Digitized by Kansas Correctional Industries

Graduation date: 1991

Richardson ground squirrels (gophers) are pests on the prairies that cause considerable agricultural and ecological damage. Traditional control methods such as the rodenticides strychnine, zinc phosphide, and anticoagulants, have proven ineffective in reducing gopher densities. In additional, current gopher control methods have the significant potential to cause primary and secondary toxicity to non-target animals. Thus, alternative methods for toxicological control of gophers are needed to mitigate these concerns. Present studies focused on the cytochrome P450 (CYP450) enzyme system responsible for xenobiotic detoxification in gophers. In vitro hepatic microsomal systems and HPLC analysis were used to elucidate general metabolic characteristics of major gopher xenobiotic metabolizing pathways. We found that the content and activity of individual components of the CYP450 system including CYP450, cytochrome b5, and NADPH-cytochrome P450 reductase in liver microsomal preparations were higher in gophers exposed to toxins used to control their population than in naïve (unexposed) gophers. When in vitro CYP450 mediated activities for five substrates [coumarin and aniline aromatic hydroxylation, 7-methoxycouamrin O-demethylation, and N-methylaniline, and N,N-dimethylaniline N-demethylation] were measured, naïve gophers were identified to have higher specific activity but similar whole body activity compared to the exposed gophers. Furthermore, there was a clearly identifiable sub-population of poor metabolizers showing considerably lower CYP450 activity within the gopher samples studied. Clotrimazole was found to be a potent inhibitor of several substrates of CYP450 enzyme-mediated reactions, which included aniline aromatic hydroxylation, N-methylaniline and N,N-dimethylaniline N-demethylation, and 7-methoxycoumarin O-demethylation. The cytotoxicity of above compounds was tested using freshly isolated gopher hepatocytes. The results showed that each compound caused considerable cytotoxicity to gopher hepatocytes. Addition of clotrimazole to the freshly isolated hepatocyte suspension increased the cytotoxicity of all tested compounds. <p>In conclusion, gophers may develop resistance to current chemical control methods through the enhancement of CYP450 system content, which can compensate the loss of enzyme activity. Furthermore, clotrimazole is a potent cytochrome P450 inhibitor, which increases the cytotoxicity caused by given compounds in gopher livers. The concept of using CYP450 enzyme inhibitor in combination with another chemical whose elimination depends on CYP450 metabolism to improve current gopher control method has practical importance.

Richardson ground squirrels (gophers) are pests on the prairies that cause considerable agricultural and ecological damage. Traditional control methods such as the rodenticides strychnine, zinc phosphide, and anticoagulants, have proven ineffective in reducing gopher densities. In additional, current gopher control methods have the significant potential to cause primary and secondary toxicity to non-target animals. Thus, alternative methods for toxicological control of gophers are needed to mitigate these concerns. Present studies focused on the cytochrome P450 (CYP450) enzyme system responsible for xenobiotic detoxification in gophers. In vitro hepatic microsomal systems and HPLC analysis were used to elucidate general metabolic characteristics of major gopher xenobiotic metabolizing pathways. We found that the content and activity of individual components of the CYP450 system including CYP450, cytochrome b5, and NADPH-cytochrome P450 reductase in liver microsomal preparations were higher in gophers exposed to toxins used to control their population than in naïve (unexposed) gophers. When in vitro CYP450 mediated activities for five substrates [coumarin and aniline aromatic hydroxylation, 7-methoxycouamrin O-demethylation, and N-methylaniline, and N,N-dimethylaniline N-demethylation] were measured, naïve gophers were identified to have higher specific activity but similar whole body activity compared to the exposed gophers. Furthermore, there was a clearly identifiable sub-population of poor metabolizers showing considerably lower CYP450 activity within the gopher samples studied. Clotrimazole was found to be a potent inhibitor of several substrates of CYP450 enzyme-mediated reactions, which included aniline aromatic hydroxylation, N-methylaniline and N,N-dimethylaniline N-demethylation, and 7-methoxycoumarin O-demethylation. The cytotoxicity of above compounds was tested using freshly isolated gopher hepatocytes. The results showed that each compound caused considerable cytotoxicity to gopher hepatocytes. Addition of clotrimazole to the freshly isolated hepatocyte suspension increased the cytotoxicity of all tested compounds. <p>In conclusion, gophers may develop resistance to current chemical control methods through the enhancement of CYP450 system content, which can compensate the loss of enzyme activity. Furthermore, clotrimazole is a potent cytochrome P450 inhibitor, which increases the cytotoxicity caused by given compounds in gopher livers. The concept of using CYP450 enzyme inhibitor in combination with another chemical whose elimination depends on CYP450 metabolism to improve current gopher control method has practical importance.

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1952. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [180]-188).

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The reproductive condition of male and female red squirrels (Tarniasciurus hudsonicus) in southern British Columbia was studied in relation to age, season, relative population level, and foods utilized. The reproductive cycle of males and females is described on the basis of gross anatomy and histological characteristics. A low population on Vancouver Island was studied in 1966 and 1967 and a high population was studied near Princeton, B.C. in 1967. The habitats are similar in both regions. The low 1966 population had a late breeding season in which all females sampled produced two large litters. The ovulation rate for the two litter season averaged 5.12 per litter. The second ovulation occurred shortly after the birth of the first litter, before the uteri and vaginae came into full estrus condition. In 1967 both the low Vancouver Island population and the high Princeton population had early breeding seasons when nearly all adults bred yet only one third of the yearling females participated. Only single litters were produced in both areas. The ovulation rate was 4.11 per litter in the low Vancouver Island population and 3.58 per litter in the high Princeton population. Preimplantation losses of about 11% were fairly constant in both years. Postimplantation losses were not present in the low 1966 population, were about 19% in the high 1967 population, and were not determined in the low 1967 population. Similarities between the high and low 1967 populations and differences between the low 1966 and low 1967 populations on Vancouver Island suggest that density was not the primary force Influencing productivity. Another explanation is found in the evaluation of the primary food sources. Conifer cones are the main winter food of the red squirrel. Lodgepole pine cones were the main food source before the highly productive breeding season in I966 while Douglas fir cones made up the diet before the less successful breeding season in 1967. The fruiting habits of the conifers is discussed and It appears that it is advantageous for the squirrel to feed on lodgepole pine cones. A good winter food supply is particularly important to the red squirrel since it breeds during the late winter and it's already high metabolic rate increases still more during cold winter weather. It is inferred that the winter food supply may influence the relative capacity of the female to produce young. The timing of the breeding season is quite variable and seems to be affected by the severity of the winter weather. / Science, Faculty of / Zoology, Department of / Graduate

Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1934. / Reprinted from American journal of anatomy, vol. 54, no. 3 (15 May 1934). Title from title screen (viewed Mar. 22, 2007). Includes bibliographical references (p. 506). Online version of the print original.

No description available.