No description available.

No description available.

No description available.

No description available.

No description available.

Functional magnetic resonance imaging (fMRI) is a non-invasive technique that allows for visualization of active brain regions. Although white matter (WM) constitutes approximately 50% of brain tissue, fMRI activation in WM has conventionally been dismissed. There are two main reasons WM fMRI remains controversial: 1) the blood oxygen level dependent (BOLD) fMRI signal depends on cerebral blood flow and volume, which are lower in WM than gray matter and 2) fMRI signal has been associated with post-synaptic potentials as opposed to action potentials. Despite these observations, there is no direct evidence against measuring fMRI activation in WM. This thesis is comprised of four manuscripts that investigate fMRI activation in WM at 4T. The first study evaluated whether it was possible to detect WM activation using an interhemispheric transfer task and examined whether certain MRI contrast mechanisms were more sensitive to activation in WM. Activation was detected in the anterior corpus callosum at the individual and group level and we discovered that T2 weighted imaging may provide increased sensitivity to activation in WM. The second study used two established interhemispheric transfer tasks to examine whether callosal activation could be experimentally manipulated using a within subjects design. The results replicated previous findings and demonstrated an ability to map functional activation in the corpus callosum that was task dependent. The third study examined WM fMRI activation in a different structure and focused on the posterior limb of the internal capsule using a motor task; activation was elicited at both individual and group levels. The fourth study linked advances in the ability to detect WM fMRI activation to current clinical approaches to the assessment of WM dysfunction. An adapted Symbol Digit Modalities Test was used to evaluate WM activation in healthy controls. The results revealed individual level activation in both the corpus callosum and internal capsule. Taken together this stream of research represents a major advance in the methods used to non-invasively study brain function. Future applications may include improved assessment methods for patients with WM dysfunction.

The vital rates of beluga, Delphinapterus leucas, harvested in northern Quebec are within the range reported by previous studies in Alaska and the Canadian and Soviet Arctic. Small sample size and inadequate estimates of survivorship rates prevent meaningful calculation of population growth rate. The pattern of changes in vital rates over the life cycle of beluga and analysis of errors associated with stage classification indicate that the demographic information in a 6 x 6 age-grouped Lefkovitch matrix is similar to that in a 38 x 38 age class Leslie matrix. A 3 stage, length-based model composed of newborns, juveniles and adults contains less demographic information than the larger matrices, but is superior to a juvenile/adult classification scheme. The 3 stage model applied to length frequency data from aerial photographic censuses should provide an alternate method of demographic analysis when harvests are small or absent. Colour is a poor criterion for stage classification. / Sensitivity analysis of fecundity and survivorship indicates that survival of gray animals (older juveniles and early breeders) has the most influence on population growth rate. Changes in fecundity have little effect on growth rate. The high sensitivity of population growth rate to juvenile and early adult survival demonstrates that these estimates should be improved if more precise knowledge of beluga demography is required for management purposes. / The age-length data used to evaluate errors associated with stage classification indicate that belugas in Hudson Bay are smaller than those elsewhere, but not to the large degree previously reported. Beluga in estuaries are represented by all size classes. Examination of the integumentary heat loss show beluga and narwhal, Monodon monoceros, to be equally insulated, but only belugas frequent warmer estuarine waters.

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No description available.

White adipose tissue (WAT) is now recognised as an endocrine organ through its secretion of hormones and protein factors - ‘adipokines’.  This thesis examined the regulation of two adipose expressed genes, retinol binding agent (RBP) involved in retinol transport, and tissue factor (TF) which initiates the extrinsic coagulation cascade.  RNA was isolated and RBP and mRNA levels determined by chemiluminescence-based Northern blotting.  TF and mRNA levels were determined by real-time PCR.  WAT RBP mRNA levels were second only to liver, and TF mRNA levels were highest in WAT depots.  RBP and TF mRNA were detected predominantly from mature adipocytes.  Obesity was not associated with altered RBP and TF gene expression except of for a significant (<i>p</i><0.05) decrease in RBP mRNA from subcutaneous WAT of obese rodent models.  Primary adipocytes were treated with <span lang=EN-GB style='font-family:Symbol'>b-agonists, dexamethasone or leptin.  Only dexamethasone significantly (<i>p</i><0.05) reduced RBP mRNA levels.  TF mRNA levels were unaltered following <span lang=EN-GB style='font-family:Symbol'>b-agonists, forskolin, or dexamethasone treatment except for a significant (<i>p</i><0.05) increase with a high dose of BRL 37344 (a <span lang=EN-GB style='font-family:Symbol'>b₃ agonist).  Administration of two isoforms of retinoic acid significantly decreased RBP gene expression, with 9-<i>cis</i> showing more potency (<i>p</i><span lang=EN-GB style='font-family:Symbol'>£ 0.001) that all-<i>trans</i> (<i>p</i><0.05.  The thiazolidinediones ciglitazone and rosiglitazone were administered, high doses significantly reducing RBP gene expression (<i>p</i> <span lang=EN-GB style='font-family:Symbol'>£ 0.001 and <i>p </i><span lang=EN-GB style='font-family:Symbol'>£ 0.05 respectively).  Fasting and cold exposure are two physiological stimuli which stimulate substrate flux and the release of fatty acids from WAT.  RBP gene expression in WAT was unaltered with fasting, cold exposure and <span lang=EN-GB style='font-family:Symbol'>b-agonist injection.  These studies suggest WAT may be an important source of RBP and TF.  In contrast to lipolysis and leptin production, the SNS does not significantly regulate RBP and TF gene expression.  The high TF gene expression in rodent WAT suggests an association between TF and the cardiovascular disease seen with obesity.