Aerobic exercise prevents rarefaction of pial collaterals and increased stroke severity that occur with aging.

Variation in extent of the brain's collateral circulation is an important determinant of variation in the severity of stroke and efficacy of revascularization therapies. However, the number and diameter of pial collateral "arterioles" decrease with aging in associated with reduced eNOS and increased oxidative stress. We tested whether exercise reduces this aging-induced rarefaction. Twelve-month-old mice were randomized to sedentary or voluntary wheel-running. At 26 months' age, permanent MCA occlusion was followed 72 h later by determination of infarct volume and vascular casting after maximal dilation. The decline in collateral number and diameter and 2.4-fold increase in infarct volume evident in 26-versus 3-month-old sedentary mice were prevented by exercise-training. In contrast, number and diameter of the posterior communicating collateral "arteries" were unaffected by aging or exercise. Interestingly, diameter of the primary intracranial arteries increased with aging. Mechanistically, genetic overexpression of eNOS inhibited age-induced collateral rarefaction, and exercise increased eNOS and SOD2 and decreased the inflammatory marker NFkB assessed in hindlimb arteries. In conclusion, exercise prevented age-induced rarefaction of pial collaterals and reduced infarct volume. Aging also promoted outward remodeling of intracranial arteries. These effects were associated with increased eNOS and reduced markers of inflammation and aging in the vascular wall.

Sphingomyelinase and ceramide analogs induce vasoconstriction and leukocyte-endothelial interactions in cerebral venules in the intact rat brain: Insight into mechanisms and possible relation to brain injury and stroke.

This study was designed to test the hypothesis that the sphingomyelin-ceramide signaling pathway may be important in proinflammatory-like responses in the intact brain. Effects of neutral sphingomyelinase (N-SMase), ceramide analogs, phosphorylcholine and ceramide metabolites were studied on rat brain cerebral (cortical) venule lumen sizes, leukocyte rolling, velocity and endothelial cell wall adhesion, microvessel permeability, microvessel rupture and focal hemorrhages using in vivo high resolution TV microscopy. Perivascular and close intra-arterial administration of N-SMase, C(2)-, C(8)-, and C(16)-ceramide, but not either phosphorylcholine, C(6)-ceramide, nervonic (C(24):1) ceramide, lignoceric (C(24):0) ceramide, C(8)-ceramide-1-phosphate, glucosylceramide or 1-0-acylceramide, resulted in potent, concentration-dependent constriction (and spasm) of cortical venules, followed by increased leukocyte rolling, decreased leukocyte velocities, increased leukocyte-endothelial wall adhesion, increased venular wall permeability, postcapillary venule rupture and, often, micro-hemorrhaging at high concentrations; angiotensin II, serotonin and PGF(2alpha) didn't demonstrate these characteristics. Pretreatment with either one of three different antioxidants, including inhibitors of NF-kappaB activation, or two different Ca(2+) channel blockers either prevented or attenuated the adverse venular effects of N-SMase and the ceramides. Likewise, pretreatment with either a PKCalpha-beta antagonist or a MAP kinase antagonist also attenuated the adverse venular effects. These results suggest that N-SMase and several ceramides can result in potent venular cerebrovasospasm, leukocyte-endothelial chemoattraction, and microvessel wall permeability changes in the intact rat brain. These proinflammatory-like actions suggest that N-SMase and ceramides could produce brain-vascular damage by reperfusion injury triggering lipid peroxidation, release of reactive oxygen species and activation of diverse signaling pathways: PKCalpha-beta isozymes, MAP kinase and NF-kappaB.

Role of aberrant nitric oxide synthase-3 expression in cerebrovascular degeneration and vascular-mediated injury in Alzheimer's disease.

Nitric oxide (NO) is an important signaling molecule that is generated through the catalytic activity of nitric oxide synthase (NOS). In the brain, NO mediates neuronal survival, synaptic plasticity, vascular smooth muscle relaxation, and endothelial cell permeability. Previous studies demonstrated aberrant expression of the NOS-III gene in neurons and glial cells in brains with Alzheimer's disease (AD). Since NOS-III is also expressed in vascular cells, and cerebrovascular disease (CVD) frequently complicates the pathology of AD, we investigated the role of NOS-III in relation to CVD in AD. Vasculopathy in AD + CVD was characterized by thickening and hyalinization of the media of small and medium-size vessels, variable degrees of beta-amyloid (A beta) deposition, and increased apoptosis of vascular smooth muscle and endothelial cells, particularly involving white matter vessels. These abnormalities were correlated with reduced levels of NOS-III expression in cerebral vessels. Double-labeling studies demonstrated that the low levels of cerebrovascular NOS-III were associated with increased levels of the pro-apoptosis gene product, p53 in smooth muscle and endothelial cells, suggesting a role for altered NOS-III expression in AD-associated vascular degeneration. Constitutively reduced cerebrovascular NOS-III expression and NO production could also lead to cerebral hypoperfusion due to impaired vasodilation responses, and diminished capacity to remove respiratory waste products and toxins from the extracellular space due to reduced capillary permeability. The role for phosphodiesterases as modulators of NOS activity is discussed, as these molecules represent potential therapeutic targets given their cell type and cyclic nucleotide specificities of action.

Aberrations in cerebral vascular functions due to Plasmodium yoelii nigeriensis infection in mice.

Plasmodium yoelii nigeriensis infection in mice caused an increase in uptake of 125I-labeled bovine serum albumin, 51Cr-labeled erythrocytes and Evans blue dye from peripheral circulation into the brain. Isolated cerebral microvessels which were characterized in terms of their morphology under scanning electron microscope and enhancement of the specific activities of biochemical markers, viz. alkaline phosphatase, gamma-glutamyl transpeptidase, and monoamine oxidase, showed significant decrease in these activities due to P. yoelii nigeriensis infection. On the other hand, relatively minor (statistically insignificant) changes occurred in the first two enzyme specific activities in the cerebral cortex and monoamine oxidase registered an increase in this tissue due to infection. Histological examination of the cerebral tissue of infected animals by light and electron microscopy showed broken blood vessel walls and leakage of erythrocytes into extravascular space, some of which contained intraerythrocytic malarial parasite in a state of cell division.

Mesenteric resistance and brain microvascular angiotensin-converting enzyme in the spontaneously hypertensive rat.

1. Angiotensin-converting enzyme (ACE) concentration was measured in mesenteric and brain microvessels from spontaneously hypertensive rats (SHR) and compared with normotensive controls using a specific radioligand binding assay. 2. Plasma angiotensin-converting enzyme activity was similar in SHR (n = 15) and normotensive controls (n = 21; 58 +/- 1 nmol HL/mL per min, vs 64 +/- 6 nmol HL/mL per min). 3. There was no significant difference between the mesenteric vascular angiotensin-converting enzyme radioligand binding site density (Bmax, fmol/mg protein) of SHR and normotensive controls (954 +/- 77 vs 890 +/- 56, P = 0.5, unpaired Student's t-test), despite significant differences in systolic blood pressure (220 +/- 8 mm Hg vs 120 +/- 6 mm Hg respectively, P less than 0.01) and increased mesenteric wet weight to bodyweight ratio in the hypertensive rats (0.28 +/- 0.02 mg/g, n = 5 vs 0.16 +/- 0.02 mg/g, n = 7, P less than 0.01). 4. Brain vascular angiotensin-converting enzyme radioligand binding site density (Bmax, fmol/mg protein) was also similar in SHR and normotensive controls (467 +/- 62, n = 5 vs 497 +/- 64, n = 5, P = 0.7, unpaired Student's t-test). 5. These results demonstrate that vascular angiotensin-converting enzyme concentration is not altered in the SHR and that vascular ACE is not increased in this form of vascular hypertrophy or regulated by the blood pressure level.

[The cholinergic and adrenergic innervation of the great cerebral vein]. / Kholinergicheskaia i adrenergicheskaia innervatsiia bol'shoi veny golovnogo mozga.

Comparative histochemical study of the nervous apparatus of the large cerebral vein system (Galen's vein) and its influxes--the interior cerebral veins and the veins of the cerebral basis, was performed in cats, rats, guinea-pigs, and humans. Deep cerebral veins were found to be rather well supplied with cholin- and adrenergic nerves. Paravasal, surface and deep adventitious plexuses are a single nervous formation having unequal structure on different depth of the vessel wall. No difference was found between the concentration of cholin- and adrenergic nerves in the wall of the large cerebral vein and its influxes in rats, cats and guinea-pigs. The density of the nervous plexus on 1 mm2 of the total preparation of the large cerebral vein wall and its influxes increases in the row: rat--guinea-pig--cat--humans.

Effect of hypercholesterolemia on cholinephosphotransferase activity in rabbit and rat vessel walls.

The activity of cholinephosphotransferase (EC 2.7.8.2, CPT) which catalyses de novo synthesis of phosphatidylcholine (PC) was studied in aortas of rabbits and rats, and in brain microvessels of rabbits with a cholesterol feeding-induced hypercholesterolemia. Cholesterol feeding produced a marked atheromatous change in rabbit aortas but not in rat aortas. The aortas of cholesterol-fed rabbits displayed a significantly higher CPT activity than the controls. On the other hand, the aortic CPT activity of cholesterol-fed rats was not different from that of control rats. The brain microvessels of cholesterol-fed rabbits having atheromatous aortic lesions did not show any lipid deposition, and CPT activity was similar to that of control rabbits. A tocopherol-deficient, high-cholesterol diet produced microscopical lipid deposits in rat aortas, and CPT activity of these aortas was significantly higher than that of aortas of rats on tocopherol-supplemented diets containing either a normal or high amount of cholesterol. The increase in CPT activity in atheromatous lesion might be closely related to lipid deposition in vessel walls and may be a cause of the increase in PC content in these lesions. Further studies are required to clarify the mechanism of activation of CPT activity in atheromatous conditions.

Blood-brain barrier monoamine oxidase: enzyme characterization in cerebral microvessels and other tissues from six mammalian species, including human.

We studied the enzyme monoamine oxidase (MAO) in isolated cerebral microvessels, and in mitochondria-enriched brain and liver preparations from six mammalian species, including human. We also studied MAO distribution in various tissues and in discrete brain regions of the rat. MAO was assessed by measuring the specific binding of [3H]pargyline, an irreversible MAO inhibitor, and the rates of oxidation of known MAO substrates: benzylamine, tyramine, tryptamine, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Molecular forms of MAO were examined by using specific MAO inhibitors, and by polyacrylamide gel electrophoresis after [3H]pargyline binding. In general, the liver from all species had higher MAO levels than the brain, with minor variation among species in their brain and liver MAO content. However, there were remarkable species differences in brain microvessel MAO, with rat microvessels having one of the highest MAO activity among all tissues, whereas MAO activities in brain microvessels from humans, mice, and guinea pigs were very low. In most rat tissues, including the brain, there was a preponderance of MAO-B over MAO-A. The only exceptions were the heart and skeletal muscle. Estimates of MAO half-life in rat brain microvessels, rat brain, and rat liver indicated that microvessel MAO had a higher turnover rate. The reasons underlying the remarkable enrichment of rat cerebral microvessels with MAO-B are unknown, but it is evident that there are marked species differences in brain capillary endothelium MAO activity. The biological significance of these findings vis a vis the role of MAO as a "biochemical blood-brain barrier" that protects the brain from circulating neurotoxins and biogenic amines should be investigated.