Blood-brain barrier permeability changes after experimental subarachnoid hemorrhage.

Basic mechanisms underlying cerebrovascular permeability responses to subarachnoid hemorrhage (SAH) are still to be defined in detail. Previous investigations examining the occurrence of blood-brain barrier (BBB) breakdown after SAH in the experimental setting have yielded conflicting results. In a rat model of SAH, we assessed BBB changes by means of the quantitative [14C]-alpha-aminoisobutyric acid technique. Experiments were carried out on the second day post-SAH. In blood-injected rats [14C]-alpha-aminoisobutyric acid transport across the BBB increased significantly in cerebral cortices and cerebellar gray matter, averaging 1.3 to 1.5 times control values. The present data indicate that SAH induces well-defined changes in BBB function, possibly involved in the pathogenesis of post-SAH cerebral dysfunction in humans. Results reported here have also potential clinical implications for the management of aneurysm patients.     

Adenosine-induced modulation of excitatory amino acid transport across isolated brain arterioles

OBJECT: Excitatory amino acid (EAA) uptake by neurons and glia acts synergistically with stereoselective transport across the blood-brain barrier (BBB) to maintain EAA homeostasis in the brain. The endogenous neuroprotectant adenosine counteracts many aspects of excitotoxicity by increasing cerebral blood flow and by producing pre- and postsynaptic actions on neurons. In the present study, the authors explored the effect of adenosine on EAA transport across the BBB. METHODS: The effects of adenosine on the permeability of the BBB and transport of aspartate and glutamate across the BBB were studied in a well-characterized isolated penetrating cerebral arteriole preparation suitable for simultaneous investigations of changes in diameter and permeability. At concentrations within the physiological to low pathophysiological range (10(-7)-10(-6) M), the net vectorial transport of [3H]L-glutamate or [3H]L-aspartate from blood to brain was significantly attenuated, whereas there was no effect of adenosine on paracellular BBB permeability to [14C]sucrose or [3H]D-aspartate. With higher concentrations of adenosine (10(-4) M and 10(-3) M) the net vectorial transport of [3H]L-glutamate and [3H]Laspartate returned toward baseline. At 10(-3) M, the permeability to [14C]sucrose was significantly altered, indicating a breakdown in the BBB. The effect of adenosine (10(-6) M) was blocked by theophylline, a blocker of the A1 and A2 receptors of adenosine. CONCLUSIONS: Adenosine-mediated modulation of glutamate and aspartate transport across the BBB is a novel physiological finding.     

Effect of x-radiation to brain on cerebral glucose utilization in the rat

We assessed, by means of the [14C]-2-deoxy-D-glucose autoradiography method, the effect of whole-brain x-radiation on local cerebral glucose utilization in the rat brain. Animals were exposed to conventional fractionation (200 +/- cGy/day given 5 days a week) to a total dose of 4000 cGy. Metabolic experiments were made 2 weeks after completion of the radiation exposure. In comparison with control and sham-irradiated animals, cerebral metabolic activity was diffusely decreased following irradiation. Statistically significant decreases in metabolic activity were observed in 13 of 27 brain regions studied. In general, brain areas with the highest basal metabolic rates showed the greatest percentage drop of glucose utilization. Post-irradiation metabolic alterations possibly provide an explanation for the syndrome of early delayed deterioration observed in humans after whole-brain radiotherapy.     

The effect of 125I interstitial radiotherapy on blood-brain barrier function in normal canine brain

Blood-brain barrier (BBB) function was studied in 14 normal dogs at time periods from 7 to 717 days after permanent insertion of 5- to 7-mCi seeds of iodine-125 (125I) for interstitial radiation. The BBB function was measured with carbon-14-labeled alpha aminoisobutyric acid (AIB) and quantitative autoradiography, and expressed as a unidirectional blood-to-brain transfer constant, K. The 125I radiation lesions consisted of three concentric histologically and functionally distinct zones: 1) a central zone of calcified necrosis; 2) a spongy fluid-filled zone; and 3) a narrow rim (2.6 +/- 0.6 mm wide) of viable brain tissue with increased permeability. Within this rim, the mean value of the K of AIB was 5.8 times that of normal cortex. Over the 7- to 392-day time period the value of K remained rather constant, and by 716 days K values had returned to normal. There was moderate regional variation in the value of K; it was highest in the white matter and lowest in the gray matter surrounding the radiation lesion. The radiation lesion progressively increased in size from 7 to 80 days, after which there was little change. This study illustrates that the geographically circumscribed radiation from 125I seeds is accompanied by similarly well-defined changes in BBB function, which may persist for over 1 year following insertion of the 125I seed. This altered BBB function is probably responsible for the cerebral edema associated with 125I interstitial radiotherapy.     

Effect of whole brain radiation on local cerebral glucose utilization in the rat

We assessed, by means of the [14C]-2-deoxy-D-glucose autoradiography method, the effect of whole-brain x-radiation on local cerebral glucose utilization in the rat brain. Animals were exposed to conventional fractionation (200 +/- 4 cGy/day, 5 days/week; total dose, 4000 cGy). Metabolic experiments were made 2 to 3 weeks after completion of the radiation exposure. In comparison with control and sham-irradiated animals, cerebral metabolic activity was diffusely decreased after irradiation. Statistically significant decreases in metabolic activity were observed in 13 of 27 brain regions studied. In general, the brain areas with the highest basal metabolic rates showed the greatest percentage of decrease in glucose utilization. The concept that radiation suppresses glucose utilization before any morphological change takes place in the cell structures was the basis of this study. Metabolic alterations after irradiation may explain the syndrome of early delayed deterioration observed in humans after whole-brain radiotherapy. These studies have applications to observations made with the [18F]-fluorodeoxyglucose method in conjunction with positron emission tomographic scans in patients receiving radiation therapy for intracranial malignancies. The data reported here also have potential clinical implications for the evaluation of a risk/benefit ratio for radiotherapy in patients with benign neurosurgical diseases or children undergoing prophylactic treatment of the central nervous system.     

Radiation-induced brain damage in children--histological analysis of sequential tissue changes in 34 autopsy cases.

The nature and sequence of the radiation-induced changes in the brain were studied postmortem in 34 children with glioma, 22 of whom underwent central nervous system radiation therapy. Twenty received whole-brain or whole-neuroaxis radiation at a total mean dosage of 4063 cGy. Brain tissue alterations were analyzed histologically by means of various staining methods, including immunohistochemical techniques. The histological features of irradiated brains were compared with those of non-irradiated brains. Microscopic findings included demyelination (seven cases), focal necrosis (six cases), cortical atrophy (four cases), endothelial proliferation (four cases), and telangiectatic vascular proliferation with vascular thickening and oozing of a thick fluid (one case). Such findings were rare in non-irradiated patients. Demyelination was observed earliest in a patient who died 5 months after radiation therapy and was more common after 9 months. Focal necrosis was first observed 9 months post-irradiation but was more advanced and extensive after 1 year. Calcified foci were found only after 60 months. Various vascular changes such as vascular thickening and thrombosis suggested ischemic insult to the brain as a late effect of radiation injury. The results of this study suggest that the immature brain may be more sensitive to radiation than is the adult brain, and that the manifestations of radiation-induced injury depend on the time elapsed after irradiation.     

Glucose transport across the rat blood-brain barrier during anesthesia

The authors studied blood-brain barrier (BBB) glucose transport kinetics in awake rats and in pentobarbital- and halothane-anesthetized rats, using a 3H2O/14C-D-glucose double-indicator method corrected for cerebral blood flow at glucose concentrations from 1 to 80 mM. At normal glucose concentrations (5 mM), total brain glucose influx was unaltered by pentobarbital. In contrast, halothane attenuated glucose transport capacity from 1.9 to 0.4 mumol/g-min-1 and increased diffusional transport, Km (Michaelis constant) was decreased sixfold, from 12 to 2 mM. Halothane appears to inhibit BBB glucose transport by competing for the glucose carrier and by altering the affinity of the carrier for glucose, perhaps by altering the environment of the carrier or the carrier itself. The finding of halothane-induced increased diffusional transport of glucose across the BBB corroborates earlier reports and more recent evidence that halothane increases the permeability of the BBB to diffusional processes.     

Rôle de la barrière hématoencéphalique dans l'homéostasie cérébrale

By a variety of mechanisms, the cerebral endothelium isolates the extracellular fluid space in the central nervous system from the plasma. The combination of physical and enzymatic mechanisms which prevent macromolecules, polar solutes, neurotransmitters, peptides, and electrolytes from passively entering the brain has been termed the blood-brain barrier (BBB). Specific mechanisms provide facilitated transport across the BBB and active secretion of extracellular fluid and CSF maintain homeostasis for nutrients and for cation and H+ respectively. Consequently, interstitial fluid volume in the CNS does not increase when the total extracellular fluid volume is increased. Total tissue volume is sensitive to osmotic forces, while oncotic forces are relatively unimportant. Most anaesthetic drugs are sufficiently lipid soluble that they enter the CNS easily by passive diffusion. Differences in the rates of CNS penetration between drugs can be predicted from their lipid solubility. Anaesthetic drugs have little effect on BBB permeability and their effects on brain oedema formation derive principally from their haemodynamics effects.     

Triglycerides induce leptin resistance at the blood-brain barrier

Obesity is associated with leptin resistance as evidenced by hyperleptinemia. Resistance arises from impaired leptin transport across the blood-brain barrier (BBB), defects in leptin receptor signaling, and blockades in downstream neuronal circuitries. The mediator of this resistance is unknown. Here, we show that milk, for which fats are 98% triglycerides, immediately inhibited leptin transport as assessed with in vivo, in vitro, and in situ models of the BBB. Fat-free milk and intralipid, a source of vegetable triglycerides, were without effect. Both starvation and diet-induced obesity elevated triglycerides and decreased the transport of leptin across the BBB, whereas short-term fasting decreased triglycerides and increased transport. Three of four triglycerides tested intravenously inhibited transport of leptin across the BBB, but their free fatty acid constituents were without effect. Treatment with gemfibrozil, a drug that specifically reduces triglyceride levels, reversed both hypertriglyceridemia and impaired leptin transport. We conclude that triglycerides are an important cause of leptin resistance as mediated by impaired transport across the BBB and suggest that triglyceride-mediated leptin resistance may have evolved as an anti-anorectic mechanism during starvation. Decreasing triglycerides may potentiate the anorectic effect of leptin by enhancing leptin transport across the BBB.     

Cerebral radioprotection by pentobarbital: dose-response characteristics and association with GABA agonist activity

Pentobarbital reduces cerebral radiation toxicity; however, the mechanism of this phenomenon remains unknown. As an anesthetic and depressant of cerebral metabolism, pentobarbital induces its effects on the central nervous system by stimulating the binding of gamma-aminobutyric acid (GABA) to its receptor and by inhibiting postsynaptic excitatory amino acid activity. The purpose of this study is to investigate the role of these actions as well as other aspects of the radioprotective activity of pentobarbital. Fischer 344 rats were separated into multiple groups and underwent two dose-response evaluations. In one set of experiments to examine the relationship of radioprotection to pentobarbital dose, a range of pentobarbital doses (0 to 75 mg/kg) were given intraperitoneally prior to a constant-level radiation dose (70 Gy). In a second series of experiments to determine the dose-response relationship of radiation protection to radiation dose, a range of radiation doses (10 to 90 Gy) were given with a single pentobarbital dose (60 mg/kg intraperitoneally). Further groups of animals were used to evaluate the importance of the timing of pentobarbital administration, the function of the (+) and (-) isomers of pentobarbital, and the role of an alternative GABA agonist (diazepam). In addition, the potential protective effects of alternative methods of anesthesia (ketamine) and induction of cerebral hypometabolism (hypothermia) were examined. Enhancement of survival time from acute radiation injury due to high-dose single-fraction whole-brain irradiation was maximal with 60 mg/kg of pentobarbital, and occurred over the range of all doses examined between 30 to 90 Gy. Protection was seen only in animals that received the pentobarbital before irradiation. Administration of other compounds that enhance GABA binding (Saffan and diazepam) also significantly enhanced survival time. Ketamine and hypothermia were without protective effect. Protection from acute radiation-induced mortality by pentobarbital in the rat model is a reproducible phenomenon and is associated with the GABA agonistic activity of the compound. This property of GABA agonists offers the potential for a novel approach to enhancement of the efficacy of radiation therapy in the treatment of brain tumors.     

New insights into the role of endothelin-1 in radiation-associated impotence.

The objectives of this work were to: (1) Determine if prostate and penile tissue levels of endothelin-1 (ET-1) are increased in a rat following pelvic irradiation. (2) Determine if an ETa receptor antagonist (BQ-123) potentiates erectile function in these irradiated animals. Rats were divided into three study groups: control, 1000 cGy and 2000 cGy. The experimental groups received a single dose of radiation to the pelvic region. A time course was established to measure the effects of irradiation on prostate and penile tissue levels of endothelin-1 (ET-1)-like immunoreactivity. The effect of intracavernous injection of BQ-123 (25 microg/30 microl) was evaluated by measuring intracavernous pressure (ICP) following cavernous nerve electrical field stimulation. In the 2000 cGy group, a significant rise in ET-1-like immunoreactivity tissue levels was observed at 20 days. A significant decrease in ICP was recorded in the 1000 and 2000 cGy irradiated rats compared to the control group. Only the 2000 cGy group had a significant improvement in erectile function following BQ-123 administration. A significant improvement was observed 20 min post-administration, lasted 90 min, and was back to pre-administered levels at 120 min. The conclusion made was that radiation-induced impotence in irradiated rats is associated with an increased production of ET-1. Preliminary results are suggestive that ETa receptor antagonist may be of use to reverse such radiation-induced impotence in these irradiated animals.     

Effects of radiation on cerebral vasculature: a review

Radiation therapy plays a critical role in the treatment of central nervous system neoplasms and cerebral arteriovenous malformations. The deleterious effects of radiation on cerebral arteries may be the primary limitation to these treatment methods, as radiation may cause a variety of cerebrovascular injuries and hemodynamic changes. Radiation-induced changes in the cerebral arterial wall are determined by a number of cellular processes in endothelium and smooth muscle cells that modulate differences in radiosensitivity and phenotypic expression. The histopathological findings in arterial radiation injury include vessel wall thickening, thrombosis, luminal occlusion, and occasional telangiectases. Mechanisms for radiation injury to blood vessels include phenotypic changes in normal vessel wall cells (especially endothelium) manifested by the expression or suppression of specific gene and protein products that affect cell cycle progression or cellular proliferation or demise via cytotoxic injury or apoptosis. This review describes the molecular and cellular events involved in the systemic and cerebral vascular response to radiation and the potential means by which these responses may be influenced to augment the therapeutic effects of radiation while minimizing the untoward consequences.     

No effect of insulin on glucose blood-brain barrier transport and cerebral metabolism in humans.

The effect of hyperinsulinemia on glucose blood-brain barrier (BBB) transport and cerebral metabolism (CMRglc) was studied using the intravenous double-indicator method and positron emission tomography using [18F]fluorodeoxyglucose as tracer (PET-FDG). Sixteen normal healthy control subjects (25 +/- 4 years old) were studied twice during a euglycemic and a euglycemic-hyperinsulinemic condition. Our hypothesis was that high physiologic levels of insulin did not affect the BBB transport or net metabolism of glucose. During insulin infusion, arterial plasma insulin levels increased from 48.5 to 499.4 pmol/l. The permeability-surface area products for glucose and FDG BBB transport obtained with the double-indicator method remained constant during hyperinsulinemia. Similarly using PET-FDG, no changes were observed in the unidirectional clearance of FDG from blood to brain. k2* (FDG transport from brain to blood) increased significantly by 15 and 18% (gray and white matter, respectively), and k4* (dephosphorylation of FDG) increased by 18%. The increase in k2* may be caused by insulin inducing a decrease in the available FDG brain pool. The increase in k4* may be related to an increased loss of labeled products during insulin fusion. Irrespective of these changes, CMRglc remained unchanged in all brain regions. We conclude that hyperinsulinemia within the normal physiologic range does not affect BBB glucose transport or net cerebral glucose metabolism.     

Impaired metabolic response to endotoxin in obstructive jaundice

Surgical management of extrahepatic cholestasis is frequently complicated by sepsis, which can be explained in part by diminished function of the reticuloendothelial system. We have explored the possibility that the metabolic response to infection may also be abnormal. Fischer 344 rats underwent either bile duct ligation (BDL) or sham operation and were studied 3 days after operation. Hepatic amino acid uptake measured in vivo by the accumulation of 14C-alpha-aminoisobutyric acid or in vitro by the rate of transport of 14C-alanine by isolated hepatocytes was unaltered in the BDL animals, while gluconeogenesis from alanine by viable hepatocytes from BDL rats was actually enhanced. However, the expected increase in hepatic amino acid uptake in response to endotoxin was diminished in the BDL animals. In addition, we observed impaired responses of the jaundiced animals to glucagon and interleukin-1, two mediators of the hepatic acute phase response to endotoxin. These data suggest that while hepatic amino acid transport is normal in the basal state, the rat with extrahepatic biliary obstruction does not respond appropriately to stress and that this defect cannot be explained solely on the basis of altered handling of endotoxin by the reticuloendothelial system.     

Effect of intracerebral and subdural hematomas on energy-dependent transport across the blood-brain barrier

Although both intracerebral and subdural hematomas induce brain edema, previous studies have indicated that they may have different cerebrovascular effects. Our own investigations have demonstrated that while subdural hematomas (SDH) are associated with ischemia this is not the case following intracerebral hematomas (ICH). Previous studies have demonstrated a decrease in energy-dependent transport of glutamine across the blood-brain barrier (BBB) following focal cerebral ischemia. The present study investigates this further by examining the effects of SDH, ICH, and intracerebral thrombin injections, an agent involved in ICH-induced injury, on blood to brain glutamine transport. The injection of 200 microL of blood into the subdural space induced a marked reduction in glutamine transport (Ki, influx rate constant) into the cerebral cortex at 4 and 24 h following SDH (sham, 105+/-4% of contralateral cortex; SDH 4 h, 63+/-5%, p<0.01; SDH 24 h, 47+/-12%, p<0.05). There were no significant changes in glutamine Ki in subcortical areas following SDH. Following ICH (200-microL clot); however, there were only modest decreases in glutamine Ki in subcortical areas (sham, 98+/-2% of right cortex; ICH 4 h, 91+/-5%, p<0.01; ICH 24 h, 91+/-2%, p<0.05). Intracerebral injection of thrombin (5U) had minimal effect on glutamine Ki, in subcortical areas, at 4 h and induced a modest decrease in transport at 24 h (sham, 98+/-2% of right cortex; thrombin 4 h, 98+/-2%; thrombin 24 h, 86+/-2%, p<0.05). The present studies demonstrate marked differences in the effects of ICH and SDH on BBB function.     

Effects of oral arginine and glutamine on radiation-induced injury in the rat

BACKGROUND: Exposure of the abdominal region to ionizing radiation is associated with serious untoward symptoms of intestinal dysfunction and some reports indicate that nutrient supplements may reduce these adverse effects. This study was designed to investigate the possible beneficial effects of oral arginine or glutamine supplementation on the radiation-induced tissue injury. MATERIALS AND METHODS: Rats were given one of three feeding regimens: standard diet and water (control group), diet and water containing 2% arginine (arginine group), diet and water containing 2% glutamine (glutamine group) for 3 days prior to radiation. All rats were then subjected to a single does of 1100 cGy to the abdomen. Several serum biochemical parameters and the histologic alterations in different segments of gastrointestinal tract and liver were measured 4 days after irradiation. RESULTS: All the arginine-fed rats developed diarrhea on Day 4 postirradiation, compared to 71% incidence in control rats and 86% in glutamine-fed rats. Serum levels of aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) in the arginine group were markedly higher than those in other groups. On histological examination, radiation caused more serious damage to various segments of intestine in the arginine-fed rats compared to rats on other feeding regimens. CONCLUSION: These observations seriously question the beneficial effects of arginine and glutamine supplementations on radiation-induced tissue injury.     

Vascular changes in the urinary bladder wall after irradiation

Seven adult rabbits were used to study radiation-induced vascular changes in the urinary bladder by angiography and scanning electron microscopy of vascular casts.The angiographic studies, in which a magnification techniques was used, revealed a state of hypervascularization in the irradiated area of the bladder. With the angiographic method, however, it was not possible to visualize specific radiation-induced vascular changes within the irradiated area of the urinary bladder. Scanning electron microscopy of vascular casts made possible a detailed study of finer vessels in which typical radiation changes, teleangiectases, could be demonstrated.     

Gehirn, Psyche und körperliche Aktivität

Modern technical and biochemical methods allow investigation of hemodynamic and metabolic responses of the human brain during muscular work. Following a general introduction to the topic results from selected studies on endogenous opioid peptides, pain sensitivity and psyche, regional cerebral blood flow and cerebral glucose metabolism, amino acid transport across the blood-brain barrier, impact of physical work on the serotonergic system, influence of oxygen partial pressure on neurotransmitters and hormones during exercise, role of the brain as performance limiting factor as well as age-related changes in cerebral blood flow and hypothalamo-pituitary-adrenal/-gonadal axis function will be presented.     

Altered Expression of Zonula Occludens-2 Precedes Increased Blood–Brain Barrier Permeability in a Murine Model of Fulminant Hepatic Failure

Brain edema secondary to increased blood–brain barrier (BBB) permeability is a lethal complication in fulminant hepatic failure (FHF). Intact tight junctions (TJ) between brain capillary endothelial cells are critical for normal BBB function. However, the role of TJ in FHF has not been explored. We hypothesized that alterations in the composition of TJ proteins would result in increased BBB permeability in FHF. In this study, FHF was induced in C57BL/6J mice by using azoxymethane. BBB permeability was assessed with sodium fluorescein. Expression of TJ proteins was determined by Western blot, and their cellular distribution was examined using immunofluorescent microscopy. Comatose FHF mice had significant cerebral sodium fluorescein extravasation compared with control and precoma FHF mice, indicating increased BBB permeability. Western blot analysis showed a significant decrease in zonula occludens (ZO)-2 expression starting in the precoma stage. Immunofluorescent microscopy showed a significantly altered distribution pattern of ZO-2 in isolated microvessels from precoma FHF mice. These changes were more prominent in comatose FHF animals. Significant alterations in ZO-2 expression and distribution in the tight junctions preceded the increased BBB permeability in FHF mice. These results suggest that ZO-2 may play an important role in the pathogenesis of brain edema in FHF.