abstract: The unique anatomical and functional properties of vasculature determine the susceptibility of the spinal cord to ischemia. The spinal cord vascular architecture is designed to withstand major ischemic events by compensating blood supply via important anastomotic channels. One of the important compensatory channels of the arterial basket of the conus medullaris (ABCM). ABCM consists of one or two arteries arising from the anterior spinal artery (ASA) and circumferentially connecting the ASA and the posterior spinal arteries. In addition to compensatory function, the arterial basket can be involved in arteriovenous fistulae and malformations of the conus. The morphometric anatomical analysis of the ABCM was performed with emphasis on vessel diameters and branching patterns. A significant ischemic event that overcomes vascular compensatory capacity causes spinal cord injury (SCI). For example, SCI complicating thoracoabdominal aortic aneurysm repair is associated with ischemic injury. The rate of this devastating complication has been decreased significantly by instituting physiological methods of protection. Traumatic spinal cord injury causes complex changes in spinal cord blood flow (SCBF), which are closely related to a severity of injury. Manipulating physiological parameters such as mean arterial pressure (MAP) and intrathecal pressure (ITP) may be beneficial for patients with a spinal cord injury. It was discovered in a pig model of SCI that the combination of MAP elevation and cerebrospinal fluid drainage (CSFD) significantly and sustainably improved SCBF and spinal cord perfusion pressure. In animal models of SCI, regeneration is usually evaluated histologically, requiring animal sacrifice. Thus, there is a need for a technique to detect changes in SCI noninvasively over time. The study was performed comparing manganese-enhanced magnetic resonance imaging (MEMRI) in hemisection and transection SCI rat models with diffusion tensor imaging (DTI) and histology. MEMERI ratio differed among transection and hemisection groups, correlating to a severity of SCI measured by fraction anisotropy and myelin load. MEMRI is a useful noninvasive tool to assess a degree of neuronal damage after SCI. / Dissertation/Thesis / Doctoral Dissertation Neuroscience 2016

Traumatic spinal cord injury (SCI) is a devastating condition for which there is no effective clinical treatment. Neuroprotective molecules that minimize tissue loss have shown promising results; however systemic delivery may limit in vivo benefits due to short systemic half-life and minimal passage across the blood-spinal cord barrier. To overcome these limitations, an injectable intrathecal delivery vehicle comprised of hyaluronan and methylcellulose (HAMC) was developed, and previously demonstrated to be safe and biocompatible intrathecally. Here, HAMC was determined to persist in the intrathecal space for between 4-7 d in vivo, indicating it as an optimal delivery system for neuroprotective agents to reduce tissue degeneration after SCI. HAMC was then investigated as an in vivo delivery system for two neuroprotective proteins: erythropoietin (EPO) and fibroblast growth factor 2 (FGF2). Both proteins demonstrated a diffusive release profile in vitro and maintained significant bioactivity during release. When EPO was delivered intrathecally with HAMC to the injured spinal cord, reduced cavitation in the tissue and significantly improved neuron counts were observed relative to the conventional delivery strategies of intraperitoneal and intrathecal bolus. When FGF2 was delivered intrathecally from HAMC, therapeutic concentrations penetrated into the injured spinal cord tissue for up to 6 h. Poly(ethylene glycol) modification of FGF2 significantly increased the amount of protein that diffused into the tissue when delivered similarly. Because FGF2 is a known angiogenic agent, dynamic computed tomography was developed for small animal serial assessment of spinal cord hemodynamics. Following SCI and treatment with FGF2 from HAMC, moderate improvement of spinal cord blood flow and a reduction in permeability were observed up to 7 d post-injury, suggesting that early delivery of neuroprotective agents can have lasting effects on tissue recovery. Importantly, the entirety of this work demonstrates that HAMC is an effective short-term delivery system for neuroprotective agents by improving tissue outcomes following traumatic SCI.

Traumatic spinal cord injury (SCI) is a devastating condition for which there is no effective clinical treatment. Neuroprotective molecules that minimize tissue loss have shown promising results; however systemic delivery may limit in vivo benefits due to short systemic half-life and minimal passage across the blood-spinal cord barrier. To overcome these limitations, an injectable intrathecal delivery vehicle comprised of hyaluronan and methylcellulose (HAMC) was developed, and previously demonstrated to be safe and biocompatible intrathecally. Here, HAMC was determined to persist in the intrathecal space for between 4-7 d in vivo, indicating it as an optimal delivery system for neuroprotective agents to reduce tissue degeneration after SCI. HAMC was then investigated as an in vivo delivery system for two neuroprotective proteins: erythropoietin (EPO) and fibroblast growth factor 2 (FGF2). Both proteins demonstrated a diffusive release profile in vitro and maintained significant bioactivity during release. When EPO was delivered intrathecally with HAMC to the injured spinal cord, reduced cavitation in the tissue and significantly improved neuron counts were observed relative to the conventional delivery strategies of intraperitoneal and intrathecal bolus. When FGF2 was delivered intrathecally from HAMC, therapeutic concentrations penetrated into the injured spinal cord tissue for up to 6 h. Poly(ethylene glycol) modification of FGF2 significantly increased the amount of protein that diffused into the tissue when delivered similarly. Because FGF2 is a known angiogenic agent, dynamic computed tomography was developed for small animal serial assessment of spinal cord hemodynamics. Following SCI and treatment with FGF2 from HAMC, moderate improvement of spinal cord blood flow and a reduction in permeability were observed up to 7 d post-injury, suggesting that early delivery of neuroprotective agents can have lasting effects on tissue recovery. Importantly, the entirety of this work demonstrates that HAMC is an effective short-term delivery system for neuroprotective agents by improving tissue outcomes following traumatic SCI.

Après un traumatisme de la moelle épinière (TM), l’ischémieest un facteur d’aggravation des lésions. Cette ischémie peut être aggravée par l’augmentation depression du liquide cérébro-spinal (LCS) par le biais d’un effet tamponnade. Or chez l’homme,après un TM avec préservation de l’intégrité de la dure-mère, la pression de LCS augmentesignificativement. On suppose donc que le maintien d’une pression de LCS à des valeursphysiologique pourrait être une méthode de limitation de l’ischémie post-traumatique et doncd’amélioration du pronostic fonctionnel. Afin de pouvoir réaliser une étude expérimentale de cesphénomènes, nous avons consacré la première partie expérimentale de cette thèse à la mise au pointd’un modèle de TM à dure-mère intacte chez le rat permettant la mesure simultanée de la pressionde LCS et de la perfusion médullaire. Nous avons confirmé expérimentalement que la pression deLCS augmente après TM. Dans la seconde partie expérimentale, nous avons mis au point unetechnique expérimentale de quantification spatiale et temporelle de la perfusion médullaire grâce àl’échographie de contraste. Cette technique permettait aussi un suivi en temps réel de l’évolution dusaignement intra-parenchymateux induit par le TM. Dans la troisième partie expérimentale, nousavons utilisé notre modèle couplé avec l’échographie de contraste et le laser Doppler pour évaluerles effets de la noradrénaline injectée à la phase aigüe d’un TM sur la perfusion médullaire et lesaignement intra-parenchymateux. Nous avons montré que la noradrénaline augmentait trèslégèrement le flux sanguin superficiel mais pas le flux sanguin profond et qu’elle augmentait lataille du saignement. / After spinal cord injury (SCI), ischaemia aggravates lesions.Increase in cerebrospinal fluid (CSF) pressure can worsens ischaemia through a tamponnade effect.In humans, it has been shown that after SCI with intact dura mater, CSF pressure significantlyincreases. Therefore, preserving CSF pressure within a physiological range may limit post-traumaischaemia and improve neurological outcome. In order to experimentally study these phenomenon,we have dedicated the first part of that work to create a model of SCI in rats preserving dura’sintegrity and allowing simultaneous measurement of spinal cord blood flow (SCBF) and CSFpressure. We have confirmed that CSF pressure increases after SCI with intact dura. In the secondexperimental part, we have developed a technique allowing to perform spatial and temporalmeasurement of SCBF thanks to contrast enhanced ultrasonography (CEU). Moreover, thistechnique allows real-time measurement of the size of the parenchymal hemorrhage. In the thirdexperimental part, we have used our experimental model in association with CEU and LaserDoppler to assess the effects of early injection of norepinephrine on SCBF and parenchymalhemorrhage. We found that norepinephrine induces a slight increase in superficial SCBF while itdoesn’t modify deep SCBF and significantly increases the size of parenchymal hemorrhage.