published_or_final_version / Nursing Studies / Master / Master of Nursing in Advanced Practice

Bipeds and quadrupeds are inherently unstable and their bodies sway during quiet stance and require complex patterns of muscle activation to produce direction-specific forces to control the body’s center of mass. The relative strength of length and force feedback within and across muscles collectively regulates the mechanical properties of the limb as a whole during standing and locomotion (Bonasera and Nichols 1994; Ross and Nichols 2009). Loss of posture control following spinal cord injury (SCI) is a major clinical challenge. While much is known about intermuscular force feedback during crossed extension reflex (XER) and locomotion in decerebrate cats, these have not been well characterized in animals with spinal cord injury. In this study, we mapped the distribution of heterogenic force feedback in hindlimb ankle extensor muscles using muscle stretch (natural stimulation) in intercollicular, non-locomoting, decerebrate cats with chronic lateral spinal hemisection (LSH). We also, determined the time of onset of redistribution of heterogenic force feedback following LSH by collecting force feedback data from cats with acute sci. In addition we revisited heterogenic force feedback between ankle extensors in decerebrate non-locomoting cats during mid-stance to ascertain whether these cats with intact spinal cord depict a certain pattern of force feedback. The goal was to ascertain whether the patterns and strength of feedback was different between the two states (cats with intact spinal cord and cats with SCI). We found that heterogenic feedback pathways remained inhibitory in non-locomoting decerebrate cats in two states. The latencies of inhibition also corresponded to those observed for force feedback from Golgi tendon organs. We observed variable patterns of force feedback between ankle extensors in decerebrate/control cats. On the other hand we observed consistent results in cats with chronic LSH exhibiting very strong distal to proximal pattern of inhibition from 2 weeks to 20 weeks following chronic LSH. The same results were obtained in acute LSH cats suggest that the change in neuromuscular system appears immediately after SCI and persists even after the animal start walking following SCI. The observed altered pattern of force feedback after spinal cord injury suggests either presence of a pattern intrinsic to the spinal cord or a unique pattern exhibited by the damaged spinal cord. The results are important clinically because even with vigorous rehabilitation attempts patients do not regain posture control after SCI even though they regain ability to walk. Therefore, to effectively administer treatment and therapy for patients with compromised posture control, a complete understanding of the circuitry is required.

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Patients suffering from central neuropathic pain have thermal sensory deficits within the painful area. Prior research proposed that the loss of thermal sensation in regions of central neuropathic pain may reflect similar central nervous system interaction between warm and cold sensory inputs that underlie the Thermal Grill Illusion (TGI) in which burning pain is felt while reduced warm/cold sensations are reported. This work presents a portable and reliable device that was used to systematically evaluate the characteristics of the TGI in healthy individuals. The results suggest that the spatial distribution of the warm and cool stimuli significantly affected the quality of perceived TGI. Additionally, simultaneous tactile and thermal stimulation was shown to be significantly less painful than thermal stimulation alone. A high correlation was also seen in the subject‘s TG intensity scores and their cold pain threshold. These results are useful for future TGI studies for central neuropathic pain.

More than one million people are living with spinal cord injury (SCI) in North America alone. Restoring lost motor function can alleviate SCI-related health problems, as well as markedly increase the quality of life enjoyed by individuals with SCI. Functional electrical stimulation (FES) can replace motor function in individuals with SCI by using short electrical pulses to generate contractions in paralyzed muscles. A wide range of FES applications have been proposed, but few application are actually available for community use by SCI consumers. A major factor contributing to this shortage of real-world FES applications is the lack of a feasible closed-loop control algorithm. The purpose of this thesis is to develop a closed-loop control algorithm that is suitable for use in practical FES applications. This thesis consists of three separate studies. The first study examined existing closed-loop control algorithms for FES applications, and showed that a method of testing FES control algorithms under realistic conditions is needed to evaluate their likely real-world performance. The second study provided such a testing method by developing a non-idealities block that can be used to modify the nominal response of electrically stimulated muscle in simulations of FES applications. Fatigue, muscle spasm, and tremor non-idealities are included in the block, which allows the user to specify the severity level for each type of non-ideal behaviour. This nonidealities block was tested in a simulation of electrically induced knee extension against gravity, and showed that the nominal performance of the controllers was substantially better than their performance in the realistic case that included the non-idealities model. The third study concerned the development and testing of a novel observer-based sliding mode control (SMC) algorithm that is suitable for use in real-world FES applications. This algorithm incorporated a fatigue minimization objective as well as co-contraction of the antagonist muscle group to cause the joint stiffness to track a desired value. The SMC algorithm was tested in a simulation of FES-based quiet standing, and the non-idealities block was used to determine the probable performance of the controller in the real world. This novel controller performed very well in simulation, and would be suitable for use in selected practical FES applications. The work contained in this thesis can easily be extended to a wide range of FES applications. This work represents a significant step forward in closed-loop control for FES applications, and will facilitate the development of sophisticated new electrical stimulation systems for use by consumers in their homes and communities.

Patients suffering from central neuropathic pain have thermal sensory deficits within the painful area. Prior research proposed that the loss of thermal sensation in regions of central neuropathic pain may reflect similar central nervous system interaction between warm and cold sensory inputs that underlie the Thermal Grill Illusion (TGI) in which burning pain is felt while reduced warm/cold sensations are reported. This work presents a portable and reliable device that was used to systematically evaluate the characteristics of the TGI in healthy individuals. The results suggest that the spatial distribution of the warm and cool stimuli significantly affected the quality of perceived TGI. Additionally, simultaneous tactile and thermal stimulation was shown to be significantly less painful than thermal stimulation alone. A high correlation was also seen in the subject‘s TG intensity scores and their cold pain threshold. These results are useful for future TGI studies for central neuropathic pain.

There are no clinically approved drug delivery strategies designed for localized and sustained release to the injured spinal cord, two features which are heavily exploited in pre-clinical demonstrations of efficacy. We have previously shown that injection of drug loaded hydrogels into the intrathecal space is safe, minimally invasive, and drug release localized to the site of injection for up to one day. In the present work we developed a platform for sustained release from 1 to 28 days based on a physical gel of methylcellulose with hyaluronan and poly(lactic-co-glycolic acid) (PLGA) nanoparticles added as gelation agents. These composite hydrogels met the design criteria of injectability, fast gelation, minimal swelling, and 28 day stability. Sustained release of 6 therapeutic molecules from the composite was achieved by encapsulation in the particles or dissolution in the hydrogel. Release of PLGA encapsulated drugs from the composite was linear for 28 days. Drugs dissolved in the hydrogel were released by Fickian diffusion. The HAMC hydrogel/PLGA nanoparticle composite was delivered to uninjured and spinal cord injured rats and the animals monitored for 14 and 28 days respectively. The composite was well tolerated in the intrathecal space with no impact on motor function as determined by the BBB scale and minimal inflammation in both studies. No increase in reactive astrocytes or cavity volume was found in clip compression spinal cord injured rats, indicating that the composite did not affect these aspects of the secondary injury cascade. We then turned to sustained release of anti-NogoA, a promising neuroregenerative molecule typically delivered for 2 - 4 weeks. Formulations of anti-NogoA or a model IgG were prepared and release was demonstrated over 28 days in vitro. Bioactivity was assessed using a novel ELISA which utilized anti-NogoA / NogoA binding to detect only active antibody, advantageous because anti-NogoA release can now be easily optimized prior to in vivo studies of efficacy. The key features of current work are the development of an intrathecal drug delivery platform, demonstration of safety in a rat model, and formulation for use with anti-NogoA.

There are no clinically approved drug delivery strategies designed for localized and sustained release to the injured spinal cord, two features which are heavily exploited in pre-clinical demonstrations of efficacy. We have previously shown that injection of drug loaded hydrogels into the intrathecal space is safe, minimally invasive, and drug release localized to the site of injection for up to one day. In the present work we developed a platform for sustained release from 1 to 28 days based on a physical gel of methylcellulose with hyaluronan and poly(lactic-co-glycolic acid) (PLGA) nanoparticles added as gelation agents. These composite hydrogels met the design criteria of injectability, fast gelation, minimal swelling, and 28 day stability. Sustained release of 6 therapeutic molecules from the composite was achieved by encapsulation in the particles or dissolution in the hydrogel. Release of PLGA encapsulated drugs from the composite was linear for 28 days. Drugs dissolved in the hydrogel were released by Fickian diffusion. The HAMC hydrogel/PLGA nanoparticle composite was delivered to uninjured and spinal cord injured rats and the animals monitored for 14 and 28 days respectively. The composite was well tolerated in the intrathecal space with no impact on motor function as determined by the BBB scale and minimal inflammation in both studies. No increase in reactive astrocytes or cavity volume was found in clip compression spinal cord injured rats, indicating that the composite did not affect these aspects of the secondary injury cascade. We then turned to sustained release of anti-NogoA, a promising neuroregenerative molecule typically delivered for 2 - 4 weeks. Formulations of anti-NogoA or a model IgG were prepared and release was demonstrated over 28 days in vitro. Bioactivity was assessed using a novel ELISA which utilized anti-NogoA / NogoA binding to detect only active antibody, advantageous because anti-NogoA release can now be easily optimized prior to in vivo studies of efficacy. The key features of current work are the development of an intrathecal drug delivery platform, demonstration of safety in a rat model, and formulation for use with anti-NogoA.

Spinal cord injury (SCI) results in a number of devastating consequences, including loss of motor function, paralysis, and neuropathic pain. Concomitant peripheral tissue injury below the lesion site can result in uncontrollable nociception that sensitizes spinal neurons and promotes chronic pain. Additionally, drugs like morphine, though critical for pain management, elicit pro-inflammatory effects that exacerbate chronic pain symptoms. Currently, there is a lack of effective therapeutic mechanisms to promote regeneration at the lesion site, and a limited understanding of regulatory mechanisms that can be utilized to therapeutically manipulate spinal cord plasticity. MicroRNAs (miRNAs) constitute novel targets for therapeutic intervention to both promote repair and regeneration, and mitigate maladaptive plasticity that leads to neuropathic pain. Microarray and qRT-PCR comparisons of contused and sham rat spinal cords at 4 and 14 days following SCI indicated that a total of 35 miRNAs were dysregulated, with miR1, miR124, and miR129 exhibiting significant down-regulation after SCI, and both miR21 and miR146a being transiently induced. Localized expression of miRNAs and cellular markers indicated that changes in miRNA regulation favor the emergence of neural stem cell niches and reversion of surviving neurons to a pre-neuronal phenotype. Additionally, both uncontrollable nociception and morphine administration resulted in further dysregulation of SCI-sensitive miRNAs, along with their mRNA targets. Morphine administration significantly induced expression of both miR21 and IL6R expression, indicating that morphine-induced miRNA dysregulation is involved in the promotion of neuroinflammation that drives increased pain-sensitivity. Similarly, uncontrollable nociception significantly modulates expression of miR124, miR129, and miR146a, which inhibit cell cycle proteins and microglial activation, and dysregulation of these miRNAs, along with BDNF and IGF-1, likely contributes towards promotion of hypersensitivity in spinal neurons that underlies neuropathic pain. Consequently, SCI- sensitive miRNAs may constitute therapeutic targets for modulation of neuroinflammation and microglial activation in order to mitigate secondary injury, promote regeneration, and prevent maladaptive plasticity that drives neuropathic pain and exacerbation of chronic pain symptoms by morphine administration.