<p> Simple environmental features can shape complex behavior. Identifying key aspects of the environment (e.g., temperature, structure, toxins) that lead to widespread consequences is of central importance in a changing world. The primary objective of my dissertation is to investigate how relatively simple aspects of the environment can influence small groups of animals in profound and complex ways. In the first three chapters, I report on experiments showing how small changes in the environment can affect the expression of behavior at different points in development and can have important physiological consequences for litters of mouse pups. I then report on two sets of experiments showing how subtle changes in the environment can dramatically affect spacing patterns and social dynamics of small groups of adult zebrafish. Together, my results emphasize the ways that subtle changes in the environment can have profound impacts on individuals and small groups. In both lines of work, I have found that a more accurate characterization of the phenomena, infant rodent development and zebrafish social behavior, requires the use of individual and group measures and that temperature, density, and pollutants can have a powerful effect on group responses. These results are important because they show that the physical environment can have profound effects on the phenotype, and that with a changing physical environment or anthropogenic change, dramatic differences may be observed in the behavior of groups.</p>

<p> Sediment bioturbators play an important ecological role and may both be affected by contaminants in the sediment and affect the fate and distribution of these contaminants. This is especially important for the many contaminants, like lead, for which sediments serve as a sink upon the contaminants&rsquo; release into the environment. In this study, I investigated the toxicity of sediment Pb to a freshwater bioturbator, the effect of bioturbation on the environmental distribution of the Pb, the effect of sediment characteristics on the bioturbation-mediated transfer of Pb from the sediment to the water column, and this transfer&rsquo;s toxicological consequences for planktonic organisms. Experiments were conducted in microcosms with control sediment or Pb-spiked sediment, the freshwater oligochaete Lumbriculus variegatus served as the model bioturbator, and the water flea Daphnia magna served as the model planktonic organism. The rate of bioturbation of the oligochaete was quantified using luminophores. </p><p> The bioturbation resulted in the transfer of Pb from the sediment to the water column. However, it did not affect Pb levels in the worm tissue or in the sediment. The environmental distribution of Pb among water column, biota, and sediment in the presence of the bioturbator was dependent on sediment characteristic like organic content, silt/clay content, and the pH of the sediment. Bioturbation by L. variegatus increased bioaccumulation of Pb in D. magna; however, this Pb had no toxic effect on survival, reproduction, and biomass of D. magna under the specific conditions used here. Quantification of the bioturbation rates of L. variegatus showed that the intensity of the bioturbation was enhanced at higher densities of the oligochaete but reduced at high sedimentary Pb concentrations. Overall this study demonstrated that bioturbation by L. variegatus can transfer Pb from the sediment to the water column, and that this transfer is dependent on sediment characteristics. The Pb transferred as a result of the bioturbation can enhance Pb availability to organisms in the water column, and potentially cause toxic effects in these organisms.</p>

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / Letters to editor

Organic xenobiotic compounds in the environment are causing widescale concern. Knowledge of the toxicity of organic xenobiotic compounds to the soil microbial biomass is essential as soil health and sustainability are essential for ecosystem function. Traditionally, chemical analysis has been used to assess contamination impacts in soils, however, compound residue cannot provide information on toxicity in environmental matrices, the toxicity of complex chemical mixtures and bioavailability. Bioluminescence bioassays, utilising the naturally bioluminescent bacterium Vibrio fischeri have been widely used to investigate the toxicity of contaminants in soil, sediment and freshwater environments. To utilise the V. fischeri bioassay all samples must be adjusted to a near neutral pH and a salinity of 2 % NaCl. Application of this assay to assess toxicity in terrestrial environments means that samples are not assessed under natural pH and saline conditions. Bioluminescent terrestrial bacteria have been constructed by inserting the lux genes, encoding of bioluminescence in marine bacterium, into the plasmid or chromosomal genome of terrestrial bacteria. The plasmid lux marked strain studied in this thesis, Pseudomonas fluorescens 10586s pUCD607, was used to develop a bioassay which could assess the toxicity of substituted benzenes in aqueous solution. The EC50 values determined for benzene and 1,2-dichlorobenzene were comparable between lux marked P. fluorescens and V. fischeri. Bioluminescence responses to substituted benzenes were investigated with a view to understanding modes of toxic action. Observed stimulation of bioluminescence in response to a number of compounds was thought to be caused by the uncoupling of proton gradients by low organic xenobiotic concentrations. Viable cell counts confirmed that stimulation of bioluminescence was not as a result of an increase in the number of viable cells. At high substituted benzene concentrations an inhibition of bioluminescence was observed. Application of quantitative structure-activity relationships (QSARs) for chlorobenzenes, utilising P. fluorescens toxicity data and physiochemical characteristics, showed that the toxic responses of these non-polar compounds were a function of compound solubility and lipophicity. QSARs applied to assess chlorobenzene toxicity could not be used to predict the toxicity of polar compounds due to the differing modes of toxic action. Correlating P. fluorescens with QSARs developed for C. meneghiniana and Pimephales promelas showed good correlation between the freshwater organisms but a poor correlation between marine bacterium V. fischeri.

Current concepts concerning nicotine's central nervous system (CNS) mechanism(s) of action suggest that this drug is producing its effects via an interaction at nicotiniccholinergic receptors (nAChRs) which open a membrane cation channel. Following initial opening of the channel, nicotine appears to induce a rapid desensitization of the nAChRs, closing the channel and resulting in a cessation of nicotine's effects. Research presented here will provide evidence of this secondary desensitization process in vivo by demonstrating nicotine's ability to induce acute tolerance in the discriminative stimulus (DS) paradigm. The ability of nicotine to elicit DS control of behavior was significantly reduced via challenge doses of (800, 1200, and 1600 ugjkg, s.c.) of nicotine administered 60-180 minutes prior to the training dose (400 ugjkg, s.c.). Eight out of twenty rats demonstrated this phenomena, with time and dose varying, suggesting that these effect may be contingent upon the individual rat studied. It appears that we have found a means of investigating cellular mechanisms in vivo using operant behavior.

Cholera toxin, obtained as crude culture filtrates of the bacterium Vibrio cholerae, was purified by a combination of ammonium sulphate fractionation, ion-exchange chromatography on DEAE-cellulose, and gel filtration cn Ultrogel AcA-44. The purified toxin migrated as a homogeneous protein on SD5 and native polyacrylamide gels, and activated / adenylate cyclase in rat liver homogenates. Activation of rat liver adenylate cyclase by cholera toxin was strictly dependent upon the presence of NAD +. In the absence of exogenous NAD+, homogenates or membrane preparations were refractory to the toxin as a result of high levels of endogenous NAD+ - utilising activities. Under conditions in which competition for NAD+ by endogenous enzymes was minimised, the activity of cholera toxin as a stimulator of adenylate cyclase was markedly enhanced and activation of the enzyme occurred with a detectable toxin-specific % incorporation of [~^c] into TCA-precipitable material from ^adenine U-^cj- NAD+. The results were consistent with the hypothesis that cholera toxin acts by catalysing the ADP-ribosylation of an intracellular membranebound acceptor protein, and that this modification is responsible for the toxin-induced stimulation of adenylate cyclase activity. Results are also presented which argue against the validity of extrapolating from studies of the NADase activity of cholera toxin to the mechanism of toxin action on adenylate cyclase. Under a variety of conditions, NADase activity appeared to proceed independently of the physiologically important ADP-ribosyltransferase activity. furthermore, culture filtrates of V. cholerae were shown to contain a highly active NADase distinct from cholera toxin, and the possibilities of NADase contamination, even in apparently pure toxin preparations, are emphasised.

<p> This dissertation includes three separate but related studies performed in partial fulfillment of the requirements for the degree of Doctor of Public Health in Environmental and Occupational Health. The main goal this dissertation was to develop and assess quantitative relationships for predicting doses associated with chronic non-cancer toxicity levels in situations where there is an absence of chronic toxicity data, and to consider the applications of these findings to chemical substitution decisions. Data from National Toxicology Program (NTP) Technical Reports (TRs) (and where applicable Toxicity Reports), which detail the results of both short-term and chronic rodent toxicity tests, have been extracted and modeled using the Environmental Protection Agency&rsquo;s (EPA&rsquo;s) Benchmark Dose Software (BMDS). Best-fit minimum benchmark doses (BMDs) and benchmark dose lower limits (BMDL) were determined. Endpoints of interest included non-neoplastic lesions, final mean body weights and mean organ weights. All endpoints were identified by NTP Pathologists in the abstract of the TRs as either statistically or biologically significant. A total of 41 chemicals tested between 2000 and 2012 were included with over 1700 endpoints for short-term (13 week) and chronic (2 year) exposures. </p><p> Non-cancer endpoints were the focus of this research. Chronic rodent bioassays have been used by many methodologies in predicting the carcinogenic potential of chemicals in humans (1). However, there appears to be less emphasis on non-cancer endpoints. Further, it has been shown in the literature that there is little concordance in cancerous endpoints between humans and rodents (2). The first study, Quantitative Relationship of Non-Cancer Benchmark Doses in Short-Term and Chronic Rodent Bioassays (Chapter 2), investigated quantitative relationships between non-cancer chronic and short-term toxicity levels using best-fit modeling results and orthogonal regression techniques. The findings indicate that short-term toxicity studies reasonably provide a quantitative estimate of minimum (and median) chronic non-cancer BMDs and BMDLs. </p><p> The next study, <i>Assessing Implicit Assumptions</i> in Toxicity Testing Guidelines (Chapter 3) assessed the most sensitive species and species-sex combinations associated with the best-fit minimum BMDL10 for the 41 chemicals. The findings indicate that species and species-sex sensitivity for this group of chemicals is not uniform and that rats are significantly more sensitive than mice for non-cancerous outcomes. There are also indications that male rats may be more than the other species sex groups in certain instances. </p><p> The third and final study, <i>Comparing Human Health</i> Toxicity of Alternative Chemicals (Chapter 4), considered two pairs of target and alternative chemicals. A target is the chemical of concern and the <i>alternative </i> is the suggested substitution. The alternative chemical lacked chronic toxicity data, whereas the target had well studied non-cancer health effects. Using the quantitative relationships established in Chapter 2, Quantitative Relationship of <i>Non-Cancer Benchmark Doses in Short-Term and Chronic Rodent Bioassays,</i> chronic health effect levels were predicted for the alternative chemicals and compared to known points of departure (PODs) for the targets. The findings indicate some alternatives can lead to chemical exposures potentially more toxic than the target chemical.</p>

Renal proximal tubular cells (&'62 90&'37) were isolated from the rat in high yield by collagenase digestion of renal cortical tissue, followed by isopycnic centrifugation in a Percoll density gradient. The cells were of high viability and their identity verified by morphology and PT specific enzyme activities. Cytochrome P450 and dependent monooxygenase activities were maintained and the rapid decline in reduced glutathione prevented by addition of glycine, glutamate and cystine to the buffers used. These parameters were also maintained in culture (24h). Cytochrome P450-dependent monooxygenase activity was induced in proximal tubular cells isolated after pretreatment of rats with 3-methylcholanthrene, particularly with ethoxyresorufin as substrate, indicating the presence of inducible P450c isoenzyme(s) in PT cells. In contrast, treatment with phenobarbitone showed no induction. Treatment in vivo with the renal toxins, gentamicin and cyclosporin A (CsA), resulted in altered glomerular function and renal parenchymal damage. Treatment with gentamicin in vivo and in vitro resulted in increased PAH uptake and decreased gamma glutamyl transferase activity, suggesting a primary effect of gentamicin on cell membranes. CsA treatment in vivo produced an effect on GSH, lipid peroxidation and succinate dehydrogenase activity in the isolated PT cells. On treatment in suspension, no significant effects were observed. Treatment with gentamicin in culture (24h) did not result in a significant effect on the cell parameters studied. In conclusion, PT cells can be isolated in high yield with good viability from the renal cortex. Cell function can be maintained both in suspension and in culture. Therefore, this system may be used as a model for the investigation of PT-specific drug-induced nephrotoxicity as well as renal cytochrome P450 isoenzyme composition and induction characteristics.

No description available.

Digitized by Kansas Correctional Industries