Intraventricular infusion of N-methyl-D-aspartate. 1. Acute blood-brain barrier consequences

Increased blood-brain barrier permeability in mammalian brain 7 days after exposure to the radiation from a GSM-900 mobile phone

Microwaves were for the first time produced by humans in 1886 when radio waves were broadcasted and received. Until then microwaves had only existed as a part of the cosmic background radiation since the birth of universe. By the following utilization of microwaves in telegraph communication, radars, television and above all, in the modern mobile phone technology, mankind is today exposed to microwaves at a level up to 10(20) times the original background radiation since the birth of universe. Our group has earlier shown that the electromagnetic radiation emitted by mobile phones alters the permeability of the blood-brain barrier (BBB), resulting in albumin extravasation immediately and 14 days after 2h of exposure. In the background section of this report, we present a thorough review of the literature on the demonstrated effects (or lack of effects) of microwave exposure upon the BBB. Furthermore, we have continued our own studies by investigating the effects of GSM mobile phone radiation upon the blood-brain barrier permeability of rats 7 days after one occasion of 2h of exposure. Forty-eight rats were exposed in TEM-cells for 2h at non-thermal specific absorption rates (SARs) of 0mW/kg, 0.12mW/kg, 1.2mW/kg, 12mW/kg and 120mW/kg. Albumin extravasation over the BBB, neuronal albumin uptake and neuronal damage were assessed. Albumin extravasation was enhanced in the mobile phone exposed rats as compared to sham controls after this 7-day recovery period (Fisher's exact probability test, p=0.04 and Kruskal-Wallis, p=0.012), at the SAR-value of 12mW/kg (Mann-Whitney, p=0.007) and with a trend of increased albumin extravasation also at the SAR-values of 0.12mW/kg and 120mW/kg. There was a low, but significant correlation between the exposure level (SAR-value) and occurrence of focal albumin extravasation (r(s)=0.33; p=0.04). The present findings are in agreement with our earlier studies where we have seen increased BBB permeability immediately and 14 days after exposure. We here discuss the present findings as well as the previous results of altered BBB permeability from our and other laboratories.

Drug therapies for stroke and traumatic brain injury often display U-shaped dose responses: occurrence, mechanisms, and clinical implications

This article explores the occurrence of U-shaped dose responses induced by neuroprotective agents in animal stroke and traumatic brain injury (TBI) screening/preclinical studies. The assessment was stimulated by suggestions that U-shaped dose responses may be common for neuroprotective agents in stroke and TBI models, and its lack of both recognition and understanding may be a factor contributing to the failure of many promising drugs to be protective in clinical trials. Over 30 agents with neuroprotective properties in animal stroke/TBI models were identified that act via U-shaped dose responses in a broad range of experimental protocols. These findings suggest that U-shaped dose responses in animal stroke/TBI models may be a general occurrence and have significant implications for drug discovery, drug development, and clinical practice.

Cerebromicrovascular endothelial cells are resistant to L-glutamate

Cerebral microvascular endothelial cells (CMVECs) have recently been implicated as targets of excitotoxic injury by l-glutamate (l-glut) or N-methyl-d-aspartate (NMDA) in vitro. However, high levels of l-glut do not compromise the function of the blood-brain barrier in vivo. We sought to determine whether primary cultures of rat and piglet CMVECs or cerebral microvascular pericytes (CMVPCs) are indeed sensitive to l-glut or NMDA. Viability was unaffected by 8-h exposure to 1-10 mM l-glut or NMDA in CMVECs or CMVPCs isolated from both species. Furthermore, neither 1 mM l-glut nor NMDA augmented cell death induced by 12-h oxygen-glucose deprivation in rat CMVECs or by 8-h medium withdrawal in CMVPCs. Additionally, transendothelial electrical resistance of rat CMVEC-astrocyte cocultures or piglet CMVEC cultures were not compromised by up to 24-h exposure to 1 mM l-glut or NMDA. The Ca(2+) ionophore calcimycin (5 microM), but not l-glut (1 mM), increased intracellular Ca(2+) levels in rat CMVECs and CMVPCs assessed with fluo-4 AM fluorescence and confocal microscopy. CMVEC-dependent pial arteriolar vasodilation to hypercapnia and bradykinin was unaffected by intracarotid infusion of l-glut in anesthetized piglets by closed cranial window/intravital microscopy. We conclude that cerebral microvascular cells are insensitive and resistant to glutamatergic stimuli in accordance with their in vivo role as regulators of potentially neurotoxic amino acids across the blood-brain barrier.

NMDA receptor antagonist felbamate reduces behavioral deficits and blood-brain barrier permeability changes after experimental subarachnoid hemorrhage in the rat

Increased levels of glutamate and aspartate have been detected after subarachnoid hemorrhage (SAH) that correlate with neurological status. The NMDA receptor antagonist felbamate (FBM; 2-phenyl-1,3-propanediol dicarbamate) is an anti-epileptic drug that elicits neuroprotective effects in different experimental models of hypoxia-ischemia. The aim of this dose-response study was to evaluate the effect of FBM after experimental SAH in rats on (1) behavioral deficits (employing a battery of assessment tasks days 1-5 post-injury) and (2) blood-brain barrier (BBB) permeability changes (quantifying microvascular alterations according to the extravasation of protein-bound Evans Blue by a spectrophotofluorimetric technique 2 days post-injury). Animals were injected with 400 muL of autologous blood into the cisterna magna. Within 5 min, rats received daily oral administration of FBM (15, 30, or 45 mg/kg) for 2 or 5 days. Results were compared with sham-injured controls treated with oral saline or FBM (15, 30, or 45 mg/kg). FBM administration significantly ameliorated SAH-related changes in Beam Balance scores on days 1 and 2 and Beam Balance time on days 1-3, Beam Walking performance on days 1 and 2, and Body Weight on days 3-5. FBM also decreased BBB permeability changes in frontal, temporal, parietal, occipital, and cerebellar cortices; subcortical and cerebellar gray matter; and brainstem. This study demonstrates that, in terms of behavioral and microvascular effects, FBM is beneficial in a dose-dependent manner after experimental SAH in rats. These results reinforce the concept that NMDA excitotoxicity is involved in the cerebral dysfunction that follows SAH.

Neurodegeneration in striatum induced by the mitochondrial toxin 3-nitropropionic acid: role of matrix metalloproteinase-9 in early blood-brain barrier disruption?

Blood-brain barrier (BBB) dysfunction is a potential mechanism involved in progressive striatal damage induced by the mitochondrial excitotoxin, 3-nitropropionic acid (3-NP). After activation by proteases and free radicals, matrix metalloproteinases (MMPs), particularly MMP-9 and -2, can digest the endothelial basal lamina leading to BBB opening. Using CD-1 mice, we show that MMP-9 expression by zymography is increased in the injured striatum compared with the contralateral striatum 2 hr after 3-NP injection [133.50 +/- 57.17 vs 50.25 +/- 13.56; mean +/- SD of optical densities in arbitrary units (A.U.); p < 0.005] and remains elevated until 24 hr (179.33 +/- 78.24 A.U.). After 4 hr, MMP-9 expression and activation are accompanied by an increase in BBB permeability. MMP inhibition attenuates BBB disruption, swelling, and lesion volume compared with vehicle-treated controls. There is a clear spatial relationship between MMP-9 expression and oxidized hydroethidine, indicating reactive oxygen species (ROS) production. Furthermore, transgenic mice that overexpress copper/zinc-superoxide dismutase (SOD1) show decreased lesion size and edema along with decreased immunoreactivity for MMP-9, compared with wild-type littermates (lesion: 38.8 +/- 15.1 and 53.3 +/- 10.3, respectively, p < or = 0.05; edema: 21.8 +/- 11.2 and 35.28 +/- 11, respectively, p < or = 0.05; MMP-9-positive cells: 352 +/- 57 and 510 +/- 45, respectively, p < or = 0.005), whereas knock-out mice deficient in SOD1 display significantly greater swelling (48.65 +/- 17; p < or = 0.05). We conclude that early expression and activation of MMP-9 by ROS may be involved in early BBB disruption and progressive striatal damage after 3-NP treatment.

Increased severity of stroke in CB1 cannabinoid receptor knock-out mice

Endogenous cannabinoid signaling pathways have been implicated in protection of the brain from hypoxia, ischemia, and trauma, but the mechanism for these protective effects is uncertain. We found that in CB1 cannabinoid receptor knock-out mice, mortality from permanent focal cerebral ischemia was increased, infarct size and neurological deficits after transient focal cerebral ischemia were more severe, cerebral blood flow in the ischemic penumbra during reperfusion was reduced, and NMDA neurotoxicity was increased compared with wild-type littermates. These findings indicate that endogenous cannabinoid signaling pathways protect mice from ischemic stroke by a mechanism that involves CB1 receptors, and suggest that both blood vessels and neurons may be targets of this protective effect.

Modulation of blood-brain barrier dysfunction and neurological deficits during acute experimental allergic encephalomyelitis by the N-methyl-D-aspartate receptor antagonist memantine

Previous studies by us have strongly indicated a role for the N-methyl-D-aspartate (NMDA) receptor in the pathogenesis of experimental allergic encephalomyelitis (EAE) and, moreover, the loss of blood-brain barrier (BBB) integrity implicit in the disease. The current investigation has used the NMDA receptor antagonist memantine to modify the neurological course of EAE and, in particular, prevent BBB breakdown. Memantine was administered orally either semiprophylactically, from day 7 postinoculation (PI), or therapeutically, 10 to 11 days PI. Semiprophylactic administration of drug at 60 mg/kg b.wt. significantly restored BBB integrity, reduced symptoms, and limited inflammatory lesions (p < 0.05), when assessed 12 days PI. Higher concentrations of memantine did not notably advance disease improvements observed at 60 mg/kg b.wt., and 40-mg/kg b.wt. doses only reduced histological scores (p < 0.05). Therapeutic application of memantine was found to be as effective as semiprophylactic dosing. Administration of drug at 60 mg/kg b.wt. was demonstrated as the optimum dose, significantly reducing disease, BBB permeability, and lesions (p < 0.01). Extended studies revealed that, after cessation of memantine treatment using either dosing regime, any subsequent appearance of disease was suppressed in severity and duration. We have provided further strong evidence in support of a role for the NMDA receptor in the development of EAE and, in particular, the loss of BBB function and recruitment of inflammatory cells. Moreover, memantine is therapeutically efficacious, suggesting the NMDA receptor as a viable pharmacological target for future treatment of human neurological conditions such as multiple sclerosis.

Stress-induced increase in extracellular sucrose space in rats is mediated by nitric oxide

Exposure to physical or psychological stress causes brain damage ranging from minimal behavioural alterations to neurodegeneration. One of the proposed mechanisms for stress-induced neurodegeneration is the overproduction of nitric oxide (NO) and related oxidative-nitrosative compounds via expression of the inducible NO synthase (iNOS). In the present investigation, the effect of acute or chronic immobilisation on blood-brain barrier (BBB) permeability and the possible role of iNOS were studied in adult male Wistar rats. Stress-induced [(14)C]-sucrose uptake by brain tissue correlates with the production of the stable NO metabolites nitrite and nitrate in both peripheral (plasma) and central (brain) compartments. Injection of the specific iNOS inhibitor 1400W (2 mg/kg, i.p.) prevents the stress-induced increase in BBB permeability. Taken together, these findings indicate that iNOS expression mediates stress-induced increase in BBB permeability and support a possible neuroprotective role for specific iNOS inhibitors in this situation.

The cytosolic antioxidant, copper/zinc superoxide dismutase, attenuates blood-brain barrier disruption and oxidative cellular injury after photothrombotic cortical ischemia in mice

Oxidative stress has been associated with the development of blood-brain barrier disruption and cellular injury after ischemia. The cytosolic antioxidant, copper/zinc superoxide dismutase, has been shown to protect against blood-brain barrier disruption and infarction after cerebral ischemia-reperfusion. However, it is not clear whether copper/zinc superoxide dismutase can protect against evolving ischemic lesions after thromboembolic cortical ischemia. In this study, the photothrombotic ischemia model, which is physiologically similar to thromboembolic stroke, was used to develop cortical ischemia. Blood-brain barrier disruption and oxidative cellular damage were investigated in transgenic mice that overexpress copper/zinc superoxide dismutase and in littermate wild-type mice after photothrombotic ischemia, which was induced by both injection of erythrosin B (30 mg/kg) and irradiation using a helium neon laser for 3 min. Free radical production, particularly superoxide, was increased in the lesioned cortex as early as 4 h after ischemia using hydroethidine in situ detection. The transgenic mice showed a prominent decrease in oxidative stress compared with the wild-type mice. Blood-brain barrier disruption, evidenced by quantitation of Evans Blue leakage, occurred 1 h after ischemia and gradually increased up to 24 h. Compared with the wild-type mice, the transgenic mice showed less blood-brain barrier disruption, a decrease in oxidative DNA damage using 8-hydroxyguanosine immunohistochemistry, a subsequent decrease in DNA fragmentation using the in situ nick-end labeling technique, and decreased infarct volume after ischemia. From these results we suggest that superoxide anion radical is an important factor in blood-brain barrier disruption and oxidative cellular injury, and that copper/zinc superoxide dismutase could protect against the evolving infarction after thromboembolic cortical ischemia.

Magnesium sulfate attenuates increased blood-brain barrier permeability during insulin-induced hypoglycemia in rats

Magnesium probably protects brain tissue against the effects of cerebral ischemia, brain injury and stroke through its actions as a calcium antagonist and inhibitor of excitatory amino acids. The effects of magnesium sulfate on cerebrovascular permeability to a dye, Evans blue, were studied during insulin-induced hypoglycemia with hypothermia in rats. Hypoglycemia was induced by an intramuscular injection of insulin. After giving insulin, each animal received MgSO4 (270 mg/kg) ip, followed by a 27 mg/kg dose every 20 min for 2.5 h. Plasma glucose and Mg2+ levels of animals were measured. Magnesium concentrations increased in the serum following MgSO4 administration (6.05 ± 0.57 vs. 2.58 ± 0.14 mg/dL in the Mg2+ group, and 7.14 ± 0.42 vs. 2.78 ± 0.06 mg/dL in the insulin + Mg2+ group, P < 0.01). Plasma glucose levels decreased following hypoglycemia (4 ± 0.66 vs. 118 ± 2.23 mg/dL in the insulin group, and 7 ± 1.59 vs. 118 ± 4.84 mg/dL in the insulin + Mg2+ group, P < 0.01). Blood-brain barrier permeability to Evans blue considerably increased in hypoglycemic rats (P < 0.01). In contrast, blood-brain barrier permeability to Evans blue was significantly reduced in treatment of hypoglycemic rats with MgSO4 (P < 0.01). These results indicate that Mg2+ greatly reduced the passage of exogenous vascular tracer bound to albumin into the brain during hypoglycemia with hypothermia. Mg2+ could have protective effects on blood-brain barrier permeability against insulin-induced hypoglycemia.Key words: blood-brain barrier, hypoglycemia, Mg2+, Evans-blue.

Age-specific N-methyl-D-aspartate-induced seizures: perspectives for the West syndrome model

PURPOSE

With intraperitoneal N-methyl-D-aspartate (NMDA; 15-200 mg/kg) administration, we attempted to develop an animal model of age-specific West syndrome to serve for testing of putative anticonvulsant drugs and to determine the mechanisms of this disorder.

METHODS

Experiments were performed in 12-, 18-, and 60-day-old (adult) rats. The effects of systemic pretreatment with hydrocortisone (5-25 mg/kg), pyridoxine (20-250 mg/kg), and sodium valproate (VPA; 200 and 400 mg/kg) against the NMDA-induced automatisms, emprosthotonic (hyperflexion), and clonic-tonic seizures were determined. NMDA-induced EEG changes and alterations of the performance in horizontal bar, rotorod, open field, and elevated plus-maze tests were recorded.

RESULTS

In young rats, hydrocortisone had proconvulsant effects. High doses of pyridoxine induced epileptiform activity independent of and distinct from that induced by NMDA. Only VPA had moderate effects against the NMDA-induced syndrome. EEG consisted of periods of suppression mixed with ictal activity of serrated waves and high-voltage chaotic EEG activity. In adult rats, EEG alterations involved spike and spike-and-wave activity. NMDA also deteriorated performance of young rats in the open field, rotorod, and elevated plus maze tests.

CONCLUSIONS

NMDA syndrome in rats fulfills some, but not all, criteria of the West syndrome model, such as occurrence of flexion seizures, nonspecific diffuse EEG changes, refractoriness to antiepileptic therapy (but a response to VPA), as well as long-term alteration of behavioral tasks. However, NMDA-induced seizures represent an acute model without the occurrence of spontaneous seizures, whereas in the clinical situation, both the seizures and neurologic deterioration are chronic. Further, in the West syndrome and the NMDA seizure model, there is an incongruent response to therapy with antiepileptic drugs.

Neutrophils do not mediate blood-brain barrier permeability early after controlled cortical impact in rats

Controlled cortical impact (CCI) produces blood-brain barrier (BBB) permeability and an acute inflammatory response in injured brain, associated with upregulation of cell adhesion molecules and accumulation of neutrophils. Nevertheless, the role of acute inflammation in the pathogenesis of BBB permeability after traumatic brain injury (TBI) is undefined. The purpose of this study was to examine the time course of acute inflammation and BBB permeability after CCI in rats and to determine the effect of neutrophil depletion on BBB permeability early after CCI. In the first protocol, four groups of rats (n = 4-7/group) were subjected to CCI. Expression of endothelial (E)-selectin on cerebrovascular endothelium, accumulation of neutrophils, and BBB permeability were measured in brain at 1, 4, 8, and 24 hours after injury by immunohistochemistry or spectrophotometric quantification of Evans blue. E-selectin upregulation and neutrophil accumulation in injured brain occurred at later times than maximal BBB permeability. In a second protocol, rats made neutropenic with a murine monoclonal IgM antibody (RP-3) specific for rat neutrophils were subjected to CCI, given Evans blue at 3.5 hours, and sacrificed at 4 hours after injury. Neutrophil depletion did not affect BBB permeability at 4 hours after CCI. We conclude that events other than those mediated by neutrophils initiate BBB permeability early after CCI.

Potent ς 1 -Receptor Ligand 4-Phenyl-1-(4-Phenylbutyl) Piperidine Modulates Basal and N -Methyl- d -Aspartate–Evoked Nitric Oxide Production In Vivo

Background and Purpose —ς-Receptor ligands ameliorate ischemic neuronal injury and modulate neuronal responses to N -methyl- d -aspartate (NMDA) receptor stimulation. Because NMDA-evoked synthesis of nitric oxide (NO) may play an important role in excitotoxic-mediated injury, we tested the hypothesis that ς-receptor ligands attenuate basal and NMDA-evoked NO production in the striatum in vivo.

Methods —Microdialysis probes were placed bilaterally into the striatum of halothane-anesthetized adult Wistar rats. Rats were divided into 7 treatment groups and perfused with artificial cerebrospinal fluid (aCSF) containing 3 μmol/L [ 14 C] l -arginine for 2 to 3 hours followed by NMDA in various combinations with the following drugs: l -nitroarginine (L-NNA); the ς 1 -receptor ligand 4-phenyl-1-(4-phenylbutyl) piperidine (PPBP); the selective ς 1 -receptor antagonist 1-(cyclopropylmethyl)-4-(2′-oxoethyl) piperidine hydrobromide (DuP 734); and the noncompetitive NMDA receptor blocker MK-801 in aCSF. Right-left differences between [ 14 C] l -citrulline in the effluent from rats treated with different drug combinations were assumed to reflect differences in NO production.

Results —After a 3-hour loading period with [ 14 C] l -arginine, addition of 1 mmol/L NMDA increased [ 14 C] l -citrulline recovery compared with aCSF alone. This NMDA-evoked increase was inhibited by 1 mmol/L of L-NNA and PPBP. Perfusion of 1 mmol/L of the ς 1 -receptor antagonist DuP 734 with 1 mmol/L PPBP augmented NMDA-evoked [ 14 C] l -citrulline recovery compared with perfusion with PPBP and NMDA. MK-801 attenuated the basal as well as NMDA-evoked [ 14 C] l -citrulline recovery. PPBP did not cause any further attenuation in the basal and NMDA-evoked [ 14 C] l -citrulline recovery in the presence of MK-801.

Conclusions —These data indicate that a ς 1 -receptor ligand attenuates basal as well as NMDA-evoked NO production. Because the attenuated NO production was reversed by DuP 734, PPBP appears to act as an agonist at the ς 1 -receptor. Attenuated NO production by ς 1 -receptor agonists provides one possible mechanism for focal ischemic neuroprotection.

Tirilazad widens the therapeutic window for riluzole-induced attenuation of progressive cortical degeneration in an infant rat model of the shaken baby syndrome

Our infant rat model of traumatic subarchnoid hemorrhage combines violent shaking and hypoxia to produce subdural hemorrhaging and progressive cortical degeneration similar to that seen in victims of the shaken baby syndrome. Anesthetized, 6-day-old male rats were subjected to one episode of shaking under hypoxic conditions. Brain histologies revealed moderate-to-severe cortical hemorrhaging at 48 h postinjury and progressive cortical degeneration, as indicated by a 15.3% and 20.2% reduction in cortical wet weight, at 7 and 14 days postinjury, respectively. The purpose of the present study was to assess the effects of two antioxidant lipid peroxidation inhibitors (tirilazad mesylate and PNU-101033E), and the glutamate release inhibitor (riluzole), upon the brain pathology seen in this model. A significant, 54.3-75.3%, reduction in cortical hemorrhaging was observed in rats that were treated with a total of three doses of tirilazad (10 mg/kg, i.p.): 10 min before or 5-30 min after injury, and again at 2 and 24 h postinjury (p < 0.01 vs. vehicle). However, treatment with tirilazad or the more potent, brain-penetrating pyrrolopyrimidine, PNU-101033E (10 min before plus 2, 24, 48, and 72 h after), did not attenuate the progressive cortical degeneration typically seen at 14 days postinjury. These results suggest that free radicals play an important role in the pathophysiology of secondary brain hemorrhaging due to shaking + hypoxia, but may not be critical in the mediation of the subsequent neurodegeneration. Rather, glutamate neurotoxicity may be a key factor here. This is suggested by our observation that the glutamate release inhibitor, riluzole, significantly reduced cortical degeneration when it was administered up to 1 h postinjury in the present model. Specifically, the cortical wet weights of rats treated with 8 mg/kg riluzole (i.p.) 10 min before or 1 h after shaking + hypoxia (and again at 24 h postinjury) were 95.3% and 97.4% of noninjured controls, respectively, at 14 days postinjury (p < 0.02 vs. vehicle). Riluzole treatment beyond 1 h (e.g., 2 or 4 h postinjury) did not reduce the neurodegeneration. Lastly, we attempted to demonstrate that the therapeutic window for riluzole-induced attenuation of cortical degeneration could be extended beyond 1 h through the use of combination therapy. In this experiment, rat pups were treated with 10 mg/kg tirilazad (i.p.) at 30 min postinjury followed by 8 mg/kg riluzole (i.p.) at 4 and 24 h postinjury. At 14 days postinjury, the cortical wet weights of these rats were 94.5% of noninjured controls, thus demonstrating significant neuroprotection (p < 0.05 vs. vehicle) and a widening of the therapeutic window from 1 to 4 h in length. These results suggest that early attenuation of free radical-induced lipid peroxidation may slow down the biochemical cascade of events related to glutamate-induced excitotoxicity and, in doing so, prolong the time during which a glutamate release inhibitor, such as riluzole, is effective.

Neurodegeneration induced by reversed microdialysis of NMDA; a quantitative model for excitotoxicity in vivo

This study characterizes a quantifiable in vivo model of excitotoxicity. In halothane anesthetized rats, microdialysis probe was implanted into somatosensory cortex/striatum and perfused by various concentrations (1, 10, 50 and 100 mmol/l) of N-methyl-d-aspartate (NMDA) for 20 min. After 24 h, histological quantification confirmed that NMDA produced a concentration-dependent excitotoxic lesion. With 10 mmol/l NMDA, coadministration of magnesium reduced significantly, and 2-amino-5-phosphonovalerate blocked completely the development of excitotoxic injury.

Changes in blood-brain barrier permeability following neurotoxic lesions of rat brain can be visualised with trypan blue

A simple method for measuring changes in blood-brain barrier (BBB) permeability following neurotoxic lesions is described. In the brains of animals perfused transcardially with a trypan blue solution at the time of sacrifice, the presence of trypan blue staining correlated with changes in BBB function seen with more traditional markers, such as albumin staining. Thus, trypan blue appears to be useful as a marker for changes in BBB permeability. We have used this method to show increases in BBB permeability in striatal lesions induced by three different neurotoxins: chronic systemic injection of 3-nitropropionic acid (3-NP) and intrastriatal injection of either quinolinic or kainic acid. Trypan blue staining was seen in all three types of lesion, with both the neuropil and some neurones being stained. In the kainic acid lesioned animals, trypan blue also stained hippocampal and cortical neurones which are known to degenerate. Our findings suggest that trypan blue makes a more sensitive marker than albumin for both BBB integrity changes and degenerating neurones. Furthermore, this method has the advantages over others of being quick, economic and compatible with most subsequent histological and immunocytochemical staining.

Biochemical characteristics of gamma-glutamyl transpeptidase in capillaries from entorhinohippocampal complex of quinolinate-lesioned rat brain

Quinolinic acid (QUIN) is an endogenous excitotoxic agonist of the N-methyl-D-aspartate (NMDA) type of glutamate receptor, which causes slowly progressing degeneration of vulnerable neurons in some brain regions. Using changes in the activity of membrane-bound gamma-glutamyl transpeptidase (GGT) as a marker of cell damage, we found a significant decrease of this enzyme activity, which was preferentially located in the ipsilateral hippocampal formation and entorhinal cortex, 4 d after the unilateral intracerebroventricular (icv) injection of 0.5 mumol QUIN. The dose of QUIN divided into two half-doses injected bilaterally led to a symmetrical decline of GGT activity in hippocampal areas. The lesion was characterized by a suppression of GGT activity in hippocampal and entorhinal capillaries, corresponding to 60 and 81% of their initial value, respectively, but no significant changes were ascertained in synaptosomal membranes. The changes in the activity of capillary GGT were associated with the decrease of apparent maximal velocity Vmaxapp, whereas apparent Michaelis constant K(m)app (0.69-0.79 mM) remained unaffected. In the nonlesioned brain, concanavalin A (Con A) affinity chromatography revealed five glycoforms of synaptosomal GGT in contrast to only one found in hippocampal and entorhinal capillaries. The results document that neither the saccharide moiety of GGT nor the value of enzyme K(m)app is significantly affected by the QUIN-induced lesion of the rat brain. However, the suppression of GGT activity, which is accompanied by a decrease in the value of Vmaxapp in brain microvessels, may suggest dysfunction of the blood-brain barrier (BBB) in the QUIN-injured rat brain.

Effect of acidotic challenges on local depolarizations evoked by N-methyl-D-aspartate in the rat striatum

We have examined how various challenges to brain acid-base homeostasis, resulting in extracellular acidosis, alter N-methyl-D-aspartate (NMDA)-evoked depolarizations in vivo. Repeated stimuli were produced by perfusion of 200 microM NMDA for 2 min through a microdialysis probe implanted into the striatum of halothane anesthetized rats. Hypercapnia reduced NMDA-evoked responses in a concentration-dependent manner, with 7.5 and 15 % CO2 in the breathing mixture reducing the depolarization amplitude to 74 % and 64 % of that of the initial stimuli, respectively. Application of 50 mM NH4+ progressively reduced dialysate pH, and a further acidification was observed when NH4+ was discontinued. Perfusion of NMDA after NH4+ application evoked smaller depolarizations (56 % of the corresponding control, 5 min after NH4+ removal), and this effect persisted for over 1 h. Perfusion of acidic ACSF did not alter the amplitude of NMDA-evoked depolarization, despite changes in dialysate pH confirming that exchange/buffering of acid equivalents took place between the perfusion medium and the surrounding tissue. This negative result probably reflected the remarkable capacity of the brain to buffer H+. Together, these results demonstrate that extracellular acidosis, such as that associated with excessive neuronal activation or ischemia, inhibits NMDA-evoked responses in vivo.

Glutamate-induced disruption of the blood-brain barrier in rats. Role of nitric oxide

BACKGROUND AND PURPOSE

The first goal of this study was to determine the effect of glutamate on permeability and reactivity of the cerebral microcirculation. The second goal of this study was to determine a possible role for nitric oxide in the effects of glutamate on the cerebral microcirculation.

METHODS

We examined the pial microcirculation in rats with intravital microscopy. Permeability of the blood-brain barrier was quantified by the clearance of fluorescent-labeled dextran (molecular weight, 10 000 D; FITC-dextran-10K) before and during application of glutamate (0.1 and 1.0 mmol/L). In addition, we examined the permeability of the blood-brain barrier during application of a nitric oxide donor, S-nitroso-acetyl-penicillamine (SNAP; 10 mumol/L). Diameter of pial arterioles was measured before and during application of glutamate or SNAP. To determine a potential role for nitric oxide in glutamate-induced effects on the cerebral microcirculation, we examined the effects of NG-monomethyl-L-arginine (10 mumol/L).

RESULTS

In control rats, clearance of FITC-dextran-10K from pial vessels was minimal, and the diameter of pial arterioles remained constant during the experimental period. Topical application of glutamate (0.1 and 1.0 mmol/L) and SNAP (10 mumol/L) produced an increase in clearance of FITC-dextran-10K and in diameter of pial arterioles. In addition, NG-monomethyl-L-arginine (10 mumol) attenuated glutamate-induced increases in permeability of the blood brain barrier and glutamate-induced dilatation of cerebral arterioles.

CONCLUSIONS

The findings of the present study suggest that glutamate, a major neurotransmitter in the brain, increases permeability of the blood-brain barrier to low-molecular-weight molecules and dilates cerebral arterioles via a nitric oxide-dependent mechanism.

Dextrorphan reduces infarct volume, vascular injury, and brain edema after ischemic brain injury

Focal cerebral ischemia confined to the cerebral cortex in the right middle cerebral artery (MCA) territory was induced by temporary ligation of the MCA and both common carotid arteries (CCAs). Reperfusion was initiated by releasing all three arterial occlusions after 90 min of ischemia. Infarct volume was morphometrically measured after triphenyltetrazolium chloride staining 24 h postischemia. Blood-brain barrier breakdown was assessed 4 h postischemia by measuring vascular permeability to fluorescein isothiocyanate-conjugated dextran (FITC-D), a macromolecule tracer. Ischemic brain edema was measured based on percent water content, 24 h postischemia. Dextrorphan (DX) 20-10 mg/kg given ip 15 min before ischemia reduced infarct volume in a dose-dependent manner with an apparent U-shaped dose-response curve; best protection was observed at 30 mg/kg. Posttreatment at 30 min, but not 60 min, was still effective. DX (30 mg/kg, given 15 min before ischemia) also reduced the postischemic increase in vascular permeability and brain edema in the right MCA cortex. Results from this study support the idea that NMDA receptor activation contributes to blood-brain barrier breakdown and brain edema after ischemic insults

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.

Effect of delayed MK-801 (dizocilpine) treatment with or without immediate postischemic hypothermia on chronic neuronal survival after global forebrain ischemia in rats

In contrast to intraischemic hypothermia, immediate postischemic hypothermia (30 degrees C) has been shown to delay but not chronically protect the CA1 hippocampus from transient global forebrain ischemia. The inability of a relatively short postischemic hypothermic period to protect chronically might involve a delayed or secondary injury mechanism. We determined whether delayed treatment with the noncompetitive N-methyl-D-aspartate receptor antagonist MK-801 (dizocilpine), alone or in combination with immediate postischemic hypothermia, would chronically protect histopathologically. Wistar rats underwent 10 min of normothermic forebrain ischemia induced by bilateral common carotid artery occlusion plus hypotension (50 mg Hg). Four ischemia groups were studied after normothermic (37 degrees C) ischemia: no treatment; 3 h of immediate postischemic hypothermia (30 degrees C); delayed MK-801 treatment (4 mg/kg) on postischemic days 3, 5, and 7; and postischemic hypothermia combined with multiple MK-801 treatments. Two months after the ischemic insult, rats were perfusion-fixed for quantitative histopathological assessment. Postischemic hypothermia alone or MK-801 treatment alone failed to protect the CA1 hippocampus chronically. However, immediate postischemic hypothermia combined with delayed MK-801 treatment led to significant increases in normal CA1 neuron counts per microscopic field compared with normothermic ischemia. For example, neuronal counts within the hippocampal CA1 areas were 58 +/- 39 (mean +/- SD) in normothermic ischemic rats compared with 395 +/- 198 in rats treated with postischemic hypothermia and MK-801. Chronic survival also led to pronounced striatal damage. Within the dorsolateral striatum, significant protection was documented with either postischemic hypothermia alone or delayed MK-801 treatment alone.

Effect of remacemide hydrochloride on subarachnoid hemorrhage-induced vasospasm in rabbits

The purpose of this study was to assess the role of an excitatory amino acid (EAA) receptor antagonist (remacemide hydrochloride) in a rabbit model of subarachnoid hemorrhage (SAH)-induced cerebral vasospasm. Cerebral angiograms were performed on 22 rabbits pre-SAH and 72 h post-SAH: 6 rabbits received an injection of mock cerebrospinal fluid (1 ml/kg) into the cisterna magna (group I, the control group); 6 rabbits were subjected to SAH but received no treatment (group II); autologous blood (1 ml/kg) from the central ear artery was injected into the cisterna magna of these rabbits; 6 rabbits were subjected to SAH (1 ml/kg) and treated with intraperitoneal (IP) bolus injections of remacemide hydrochloride (15 mg/kg) every 12 h beginning 30 minutes after SAH (group III); and 4 rabbits were not subjected to SAH but received IP bolus injections of remacemide hydrochloride every 12 h (group IV). Digital subtraction angiography was used to measure the diameter of the basilar artery. At 72 h post-SAH, vasospasm was evident in all untreated rabbits. The diameter of the basilar artery was reduced significantly below pre-SAH levels by 35.3 +/- 5.8% (mean +/- standard error of the mean). Treatment with remacemide hydrochloride significantly ameliorated vasospasm (27.3 +/- 5.4%, p < 0.001). These findings suggest that in this model EAAs may cooperate in the genesis of SAH-induced cerebral vasospasm and that NMDA receptor antagonism with remacemide hydrochloride can partially prevent the SAH-induced vasospasm of a large cerebral artery.

Neurotoxicity of albumin in vivo

The neurotoxicity of albumin was studied in the rat. Solutions of rat albumin (3, 10 and 30 mg/ml) essentially free of fatty acids and globulins were injected into one neostriatum, physiological saline into the other. Injections were also performed with sodium glutamate (10 and 30 mM). Both albumin and glutamate produced lesions in a concentration-dependent manner. Thus 3, 10 and 30 mg/ml albumin produced lesions in excess of saline of 22 +/- 24 microns3, 67 +/- 25 microns3 and 170 +/- 44 microns3, (P = 0.82, 0.03 and 0.0005, respectively). 10 and 30 mM sodium glutamate caused lesions of 45 +/- 14 microns3 and 315 +/- 56 microns3 in excess of saline (P = 0.04 and 0.0004, respectively). Injection of 10 mg/ml albumin together with 10 mM sodium glutamate caused lesions of 70 +/- 11 microns3 in excess of saline (P = 0.005). This was not significantly different from the lesions caused by any of the two substances alone. Thus no potentiating effect of one substance on the toxicity of the other was seen in this study. The neurotoxicity of albumin could be of importance in disease states which are accompanied by leakiness of the blood-brain barrier.

MK-801 and memantine protect cultured neurons from glutamate toxicity induced by glutamate carboxypeptidase-mediated cleavage of methotrexate

Cleavage of methotrexate into glutamate and diaminomethylpteroate by intrathecal glutamate carboxypeptidase is a new approach to the treatment of acute methotrexate neurotoxicity. The simulation of glutamate carboxypeptidase rescue from high-dose methotrexate in neuron astrocyte cocultures of rat cerebellum or cerebral cortex resulted in a selective, concentration-dependent neurotoxicity. The neurotoxicity was caused by the enzymatic release of glutamate from methotrexate at lower concentrations of methotrexate, and by both glutamate and diaminomethylpteroate at concentrations of methotrexate exceeding 200 microM. The good neuroprotection afforded by MK-801 and memantine suggested that glutamate toxicity was mediated by N-methyl-D-aspartate receptors. Methotrexate alone was not toxic to astrocytes, neurons, or the neurite networking. [3H]thymidine and [3H]deoxyuridine incorporation studies showed that astrocyte proliferation in the presence of methotrexate was maintained by the reutilization of pyrimidine bases for DNA synthesis. N-methyl-D-asparate receptor antagonists should be coadministered in future experimental and clinical trials examining intrathecal glutamate carboxypeptidase rescue of methotrexate toxicity.

Interaction between free radicals and excitatory amino acids in the blood-brain barrier disruption after iron injury in the rat

Excitatory amino acids and oxygen free radicals have been reported to cooperate in the genesis of brain injury in vivo and in vitro. In this study, we tested the capacity of a noncompetitive N-methyl-D-aspartate receptor antagonist, MK-801, and a 21-aminosteroid, U-74006F, tirilazad mesylate, to block the opening of the blood-brain barrier after subarachnoid injection of FeCl2, which is believed to cause a primarily "pure" free radical insult. Subarachnoid injection of FeCl2 resulted in a significant 10-fold increase in Evans blue extravasation while sham injection or NaCl injection had no effect. Pretreatment with either MK-801 or U-74006F significantly reduced the FeCl2-induced increase in capillary permeability by 43 and 63%, respectively (p < 0.05). Combined treatment with MK-801 and U-74006F resulted in a 65% reduction in vascular leakage that was not significantly greater than pretreatment with either drug alone. These results show that both excitatory amino acids and free radicals can damage the cerebral microvasculature and that an excitatory amino acid antagonist can partially protect the blood-brain barrier after free radical-induced injury.

Intraventricular infusion of N-methyl-D-aspartate. 2. Acute neuronal consequences

This study documents the ultrastructural features of acute neuronal injury following N-methyl-D-aspartate (NMDA) receptor activation. NMDA (100 nmol/microliters) or vehicle was infused over a 15-min period into the lateral ventricle of adult rats. After perfusion fixation, specimens demonstrating normal and abnormal patterns of vascular permeability to horseradish peroxidase were sampled for ultrastructural analysis. In NMDA-infused rats, brain regions exhibiting protein extravasation contained swollen dendritic profiles and abnormal neuronal perikarya. Although periventricular regions were most severely affected, parenchymal abnormalities were also detected in the cerebral cortex, septum, striatum, thalamus, hypothalamus and cerebellum. Mildly affected dendrites contained dark compact mitochondria, while in severely swollen dendrites mitochondria were enlarged with ruptured cristae. Focal sites of plasma membrane disruption were also detected within swollen dendrites. Swollen neurons commonly displayed peripheral pallor and increased numbers of cytoplasmic vacuoles. Other neurons appeared dark and shrunken, some containing disrupted mitochondria and pyknotic nuclei. Pretreatment with the NMDA antagonist MK-801 (2 mg/kg) attenuated the neuronal and dendritic alterations. In conditions where cerebrospinal fluid levels of glutamate are abnormally elevated, excessive NMDA receptor activation may lead to early vascular and neuronal complications which could work in concert to promote brain injury.