Observations on penetration of serum proteins into the central nervous system

Contribution of Fibrinogen to Inflammation and Neuronal Density in Human Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and disability, particularly among the young. Despite this, no disease-specific treatments exist. Recently, blood-brain barrier disruption and parenchymal fibrinogen deposition have been reported in acute traumatic brain injury and in long-term survival; however, their contribution to the neuropathology of TBI remains unknown. The presence of fibrinogen-a well-documented activator of microglia/macrophages-may be associated with neuroinflammation, and neuronal/axonal injury. To test this hypothesis, cases of human TBI with survival times ranging from 12 h to 13 years (survival <2 months, n = 15; survival >1 year, n = 6) were compared with uninjured controls (n = 15). Tissue was selected from the frontal lobe, temporal lobe, corpus callosum, cingulate gyrus, and brainstem, and the extent of plasma protein (fibrinogen and immunoglobulin G [IgG]) deposition, microglial/macrophage activation (CD68 and ionized calcium-binding adapter molecule 1 [Iba-1] immunoreactivity), neuronal density, and axonal transport impairment (β-amyloid precursor protein [βAPP] immunoreactivity) were assessed. Quantitative analysis revealed a significant increase in parenchymal fibrinogen and IgG deposition following acute TBI compared with long-term survival and control. Fibrinogen, but not IgG, was associated with microglial/macrophage activation and a significant reduction in neuronal density. Perivascular fibrinogen deposition also was associated with microglial/macrophage clustering and accrual of βAPP in axonal spheroids, albeit rarely. These findings mandate the future exploration of causal relationships between fibrinogen deposition, microglia/macrophage activation, and potential neuronal loss in acute TBI.

Functional recovery of neuronal activity in rat whisker-barrel cortex sensory pathway from freezing injury after transplantation of adult bone marrow stromal cells

The effect of transplantation of adult bone marrow stromal cells (MSCs) into the freeze-lesioned left barrel field cortex in the rat was investigated by measurement of local cerebral glucose utilization (lCMR(glc)) in the anatomic structures of the whisker-to-barrel cortex sensory pathway. Bone marrow stromal cells or phosphate-buffered saline (PBS) were injected intracerebrally into the boundary zone 1 h after induction of the freezing cortical lesion. Three weeks after surgery, the 2-[(14)C]deoxyglucose method was used to measure lCMR(glc) during right whisker stimulation. The volume of the primary necrotic freezing lesion was significantly reduced (P<0.05), and secondary retrograde degeneration in the left ventral posteromedial (VPM) thalamic nucleus was diminished in the MSC-treated group. Local cerebral glucose utilization measurements showed that the freezing cortical lesion did not alter the metabolic responses to stimulation in the brain stem trigeminal nuclei, but eliminated the responses in the left VPM nucleus and periphery of the barrel cortex in the PBS-treated group. The left/right (stimulated/unstimulated) lCMR(glc) ratios were significantly improved in both the VPM nucleus and periphery of the barrel cortex in the MSC-treated group compared with the PBS-treated group (P<0.05). These results indicate that MSC transplantation in adults may stimulate metabolic and functional recovery in injured neuronal pathways.

Ischaemic brain oedema

Ischaemic brain oedema appears to involve two distinct processes, the relative contribution and time course of which depend on the duration and severity of ischaemia, and the presence of reperfusion. The first process involves an increase in tissue Na+ and water content accompanying increased pinocytosis and Na+, K+ ATPase activity across the endothelium. This is apparent during the early phase of infarction and before any structural damage is evident. This phenomenon is augmented by reperfusion. A second process results from a more indiscriminate and delayed BBB breakdown that is associated with infarction of both the parenchyma and the vasculature itself. Although, tissue Na+ level still seems to be the major osmotic force for oedema formation at this second stage, the extravasation of serum proteases is an additional potentially deleterious factor. The relative importance of protease action is not yet clear, however, degradation of the extracellular matrix conceivably leads to further BBB disruption and softening of the tissue, setting the stage for the most pronounced forms of brain swelling. A number of factors mediate or modulate ischaemic oedema formation, however, most current information comes from experimental models, and clinical data on this microcosmic level is lacking. Clinically significant brain oedema develops in a delayed fashion after large hemispheric strokes and is a cause of substantial mortality. Neurological signs appear to be at least as good as direct ICP measurement and neuroimaging in detecting and gauging the secondary damage produced by stroke oedema. The neuroimaging characteristics of the stroke, specifically the early involvement of greater than half of the MCA territory, are, however, highly predictive of the development of severe oedema over the subsequent hours and days. None of the available medical therapies provide substantial relief from the oedema and raised ICP, or at best, they are temporizing in most cases. Hemicraniectomy appears most promising as a method of avoiding death from brain compression, but the optimum timing and manner of patient selection are currently being investigated. All approaches to massive ischaemic brain swelling are clouded by the potential for survival with poor functional outcome. It is possible to manage blood pressure, serum osmolarity by way of selective fluid administration, and a number of other systemic factors that exaggerate brain oedema. Broad guidelines for treatment of stroke oedema can therefore be given at this time.

Kinetics of Photofrin II in perifocal brain edema

Photodynamic therapy is under intense investigation as a possible adjuvant for the treatment of malignant tumors of the central nervous system. It relies on the fact that photosensitizers are selectively taken up or retained by malignant tissue. However, most brain tumors are accompanied by substantial vasogenic edema as a consequence of blood-brain barrier disruption within the tumor, leading to extravasation and propagation of plasma constituents into the surrounding brain tissue. Systemically administered photosensitizers may enter healthy tissue together with the edema fluid, possibly leading to sensitization of tissues outside the tumor. To test this hypothesis, vasogenic edema was induced by cold injury to the cortex in rats. The edema thus obtained is highly reproducible and very similar to tumor-associated edema. Just after injury induction, Photofrin II (PF-II), a commonly used photosensitizing agent, was administered at a dose of 5 mg per kilogram of body weight along with fluorescein isothiocyanate (FITC)-labeled albumin to mark edema advancement. After 1, 4, 12, or 24 hours, the brains were removed and frozen, and cryosections were studied with high-sensitivity video fluorescence microscopy for edema extravasation within the lesion and propagation of PF-II into the surrounding gray matter. PF-II advanced with edema along the corpus callosum underlying the cortex to a distance of 5 mm from the lesion after 4 hours. With the exception of the lesion, PF-II fluorescence returned to baseline after 24 hours, indicating subsequent washout. Propagation was comparable to the spreading of FITC-marked albumin. The authors conclude that photosensitizers spread with edema, an observation that may be pertinent to a number of questions concerning photodynamic therapy of cerebral tumors.

Aggravation of vasogenic cerebral edema by multiple-dose mannitol

The authors investigated the pharmacokinetics of mannitol administered for treatment of vasogenic cerebral edema. A cortical cold injury was produced in 23 cats maintained under general anesthesia for 5 or 21 hours. Control animals received no mannitol, while treatment groups received either a single dose or five doses administered at 4-hour intervals of 0.33 gm/kg radiolabeled mannitol. Liquid scintillation counting was carried out to determine the concentrations of mannitol in the cerebral tissue, cerebrospinal fluid, plasma, and urine. Cerebral water content and linear progression of edema were also measured. Rapid plasma clearance prevented accumulation of mannitol after multiple intravenous injections, as 84% +/- 2% (mean +/- standard error of the mean) of the infused mannitol was excreted through the urine. However, there was progressive accumulation of mannitol within the cerebral tissue, especially in the edematous white matter where it reached a level of 0.33 +/- 0.03 mg/gm after five doses, exceeding the trough plasma concentrations by a ratio of 2.69:1. Water content measurement showed that a single dose of mannitol failed to reduce cerebral water content or edema progression at 4 hours postinjection, while multiple doses produced a 3% increase in water content in edematous regions (p greater than 0.0003). The results of this study demonstrated a reversal of the osmotic concentration gradient between edematous brain and plasma following multiple mannitol injections, associated with exacerbation of vasogenic cerebral edema.

Ontogenesis of transthyretin gene expression in chicken choroid plexus and liver

1. Chicken liver transthyretin cDNA hybridizes strongly with choroid plexus transthyretin mRNA from chickens, pigeons, quails and ducks. 2. In the chicken at hatching the choroid plexus has reached 70%, total brain 30%, and liver 5.8% of their organ masses in adults. 3. The proportion of transthyretin mRNA in total RNA is 0.45-times the adult value in the choroid plexus of the chicken at hatching. 4. In the liver at hatching, the proportion of transthyretin mRNA in total RNA is 1.1-times the value in adult chickens. 5. The pattern of maturation of transthyretin gene expression in chicken liver is comparable to that in precocial, but differs from that in altricial mammals.

Autoradiographic patterns of brain interstitial fluid flow after collagenase-induced haemorrhage in rat

Cerebral oedema accompanies intracerebral haemorrhage. We induced intracranial bleeding by the intracerebral injection of bacterial collagenase. There was oedema observed both at the haematoma site in the caudate/putamen and bilaterally in the hippocampal regions. To determine the role of vasogenic oedema spread from the site of injury, we studied by autoradiography the distribution of extracellular markers injected along with the collagenase. Both 14C-dextran (m.w. 70,000) and 14C-sucrose (m.w. 341) spread away from the injection site into both hippocampal regions in a similar pattern, suggesting bulk flow. Vasogenic oedema secondary to a haemorrhagic lesion in the caudate/putamen is an important cause of the oedema observed in both hippocampal regions in our model.

Effects of etoposide-induced blood-brain barrier disruption on brain water, intracranial pressure, and cerebral vasomotor tone

This study investigated the effects of hypertension and water loading on etoposide-induced, reversible blood-brain barrier disruption in a rat model. Twenty-nine animals were divided into four groups: group 1--intracarotid (i.c.) injection of saline followed in 1 h by 5 ml i.c. water; group 2--i.c. etoposide followed by i.c. water; group 3--i.c. saline followed by i.v. metaraminol to increase systemic blood pressure; group 4--i.c. etoposide followed by i.v. metaraminol. Systemic blood pressure and intracranial pressure were monitored continuously. Evans blue staining of the brain was used as a monitor of blood-brain barrier disruption. Animals were killed 1 h after either aramine or water infusion, and the brains removed and inspected for the degree of disruption. After dehydration, brain water was calculated for each hemisphere. Two-thirds of the animals infused with etoposide had evidence of barrier disruption, whereas none of the control animals infused with saline were disrupted. Neither control groups 1 or 3 showed significant change in intracranial pressure after water loading or augmentation of systemic blood pressure, respectively. Group 4 animals failed to demonstrate any significant change in intracranial pressure despite marked barrier disruption and acute hypertension (within the limits of normal autoregulation). A small but statistically significant increase in intracranial pressure was noted in group 2 animals with the greatest degree of barrier disruption. A significant increase in brain water was observed ipsilateral to etoposide infusion in only those animals with the most marked barrier disruption. These results indicate that etoposide-induced blood-brain barrier disruption caused significant increases in brain water without significant alteration of cerebral vasomotor tone or increases in intracranial pressure after water loading except in the most severe disruption. The classic untoward consequences of vasogenic edema were not encountered in the present model.

Acute responses to experimental blunt head trauma: topography of white matter edema

The location of edema and territory of extravasation of serum protein were examined in the white matter of cats with different forms of intracranial pathology following an impact-acceleration injury to the head. Edema was tested with an organic density gradient and Evans blue dye was used as a marker for breakdown of the blood-brain barrier. Animals with tissue hemorrhage (contusions) involving both cerebral cortex and white matter had a substantial, progressive accumulation of Evans blue-stained edema near tissue hemorrhage during the 6 h following trauma. In addition, this category of cats had a widespread, mild edema at 15 min after injury that was usually unaccompanied by Evans blue stain. Cats with cortical contusions had rather mild edema neighboring tissue hemorrhage; animals with subarachnoid hemorrhage in the absence of cerebral contusions had neither measurable edema nor (usually) visible Evans blue staining. We conclude that: acute traumatic cerebral edema varies considerably in presence, magnitude and territory with different forms of intracranial pathology; and mechanically induced edema can occur that is independent of spread of fluid from areas of tissue hemorrhage.

Acute responses to experimental blunt head trauma. Topography of cerebral cortical edema

Anesthetized cats subjected to impact followed by acceleration and rotation of the skull were sacrificed at 15 minutes or 6 hours after injury and were selected for study if unilateral cerebral contusion was present. Widespread areas of cerebral cortex were examined bilaterally for edema, using measurement of tissue density with an organic gradient, and for breakdown of the blood-brain barrier to plasma protein tagged with Evans blue dye. At both times tested, a halo of vasogenic edema (Evans blue stain plus decreased density) was present in the cortex surrounding areas of contusion. At 15 minutes after injury, animals with deep contusions also had a slight decrease in density without Evans blue staining, interpreted as cytotoxic edema, in some gyri neighboring the contusion. At 6 hours, cytotoxic edema was not evident, but some animals had vasogenic edema in the gyri adjoining the contusion. Most gyri contralateral to contused areas had neither Evans blue staining nor changes in tissue density. These findings suggest that, with the present head-injury model, acute changes in tissue density and vascular permeability occur in the cerebral cortex of hemispheres with contusion. These responses are related topographically to contusion sites, and change over the two times studied. The authors conclude that events in addition to spread of fluid from areas of contusion contribute to the edema of head injury, and that more than one form of edema can follow mechanical trauma to the brain.

Acute changes in regional brain water content following experimental closed head injury

A Remington humane stunner was used to deliver blows to the skulls of anesthetized cats. The animals were sacrificed at 30 minutes or 1, 2, or 6 hours after trauma and selected for data collection on the basis of the following two categories of gross intracranial pathology: 1) unilateral contusion, with subarachnoid hemorrhage (SAH); or 2) SAH only. For selected cats, specific gravity was measured in 5- to 10-mg samples of uncontused tissue taken from coronal slices at the level of the frontoparietal suture. The regions tested included dorsal cerebral cortex, subcortical white matter, deep white matter, and caudate nucleus. Specific gravity data from injured animals were compared with those from similar areas in uninjured anesthetized cats to test for cerebral edema. At 30 minutes after head injury, contused hemispheres had significant edema of all tested except the caudate nucleus. Edema of the subcortical and deep white matter increased with time after the injury. Increase in water content of the cerebral cortex was transient and appeared unrelated to contusion. The caudate nucleus was edematous only at 6 hours, suggesting movement of fluid from the deep white matter compartment into the nucleus. The hemispheres opposite the contusion and those related to SAH had, with one exception, an absence of edema in the white matter and caudate nucleus, but a transient increase in water content of the cerebral cortex. These findings suggest that, in the presence of contusion, cerebral edema can contribute to brain swelling as early as 30 minutes after closed head trauma. In addition, a transient and minimal cortical edema, perhaps related to ischemia, occurred in all groups of hemispheres examined.

Dynamics of cerebral edema. The role of an intact vascular bed in the production and propagation of vasogenic brain edema

Brain edema was produced in cats by a standardized cortical freezing lesion. With a careful microsurgical tehnique, the injured cortex was removed as a single piece, either immediately after induction or at 2, 4, or 8 hours after lesion production. The injured brain was either discarded or replaced in its bed. Brain edema and the defect in the blood-brain barrier were assessed by determining percent dry weight, increase in volume of white matter, and spread of Evans' blue by planimetry. The results indicate that 1) if the lesion is removed immediately after production, formation of the expected vasogenic brain edema is completely abolished; 2) replacement of the frozen brain is unable to induce significant increase in permeability of the surrounding blood-brain barrier or a significant amount of brain edema; and 3) if the lesion is removed at 2, 4, or 8 hours with or without replacement, advancement of the edema front and increase in the amount of edema is stopped. It appears that an intact vascular bed is necessary for the extracellular fluid component of brain edema, and that no edemagenic factors exist within the injured brain in this model that influence either the production or propagation of the increased extracellular fluid volume.

Protective effects of steroids on the corticomicrocirculation injured by cold

✓ Early microcirculatory changes after focal cold injury of the cerebral cortex were examined in dogs with and without steroids by serial fluorescein angiography of the brain (FAB), by measurement of the diameter of epicerebral vessels, and by measurement of cerebral blood flow with the clearance method using krypton-85 and xenon-133. Changes in the transcerebral vessels were examined by x-ray projection microangiography.

Within 30 minutes of the injury, the cortical area injured by a temperature of −65° C showed a reduction in blood flow of 60%. When treated with steroids and while still at the same temperature, blood flow was reduced by only 35%. Serial FAB revealed slowing and arrest of flow in the epicerebral microcirculation which could be noted first in the small veins, then in the medium-sized veins and small arteries. Fluorescein dye leaked from the epicerebral vessels, around the small veins, then around larger veins and small arteries. Some leakage of dye from medium-sized arteries was noted 2 hours after injury. This sequence of slowing and arrest of the microcirculation, with exit of dye from intact arterial vessels, identified here for the first time in relation to a cortical freezing lesion, may help to explain the development of later brain edema which spreads widely in the subcortical white matter. After steroids, improvement of the microcirculation was present as defined by cortical blood flow, fluorescein angiography, and x-ray projection microangiography.

The effects of glucosteroids on experimental cold-induced brain edema. Gross morphological alterations and vascular permeability changes

✓ Although the beneficial effects of glucosteroids on brain edema are well documented and generally accepted clinically, investigations into their effects on experimental brain edema have been somewhat contradictory. In this study brain edema was produced by local cortical freezing in animals pretreated with glucosteroids and in untreated animals. Gross estimation of edema, wet weight-dry weight determination, and mechanical planimetry of areas of extravasated dye indicated a statistically significant reduction in edema of both white and gray matter at 24, 48, and 72 hours. Gross estimation of edema indicated a persisting effect with resolution of edema at 5 days in treated animals and from 7 to 12 days in untreated animals. These studies substantiate initial investigations and indicate a primary reduction in brain edema by glucosteroids. At least one of the effects of the glucosteroids appears to be reduction of the abnormal vascular permeability causing brain edema.

Transorbital approach to the middle cerebral artery of the squirrel monkey: a technique for experimental cerebral infarction applicable to ultrastructural studies

An appropriate surgical technique for the production of cerebral infarction must fulfill, among others, the following criteria in order to be suitable for electron microscopy (EM) studies: (1) the method of arterial occlusion should yield a high percentage of infarcts with predictable average size; (2) there must be avoidance of surgical manipulation (i.e., retraction) of the cerebral tissues or exposure of the same to the atmosphere; and (3) the method for occluding the artery must be one that permits fixation by perfusion of the ischemic and nonischemic brain.

Modifications to a previously devised method for induction of cerebral infarct are herein described. This new surgical approach has made it possible to conduct detailed and sequential ultrastructural analysis of experimental cerebral infarctions.