The aim of this study was to assess sensitivity of early life stage zebrafish to cadmium (Cd). Embryos and larva were exposed to Cd before the formation of skeletal elements. Exposure times were selected to determine whether Cd perturbed developmental processes that lead to skeletal deformities, and to characterize the types of skeletal deformities that occurred. Embryo/larva were exposed to 3μM, 10μM, 30μM, 100μM, 300μM, and 1000μM Cd at 12-36 hours post fertilization (hpf), 36-60hpf, 60-84hpf, and 144-168hpf in one series of experiments. This experiment was conducted at circumneutral pH. A second series of experiments with these same Cd concentrations were also conducted at pH 6 with embryo/larva exposed at 12-36hpf, 36-60hpf, and 60-84hpf. The fish that survived the exposures were raised for 40-60 days whereupon the surviving fish were overdosed with MS222, and X-rayed. The later early life stage fish were more sensitive to Cd toxicity; the chorion appeared to protect the earlier exposed embryos (zebrafish hatch 48-72hpf). Embryo/larva were more resistant to toxicity from dissolved Cd (pH 6) than particulate Cd (circumneutral pH); absence of functional gills during early life stages perhaps explained resistance to dissolved Cd. Notochord lesions (typically lethal within two weeks) occurred when embryos were exposed 12-36hpf. There was no evidence for sensitivity of early life stage zebrafish to Cd induced skeletal deformities that occurred within 40-60 days of Cd exposures. / Graduation date: 2004

published_or_final_version / Physiology / Master / Master of Philosophy

Anthropogenically driven climate change not only results in rising of sea temperature but also leads to more frequent and longer-lasting cold and heat waves. Meanwhile, coastal marine ecosystems are constantly challenged by increasing threats of chemical pollution. Temperature and chemical stressors can jointly affect the livelihood of marine organisms, but their combined effects are still poorly understood. Therefore, this study aimed to investigate the effects of thermal stress and chemical exposure on the marine medaka Oryzias melastigma, copepod Tigriopus japonicus and rotifer Brachionus koreanus. The four selected chemical contaminants included copper sulphate pentahydrate (Cu), dichlorophenyltrichloroethane (DDT), triphenyltin chloride and copper pyrithione. It was hypothesized that marine organisms are more susceptible to chemical exposure at both cold and warm extremes. In vivo acute ecotoxicity tests were conducted over a wide temperature range to ascertain the relationship between thermal stress and chemical toxicity. For O. melastigma larvae, the lowest toxicity occurred at an optimum temperature range; the chemical toxicity further increased with temperature increase or decrease from this optimum, and exacerbated at extremely low and high temperatures. For T. japonicus and B. koreanus, the chemical toxicity generally increased with increasing temperature. Such inter-species dissimilarities were possibly due to differences in the uptake route, detoxification mechanism, avoidance behaviour and physiological response between the fish and the copepod or rotifer. Experiments were conducted to evaluate the temperature-dependent physiological and biochemical responses, and thermal tolerance of O. melastigma larvae. The growth in the fish larvae showed an inverse and negatively skewed V-shape relationship with temperature, with a significant reduction in performance at both low and high thermal extremes. A mismatch between demand and supply of oxygen and energy under extremely cold and warm conditions was probably the primary cause of growth inhibition and metabolic impairment, leading to a temporary adaptation by a shift to anaerobiosis and an induction of heat shock proteins (HSPs). Temperatures at both cold and warm extremes increased toxicities of DDT and Cu to O. melastigma larvae, resulting in restricted growth and interrupted oxygen consumption rate. The fish larvae modulated their metabolic pathway and produced stress proteins (i.e., HSPs and metallothioneins) for adaptation to the combined stress. However, such responses were disrupted by combinations of thermal extremes, in particular high temperature, and high chemical concentration. Most importantly, both DDT and Cu exposure significantly reduced the thermal tolerance of the fish larvae. The interacting effect of temperature and Cu was also investigated on T. japonicus. The results showed that their combined effect could significantly reduce the survival, lengthen the developmental time and change the sex ratio of the copepod. Transcriptions of several stress-related genes (i.e., glutathione reductase, glutathione S-transferases and HSPs) in the adult T. japonicus were significantly affected by the joint-effect of temperature and Cu exposure, implying that these genes played essential roles in protecting the cellular integrity against the stresses. This study advanced the understanding on the temperature-dependent toxicity of chemical contaminants to marine organisms, and provided valuable information and empirical models for deriving water quality criteria of chemical contaminants at various temperatures. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

No description available.

No description available.

Liver X receptor (LXR), farnesoid X receptor (FXR) and peroxisome proliferator-activated receptor (PPAR) are adopted orphan nuclear receptors that function as lipid sensors. These receptors respond to cellular lipid levels and regulate the expression of target gene. Previously, it was demonstrated that low doses of chlordecone (CD) pretreatment disturbed exogenous cholesterol distribution and cellular lipid transport, storage and metabolism pathway. The aim of this study was to determine whether low doses of CD affect nuclear receptor (LXR��/FXR or PPAR��)-mediated lipid homeostasis. Thus, hepatic microsomal protein contents of cytochrome P450 7a (cyp7a, regulated by LXR��/FXR), and P450 4a1 (cyp4a1, regulated by PPAR��) were determined in male C57BL/6N mice, fed AIN76 or AIN93M diet, received CD (2.5, 5.0 or 15 mg CD/kg body weight). Western blot analysis was used for protein measurements using appropriate antibodies. Cyp7a and cyp4a1 protein levels were confirmed by enzyme activities, cholesterol 7��-hydroxylase and lauric acid hydroxylase activities, respectively. Plasma total cholesterol and triglycerides, body and liver weights were also measured in these dose-response experiments. Plasma total cholesterol and triglycerides levels from animals fed AIN 93M diet were significantly lower than those from animals fed AN 76 diet. However, neither total plasma cholesterol nor triglycerides levels were changed in CD-treated mice fed AN 76 or AN 93M diet. Cyp7a protein level or its enzyme activity was not altered by CD treatment. Likewise, cyp4a1 protein level or its activity was not affected by CD treatment. In summary, the results of the present study do not support the hypothesis that CD treatment alters nuclear receptor (LXR��/FXR or PPAR��)-mediated lipid homeostasis. / Graduation date: 2002

Numerous natural and anthropogenic chemicals interact with endocrine systems of animals. The most widely studied of these endocrine active chemicals (EACs) are estrogen receptor agonists and antagonists. Because of the many important roles of estrogens in animals, xenoestrogens have the potential to impact environmental health. It has been proposed that xenoestrogen contaminants are responsible for recent increases in estrogen dependent human diseases and sexual and developmental abnormalities in wildlife. Aquatic species are particularly susceptible to persistent EACs that accumulate in sediments and biomagnify along trophic levels. Rainbow trout, Oncorhynchus mykiss, commonly used in biomedical research and as a sentinel species, was chosen as a model for studying mechanisms of xenoestrogen activity. The aims of this research were to assess the estrogenic activity of individual persistent, organic contaminants and simple mixtures in vivo. Emphasis was placed on determining the potential for xenoestrogens to alter sexual development or to induce sexually dimorphic biochemical responses. Gonadal abnormalities in trout exposed as embryos to the xenoestrogen o,p'-DDE showed that xenobiotics can affect trout sexual development. However, the absence of endocrine disruption by low doses of o,p'-DDE, by the xenoestrogens chlordecone and octylphenol, or by the anti-androgen p,p'-DDE, suggested that lethality is likely to precede endocrine disruption in highly exposed, feral salmonid populations. Sexually distinct responses in immature trout were documented with respect to vitellogenin induction (2 to 4 fold higher in females) and cytochrome P450 expression. Sex differences occurred only when doses of estrogens or xenoestrogens were below levels that cause maximal estrogenic responses. Evidence suggests that estrogen regulation may be fundamentally different in immature males and females, which may have implications for natural populations exposed to xenoestrogens. Vitellogenin induction and P450 modulation were responsive to mixtures of estrogens and xenoestrogens in a manner suggestive of additive activation of estrogen receptors. Cytochrome P450 dependent induction of lauric acid hydroxylation was observed for the first time in trout, in response to tamoxifen and mixtures of tamoxifen and 17��-estradiol. The estrogenic activity of tamoxifen and 4-hydroxy-2',4',6'-trichlorobiphenyl were greater in vivo than what was predicted by in vitro studies, which emphasized the need for mechanism based investigations of xenoestrogens in whole organisms. / Graduation date: 1999

Graduation date: 1996

No description available.

Graduation date: 1994