Multivoxel 1H-MRS of stroke

Proton nuclear magnetic resonance spectroscopy is a noninvasive technique allowing the localized, in vivo detection of proton-containing brain metabolites. We used this technique to study eight patients with cerebral infarction or ischemia. A stimulated echo-pulse sequence with chemical shift imaging was used to acquire spectra from multiple contiguous 4-cc volumes extending from the site of ischemia to the opposite hemisphere. Six patients had a reduction in the signal from N-acetyl groups (NAG) in the stroke area compared with controls, and those with the lowest NAG to phosphocreatine/creatine ratios had the least recovery of function. Lactate was observed within the infarcted region in two patients at 9 and 11 days after infarction and may have been present in other patients up to 15 weeks after stroke.

TIMP-2 reduces proteolytic opening of blood-brain barrier by type IV collagenase

Intracerebral hemorrhage occurs in tumors, stroke and head trauma. Proteolysis of the extracellular matrix around cerebral capillaries by naturally occurring mammalian 72-kDa type IV collagenase may initiate this pathologic event. To investigate this hypothesis adult rats underwent intracerebral injection of type IV collagenase purified from human melanoma cells. Histologically, at 4 h there was perivascular cellular infiltration with hemorrhage, and by 24 h there was infarction with necrosis, edema and hemorrhage. Ultrastructurally, the basal lamina of endothelial cells was disrupted at 2 h. Brain uptake of [14C]dextran and [3H]sucrose increased after intracerebral injection of type IV collagenase compared to controls (P less than 0.0001). Tissue inhibitor of metalloproteinase-2 (TIMP-2) reduced the tracer uptake (P less than 0.02). Metalloproteinase inhibitors reduce extracellular matrix proteolysis and protect the blood-brain barrier.

The spectrum of lacunar infarction in the elderly

Lacunar infarcts are small subcortical ischemic brain lesions caused by occlusion of a perforating arteriole. The occlusion results from thickening of the arteriolar wall (arteriolosclerosis), is related to aging, and is accelerated by arterial hypertension. The infarction is usually associated with one of several clinical lacunar syndromes, depending on the exact location of the lesion. Patient evaluation should include the documentation of infarct size and location with imaging studies and the search for uncommon hematologic derangements that predispose to thrombosis. Recovery from a single lacunar infarction is usually very good. Most important in prevention of lacunar infarction recurrence is control of hypertension. Aspirin therapy also appears to be beneficial.

Effect of hypoxia on cerebral metabolites measured by proton nuclear magnetic resonance spectroscopy in rats

Proton nuclear magnetic resonance spectroscopy is a unique method to monitor noninvasively the concentrations of cerebral metabolites. N-Acetyl-L-aspartate, the concentration of which is assumed to be stable during hypoxia, has been used to form ratios with lactate. To determine the stability of the signal from N-acetyl-L-aspartate, we used a model of graded hypoxia in rats to monitor the percentage changes from baseline of the peak heights for lactate, lipids, and N-acetyl-L-aspartate. Anesthetized adult rats were exposed sequentially to 15% and 10% O2 while proton nuclear magnetic resonance spectra were collected with a surface coil in a 7-T 89-mm-bore spectrometer. Brain lactate concentration was either increased by feeding or infusion of glucose (n = 9) or lowered by fasting (n = 7). After death the brains were removed and frozen, and the water- and lipid-soluble compounds were extracted to identify the origin of the signals. We analyzed the data both as the percentage change from baseline for heights of the lactate (1.33 ppm), lipids (1.5 ppm), and N-acetyl-L-aspartate (2.02 ppm) peaks and as the ratios of heights of the 1.33 and 2.02 and the 1.5 and 2.02 ppm peaks. Both hypoxic episodes caused a 45% decrease from baseline in the 2.02 ppm peak. During the second hypoxic episode, the 1.33:2.02 ppm peak height ratio increased significantly in hyperglycemic rats (p less than 0.05) but was unchanged in hypoglycemic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagenase-induced intracerebral hemorrhage in rats

Intracranial bleeding is an important cause of brain masses and edema. To study the pathophysiology of intracerebral hemorrhage, we produced experimental hemorrhages in 53 rats and characterized the lesion by histology, brain water content, and behavior. Adult rats had 2 microliters saline containing 0.5 unit bacterial collagenase infused into the left caudate nucleus. Histologically, erythrocytes were seen around blood vessels at the needle puncture site within the first hour. By 4 hours there were hematomas, the size of which depended on the amount of collagenase injected. Necrotic masses containing fluid, blood cells, and fibrin were seen at 24 hours. Lipid-filled macrophages were observed at 7 days and cysts at 3 weeks. Water content was significantly increased 4, 24, and 48 hours after infusion at the needle puncture site and for 24 hours in posterior brain sections. Behavioral abnormalities were present for 48 hours, with recovery of function occurring during the first week. Brain tissue contains Type IV collagen in the basal lamina. Collagenase, which occurs in an inactive form in cells, is released and activated during injury, leading to disruption of the extracellular matrix. Collagenase-induced intracerebral hemorrhage is a reproducible animal model for the study of the effects of the hematoma and brain edema.

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.

Neurologic involvement in toxemia of pregnancy: reversible MRI lesions

Three women presenting with toxemia of pregnancy revealed reversible increased signal intensity on T2-weighted images by MRI. Overall, neuroradiologic techniques, with MRI the most sensitive, help elucidate the pathophysiology and facilitate the diagnosis in this condition.

Clinical significance of MRI white matter lesions in the elderly

The clinical relevance of white matter hyperintensities (WMH) seen on MRIs of elderly individuals is controversial. To resolve this issue, we performed MRI and neuropsychological testing on 46 healthy participants in the longitudinal Aging Process Study at the University of New Mexico. We graded the MRIs for severity of WMH using a scale tested on an elderly patient population. We found that 22% of normal subjects had moderate lesions and 9% had severe lesions. All subjects had normal neurologic examination findings and were within normal limits on a battery of neuropsychological tests. Neuropsychological performance decreased and the severity of WMH increased with age. However, when the data were corrected for age, there was no correlation between neuropsychological function and the presence of WMH. We conclude that white matter changes in the elderly by themselves are of doubtful clinical significance.

13C nuclear magnetic resonance evidence for gamma-aminobutyric acid formation via pyruvate carboxylase in rat brain: a metabolic basis for compartmentation

The compartmentation of amino acid metabolism is an active and important area of brain research. 13C labeling and 13C nuclear magnetic resonance (NMR) are powerful tools for studying metabolic pathways, because information about the metabolic histories of metabolites can be determined from the appearance and position of the label in products. We have used 13C labeling and 13C NMR in order to investigate the metabolic history of gamma-aminobutyric acid (GABA) and glutamate in rat brain. [1-13C]Glucose was infused into anesthetized rats and the 13C labeling patterns in GABA and glutamate examined in brain tissue extracts obtained at various times after infusion of the label. Five minutes after infusion, most of the 13C label in glutamate appeared at the C4 position; at later times, label was also present at C2 and C3. This 13C labeling pattern occurs when [1-13C]glucose is metabolized to pyruvate by glycolysis and enters the pool of tricarboxylic acid (TCA) intermediates via pyruvate dehydrogenase. The label exchanges into glutamate from the TCA cycle pool through glutamate transaminases or dehydrogenase. After 30 min of infusion, approximately 10% of the total 13C in brain extracts appeared in GABA, primarily (greater than 80%) at the amino carbon (C4), indicating that the GABA detected is labeled through pyruvate carboxylase. The different labeling patterns observed for glutamate and GABA show that the large detectable glutamate pool does not serve as the precursor to GABA. Our NMR data support previous experiments suggesting compartmentation of metabolism in brain, and further demonstrate that GABA is formed from a pool of TCA cycle intermediates derived from an anaplerotic pathway involving pyruvate carboxylase.

The effect of arginine vasopressin and V1 receptor antagonist on brain water in cat

Arginine vasopressin (AVP) is important in brain water regulation. To better understand the effect of AVP released by extrahypothalamic fibers in brain, we microinfused AVP into intact brain and studied its effect on brain water and electrolytes. Adult cats had 5 ng of AVP infused into the caudate nuclei. Four h after infusion the brains were removed for measurement of water and electrolyte contents. Animals infused with AVP were compared to controls infused with saline. AVP increased water content significantly in gray and white matter sites, while electrolyte content was unchanged. Another group of animals had intracerebral infusions with 5 ng of AVP and 50 ng of a V1 receptor antagonist, (d(CH2)5Tyr-(Me)AVP). The antagonist blocked the increase in water, suggesting a V1 receptor mediated the action.

Amantadine, fatigue, and multiple sclerosis

In a double-blind placebo-controlled crossover study of ten patients with multiple sclerosis, we found amantadine hydrochloride therapy to be effective in improving fatigability in six. Administration of the drug was associated with significantly higher levels of beta-endorphin-beta-lipotropin and responders had significantly higher levels than nonresponders. Lactate levels were significantly higher and pyruvate levels lower in nonresponders. Amantadine given for fatigue to patients with multiple sclerosis is associated with measurable changes in levels of metabolites and peptides in the circulation.

Selective effect of mannitol-induced hyperosmolality on brain interstitial fluid and water content in white matter

We studied the effect of mannitol-induced hyperosmolality on brain interstitial fluid (ISF) by autoradiography. Adult cats underwent intracerebral infusion of the extracellular marker, 14C-sucrose. Nine animals were given 2g/kg of mannitol intravenously, and another nine animals without mannitol were controls. Plasma and cerebrospinal fluid (CSF) osmolalities were measured. After 2 hr the brains were removed for determination of water and electrolyte content and for preparation of the autoradiograms. Diffusion coefficients were calculated for intracerebral transport with equations for radial diffusion. We found that mannitol increased the plasma osmolality but did not affect that of the CSF. Water and potassium contents were significantly lower in the white matter of mannitol-treated animals than in controls. Diffusion was reduced in the direction of gray matter into the white matter. We conclude that lower doses of mannitol control CSF pressure by selectively removing water from white matter, reducing the CSF volume, and affecting molecular transport at the gray/white interface.

Mannitol-induced hyperosmolality and cerebrospinal fluid vasopressin in anesthetized cats

Arginine-vasopressin (AVP) has been found to influence brain water. Since AVP is released by hyperosmolality into plasma we determined the role of AVP in controlling cerebrospinal fluid (CSF) pressure. Adult cats were anesthetized with pentobarbital and samples of plasma and cisternal CSF were collected 1 or 2 h before i.v. infusion of 2 g/kg of mannitol and for 2 h afterwards. We found a significant increase in plasma osmolality from 320.0 +/- 1.6 to 331.6 +/- -3.4 mOsm/l (mean +/- S.E.M.), while CSF osmolality was unchanged. Prior to mannitol infusion, AVP was elevated to 105 +/- 19 pg/ml in plasma and to 136 +/- 19 pg/ml (mean +/- S.E.M.) in CSF. After infusion of mannitol AVP levels were unchanged in either plasma or CSF. The reduction of CSF pressure by mannitol is independent of AVP in the anesthetized cat.

Effect of vasopressin on ependymal and capillary permeability to tritiated water in cat

Ependymal cells line the cerebral ventricles forming the interface that separates the cerebrospinal (CSF) and interstitial fluids (ISF). Extracellular molecules move between ependymal cells, whereas lipid soluble molecules pass both between and through cells. We measured the transfer of tritiated water (TOH) from CSF to blood across the ependymal and capillary interfaces by ventriculocisternal (VC) steady-state tissue clearance. Adult cats anesthetized with pentobarbital sodium underwent VC perfusion with the extracellular marker [14C]sucrose and TOH added to the artificial CSF. Brain tissue was analyzed for depth of penetration of the isotopes into periventricular gray matter. We found that TOH distribution space was lower than expected from water content measurements, whereas sucrose space was normal. Using VC steady-state equations we calculated an ependymal permeability that was similar to the permeability of the cerebral capillary. When arginine vasopressin (AVP) was added to the perfusate in different amounts, both capillary transfer times and ependymal permeability increased. Our results show that the ependyma may be important in water movement in the brain and support the suggestion that AVP influences water exchange in mammalian brain tissue.

Correlation between G2m(n) immunoglobulin allotype and human antibody response and susceptibility to polysaccharide encapsulated bacteria

To determine whether genetic factors influence the human antibody response to polysaccharides, we correlated Ig allotypes with the concentrations of antibody to 14 bacterial capsular antigens in 130 actively immunized Caucasian adults. The 88 individuals possessing G2m(n), an allotype antigen of IgG2 subclass heavy chains, had significantly higher postimmunization antibody levels to Haemophilus influenzae type b (Hib) and 8 of 11 pneumococcal types (P less than 0.05) than the 42 lacking this antigen. For Hib, pneumococcus type 14, and meningococcus group C, an increased response was observed in IgG class but not in IgM or IgA classes of antibody. The G2m(n) positive individuals also had higher preimmunization antibody levels to most polysaccharide antigens. Total IgG2 concentrations were correlated with the mean postimmunization antibody concentrations to pneumococci (P = 0.005), but this correlation was independent of G2m(n) by multiple regression analysis. To determine if the lack of G2m(n) was associated with increased susceptibility to infection, we compared the frequencies of various Ig allotypes in 98 children infected with Hib and 98 matched controls. Caucasian children with Hib infections other than epiglottitis were significantly more likely to lack the G2m(n) allotype than controls (P less than 0.05). G2m(n) negative Caucasian children less than or equal to 18 mo old have a 5.1-fold higher risk of nonepiglottitic Hib infections than G2m(n) positive children (P less than 0.01). We conclude that allotypic variants of the gamma-2 heavy chain genes, or genes in linkage equilibrium with them, exert a regulatory influence on the caucasian antibody response to a variety of immunologically distinct bacterial polysaccharide antigens. Young Caucasian children of the low responder phenotype, i.e., those lacking the G2m(n) allotype, are genetically predisposed to Hib and perhaps other bacterial infections.

Pathophysiology of periventricular tissue changes with raised CSF pressure in cats

Intraventricular pressure (IVP) is increased in the early stages of acute hydrocephalus. Pressure falls, however, when compensatory routes for cerebrospinal fluid (CSF) absorption develop. In order to better understand the pathophysiology of acute hydrocephalus, the authors performed ventriculocisternal perfusions on adult cats with outflow pressures maintained at either -5, 20, or 40 cm H2O. Cerebral blood flow (CBF) was determined by the iodoantipyrine method. Penetration of an extracellular marker, horseradish peroxidase (HRP), was visualized histologically. Capillary transfer of radiolabeled molecules from CSF to blood was measured by steady-state tissue clearance. Increased IVP had several effects: 1) significant reduction in mean CBF in the periventricular white matter; 2) penetration of the HRP into deep white matter; and 3) prolongation of steady-state tissue clearance half-time for (14C)-ethylene glycol in the caudate nucleus. Reduced blood flow to periventricular white matter and impaired molecular clearance in the caudate nucleus may contribute to the clinical symptoms in acute hydrocephalus.

Time course of blood nerve barrier reconstitution after sectioning: implications for xenograft studies

The time course of blood-nerve barrier recovery in mouse nerves was studied after proximal and distal segmental sciatic sections. Transfer constants for uptake of isotopically labeled sucrose and urea were determined. Sectioned segments were examined ultrastructurally. Marked alterations in isotope uptake for 2 months with gradual restoration of blood-nerve barrier by 6 months was found. Ultrastructure of sectioned segments showed increased numbers of perineurial compartments. Human nerve xenografts to immunosuppressed animals remain hypomyelinated for 6 months which may be related to damage to the blood-nerve barrier.

The effect of increased CSF pressure on interstitial fluid flow during ventriculocisternal perfusion in the cat

Transependymal absorption of cerebrospinal fluid (CSF) in hydrocephalus is suggested by periventricular edema, but the necessary bulk flow of interstitial fluid (ISF) has not been found. We performed ventriculocisternal perfusions in adult cats using CSF with the extracellular marker [3H]sucrose. CSF pressure was maintained at -5(control), 20 or 40 cm H2O for 2 or 4 h. Some animals had perfusions with isotope for the full experiment while others had an isotope-free perfusion for 2 h followed by a delayed-pulse with isotope. Apparent diffusion coefficients and distribution spaces for sucrose were determined from depth of isotope penetration. White matter apparent diffusion coefficients were statistically increased compared to controls for the 4-h 20 cm H2O and 2-h 40 cm H2O experiments. Apparent diffusion coefficients for delayed-pulse experiments at increased pressure were greater than those of full-pulse. Sucrose distribution spaces were not enlarged at the various pressures. Alteration of ISF transport in periventricular white matter occurred with increased pressure. These time-dependent changes in bulk flow rate indicate either a decrease in normal ISF flow toward the ventricle or reversal of transependymal ISF flow.

Gray and white matter brain-blood transfer constants by steady-state tissue clearance in cat

Capillary transfer constants for gray matter have been measured by others from steady-state tissue clearance during ventriculocisternal perfusion. Similar studies in white matter, however, are complicated by the bulk flow of interstitial fluid (ISF). Recently we determined the velocity of bulk flow of ISF under normal conditions. We now report capillary transfer constants in gray and white matter by steady-state tissue clearance in the cat. Adults cats underwent a 2, 3, or 4 h ventriculocisternal perfusion with artificial cerebrospinal fluid containing [3H]sucrose and either [14C]urea or [14C]ethylene glycol. Diffusion coefficients and velocity of bulk flow were determined from tissue concentrations of the extracellular marker, sucrose. Steady-state tissue concentrations of urea and ethylene glycol were used to calculate transfer of those compounds from the brain to the blood. Urea reached steady-state by the third hour; capillary transfer constants were similar in gray and white matter. Ethylene glycol reached steady-state by the second hour; however, capillary transfer was more rapid in the gray matter than in white.

Bulk flow of brain interstitial fluid under normal and hyperosmolar conditions

Although bulk flow of brain interstitial fluid (ISF) occurs with changes in hydrostatic and osmotic pressures, under normal conditions only diffusion of molecules in the ISF has been reported. Extrachoroidal cerebrospinal fluid (CSF) production and intracerebral injection studies, however, provide indirect evidence for the bulk flow of ISF under normal conditions. We studied tissue penetration profiles of an extracellular molecule in gray and white matter after 1-, 2-, 3-, and 4-h ventriculocisternal perfusions. Gray matter apparent diffusion coefficients were similar at different times as expected with diffusion; however, white matter coefficients decreased significantly with time, suggesting bulk flow of ISF. White matter data was reanalyzed for both bulk flow and diffusion; we calculated a diffusion coefficient of 3.00 x 10(-6) cm2/s and a velocity for ISF of 10.5 micrometers/min toward the ventricle. Additional animals were given 20% mannitol (1.5--3 g/kg) intravenously prior to a /-h ventriculocisternal perfusion. Mannitol produced a significant bulk flow of ISF away from the ventricle in gray matter. We estimate that 30% of extrachoroidal CSF production is from flow of ISF in white matter.

Subcortical arteriosclerotic encephalopathy (Binswanger): computerized tomography

The subcortical arteriosclerotic encephalopathy of Binswanger is characterized clinically by hypertension, dementia, spasticity, syncope, and seizures. It is usually diagnosed pathologically by the finding in white matter of diffuse demyelination or foci of necrosis plus arteriosclerotic and hypertensive vasculopathy. We present a case in which the diagnosis was made on the basis of the clinical course and a computerized tomogram which demonstrated extensive white matter degeneration. Postmortem examination confirmed both the diagnosis and the extent of the degeneration as shown by CT scan.