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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Nov 2019)
Spinal cord injury (SCI) interrupts communication between the brain and peripheral organs resulting in profound and long-lasting effects, including clinically important dysfunction of the pelvic viscera (PV). Sensory and autonomic peripheral neurons innervating the PV are contained in the dorsal root ganglia (DRG) and pelvic ganglia (PG), respectively. Previous studies have identified changes in these neurons after SCI, but questions remain about the relationship between injury level and changes in peripheral targets and ganglia. In this dissertation, I addressed these questions using male Wistar rats with a high thoracic transection (T3x), which eliminates the majority of supraspinal connections to sympathetic preganglionics (including those innervating the splanchnic bed and adrenal glands), or a high lumbar transection (L2x), which preserve these connections but directly damage neurons innervating the pelvic peripheral ganglia and PV. I examined gene expression changes in DRGs and PGs one month post-T3x using RNA sequencing and found indications for unexpected neuron-target interactions, including changes in growth factor signaling and cell communication. In the PG, decreased expression of tyrosine hydroxylase (TH) after T3x was supported by atrophy of sympathetic (TH-positive) neurons. SCI results in bladder hypertrophy, and though L2x resulted in increased bladder weights compared to both T3x and naïve animals, the expression of TH in the PG decreased and TH-positive neuron hypertrophy was only transient. These results indicate a more complex relationship between target size and neurotrophism than generally accepted. Examination of PV changes after high and low SCI revealed different patterns of bladder activity. Two days after injury, there was augmented bladder activity at low intravesical pressures in L2x compared to T3x and naïve animals. I found that disrupting signal transmission through the PG did not change the bladder activity patterns, however, bilateral adrenalectomy concurrent to L2x resulted in bladder activity patterns that more closely resembled the T3x injury. Further to this, circulating catecholamine levels were higher in animals with intact innervation to the adrenal gland, implicating adrenal function in bladder changes after SCI. The findings in this thesis highlight the importance of studying injury level both from the perspective of both local circuitry and systemic changes.
No abstract available.
No abstract available.
Master's Student Supervision (2010 - 2018)
Spinal cord injury (SCI) has the potential to disrupt autonomic pathways in the spinal cord leading to a range of autonomic dysfunctions. The cardiovascular (CV) and metabolic sequelae can restrict the lives of individuals with SCI and contribute to the deterioration of their cardiometabolic health. Here I investigated the whole-body CV and metabolic ramifications of experimental SCI in rats. Complete thoracic SCI was performed at two different levels in order to determine whether these outcomes demonstrated a level dependence. High-(T3) and low-(T10) thoracic SCI both result in flaccid hindlimb paralysis, but have different effects on the level of supraspinal autonomic control. CV and metabolic function were assessed at several times post-injury to investigate changes over time. Animals with acute high-thoracic SCI displayed resting hypotension that resolved with time post-injury. However, their capacity to control blood pressure (BP) in response to physiological stimuli remained deficient; animals with high-thoracic SCI displayed pronounced orthostatic hypotension (OH) and severe episodes of sensory stimulation-induced hypertension known as autonomic dysreflexia (AD). The resting BP and heart rate of animals with low-thoracic SCI, and their ability to respond to orthostatic stress, was indistinguishable from sham controls. Lipid metabolism was also disordered by SCI in a level-dependent pattern. Animals with high-thoracic SCI carried increased white adipose tissue and had higher circulating triacylglycerol levels compared to animals with low-thoracic SCI and sham controls. However, there was no difference in the distribution of cholesterol-carrying lipoproteins. Carbohydrate metabolism in animals with SCI did not support the diabetic profile suggested by the lipid results. Overall, animals with SCI were more sensitive to glucose and insulin than sham-injured animals. The pronounced ketone response to fasting in animals with high-thoracic SCI suggests that there are diverse effects on substrate metabolism.This work introduces simple tests that can be performed to investigate several important and understudied autonomic outcomes of SCI. The results reveal the importance of the intact autonomic nervous system in regulating CV and metabolic function. The disparity between motor and autonomic function encourages modifying our current conventions so that we stratify subjects by their autonomic injury level and their motor deficits.