Early changes in blood brain barrier permeability to small molecules after transient cerebral ischemia

Blood-brain barrier integrity and brain water and electrolytes during hypoxia/hypercapnia and hypotension in newborn piglets

This study examines the effects of hypoxia/hypercapnia and hypoxia/hypercapnia with hypotension (hypotensive-hypoxia/hypercapnia) on blood-to-brain transfer constants (K1) for sodium and mannitol and brain water and electrolyte contents in newborn piglets. Hypoxia/hypercapnia was induced for 60 min with the piglets breathing a gas mixture of 15% carbon dioxide, 10-12% oxygen, and 73-75% nitrogen adjusted to achieve an arterial pH less than 7.15, pO2 less than 40, and pCo2 greater than 60 mmHg and hypotension for 20 min by rapid phlebotomy to achieve a mean arterial blood pressure less than 40 mmHg. Piglets were studied during 1 h of, and 24 h after resuscitation from hypoxia/hypercapnia (arterial pH 6.9 +/- 0.18, pO2 36 +/- 6 mmHg, pCO2 68 +/- 8 mmHg, mean +/- S.D.) and 10 min, and 24 h after resuscitation from hypotensive-hypoxia/hypercapnia (mean arterial blood pressure 28 +/- 10 mmHg, mean +/- S.D.). Values for K1 for sodium and mannitol, measured using the integral technique were 15.9 and 5.2 ml.g-1.min-1 x 10(4) respectively, in 2-4-day-old controls, suggesting that the barrier is fully developed in newborn piglets. Values were not different during or after hypoxia/hypercapnia or 24 h after hypotensive-hypoxia/hypercapnia. Ten to forty min after hypotensive-hypoxia/hypercapnia, there was a proportional decrease in the K1 for sodium and mannitol of about 40%. These results suggest that the newborn piglet is similar to the adult with respect to impermeability of the blood-brain barrier to ions and small molecules and resistance of this barrier to systemic hypoxia/hypercapnia and hypotension.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebrovascular permeability and cognition in the aging rat

Regional cerebrovascular permeability-capillary surface area products (rPS) and brain vascular space (BVS) were measured in aging, conscious, unrestrained Sprague-Dawley rats. Three groups of animals were examined: young-mature (6 months), middle-aged (12-14 months), and old (24-26 months) rats. Complex maze learning had been previously characterized in these same animals. Maze learning declined with age. Brain vascular space did not differ significantly with age in any brain region. However, small, but significant age-dependent decreases in rPS (25-33%) were observed. These decreases occurred mainly in the old animals in the basal ganglia and parietal cortex, and in the middle-aged and old rats in the olfactory bulbs. Significant and unexpected positive average correlations between brain permeability-capillary surface area products (PS) and learning errors occurred primarily in young rats and were attributable mainly to changes in 5 of 14 brain regions; hypothalamus, hippocampus, parietal cortex, septal area and superior colliculus. The higher correlations between maze learning errors and PS in young animals may indicate dynamic regulation of this cerebrovascular parameter which is lessened with aging. Average correlations between PS and cerebral blood flow also were determined and found to be generally small and not significant for most brain regions and age groups.

Blood-brain barrier permeability to micromolecules and edema formation in the early phase of incomplete continuous ischemia

The distribution patterns of ionic Lanthanum (La3+; mol. wt. 139) were evaluated after 15, 30 and 60 min of middle cerebral artery occlusion in perfused-fixed rats. Blood-brain barrier (BBB) permeability to Evans blue (EB) and horseradish peroxidase (HRP; mol. wt. 40,000) in vivo was also evaluated. Brain tissue specific gravity was measured. An increase in brain water content was found as early as 30 min following occlusion. HRP and EB extravasation was not observed. La3+ crossed the interendothelial clefts of venules and capillaries at 30 and 60 min and was seen in both extracellular and intracellular brain compartments at 60 min. La3+ extravasation was seen in nonedematous areas bordering the regions of water accumulation. Our findings suggest that the early phase of incomplete continuous ischemia is accompanied by changes in BBB permeability and the interendothelial clefts of venules and capillaries seem to represent one of the early sites of ischemic damage.

Regional cerebral metabolites, blood flow, plasma volume, and mean transit time in total cerebral ischemia in the rat

Cerebral high-energy metabolites and metabolic end products were measured during and following total cerebral ischemia in the rat. During cerebral ischemia, lactate accumulation was greatest in the hippocampus, followed by the cerebral cortex and striatum. Following reperfusion, the rate of lactate clearance was slower in the hippocampus than in the other two regions. Regional CBF, cerebral plasma volume (CPV), and calculated mean transit time (MTT) were determined following reflow of ischemic tissue. During hyperemia, CPV, used as an indicator of capillary volume, increased concomitantly with CBF while the MTT remained near the control value, suggesting that the linear flow rate through the vasculature was unchanged. During hypoperfusion, CPV returned to control values, but there was a significant increase in MTT that would result from a decreased linear velocity. The finding of normal tissue energy charge, pHi, and concentration of other metabolites during hypoperfusion shows that hypoperfusion does not result in CBF-metabolic mismatch.

Delayed institution of hypertension during focal cerebral ischemia: effect on brain edema

The effect of induced hypertension instituted after a 2-h delay following middle cerebral artery occlusion (MCAO) on brain edema formation and histochemical injury was studied. Under isoflurane anesthesia, the MCA of 14 spontaneously hypertensive rats was occluded. In the control group (n = 7), the mean arterial pressure (MAP) was not manipulated. In the hypertensive group (n = 7), the MAP was elevated by 25-30 mm Hg beginning 2 h after MCAO. Four hours after MCAO, the rats were killed and the brains harvested. The brains were sectioned along coronal planes spanning the distribution of ischemia produced by MCAO. Specific gravity (SG) was determined in the subcortex and in two sites in the cortex (core and periphery of the ischemic territory). The extent of neuronal injury was determined by 2,3,5-triphenyltetrazolium staining. In the ischemic core, there was no difference in SG in the subcortex and cortex in the two groups. In the periphery of the ischemic territory, SG in the cortex was greater (less edema accumulation) in the hypertensive group (1.041 +/- 0.001 vs 1.039 +/- 0.001, P less than 0.05). The area of histochemical injury (as a percent of the cross-sectional area of the hemisphere) was less in the hypertensive group (33 +/- 3% vs 21 +/- 2%, P less than 0.05). The data indicate that phenylephrine-induced hypertension instituted 2 h after MCAO does not aggravate edema in the ischemic core, that it improves edema in the periphery of the ischemic territory, and that it reduces the area of histochemical neuronal dysfunction.

The effect of CO2 and non-CO2-generating buffers on cerebral acidosis after cardiac arrest: A 31P NMR study

There is controversy regarding the use of alkalinizing agents during reperfusion after cardiac arrest. The potential deleterious effects of sodium bicarbonate (bicarb) administration, including paradoxic cerebral acidosis, have led to the search for alternative agents. Tromethamine (tris) is a non-CO2-generating buffer that has been proposed for use during cardiopulmonary resuscitation. The purpose of this experiment was to compare the ability of tris with bicarb to correct brain pH (pH B) during reperfusion after a 12-minute cardiac arrest. Adult mongrel dogs were instrumented and placed in the bore of a Bruker Biospec 1.89 tesla superconducting magnet system. Ventricular fibrillation was induced; after 12 minutes, cardiopulmonary bypass was initiated and maintained for two hours with minimum flows of 80 mL/kg/min. Bicarb (n = 5) or tris (n = 5) were administered to correct arterial pH as rapidly as possible. 31P NMR spectra were obtained at baseline and throughout ischemia and reperfusion. The pH B was determined with the inorganic phosphate relative to the phosphocreatine resonance signal shift. Profile analysis indicates a difference between groups (P less than .02) related to an initial delay in pH B correction in the tris group. By 48 minutes of reperfusion, pH B did not differ between the groups. Moreover, there was no evidence of paradoxic cerebral acidosis in the bicarb group. Although tris corrects blood pH as quickly as bicarb, it is less effective in correcting pH B. Absence of paradoxic acidosis may be caused by efficient elimination of CO2 by cardiopulmonary bypass.

Transient blood-brain barrier permeability following profound temporary global ischaemia: an experimental study using 14C-AIB

The influence of reperfusion after profound incomplete forebrain ischaemia on blood-brain barrier (BBB) permeability to a small protein tracer was studied in male Sprague-Dawley rats. The mean cortical blood to brain transfer constant (Ki) for 14C-amino isobutyric acid (AIB) was significantly greater at 3 and 6 h of reperfusion, 2.5 times the mean values of controls (p less than 0.05) (2.5 microliter g-1 min-1 and 1.0 microliters g-1 min-1 respectively), but had returned to control values after reperfusion for 24 h. Analysis of distribution of Ki values showed that following 15 min and 30 min of profound ischaemia, there was a significant increase in transfer of AIB across the blood-brain barrier (BBB) after recirculation for up to 6 h, though there was no evidence of protein extravasation as assessed by Evans Blue (EB) dye. After 24 h of reperfusion, the BBB to AIB was restored, and Ki values had returned to control values. It is concluded that following transient global ischaemia, the BBB may recover rapidly.

Effect of aging on the blood-brain barrier

Aging is commonly associated with progressive deterioration in central nervous system (CNS) function. Nutritional factors or environmental toxins have important effects on CNS degenerative changes. The blood-brain barrier (BBB) is a major modulator of nutrient delivery to the CNS. The tight junctions and the paucity of pinocytosis or fenestrations in brain capillary endothelium act as an effective barrier between the CNS and the circulating toxic agents. Senescence is associated with significant, though often subtle, changes in BBB. Conditions which are commonly associated with aging, such as hypertension and cerebrovascular ischemia, aggravate the age-related alterations in BBB function. The histologic changes in brain vasculature with aging is region selective and species specific. The common age-related histologic changes include loss of capillary endothelial cells, elongation of the remaining endothelial cells, and decreased capillary diameter in rat cortex, but not in the monkey or human cortex, and a decrease in the number of mitochondria in endothelial cells of the brain capillaries in the monkey but not in the rat. The age-related alterations in BBB transport function include a decrease in BBB choline transport with aging and decreased brain glucose influx. The BBB neutral amino acid transport appears to be unaltered in the aged mice. Most of the studies reported so far have failed to show a significant age-related alteration in BBB permeability to water-soluble substances and high molecular weight solutes in the absence of neurological disease. A more profound change in BBB permeability appears to be associated with Alzheimer's disease. Immunohistological studies have demonstrated the presence of serum proteins in the cerebrovascular amyloid in patients with Alzheimer's disease.(ABSTRACT TRUNCATED AT 250 WORDS)

[Cerebrospinal fluid in cerebrovascular disorders. Study of 1500 cases]

In order to evaluate information on acute stroke through the study of cerebrospinal fluid (CSF) data em 1500 patients were analysed in the first 48 hours following stroke. Cases were distributed in three groups according to CSF basic findings: type 1, CSF without erythrocytes and without xanthochromia; type 2, CSF without erythrocytes and with xanthochromia; type 3, CSF with erythrocytes and with xanthochromia. Data on each type are discussed as well as correlation findings. Systemic metabolic disturbances, blood-brain barrier impairment and central nervous system lesions are discussed as to the role they have in CSF changes observed in stroke. Indication of CSF exam in stroke is reviewed taking into account progress in neuroimaging techniques.

Regional studies of blood-brain barrier transport of glucose and leucine in awake and anesthetized rats

D-Glucose and L-leucine are transported across the blood-brain barrier (BBB) by two separate carrier-mediated facilitated diffusion mechanisms. In the awake rat there are regional differences in blood-to-brain glucose transport among the cerebral cortex, cerebellum, hippocampus, and striatum. To determine whether these are due to variations in the regional density or affinity of the glucose transporter moiety of brain capillaries or are secondary to regional tissue perfusion and capillary arrangement characteristics, we studied regional blood-to-brain transport of L-leucine in awake rats; regional blood-to-brain transport of both glucose and leucine under chloral hydrate anesthesia, a condition associated with altered regional brain blood flow (BF) and metabolism; and regional brain vascular volume, derived from the L-glucose and insulin spaces, in both awake and anesthetized rats. We found the same regional differences in blood-to-brain leucine transport in awake rats as we previously described for D-glucose transport. These regional differences in glucose and leucine transport disappear under chloral hydrate anesthesia, as regional differences in BF are abolished. However, we found regional differences in the brain vascular volumes, which are evident in wakefulness and persist during anesthesia. These results suggest that the regional differences in blood-to-brain transport are due mainly to local tissue perfusion and capillary arrangement characteristics rather than to intrinsic regional differences in the transport systems of the BBB.

Recirculation after cerebral ischemia. Simultaneous measurement of cerebral bloodflow, brain edema, cerebrovascular permeability and cortical EEG in the rat

The 4-vessel occlusion rat model of cerebral ischemia was modified to permit the simultaneous measurement of cerebral blood flow (hydrogen clearance), brain edema (specific gravity), cerebrovascular permeability (14C-AIB) and electrocardiogram. Surgery was performed in one stage in the anesthetised, paralysed and ventilated rat and severe hemispheric ischemia was produced in all animals. Electrode implantation did not alter cortical specific gravity or Ki for 14C-AIB. During 4-vessel occlusion mean cortical CBF was 5.8 +/- 1.4 ml-1 100 g-1 min. and this was associated with an isoelectric ECoG; 15 min of ischemia produced a significant reduction in mean cortical specific gravity (increase in brain edema). Following 15 min ischemia, 180 min of recirculation were permitted. Post-ischemic blood flow showed an immediate hyperemia (CBF = 202 +/- 12 ml-1 100 g-1 min.) followed by hypoperfusion (CBF = 58 +/- 8 ml-1 100 g-1 min). There was an early further decrease in cortical specific gravity. Further recirculation led to a significant increase in cortical specific gravity (resolution of brain edema). The transfer constant (Ki) for 14C-AIB was not altered at any stage in recirculation. This appears to be a model of pure cytotoxic edema until 180 min recirculation after 15 min cerebral ischemia. Recirculation permitted return of cortical electrical activity.

Duration of ischemia influences the development and resolution of ischemic brain edema

The influence of the duration of ischemia on the development and resolution of post-ischemic brain edema (SG method) was studied in anesthetized rats. Edema developed during ischemia and the amount of edema was related to the duration of ischemia (r = 0.843, p less than 0.001). With recirculation to three hours, the major determinant of the amount of edema was still the duration of the preceding ischemia (p less than 0.001). Resolution of brain edema only occurred following fifteen minutes ischemia. Post-ischemic blood-brain barrier breakdown (14C-AIB, EB albumin) was greatest following longer ischemia. Where present, the BBB leakage was simultaneously to large and small molecules.

Rapid increase in blood-brain barrier permeability during severe hypoxia and metabolic inhibition

The influence of lack of oxygen and metabolic inhibitors on the integrity of cerebral microvascular endothelium is undefined due to conflicting experimental evidence. A newly developed technique for continuous measurement of the electrical resistance of the microvascular endothelium was applied to the pial venules of the frog subjected to severe hypoxia and inhibition of endothelial ATP-production by means of cyanide (1 mM) and iodo-acetate (1 mM) for periods of 15 min. Severe hypoxia as well as application of the metabolic inhibitors decreased the electrical resistance within 2-5 min. The effect of the glycolysis-blocking agent, iodo-acetate, was particularly powerful. The maximal response, obtained in a 15 min period of exposure, was a 30-50% resistance decrease, corresponding to a 50-100% increase in the permeability to small ions. The rapid rise in permeability demonstrates that the cerebral endothelial cells depend critically on uninterrupted energy conversion to maintain the barrier function.