted image analysis. Using C57BL/6J (B6) mice infected with Plasmodium berghei ANKA strain as an experimental cerebral malaria model and B6 mice infected with P. berghei NK65 strain or Plasmodium yoelii as non-cerebral malaria models, we revealed that the permeability of the blood-cerebrospinal fluid barrier increased during experimental cerebral malaria but not during non-cerebral malaria. We observed haemorrhaging in the cerebral ventricles and hemozoin-like structures in the choroid plexus, which is a key component of the blood-cerebrospinal fluid barrier, in cerebral malaria mice. Taken together, this evidence indicates that the blood-cerebrospinal fluid barrier is disrupted in experimental cerebral malaria, whereas it remains intact in non-cerebral malaria. We also found that P. berghei ANKA parasites and CD8⁺ T cells are involved in the blood-cerebrospinal fluid barrier disruption in experimental cerebral malaria. An understanding of the mechanisms underlying cerebral malaria might help in the development of effective strategies to prevent and manage cerebral malaria in humans.

A headache-free reversible cerebral vasoconstriction syndrome (RCVS) with symptomatic brain stem ischemia at late pregnancy as a rare manifestation of RCVS resolved with termination of pregnancy by semi-urgent cesarean section

A 32-year-old pregnant woman in her 39th week of pregnancy presented at the emergency room complaining of sudden-onset dizziness with gaze disturbance and was admitted to our hospital. Her past medical history included hypertension, diabetes mellitus and infarction in the right medulla oblongata 18 months prior to this event. Magnetic resonance (MR) angiography showed multiple irregular stenosis of the intracranial arterial system. Although MR images revealed no fresh ischemic or hemorrhagic lesions, she was diagnosed with reversible cerebral vasoconstriction syndrome (RVCS) associated with pregnancy. Cesarean section immediately resolved the headache-free ischemic RCVS. The postpartum course of the patient was uneventful as well as that of her baby. Follow-up MR angiography showed improvement of intracranial vasoconstriction and follow-up MR imaging showed improvement of a left medial pontine ischemic lesion on diffusion-weighted image. This report describes a rare manifestation of pregnancy-related RCVS.

Cerebral blood flow regulation, exercise and pregnancy: why should we care?

Cerebral blood flow (CBF) regulation is an indicator of cerebrovascular health increasingly recognized as being influenced by physical activity. Although regular exercise is recommended during healthy pregnancy, the effects of exercise on CBF regulation during this critical period of important blood flow increase and redistribution remain incompletely understood. Moreover, only a few studies have evaluated the effects of human pregnancy on CBF regulation. The present work summarizes current knowledge on CBF regulation in humans at rest and during aerobic exercise in relation to healthy pregnancy. Important gaps in the literature are highlighted, emphasizing the need to conduct well-designed studies assessing cerebrovascular function before, during and after this crucial life period to evaluate the potential cerebrovascular risks and benefits of exercise during pregnancy.

Cerebrovascular Dysfunction in Preeclamptic Pregnancies

Preeclampsia is a hypertensive, multisystem disorder of pregnancy that affects several organ systems, including the maternal brain. Cerebrovascular dysfunction during preeclampsia can lead to cerebral edema, seizures, stroke, and potentially maternal mortality. This review will discuss the effects of preeclampsia on the cerebrovasculature that may adversely affect the maternal brain, including cerebral blood flow (CBF) autoregulation and blood-brain barrier disruption and the resultant clinical outcomes including posterior reversible encephalopathy syndrome (PRES) and maternal stroke. Potential long-term cognitive outcomes of preeclampsia and the role of the cerebrovasculature are also reviewed.

Ischemia-reperfusion injury in stroke

Despite ongoing advances in stroke imaging and treatment, ischemic and hemorrhagic stroke continue to debilitate patients with devastating outcomes at both the personal and societal levels. While the ultimate goal of therapy in ischemic stroke is geared towards restoration of blood flow, even when mitigation of initial tissue hypoxia is successful, exacerbation of tissue injury may occur in the form of cell death, or alternatively, hemorrhagic transformation of reperfused tissue. Animal models have extensively demonstrated the concept of reperfusion injury at the molecular and cellular levels, yet no study has quantified this effect in stroke patients. These preclinical models have also demonstrated the success of a wide array of neuroprotective strategies at lessening the deleterious effects of reperfusion injury. Serial multimodal imaging may provide a framework for developing therapies for reperfusion injury.

Posterior reversible encephalopathy syndrome in an adult patient undergoing peritoneal dialysis: a case report and literature review

Background

Posterior reversible encephalopathy syndrome (PRES) is a clinical and radiological entity characterized clinically by headache, altered mental status, seizures, visual disturbances, and other focal neurological signs, and radiographically by reversible changes on imaging. A variety of different etiologies have been reported, but the underlying mechanism is thought to be failed cerebral autoregulation. To the best of our knowledge, we report the third known case of PRES in an adult receiving intermittent peritoneal dialysis (PD).

Case presentation

A 23-year-old male receiving PD was brought to hospital after experiencing a generalized seizure. On presentation he was confused and hypertensive. An MRI brain was obtained and showed multiple regions of cortical and subcortical increased T2 signal, predominantly involving the posterior and paramedian parietal and occipital lobes with relative symmetry, reported as being consistent with PRES. A repeat MRI brain obtained three months later showed resolution of the previous findings.

Conclusion

Due to having a large number of endothelium-disrupting risk factors, including hypertension, uremia, and medications known to disrupt the cerebrovascular endothelium, we suggest that those with end-stage renal disease (ESRD) receiving PD are at high risk of developing PRES. Furthermore, we surmise that PRES is likely more prevalent in the ESRD population but is under recognized. Physicians treating those with ESRD must have a high index of suspicion of PRES in patients presenting with neurological disturbances to assure timely diagnosis and treatment.

Leukoencephalomyelopathy of mature captive cheetahs and other large felids: a novel neurodegenerative disease that came and went?

A novel leukoencephalomyelopathy was identified in 73 mature male and female large captive felids between 1994 and 2005. While the majority of identified cases occurred in cheetahs (Acinonyx jubatus), the disease was also found in members of 2 other subfamilies of Felidae: 1 generic tiger (Panthera tigris) and 2 Florida panthers (Puma concolor coryi). The median age at time of death was 12 years, and all but 1 cheetah were housed in the United States. Characteristic clinical history included progressive loss of vision leading to blindness, disorientation, and/or difficulty eating. Neurologic deficits progressed at a variable rate over days to years. Mild to severe bilateral degenerative lesions were present in the cerebral white matter and variably and to a lesser degree in the white matter of the brain stem and spinal cord. Astrocytosis and swelling of myelin sheaths progressed to total white matter degeneration and cavitation. Large, bizarre reactive astrocytes are a consistent histopathologic feature of this condition. The cause of the severe white matter degeneration in these captive felids remains unknown; the lesions were not typical of any known neurotoxicoses, direct effects of or reactions to infectious diseases, or nutritional deficiencies. Leukoencephalomyelopathy was identified in 70 cheetahs, 1 tiger, and 2 panthers over an 11-year period, and to our knowledge, cases have ceased without planned intervention. Given what is known about the epidemiology of the disease and morphology of the lesions, an environmental or husbandry-associated source of neurotoxicity is suspected.

Quantitative fluorescence microscopy provides high resolution imaging of passive diffusion and P-gp mediated efflux at the in vivo blood-brain barrier

Quantitative fluorescent microscopy is an emerging technology that has provided significant insight into cellular dye accumulation, organelle function, and tissue physiology. However, historically dyes have only been used to qualitatively or semi-quantitatively (fold change) determine changes in blood-brain barrier (BBB) integrity. Herein, we present a novel method to calculate the blood to brain transfer rates of the dyes rhodamine 123 and Texas red across the in situ BBB. We observed that rhodamine 123 is subject to p-glycoprotein mediated efflux at the rat BBB and can be increased nearly 20-fold with p-glycoprotein inhibition. However, Texas Red appears to not be subject to MRP2 mediated efflux at the rat BBB, agreeing with literature reports suggesting MRP2 may lack functionality at the normal rat BBB. Lastly, we present data demonstrating that once dyes have crossed the BBB, diffusion of the dye molecule is not as instantaneous as has been previously suggested. We propose that future work can now be completed to (1) match BBB transfer coefficients to interstitial diffusion constants and (2) use dyes with specific affinities to cellular organelles or that have specific properties (e.g., subject to efflux transporters) to more fully understand BBB physiology.

Cerebral blood flow, sympathetic nerve activity and stroke risk in obstructive sleep apnoea. Is there a direct link?

Obstructive sleep apnoea (OSA) is significantly associated with the risk of stroke, and this association is independent of other risk factors, including hypertension, atrial fibrillation and diabetes mellitus. Therefore, additional pathogenic mechanisms may exist, which contribute to the increased risk of stroke. OSA is characterized by prolonged sympathetic overactivity; however the role of the sympathetic nervous system in regulating cerebral circulation remains a matter of controversy. Converging data indicate that brain perfusion is significantly distorted in OSA, with reported decreases in cerebral blood flow as well as intermittent surges in blood pressure and cerebral blood flow velocity. Based on recent research, there is accumulating evidence that sympathetic nerve activity is an important element in brain protection against excessive increases in perfusion pressure during blood pressure surges and flow during rapid eye movement sleep. The aim of this article was to review: (i) the current physiological knowledge related to the role of the sympathetic system in the regulation of cerebral blood flow, (ii) how the influence of the sympathetic system on cerebral vessels is affected by apnoea (increased PaCO(2)) and (iii) the potential significance of the pathological sympathetic system/PaCO(2) interplay in OSA. Sympathetic system seems to be at least partially involved in pathogenesis of distorted haemodynamics and stroke in OSA patients. However, there are still several open questions that need to be addressed before the effective therapeutic strategies can be implemented.

Bolus injection of hypertonic solutions for cerebral edema in rats: challenge of homeostasis of healthy brain

Hypertonic solutions are mainstay of osmotherapy to cerebral edema. How hypertonic solutions affect healthy brain homeostasis, however, is not fully understood. Using rat model of cerebral edema induced by local cryoinjury, we found with immunohistochemistry that less microglial activation in healthy hemishere 24 h after hypertonic saline (HS, 3% NaCl) administration, compared to mannitol (20%, the same osmotic concentration of 3% NaCl) while dehydrating the brain tissue. To see whether blood-brain barrier (BBB) or aquaporin-4 (AQP4) contribute to this difference, HS or mannitol was intra-arterially injected to normal rats, and BBB opening, ultrastructure and AQP4 immunoreactivity were examined. Evans blue extravasation indicated that BBB was opened much lighter in HS group than mannitol group at the same time points. Electron microscopy also showed edema around the capillaries slightly lighter in HS than mannitol group 24 h after injection. Meanwhile, HS injection led to AQP4 down regulation in expression similarly as mannitol, compared with NS group. These data suggested that bolus injection of hypertonic agents may lead to microglia activation in healthy brain in different extent, due to BBB compromise, instead of water movement or AQP4 expression. Hence in clinical application, BBB of healthy brain should be considered in perspective to maintain the brain homeostasis.

Seizures in Women with Preeclampsia: Mechanisms and Management

Eclampsia is defined in the obstetrical literature as the occurrence of unexplained seizure during pregnancy in a woman with preeclampsia. In the Western world, the incidence of eclampsia is ~1 per 2000 to 1 per 3000 pregnancies, but the incidence is 10-fold higher in tertiary referral centers and undeveloped countries where there is poor prenatal care, and in multi-fetal gestations. Nearly 1 in 50 women with eclampsia die as do 1 in 14 of their offspring, and mortality rates are considerably higher in undeveloped countries. Eclampsia is also associated with significant life-threatening complications, including neurological events. Seizure acutely can cause stroke, haemorrhage, oedema and brain herniation and thus lead to epilepsy and cognitive impairment later in life.

Vascular Protection Following Cerebral Ischemia and Reperfusion

Despite considerable research that has contributed to a better understanding of the pathophysiology of stroke, translation of this knowledge into effective therapies has largely failed. The only effective treatment for ischemic stroke is rapid recanalization of an occluded vessel by dissolving the clot with tissue plasminogen activator (tPA). However, stroke adversely affects vascular function as well that can cause secondary brain injury and limit treatment that depends on a patent vasculature. In middle cerebral arteries (MCA), ischemia/reperfusion (I/R) cause loss of myogenic tone, vascular paralysis, and endothelial dysfunction that can lead to loss of autoregulation. In contrast, brain parenchymal arterioles retain considerable tone during I/R that likely contributes to expansion of the infarct into the penumbra. Microvascular dysregulation also occurs during ischemic stroke that causes edema and hemorrhage, exacerbating the primary insult. Ischemic injury of vasculature is progressive with longer duration of I/R. Early postischemic reperfusion has beneficial effects on stroke outcome but can impair vascular function and exacerbate ischemic injury after longer durations of I/R. This review focuses on current knowledge on the effects of I/R on the structure and function of different vascular segments in the brain and highlight some of the more promising targets for vascular protection.

PROTECTION OF BLOOD-BRAIN BARRIER BREAKDOWN BY NIFEDIPINE IN ADRENALINE-INDUCED ACUTE HYPERTENSION

The question of whether influxes of ionic Ca+2 into cerebral endothelium plays an important role in increased vascular permeability consequent to an acute hypertension is not accurately resolved. We tested the effect of nifedipine, a calcium entry blocker, on the cerebrovascular permeability for proteins in adrenalin-induced acute hypertension. The experiments were carried out on male Wistar rats. The experimental groups consisted of normotensive saline controls, adrenaline-induced hypertensive rats, and adrenalin-induced hypertensive rats as pre-treated or post-treated with a bolus of nifedipine. Brains of hypertensive rats showed increased permeability to Evans Blue-Albumin complex, when blood pressure elevated rapidly to more than 170 mmHg. The number and size of areas of Evans-Blue extravasation were smaller if an increase in blood pressure was prevented. The short lasting elevation of blood pressure did not result in protein extravasation in brains of hypertensive rats. The results suggest that nifedipine can modify the permeability disruptions observed in acutely hypertensive rats. The data also support the hypothesis that Ca+2 may be responsible for the changes in permeability of BBB in hypertension by mediating the contraction of vascular muscles.

HAEMODYNAMIC CONTRIBUTIONS TO THE PATHOGENESIS OF PREECLAMPSIA AND ECLAMPSIA

Current hypotheses regarding the origins of preeclampsia have focused on the “Two stage model”. This model suggests that the primary steps in the pathophysiologic sequence of preeclampsia are initiated by abnormal placentation including the classic finding of abnormal trophoblast invasion of maternal decidual spiral arteries. The second stage of the sequence includes the elaboration of a single or multiple substances from these disordered placentas which contribute to the generalized maternal systemic illness, eventually manifesting as endothelial injury, hypertension and proteinuria. Recent studies have focused on the role of pro and anti-angiogenic peptides as potential placentally derived aetiologic agents in this pathophysiologic sequence, although other placental products have been highlighted in recent research. Despite the fact that this modeling of preeclampsia has widespread support significant limitations to this hypothesis can be identified.

Pathogenesis of état criblé in experimental hypertensive rats

The pathogenesis of état criblé in experimental hypertensive rat brain was studied. Macroscopically, the hypertensive rat brain showed marked subarachnoidal edema. Cystic dilatation of the subarachnoid space, softening, and perivascular dilatation or état criblé, in the caudate putamen, frontoparietal cortex, and basal ganglia were observed by light microscope. Perivascular dilatation was noted not only around the intracerebral arteries and arterioles but also around the veins and venules. Transmission and scanning electron microscopy also confirmed the presence of perivascular dilatation around the same vessels. In addition, transmission electron microscopy confirmed the increased permeability of the endothelial cells in the intracerebral arteries, arterioles, veins, venules, and capillaries of brains with état criblé. Severe medial cell injuries of the arteries and arterioles and edema-induced destruction of the brain around the dilated perivascular space were also observed. Scanning electron microscopy revealed mild or cystic dilatation of the perivascular space, a net-like structure on both sides of the arachnoidal cells resulting in markedly dilated and numerically increased fenestra, and degenerative changes in the perivascular brain tissue. In conclusion, état criblé in experimental hypertensive rat brain results from an increase in perivascular fluid-induced degeneration of the perivascular brain tissue that is in turn induced by an increase in the permeability of blood vessels.

Pregnancy prevents hypertensive remodeling and decreases myogenic reactivity in posterior cerebral arteries from Dahl salt-sensitive rats: a role in eclampsia?

Previous studies have demonstrated that pregnancy prevents protective hypertension-induced remodeling of cerebral arteries using nitric oxide synthase (NOS) inhibition to raise mean arterial pressure (MAP). In the present study, we investigated whether this effect of pregnancy was specific to NOS inhibition by using the Dahl salt-sensitive (SS) rat as a model of hypertension. Nonpregnant ( n = 16) and late-pregnant ( n = 17) Dahl SS rats were fed either a high-salt diet (8% NaCl) to raise blood pressure or a low-salt diet (<0.7% NaCl). Third-order posterior cerebral arteries were isolated and pressurized in an arteriograph chamber to measure active responses to pressure and passive remodeling. Several vessels from each group were stained for protein gene product 9.5 to determine perivascular nerve density. Blood pressure was elevated in both groups on high salt. The elevated MAP was associated with significantly smaller active and passive diameters ( P < 0.05) and inward remodeling in the nonpregnant hypertensive group only. Whereas no structural changes were observed in the late-pregnant hypertensive animals, both late-pregnant groups had diminished myogenic reactivity ( P < 0.05). Nerve density in both the late-pregnant groups was significantly greater when compared with the nonpregnant groups, suggesting that pregnancy has a trophic influence on perivascular innervation of the posterior cerebral artery. However, hypertension lowered the nerve density in both nonpregnant and late-pregnant animals. It therefore appears that pregnancy has an overall effect to prevent hypertension-induced remodeling regardless of the mode of hypertension. This effect may predispose the brain to autoregulatory breakthrough, hyperperfusion, and eclampsia when MAP is elevated.

Effects of electromagnetic radiation of mobile phones on the central nervous system

With the increasing use of mobile communication, concerns have been expressed about the possible interactions of electromagnetic radiation with the human organism and, in particular, the brain. The effects on neuronal electrical activity, energy metabolism, genomic responses, neurotransmitter balance, blood-brain barrier permeability, cognitive function, sleep, and various brain diseases including brain tumors are reviewed. Most of the reported effects are small as long as the radiation intensity remains in the nonthermal range, and none of the research reviewed gives an indication of the mechanisms involved at this range. However, health risks may evolve from indirect consequences of mobile telephony, such as the sharply increased incidence rate of traffic accidents caused by telephony during driving, and possibly also by stress reactions which annoyed bystanders may experience when cellular phones are used in public places. These indirect health effects presumably outweigh the direct biological perturbations and should be investigated in more detail in the future.

Middle cerebral artery function after stroke: the threshold duration of reperfusion for myogenic activity

BACKGROUND AND PURPOSE

Myogenic activity of the cerebral arteries is an important contributor to autoregulation of cerebral blood flow. Previous studies have demonstrated that increasing periods of ischemia diminished the amount of myogenic tone in cerebral arteries. In the present study, we investigated the effect of different periods of postischemic reperfusion on the myogenic behavior of middle cerebral arteries (MCAs). We measured both the amount of spontaneous myogenic tone that developed at 75 mm Hg and the contractile response to increased transmural pressure (TMP), ie, myogenic reactivity.

METHODS

The MCA occlusion model was used in male Wistar rats (n=45) to induce 30 minutes of temporary ischemia, followed by different periods of reperfusion (0 or sham; 30 minutes; and 6, 12, 18, 20, and 22 hours), confirmed by laser Doppler flowmetry. MCAs were studied in vitro using an arteriograph system that allowed control of TMP and measurement of lumen diameter. After equilibration for 1 hour at 75 mm Hg, TMP was increased stepwise in 25-mm Hg increments to 125 mm Hg and lumen diameter measured at each pressure. The amount of spontaneous myogenic tone was determined in both ischemic and contralateral arteries for each reperfusion period and compared with the right and left MCAs in the sham group. Arteries were then fixed with 10% formalin pressurized in the arteriograph bath and stained for filamentous (F)-actin with fluorescently labeled phalloidin, a specific probe for F-actin. The amount of F-actin was quantified using confocal microscopy.

RESULTS

MCAs from the sham-operated control group possessed considerable myogenic tone (35%). However, the amount of tone in ischemic MCAs progressively diminished as the reperfusion duration increased. In addition, sham-operated control arteries responded myogenically to increases in TMP, decreasing diameter as pressure increased. There was a similar response in arteries exposed to 30 minutes and 6 hours of reperfusion, all producing a negative slope on the pressure-diameter curve; however, myogenic reactivity was diminished at the longer periods of reperfusion, producing a positive slope of the graph. The slopes of the pressure-diameter curves were as follows: -0.10+/--0.06 (sham), -0.07+/--0.12 (30 minutes), -0.08+/--0.11 (6 hours), +0.09+/-0.09 (12 hours), +0.25+/-0.16 (18 hours), +0.38+/-0.09 (20 hours), and +0.57+/-0.09 (22 hours). F-actin content was significantly less only in ischemic MCAs at 6 and 12 hours of reperfusion.

CONCLUSIONS

These results demonstrate that longer periods of reperfusion significantly diminish myogenic activity of MCAs. Understanding how different periods of ischemia and reperfusion affect the function of the cerebral circulation may promote more effective treatment of ischemic stroke.

Dynamic cerebral microcirculatory changes in transient forebrain ischemia in rats: involvement of type I nitric oxide synthase

The diameter of surface microvessels and the erythrocyte velocity and flux through intraparenchymal capillaries in the parietal cortex were measured during transient global cerebral ischemia and reperfusion using laser-scanning confocal fluorescence microscopy in anesthetized rats. The role of nitric oxide (NO) from neurons in the microcirculatory changes was also investigated using 7-nitro-indazole (7-NI, 25 mg/kg, i.p.). Wistar rats (4 per group) equipped with a closed cranial window were given fluorescein isothiocyanate (FITC)-Dextran and FITC-labeled erythrocytes intravenously to respectively visualize the microvessels and the erythrocytes in the capillaries. Experiments were videorecorded on-line. Forebrains were made ischemic for 15 minutes and then reperfused for 120 minutes under the microscope. Ischemia was associated with a flattened EEG, a low persistent blood flow, and a transient leakage of fluorescein across the arteriole wall. Unclamping the carotid arteries led to immediate high blood flow in the arterioles, but it was not until 5 minutes later that the arterioles dilated significantly (181% +/- 27%) and erythrocyte velocity in the capillaries increased significantly (460% +/- 263%). Neither nonperfused capillaries nor erythrocyte capillary recruitment occurred. 7-Nitro-indazole significantly reduced the arteriole dilatation and prevented the increase in erythrocyte velocity and flux through capillaries in early reperfusion. 7-Nitroindazole had no influence on the fluorescein leakage. The current study suggests a partial role for NO released from neurons in the postischemic microcirculatory changes and provides new findings on the timing of arteriole dilatation and blood-brain barrier opening, and on erythrocyte capillary circulation in global ischemia.

Intracranial pressure, cerebral perfusion pressure, and SPECT in the management of patients with SAH Hunt and Hess grades I-II

The objective of our study was to examine the course of intracranial pressure (ICP) in patients with SAH Hunt and Hess grades I-II and to analyze the relationship between ICP, cerebral perfusion pressure (CPP) and cerebral blood flow (CBF). Twenty-three patients were studied. ICP, arterial blood pressure (ABP) and CPP were continuously recorded. The measurements of CBF with single-photon emission computed tomography (SPECT) were performed in fifteen patients, who showed TCD flow velocities exceeding 120 cnlJsec. In the first two days after SAH four patients (15%) showed a normal ICP, six (25%) patients had a moderate increase of ICP ranged from 15 to 25 mm Hg and thirteen (60%) patients had ICP values higher than 25 mm Hg. Seven of these patients, with ICP values higher than 40 mm Hg, showed clinical signs of delayed ischaemia. After the treatment with osmotic diuretic, ICP decreased and a clinical improvement was observed with the exception of one patient. In this patient, the SPECT study showed middle cerebral hypoperfusion concordant with the clinically ischaemic hemisphere. Our study showed the utility of the monitoring of these parameters in patients with lower grade SAH, because it allows the modulation of the therapeutic approach and defines the onset of neurological deficits secondary to cerebral ischaemia in all grades of SAH.

Stress-induced increase in blood-brain barrier permeability in control and monosodium glutamate-treated rats

Glutamate administration in neonatal rats causes reversible changes in blood-brain barrier (BBB) permeability and known neurotoxic lesions. This study was aimed to evaluate whether glutamate administered to neonatal rats influences properties of the developing BBB with consequences on adult BBB function. The vulnerability of the BBB was examined after short-lasting stress exposure by measurement of plasma albumin extravasation using immunoelectrophoresis. In control rats, 30 min of immobilization stress resulted in increased endogenous albumin extravasation in the hypothalamus, hippocampus, brain stem and cerebellum, but not in the cortex and striatum. Basal levels of albumin in adult glutamate-treated rats (4 mg monosodium glutamate/g BW, IP, five times during neonatal period) were significantly lower in the hypothalamus compared to that in controls. Stress-induced increase in albumin levels was lower in the brain stem, higher in the hypothalamus, and similar in other brain regions studied in glutamate-treated rats in comparison with controls. It is concluded that short-lasting immobilization stress increased BBB permeability in some but not all brain regions studied. Glutamate treatment of neonatal rats resulted in low basal albumin levels in the hypothalamus but did not exert a pronounced influence on adult BBB function. BBB vulnerability in glutamate-treated rats during stress exposure was increased in the hypothalamus and decreased in the brain stem.

Effects of intravenous phenylephrine on blood pressure, nociception, and neural activity in the rostral ventral medulla in rats

Acute or chronic increases in arterial blood pressure are associated with decreases in nociception. In addition, acute increases in arterial blood pressure inhibit ON cells and excite OFF cells of the rostral ventral medulla (RVM). The current study tested whether the antinociception produced by increases in blood pressure is dependent on changes in the activity of ON and/or OFF cells. Single unit activity of ON or OFF cells was recorded in the RVM during increases in blood pressure produced by intravenous infusion of phenylephrine (1, 2.5, or 10 micrograms/min for 21 min) in lightly anesthetized rats. Nociception was measured using the tail flick test. Phenylephrine dose-dependently increased mean arterial pressure and tail flick latency, but had inconsistent effects on neural activity in the RVM. In a second study, the effects of phenylephrine infusion on tail flick latency was determined before and after saline or lidocaine microinjections into the RVM. Lidocaine had no effect on the ability of phenylephrine to inhibit the tail flick reflex. These data suggest that the RVM, and therefore ON and OFF cells, is not required for phenylephrine-induced antinociception.

Effects of a selective endothelin A-receptor antagonist, BQ-123, in salt-loaded stroke-prone spontaneously hypertensive rats

1. We examined the effects of a selective endothelin A (ETA)-receptor antagonist, BQ-123, on the development of hypertension and organ damage in stroke-prone spontaneously hypertensive rats (SHRSP) given 1% NaCl for 6 weeks. 2. BQ-123 at doses of 0.7, 2.1 and 7.1 mg/day was continuously administered for 6 weeks to 8 week old salt-loaded SHRSP, who were given water containing 1% NaCl for the following 6 weeks, via a subcutaneous osmotic minipump. 3. Development of high blood pressure was accelerated in salt-loaded SHRSP compared with that in non-salt-loaded SHRSP. After 6 weeks of salt-loading, incidence of cerebral infarction, renal sclerosis and renal fibrosis were greater in salt-loaded than non-salt-loaded SHRSP. 4. BQ-123 attenuated the age-related rise in blood pressure in a dose-dependent manner. The effect coincided with reduction in the incidence of cerebral infarction and prevention of renal sclerosis and fibrosis. Kidney function was improved as observed by an increase in glomerular filtration rate and decreases in urinary protein excretion, blood urea nitrogen and fractional sodium excretion. Furthermore, BQ-123 prevented increases in the heart weight/bodyweight ratio and aortic wall thickness in salt-loaded SHRSP. 5. These results suggest that endogenous endothelin-1 (ET-1) and ETA-receptors may be, at least in part, involved in the pathogenesis of hypertension and organ damage in salt-loaded SHRSP.

Contribution of brain injury to hypertension following intravenously-administered pancuronium in rats

Abnormal hypertension sometimes occurs following intravenous administration (i.v.) of pancuronium in patients with brain injury. The present experiment was designed to determine whether brain injury contributes to the hypertensive response of i.v. pancuronium. Forty-six Wister strain rats were studied, of which 39 had induced brain injury at (a) upper pons (b) midbrain (c) thalamus region (excluding hypothalamus) and (d) cerebellum or a combination of these sites. The injury was made by single insertion of a 22 Gauge needle through the skull surface. The quantity of pancuronium solution administered i.v. in each case was 1.0 ml containing either 0.8 mg/kg or 8 mg/kg of pancuronium. Group A (n = 7) had no brain injury and the mean arterial pressure (MAP) did not change following i.v. administration of pancuronium. In Group B (n = 9) (a+b+c, 8.0 mg/kg) MAP rose from 90.9 +/- 15.4 to 102 +/- 22.0 mmHg and in Group C (n = 7) (a+b+c, 0.8 mg/kg) MAP rose from 148.4 +/- 13.3 to 160 +/- 14.4 mmHg. In Group D (n = 5) (b+c, 8.0 mg/kg) MAP remained unchanged. In Group E (n = 5) (a, 8.0 mg/kg) MAP rose from 130.3 +/- 18.7 to 146 +/- 27.6 mmHg and in Group F (n = 6) (a, 0.8 mg/kg) MAP rose from 129.7 +/- 15.6 to 135.8 +/- 13.8 mmHg. In Group G (n = 7) (d, 8.0 mg/kg) MAP remained unchanged. Since the MAP was elevated in only those groups that received injury in the upper pons, we concluded that injury in the upper pons can lead to hypertension following i.v. administration of pancuronium.

Comparison of c-fos expression in the lamina terminalis of conscious rats after intravenous or intracerebroventricular angiotensin

Fos immunoreactivity in the rat brain after intracerebroventricular (ICV) angiotensin II (ANG II) was compared with that induced by intravenous ANG II. ANG II was infused into the lateral ventricle (at 1 ng/min) or femoral vein (at 5 micrograms/h) of conscious rats. After 90 min, rats were killed and Fos was detected by immunohistochemistry. Both infusions caused Fos immunoreactivity to be present in the lamina terminalis, hypothalamic supraoptic, and paraventricular nuclei, bed nucleus of the stria terminalis, and central amygdaloid nucleus. However, distributions of Fos immunoreactivity within the lamina terminalis differed with the different routes of infusion. Intravenous ANG II caused intense Fos immunoreactivity mainly in the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT). By contrast, ICV ANG II caused intense Fos immunoreactivity predominantly in the median preoptic nucleus and juxtaventricular neurons of the SFO and OVLT. These results suggest that IV ANG II induces behavioural and endocrine responses by direct actions on the SFO and OVLT, whereas ICV ANG II directly stimulates neurons in the median preoptic nucleus as well neurons in the SFO and OVLT.

Variable restriction of albumin diffusion across inflamed cerebral microvessels of the anaesthetized rat

1. The possibility of restricted diffusion of macromolecules in single cerebral venular capillaries that have become leaky due to inflammation was investigated by comparing the permeabilities to Lucifer Yellow (457 Da; PLY) and rhodamine-labelled albumin (69 kDa; PRh-A). 2. The dyes were trapped between two micro-occlusion probes and the permeabilities were measured from the rates of decrease in dye fluorescence at low intraluminal hydrostatic pressure. 3. Removal of one probe had little effect on PLY but did reduce PRh-A, consistent with the influence of convection on diffusion through 22 nm wide transendothelial slits 1 micron deep. 4. Direct comparisons were made over time between PLY and PRh-A in six vessels while hydrostatic pressure effects were controlled. In all vessels PRh-A:PLY varied from being similar to the ratio of the free diffusion coefficients to virtually zero even though PLY remained high. The question of the source of this variable restriction to albumin is discussed in terms of the secretion and sloughing of glycosaminoglycans and the possible role of transient formation of transendothelial gaps.

Heterogeneity of vascular dementia: mechanisms and subgroups

Today, multiple, thromboembolically generated cerebral infarcts are regarded as the main pathogenetic pathway of vascular dementia (VAD), with multi-infarct dementia (MID) as its clinical counterpart. However, taking into account other vascular mechanisms that may influence the brain, such as vessel-wall damage (atherosclerosis, hyalinosis, amyloid angiopathy, or blood-brain barrier dysfunction), cerebrovascular insufficiency (disturbance of systemic circulation, perfusion vulnerability related to the vascular anatomy of the brain, or disturbance of autoregulation), and hyperviscosity, it is evident that MID is not the only VAD category. The diagnosis of MID ought to be reserved for the combination of progressive dementia associated with cerebral ischemic events and evidence of infarction that is mainly associated with the large cerebral arteries. Subcortical white-matter dementia characterized by frontosubcortical symptomatology, white-matter lesions, and small-vessel involvement with or without lacunes/infarcts--a combination of lacunar dementia and Binswanger's disease--appears to be another important VAD disease.

Moderate hypothermia reduces blood-brain barrier disruption following traumatic brain injury in the rat

The effects of moderate hypothermia on blood-brain barrier (BBB) permeability and the acute hypertensive response after moderate traumatic brain injury (TBI) in rats were examined. TBI produced increased vascular permeability to endogenous serum albumin (IgG) in normothermic rats (37.5 degrees C) throughout the dorsal cortical gray and white matter as well as in the underlying hippocampi as visualized by immunocytochemical techniques. Vascular permeability was greatly reduced in hypothermic rats cooled to 30 degrees C (brain temperature) prior to injury. In hypothermic rats, albumin immunoreactivity was confined to the gray-white interface between cortex and hippocampi with no involvement of the overlying cortices and greatly reduced involvement of the underlying hippocampi. The acute hypertensive response in normothermic rats peaked at 10 s after TBI (187.3 mm Hg) and returned to baseline within 50 s. In contrast, the peak acute hypertensive response was significantly (P < 0.05) reduced in hypothermic rats (154.8 mm Hg, 10 s after TBI) and returned to baseline at 30 s after injury. These results demonstrate that moderate hypothermia greatly reduces endogenous vascular protein-tracer passage into and perhaps through the brain. This reduction may, in part, be related to hypothermia-induced modulation of the systemic blood pressure response to TBI.

Blood-brain barrier integrity and brain water and electrolytes during hypoxia/hypercapnia and hypotension in newborn piglets

This study examines the effects of hypoxia/hypercapnia and hypoxia/hypercapnia with hypotension (hypotensive-hypoxia/hypercapnia) on blood-to-brain transfer constants (K1) for sodium and mannitol and brain water and electrolyte contents in newborn piglets. Hypoxia/hypercapnia was induced for 60 min with the piglets breathing a gas mixture of 15% carbon dioxide, 10-12% oxygen, and 73-75% nitrogen adjusted to achieve an arterial pH less than 7.15, pO2 less than 40, and pCo2 greater than 60 mmHg and hypotension for 20 min by rapid phlebotomy to achieve a mean arterial blood pressure less than 40 mmHg. Piglets were studied during 1 h of, and 24 h after resuscitation from hypoxia/hypercapnia (arterial pH 6.9 +/- 0.18, pO2 36 +/- 6 mmHg, pCO2 68 +/- 8 mmHg, mean +/- S.D.) and 10 min, and 24 h after resuscitation from hypotensive-hypoxia/hypercapnia (mean arterial blood pressure 28 +/- 10 mmHg, mean +/- S.D.). Values for K1 for sodium and mannitol, measured using the integral technique were 15.9 and 5.2 ml.g-1.min-1 x 10(4) respectively, in 2-4-day-old controls, suggesting that the barrier is fully developed in newborn piglets. Values were not different during or after hypoxia/hypercapnia or 24 h after hypotensive-hypoxia/hypercapnia. Ten to forty min after hypotensive-hypoxia/hypercapnia, there was a proportional decrease in the K1 for sodium and mannitol of about 40%. These results suggest that the newborn piglet is similar to the adult with respect to impermeability of the blood-brain barrier to ions and small molecules and resistance of this barrier to systemic hypoxia/hypercapnia and hypotension.(ABSTRACT TRUNCATED AT 250 WORDS)

Clearance of brain edema and macromolecules through the cortical extracellular space

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

Age-dependent alteration in regional cerebrovascular permeability during drug-induced epilepsy

Age-related changes in blood-brain barrier permeability were investigated during pentylenetetrazol-induced seizures in rats aged from 15 days to 120 days. Tracers such as [14C]sucrose and [3H]inulin which diffuse very slowly across the intact endothelium were simultaneously injected i.v. in rats treated with pentylenetetrazol (PTZ) or in control animals. Permeability-surface area products (PA) were determined in 9 brain regions. Pentylenetetrazol-induced seizures caused a significant increase in PA for both sucrose and inulin in all brain regions studied. Blood-brain barrier dysfunction was present only in animals in which the mean arterial blood pressure rose at seizure onset. Although increased blood-brain barrier permeability was found partly in similar areas in both young and adult rat brains, in adults the increase was the highest in the preoptic area, septum, colliculus inferior, hypothalamus and in the cerebellum while the increase was comparatively much smaller in the same areas of young brains. The increase in blood-brain barrier permeability was extremely high in the hippocampus, hypothalamus and cerebellum of 15-day-old rat brain and, was least affected in the corpus striatum and cerebral cortex in contrast to older rats. From the results obtained it may be concluded that the increased cerebrovascular permeability induced by pentylenetetrazol differs markedly in localization in young and adult rats. The age-dependent increased blood-brain barrier integrity is not over all dependent on variations in the blood pressure, but rather on progressive maturation of capillaries and changes in their internal structure, and local phenomena in neuronal activity during the seizures.

Time course of the impairment of cerebral autoregulation during chronic cerebral vasospasm after subarachnoid hemorrhage in primates

The time course of the impairment of cerebral autoregulation during chronic cerebral vasospasm after subarachnoid hemorrhage was studied in 18 monkeys. Changes in cerebral blood flow (CBF) at the regional level and central conduction times during either graded hypo- or hypertension were evaluated in these animals at three stages (3, 7, and 14 days) following the introduction of an autologous blood clot around the right middle cerebral artery (MCA). Angiograms revealed a reduction in vessel caliber (compared to the baseline level in the involved MCA) of 30% at 3 days, 50% at 7 days, and 10% at 14 days. At all stages, CBF remained constant at mean arterial blood pressures (MABP) of 60 to 160 mm Hg in the noninvolved hemisphere. In contrast, at the 3- and 7-day stages, there was an impairment of autoregulation in the involved hemisphere at MABP of 40 to 180 mm Hg. The right hemispheric CBF was significantly (p less than 0.05) lower than that in the left throughout the period of investigation at MABP below 120 mm Hg, but rose to exceed the left CBF at MABP above 180 mm Hg at the 7-day stage and 160 mm Hg at the 14-day stage. The right-sided central conduction time showed significant (p less than 0.05) prolongation at MABP below 60 mm Hg at the 3-day stage and 40 mm Hg at the 7-day stage. It is suggested that these results may help to develop guidelines for hemodynamic therapy for vasospasm in its various stages.

Effect of chronic hypertension on the blood-brain barrier permeability of libenzapril

Very little information is available on the permeability of the blood-brain barrier (BBB) to small polar drugs in chronic hypertension. The blood and cerebrospinal fluid (CSF) pharmacokinetics of libenzapril (LZP), a potent angiotensin converting enzyme inhibitor, were investigated in hypertensive (SH) and normotensive (SD) rats. Following intravenous bolus administration of this hydrophilic drug, the terminal rate constant for elimination (beta), steady-state volume of distribution (Vdss), and systemic clearance (CL) were similar in these two animal groups. Other pharmacokinetic parameters (Cpo, alpha, k12, and k21) were significantly (P less than 0.05) greater in the hypertensive group, except for the volume of the central compartment (Vc) and ratio of Vc to Vdss, which were smaller in SH rats. The ratio of area under the concentration-time curve (AUC) in CSF to blood was about twofold higher in SH rats compared to normotensive rats, showing increased BBB permeability in hypertensive rats. An acute brain uptake study was also performed in SH, SD, and WK rats by intracarotid administration of 14C-LZP along with 3H2O as a reference marker. Both LZP and water transport was found to be significantly higher (about two- to five-fold) in six of the seven different brain regions in SH rats as compared to the normotensive (SD and WK) controls. Because of this simultaneous increase in concentrations of both the drug and the reference marker, BUI values were not affected. Regional brain concentrations in SH rats were also linearly correlated with the mean arterial pressure (MAP) values, providing further evidence of the systemic pressure related increase in BBB permeability.

Superoxide dismutase decreases mortality, blood pressure, and cerebral blood flow responses induced by acute hypertension in rats

Oxygen radicals are known to be produced by the cerebral vasculature during acute, pressor-induced hypertension and are also known to inactivate endothelium-derived relaxing factor. The objective of our present study was to determine if the oxygen radical scavenger superoxide dismutase (24,000 units/kg plus 1,600 units/kg/min) alters the pressor, cerebral blood flow, and mortality responses to systemic norepinephrine in rats. Increasing doses (0.01-30 micrograms/kg i.v.) of norepinephrine were given by bolus injection to eight rats, and changes in the cortical microcirculatory blood flow were measured by laser-Doppler flowmetry. Superoxide dismutase shifted the norepinephrine-blood pressure and -cerebral blood flow dose-response curves moderately, but significantly, to the right such that it took more norepinephrine to reach a given blood pressure. However, superoxide dismutase had no effect on the autoregulation of cerebral blood flow. Additionally, whereas five (63%) of the eight control rats died after the 10 micrograms/kg norepinephrine dose, all eight rats treated with superoxide dismutase survived this dose. The mechanism by which superoxide dismutase reduced mortality is uncertain. The blood pressure and cerebral blood flow results suggest that superoxide dismutase prevents oxygen radicals from destroying endothelium-derived relaxing factors, which reduce the pressor effects of norepinephrine.