Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaf 147-169) Also available in print.

Thesis (Ph.D.) in Zoology--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 102-111).

No description available.

No description available.

There is considerable recent experimental evidence that suggests that stress plays a major role in the development of dependence on drugs of abuse, but the potential mechanisms involved are not yet fully understood. The aims of this thesis were (I) to examine the effect of stress, and of drugs that act on the hypothalamic-pituitary-adrenal axis, on alcohol consumption in the C57 strain of mice. (II) to investigate whether corticosterone levels or spontaneous locomotor activity could be used to predict subsequent alcohol consumption in mice. (Ill) to investigate long-term neurochemical changes during abstinence following chronic alcohol administration. (IV) to develop a method for measuring brain corticosterone levels. Neither total corticosterone levels nor spontaneous locomotor activity could predict alcohol preference. Saline vehicle injections increased alcohol preference in low alcohol preferring, and raised both circulating corticosterone levels and brain corticosterone. The brain concentrations of corticosterone were measured by a novel procedure developed during the thesis. A CRF antagonist (a-helical CRF) increased alcohol preference in low preferring mice, as did the ACTH fragment 4-10. In high preferring mice, ACTH 4-10 reduced alcohol preference, whereas a-helical CRF did not alter preference in these mice. Inhibition of corticosterone synthesis reduced alcohol preference in high alcohol preferring mice but, blockade of corticosterone receptors with specific antagonists did not alter alcohol preference. Chronic alcohol treatment followed by six days abstinence increased free circulating corticosterone levels and this treatment also increased hippocampal corticosterone levels. Dopamine Dl-like receptor affinity was increased following the same chronic treatment schedule. These results demonstrate an important link between the activation of the hypothalamic-pituitary-adrenal axis and alcohol consumption. The results of the chronic treatment experiments provide useful information that may aid the understanding of the phenomenon of relapse to drinking common in abstaining alcoholics.

In the mid-1980's until the late 1990's, Lesser Scaup (<i>Aythya affinis</i>)populations in the boreal forest declined and have remained at historical low levels since that time. This has resulted in a population well below conservation goals. Potential causes for this population decline include a reduction in productivity, which could be related to changes in boreal forest habitat, nutritional condition during reproduction, or due to contaminants acquired during migration or wintering. Though several studies have assessed contaminant levels in Lesser Scaup on wintering, staging and migration routes, relatively little data exist from northern boreal forest areas, one of the core breeding habitats of the Lesser Scaup population and where population declines appear to be most severe. To this end,male Lesser Scaup were trapped from sites in the northern boreal forest in 2004 and 2005 to assess trace element contaminant levels. Previous research has shown that trace elements including cadmium and selenium can influence hormonal status in waterfowl. Specifically, a positive relationship between cadmium and corticosterone and a negative correlation between liver selenium and corticosterone have been observed. The purpose of this study was to test the hypothesis that trace element contaminants can influence hormonal status and related physiological functions in male Lesser Scaup, and that interactions between contaminants, physiological variables such as body condition and social status can modify expression of toxic effects. Blood samples were collected from trapped males to assess stress related changes in blood chemistry (corticosterone, testosterone, glucose and thyroxine) and males were then collected for contaminant analysis and assessment of reproductive physiology. The geometric mean levels of kidney cadmium, liver selenium and liver mercury were 9ppm, 4.33 ppm, 1.31 ppm dry weight respectively. Several variables and interactions including pair status, cadmium, selenium, mercury, body condition and body size influenced corticosterone levels. In male Scaup with high cadmium levels, corticosterone was negatively related to liver selenium in birds with good body condition (R2=0.701,n=9, P=0.005) but not in birds with poor body condition (R2=0.033, n=10,P=0.61). Likewise, in birds with high cadmium, a negative association was found between liver mercury and corticosterone in structurally smaller males (R2=0.491,n=10, P=0.024), whereas no such relationship was found in larger males(R2=0.307, n=9, P=0.12). In birds with low cadmium and low mercury, selenium and corticosterone were negatively correlated (R2=0.568, n=10, P=0.012) while no association was found in males with high mercury (R2=0.325, n=10, P=0.085). Unpaired birds had higher corticosterone than in ducks with low cadmium(F1,17=6.70, P=0.023), while there was no difference between groups in ducks with high cadmium. Glucose levels were not influenced by contaminants or other variables in this study (R2=0.551, F21,17=0.99, P=0.51). Thyroxine levels were positively correlated to mercury levels in paired birds (R2=0.485, n=19, P<0.001)but were not related in unpaired birds (R2=0.063, n=20, P=0.28). Thyroxine levels also showed a relationship with date of capture (F1,37=6.77, n=39, P=0.014). Pair status was influenced by body condition and body size (P2 =9.997, df=2, P=0.007)with larger birds being in better condition and larger, while hormone levels and testicular morphology did not appear to influence pair status. Mass of testes (F9,27=0.45, P=0.90) and testosterone concentrations (F10,28=0.31, P=0.10) were not influenced by contaminant levels, body condition or body size. Seminiferous tubule diameter was positively related to testes mass (R2=0.397, n=39, P<0.0001) and negatively related to liver selenium levels (R2=0.123, n=39, P=0.009). To clarify the influence of selenium on corticosterone, captive male Lesser Scaup were fed diets dosed with selenomethionine. Dose groups accumulated different levels of selenium (control group=0.19 ng/ml, 7.5 ppm group=0.74 ng/ml and 15 ppm=1.01 ng/ml) (F2,12=155.12; P<0.001) but this appeared to have no effect on corticosterone levels (Wilks Lambda=0.659, F4,10=1.29, P=0.34) or behavioral patterns (Wilks Lambda=0.659, F4,10=1.294, P=0.34) in captive birds. Results from the field portion of this study support the hypothesis that trace element levels can influence hormonal status in wild Lesser Scaup and that interactions of contaminants and physiological variables can modify expression of toxic effects. Studies such as this one display the complex nature of biological systems and emphasize the importance of considering interactions between different contaminants and other variables to clearly assess their influences on physiology.

In the mid-1980's until the late 1990's, Lesser Scaup (<i>Aythya affinis</i>)populations in the boreal forest declined and have remained at historical low levels since that time. This has resulted in a population well below conservation goals. Potential causes for this population decline include a reduction in productivity, which could be related to changes in boreal forest habitat, nutritional condition during reproduction, or due to contaminants acquired during migration or wintering. Though several studies have assessed contaminant levels in Lesser Scaup on wintering, staging and migration routes, relatively little data exist from northern boreal forest areas, one of the core breeding habitats of the Lesser Scaup population and where population declines appear to be most severe. To this end,male Lesser Scaup were trapped from sites in the northern boreal forest in 2004 and 2005 to assess trace element contaminant levels. Previous research has shown that trace elements including cadmium and selenium can influence hormonal status in waterfowl. Specifically, a positive relationship between cadmium and corticosterone and a negative correlation between liver selenium and corticosterone have been observed. The purpose of this study was to test the hypothesis that trace element contaminants can influence hormonal status and related physiological functions in male Lesser Scaup, and that interactions between contaminants, physiological variables such as body condition and social status can modify expression of toxic effects. Blood samples were collected from trapped males to assess stress related changes in blood chemistry (corticosterone, testosterone, glucose and thyroxine) and males were then collected for contaminant analysis and assessment of reproductive physiology. The geometric mean levels of kidney cadmium, liver selenium and liver mercury were 9ppm, 4.33 ppm, 1.31 ppm dry weight respectively. Several variables and interactions including pair status, cadmium, selenium, mercury, body condition and body size influenced corticosterone levels. In male Scaup with high cadmium levels, corticosterone was negatively related to liver selenium in birds with good body condition (R2=0.701,n=9, P=0.005) but not in birds with poor body condition (R2=0.033, n=10,P=0.61). Likewise, in birds with high cadmium, a negative association was found between liver mercury and corticosterone in structurally smaller males (R2=0.491,n=10, P=0.024), whereas no such relationship was found in larger males(R2=0.307, n=9, P=0.12). In birds with low cadmium and low mercury, selenium and corticosterone were negatively correlated (R2=0.568, n=10, P=0.012) while no association was found in males with high mercury (R2=0.325, n=10, P=0.085). Unpaired birds had higher corticosterone than in ducks with low cadmium(F1,17=6.70, P=0.023), while there was no difference between groups in ducks with high cadmium. Glucose levels were not influenced by contaminants or other variables in this study (R2=0.551, F21,17=0.99, P=0.51). Thyroxine levels were positively correlated to mercury levels in paired birds (R2=0.485, n=19, P<0.001)but were not related in unpaired birds (R2=0.063, n=20, P=0.28). Thyroxine levels also showed a relationship with date of capture (F1,37=6.77, n=39, P=0.014). Pair status was influenced by body condition and body size (P2 =9.997, df=2, P=0.007)with larger birds being in better condition and larger, while hormone levels and testicular morphology did not appear to influence pair status. Mass of testes (F9,27=0.45, P=0.90) and testosterone concentrations (F10,28=0.31, P=0.10) were not influenced by contaminant levels, body condition or body size. Seminiferous tubule diameter was positively related to testes mass (R2=0.397, n=39, P<0.0001) and negatively related to liver selenium levels (R2=0.123, n=39, P=0.009). To clarify the influence of selenium on corticosterone, captive male Lesser Scaup were fed diets dosed with selenomethionine. Dose groups accumulated different levels of selenium (control group=0.19 ng/ml, 7.5 ppm group=0.74 ng/ml and 15 ppm=1.01 ng/ml) (F2,12=155.12; P<0.001) but this appeared to have no effect on corticosterone levels (Wilks Lambda=0.659, F4,10=1.29, P=0.34) or behavioral patterns (Wilks Lambda=0.659, F4,10=1.294, P=0.34) in captive birds. Results from the field portion of this study support the hypothesis that trace element levels can influence hormonal status in wild Lesser Scaup and that interactions of contaminants and physiological variables can modify expression of toxic effects. Studies such as this one display the complex nature of biological systems and emphasize the importance of considering interactions between different contaminants and other variables to clearly assess their influences on physiology.

The Effects of a glucocorticoid-antagonist on IGF1-stimulated glucose uptake in skeletal muscle of hindlimb suspended rats. Barnes B.R., T.C. Selix, D.C. Wright, and B.W. Craig. Ball State University, Muncie, IN.The purpose of this investigation was to determine the effects of a glucocorticoid-antagonist (RU486) on insulin-like-growth-factor-1 (IGF1)stimulated glucose transport following two weeks of hindlimb suspension (HS) on 100 gm male rats. After two weeks of HS and/or oral RU486 administration the animals were anesthetized, and the soleus (SOL) and extensor digitorum longus (EDL) muscles isolated and clamped at their resting length. Following an incubation series to prepare the muscle, the muscle was incubated in radioactive 3-O-methylglucose for 10 min. in the presence/absence of 75 ng/ml of IGF1, digested with 0.5 NaOH, and the amount of glucose transported measured. Two weeks of RU486 treatment significantly (P:5 0.05) elevated IGF1-stimulated glucose transport of SOL (0.576 ± 0.071 vs 1.405 ± 0.172), whereas the EDL was unaffected (2.728 0.258 vs 2.613 ± 0.182). The removal of glucocorticoids via RU486 administration significantly increased glucose uptake in HS exposed soleus muscles. The EDL was not affected by RU486 treatment. / School of Physical Education

Thesis (M.S.) in Zoology--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 88-95).

No description available.