Within two minutes of global ischemia or focal stroke, a sudden loss of neuronal and glial membrane potential induces anoxic depolarization (AD) that propagates across gray matter of the cerebral hemispheres at 2-5 mm/min. It induces terminal neuronal damage, forming the initial ischemic core. In healthy gray matter, a milder version termed spreading depression (SD) does not cause tissue damage and generates the migraine aura, often a marching sensory deficit preceding the pain. AD and SD have been well studied in the cerebral and cerebellar cortices, but not the in the brainstem. We induced AD in coronal brain slices of mouse using oxygen/glucose deprived (OGD) saline. SD was induced by briefly elevating the extracellular K+ concentration. AD or SD propagation was imaged as a moving front of elevated light transmittance (LT) in cerebral and cerebellar cortices. Most ventral brainstem areas did not support AD or SD but in the dorsal brainstem some LT mini-fronts were observed in the superficial superior colliculus (SC), edges of inferior colliculus (IC), periaqueductal gray (PAG), tegmental nucleus (TN) and solitary nucleus (SolN). Their AD/SD characteristics were compared to those in the ‘higher’ brain regions. Although time of onset was not different, the present AD and SD propagated more slowly in brainstem gray matter. A non-specific glutamate receptor antagonist kynurenic acid (KYNA) successfully blocked the SD but not AD in PAG, TN and SolN. Two-photon laser scanning microscopy (2-PLSM) of live YFP+ mice brain slices showed that pyramidal neurons in ‘higher’ hippocamal CA1 irreversibly swelled and formed dendritic beads while neurons in the ‘lower’ mesencephalic trigeminal nucleus (Mes) of the midbrain-pons did not significantly swell or display any sign of injury. Finally, dendritic beading was induced in intact mouse neocortex and hippocampus by cardiac perfusion with OGD saline or ice-cold saline. However, dendrites in the brainstem from the same mice showed no obvious beading. Taken together, our study supports the concept that most brainstem regions are comparatively resistant to AD/SD compared to the ‘higher’ regions of cerebral and cerebellar cortices. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2012-10-01 13:42:14.325

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Der Schlaganfall steht hinter den Herz- und Tumor-Erkrankungen an dritter Stelle aller Todesursachen. Der wichtigste Faktor für die Vermeidung dauerhafter Invalidität und die Wiederherstellung maximaler Lebensqualität ist die Verhinderung von sekundären Komplikationen. Dabei stellt die Infarktprogression eine der schwerwiegendsten Komplikationen dar. Im Rahmen dieser Arbeit konnte bei insgesamt 45 Patienten mit einem malignen Schlaganfall mittels serieller MRT-Aufnahmen bestimmt werden, ob eine Infarktprogression vorlag. Ein Schwerpunkt der Arbeit war es, die hämodynamische Antwort und die zeitliche und räumliche Ausbreitung von Spreading Depolarizationen (CSD) im Periinfarktgewebe von Patienten mit malignem Schlaganfall zu untersuchen. In dieser Studie konnte zum ersten Mal die zeitliche und räumliche Ausbreitung von CSDs und deren hämodynamische Kopplung am humanen Kortex gezeigt werden. In einer zweiten Substudie wurden mit Hilfe der zerebralen Mikrodialyse die Konzentrationen von Glutamat, Glukose, Laktat und Pyruvat im Periinfarktgewebe bestimmt. Damit sollte im Besonderen geklärt werden, ob es Unterschiede in den Konzentrationen bei Patienten mit Infarktprogression zu Patienten ohne Infarktprogression gibt. Zusammenfassend war ein bemerkenswerter Anteil von verzögerter Infarktprogression nach Dekompression bei Patienten mit malignem Schlaganfall assoziiert mit veränderten biochemischen Markern innerhalb der Periinfarktregion. Des Weiteren wurde untersucht, inwiefern CSDs mit einer veränderten Konzentration von Glutamat, Glukose, Laktat und Pyruvat einhergeht. Hierzu wurde eine Korrelation zwischen CSDs und den Mikrodialysekonzentrationen von Glutamat, Glukose, Laktat und Pyruvat erstellt. / Stroke is the third leading cause of death. The most important factor in preventing permanent disability and recovering quality of life is the prevention of secondary complications. Infarct progression is one of the most serious complications after stroke. In the present study we determined by volumetric analysis from serial magnetic resonance imaging in 45 patients with malignant hemispheric stroke whether an infarct progression was present or not. The next aim was to investigate the hemodynamic response pattern and spatiotemporal propagation of cortical spreading depolarization (CSD) in the peri-infarct region of malignant hemispheric stroke. For the first time, intraoperatively the spatiotemporal propagation of CSDs and their hemodynamic coupling in the human cerebral cortex was visualized. In a second study, the levels of glutamate, glucose, lactate and pyruvate in the peri-infarct region using cerebral microdialysis in patients with malignant stroke were investigated. In particular, it was necessary to clarify whether there are differences in the metabolic changes are associated with delayed infarct progression. In summary, we observed a notable proportion of delayed infarct progression after decompressive surgery in patients with malignant hemispheric stroke associated with a disarrangement of biochemical markers within the peri-infarct region. Furthermore I investigated how CSDs are associated with metabolic changes. For this, a correlation between CSD and the concentrations of glutamate, glucose, lactate and pyruvate was prepared.

Traumatic brain injury (TBI) is a leading cause of disability worldwide. Annually, 150 to 200/1,000,000 people become disabled as a result of brain trauma. Axonal degeneration is a critical, early event following TBI of all severities but whether axon degeneration is a driver of TBI remains unclear. Molecular pathways underlying the pathology of TBI have not been defined and there is no efficacious treatment for TBI. Despite this significant societal impact, surprisingly little is known about the molecular mechanisms that actively drive axon degeneration in any context and particularly following TBI. Although severe brain injury may cause immediate disruption of axons (primary axotomy), it is now recognized that the most frequent form of traumatic axonal injury (TAI) is mediated by a cascade of events that ultimately result in secondary axonal disconnection (secondary axotomy) within hours to days. Proposed mechanisms include immediate post-traumatic cytoskeletal destabilization as a direct result of mechanical breakage of microtubules, as well as catastrophic local calcium dysregulation resulting in microtubule depolymerization, impaired axonal transport, unmitigated accumulation of cargoes, local axonal swelling, and finally disconnection. The portion of the axon that is distal to the axotomy site remains initially morphologically intact. However, it undergoes sudden rapid fragmentation along its full distal length ~72 h after the original axotomy, a process termed Wallerian degeneration. Remarkably, mice mutant for the Wallerian degeneration slow (Wlds) protein exhibit ~tenfold (for 2–3 weeks) suppressed Wallerian degeneration. Yet, pharmacological replication of the Wlds mechanism has proven difficult. Further, no one has studied whether Wlds protects from TAI. Lastly, owing to Wlds presumed gain-of-function and its absence in wild-type animals, direct evidence in support of a putative endogenous axon death signaling pathway is lacking, which is critical to identify original treatment targets and the development of viable therapeutic approaches. Novel insight into the pathophysiology of Wallerian degeneration was gained by the discovery that mutant Drosophila flies lacking dSarm (sterile a/Armadillo/Toll-Interleukin receptor homology domain protein) cell-autonomously recapitulated the Wlds phenotype. The pro-degenerative function of the dSarm gene (and its mouse homolog Sarm1) is widespread in mammals as shown by in vitro protection of superior cervical ganglion, dorsal root ganglion, and cortical neuron axons, as well as remarkable in-vivo long-term survival (>2 weeks) of transected sciatic mouse Sarm1 null axons. Although the molecular mechanism of function remains to be clarified, its discovery provides direct evidence that Sarm1 is the first endogenous gene required for Wallerian degeneration, driving a highly conserved genetic axon death program. The central goals of this thesis were to determine (1) whether post-traumatic axonal integrity is preserved in mice lacking Sarm1, and (2) whether loss of Sarm1 is associated with improved functional outcome after TBI. I show that mice lacking the mouse Toll receptor adaptor Sarm1 gene demonstrate multiple improved TBI-associated phenotypes after injury in a closed-head mild TBI model. Sarm1-/- mice developed fewer beta amyloid precursor protein (βAPP) aggregates in axons of the corpus callosum after TBI as compared to Sarm1+/+ mice. Furthermore, mice lacking Sarm1 had reduced plasma concentrations of the phosphorylated axonal neurofilament subunit H, indicating that axonal integrity is maintained after TBI. Strikingly, whereas wild type mice exhibited a number of behavioral deficits after TBI, I observed a strong, early preservation of neurological function in Sarm1-/- animals. Finally, using in vivo proton magnetic resonance spectroscopy, I found tissue signatures consistent with substantially preserved neuronal energy metabolism in Sarm1-/- mice compared to controls immediately following TBI. My results indicate that the Sarm1-mediated prodegenerative pathway promotes pathogenesis in TBI and suggest that anti-Sarm1 therapeutics are a viable approach for preserving neurological function after TBI.