An experimental evaluation of a concept to improve conventional aortic prostheses.

Conventionally used textile prosthesis for traditional open surgical repair (OSR) of aortic aneurysms have a lower compliance than the native aortic tissue. Graft placements lead to an acute drop in compliance which effects cardiovascular risk and the development of graft related complications. A custom-made spring casing was applied to a Dacron graft segment under physiological pressure conditions within a five-element biventricular mock circulation loop, to investigate experimentally a concept to improve the compliance of a conventional aortic prosthesis by changing the transverse graft cross-section. Two different prosthesis locations, proximal and distal of compliant silicone tubing were used to study uniaxial graft compression with an elastic device. To characterise the devices' performance by means of pulse pressure (PP), diastolic pressure (Pdia) and pulse wave velocity(PWV), fluid pressures and flow were recorded. In a proximal graft setting (ascending aorta repair) elastic uniaxial compression with a custom-made spring casing (2 cm width) could significantly reduce PP by 10-14% (p < .001) and slowed PWV from 6.7 to 5.2 m/s (22%, p = .002). Applied to a graft in a distal position, the spring casing demonstrated less impact on PP (2-10%), but significantly reduced PWV in this mock aorta segment from 13.7 to 5.5 m/s (60%, p = .004). In conclusion, a newly conceptualised spring casing applied to the external wall of synthetic aortic grafts can reduce PP and slow PWV. By restoring elastic aortic recoil in stiff textile aortic prostheses, the presented concept is a potential solution to improve long-term aortic prosthesis related complications.

Winter diet of brown trout Salmo trutta in groundwater-dominated streams: influence of environmental factors on spatial and temporal variation.

Winter diet composition of brown trout Salmo trutta was quantified from November to March in 35 temperate groundwater-dominated streams in south-eastern Minnesota, U.S.A., in relation to stream physical characteristics including drainage area, channel slope and influence of groundwater on stream thermal regime. Aquatic invertebrates made up the majority of S. trutta diet in all streams and sampling periods and individual S. trutta typically had consumed 30 or more prey items at each sampling event. Differences in diet composition were greater among streams than between sampling periods within a stream, with Gammarus spp., Brachycentrus spp., Glossosoma spp., Chironomidae and Physella spp. the most common taxa. Landscape-scale stream characteristics were not significantly associated with S. trutta consumption or diet composition. Winter was period of significant activity in groundwater-dominated streams, as S. trutta fed on a variety of aquatic prey taxa highlighting the importance of winter base-flow in moderating S. trutta populations in seasonally cold catchments.

Early detection of cryptic memory and glucose uptake deficits in pre-pathological APP mice.

Earlier diagnosis and treatment of Alzheimer's disease would greatly benefit from the identification of biomarkers at the prodromal stage. Using a prominent animal model of aspects of the disease, we here show using clinically relevant methodologies that very young, pre-pathological PDAPP mice, which overexpress mutant human amyloid precursor protein in the brain, exhibit two cryptic deficits that are normally undetected using standard methods of assessment. Despite learning a spatial memory task normally and displaying normal brain glucose uptake, they display faster forgetting after a long delay following performance to a criterion, together with a strong impairment of brain glucose uptake at the time of attempted memory retrieval. Preliminary observations suggest that these deficits, likely caused by an impairment in systems consolidation, could be rescued by immunotherapy with an anti-ß-amyloid antibody. Our data suggest a biomarker strategy for the early detection of ß-amyloid-related abnormalities.

Mechanism of acute tryptophan depletion: is it only serotonin?

The method of acute tryptophan depletion (ATD), which reduces the availability of the essential amino acid tryptophan (TRP), the dietary serotonin (5-hydroxytryptamine (5-HT)) precursor, has been applied in many experimental studies. ATD application leads to decreased availability of TRP in the brain and its synthesis into 5-HT. It is therefore assumed that a decrease in 5-HT release and subsequent blunted neurotransmission is the underlying mechanism for the behavioural effects of ATD. However, direct evidence that ATD decreases extracellular 5-HT concentrations is lacking. Furthermore, several studies provide support for alternative underlying mechanisms of ATD. This may question the utility of the method as a selective serotonergic challenge tool. As ATD is extensively used for investigating the role of 5-HT in cognitive functions and psychiatric disorders, the potential of alternative mechanisms and possible confounding factors should be taken into account. It is suggested that caution is required when interpreting ATD effects in terms of a selective serotonergic effect.

Winter growth, development, and emergence of Diamesa mendotae (Diptera: Chironomidae) in Minnesota streams.

Diamesa mendotae Muttkowski is commonly observed emerging during winter at low air temperatures from Minnesota streams, but little is known about the winter dynamics of this and other winter-emerging aquatic insects. Biweekly collections of surface-floating pupal exuviae indicated that this species emerged from October through May, when water temperatures were less than approximately 10 degrees C. Emergence occurred continuously through winter, with a lull during January and February. Development of larvae from in situ growth enclosures supported emergence data and indicated that the reduction and halt of emergence in the spring was related to increasing water temperatures (> 10 degrees C), which were unsuitable for the growth or survival of the larvae. Development continued through January when water temperatures were at their lowest for the study stream and therefore did not explain the mid-winter lull in emergence. Growth rates of D. mendotae were not greater than other chironomid taxa at similar temperatures, indicating that lower critical thermal limits for growth allow this species to dominate ground-water influenced streams during the winter in Minnesota. The results of this study show that D. mendotae is well suited for growth and development at low temperatures and provides an assessment of important factors that regulate this species at low water and air temperatures.

Acute tryptophan depletion in rats alters the relationship between cerebral blood flow and glucose metabolism independent of central serotonin.

Acute tryptophan depletion (ATD) decreases the 5-HT precursor tryptophan (TRP) in blood and is used both clinically and preclinically to investigate the involvement of 5-HT in the development of depressive symptomatology. Depression is associated with both central 5-HT dysfunction and abnormalities in the normal relationship between regional cerebral blood flow (CBF) and glucose metabolism (CMRG). In this study, ATD was applied in Wistar rats to investigate the cerebrovascular effects of acute changes in peripheral TRP. Rats were orally fed with a protein-carbohydrate mixture, either containing or lacking TRP. Four hours later, CBF or CMRG was measured by quantitative autoradiographic imaging in 43 brain regions of interest (ROI). In plasma, ATD resulted in a 40% reduction in the ratio of TRP to the sum of other large neutral amino acids, but had no measurable effect upon TRP or 5-HT levels in hippocampus or prefrontal cortex. Nevertheless, ATD significantly reduced local CBF in 11 of the 43 brain ROIs, while local CMRG remained unchanged. Global analysis of all 43 ROIs revealed a close correlation between CBF and CMRG within both treatment groups. However, the overall ratio (=slope) after ATD (m=1.07) was significantly decreased compared to the control group (m=1.27), indicating a state of relative cerebral oligaemia. Since ATD induced a significant lowering of peripheral TRP, without affecting central TRP or 5-HT concentrations, the decrease in CBF and global change in the flow-metabolism relationship cannot be directly attributed to decreases in brain TRP availability. This could be explained if the raphe were selectively vulnerable to ATD, but the exact mechanism remains unknown. Nevertheless, these data suggest that cerebrovascular disturbances should be considered as a potential contributory factor in studies of serotonergic dysfunction, including depression, with important implications for imaging studies that use CBF alone as a measure of neuronal function.