Background: Spinal cord injury (SCI) is heterogeneous in nature and can be complicated by inflammation and scarring in the subarachnoid space (arachnoiditis). The constellation of traumatic injury and arachnoiditis can lead to extensive intraparenchymal cysts or post-traumatic syringomyelia (PTS), due to alterations in fluid flow and pressure dynamics in the subarachnoid space. Hypothesis: Intrathecal injection of a bioengineered hydrogel containing hyaluronan (HA) will improve functional recovery following severe spinal cord injury associated with arachnoiditis. Methods: Acute to subacute pathophysiological events were characterized in non-injured sham rats, rats receiving a clip compression/contusion injury (SCI), rats receiving an intrathecal kaolin injection (Arachnoiditis) and in rats receiving SCI plus kaolin injection (PTS). Next, a HA containing hydrogel (HAMC) or artificial cerbralspinal fluid (aCSF) control was injected into the subarachnoid space 24 hours following PTS injury. To assess treatment efficacy, subacute pathophysiology was assessed as was long-term neurobehavioural and neuroanatomical recovery. Finally, in vitro studies examined the effect of HA on TLR4 activation using lipopolysaccharide in primary rat microglial cultures. Results: PTS animals exhibited a greater parenchymal injury response as compared to the sum of SCI alone or arachnoiditis alone. Injection of HAMC reduced the extent of scarring and inflammation in the subarachnoid space and improved neurobehavioural and neuroanatomical recovery relative to aCSF controls. These improvements were associated with reduced chondroitin sulfate proteoglycan and IL-1α expression and a trend towards and axonal preservation. In vitro studies demonstrated that HA is capable of reducing TLR4 mediated inflammation in microglia. Conclusions: Acute arachnoiditis potentiates the intensity of intraparenchymal inflammatory and scarring events following SCI. When HAMC was injected intrathecally following PTS injury, it mitigated some of the pernicious effects of arachnoiditis. Part of the therapeutic action of HAMC can be attributed to the ability of HA to reduce TLR4 mediated inflammation in microglia, possibly through an extracellular mechanism.

The role of gap junctions in modulating the dynamics of axonal dysfunction in spinal cord white matter injury remains uncertain; hence, I examined the functional role and changes in expression of gap junctions following CNS injury. I hypothesized that inhibition of gap junctions improves axonal conduction during oxygen and glucose deprivation (OGD) in vitro. Carbenoxolone and octanol, gap junction blockers, did not change CAP amplitude in non-injured tissue, yet they significantly reduced the extent of its decline during OGD. No difference in mRNA expression of connexins 32, 36 was found. However, during OGD in the presence of gap junction blockers, expression of connexins 30, 43 was downregulated. Immunohistochemistry confirmed the presence of connexins in spinal cord slices: connexins 30, 43 overlapping with GFAP, connexin 32 with MBP and connexin 36 with CC1. Thus, blocking gap junctions enhances axonal conduction during OGD and promotes dynamic changes in connexin mRNA expression.

Individuals who sustain a spinal cord injury (SCI) experience sublesional osteoporosis (SLOP) which affects the bones of the lower extremities. As a result, these bones become fragile and susceptible to fractures. To tackle SLOP pharmacological and rehabilitation interventions have been proposed; however few have produced a significant and sustainable increase in bone mineral density (BMD). This study investigated whole-body vibration (WBV) as an alternative to tackling SLOP in SCI. Two commercially available vibration platforms, WAVE® and Juvent™, were tested for feasibility and efficacy in the SCI population. The effects of knee angle, frequency and amplitude of vibration in propagation characteristics were also assessed. The results demonstrated that variations in frequency generate the most noticeable changes in propagation characteristics, followed by variations in knee angle and amplitude. The recommended vibration parameters which could potentially have the greatest osteogenic effect on the bones of the lower extremity are 160o, 45 Hz, and 0.6 mm on the WAVE® platform.

In this thesis sensorimotor integration in the human spinal cord was investigated in the intact (Chapters 2 and 3) and injured nervous systems (Chapter 4-stroke; Chapter 5-spinal cord injury (SCI)). In Chapter 2, I characterized a short-latency reflex pathway between sensory receptors of the lower leg and the erector spinae (ES) muscles of the lower back that may play a role in the maintenance of posture and balance. The ES reflexes were evoked bilaterally by taps applied to the Achilles tendon and were modulated by task. Furthermore, these reflexes involved a larger contribution from cutaneous receptors in the lower limb, rather than muscle spindles. In Chapter 3, I investigated changes in reflex transmission along the H-reflex pathway throughout 10 s trains of neuromuscular electrical stimulation (NMES) using physiologically relevant frequencies (5-20 Hz) and during functionally relevant tasks (sitting and standing) and background contraction amplitudes (up to 20% MVC). The results of this study revealed strong post-activation depression of reflex amplitudes, followed by significant recovery during the stimulation, both of which were influenced by stimulation frequency and background contraction amplitude, but not task. During 10 Hz stimulation, reflex amplitudes showed complete recovery (i.e. back to their initial values), and at times, complete recovery occurred by the third reflex in the train. These results demonstrate that transmission along the H-reflex pathway is modulated continuously during periods of repetitive input. In Chapters 4 and 5, I studied the extent to which a novel stimulation protocol that incorporated wide pulse widths (1 ms) and high frequencies (up to 100 Hz) (wide-pulse NMES; WP-NMES), could enhance electrically-evoked contractions through a central contribution in individuals with stroke or SCI. This central effect arises from the electrical activation of sensory axons, which in turn, reflexively recruit motoneurons in the spinal cord. After stroke, contractions evoked by WP-NMES were larger in the paretic arm than the non-paretic arm. After SCI, transmission along the H-reflex pathway was observed throughout trains of WP-NMES; direct evidence of a central contribution. These results suggest that maximizing the central contribution during WP-NMES may be useful for maintaining muscle quality after neurological injury.

Functional electrical stimulation (FES) is a rehabilitative technology that can be used to improve walking in individuals with mobility impairments due to neurologic injury or disease. Feedback is essential for efficient FES-assisted walking. The overall goal of my project was to investigate external sensors to provide feedback for FES-assisted walking. The current study evaluated accelerometers, force sensitive resistors, segment orientation angles, and segment angular velocities to determine which were appropriate for determining the activation and deactivation of six major muscles used for walking. The results demonstrated that the segment orientation angles were the most appropriate sensors. Using the segment angle of the thigh, shank, and foot, the activation and deactivation times of the six muscles investigated could be determined within 6% of the step cycle. The shank segment angle performed the best for determining the activation and deactivation times when only one sensor was desired.

Brainstem derived noradrenaline (NA) in the spinal cord functions both to increase motoneuron excitability, by facilitating calcium-mediated persistent inward currents (Ca PICs), and to inhibit sensory afferent transmission to motoneurons (excitatory postsynaptic potentials; EPSPs). Spinal cord injury (SCI) results in a reduction of NA, causing a loss of Ca PICs in motoneurons below the lesion and exaggerated EPSPs to emerge. With time motoneuron Ca PICs gradually recover and are readily triggered by the exaggerated EPSPs, resulting in the development of muscle spasms. The role of the NA in the recovery of Ca PICs and muscle spasms after chronic SCI is examined in this thesis using a rat model of spasticity incorporating both the awake rat (in vivo) and the isolated rat spinal cord (in vitro). Specific activation of the adrenergic 1 receptor with agonists facilitated Ca PIC and spasms, whereas activation of the adrenergic 2 receptor with agonists decreased the EPSPs that trigger spasms. Both receptors were endogenously activated by a ligand in vivo, though the 1 receptor additionally exhibits constitutive activity (activity in the absence of NA), predominantly in vitro. The adrenergic 2 receptor was not found to be endogenously active in vitro. Use of amphetamine in rats, which causes a forced efflux of endogenous NA, confirmed the identity of the endogenous ligand as NA and demonstrated that a residual source of NA capable of facilitating the Ca PIC and spasms persists below a chronic transection. Immunohistochemical labelling for an enzyme involved in the synthesis of NA (dopamine--hydroxylase) revealed that NA is not synthesized in the spinal cord below a chronic transection, indicating that the endogenous NA is not intrinsic to the spinal cord. Peripheral injections of NA were used to demonstrate that the residual NA instead originates in the periphery (blood) and is both passively and actively transported across a compromised blood-brain barrier (BBB) after chronic injury. The peripherally derived NA activates central adrenergic receptors to modulate motoneuron excitability, sensory synaptic transmission and muscle spasms after chronic SCI. This novel finding highlights the importance of understanding the adaptations of neurotransmitter systems after injury when developing effective treatment strategies for spasticity.

This study aimed to model the trajectories of life satisfaction as influenced by functional impairment and family satisfaction over a five-year period following spinal cord injury, severe burns, and lower-extremity fractures. Marital status and injury type were included to estimate predicted life satisfaction over the five-year period post-injury. Measures: Six-hundred sixty-two participants completed the Functional Independence Measure, Family Satisfaction Scale, and Life Satisfaction Inventory at 12, 24, 48, and 60 months post-injury. Results: Family satisfaction was a consistent predictor of life satisfaction across models. Consistent with past research (Resch et al., 2009), functional impairment was significantly predictive of life satisfaction. Conclusions: Individuals predicted to be most at risk were those individuals with severe burns, who were divorced or separated, with low family satisfaction, and/or high functional impairment.

Bone marrow-derived mesenchymal stem cells (MSC) have been shown to provide neuroprotection after transplantation into the injured nervous system. The present thesis investigates whether adult human and rat MSC differentiated along a Schwann cell lineage could increase their expression of neurotrophic factors and promote regeneration after transplantation into the injured peripheral nerve and spinal cord. Human and rat mesenchymal stem cells (hMSC and rMSC) expressed characteristic stem cell surface markers, mRNA transcripts for different neurotrophic factors and demonstrated multi-lineage differentiation potential. Following treatment with a cocktail of growth factors, the hMSC and rMSC expressed typical Schwann cells markers at both the transcriptional and translational level and significantly increased production of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF). Age and time in culture are of relevance for clinical settings and growth-promoting effects of hMSC from young donors (16-18 years) and old donors (67-75 years) were compared. Undifferentiated hMSC from both young and old donors increased total neurite length of cultured dorsal root ganglion (DRG) neurons. Differentiation of hMSC from the young donors, but not the eldery donors, further enhanced the neurite outgrowth. Undifferentiated hMSC were cultured for eleven weeks in order to examine the effect of in vitro expansion time on neurite outgrowth. hMSC from the young donors maintained their proliferation rate and their ability to enhance neurite outgrowth from DRG neurons. Using a sciatic nerve injury model, a 10mm gap was bridged with either an empty tubular fibrin glue conduit, or conduits containing hMSC, with and without cyclosporine treatment. Cells were labeled with PKH26 prior to transplantation. At 3 weeks after injury the conduits with cells and immunosuppression increased regeneration compared with an empty conduit. PKH26 labeled human cells survived in the rat model and the inflammatory reaction could be suppressed by cyclosporine. After cervical C4 hemisection, BrdU/GFP-labeled rMSC were injected into the lateral funiculus rostral and caudal to the spinal cord lesion site. Spinal cords were analyzed 2-8 weeks after transplantation. Transplanted MSC remained at the injection sites and in the trauma zone for several weeks and were often associated with numerous neurofilament-positive axons. Transplanted rMSC induced up-regulation of vascular endothelial growth factor in spinal cord tissue rostral to the injury site, but did not affect expression of brain-derived neurotrophic factor. Although rMSC provided neuroprotection for rubrospinal neurons and significantly attenuated astroglial and microglial reaction, cell transplantation caused aberrant sprouting of calcitonin gene-related peptide immunostained sensory axons in the dorsal horn. In summary these results demonstrate that both rat and human MSC can be differentiated towards the glial cell lineage, and show functional characteristics similar to Schwann cells. hMSC from the young donors represent a more favorable source for neurotransplantation since they maintain proliferation rate and preserve their growth-promoting effects in long-term cultures. The data also suggest that differentiated MSC increase expression of neurotrophic factors and support regeneration after peripheral nerve and spinal cord injury.

Relatively few studies have examined the effects of nociception pe se on sympathetic nerve activity in awake healthy human subjects. Painful stimuli can produce differential responses from cutaneous and muscle postganglionic sympathetic neurones in the anaesthetised cat, and some animal and human studies suggest that nociceptive stimuli originating in different tissues may produce differential sympathetic effects- deep nociception causing vasodepressive and superficial nociception triggering an excitatory effect on cardiovascular state. It is important to understand how the sympathetic nervous system responds to nociception in healthy subjects in order to make more meaningful comparisons with the behaviour which occurs following damage to sympathetic pathways, e.g. nerve lesions (chronic regional pain syndromes) and spinal cord injury (autonomic dysreflexia (AD)). Additionally, it has been suggested that muscle spindles afferents may play a role in chronic pain, most notably the 'vicious cycle' of pain. While this has been investigated in animal studies, it has not been thoroughly investigated in healthy human subjects. Muscle spindle and sympathetic nerve activity from muscle and skin postganglionic neurones were directly recorded in healthy awake human subjects using microneurography; effector organ responses (blood pressure, heartrate, skin blood flow and sweat release) were recorded in both healthy and spinal cord injured subjects. Deep and superficial nociception was induced by intramuscular and subdermal injections of hypertonic saline given at unexpected times and in quasi-random order. Regardless of the origin of nociception (deep or superficial), general responses tended to be excitatory with increases seen in muscle and skin sympathetic nerve activity, heartrate, blood pressure and sweat release. A gender effect was noted regarding skin blood flow, with males largely showing decreases and females increases. No changes were noted in spindle firing rates and painful stimuli did not significantly increase effector organ responses in spinal cord injured subjects. Contrasting with previous studies, we did not see a differential sympathetic response or change in spindle firing rate to painful stimuli originating in different tissues. While it is believed that noxious stimuli trigger AD, we did not see exaggerated sympathetic responses in spinal cord injured subjects. More investigation is required regarding innocuous triggers of AD.

Relatively few studies have examined the effects of nociception pe se on sympathetic nerve activity in awake healthy human subjects. Painful stimuli can produce differential responses from cutaneous and muscle postganglionic sympathetic neurones in the anaesthetised cat, and some animal and human studies suggest that nociceptive stimuli originating in different tissues may produce differential sympathetic effects- deep nociception causing vasodepressive and superficial nociception triggering an excitatory effect on cardiovascular state. It is important to understand how the sympathetic nervous system responds to nociception in healthy subjects in order to make more meaningful comparisons with the behaviour which occurs following damage to sympathetic pathways, e.g. nerve lesions (chronic regional pain syndromes) and spinal cord injury (autonomic dysreflexia (AD)). Additionally, it has been suggested that muscle spindles afferents may play a role in chronic pain, most notably the 'vicious cycle' of pain. While this has been investigated in animal studies, it has not been thoroughly investigated in healthy human subjects. Muscle spindle and sympathetic nerve activity from muscle and skin postganglionic neurones were directly recorded in healthy awake human subjects using microneurography; effector organ responses (blood pressure, heartrate, skin blood flow and sweat release) were recorded in both healthy and spinal cord injured subjects. Deep and superficial nociception was induced by intramuscular and subdermal injections of hypertonic saline given at unexpected times and in quasi-random order. Regardless of the origin of nociception (deep or superficial), general responses tended to be excitatory with increases seen in muscle and skin sympathetic nerve activity, heartrate, blood pressure and sweat release. A gender effect was noted regarding skin blood flow, with males largely showing decreases and females increases. No changes were noted in spindle firing rates and painful stimuli did not significantly increase effector organ responses in spinal cord injured subjects. Contrasting with previous studies, we did not see a differential sympathetic response or change in spindle firing rate to painful stimuli originating in different tissues. While it is believed that noxious stimuli trigger AD, we did not see exaggerated sympathetic responses in spinal cord injured subjects. More investigation is required regarding innocuous triggers of AD.