Disruption of blood-brain barrier following bilateral carotid artery occlusion in spontaneously hypertensive rats. A quantitative study

Vulnerability of the Hippocampus to Insults: Links to Blood-Brain Barrier Dysfunction

The hippocampus is a critical brain substrate for learning and memory; events that harm the hippocampus can seriously impair mental and behavioral functioning. Hippocampal pathophysiologies have been identified as potential causes and effects of a remarkably diverse array of medical diseases, psychological disorders, and environmental sources of damage. It may be that the hippocampus is more vulnerable than other brain areas to insults that are related to these conditions. One purpose of this review is to assess the vulnerability of the hippocampus to the most prevalent types of insults in multiple biomedical domains (i.e., neuroactive pathogens, neurotoxins, neurological conditions, trauma, aging, neurodegenerative disease, acquired brain injury, mental health conditions, endocrine disorders, developmental disabilities, nutrition) and to evaluate whether these insults affect the hippocampus first and more prominently compared to other brain loci. A second purpose is to consider the role of hippocampal blood-brain barrier (BBB) breakdown in either causing or worsening the harmful effects of each insult. Recent research suggests that the hippocampal BBB is more fragile compared to other brain areas and may also be more prone to the disruption of the transport mechanisms that act to maintain the internal milieu. Moreover, a compromised BBB could be a factor that is common to many different types of insults. Our analysis indicates that the hippocampus is more vulnerable to insults compared to other parts of the brain, and that developing interventions that protect the hippocampal BBB may help to prevent or ameliorate the harmful effects of many insults on memory and cognition.

TRPM4 blocking antibody reduces neuronal excitotoxicity by specifically inhibiting glutamate-induced calcium influx under chronic hypoxia

Excitotoxicity arises from unusually excessive activation of excitatory amino acid receptors such as glutamate receptors. Following an energy crisis, excitotoxicity is a major cause for neuronal death in neurological disorders. Many glutamate antagonists have been examined for their efficacy in mitigating excitotoxicity, but failed to generate beneficial outcome due to their side effects on healthy neurons where glutamate receptors are also blocked. In this study, we found that during chronic hypoxia there is upregulation and activation of a nonselective cation channel TRPM4 that contributes to the depolarized neuronal membrane potential and enhanced glutamate-induced calcium entry. TRPM4 is involved in modulating neuronal membrane excitability and calcium signaling, with a complex and multifaceted role in the brain. Here, we inhibited TRPM4 using a newly developed blocking antibody M4P, which could repolarize the resting membrane potential and ameliorate calcium influx upon glutamate stimulation. Importantly, M4P did not affect the functions of healthy neurons as the activity of TRPM4 channel is not upregulated under normoxia. Using a rat model of chronic hypoxia with both common carotid arteries occluded, we found that M4P treatment could reduce apoptosis in the neurons within the hippocampus, attenuate long-term potentiation impairment and improve the functions of learning and memory in this rat model. With specificity to hypoxic neurons, TRPM4 blocking antibody can be a novel way of controlling excitotoxicity with minimal side effects that are common among direct blockers of glutamate receptors.

The effects of hypoglycemic and alcoholic coma on the blood-brain barrier permeability

In this investigation, the effects of hypoglycemic coma and alcoholic coma on the blood-brain barrier (BBB) permeability have been compared. Female adult Wistar albino rats weighing 180-230 g were divided into three groups: Control group (n=8), Alcoholic Coma Group (n=18), and Hypoglycemic Coma group (n=12). The animals went into coma approximately 3-4 hours after insulin administration and 3-5 minutes after alcohol administration. Evans blue (4mL/kg) was injected intravenously as BBB tracer. It was observed that the alcoholic coma did not significantly increase the BBB permeability in any of the brain regions when compared to control group. Changes in BBB permeability were significantly increased by the hypoglycemic coma in comparison to the control group values (p<0.01). Our findings suggest that hypoglycemic and alcoholic coma have different effects on the BBB permeability depending on the energy metabolism.

Differential receptor-mediated drug targeting to the diseased brain

The brain is not directly accessible for intravenously administered macro- and most small molecular drugs because of the presence of the blood-brain barrier (BBB). In this respect the BBB functions as a physical and metabolic barrier which is presented by the endothelial cells in brain capillaries. In order to overcome the BBB, therapeutic compounds have been targeted to internalizing receptors at the BBB. In this review we summarize the different approaches that have been described in current literature, including the possible difficulties for clinical application. Particularly, we focus on the possible impact of brain diseases on receptor-mediated transport to the BBB/brain and how this may affect various targeting strategies. Moreover, it is our opinion that a differential drug targeting/delivery approach should be applied to treat central nervous system (CNS) diseases that are related to the BBB alone, and for CNS diseases that are related to both the brain and the BBB.

Three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging findings in patients with sudden sensorineural hearing loss

OBJECTIVE

To evaluate the inner ear in sudden sensorineural hearing loss (SNHL) using three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) magnetic resonance imaging (MRI) at 3 Tesla (T).

BACKGROUND

3D-FLAIR MRI has recently been developed to detect high concentrations of protein or hemorrhage. Application of this method to sudden SNHL has not been described.

METHODS

We used 3D-FLAIR at 3 T with and without gadolinium enhancement to evaluate eight patients with sudden SNHL.

RESULTS

In four of eight ears with idiopathic sudden SNHL, high precontrast signals were observed within the inner ear on 3D-FLAIR. The high-signal areas observed on 3D-FLAIR were not detected by T1- or T2-weighted MRI in any of these patients. In one of these four ears, significant gadolinium enhancement was observed on 3D-FLAIR.

CONCLUSION

Half the patients with sudden SNHL examined had high signals in the SNHL-affected ear on 3D-FLAIR at 3 T. High precontrast signals in the inner-ear fluid space may reflect minor hemorrhage, or an increased concentration of protein that had passed through blood vessels with increased permeability, or had originated from disrupted cells in the inner ear. Gadolinium enhancement in one ear suggested the breakdown of the blood-labyrinth barrier. 3D-FLAIR MRI should contribute markedly to the elucidation of pathologic conditions in the inner ears of patients with idiopathic sudden SNHL.

Cerebral microvascular pathology in aging and Alzheimer's disease

The aging of the central nervous system and the development of incapacitating neurological diseases like Alzheimer's disease (AD) are generally associated with a wide range of histological and pathophysiological changes eventually leading to a compromised cognitive status. Although the diverse triggers of the neurodegenerative processes and their interactions are still the topic of extensive debate, the possible contribution of cerebrovascular deficiencies has been vigorously promoted in recent years. Various forms of cerebrovascular insufficiency such as reduced blood supply to the brain or disrupted microvascular integrity in cortical regions may occupy an initiating or intermediate position in the chain of events ending with cognitive failure. When, for example, vasoconstriction takes over a dominating role in the cerebral vessels, the perfusion rate of the brain can considerably decrease causing directly or through structural vascular damage a drop in cerebral glucose utilization. Consequently, cerebral metabolism can suffer a setback leading to neuronal damage and a concomitant suboptimal cognitive capacity. The present review focuses on the microvascular aspects of neurodegenerative processes in aging and AD with special attention to cerebral blood flow, neural metabolic changes and the abnormalities in microvascular ultrastructure. In this context, a few of the specific triggers leading to the prominent cerebrovascular pathology, as well as the potential neurological outcome of the compromised cerebral microvascular system are also going to be touched upon to a certain extent, without aiming at total comprehensiveness. Finally, a set of animal models are going to be presented that are frequently used to uncover the functional relationship between cerebrovascular factors and the damage to neural networks.

Blocking the glycine-binding site of NMDA receptors prevents the progression of ischemic pathology induced by bilateral carotid artery occlusion in spontaneously hypertensive rats

This study was designed to investigate the participation of N-methyl-D-aspartate (NMDA) receptors in the progression of the pathology induced by bilateral carotid artery occlusion (BCAo) in spontaneously hypertensive rats (SHRs). We examined the effects of the selective NMDA receptor glycine-binding site antagonist SM-18400 on the mortality rate, deterioration of neurological signs, and formation of brain edema in the SHR-BCAo model. SM-18400 (15 or 30 mg/kg) was administered via the tail vein immediately and 2 h after BCAo. Neurological signs were monitored continuously for 8 h after BCAo, and the mortality rates were followed for 5 days. All SM-18400-treated animals were still alive 5 h after BCAo, whereas 38% of the animals died in the vehicle-treated group. The mortality rates of the SM-18400-treated groups were still lower than those of the vehicle-treated group 5 days after BCAo. In addition, SM-18400 markedly prevented the deterioration of neurological signs. The water content of the telencephalon and diencephalon/mesencephalon in the vehicle-treated group, measured 3 h after BCAo, was significantly higher than in the sham-operated group. SM-18400 significantly inhibited the increase in water content in both regions in a dose-dependent manner. These findings suggest that NMDA receptors participate in the increase in the mortality rate, deterioration of neurological signs, and formation of brain edema following ischemic brain damage in the SHR-BCAo model, and that SM-18400 can prevent ischemic insults.

Tumor necrosis factor alpha expression produces increased blood-brain barrier permeability following temporary focal cerebral ischemia in mice

Alteration of blood-brain barrier (BBB) function occurs in both permanent and temporary cerebral ischemia. Studies in vivo and in vitro have shown that tumor necrosis factor-alpha (TNFalpha) is involved in changes of BBB permeability. However, the relationship between TNFalpha expression and BBB disruption during reperfusion is unclear. The aim of this study is to find the cell source of TNFalpha and to determine the relationship between TNFalpha expression and BBB disruption following temporary focal cerebral ischemia in mice. Adult CD-1 mice received 1 h middle cerebral artery occlusion (MCAO) followed by 2 h, 6 h, 12 h, 24 h, and 48 h of reperfusion. MCAO was achieved using an intraluminal suture technique and reperfusion was performed by the suture withdrawal. Neutralizing monoclonal anti-mouse TNFalpha antibody was administrated intraventricularly immediately after reperfusion. TNFalpha expression was determined by double labeling immunohistochemistry. BBB permeability was determined by albumin immunostaining. TNFalpha immunoreactivity (IR) was observed in the ipsilateral hemisphere from 1 h MCAO with 2 h reperfusion. TNFalpha positive cells included neurons, astrocytes, and ependymal cells. BBB disruption was detected beginning at 6 h reperfusion but was not present at 2 h of reperfusion. The areas of BBB disruption were significantly enlarged at 12 h reperfusion and plateaued at 24 h to 48 h reperfusion. BBB disruptions were significantly attenuated in the anti-TNFalpha antibody treated mice (p<0.05). Our results demonstrate that TNFalpha IR existed in neurons, astrocytes, and ependymal cells during reperfusion. TNFalpha IR following temporary focal cerebral ischemia precedes increased BBB permeability. Treatment with TNFalpha antibody reduces BBB disruption, suggesting TNFalpha may be an important mediator in altering BBB permeability during reperfusion.

Protection against blood-brain barrier disruption in focal cerebral ischemia by the type IV phosphodiesterase inhibitor BBB022: a quantitative study

We examined the effect of BBB022, a type IV phosphodiesterase inhibitor, on blood-brain barrier (BBB) integrity after transient middle cerebral artery occlusion (MCAo) in rats. Male Sprague-Dawley rats were anesthetized with halothane and subjected to 120 min of temporary MCAo by retrograde intraluminal insertion of a nylon suture coated with poly-L-lysine. The drug (BBB022 in saline, 1 mg kg-1 h-1, i.v.) or vehicle (0.9% saline, 1-2 ml kg-1 h-1) was administered by infusion after the onset of MCAo. Four animal groups were studied: Groups A and B were treated by infusion of vehicle or drug over 5 h, and groups C and D over 48 h. Damage to the BBB was judged by extravasation of Evans blue (EB) dye, which was administered i.v. at 3 h after the onset of MCAo in groups A and B; and at 46 h in groups C and D. Fluorometric quantitation of EB was performed 1 or 2 h later in six brain regions. In the 5-h infusion series (group B), BBB022 decreased dye extravasation in the ipsilateral cortex, striatum and hemisphere (hemisphere mean+/-S.E.M. : 41.2+/-5.4 vs. 82.4+/-9.2 microg/g, p=0.005) compared to the vehicle-treated group (A). The 48-h infusion of BBB022 (group D) also decreased dye extravasation in the ipsilateral cortex (7.4+/-2. 5 vs. 29.0+/-8.3 microg/g, p=0.05), striatum (17.2+/-2.2 vs. 50. 8+/-12.1 microg/g, p=0.03) and hemisphere (30.7+/-4.0 vs. 93.2+/-18 microg/g, p=0.01) compared to the vehicle-treated group (C). BBB022 also significantly improved the neurological score at 3 and 5 h after MCAo (in the 5-h infusion group) and at 60 min, 24 h and 48 h (in the 48-h infusion group) compared to the vehicle groups. These data indicate that BBB022 prevents ischemic damage to the BBB after focal cerebral ischemia in rats.

Quantitative evaluation of blood-brain barrier permeability following middle cerebral artery occlusion in rats

A sensitive quantitative fluorescence method was used to explore the time course and regional pattern of blood-brain barrier (BBB) opening after transient middle cerebral artery occlusion (MCAo). Male Sprague-Dawley rats were anesthetized with halothane and subjected to 2 h of temporary MCAo by retrograde insertion of an intraluminal nylon suture, coated with poly-L-lysine, through the external carotid artery into the internal carotid artery and MCA. Damage to the BBB was judged by extravasation of Evans Blue (EB) dye, which was administered either 2, 3, 24 or 48 h after onset of MCAo. Fluorometric quantitation of EB was performed 1 or 2 h later in six brain regions. Cerebral infarction volumes were quantitated from histopathological material at 72 h. EB extravasation first became grossly visible in the ipsilateral caudoputamen and neocortex following 3 h of MCAo, was grossly unapparent at 24-26 h, and was maximal at 48-50 h. Fluorescence quantitation confirmed that BBB opening was absent at 2-3 h but present at all later times. In the hemisphere ipsilateral to MCAo, a 179% mean increase in extravasation of EB (compared to sham rats) was measured at 4 h, 407% at 5 h, 311% at 26 h and 264% at 50 h. (in each case, P < 0.05 vs. sham). The volume of infarcted tissue at 72 h in this model was 163.6 +/- 7.7 mm3. Our results indicate that an initial, acute disruption of the BBB occurs between 3 and 5 h following MCAo, and that a later, more widespread increase in regional BBB permeability is present at 48 h. Regional measurement of Evans Blue extravasation offers a precise means of quantitating BBB disruption in focal cerebral ischemia; this method will be of considerable utility in assessing the BBB-protective properties of pharmacological agents.

Post-ischemic administration of HU-211, a novel non-competitive NMDA antagonist, protects against blood-brain barrier disruption in photochemical cortical infarction in rats: a quantitative study

We examined the effect of HU-211, a synthetic non-psychotropic cannabinoid with non-competitive N-methyl-D-aspartate (NMDA) antagonist properties, on blood-brain barrier (BBB) integrity after photochemically induced cortical infarction. Evans blue dye was used as a BBB permeability indicator after unilateral thrombotic cortical infarction was produced photochemically by 560 nm light irradiation of the cortex in male Wistar rats receiving rose bengal intravenously. HU-211 was injected in a dose of 4 mg/kg i.v. 30 min after stroke. Fluorometric measurement of Evans blue was performed 24 h later in six brain regions. Treatment with HU-211 significantly decreased extravasation of dye into the area of infarct (406 +/- 19 vs. 539 +/- 33 micrograms/g, mean +/- S.E.M.) as well as other sites of the affected hemisphere (866 +/- 68 vs. 1096 +/- 68 micrograms/g) compared to the vehicle group. These data indicate that HU-211 is an effective drug in protecting against the effects of focal ischemia-induced BBB disruption in the rat and suggest that the drug may be an effective treatment against the ischemic cell death and BBB disruption that can occur clinically following a stroke or cardiac arrest.

Neuropathological changes following occlusion of the superior sagittal sinus and cerebral veins in the cat

Superior sagittal sinuses (SSS) of 36 mongrel cats were occluded by polymer injection. Immediately prior to the occlusion, Evans-blue (EB) was administered intravenously. The cats were killed 1,3,6,12,24,72 and 120 h after sinus occlusion. Two sham-operated cats were killed 6 h and two 120 h after the operation. In 16 cats in which the occlusion was limited to the SSS, as well as in the sham-operated cats, no EB extravasation was present. However, ultrastructurally in two animals, the extracellular spaces were moderately enlarged, corresponding to increased permeability for water without opening of the BBB for proteins. In 20 cats in which cortical veins were occluded, in addition to the SSS, EB was extravasated. In nine of these cats, which had moderate oedema, EB-staining was present only in the cortex. In 11 cats with severe oedema, massive EB was extravasated. In nine of these cats, which had moderate oedema, EB-staining was present only in the cortex. In 11 cats with severe oedema, massive EB extravasation was observed also in the white matter. The U-fibre layer was free of EB, suggesting that the extension of oedema was blocked by this zone. Cats with severe oedema showed extensive haemorrhagic cerebral infarction widely, but not completely, overlapping with ischaemic necrosis, and corresponding to the differences in the territories of arterial supply and of venous drainage. Seven animals displayed haematomas in the parasagittal white matter. Electron microscopy (EM) showed damage to the endothelium of capillaries and venules with extravasation of platelets. In cats which survived longer than 24 h, the extracellular spaces were filled with proteinaceous transudate.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of ischemic and postischemic damage to brain metabolism and circulation by a novel Ca2+ channel antagonist, NC-1100, in spontaneously hypertensive rats

We investigated the effect of a newly synthesized Ca2+ channel antagonist, NC-1100, on cerebral blood flow (CBF) and metabolism in spontaneously hypertensive rats. The rats received a bolus injection of 0.2 or 1.0 mg/kg NC-1100 i.v. and 1-h cerebral ischemia was then induced by bilateral carotid artery occlusion (group 1). The rats in group 2 were continuously infused with NC-1100 0.03 or 0.1 mg/kg per min, starting immediately after bilateral carotid artery occlusion, for the 1 h of ischemia and following 3-h recirculation. Group 1: during ischemia, CBF in all rats decreased to 6-8% of the resting values. At 1 h cerebral ischemia, brain tissue lactate increased 11.5-, 10.1- and 9.8-fold of the normal control given vehicle or NC-1100, 0.2 and 1.0 mg/kg, respectively. The ATP levels were better preserved by NC-1100 administration; 0.61 +/- 0.04 (mean +/- S.E.M.), 0.80 +/- 0.09 and 0.97 +/- 0.14 mmol/kg (P < 0.05 vs. vehicle), respectively. Group 2: during recirculation, CBF in NC-1100-treated rats returned to 83-90% of the resting values, but to only 65% in the vehicle group. Postischemic brain lactate at 3 h was less well preserved and ATP was dose dependently better preserved in NC-1100- than vehicle-treated rats. It is considered that pre- as well as postischemic administration of a Ca2+ channel antagonist, NC-1100, is beneficial to attenuate and also ameliorate the metabolic and circulatory derangement in the ischemic brain.