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

Tumor-associated neurological dysfunction prevented by lazaroids in rats

The efficacy of U-74006F and U-78517F in the treatment of blood-tumor barrier permeability and tumor-associated neurological dysfunction was evaluated in a brain-tumor model in rats. U-74006F is a 21-aminosteroid and U-78517F is a 2-methylamino chroman. Rats with stereotactically implanted Walker 256 tumors were treated with methylprednisolone, U-74006F, U-78517F, or vehicle (0.05 N HCl) on Days 6 through 10 following implantation. Neurological function and vascular permeability were assessed on Day 10. Methylprednisolone and U-74006F were equally effective at preventing neurological dysfunction compared to the control group (p less than 0.01); U-78517F was slightly less effective than U-74006F and methylprednisolone but was significantly better than vehicle in preventing neurological dysfunction. Delivery of methylprednisolone resulted in a significant decrease in tumor vascular permeability (p less than 0.006) while U-74006F and U-78517F had no effect on permeability. This suggests that U-74006F and U-78517F prevented tumor-associated neurological dysfunction by a mechanism other than decreasing permeability in tumor capillaries, and that U-74006F or U-78517F could prove useful in the treatment of brain tumors.

A novel treatment for ischemic intracranial hypertension in cats

There is no accepted efficacious treatment for ischemic cerebral edema. We show in a cat model of focal cerebral ischemia that infarct volume can be reduced (p less than 0.05) by ventriculocisternal perfusion with an oxygenated fluorochemical emulsion (bis-perfluorobutylethylene). An accompanying effect of such ventriculocisternal perfusion is a reduction in intracranial pressure. At 18 hours following the start of the perfusion, there was a significant (p less than 0.05) difference in intracranial pressure between nonperfused controls (mean 11.4 [range 2.3-23.0] torr, n = 6) and cats perfused with an oxygenated nutrient solution not containing fluorochemical (mean 11.3 [range 3.0-29.0] torr, n = 8) or animals perfused with the oxygenated fluorochemical emulsion (mean 2.21 [range 0-3.5] torr, n = 7). Perfusion with this oxygenated fluorochemical emulsion warrants further study as a treatment for elevated intracranial pressure.

Cerebrovascular and metabolic effects on the rat brain of focal Nd:YAG laser irradiation

To investigate the effects of focal neodymium:yttrium-aluminum-garnet (Nd:YAG) laser irradiation (lambda = 1060 nm) on regional cerebral blood flow, cerebral protein synthesis, and blood-brain barrier permeability, the parietal brain surface of 44 rats was irradiated with a focused laser beam at a constant output energy of 30 J. Survival times ranged from 5 minutes to 48 hours. Laser irradiation immediately caused well-defined cortical coagulation necrosis. Within 5 minutes after unilateral irradiation, 14C-iodoantipyrine autoradiographs demonstrated severely reduced blood flow to the irradiation site and perilesional neocortex, but a distinct reactive hyperemia in all other areas of the forebrain. Apart from a persistent ischemic focus in the vicinity of the cortical coagulation necrosis, blood flow alterations in remote areas of the brain subsided within 3 hours after irradiation. Autoradiographic assessment of 3H-tyrosine incorporation into brain proteins revealed rapid onset and prolonged duration of protein synthesis inhibition in perifocal morphologically intact cortical and subcortical structures. Impairment of amino acid incorporation proved to be completely reversible within 48 hours. Immunoautoradiographic visualization of extravasated plasma proteins using 3H-labeled rabbit anti-rat immunoglobulins-showed that, up to 1 hour after irradiation, immunoreactive proteins were confined to the neocortex at the irradiation site. At 4 hours, vasogenic edema was present in the vicinity of the irradiation site and the subcortical white matter, and, at later stages (16 to 36 hours), also extended into the contralateral hemisphere. Although this was followed by a gradual decrease in labeling intensity, resolution of edema was still not complete after 48 hours. Analysis of sequential functional changes in conjunction with morphological alterations indicates that the evolution of morphological damage after laser irradiation does not correlate with the time course and spatial distribution of protein synthesis inhibition or vasogenic edema. Although the central coagulation necrosis represents a direct effect of radiation, the final size of the laser-induced lesion is determined by a delayed colliquation necrosis due to persistent perifocal ischemia. Extent and severity of ischemia in a zone with initial preservation of neuroglial cells can be explained by the optical properties of the Nd:YAG laser; extensive scattering of light within brain parenchyma associated with a high blood-to-brain absorption ratio selectively affects blood vessels outside the irradiation focus.

Angiotensin peptide regulation of fluid-phase endocytosis in brain microvessel endothelial cell monolayers

An in vitro model comprised of primary cultures of brain microvessel endothelial cells was used to investigate angiotensin II (Ang II) effects on blood-brain barrier fluid-phase endocytosis. The effects of Ang II, saralasin, sarathrin, bradykinin (BK), and phorbol myristate acetate (PMA) on brain microvessel endothelial cell fluid-phase endocytosis were determined using the fluorescent marker, Lucifer yellow. Nanomolar concentrations of saralasin (a partial Ang II agonist) stimulated brain microvessel endothelial cell endocytosis by 30% whereas Ang II treatment enhanced Lucifer yellow uptake by 20%. Sarathrin (an Ang II antagonist) had no effect on Lucifer yellow uptake. Nanomolar concentrations of BK and PMA also stimulated Lucifer yellow uptake by the brain microvessel endothelial cell by 40 and 95%, respectively. Stimulatory effects of Ang II and saralasin on Lucifer yellow uptake by brain microvessel endothelial cells could be completely blocked by pretreatment with either sarathrin or indomethacin (an inhibitor of prostaglandin synthesis). In contrast, the effects of neither BK nor PMA on brain microvessel endothelial cell uptake of Lucifer yellow ere altered by indomethacin pretreatment. Results indicated that Ang II, saralasin, BK, and PMA produce similar stimulatory effects on brain microvessel endothelial cell fluid-phase endocytosis with only Ang II and saralasin, producing increases in brain microvessel endothelial cell fluid-phase endocytosis that appeared to be mediated by prostaglandins.

Changes in blood-brain barrier and cerebral blood flow following elevation of circulating serotonin level in anesthetized rats

Plasma serotonin (5-HT) was elevated by an intravenous infusion of this amine into urethane-anaesthetized rats and the concentration approximated that present in various neurological diseases and mental abnormalities. An infusion of 10 micrograms per kg body weight for 10 min significantly increased blood-brain barrier (BBB) permeability to Evans blue and 131I-sodium measured in whole brain. Regional BBB determinations with labelled 131I-sodium showed that the permeability to this compound was increased in the cerebral cortex, hippocampus, caudate nucleus, hypothalamus, colliculus and the cerebellum but not in the pons and the medulla oblongata. Regional blood flow was reduced in the same parts which showed BBB abnormality tested with 125I-labeled microspheres. Pretreatment with cyproheptadine, a 5-HT2 receptor antagonist, prevented the BBB increase and the regional blood flow was near normal values. Similar effects were obtained with indomethacin, a prostaglandin synthesis inhibitor. Vinblastine, known to influence vesicular transport, eliminated extravasation of the tracers but the regional blood flow remained depressed. A hypothesis is put forward that serotonin after binding to its receptor in the cerebral vessels stimulates prostaglandin which either directly or by means of cyclic adenosine monophosphate causes an increased vesicular transport across the endothelial cells and thus an extravasation of tracer substances in the brain. Obviously, this form of exudation can be influenced by pharmacological means.

Increased 5-hydroxytryptamine immunoreactivity in traumatized spinal cord. An experimental study in the rat

The possibility that serotonin (5-hydroxytryptamine, 5-HT) is involved in the early tissue reactions occurring in spinal cord trauma was examined in a rat model using an immunocytochemical technique. The injury was made in the form of a 5-mm long and 2.5-mm wide lesion of the right dorsal horn at the level of T10-11. Injured rats, pretreated with the 5-HT synthesis blocking agent, p-chlorophenyl alanine (p-CPA) were compared with untreated injured controls and the animals were allowed to survive for 5 h. The distribution of 5-HT was examined in proximal and distal cross- sections of the cord, located 2 and 5 mm away from the injury. Normal rats showed immunoreactive material in nerve cell processes and in a few nerve cell bodies of the ventral horns. The trauma to the spinal cord caused a marked increase in 5-HT immunoreactivity in the segments located 2 mm proximal and distal to the injury, particularly in the ipsilateral ventral horn. The segment located 5 mm distal to the lesion showed a similar increase in immunoreactivity but it was apparently less pronounced in the corresponding proximal segment. Treatment with p-CPA markedly reduced the trauma-induced increase in 5-HT immunoreactivity in all the segments. These immunohistochemical findings were in line with the changes in the contents of 5-HT measured biochemically in corresponding spinal cord segments. At the onset of the trauma to the spinal cord 5-HT is thus present in the tissue, mainly in the form of 5-HT-containing nerve cell processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of p-chlorophenylalanine on microvascular permeability changes in spinal cord trauma. An experimental study in the rat using 131I-sodium and lanthanum tracers

The possibility that serotonin can take part in the initiation of the increased microvascular permeability occurring in a spinal cord trauma was investigated in a rat model with 131I-sodium and lanthanum as tracers. We influenced the serotonin content in the tissue pharmacologically by treating animals with a serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA), before the production of the injury and compared the results with injured, untreated controls. A small incision was made in the dorsal horn of the lower thoracic cord. It caused a progressive extravasation of 131I-sodium in the damaged segment, measured after 1, 2 and 5 h. Rostral and caudal segments also showed a significant but lower accumulation of 131I-sodium. Lanthanum added to the fixative was used as an ionic tracer detectable by electron microscopy. The endothelial cells of microvessels removed from the perifocal region after 5 h showed a marked increase in the number of lanthanum-filled vesicles. Many endothelial cells had a diffuse penetration of the tracer into the cytoplasm and the basement membrane. However, the tight junctions usually remained closed to lanthanum. Pretreatment with p-CPA markedly reduced the extravasation of 131I-sodium measured at 5 h in the traumatized cord. At the cellular level, the endothelial vesicles filled with lanthanum approached the condition of uninjured animals. The diffuse infiltration of lanthanum into endothelial cells and its spread into the basement membrane of the vascular wall were usually absent. Our results indicate that serotonin plays a role in the initiation of the increased microvascular permeability which occurs in spinal cord injuries.

Edema formation and cellular alterations following spinal cord injury in the rat and their modification with p-chlorophenylalanine

The possibility that serotonin can modify the early pathological sequences occurring in spinal cord trauma was investigated in a rat model. To that end we took advantage of the possibility of influencing serotonin pharmacologically by treating animals with a serotonin synthesis inhibitor, p-chlorophenylalanine (p-CPA) before the production of the injury and compared the results with injured, untreated controls. A unilateral incision was made into the dorsal horn of the lower thoracic cord (about 2.5 mm deep, 4.5 mm long) and the rats were allowed to survive up to 5 h after the trauma. The injured region from untreated animals showed macroscopically at that time a pronounced swelling and the water content had increased by 3.5% as compared to intact controls. The segments rostral and caudal to the lesion also exhibited a profound increase in water content. Light microscopy revealed a significant expansion of the spinal cord as compared to controls. The swelling was most pronounced in the gray matter on the injured side. Electron microscopy showed distorted neurons, swollen astrocytes and extracellular edema in the gray matter in and around the primary lesion. There was also a sponginess in the surrounding white matter with disruption of myelin, collapsed axons and widened periaxonal spaces. Pretreatment of the rats with p-CPA significantly reduced the swelling of the injured spinal cord and there was no visible expansion. The ipsilateral edema in the central gray matter was considerable less pronounced as compared to that in untreated animals. The increase in water content was less than 1% in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Early polymorphonuclear leukocyte accumulation correlates with the development of posttraumatic cerebral edema in rats

To evaluate the role of polymorphonuclear leukocytes (PMNs) in the development of posttraumatic cerebral edema, we quantitatively assessed the time course and magnitude of PMN accumulation and its relationship to cerebral edema formation after cerebral trauma in 78 rats. 111In-labeled PMN accumulation was measured in 26 rats in the first 8 h after right hemispheric percussive cerebral trauma or a sham control condition. 51Cr-labeled erythrocyte accumulation was measured simultaneously in 22 rats to assess the contribution of expansion of blood volume to early posttraumatic PMN accumulation. Edema formation [right-left (R-L) hemispheric difference in percent brain water], R-L hemispheric labeled-PMN accumulation, and blood volume index-adjusted PMN accumulation were measured between 0-2 h and 4-8 h posttrauma. PMN accumulation was elevated markedly in the first 2 h posttrauma compared with values in sham controls (13.45 +/- 2.53 vs -0.03 +/- 0.31, p less than 0.01) but not when adjusted for blood volume index (BVI), suggesting that PMN accumulation in the first 2 h posttrauma was due to expansion of blood volume. Between 4 and 8 h posttrauma, however, both total (2.56 +/- 0.82 vs -0.29 +/- 0.52) and BVI-adjusted (8.78 +/- 3.97 vs -0.48 +/- 0.79) PMN accumulation were elevated (p less than 0.05) compared with sham. Brain edema and total PMN accumulation were significantly correlated at both 2 h and 8 h posttrauma (r2 = 0.77, p less than 0.001, and r2 = 0.69, p less than 0.002, respectively), but a significant correlation between edema and BVI-adjusted PMN accumulation was observed only at 8 h posttrauma (r2 = 0.96, p less than 0.001). These data show that PMN accumulation after traumatic brain injury occurs with an initial phase explained by an increase in blood volume in the first 2 h posttrauma followed by a subsequent acute inflammatory phase. The significant correlation between PMN accumulation and the development of cerebral edema is the first quantitative relationship demonstrated between PMN accumulation and a relevant pathophysiological variable. A causal role for PMNs in the genesis of posttraumatic cerebral edema has yet to be proved.

Brain oedema and cellular changes induced by acute heat stress in young rats

Exposure of young animals (70-80 g, Age 6-7 weeks) to heat stress (HS) at 38 degrees C for 4 h in a B.O.D. incubator (rel humid 50-55%, wind vel 28.6 cm/sec) resulted in a 4.41% increased brain water content from the control value. Morphological studies in parietal cerebral cortex at light microscopical level revealed chromatolysis and appearance of dark neurons. Electron microscopy of similar regions showed perivascular oedema, vacuolation and collapsed microvessels. The swelling of astrocytes and of postsynaptic membranes was frequent. A diffuse infiltration of lanthanum (La[NO3]3) in endothelial cell cytoplasm and in the vesicles was very common. Occasionally, the lanthanum was seen in the basement membrane but the tight junctions were mainly intact. At this time period, a significant increase in blood-brain barrier (BBB) permeability as well as 5-HT levels in brain and plasma were observed. Pretreatment with p-CPA (a 5-HT synthesis inhibitor) prevented the increase of brain water content. BBB permeability and 5-HT levels in brain and plasma. Cyproheptadine (a 5-HT2 receptor antagonist) treatment significantly reduced the occurrence of increased brain water content and the BBB permeability. The 5-HT level continued to remain high. These results point out a probable role of 5-HT in pathophysiology of HS via 5-HT2 receptors.

Alteration of substance P after trauma to the spinal cord: an experimental study in the rat

The distribution of substance P was determined in the rat spinal cord and brain after a focal traumatic injury to the thoracic region (T10-11) of the spinal cord. There was at 1 and 2 h after the injury a statistically significant increase of the substance P content not only in the injured segment but also in samples removed 5 mm proximal (T9) and distal (T12) to the lesion. At 5 h the substance P content of the injured segment of the cord was reduced by 30% compared with controls. However, there was a significant increase in the concentration of this peptide in segments located 5 mm cranial and caudal to the injury (65% and 22%, respectively). Interestingly, the whole brain content of substance P showed a statistically significant 22% increase from control values at 5 h after the injury. At 1 and 2 h after the spinal cord injury there was a significant decrease in whole brain substance P concentration by 25% and 65%, respectively. Pretreatment with p-chlorophenylalanine (a serotonin synthesis inhibitor) markedly reduced the endogenous content of substance P in whole brain of normal animals. In these animals, the spinal cord content of the peptide was elevated by 83-123% as compared to untreated control animals. Spinal cord trauma inflicted on p-chlorophenylalanine-treated animals did not affect the brain peptide level at all. However, a profound decrease was noted in all the spinal cord segments at 5 h as compared to the untreated traumatized group. The decrease in this peptide was more pronounced in the cranial and the injured segments as compared to the caudal one.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the arachidonate lipoxygenase inhibitor BW755C on traumatic and peritumoural brain oedema

The abstract BW755C is a novel non-steroidal anti-inflammatory agent. It inhibits synthesis of prostaglandins and leukotrienes by inhibition in the cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism. Cold injury induced vasogenic oedema was produced in 18 cats. The animals were sacrificed at six and twenty-four hours. One group was treated with BW755C. Seventeen white rabbits bearing an experimental brain tumour VX-2 carcinoma were treated for five consecutive days from the eight day after tumour injection to the thirteenth day. Untreated tumour bearing rabbits were used as control. Brain water content was measured by specific gravity method. BW755C did not reduce the water content following cold injury. There was no effect upon peritumoural oedema. The use of this novel blocking agent with diffuse effects in the arachidonic cascade was not beneficial for the reduction or prevention of brain oedema.

Early accumulation of serotonin in rat spinal cord subjected to traumatic injury. Relation to edema and blood flow changes

Changes in the concentration of serotonin (5-hydroxytryptamine) in the early period after a focal traumatic injury to rat spinal cord were determined and related to the formation of edema and alterations in blood flow. A unilateral, 5-mm-long and 3-mm-deep traumatic injury located 2 mm from the midline was created in the T10-11 segment of the cord. Five hours after the injury the serotonin concentration in the traumatized segment had increased more than 100% compared with controls. There was also a progressive increase in water content of the traumatized segment measured 1-5 h after the injury. On the other hand, the spinal cord blood flow showed a progressive decrease to about 35% of its initial value at 5 h. Pretreatment with p-chlorophenylalanine, a serotonin synthesis inhibitor, impeded the elevation in water content measured 5 h after the trauma. The spinal cord blood flow remained close to normal values and the increase in serotonin was absent. Our results show that trauma to the rat spinal cord will induce changes in the serotonin concentration of the tissue and that the associated formation of edema and blood flow alterations can be alleviated in serotonin depleted rats. Obviously, serotonin plays a significant role in the pathophysiology of traumatic injury of rat spinal cord.

The effects of pinacidil and tolbutamide in feline pial arteries in situ

The vasomotor effect of the K+ channel opener pinacidil was investigated in feline pial arteries of the parietal cortex. Perivascular microapplication (5 microliters in 40 sex) and an image splitting method for the measurement of vascular diameter were employed. Pinacidil (10(-11) - 10(-7) M) induced concentration-dependent dilatations at 10(-9) M and higher concentrations. A maximal dilatation of about 42% was achieved at 10(-8) M, the dilatation at 10(-7) M was reduced to 22%. The sulphonylurea tolbutamide exerted per se no effect in pial arteries but it blocked concentration-dependently the pinacidil induced dilatation. This is consistent with the presence of ATP-sensitive K+ channels in pial arteries which are closed under resting conditions.

Role of histamine in traumatic brain edema. An experimental study in the rat

The possibility that histamine plays a role in the formation of traumatic brain edema was investigated in the rat. A 3 mm deep and 3 mm long stab injury was performed in the right parietal cortex under urethane anaesthesia. The brain water content and histamine levels in plasma and brain were measured at the end of 1, 2 and 5 h periods after trauma. There was a 3.46% increase in brain water content in the traumatized hemisphere from the value in the control group at 5 h. The histamine content was increased by 107% in plasma and 51% in the traumatized brain hemisphere from the control value at this time period. The increased brain water content as well as the elevated plasma and brain histamine levels were prevented by prior treatment with the histamine H2-receptor antagonist cimetidine. Mepyramine (a histamine H1-receptor antagonist) failed to reduce the increased brain water content and the histamine levels in plasma and brain remained high. The results strongly indicate that histamine has a role in the formation of early traumatic brain edema and that this reaction can be influenced by pharmacological procedures.

Dissociation of GFAP intermediate filaments in EAE: observations in the lumbar spinal cord

Acute experimental allergic encephalomyelitis (EAE) in the Lewis rat is a cell-mediated autoimmune disease of central nervous system myelin. The lesion has been characterized by breakdown of the blood-brain barrier, edema, and periventricular infiltration of macrophages and lymphocytes. At the early stage of the disease, the astrocytes show a marked increase in immunostaining for glial fibrillary acidic protein (GFAP). A corresponding increase in GFAP content, however, cannot be demonstrated. Electron microscopic examination of the early lesion shows a typical reactive astrocytic response expressed by an enlarged watery cytoplasm, particularly at the level of the processes surrounding neurons and blood vessels and in the neuropil itself. The astroglial processes contain numerous glycogen particles (aggregates and single particles). Glial filaments are also conspicuous and are arranged in small bundles or loose thin filaments adjacent to the bundles. The glial filaments that normally appear as tight bundles have expanded and appear less dense. We suggest that the increase in GFAP immunostaining of the astrocytes in the early lesion is due in part to edema, which causes dissociation of the filaments and thereby exposes more antigenic sites to the antibodies.