No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 1991.

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 106-126).

Thesis (Ph. D.)--University of Hong Kong, 1992. / Photocopy of typescrpt.

Thesis (M.D.)--University of Hong Kong, 1988. / Also available in print.

Submitted by Ana Maria Fiscina Sampaio (fiscina@bahia.fiocruz.br) on 2012-05-31T19:55:30Z No. of bitstreams: 1 Adenizar Chagas Júnior. O Imprint como método para detecção de Leptospira SSP. 2009.pdf: 396164 bytes, checksum: 8f423288d4f795e861df22e9de3acb59 (MD5) / Made available in DSpace on 2012-05-31T19:55:30Z (GMT). No. of bitstreams: 1 Adenizar Chagas Júnior. O Imprint como método para detecção de Leptospira SSP. 2009.pdf: 396164 bytes, checksum: 8f423288d4f795e861df22e9de3acb59 (MD5) Previous issue date: 2009 / Fundação Oswaldo Cruz. Centro de Pesquisas Gonçalo Moniz. Salvador, Bahia, Brasil / Na determinação da eficácia de novas candidatas à vacina para leptospirose, o marcador primário considerado é a mortalidade, e um marcador secundário importante é a indução de uma imunidade estéril. Entretanto, a avaliação da imunidade estéril é dificultada pelo tempo demandado e pela complexidade de métodos como o isolamento pela cultura. Neste estudo, foi avaliado o uso do método do imprint (ou touch preparation) na detecção da presença de leptospiras em tecidos de hamsters infectados com L. interrogans sorovar Copenhageni. Comparado com a cultura, o imprint demonstrou igual ou melhor detecção de leptospiras em amostras de rim, fígado, pulmão e sangue coletadas após a infecção obtendo uma concordância geral boa (κ = 0.61). Além disso, na avaliação de hamsters imunizados com uma proteína recombinante de Leptospira candidata à vacina e subsequente desafio com leptospiras patogênicas, a concordância entre a cultura e o imprint foi alta (κ = 0.84). Estes achados indicam que o imprint é um método rápido para a observação direta de Leptospira spp. e que pode ser facilmente aplicado na avaliação de animais infectados experimentalmente com leptospiras e na determinação de imunidade esterilizante durante avaliações de potenciais candidatas à vacina. / In determining the efficacy of new vaccine candidates for leptospirosis the primary endpoint is death and an important secondary endpoint is sterilizing immunity. However, evaluation of this endpoint is often hampered by the time consuming demands and complexity of methods such as culture isolation (CI). In this study, we evaluated the use of an imprint (or touch preparation) method (IM) in detecting the presence of leptospires in tissues of hamsters infected with L. interrogans serovar Copenhageni. Compared to CI, the IM exhibited equal or improved detection of leptospires in kidney, liver, lung and blood samples collected post-infection and the overall concordance was good (κ = 0.61). Furthermore, in an evaluation of hamsters immunized with a recombinant Leptospira protein-based vaccine candidate and subsequently challenged with leptospires, the agreement between the CI and IM was very good (κ = 0.84). These finding indicate that the IM is a rapid method for the direct observation of Leptospira spp. that can be readily applied to evaluating Leptospira infection in experimental animals and determining sterilizing immunity when screening potential vaccine candidates.

When given a choice between two foods of equal caloric value but different flavors, rats show a robust preference for that food whose flavor was previously associated with a higher calorie food. This finding suggests that rodents may identify food quality by sensory signals such as taste. The first portion of this thesis explores this flavor-calorie conditioning effect in other rodents, namely hamsters and gerbils. When hamsters were tested in the same paradigm as rats, the conditioning effect was not observed. This discrepancy may have resulted from the hamsters' ability to store food mash in their cheekpouches. Accordingly, hamsters were next presented with liquid diets which could not be cheekpouched. The conditioning effect was observed when different flavors were associated with different quality liquid diets. However, the effect was less robust than that discovered for rats. A second species, gerbils, did show robust conditioning effects. Thus, unlike rats and gerbils who show a robust flavor-calorie conditioning effect, hamsters are less likely to identify food quality by using taste cues. Once conditioned to detect caloric density by using flavor cues, hamsters and gerbils were placed on an 8-arm radial maze that consisted of four arms baited with high-calorie liquid and four arms baited with low-calorie liquid. The purpose of this second, part of the thesis research was to investigate the rodents' preference for food locations that contained food of varying qualities. Both species were expected to visit and drink first from the arm locations containing the higher calorie liquid. Although hamsters did not visit more high-calorie arm locations, they did drink from these arms more often. When visiting arm locations, hamsters appeared to use a circling strategy that began in the same arm each trial and consisted of visits to consecutive arms. Gerbils neither visited nor drank more often from the high-calorie arm locations. Gerbils also did not appear to use a circling strategy. Thus, when foraging on an 8-arm radial maze for food of varying quality, hamsters' use of a circling strategy prohibited them from first visiting high-calorie arms but not from preferentially drinking from these locations. Unlike hamsters, gerbils did not adopt a strategy to collect food rewards and were not selective about the food reward that was consumed. The foraging strategies of hamsters was further explored in the third part of the thesis. Hamsters were allowed to forage on an equally-baited 17-arm radial maze. Each arm location was baited with a sunflower seed. Once again, hamsters visited arm locations by using a circling strategy which consisted of visits to consecutive arms. However, on the larger maze hamsters did not begin each trial in the same arm location. In addition, hamsters that were placed on the same maze with 4 of the 17 baited arms blocked, given 13 arm location choices, removed from the maze while the blocks were also removed, and placed back on the maze to select 4 additional arm locations, did not preferentially select the previously blocked arms. Thus, hamsters whose response algorithm was disrupted did not show a memory-based strategy for collecting seeds from the maze. The major conclusions from this research are that 1.) Hamsters can learn to associate caloric density and flavor cues, but the learned effect is easily extinguished. 2.) This dietary information may be used when deciding what to eat but not where to forage. 3.) Hamsters appear to be harvesters who visit all foraging locations by adopting a response strategy. 4.) Gerbils can also learn to associate caloric density and flavor, and the learned effect is robust. 5.) Gerbils do not appear to use this information when deciding which foods to eat or where to forage. It will be interesting for future studies to see if rats use flavor-calorie information in foraging settings. / Arts, Faculty of / Psychology, Department of / Graduate

The last step in sphingomyelin's de novo biosyn-thetic pathway was investigated in Baby Hamster Kidney (BHK-21F) cells in tissue culture. Three types of pulse-chase experiments were done to try to identify the precursor for sphingomyelin's phosphocholine moiety. First, [Me- ³H]-choline was used to monitor the movement of the choline moiety in all the possible phosphocholine donors: ie. phosphocholine, CDP-choline, phosphatidylcholine, lysophospha-tidylcholine, and glycerophosphocholine. Radioactivity was observed in phosphocholine before appearing in phosphatidylcholine, glycerophosphocholine, and sphingomyelin. Specific radioactivities of phosphatidylcholine and sphingomyelin revealed a peculiar pattern, if representative of a precursor-product relationship between these two phospholipids. Their specific radioactivities became equal at 22 hours of chase and remained quite similar for the next 24 hours. The other two types of pulse-chase experiments both utilized prelabeled BHK phosphatidyl[Me- ³H]choline in phospholipid vesicles as their 'pulse' source. Phospholipid Exchange Protein(PLEP)-mediated exchange and polyethylene glycol/phytohemagglutinin (PEG/PHA)-mediated fusion between phospholipid vesicles and BHK cells were used to introduce the labeled phosphatidylcholine. In addition, in the 'fusion' experiments, other labeled compounds (glycerophosphocholine and sphingomyelin) were substituted for labeled phosphatidylcholine. PLEP- mediated exchange of labeled phosphatidylcholine did not result in enough transfer of radioactivity into the cell to adequately monitor individual cell phospholipids or any transfer of label - ie. from phosphatidylcholine to sphingomyelin. However, PEG/PHA-mediated fusion of vesicles and cells did result in enough radioactivity showing up in the cells. When labeled phosphatidylcholine was used, the radioactivity ratio between it and sphingomyelin averaged around 16, depending on the length of the chase (2-52 hours)m The use of either labeled glycerophosphocholine or sphingomyelin resulted in a ratio of about 1.8. One 'cold-trap1 experiment was done by including a large amount of unlabeled glycerophosphocholine with labeled phosphatidylcholine in the vesicle preparation. The resultant radioactivity in sphingomyelin was 50% less than previously, but phosphatidylcholine's had remained the same. The evidence seems to indicate a reversible precursor-product relationship between phosphatidylcholine and sphingomyelin, but does not clearly show whether or not any other intermediate (such as glycerophosphocholine) is also involved. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

This study aimed to investigate lipoprotein metabolism in male hamsters fed diets considered to be atherogenic in humans. Livers from adult male hamsters were selected to study aspects of apolipoprotein B metabolism. Isolated hepatocytes in suspension were compared with those maintained under tissue culture conditions. Liver slices were also prepared and compared with isolated suspended hepatocytes. Freshly prepared hepatocytes from the animals were incubated with radiolabelled precursors in suspension, or they were maintained under tissue culture conditions; liver slices were also investigated. The rates of total protein synthesis were of the same order in each of these systems, but protein secretion was impaired in liver slices, probably as a result of diffusion problems associated with the altered architecture of the sliced tissue. Albumin constituted 40 - 50% of the secreted proteins in each system. The rates of VLDL synthesis were increased in cells and slices prepared from animals previously fed sucrose- or fat-rich diets, but the secretion of VLDL was inhibited when diets contained unsaturated fat. The overall synthesis of apolipoprotein B was enhanced by fat-feeding; in the case of suspended hepatocytes, secretion of this protein was decreased when the preceding diet contained fats that were unsaturated; while in the case of liver slices, secretion was paradoxically enhanced. Apolipoprotein B was not degraded at significant rates in hepatocytes prepared from either control or fat-fed hamsters.