Mediators of blood-brain barrier dysfunction and formation of vasogenic brain edema

Increased ornithine decarboxylase activity and protein level in the cortex following traumatic brain injury in rats

There is increasing evidence that the elevated levels of polyamines play an important role in the secondary injury following traumatic brain injury (TBI). Ornithine decarboxylase (ODC) is the rate-limiting enzyme of polyamine biosynthesis. Presently, we measured the ODC protein levels by Western blot analysis in the cerebral cortex of rats sacrificed at 2 h, 6 h, 24 h, 72 h and 168 h after controlled cortical impact injury. TBI resulted in a significant increase in ODC protein levels (2.5 to 5.5 fold, P<0.05) and enzyme activity (13 to 21 fold, p<0.01) between 2 and 6 h after the injury. ODC protein levels and enzyme activity returned to normal, control levels by 72 h after the injury. Increased ODC protein and enzyme activity could contribute to vasogenic edema and the pathogenesis of neuronal dysfunction after TBI by stimulating the formation of polyamines.

Role of neurochemicals in brain edema and cell changes following hyperthermic brain injury in the rat

The involvement of three potent neurochemical mediators of the edema formation such as serotonin, prostaglandins and opioids in the pathophysiology of hyperthermic brain injury was examined in a rat model using a pharmacological approach. Hyperthermic brain injury was induced in conscious young rats by exposing them to heat stress at 38 degrees C for 4 h. In these rats the blood-brain barrier (BBB) permeability, brain edema, cerebral blood flow (CBF), heat shock protein 72 kD (HSP) response and cell changes were examined. Pretreatment with ketanserin (a serotonin-2 receptor antagonist), indomethacin (prostaglandin synthesis inhibitor) and naloxone (opioid receptor antagonist) in separate groups of rats reduced hyperthermia and HSP response following heat stress and significantly attenuated changes in the BBB permeability, brain edema, CBF and cell reaction. These results suggest that the pathophysiology of hyperthermic brain injury is a complex mechanisms and several neurochemicals are involved in the brain pathology caused by heat stress.

Glioma prostaglandin levels correlate with brain edema

The present study was designed to prospectively investigated the prostaglandin (PG) levels and extent of peritumoral edema in 30 cases of glioma by using methods of radioimmunoassay and imaging. Both TXB2 and 6-keto-PGF1 alpha levels in all glioma groups went up over that in the control group. TXB2 level and ratio of TXB2/6-keto-PGF1 alpha were markedly increased with the extent of tumor malignancy. Water concentration in anaplastic astrocytoma and glioblastoma were significantly elevated. Difference in TXB2 level and TXB2/6-keto-PGF1 alpha ratio among three edema grades were statistically significant. TXB2 level and ratio of TXB2/6-keto-PGF1 alpha were closely correlated with water concentration (r1 = 0.53, r2 = 0.72, P < 0.01). Our findings suggested that the metabolism of PG in glioma were in the state of disorder, and that the imbalance between PGI2 and TXA2 may be one of factors which affect the formation of peritumoral edema.

Intra-arterial administration of carboplatin and the blood brain barrier permeabilizing agent, RMP-7: a toxicologic evaluation in swine

RMP-7 is a bradykinin B2 receptor agonist shown to permeabilize the blood-brain barrier, especially that associated with brain tumors, when administered via both intracarotid and intravenous routes. Both routes of administration are currently being tested in human trials in combination with the chemotherapeutic agent carboplatin as therapy for gliomas. As an essential prerequisite to the initial intracarotid clinical trials, the potential neurotoxicity of intra-arterial administration of RMP-7 (at a high or low dose), alone and in combination with carboplatin, was assessed in anesthetized Red Duroc swine. Five treatment groups were evaluated with each pig receiving a series of alternating, intra-arterial infusions of RMP-7 (or saline) followed by carboplatin (or saline), as follows: (1) vehicle control: saline/saline; (2) carboplatin only control: saline/carboplatin (50 mg total); (3) RMP-7 only control: RMP-7 (750 ng/kg)/saline; (4) low dose combination: RMP-7 (75 ng/kg)/carboplatin (50 mg total); and (5) high dose combination: RMP-7 (750 ng/kg)/carboplatin (50 mg total). For each subject, one of the alternating dosing sequences (above) was repeated four times during a single dosing session which lasted approximately 40 minutes. Assessments during the in-life phase of the study in the pre- and post-treatment periods consisted of heart rate, arterial blood pressure (systolic, diastolic, and mean), blood gases, body weight, general clinical observations (including evaluation for neurological deficit) and clinical pathology (including a comprehensive battery of standard blood coagulation, hematological and serum chemistry tests). In addition, during the time of treatment, heart rate and arterial blood pressure were monitored. The animals were terminated two weeks after dosing and the brain and rete mirabile (distal to site of infusion) were evaluated for gross and histopathological abnormalities. The histopathology analysis included a reader-blinded analysis using low and high power light microscopic examination of both H&E and Kluver-Berrera stained sections through several key cortical and subcortical brain regions. Transient decreases in arterial blood pressure (mean of 10-25 mmHg) were observed in both groups receiving the high dose of RMP-7 (i.e., 750 ng/kg). No other side effects attributable to RMP-7 and/or carboplatin were observed, and clinical observations revealed no evidence of neurologic deficits. Post-mortem examination revealed no evidence of CNS or cerebral vascular pathology attributable to carboplatin and RMP-7. This study demonstrates that intracarotid administration of the maximum tolerated dose of RMP-7 (750 ng/kg) alone, or in combination with carboplatin (50 mg) is not accompanied by any serious adverse effect, apparent cerebrovascular abnormality or neuropathologic consequence and offers further evidence for the safety of this novel therapeutic approach for enhancing delivery of chemotherapeutics to brain tumors.

Effects of the bile salt sodium deoxycholate, protamine, and inflammatory mediators on the potassium permeability of the frog nerve perineurium

An electrophysiological method was used to measure the potassium permeability (PK) of the perineurium of the sciatic nerve of frogs Rana temporaria and R. pipiens. Isolated but intact nerves were mounted in a grease-gap chamber, and compound action potential and DC potential monitored. Change in the DC potential (delta DC) in response to challenge with 100 mM [K+] Ringer was used to assess the K+ permeability of the perineurium, since change in DC potential under these conditions reflected changes in the axonal resting potential. The permeability of the perineurium was calculated from the published calibration curve relating delta DC to bathing [K+] in desheathed nerves of Abbott et al. (1997). In the control condition, PK was < 1.1 x 10(-6) cm.s-1. The bile salt sodium deoxycholate (DOC, 1-4 mM) caused a dose-dependent increase in PK, which reached a maximum of 1.7 x 10(-5) cm.s-1 after 2-min exposure to 4 mM DOC, but access of K+ to the endoneurial compartment was more restricted after DOC than after desheathing. Protamine phosphate (1 mM) and protamine sulphate (0.1-5 mg/ml equals 0.125-6.25 mM) had no effect on PK. Neither histamine (0.4-40 mg/ml), bradykinin (0.1-5 mg/ml) nor serotonin (5-hydroxytryptamine, 0.1-5 mg/ml) affected PK. The frog nerve perineurium appears to be relatively insensitive to chemical agents and inflammatory mediators, in contrast to the endothelial cells forming the endoneurial blood-nerve barrier and the blood-brain barrier.

Mast cell specific proteases in rat brain: changes in rats with experimental allergic encephalomyelitis

Mast cell populations were identified within brain parenchyma by their specific proteases, using antibodies for immunohistochemistry and ELISAs, and riboprobes were developed for in situ hybridisation. Connective tissue mast cells expressing rat mast cell protease I (RMCPI) mRNA and immunoreactivity were observed in thalamus and showed no degranulation at 3, 8 and 13 days after induction of experimental allergic encephalomyelitis (EAE). Mucosal-like mast cells were clearly demonstrated in control rats by measuring RMCPII and by visualising cells expressing RMCPII mRNA and immunoreactivity. At day 13, but not 3 and 8 post immunisation, the number of RMCPII-expressing cells markedly increased in the EAE-induced group, mainly within brainstem and spinal cord close to inflammed blood vessels. The markers of histaminergic neurons were marginally affected 13 days after immunisation and the increase of [3H] histamine synthesis elicited by the H3-receptor antagonist, thioperamide, was not modified in any region of the brain. It is concluded that the cerebral RMCPII-expressing mast cells could play a role during EAE.

Neuronal cell loss in the CA3 subfield of the hippocampus following cortical contusion utilizing the optical disector method for cell counting

Unilateral cortical contusion in the rat results in cell loss in both the cortex and hippocampus. Pharmacological intervention with growth factors or excitatory neurotransmitter antagonists may reduce cell loss and improve neurological outcome. The window of opportunity for such intervention remains unclear because a detailed temporal analysis of neuronal loss has not been performed in the rodent cortical contusion model. To elucidate the time course of hippocampal CA3 neuronal death ensuing cortical contusion, we employed the optical disector method for assessing the total number of CA3 neurons at 1 and 6 hours, 1, 2, 10, and 30 days following injury. This stereological technique allows reporting of total cell numbers within a given region and is unaffected by change in the volume of the structure or cell size. A rapid and significant reduction in neurons/mm3 in the ipsilateral CA3 field was observed by 1 h following trauma. However, a significant increase in neurons/mm3 was seen at 30 days postinjury. This surprising finding is a result of CA3 volume shrinkage and redistribution of CA3 neurons. Utilization of the optical disector reveals that regardless of an increase in neurons/mm3 at 30 days following injury, CA3 cell loss reaches 41% of control animals by 1 day posttrauma and remains near that level at all subsequent time points examined. It is estimated that there are about 156,000 neurons in the CA3 region in control animals. By 1 h following cortical contusion the cell population decreases to 93,000 neurons indicating a very rapid cell loss. This suggests a window of less than 24 h for pharmacological intervention in order to save CA3 neurons following cortical contusion.

The biphasic opening of the blood-brain barrier in the cortex and hippocampus after traumatic brain injury in rats

This study examined the time course of the blood-brain barrier (BBB) opening and correlated this with brain edema formation after a lateral controlled cortical impact (CCI) brain injury in rats. Quantitative measurement of Evans blue (EB) extravasation using fluorescence was employed at 2, 4, 6 h and 1, 2, 3, 4 and 7 days after injury. Brain edema was measured by specific gravity of the tissue at corresponding time points. Two prominent EB extravasations were observed at 4-6 h and 3-day after injury in the injury-site cortex and the ipsilateral hippocampus. Brain edema became progressively more severe over time and peaked at 24 h after injury and began to decline after day 3. These results suggest that there is a biphasic opening of the BBB after CCI brain injury and the second opening of the BBB does not contribute to a further increase in edema formation.

Role of nitric oxide in histamine-induced increases in permeability of the blood-brain barrier

While previous studies have examined the effects of histamine on the permeability of the blood-brain barrier and reactivity of cerebral blood vessels, cellular mechanisms which account for histamine-induced affects on the cerebral microcirculation are not clear. The goals of this study were to determine the role of nitric oxide in histamine-induced increases in permeability of the blood-brain barrier and dilatation of pial arterioles. We examined the pial microcirculation in rats using intravital fluorescence microscopy. Permeability of the blood-brain barrier (clearance of fluorescent-labeled dextran; molecular weight 10,000 daltons; FITC-dextran-10K) and diameter of pial arterioles were measured in the absence and presence of histamine (10 and 100 microM). During superfusion with vehicle (saline), clearance of FITC-dextran-10K from pial vessels was minimal and diameter of pial arterioles remained constant. Topical application of histamine (10 and 100 microM) produced an increase in clearance of FITC-dextran-10K and diameter of pial arterioles. To determine a potential role for nitric oxide in histamine-induced increases in permeability of the blood-brain barrier and dilatation of pial arterioles, we examined the effects of NG-monomethyl-L-arginine (L-NMMA; 10 microM). L-NMMA inhibited histamine-induced increases in permeability of the blood-brain barrier and attenuated histamine-induced dilatation of cerebral arterioles. The findings of the present study suggest that histamine increases permeability of the blood-brain barrier and diameter of pial arterioles via the synthesis/release of nitric oxide or a nitric oxide containing compound.

Angiotensin II-induced fluid phase endocytosis in human cerebromicrovascular endothelial cells is regulated by the inositol-phosphate signaling pathway

The involvement of the early signaling messengers, inositol tris-phosphate (IP3), intracellular calcium, [Ca2+]i, and protein kinase C (PKC), in angiotensin II (AII)-induced fluid phase endocytosis was investigated in human brain capillary and microvascular endothelial cells (HCEC). ALL (0.01-10 microM) stimulated the uptake of Lucifer yellow CH, an inert dye used as a marker for fluid phase endocytosis, in HCEC by 50-230%. AII also triggered a fast accumulation of IP3 and a rapid increase in [Ca2+]i in cells loaded with the Ca(2+)-responsive fluorescent dye fura-2. The prompt AII-induced [Ca2+]i spike was not affected by incubating HCEC in Ca(2+)-free medium containing 2 mM EGTA or by pretreating the cultures with the Ca2+ channel blockers, methoxyverapamil (D600; 50 microM), nickel (1 mM), or lanthanum (1 mM), suggesting that the activation of AII receptors on HCEC triggers the release of Ca2+ from intracellular stores. The AII-triggered increases in IP3, [Ca2+]i, and Lucifer yellow uptake were inhibited by the nonselective AII receptor antagonist, Sar1, Val5, Ala8-AII (SVA-AII), and by the phospholipase C (PLC) inhibitors, neomycin and U-73122. By contrast, the protein kinase C (PKC) inhibitors, staurosporine and calphostin C, failed to affect any of these AII-induced events. This study demonstrates that increased fluid phase endocytotosis induced by AII in human brain capillary endothelium, an event thought to be linked to the observed increases in blood-brain barrier permeability in acute hypertension, is likely dependent on PLC-mediated changes in [Ca2+]i and independent of PKC.

Role of activation of bradykinin B2 receptors in disruption of the blood-brain barrier during acute hypertension

Cellular mechanisms which account for disruption the blood-brain barrier during acute hypertension are not clear. The goal of this study was to determine the role of synthesis/release of bradykinin to activate B2 receptors in disruption of the blood-brain barrier during acute hypertension. Permeability of the blood-brain barrier was quantitated by clearance of fluorescent-labeled dextran before and during phenylephrine-induced acute hypertension in rats treated with vehicle and Hoe-140 (0.1 microM). Phenylephrine infusion increased arterial pressure, arteriolar diameter and clearance of fluorescent dextran by a similar magnitude in both groups. These findings suggest that disruption of the blood-brain barrier during acute hypertension is not related to the synthesis/release of bradykinin to activate B2 receptors.

Passage of peptides across the blood-brain barrier: pathophysiological perspectives

Blood-borne peptides are capable of affecting the central nervous system (CNS) despite being separated from the CNS by the blood-brain barrier (BBB), a monolayer comprised of brain endothelial and ependymal cells. Blood-borne peptides can directly affect the CNS after they cross the BBB by nonsaturable and saturable transport mechanisms. The ability of peptides to cross the BBB to a meaningful degree suggests that the BBB may act as a modulatory pathway in the exchange of informational molecules between the brain and the peripheral circulation. The permeability of the BBB to peptides is a regulatory process affected by developmental, physiological, and pathological events. This regulation sets the stage for the relation between peptides and the BBB to be involved in pathophysiological events. For example, some of the classic actions of melanocortins on the CNS are explained by their abilities to cross the BBB, whereas aspects of feeding and alcohol-related behaviors are associated with the passage of other specific peptides across the BBB. The BBB should no longer be considered a static barrier but should be recognized as a regulatory interface controlling the exchange of informational molecules, such as peptides, between the blood and CNS.

Pericytosis and edema generation: a unique clinicopathological variant of meningioma

OBJECTIVE

We report a group of eight patients with a distinctive histological variant of meningioma that is associated with severe peritumoral edema. The clinical presentation, radiographic findings, and histology of this type of tumor may lead to misdiagnosis as an aggressive or malignant process.

METHODS

We reviewed the histology from patients who had removal of meningiomas performed in our institution between 1978 and 1992. Tumors having abnormal proliferation of cells in the intramural vascular spaces were selected for study; case histories and radiographs were reviewed. Tumor material was subjected to special stains, immunocytochemical examination, and election microscopy.

RESULTS

Several lesions were misread radiographically as being malignant. Patients underwent craniotomy with complete excision of the tumor. All lesions were small (< or = 3 cm), and no brain invasion, unusual tumor vascularity, or dural sinus involvement was noted in any case. Histologically, the meningioma pattern in each case was meningothelial and benign in appearance. The immunocytochemical and electron microscopic features of the unusual cells in the blood vessel walls are most consistent with their being of pericytic origin. All patients have remained asymptomatic and without evidence of tumor recurrence with follow-up from 3 to 12 years.

CONCLUSION

These tumors showed proliferation of pericytes in blood vessel walls and represent a new subtype of meningothelial meningioma. The apparently benign nature of these lesions necessitates their recognition. Characteristic findings of pericytic proliferation associated with edema generation have led us to descriptively term this the PEG variant of meningioma.

Blood-brain barrier breach following cortical contusion in the rat

Adult Fisher 344 rats were subjected to a unilateral impact to the dorsal cortex above the hippocampus at 3.5 m/second, resulting in a 2-mm cortical depression. This caused severe cortical damage and neuronal loss in hippocampus subfields CA1, CA3, and hilus. Breakdown of the blood-brain barrier (BBB) was assessed by injecting the protein horseradish peroxidase (HRP) 5 minutes prior to or at various times after injury (5 minutes, 1, 3, 6, and 12 hours, 1, 2, 5, and 10 days). Animals were killed 1 hour after HRP injection and brain sections were reacted with diaminobenzidine to visualize extravascular accumulation of the protein. Maximum staining occurred in animals injected with HRP 5 minutes prior to or 5 minutes after cortical contusion. Staining at these time points was observed in the ipsilateral cortex of the impact area and areas adjacent to it, as well as in the ipsilateral hippocampus. Some modest staining occurred in the dorsal contralateral cortex near the superior sagittal sinus. Cortical HRP staining gradually decreased at increasing time intervals postinjury. By 10 days, no HRP staining was observed in any area of the brain. In the ipsilateral hippocampus, HRP staining was absent by 3 hours postinjury and remained so at the 6- and 12-hour time points. Surprisingly, HRP staining was again observed in the ipsilateral hippocampus 1 and 2 days after cortical contusion, indicating a biphasic opening of the BBB following head trauma and a possible second wave of secondary brain damage days after the contusion injury. These data indicate that regions not initially destroyed by cortical impact, but evidencing BBB breach, may be accessible to neurotrophic factors administered intravenously both immediately and days after brain trauma.

Effect of the bradykinin B2 receptor antagonist Hoe140 in experimental pneumococcal meningitis in the rat

To elucidate the role of bradykinin in the complex pathophysiology of bacterial meningitis we investigated the effect of the bradykinin B2 receptor antagonist Hoe140, icatibant (D-Arg[Hyp3-Thi5-D-Tic7-Oic8]-bradykinin), on pathophysiological alterations in experimental pneumococcal meningitis. Untreated rats injected intracisternally (i.c.) with heat-killed pneumococci developed an increase of regional cerebral blood flow (185.4 +/- 27.4%, baseline 100%, mean +/- S.D.), brain water content (79.16 +/- 0.23%), intracranial pressure (21.4 +/- 6.0 mm Hg), and white blood cell count in the cerebrospinal fluid (CSF) (4621 +/- 1894 cells/microliter) within 6 h after i.c. challenge. Treatment with Hoe140 (0.1 mg/kg i.v. at baseline and 0.05 mg/kg s.c. at 2 h after i.c. challenge) attenuated the increase of brain water content (78.53 +/- 0.28%; P < 0.05), intracranial pressure (7.5 +/- 2.2 mm Hg; P < 0.05), and regional cerebral blood flow (128.6 +/- 23.1%; P < 0.05), and reduced CSF pleocytosis (2690 +/- 1898 cells/microliter. N.S.). When treatment was started 4 h after i.c. challenge Hoe140 reduced intracranial pressure (P < 0.05), but was no more capable to significantly influence the other pathophysiological parameters. Treatment with lower (0.01 mg/kg i.v. at baseline, followed by 0.005 mg/kg s.c. at 2 h) and higher (2 mg/kg i.v., followed by 1 mg/kg s.c. at 2 h) concentrations of Hoe140 was ineffective. Likewise, i.c. injection of Hoe140, at different dosages (4 nmol, 40 nmol, 400 nmol) did not significantly alter the pathophysiological parameters in pneumococci-induced meningitis, but caused changes in mean arterial blood pressure at dosages greater than 4 nmol. We conclude that bradykinin is involved as an inflammatory mediator of microvascular changes, brain edema, and increased intracranial pressure during the early phase of experimental pneumococcal meningitis.

Protective effect of the 5-lipoxygenase inhibitor AA-861 on cerebral edema after transient ischemia

This study examined the effect of AA-861, a specific 5-lipoxygenase inhibitor, on brain levels of leukotriene C4 (LTC4) and correlated any changes with changes in edema formation and cerebral blood flow (CBF) after transient ischemia in gerbils. Brain levels of LTC4 were observed to be increased at 1, 2, and 6 hours of reperfusion following 20 minutes of occlusion. At 2 hours of reperfusion, a pretreatment dose of 1000 mg/kg of AA-861 was required to inhibit more than 90% of the reperfusion-induced increases in brain LTC4. At this dose, inhibition of LTC4 production was observed at 2 and 6 hours of reperfusion. The specific gravity of both the cortex and subcortex was decreased at 6 hours of reperfusion after 20 minutes of occlusion. At 2 hours of reperfusion, no significant difference was observed in the specific gravity of the cortex and subcortex regions of gerbils pretreated with AA-861 or with vehicle, but at 6 hours of reperfusion significant positive differences were observed. Cerebral blood flow decreased to approximately 10% of preocclusion values during occlusion and returned to near-preocclusion values after 10 minutes of reperfusion. No significant differences were observed in regional CBF in the AA-861- and vehicle-pretreated gerbils during reperfusion. These findings indicate that LTC4 production after transient cerebral ischemia may be an important contributor to the development of cerebral edema and that CBF does not mediate the LTC4-involved development of edema.

Vasomotor and permeability effects of bradykinin in the cerebral microcirculation

All components of an intracerebral kallikrein-kinin system have been described. Thus, bradykinin (BK) acting from the parenchymal site as well as from the blood site may influence cerebral microcirculation. BK is a potent dilator of extra- and intraparenchymal cerebral arteries when acting from the perivascular site. The vasomotor effect of BK is mediated by B2 receptors which appear to be located at the abluminal membrane of the endothelial cell. The effect of BK is mediated by NO. prostanoids, free radicals, H2O2 or leukotrienes depending on the animal species and on the location of the artery. Selective opening of the blood-brain barrier for small tracers (Na(+)-fluorescein; MW, 376) has been found in cats during cortical superfusion or intraarterial application of BK. This leakage is mediated by B2 receptors located at the luminal and abluminal membrane of the endothelial cells. Formation of brain edema has been found after ventriculo-cisternal perfusion or interstitial infusion of BK. This can be explained by increase of vascular permeability and cerebral blood flow due to arterial dilation thus enhancing driving forces for the extravasation. An increase of the BK concentration in the interstitial space of the brain up to concentrations which induce extravasation, dilatation and oedema formation has been found under several pathological conditions. Thus, BK may be involved in oedema formation after cold lesion, concussive brain injury, traumatic spinal cord and ischemic brain injury. The mediator role of BK in brain edema is further supported by therapeutic results. Brain swelling due to cold lesion or ischemia could be diminished by treatment with kallikrein-inhibitors. Similarly, dilatation of cerebral arterioles after concussive brain injury was reduced by blockade of B2 receptors. Thus, all criteria favour BK as one mediator of vasogenic oedema.

Open-label titration study of the safety of RMP-7 in patients with the acquired immune deficiency syndrome

RMP-7, a nine-amino acid bradykinin analogue, has been shown in animals to temporarily increase the permeability of the blood brain barrier to small molecules including amphotericin B, when administered intravenously. We sought to evaluate the safety of escalating doses of RMP-7 administered to human volunteers with the acquired immune deficiency syndrome (AIDS). Six HIV antibody-positive adults with CD4+ cell counts <50/mm3 received three increasing doses of RMP-7 on successive days: 30 ng/kg, 100 ng/kg and 300 ng/kg infused over 2, 2 and 10 min, respectively. Adverse experiences were dose-related, mild-moderate in intensity, primarily related to vasodilation and resolved rapidly without sequelae. Mean maximum increases in pulse rate at 30 ng/kg, 100 ng/kg and 300 ng/kg were 4.0, 7.8 and 28.2 beats per min, respectively. The maximum changes in average mean arterial pressure were +7.7, +5.6 and -0.2 mmHg from baseline, respectively. Minor increases in liver enzymes were noted in three patients, all with pre-existing enzyme elevations. Despite the high frequency of both occult and overt cardiovascular abnormalities in advanced HIV infection, RMP-7 is shown to be safe in this group of AIDS patients at all dosage levels tested, with adverse effects similar to previous experience in healthy humans.

Inflammation in EAE: role of chemokine/cytokine expression by resident and infiltrating cells

Experimental allergic encephalomyelitis (EAE) is an inflammatory demyelinating disease of the central nervous system (CNS) which has many clinical and pathological features in common with multiple sclerosis (MS). Comparison of the histopathology of EAE and MS reveals a close similarity suggesting that these two diseases share common pathogenetic mechanisms. Immunologic processes are widely accepted to contribute to the initiation and continuation of the diseases and recent studies have indicated that microglia, astrocytes and the infiltrating immune cells have separate roles in the pathogenesis of the MS lesion. The role of cytokines as important regulatory elements in these immune processes has been well established in EAE and the presence of cytokines in cells at the edge of MS lesions has also been observed. However, the role of chemokines in the initial inflammatory process as well as in the unique demyelinating event associated with MS and EAE has only recently been examined. A few studies have detected the transient presence of selected chemokines at the earliest sign of leukocyte infiltration of CNS tissue and have suggested astrocytes as their cellular source. Based on these studies, chemokines have been postulated as a promising target for future therapy of CNS inflammation. This review summarized the events that occur during the inflammatory process in EAE and discusses the roles of cytokine and chemokine expression by the resident and infiltrating cells participating in the process.

Effect of difluoromethylornithine treatment on regional ornithine decarboxylase activity and edema formation after experimental brain injury

This study examined the effect of difluoromethylornithine (DFMO) on regional activities of ornithine decarboxylase (ODC) and edema formation in bilateral cerebral cortex and hippocampus after a unilateral controlled cortical-impact (CCI) injury in rats. To measure the activity of ODC, the brains of injured and control rats were frozen in situ at 30 min, 3, 6, and 24 h after CCI brain injury of moderate severity. The specific gravity, an indicator of edema formation, was examined in decapitated animals at corresponding time points. Brain injury induced significant increases of ODC in the ipsilateral hippocampus, adjacent and injury-site cortices, and in the contralateral cortex and hippocampus at 3 and 6 h after injury. No significant edema formation was found in any brain region at 30 min after injury. A significant edema formation was first found only in the injury-site cortex at 3 h after injury. At 6 and 24 h after injury, significant edema was found in all regions ipsilateral to the injury-site. At 24 h after injury, significant but less severe edema was also found in the contralateral cortex and hippocampus. DFMO, an irreversible inhibitor of ODC, abolished the increase in ODC in all regions. It also attenuated edema formation in the adjacent cortex and in the contralateral cortex and hippocampus. These findings indicate that polyamines may play a role in posttraumatic brain edema formation, particularly in important brain regions remote from the injury-site.

Reversion of phenotype of endothelial cells in brain tissue around glioblastomas

With the aim of studying the putative involvement of peritumoral microvessels in the formation of brain edema, small pieces of peritumoral brain tissue were removed from six patients with glioblastoma multiforme submitted to surgery. All patients had cerebral edema, as shown by preoperative C.T. and N.M.R. Control specimens were obtained from four patients undergoing ventriculo-peritoneal shunt. The tissue fragments were fixed in glutaraldehyde-osmium and embedded in Epon. In semi-thin sections observed under light microscopy peritumoral endothelial cells exhibited voluminous cytoplasm and nucleus. Under the electron microscope, capillary cells from glioblastoma patients differed from controls mainly by showing nuclei rich in euchromatin, cytoplasm rich in pinocytotic vesicles and with occasional fenestrations. All these morphological characteristics are compatible with a process of reversion of phenotype of capillaries around glioblastomas to that of periphery as well as an increase in permeability. Both events may be due to diffusion of a tumoral vascular permeability/endothelial growth factor. This peripheral vessel phenotype of peritumoral microvessels supports their participation in the formation of brain edema and may provide a new clue for therapeutic intervention: for example it fits quite well to the known increase in permeability by leukotrienes and decrease in permeability by corticosteroids in tumoral edema.

Bradykinin dilates rat middle cerebral artery and its large branches via endothelial B2 receptors and release of nitric oxide

Ring segments of rat middle cerebral artery (MCA) were prepared for measurement of isometric force and precontracted with 10(-4) M uridine triphosphate (UTP). Concentration-effect curves (CEC) were constructed for bradykinin (BK, 10(-8)(-10)(-1) M) in segments with functionally intact (E+) or denuded (E-) endothelium. E- segments did not dilate to BK. The BK receptor was characterized by application of specific B1 or B2 antagonists [des-Arg4-Leu8] BK (10(-5) M) and [D-Arg4-Hyp3-Thi5-D-Tic7-Oic8] BK (HOE140, 3 x 10(-7) M), respectively, or B2 agonist [des-Arg9] BK (10(-8)-10(-4) M). Involvement of nitric oxide (NO) was tested with NG-nitro-L-arginine (LNNA, 10(-4) M). BK induced concentration-dependent relaxation with a maximal effect (Emax) of 40.86 +/- 1.50% at 10(-4) M and a pD2 (-log10 EC50) of 6.818 +/- 0.044. This relaxation could be prevented with HOE140 or LNNA, but was not influenced by [des-Arg(9)-Leu] BK. [des-Arg9] BK did not induce any effect. These results demonstrate that BK induced relaxation via endothelial B2 receptors and release of NO in isolated rat MCA.

[Transvascular fluid exchange disturbed by capillary injuries]

Fluid exchange disorders due to capillary lesions are numerous and their extent depends on the underlying disease as well as the capillary structure of the affected organ. The inflammatory cascade, triggered by sepsis or reperfusion injury, is mediated by several humoral mediators and activated blood cells. These include pro-inflammatory cytokines, arachidonic acid, proteases, oxygen free radicals, polymorphonuclears, procoagulant, complement and fibrinolytic system. The interaction between these mediators leads to a loss of endothelial integrity, a loss of basment membrane and a disruption of the interstitial matrix, with wasting of the endothelial cytoskeleton. The alteration in permeability induces transcapillary exudation of water and protein in the interstitial space, leading to organ dysfunction, mainly the lungs and splanchnic organs. Nitric oxyde, by modulating the response of the endothelium to the cellular interaction may protect against capillary injury. Capillary "stress lesions" following microvascular hypertension are the physiological basis of neurogenic or high altitude pulmonary oedema, and overinflation injury from mechanical ventilation. The anatomic specific features of the cerebral capillaries resulted in the well known concept of blood brain barrier with it's changeing morphology. Under the effect of humoral mediators and cellular interactions, the endothelial cells are able, via a calcium-mediated mechanism, to contract and to modify capillary permeability, leading to vasogenic oedema.

Regional activity of ornithine decarboxylase and edema formation after traumatic brain injury

This study examined ornithine decarboxylase (ODC) activity and edema formation bilaterally in brain cortices and hippocampi after lateral controlled cortical-impact injury in rats. To measure the activity of ODC, the brains of injured and control rats were frozen in situ at 30 minutes and at 6, 24, and 72 hours after controlled cortical-impact injury of moderate severity. The specific gravity of these regions was examined in decapitated animals at corresponding time points as an indicator of edema formation. Thirty minutes after injury, ODC activity did not increase in the injury-site cortex and ipsilateral hippocampus. At 6 hours after injury, ODC activity had increased by nine times that of the control in the injury-site cortex, by five times in the adjacent cortex, and by five and one-half times in the ipsilateral hippocampus. Twenty-four hours after injury, ODC activity had increased by three times that of the control in the injury-site cortex and two times in the ipsilateral hippocampus. Seventy-two hours after injury, activity had returned to control levels. ODC activity increased significantly in the contralateral cortex and hippocampus only at 6 and 24 hours. The injury-site and adjacent cortices and the ipsilateral hippocampus showed significant edema at 6, 24, and 72 hours but not at 30 minutes after injury. These findings indicate that polyamine metabolism is significantly altered in traumatic brain injury. The temporal association between ODC activity and edema formation indicates that polyamines might be a contributing factor in edema formation after traumatic brain injury. The delayed induction of ODC after brain injury suggests a potential therapeutic window for future pharmacological intervention to decrease posttraumatic secondary cerebral injury.

Polyamines induce blood-brain barrier disruption and edema formation in the rat

Polyamines (PA) are derived from ornithine by the enzyme ornithine decarboxylase (ODC), which is activated very rapidly as acute and delayed responses to brain ischemia and trauma. Polyamines play a role in the disruption of the blood-brain barrier (BBB) in different pathological states. This study examined the effect of exogenous polyamines, administered intracerebrally (i.c.v.) or intracarotidly on BBB function. Putrescine, spermidine and spermine, given individually, were found to disrupt BBB integrity within 15 min of i.c.v. administration (p = 0.03; p = 0.0013; p = 0.042 vs saline treated rats, respectively). The effect was still evident after 1 h; however, since the saline treated rats also showed increased permeability of Evans blue at this time, there was no statistical difference between polyamines or saline treated rats 1 h post injection. When injected into the carotid artery, rapid increase in BBB permeability was found 1 min after putrescine and spermidine (p < 0.01 vs saline), with a slight decline at 15 min. A slower effect was noticed after spermine administration which reached significance only at 15 min. These results suggest a role for PA as mediators of vasogenic edema formation in the brain soon after brain injuries which induce increased production of these compounds.

Pathway across blood-brain barrier opened by the bradykinin agonist, RMP-7

The route taken by lanthanum (MW 139) across cerebral endothelium was delineated when the blood-brain barrier was opened by RMP-7, a novel bradykinin agonist. Balb C mice were infused through a jugular vein with LaCl3 with or without RMP-7 (5 micrograms/kg). Ten minutes later, the brains were fixed with aldehydes and processed for electron microscopy. The patency of the junctions between endothelial cells was estimated by counting the number of junctions penetrated by LaCl3. Tracer penetrated the junctions in about 25% of microvessels in vehicle infused, control mice and about 58% in the RMP-7 group, where more junctions per vessel were also penetrated. The LaCl3 then penetrated the basal lamina in about 20% of all microvessels in the RMP-7 group, versus 0.50% in the control group. From the basal lamina, the tracer entered perivascular spaces in about 13% of all microvessels in the RMP-7 group and about 0.07% in the controls. Very few endocytic pits or vesicles in the RMP-7 group were labeled, so LaCl3 did not cross endothelium by transcytosis. The increased number of tight junctions penetrated by tracer and its spread into periendothelial basal lamina and interstitial clefts indicated, therefore, a paracellular route of exudation in the RMP-7 treated animals.

Probable involvement of serotonin in the increased permeability of the blood-brain barrier by forced swimming. An experimental study using Evans blue and 131I-sodium tracers in the rat

The possibility that endogenous serotonin (5-hydroxytryptamine, 5-HT) participates in alteration of the blood-brain barrier (BBB) following short-term forced swimming (FS) exercise was examined in a rat model. Subjection of conscious young (age 8-9 weeks, 80-90 g) animals to continuous FS (at a water temperature of 30 +/- 1 degrees C) for 30 min, increased the permeability of the BBB to Evans blue albumin (EBA) and 131I-sodium in six and nine brain regions, respectively. The EBA staining was noted in posterior cingulate cortex, parietal, occipital cortices, cerebellar vermis, medial lateral cerebellar cortices and dorsal surface of hippocampus. In addition to these brain regions, the BBB permeability to 131I-sodium was further extended to caudate nucleus, thalamus and hypothalamus. This effect of FS on the BBB permeability was absent in adult (age 24-30 weeks, 300-400 g) animals. Measurement of 5-HT showed a profound increase of plasma and brain in young rats by 180% and 250%, respectively, from the control group. Adult animals showed only a minor increase in brain and plasma 5-HT levels. In young animals, pretreatment with p-CPA (a 5-HT synthesis inhibitor) and indomethacin (a prostaglandin synthesis inhibitor) prevented the FS induced increase in BBB permeability and 5-HT levels. Destruction of serotonergic neurons with 5,7-dihydroxytryptamine (5,7-DHT) reduced the breakdown of the BBB and attenuated the brain 5-HT level without affecting the plasma 5-HT. Cyproheptadine, ketanserin (5-HT2 receptor antagonists) and vinblastine (a vesicular transport inhibitor) prevented the increased permeability of the BBB alone. The plasma and brain 5-HT continued to remain high. These observations suggest that (i) 5-HT plays an important role in the breakdown of BBB permeability in FS, (ii) this effect of 5-HT on BBB permeability is mediated by 5-HT2 receptors, and (iii) FS induced increase in BBB permeability is age dependent.

Effect of inflammatory agents on electrical resistance across the blood-brain barrier in pial microvessels of anaesthetized rats

The effect of histamine, bradykinin and serotonin on blood-brain barrier permeability was investigated using in situ measurement of transendothelial electrical resistance in pial microvessels of anaesthetized rats. Mean resistance of vessels superfused with artificial cerebrospinal fluid was 1800 omega cm2, indicating a tight barrier with extremely low ion permeability. In paired experiments from continuous measurements in single vessels, addition of 10(-3) M serotonin to the solution bathing the brain had no marked effect on resistance; whereas both histamine and bradykinin, applied at a concentration of 10(-4) M, caused a rapid and reversible decrease in resistance. Mean resistance was 408 and 505 omega cm2 in 10(-4) M histamine and bradykinin, respectively, and approximately 50% of vessels had a resistance less than 250 omega cm2, compared to 12% in controls, indicating a leaky blood-brain barrier that is not capable of normal brain ion homeostasis. Histamine and bradykinin had similar dose-response relations, and a maximal effect was observed between 20 and 50 microM. Thus, histamine and bradykinin act at the abluminal (brain-facing) membranes of the cerebral endothelium to mediate blood-brain barrier opening. These results support a role for histamine and bradykinin in brain oedema formation.

Impairment of blood-brain barrier function by serotonin induces desynchronization of spontaneous cerebral cortical activity: experimental observations in the anaesthetized rat

The possibility that elevation of serotonin in the circulation, which is found in various pathological states, influences the spontaneous cerebral cortical activity was examined in a rat model. The electroencephalogram was recorded using bipolar epidural electrodes placed over the frontal and parietal cerebral cortex. Intravenous infusion of serotonin (10 micrograms/kg per min for 10 min) decreased the electroencephalogram amplitude in both frontal and parietal recordings within 4 min of infusion. This decrease in amplitude was reversible, Pretreatment with cyproheptadine (a potent serotonin2 receptor antagonist) prevented the serotonin-induced decrease of the electroencephalogram amplitude. The blood-brain barrier permeability to Evans Blue and [131I]sodium was increased in frontal and parietal cortex. This increase in blood-brain barrier permeability was absent in animals pretreated with cyproheptadine. These results provide direct evidence that an elevated level of serotonin in blood has the capacity to influence spontaneous cortical electrical activity. This effect of serotonin on electroencephalogram appears to be due to its ability to enter into the brain parenchyma by inducing a short-term breakdown of the blood-brain barrier, probably via serotonin2 receptors.

The blood-brain barrier disruption to circulating proteins in the early period after fluid percussion brain injury in rats

Breakdown of the blood-brain barrier (BBB) immediately after traumatic brain injury is not clearly understood. In the present study we focused on the integrity of the BBB to circulating proteins within the first hour after injury. For this purpose, vascular permeability to endogenous albumin and to the exogenous protein tracer horseradish peroxidase (HRP) was examined after a lateral fluid percussion brain injury in rats. Albumin was immunolocalized in brain sections at 3 and 60 min after impact. This distribution was compared with the histochemical localization of HRP given before impact at the same time points. In a separate experiment HRP was given prior to sacrifice to determine the time course for the barrier disruption. Permeability to this protein was assessed at 13, 30, and 60 min after impact. Prominent extravasation of albumin occurred within 3 min of injury and was present in multiple foci within the injured hemisphere. At 60 min the extravasated albumin was present in the same sites, where it was widely distributed. Throughout the related brain parenchyma, little difference was found between the extravascular distribution of albumin and HRP. In the delayed administration paradigm breakdown of the BBB was noted in the impact site, hemorrhagic site in the deep cortical layer, hippocampus, thalamus, and midbrain at 13 min after injury. This injured barrier was restored in most regions by 30 min. However, the impact site and hemorrhagic site remained permeable up to 60 min postinjury. In addition, newly developed barrier disruption to HRP occurred in the parasagittal cortex at 30 and 60 min. In conclusion, widespread breakdown of the BBB to circulating proteins occurred within a few minutes after traumatic brain injury. The time course for this barrier disruption is characterized by three different patterns: (1) transient, (2) prolonged, and (3) delayed opening. This variation in the development of barrier disruption may be related to the secondary barrier failure as well as the primary opening after injury.

Effect of rapid correction of hyponatremia on the blood-brain barrier of rats

Brain demyelination sometimes follows rapid correction of hyponatremia, especially if the hyponatremia is chronic. During correction brain water decreases and the brain shrinks. The present study examined whether such shrinkage might be sufficient to disrupt the tight junctions of the blood-brain barrier. Barrier intactness was evaluated using magnetic resonance imaging and intravenous gadolinium contrast administration. Hypertonic saline infusion rapidly increased the plasma sodium concentration and caused barrier disruption more frequently in chronic than in acute hyponatremic rats. Similar increases in plasma sodium concentration did not disrupt the barrier in normonatremic rats. The disruption appeared to be due to altered plasma osmolality since infusion of hypertonic mannitol, which raised plasma osmolality without changing the plasma sodium concentration, disrupted the barrier in hyponatremic but not normonatremic rats. Moreover, the osmotic threshold for barrier disruption was lowest in chronic hyponatremia, intermediate in acute hyponatremia, and highest in normonatremia. The greater susceptibility to osmotic disruption in chronic hyponatremia suggests that blood-brain barrier disruption may play a significant role in causing the demyelination sometimes found following too rapid correction of hyponatremia, possibly through exposure of oligodendrocytes to plasma macromolecules such as complement.

The role of chemical, physical, or viral exposures and health factors in neurocarcinogenesis: implications for epidemiologic studies of brain tumors

This review highlights some future prospects and implications for epidemiologic research on the etiology of nervous system tumors. It reviews some points regarding physiology of the nervous system, in connection with mechanisms of neurocarcinogenesis, and experimental studies in animals. The results of epidemiologic studies are summarized in the light of the biological and experimental observations. The following aspects are particularly emphasized: (i) higher susceptibility of the developing nervous system to neurocarcinogenic agents (in the fetus and after birth); (ii) possible implications of knowledge about mechanisms of neurocarcinogenesis regarding crossing of the blood-brain barrier, activation of oncogenes and inactivation of anti-oncogenes, relationship between chemical structure and neurocarcinogenic action; (iii) necessity of further investigation concerning the occurrence of nitrosoureas and their precursors in the environment, and the potential role of nitroso compounds in the development of human brain tumors; (iv) lack of information about promoting or inhibiting neurocarcinogenic effects, and co-carcinogenesis--among others, interaction between X-irradiation and exposure to neurocarcinogenic nitrosoureas; (v) need for studying the potential neurocarcinogenic risk of polyomaviruses BKV, JCV, and SV40 to humans.

Permeability of the blood-brain barrier to melanocortins

Adrenocorticotropin (ACTH)-related compounds, termed melanocortins, produce a large number of effects on the central nervous system (CNS) after their peripheral administration. Some of the CNS effects of ACTH are mediated through the release of glucocorticoids from the adrenal gland, but there are fragments and analogues of ACTH that do not act on the adrenals. This raises the possibility that some blood-borne melanocortins may be acting directly on the brain, which would necessitate their crossing the blood-brain barrier (BBB). We review here the literature showing that melanocortins can affect the BBB in several ways, including an alteration of the permeability of the BBB to other substances.

Radiation-induced changes in the profile of spinal cord serotonin, prostaglandin synthesis, and vascular permeability

PURPOSE

To investigate the profile of biochemical and physiological changes induced in the rat spinal cord by radiation, over a period of 8 months.

METHODS AND MATERIALS

The thoraco-lumbar spinal cords of Fisher rats were irradiated to a dose of 15 Gy. The rats were then followed and killed at various times afterward. Serotonin (5-HT) and its major metabolite 5-hydroxyindole-3-acetic acid (5-HIAA) were assayed as well as prostaglandin synthesis. Microvessel permeability was assessed by quantitative evaluation of Evans blue dye extravasation.

RESULTS

None of the rats developed neurologic dysfunction, and histologic examination revealed only occasional gliosis in the ventral white matter at 240 days after irradiation. Serotonin levels were unchanged at 2, 14, and 56 days after radiation but increased at 120 and 240 days in the irradiated cord segments when compared to both the nonirradiated thoracic and cervical segments (p < 0.01) and age-matched controls (p < 0.03). The calculated utilization ratio of serotonin (5-HIAA/5-HT) remained unchanged. Immediately after radiation (at 3 and 24 h) an abrupt but brief increase in the synthesis of prostaglandin-E2 (PGE2), thromboxane (TXB2), and prostacyclin [6 keto-PGF1 alpha (6KPGF)] was noted, which returned to normal at 3 days. This was followed after 7 and 14 days by a significant fall off in synthesis of all three prostaglandins. Thereafter, at 28, 56, 120, and 240 days, escalated production of thromboxane followed, while prostacyclin synthesis remained markedly reduced (-88% of control level at 240 days). Up to 7 days after radiation the calculated TXB2/6KPGF ratio remained balanced, regardless of the observed abrupt early fluctuations in their rate of synthesis. Later, between 7 and 240 days after radiation, a significant imbalance was present which became more pronounced over time. In the first 24 h after radiation, a 104% increase in microvessel permeability was observed which returned to normal by 3 days. Normal permeability was maintained at 14 and 28 days, but at 120 and 240 days a persistent and significant increase of 98% and 73% respectively above control level was noted.

CONCLUSIONS

Radiation induces severe impairment in microvessel function even in the histologically unaffected spinal cord, and alters the secretory phenotype of various cell systems in the central nervous system.

Kinins and kinin receptors in the nervous system

Kinins, including bradykinin and kallidin, are peptides that are produced and act at the site of tissue injury or inflammation. They induce a variety of effects via the activation of specific B1 or B2 receptors that are coupled to a number of biochemical transduction mechanisms. In the periphery the actions of kinins include vasodilatation, increased vascular permeability and the stimulation of immune cells and peptide-containing sensory neurones to induce pain and a number of neuropeptide-induced reflexes. Mechanisms for kinin synthesis are also present in the CNS where kinins are likely to initiate a similar cascade of events, including an increase in blood flow and plasma leakage. Kinins are potent stimulators of neural and neuroglial tissues to induce the synthesis and release of other pro-inflammatory mediators such as prostanoids and cytotoxins (cytokines, free radicals, nitric oxide). These events lead to neural tissue damage as well as long lasting disturbances in blood-brain barrier function. Animal models for CNS trauma and ischaemia show that increases in kinin activity can be reversed either by kinin receptor antagonists or by the inhibition of kinin production. A number of other central actions have been attributed to kinins including an effect on pain signalling, both within the brain (which may be related to vascular headache) and within the spinal dorsal horn where primary afferent nociceptors can be stimulated. Kinins also appear to play a role in cardiovascular regulation especially during chronic spontaneous hypertension. Presently, however, direct evidence is lacking for the release of kinins in pathophysiological conditions of the CNS and it is not known whether spinal or central neurones, other than afferent nerve terminals, are sensitive to kinins. A more detailed examination of the effects of kinins and their central pharmacology is necessary. It is also important to determine whether the inhibition of kinin activity will alleviate CNS inflammation and whether kinin receptor antagonists are useful in pathological conditions of the CNS.

Enzymatic barrier protects brain capillaries from leukotriene C4

Leukotriene C4 (LTC4) increases vascular permeability in systemic, brain tumor, and ischemic brain capillaries, but not in normal brain capillaries. This study examines whether the abundance of gamma-glutamyl transpeptidase (gamma-GTP) in normal brain capillaries might act as an enzymatic barrier to vasoactive leukotrienes in the brain. Blood-brain barrier (BBB) permeability was determined by quantitative autoradiography using 14C-aminoisobutyric acid. Ischemia was produced by occluding the middle cerebral artery. Seventy-two hours after occlusion, gamma-GTP activity in ischemic brain disappeared, and LTC4 (4-micrograms total dose), which was infused into the carotid artery ipsilateral to the occlusion, selectively increased permeability, Ki, approximately twofold within core ischemic tissue and adjacent tissue, compared to vehicle alone in seven brains (15.53 +/- 6.03 vs. 7.29 +/- 3.36, p < 0.05, and 8.76 +/- 4.02 vs. 4.32 +/- 2.65, p < 0.05, respectively). No effect on BBB was seen in nonischemic brain tissue. Twenty-four hours postocclusion, gamma-GTP activity was still present, and LTC4 infusion did not increase permeability within ischemic tissue. However, inhibition of gamma-GTP with acivicin allowed LTC4 to increase permeability even 24 hours after occlusion in ischemic core and adjacent tissue compared to vehicle alone in seven brains (17.21 +/- 16.32 vs. 8.23 +/- 6.58, p < 0.05, and 11.78 +/- 7.96 vs. 4.56 +/- 1.93, p < 0.01, respectively). Acivicin almost completely blocked both the histochemical activity of gamma-GTP in brain capillaries and the metabolism of LTC4 in isolated bovine capillaries. These findings suggest that gamma-GTP may help normal brain capillaries resist the vasoactive effects of LTC4. In contrast, gamma-GTP is lost in injured brain capillaries, which allows LTC4 (in combination with other factors) to increase vascular permeability in ischemic brain and brain tumors.

Opening of the blood-brain barrier during cortical superfusion with histamine

Histamine may influence cerebral microcirculation from the intravascular and parenchymal side. The latter route can be simulated by cortical superfusion. The effect of cortical superfusion with histamine (10(-9)-10(-3) M) on blood-brain barrier (BBB) permeability was studied in the cat by measuring extravasation of the tracers Na(+)-fluorescein (MW 376) or fluorescein isothiocyanate (FITC) labelled dextran (MW 62,000 or 145,000) by intravital fluorescence microscopy. Histamine induced an opening of BBB resulting in extravasation of small and large molecular weight tracers with threshold concentrations of 10(-9), 10(-8) and 10(-6) M for Na(+)-fluorescein, FITC-dextran 62,000 and 145,000, respectively. Once tracer extravasation had started the degree of extravasation increased with increasing concentrations of histamine in the superfusion fluid. Similar to histamine the H2 agonist impromidine (3 x 10(-12)-3 x 10(-9) M) induced a concentration dependent extravasation of Na(+)-fluorescein. 2-Pyridylethylamine which is 3-4 times more selective for H1 than for H2 receptors also induced an extravasation of Na(+)-fluorescein. Cortical superfusion with mepyramine (10(-7) M) or cimetidine (10(-4) M), which block the H1 and H2 receptors, respectively, already induced significant extravasation of Na(+)-fluorescein by themselves. These compounds could thus not be used as competitive antagonists to block histamine-induced extravasation. However, our data are in accord with data obtained during intravascular and topical application of histamine and support the hypothesis that H2 receptors at the luminal and abluminal membrane of the endothelium mediate the opening of the BBB.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross talk among cyclic AMP, cyclic GMP, and Ca(2+)-dependent intracellular signalling mechanisms in brain capillary endothelial cells

C-type natriuretic peptide and sodium nitroprusside, a nitric oxide donor molecule, induced large increases in cyclic GMP formation in cultured rat brain capillary endothelial cells. Isoproterenol, a potent agonist of adenylate cyclase, potentiated the actions of C-type natriuretic peptide and of sodium nitroprusside. These actions were not observed in the presence of isobutylmethylxanthine and were mimicked by forskolin. Endothelin-1 had no action on basal cyclic GMP levels. It reduced cyclic GMP formation induced by C-type natriuretic peptide and sodium nitroprusside by about 50%. These actions involved an ETA receptor subtype and a Ca(2+)-dependent and protein kinase C-independent mechanism. Finally, increasing cyclic GMP slightly prolonged intracellular Ca2+ transients induced by endothelin-1. The results suggest the presence of extensive cross talk among cyclic AMP, cyclic GMP, and Ca(2+)-dependent mechanisms in endothelial cells of brain microvessels. The relevance of the results to the regulation of the blood-brain barrier permeability is discussed.

Early microvascular and neuronal consequences of traumatic brain injury: a light and electron microscopic study in rats

The purpose of this study was to document the early morphologic consequences of moderate traumatic brain injury (TBI) in anesthetized Sprague-Dawley rats. Normothermic rats (37 degrees C) were injured with a fluid percussion pulse (1.7-2.1 atm) administered by an injury cannula positioned parasagittally over the right cerebral cortex (n = 7). At 45 min following TBI, rats were injected with the protein tracer horseradish peroxidase (HRP) and perfusion fixed or immersion fixed 15 min later for light and electron microscopic analysis. Blood-brain barrier (BBB) breakdown to HRP was present overlying the pial surface and superficial cortical layers of the injured hemisphere. A focal area of severe HRP leakage was also present at the gray-white interface of the lateral cortex. Light microscopic examination of this site revealed petechial hemorrhages associated with small venules. Dark shrunken neurons and swollen astrocytes were detected within cortical areas overlying the evolving contusion, CA3 and CA4 hippocampal subsectors, and lateral thalamus. Ultrastructural studies obtained evidence for irreversible neuronal injury and mechanical damage to vessel walls at this early posttraumatic period. In nonperfused traumatized rats, luminal platelet aggregates were also detected at sites of hemorrhage. In this model of TBI, a consistent pattern of microvascular and neuronal abnormalities can be documented in the early posttraumatic period. Pathomechanisms underlying these early changes are discussed in terms of primary and secondary injury processes.

Computerised image analysis in conjunction with fluorescence microscopy for the study of blood-brain barrier permeability in vivo

The present paper describes a new method using computerised image analysis techniques for quantification of tracer extravasation over the blood-brain barrier as studied by intravital fluorescence microscopy. Cats were equipped with an open cranial window and continuously infused with fluorescein isothiocyanate-labelled dextran (FITC-dextran, mol. wt. 70,000) to maintain a steady plasma concentration. Several cortical fields were recorded in each experiment and the images stored on video tape for off-line analysis. This procedure, which largely eliminates the superficial pial vasculature and allows extraction of the extravasation areas, consists of the following steps: (1) averaging of images, (2) software shading correction based on the original images for compensation of optical non-uniformity, (3) correction of displacement artefacts, (4) intensity adjustment, (5) generation of subtraction images by subtracting the first image of a series from the subsequent ones, (6) median filtering and thresholding, (7) a length recognition algorithm, and (8) elimination of small areas. Compared to the previously described method, step (2) has been newly developed and steps (4) and (8) added to enhance sensitivity for detecting tracer extravasation. The degree of extravasation in a cortical field at a given time point [E(f) value] was calculated as the mean intensity of the remaining pixels. The E(f) is a quantitative value computed by a fully automatised procedure which takes into account the number, as well as the size and intensity, of extravasation areas in a given cortical field. The E(f) values obtained at different times in a series of experiments were averaged to give the E(I) value.(ABSTRACT TRUNCATED AT 250 WORDS)

Traumatic optic neuropathy

Knowledge concerning the pathophysiologic mechanisms of traumatic optic neuropathy is limited. The optic nerve is a tract of the brain. Therefore, the cellular and biochemical pathophysiology of brain and spinal cord trauma and ischemia provide insight into mechanisms that may operate in traumatic optic neuropathy. The dosage of methylprednisolone (30 mg/kg/6 hours) which was successful in the National Acute Spinal Cord Injury Study 2 (NASCIS 2) evolved from the unique pharmacology of corticosteroids as antioxidants. The management of traumatic optic neuropathy rests on an accurate diagnosis which begins with a comprehensive clinical assessment and appropriate neuroimaging. The results of medical and surgical strategies for treating this injury have not been demonstrated to be better than those achieved without treatment. The spinal cord is a mixed grey and white matter tract of the brain in contrast to the optic nerve which is a pure white matter tract. The treatment success seen with methylprednisolone in the NASCIS 2 study may not generalize to the treatment of traumatic optic neuropathy. Conversely, if the treatment does generalize to the optic nerve, NASCIS 2 data suggests that treatment must be started within eight hours of injury, making traumatic optic neuropathy one of the true ophthalmic emergencies. Given the uncertainties in the treatment, ophthalmologists involved in the management of traumatic optic neuropathy are encouraged to participate in the collaborative study of traumatic optic neuropathy.

A double-blind study of neurotropin in patients with acute ischemic stroke

Neurotropin was found to reduce brain oedema in an experimental model of brain infarction in the guinea-pig. A randomized double-blind controlled trial with Neurotropin was performed in 220 patients admitted within 24 h after an acute ischemic stroke. 35 of the neurotropin and 41 of the placebo-randomized patients had to be excluded. 10 included patients in the neurotropin and 13 in the placebo-treated group died within the study period of 15 days. A better clinical outcome was observed in the 65 included surviving neurotropin compared with the 56 placebo-treated patients. The size of the infarct and of the oedema zones was significantly more decreased on CT scans from Day 11 compared with Day 3 after stroke in the neurotropin than in the placebo treated group. Neurotropin is helpful in treating brain oedema, related to acute ischemic stroke.

Histamine-induced microvascular leakage in pial venules: differences between the SJL/J and BALB/c inbred strains of mice

The actions of histamine on pial venule leaky site formation were measured intravitally in two inbred strains of mice (BALB/c and SJL/J). Pial venules were visualized using a cranial window microscopy technique, and microvascular leaky site formation was assessed visually using a fluorescein-dextran indicator. SJL/J mice were found to be sensitive to histamine-induced leakage, whereas the BALB/c strain was refractory. Exposure to pertussis toxin enhanced the sensitivity to histamine in the SJL/J strain, but little effect was observed for BALB/c mice. However, the employment of a polymerase chain reaction (PCR) technique for the detection of mRNA for histamine H1 receptor identified receptor-specific message in isolated cerebrovascular endothelium from both strains of mice. The lack of pial responsiveness in the BALB/c mice remains unexplained. Mast cells in the dura mater were found to be more numerous in SJL/J mice than in BALB/c mice. This observation supports previous observations of strain-specific differences in CNS inflammation. The results support the concept that genetically controlled differences in vascular sensitivity and localization of CNS-associated mast cells may play important roles in the generation of vasogenic edema and inflammation in CNS trauma and disease.

Dexamethasone down-regulates endothelin receptors in human cerebromicrovascular endothelial cells

Human cerebromicrovascular endothelial cells (HBEC) in culture express high affinity ETA receptors coupled to phospholipase C activation. Pretreatment of HBEC with 1 microM dexamethasone for 24 h decreased the number of the ET-1 binding sites (Bmax) on HBEC (96 fmol/mg protein vs 57 fmol/mg protein) without changing the binding affinity (KD) (101 pM vs 92 pM) or displacing profile (ET-1 = ET-2 > ET-3 > S6c). Dexamethasone-pretreated HBEC also exhibited a 40% reduction in the maximal ET-1-stimulated inositol triphosphate (IP3) production, whereas half-maximal stimulatory concentration (EC50) was not affected. This effect of dexamethasone was concentration-dependent, and most pronounced after 24 h of pretreatment. The inhibitory effect of dexamethasone on the ET-1-induced IP3 production was abolished by glucocorticoid-receptor antagonist cortexolone. In contrast, vasopressin-mediated IP3 response in HBEC was not changed by dexamethasone. Cyclo-oxygenase inhibitors indomethacin and acetylsalicylic acid did not influence the ET-1-induced IP3 production by HBEC. The down-regulation of ETA receptors in HBEC by dexamethasone, may represent one of the mechanisms involving the described effects of glucocorticoids on cerebromicrovascular function (i.e. changes in blood brain barrier properties, secretion of vasoactive factors, vascular morphogenesis).