Ultrastructural analysis of platelets and fibrin networks in stroke patients

Ischaemic stroke represent more than 80% of the total stroke instances. The location of the occlusion and the amount of brain tissue involved determines the effect of the stroke. Stroke can result in paralysis, memory loss, speech impairment and even a “lock-in” state. The amount of neuronal damage will determine whether these symptoms will be temporary or permanent. Stroke is deemed the second leading cause of death for individuals over the age of 60. According to the World Stroke Organization (WSO) every six seconds stroke claims a life, regardless of age or gender. Stroke is a global burden and the medical costs and disability related to stroke in America for 2010 was projected at almost $73.7 billion. The morphology of platelets, fibrin networks and erythrocytes as well as the differential white blood cell counts of 20 thrombo-embolic ischaemic stroke patients were investigated. Internal and external alterations were revealed in the platelets of stroke patients when compared to healthy controls. The decreased numbers of alpha granules in the platelets of the stroke patients indicated these platelets to be activated. Substances released by activated platelets promote fibrin network structure, specifically the formation of fibrin strands and accumulation of additional platelets. The fibrin network of healthy individuals consists of major, thick fibers with minor, thin fibers distributed between them. The fibrin network of stroke patients exhibited an abnormally layered and matted ultrastructure comprising of mainly thin, minor fibrin fibers packed closely together. An uncharacteristic circular morphology was also observed. These alterations in the fibrin network indicate the activated platelets to be actively involved in the thrombotic event. Neuronal damage related to stroke is also advanced by the vasoactive substances released by activated platelets. It can therefore be deduced that the morphology of the fibrin network is altered long before the concrete thrombotic event transpire. Large numbers of abnormal erythrocytes were distinguished in the blood of stroke patients. Among these abnormal forms of erythrocytes specifically codocytes, knizocytes, stomatocytes and echinocytes were identified. Abnormal erythrocyte forms were significantly increased in hypertensive patients and females independently. Alterations in the ultrastructure of erythrocytes disturb blood flow in the microcirculation and could possibly augment the ischaemic event. Inflammation is closely related to ischaemic stroke. An increased monocyte count and a reduced number of neutrophils were a significant feature among all the stroke patients of this study. Patients with hypertension as well as patients consuming aspirin on a daily basis showed the greatest influence on the observed differential white blood cell counts. These morphological alterations observed in the platelets, fibrin network and erythrocytes as well as the differential white blood cell count could be incorporated in an analysis regime that could probably indicate an impending thrombotic event. Therefore treatment could be initiated before the ischaemic event to possibly prevent the stroke. For future studies a larger study population, a more refined patient enrolment as well as the analysis of follow-up blood samples from patients could substantiate the above-mentioned findings and provide additional information concerning the thrombotic event and the effectiveness of treatment procedures.Dissertation (MSc)--University of Pretoria, 2010.AnatomyUnrestricte

MINODU: Fostering Local Sustainable Development Through Technology and Research

Rapid climate change is exposing subsistence farmers to enormous challenges, especially in Sub-Saharan Africa. Several foreign aid programs have been set up to cope with these issues, many of which have focused on technical solutions. However, there seems to be a large gap between scientific research and the needs of local communities. Besides focusing on new ways to improve the resilience of local food production, there is also an urgent need to adapt available knowledge to the local context. Based on experiences from a project to co-create community networks in Togo in 2020, we aim to empower local stakeholders, including farmers and scientists, to adapt existing knowledge of sustainable crop farming to current practices. New modes of knowledge exchange can be established with the help of participatory design. These methods may help to foster a collective approach to learning that enables people to cope with global challenges on a local level, all while valuing the traditional practices of local farmers and enriching them with scientific knowledge

Southern California's megaflood event of ca. 1605 AD linked to large-scale atmospheric forcing

A distinct, 1- to 2-cm-thick flood deposit found in Santa Barbara Basin with a varve-date of 1605 AD ± 5 years testifies to an intensity of precipitation that remains unmatched for later periods when historical or instrumental records can be compared against the varve record. The 1605 AD ± 5 event correlates well with Enzel's (1992) finding of a Silver Lake playa perennial lake at the terminus of the Mojave River (carbon-14-dated 1560 AD ± 90 years), in relative proximity to the rainfall catchment area draining into Santa Barbara Basin. According to Enzel, such a persistent flooding of the Silver Lake playa occurred only once during the last 3,500 years and required a sequence of floods, each comparable in magnitude to the largest floods in the modern record. To gain confidence in dating of the 1605 AD ± 5 event, we compare Southern California's sedimentary evidence against historical reports and multi-proxy time-series that indicate unusual climatic events or are sensitive to changes in large-scale atmospheric circulation patterns. The emerging pattern supports previous suggestions that the first decade of the 17th century was marked by a rapid cooling of the Northern Hemisphere, with some indications for global coverage. A burst of volcanism and the occurrence of El Nino seem to have contributed to the severity of the events. The synopsis of the 1605 AD ± 5 years flood deposit in Santa Barbara Basin, the substantial freshwater body at Silver Lake playa, and much additional paleoclimatic, global evidence testifies for an equatorward shift of global wind patterns as the world experienced an interval of rapid, intense, and widespread cooling

Seasonal resolution of laminated sediments in Santa Barbara Basin: its significance in paleoclimatic studies

Sediments in Santa Barbara Basin contain microfossil and sedimentological information that allows reconstruction of major features of the California Current such as water temperature, strength of upwelling, and productivity. ... Until now, investigations of Santa Barbara Basin sediments have utilized analytical techniques that could not resolve seasonal laminae, permitting annual resolution of variations in sediment composition and structure only. ... Based on a successful technique for preparation of epoxy-embedded and highly polished thin-sections that permit economical optical and electron microscope evaluation of laminated sequences, it is our long-term goal to reconstruct, with unprecedented detail, the history of sedimentation processes in the Santa Barbara Basin by developing ultra-high-resolution time series of biotic and detrital proxies

First record of Lingulodinium polyedrum (Dinophyceae) resting cysts in coastal sediments from the Inner Sea of Chiloé, Los Lagos Region, southern Chile (~41°-43°S).

Quistes de resistencia del dinoflagelado potencialmente toxico Lingulodinium polyedrum (Stein) Dodge son registrados por primera vez en sedimentos costeros del Mar Interior de Chiloe. Se entrega informacion de abundancia, distribucion, descripcion y fotomicrografias de la especie. Se confirma la presencia de L. polyedrum en aguas costeras del sur de Chile

GERMINATION OF RESTING STAGES OF DIATOMS AND DINOFLAGELLATES IN MARINE SEDIMENTS FROM TWO UPWELLING AREAS OF CHILE

Con el fin de evaluar la potencial germinación de los estados de resistencia de las diatomeas y dinofiagelados preservados en sedimentos superficiales, se cultivaron bajo condiciones de laboratorio sedimentos de las bahías de Mejillones (23° S) y Concepción (36° S), Chile: Ciclo L:0 12:12 h, intensidad de luz 140 umol m²s_1, temperatura ambiente y 35,4 unidades de salinidad. Las principales especies de diatomeas presentes en los sedimentos fueron Skeletonema japonicum y esporas de Chaetoceros. Los quistes de dinofiagelados estuvieron representados por Diplopsalis, Scrippsiella, Woloszynskia y las especies Protoperidinium avellanum y P. leonis. Después de 20 días de cultivo, se registró germinación y crecimiento de S. japonicum y de varias especies de Chaetoceros, sin embargo su abundancia fue baja. Las diatomeas con crecimiento abundante fueron Stauroneis legleri, Pseudostaurosira trainorii, Pseudostaurosira sp.l, Pseudostaurosira sp. 2 y Navícula pseudoreinhardtii. El dinoflagelado Woloszynskia sp. también germinó y creció abundantemente. Este trabajo incluye una breve descripción de las especies cultivadas y algunos aspectos de su ecología. Se discuten las posibles causas de la pobre germinación de las diatomeas planctónicas, siendo la baja concentración de oxígeno disuelto en las aguas de fondo uno de los principales factores que presumiblemente afectaron la sobrevivencia de las esporas de resistencia. With the aim to assess germination of diatom and dinofiagellates resting spores we cultured under laboratory conditions surface sediments collected in the Mejillones Bay (23° S) and off Concepción (36° S), Chile. These sediments were cultured in the laboratory with a 12:12 h L/D cycle, light intensity of 140 umol m² s"¹, at room temperature, and with a salinity of 35.4 units. The main diatom species in the sediments were Skeletonema japonicum and Chaetoceros spores. Dinofiagellate cysts were represented by the genera Diplopsalis, Scrippsiella, and Woloszynskia and the species Protoperidinium avellanum and P. leonis. After 20 days of culturing, germination and growth was recorded for S. japonicum and several of the Chaetoceros species, although their abundance was low. The diatoms with abundant growth were Stauroneis legleri, Pseudostaurosira trainorii, Pseudostaurosira sp.l, Pseudostaurosira sp. 2, and Navícula pseudoreinhardtii. The dinofiagellate Woloszynskia sp. also germinated and grew abundantly in the culture. This study includes a brief description of the cultured species and some aspects of their ecology. In addition, we discuss the possible causes for low levels of germination in planktonic diatoms, finding low dissolved oxygen concentrations in the bottom waters to be one of the main factors that presumably affected the survival of resting spores in the sediment

Sediment provenance in the Baker-Martínez fjord system (Chile, 48°s) indicated by magnetic susceptibility and inorganic geochemistry

Fjord sediments are increasingly used as high-resolution archives of climate and environmental change, including variations in glacier mass balance and terrestrial hydrology. To accurately interpret such sediment records, it is crucial to comprehend sediment transport processes and determine sediment provenance. With this in mind, our main objective is to identify cost-effective parameters that can be used to reconstruct relative variations in the origin of sediments deposited in the Baker-Martínez fjord system, which is located between the Northern (NPI) and Southern (SPI) Patagonian Icefields. We focus on estimating the proportions of sediment derived from each icefield, taking advantage of the clearly distinct lithologies that underlie NPI (Patagonian Batholith) and SPI (Eastern Andean Metamorphic Complex) glaciers. The magnetic susceptibility and inorganic geochemistry of 21 surface sediment samples collected along the fjord system and that of suspended sediment samples from the four main rivers that discharge at its heads were investigated. Results indicate that sediments derived from the NPI are characterized by higher magnetic susceptibility and log(Ti/Al) values than those from the SPI, reflecting the mafic nature of the batholith. In fjords that receive contributions from both the NPI and SPI, magnetic susceptibility and log(Ti/Al) primarily reflect sediment provenance. In fjords receiving sediment from only one icefield, however, these parameters are positively correlated with grain size and reflect the progressive settling of particles from the surficial plume. Our results suggest that magnetic susceptibility and log(Ti/Al) can be used to reconstruct sediment provenance within the Baker-Martínez fjord system, but that only log(Ti/Al) can provide quantitative estimates of the proportions of sediment derived from each icefield. Ultimately, applying these provenance indicators to long sediment cores from the Baker-Martínez fjord system could allow reconstructing relative variations in sediment input from each icefield, which may in turn be interpreted as changes in river discharge and/or glacier mass balance

Sediment provenance indicated by magnetic susceptibility and inorganic geochemistry in the Baker-Martínez fjord system (Chile, 48°S)

Patagonian fjord sediments are increasingly used as high-resolution archives of past climate and environmental change, including variations in glacier mass balance, flood frequency, and seismic activity. To accurately interpret these proxy records, it is crucial to comprehend modern day sedimentation processes and determine the provenance of the sediments. With this in mind, the main objective of this study is to identify parameters that can be used to reconstruct sediment provenance in the fjords of Chilean Patagonia. We focus on the Baker-Martínez fjord system, which is located between the Northern and Southern Patagonian Icefields and seems particularly sensitive to climate change. This fjord system connects the terrestrial ecosystems of Patagonia with the SE Pacific Ocean, and most of its sediment originates from glacier-fed rivers draining either the Patagonian Batholith (PB; Baker and Huemules rivers) to the north, or the Eastern Andes Metamorphic Complex (EAMC; Bravo and Pascua rivers) to the south. Eighteen surface sediment samples from across the Baker-Martínez fjord system and 44 suspended sediment samples from two sequential (Baker fjord) and one continuous (Steffen fjord) sediment trap were investigated. In addition, we analyzed suspended sediment samples collected at the mouths of the four main rivers that drain the PB and EAMC to define end-members. We focus on mass-specific magnetic susceptibility (MS) and inorganic geochemistry, which seem to be particularly promising in this fjord system dominated by lithogenic sediments (97–85 wt%). Our results indicate that sediments derived from the PB are characterized by high MS, Ti/Al, and Fe/Al values, reflecting the granodioritic nature of the batholith (rich in pyroxene and amphibole). In contrast, sediments from the southern EAMC-derived rivers have significantly lower MS, Ti/Al, and Fe/Al values. The sediment trap results reveal MS values that increase with increasing Baker river discharge, either during the summer melt season, or during high precipitation events (rain-on-snow) in winter. Likewise, the MS, Ti/Al and Fe/Al values of the fjord surface sediments are also directly related to sediment provenance. In fjords fed by only one river (e.g., Martínez channel), however, the MS is significantly correlated with mean grain size (r = 0.90; p < 0.01) and with the proportion of lithogenic particles (r = 0.73; p < 0.05). The latter observation means that future research is needed to correct the MS and geochemical data for grain-size before using them as quantitative provenance indicators. This study suggests that, after grain-size correction, MS and inorganic geochemistry (Ti/Al and Fe/Al) can be used to reconstruct sediment provenance within the Baker-Martínez fjord system. Ultimately, applying these provenance indicators to long sediment cores from the same fjord system will allow us to reconstruct variations in the behavior of outlet glaciers from both icefields independently

Diatom and silicoflagellate fluxes at the Walvis Ridge: An environment influenced by coastal upwelling in the Benguela system

Seasonal fluctuations in the total particle, biogenic opal, diatom and silicoflagellate fluxes were observed in sediment traps deployed at 599 m and 1648 m in the Walvis Ridge area, within the Benguela upwelling system, from March 1989 to March 1990 (station WR 2: 20°02.8′S, 09°09.3′E). Fluxes were directly related to wind stress variations (wind maxima preceding flux maxima by several weeks), and inversely related to SST changes (derived from measured concentrations of C37 alkenones; range: 14.6°–23.6°C). The biogenic particle composition at different depths reflected the complicated hydrology of the area with a combination of tropical, temperate and subantarctic water masses. Biogenic opal content varied from about 2 to 12% of the total mass flux in the upper trap and from about 4 to 17% in the lower trap. Diatoms were the main contributor to the opal fraction (mean daily flux of ca. 5.5 * 106 valves m−2 day−1), followed by silicoflagellates (ca. 2.6 * 105 skeletons m−2 day−1). Two seasonal maxima, in May and June (austral autumn) and from October to November (austral spring), were observed; silicoflagellates yielded also a third moderate maximum in August/September (austral winter). At 1648 m fluxes peaked from May to July (data were available for the period 18 Mar to 27 Aug 1989 only). Few diatoms were abundant; 19 taxa accounted for 50% of all the diatoms identified, and about 32 for the 75% level. Specific diversity of diatoms at 599 m was highest during times of lowest fluxes, in the austral winter, late spring and summer. The diatom taxa occurring at 599 m and at 1648 m were the same, with some flux enrichment with depth due to advection of particles into the lower trap by resuspension and downslope movement. The relatively high concentrations of the Antarctic-Subantarctic species Fragilariopsis kerguelensis in the upper trap solely, was probably linked to selective entrainment and transport within a ring of southerly origin (south of the Subantarctic/Subtropical Convergence Zone). The enrichment of moderately resistant and robust taxa in the sediments in conjunction with the rarity or absence of delicate taxa points to preferential concentration in the sediments of some taxa and dissolution of others. The occurrence of phytoliths in the traps and in the sediment sample can be linked to the “berg” winds, which are typical for the entire Benguela region during fall and winter