Extravasation of polymorphonuclear leukocytes from the cerebral microvasculature

Postcapillary venules represent the segment of the microvasculature most vulnerable to inflammatory processes. While there is a considerable body of data on the peripheral vasculature, little is known about the primary events occurring during inflammatory reactions in cerebral blood vessels. We introduce here a model by which the migration of polymorphonuclear leukocytes through the CNS endothelial barrier can be studied. Alpha-bungarotoxin is used as a chemotactic agent and is shown, for the first time, to act by activating the complement cascade. Leukocytes migrate through the endothelium transcellularly. Two modes of migration are described: a direct mode whereby the cells use temporary pores in the vessel wall as portals, and an indirect mode whereby the leukocytes leave the vascular compartment after being enveloped by and incorporated into endothelial cells. The functional implications of these findings lead us to conclude that the direct mode of migration is a causal agent in the massive breakdown of the blood-brain barrier under acute inflammatory conditions.     

3D models of blood flow in the cerebral vasculature

The circle of Willis (CoW) is a ring-like arterial structure located in the base of the brain and is responsible for the distribution of oxygenated blood throughout the cerebral mass. To investigate the effects of the complex 3D geometry and anatomical variability of the CoW on the cerebral hemodynamics, a technique for generating physiologically accurate models of the CoW has been created using a combination of magnetic resonance data and computer-aided design software. A mathematical model of the body's cerebral autoregulation mechanism has been developed and numerous computational fluid dynamics simulations performed to model the hemodynamics in response to changes in afferent blood pressure. Three pathological conditions were explored, namely a complete CoW, a fetal P1 and a missing A1. The methodology of the cerebral hemodynamic modelling is proposed with the potential for future clinical application in mind, as a diagnostic tool.     

Changes in the levels of cerebral and extracerebral sterols in the brain of patients with Alzheimer's disease

24S-hydroxycholesterol is a side-chain oxidized oxysterol formed in the brain that is continuously crossing the blood-brain barrier to reach the circulation. There may be an opposite flux of 27-hydroxycholesterol, which is formed to a lower extent in the brain than in most other organs. Here we measured cholesterol, lathosterol, 24S- and 27-hydroxycholesterol, and plant sterols in four different brain areas of deceased Alzheimer's disease (AD) patients and controls. 24S-hydroxycholesterol was decreased and 27-hydroxycholesterol increased in all the brain samples from the AD patients. The difference was statistically significant in four of the eight comparisons. The ratio of 27-hydroxycholesterol to 24S-hydroxycholesterol was significantly increased in all brain areas of the AD patients and also in the brains of aged mice expressing the Swedish Alzheimer mutation APP751. Cholesterol 24S-hydroxylase and 27-hydroxylase protein was not significantly different between AD patients and controls. A high correlation was observed between the levels of 24S-hydroxycholesterol and lathosterol in the frontal cortex of the AD patients but not in the controls. Most probably the high levels of 27-hydroxycholesterol are due to increased influx of this steroid over the blood-brain barrier and the lower levels of 24S-hydroxycholesterol to decreased production. The high correlation between lathosterol and 24-hydroxycholesterol is consistent with a close coupling between synthesis and metabolism of cholesterol in the frontal cortex of the AD brain.     

Distribution and submicroscopic immunogold localization of cellular prion protein (PrPc) in extracerebral tissues

In transmissible spongiform encephalopathies (TSE), such as scrapie in animals and Creutzfeldt-Jakob disease in humans, the central event is the conversion of a host-encoded amyloidogenic protein (PrPc) into an abnormal isoform (PrPsc) that accumulates as amyloid in TSE brain. PrPc is a membrane sialoglycoprotein synthesized in the central nervous system and elsewhere. We have examined the ultrastructural localization of PrPc in numerous hamster and some human extracerebral tissues, by means of a post-embedding electron-microscopic method combined with immunogold labeling. In stomach, intestine, lung, and kidney from hamsters, and in stomach, kidney, and spleen from humans, immunogold labeling specific for PrPc is observed on various cellular substructures related to secretory pathways: Golgi apparatus, secretory globules, and plasma membrane. In mucous epithelial cells of stomach and intestine, PrPc appears to be concentrated in secretory globules, suggesting a role for PrPc in the secretory function of the digestive tract. The secretory aspect of PrPc may be a key to understanding the physiopathological mechanisms underlying TSE.     

Modularity in the skull and cranial vasculature of laboratory mice: implications for the evolution of complex phenotypes

The generation of coordinated morphological change over time results from the interconnectedness of evolution and development. The modular architecture of development results in varying degrees of integration and independence among parts of the phenotype, and facilitates the production of phenotypic variation in complex anatomical units composed of multiple tissue types. Here we use geometric morphometrics to investigate modularity in the arterial Circle of Willis (CW) and skull of the CD-1 laboratory mouse. We contrast a hypothesis of tight integration between these tissues with a hypothesis of more modular organization, to determine the level at which natural selection works to generate coordinated change. We report a complex pattern of covariation that indicates that the skull and CW are highly integrated and developmentally linked. Further, we report higher levels of fluctuating asymmetry in the CW than in the skull, suggesting a greater potential for lability in this tissue. These results suggest that epigenetic interactions or genetic influences on regional development are more important determinants of covariation structure than the factors that produce covariation within individual tissues or organ systems.     

An improved apparatus for blood perfusion of the canine cerebral vasculature

An improved perfusion apparatus is described which consists of a membrane oxygenator, roller pump, reservoir, heat exchanger, blood filter, and inert tubing. Heparinized blood may be used and is delivered at flow rates from 10 to 250 ml/min. Dogs are anesthetized with halothane and their cerebral arterial blood supply isolated by the method of Gilboe et al. (8). When the canine brain is perfused for 5 hr using the described apparatus, the rates of cerebral oxygen and glucose consumption are 5.19±0.12 ml/100 g/min and 39.9±6.5 mol/100 g/min, respectively. Of the total glucose consumed by the brain, about 1/4 is contributed by the erythrocytes. An equivalent of about 9% of the consumed glucose is returned to the blood as lactate. Electron microscopic examination of cerebral cortex samples reveals no differences between 5-hr perfused brain and appropriate nonperfused controls. It is concluded that the apparatus is a useful system for organ perfusion and that the canine brain perfused by this method remains physiologically and metabolically active for at least 5 hr.With the technical assistance of Evelyn Townsend.     

The effects of perfusion of the cutaneous vasculature on sodium uptake across isolated frog skin

Perfusion of cutaneous capillaries in isolated frog skin may remove an unstirred layer along the basolateral membrane of the epidermis that may affect the rate of cutaneous Na(+) uptake. To test this hypothesis, the cutaneous artery and vein of a bullfrog were cannulated to allow perfusion of isolated flank skin while the rate of Na(+) influx was determined. Rates of sodium influx with and without perfusion were determined in the same experiment. Na(+) uptake increased by 59+/-4.8% during the 1st 0.5 h of perfusion relative to the control, pre-perfusion period and then remained at 26+/-5.3% above control values. Concomitant with the increase in sodium uptake, the transepithelial potential difference fell by ca. 10% within the 1st 0.5 h of perfusion. The amount of labeled sodium leaving the skin in the venous effluent decreased exponentially in the 1st 0.5 h of perfusion, suggesting a wash out of an unstirred layer within the interstitial fluid. Sodium in the venous outflow accounted for ca. 25% of the sodium uptake during each perfusion period. Perfusion of the cutaneous vasculature thus has a significant effect on Na(+) transport and may potentially play a role in the acute regulation of cutaneous ion transport.     

Lower cranial nerve motor function in unilateral vascular lesions of the cerebral hemisphere.

Motor function subserved by cranial nerves V, VII, X, XI, and XII was assessed in 100 patients with hemiparesis due to a unilateral vascular lesion of the cerebral hemisphere. Several of the findings were not described clearly in many of the standard textbooks of neurology. Weakness of sternomastoid when present was always contralateral to the hemiparesis. This emphasises the principle that the cerebral hemisphere controls movement of the body parts in or towards the contralateral half of the body rather than simply the contralateral muscle groups. An apparent exception to this was seen, however, in the small group of patients who had unilateral weakness of the tongue. In those patients deviation of the tongue was towards the hemiparetic side--that is, the cerebral hemisphere controlled the contralateral half of the tongue and hence protrusion towards the ipsilateral side. Mild dysarthria was common with both right and left sided hemiparesis.     

Cell-type-specific responses to the microbiota across all tissues of the larval zebrafish

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