During landing, the human body is required to absorb impact forces throughout its tissues. Muscle and connective tissue is able to dissipate much of this force, however, a portion of the impact is delivered to the bones. Forces acting on the human skeleton can cause microscopic fractures which may lead to stress fracture. The present study seeks to calculate changes in the magnitude of strain using noninvasive methods. A musculoskeletal model representing a healthy male subject (22 years, 78.6 kg, 1.85 m) was created. A flexible tibia, created from a computed tomography scan of the subject’s right tibia, was included in the model. Motion capture data were collected while the subject performed drop landings from three separate heights (26, 39, and 52 cm) and used to compute simulations in LifeMOD. Surface electromyography and joint angle data were compared to their simulated counterparts using a cross correlation. Maximum magnitudes of principal and maximum shear strain were computed. The model had reasonable agreement between joint angle curves. A large Cohen’s d effect size showed that our subject had increased tibial strain and strain rate as the drop height increased. This study demonstrates a valid method of simulating tibial strain during landing movements. Future studies should focus on recruiting a larger sample and applying this method. / School of Physical Education, Sport, and Exercise Science

No description available.

Effects of growth environment (E) on carbon isotope discrimination (Delta), water-use efficiency (WUE), leaf movement (LM) and nutrition of bush bean were examined. Environments in greenhouse (GR), open air (E0), perforated (E1) and non-perforated (E2) plastic covers in combination with well-watered (W0), moderately-watered (W 1), and water-stressed (W2) plants were used. Soil water content (WC), E, and E x WC interaction significantly affected Delta, WUE, dry matter (DM) and water use. WUE, photosynthetic rate, and leaf nitrogen increased; while Delta, DM, and transpiration decreased with water stress in GR, and E0. WUE in E2 either decreased or remained almost constant with decrease of WC. WUE of W0, and Delta in E2 were independent of growing environment, and WC, respectively. WUE and Delta correlations were significant in GR, E0, and E 1. LM was more paraheliotropic inside plastic coverings than those in E0. LM and pulvinus water content were affected by WC and temperature. High correlations were found between LM and the transmission of beta-rays from a beta-ray gauging system, WC, and leaf water potential. A high correlation was also found between leaf angle and 45Ca activity ratio between the extensor and flexor parts of the pulvinus. 32P uptake increased with increased root temperature, and decreased in presence of iron in the medium. Q10 values showed 32P uptake with and without the presence of iron to be mostly diffusion-controlled, but leaf movements were active processes requiring the expenditure of energy.

The genome of living organisms is constantly subjected to the environmental influences that result in different negative, negligible or positive impacts. The ability to maintain the genome integrity and simultaneously provide its flexibility is the main determinant for the evolutionary success of any species. One of the important aspects of genome maintenance is the precise regulation of the DNA repair machinery. Results reported here indicate the existence of a tight, age-dependent regulation of homologous recombination, one of the two main DNA double-strand break repair pathways. We show that recombination is influenced by conditions such as the change of temperature (cold or warm), day length, water availability (drought or overwatering stress) and salinity. These stresses not only influence the genome stability of stress-subjected generations but also change the recombination in subsequent generations. This indicates the possible involvement of homologous recombination in plant evolution and development of plant stress tolerance. / xiv, 121 leaves ; 29 cm.

This thesis examines the behavioral, structural, cellular, and epigenetic changes observed in offspring exposed to different prenatal stressors. A number of questions were answered in this thesis that contribute to a basic understanding of the mechanisms by which early experiences alter long-term outcomes. These include: 1) What epigenetic modifications are associated with prenatal stress? 2) What are the structural and cellular changes in the brains of offspring that correspond to prenatal stress exposure? 3) How do these epigenetic and structural changes manifest as behavioral changes? And 4) What are the consequences of varying the level of prenatal stress?The key findings were that not all prenatal stress is the same. Variations to the intensity and nature of the stress dramatically alter offspring outcomes. Second, prenatal stress produces changes at many levels and these changes can be functionally related. Expression changes were identified in genes involved in altering dendritic morphology, which in turn modifies behaviour. For the first time, a comprehensive examination of brain plasticity occurred following prenatal stress. Additionally, this thesis demonstrated that brain changes related to prenatal stress are age-dependent and sex-dependent. The effects of prenatal stress on the pre-weaning brain are dramatically different than those observed in adulthood. Also, the sex of the offspring significantly influences neuroanatomical and epigenetic modifications. This finding is of critical importance because a majority of prenatal stress research is conducted on male offspring only. Taken together these discoveries emphasize that perturbations to development during the prenatal period produce persistent changes in the structure and functioning of the brain that will influence all subsequent experiences / xx, 201 leaves ; 29 cm

Stress is thought to be antithetical to play. However, this thesis shows that mild stress (e.g., social deprivation) enhances rough-and-tumble play, as opposed to other social behaviors, in adolescent rats. Social deprivation results in both higher levels of corticosterone (a stress hormone) and higher levels of play. When non-socially deprived rats were injected with ACTH (a precursor to corticosterone), the frequency of play was elevated to levels comparable to that seen when juveniles were socially deprived. Moreover, corticosterone was reduced by the opportunity to play, but not when given social contact (but no play) or solitary exercise (i.e. a running wheel). Therefore, this thesis provides evidence that play is not only enhanced by mild stress, but that it is used by animals to reduce stress. / vi, 70 leaves ; 29 cm.

Selenium (Se), an essential element, can bioaccumulate and become toxic. The main toxicity symptom in fish, teratogenicity, is mediated by oxidative stress; however, little is known about the effect of Se on the physiological stress response (PSR). The effects of Se on the PSR and oxidative stress parameters were investigated in rainbow trout, brook trout, and white suckers. The PSR was activated by acute and sub-chronic laboratory exposures to NaSeO3, but not exposure to environmental levels of Se. Species-specific sensitivity to Se may be explained by biochemical differences. Rainbow trout (exhibit oxidative damage with Se exposure) have greater GSH reserves (cycles with Se causing oxidative stress) than brook trout. Selenium in agricultural drain water did not accumulate to dangerous levels in white suckers, but additional stressors (e.g. pesticides) were present. Differences in sensitivity to Se may alter competitive interactions between species, changing community compositions and putting additional pressure on threatened species. / xiii, 150 leaves ; 29 cm.

Stress is one of the most critical influences on behavior, performance and disease. Recent findings from our laboratory have shown that stress represents a major modulator of motor function in the intact and damaged brain. The mechanisms by which stress and stress hormones affect motor system function, however, have not yet been determined. The objective of this thesis was to determine the route of action of stress and stress hormones on the motor system in a rat model. The first experiment investigates whether corticosterone is involved in mediating stress-induced motor impairments. The second experiment compares the role of glucocorticoid and mineralocorticoid receptors in regard to modulating the motor response to stress. The third experiment determines the differential effects of stress on motor function in males and females. The final experiment systematically describes changes in neuronal cell signaling that affect normal function of motor areas. The results indicate that disturbance of fine motor control by stress is not associated with stress hormone increases. Furthermore, it is modulated through the glucocorticoid and mineralocorticoid receptors. Stress differentially impairs motor function in males and females. These changes in motor behaviour could possibly be the result of changes in neuronal cell signaling within the motor system. This research provides new insights into physiological influences in motor system function and disorders of the motor system. / ix, 128 leaves : ill. (some col.) ; 29 cm.

Fish are exposed to multiple stressors in their environment. The interactive effects of pesticide exposure and increased temperature on the physiological stress response were investigated in a comparative field study with cold-water (whitefish, Prosopium williamsoni) and cool-water (sucker, Catostomus) fish from the Oldman River, Alberta, Canada, and in a laboratory study with rainbow trout, Oncorhynchus mykiss. Physiogical stress indicators were measured, and exposure to pesticides was estimated using acetylcholinesterase (AChE) inhibition. Species-specific differences in AChE activities and responses of the physiological stress axis were detected in whitefish and suckers, suggesting that whitefish are a more sensitive species to temperature and pesticide stress. In vivo Dimethoate exposure inhibited AChE activity in various tissues and disrupted the physiogical stress response. Commercial Dimethoate, in vitro, caused a decrease in viability and cortisol secretion while pure grade Dimethoate did not. The results from this study can be used in predictions of fish vulnerability to stress. / ix, 137 leaves : ill. ; 29 cm.

Manganese-Enhanced Magnetic Resonance Imaging (MEMRI) has proven itself to be a beneficial technique in the field of Neuroscience. This thesis applies MEMRI to studies in neuroscience by first establishing the limitations concerning the use of MEMRI in live rats. Experiment 1 used an osmotic pump for manganese (Mn) delivery to the lateral ventricles for acquisition of anatomical images using MEMRI. From my knowledge, this was the first method demonstrating slow infusion of Mn to the lateral ventricles. In Experiment 2, MEMRI was used for volumetric analysis the whole brain and hippocampus of prenatally stressed rats. To my knowledge, this study was the first to investigate the effect of generational prenatal stress on the structure of a rat’s brain using MEMRI and histology. Additionally, Experiment 2 investigated the use of a subcutaneous osmotic pump to deliver Mn for MEMRI. A summary on the use of MEMRI in Neuroscience concludes this thesis, with a discussion on the methods used and related technical considerations. / xi, 84 leaves ; 29 cm