Intracerebral hemorrhage (ICH) results in secondary brain injury caused partially by blood and its metabolites. Survivors of ICH are often left with severe disabilities, therefore, decreasing the extent of this secondary injury may improve functional outcome of patients. Incubation of mouse brain slices with partially oxidized bilirubin, a neurotoxic blood breakdown product, caused a dose- and time-dependent decrease in axonal function, suggesting a reduced number of conducting myelinated axons. These effects did not occur when tissue was incubated with non-oxidized bilirubin. Injection of bilirubin into the corpus callosum of mice caused functional impairment of unmeylinated axons; however, immunohistochemical staining of the tissue showed evidence of structural damage to both oligodendrocytes and axons. This data provides evidence for functional and structural damage to white matter in the presence of partially oxidized bilirubin Therefore, diminishing the duration of presence of bilirubin and its oxidation in the brain warrants study as a means of decreasing secondary brain injury after ICH.

Intracerebral hemorrhage (ICH) is a devastating form of stroke that results from rupture of a blood vessel in the brain. Tissue inside the hematoma is irreversibly damaged soon after ICH onset and when this thesis research began, there was a dearth of information regarding pathological changes outside the hematoma. Inflammation is often proposed as a mechanism of injury, but very little information was available to show that inflammatory cells were in the right place at the right time to cause secondary brain injury. Using the collagenase-induced model of ICH, this work sought to better define spatial and temporal relationships between secondary brain injury and the inflammatory response after ICH. To test the hypothesis that reducing inflammation can protect the brain from secondary injury, minocycline, an antibiotic with established anti-inflammatory effects, was administered 6 hours after ICH onset. A small number of neurons die in the parenchyma bordering the hematoma between 6 hours and 3 days after ICH onset. This area was not associated with neutrophil infiltration, and most activated microglia/macrophages did not accumulate until after most neuron death had occurred. Despite a pronounced microglial response and prolonged increase in expression of many inflammatory genes, including complement receptor-3, interleukin-1 beta, interleukin-6, and interleukin-1 converting enzyme, no dying neurons were observed further outside the hematoma at any time. Interestingly, less early neuron death was observed in aged than in young animals, without a concomitant difference in the amount of tissue lost at 28 days. However, aged animals had less early microglial activation and a larger residual lesion, which might have resulted from impaired phagocytosis by activated microglia/macrophages. Minocycline was less effective in reducing microglial activation in aged animals, and did not reduce neuron death in either young or aged animals. Edema and BBB disruption was associated with degradation of the basal lamina protein, collagen type IV, and that damaged vessels are associated with tumor necrosis factor-alpha (TNFα)-positive neutrophils and active matrix metalloprotease-12 (MMP-12), all of which were reduced by delayed minocycline treatment. In contrast to ischemic stroke, there is a limited ‘penumbra’ outside the hematoma. Nevertheless, BBB damage in this region appears to be a potential target for protection. Furthermore, the prominent inflammatory response that continues for days after ICH does not appear to be associated with damage to other areas of the brain. Minocycline appears to protect the BBB by reducing neutrophil infiltration and the MMP-12 mediated basal lamina degradation. Future studies should investigate other targets for protection (i.e., white matter injury), and seek drugs that modulate the inflammatory response in aged animals and promote lesion resolution.

Hyperthermia worsens outcome after ischemia. While it seems reasonable that hyperthermia would also worsen outcome after intracerebral hemorrhage (ICH), clinical studies attempting to find a causative relationship between hyperthermia and outcome have been inconclusive. We induced ICH with an injection of autologous whole blood (100 l) immediately followed by 3 hours of hyperthermia (HYPER; 39C) or normothermia (NORMO; 37C). Surprisingly, hyperthermia reduced edema at 72 hours, and improved outcome on day 3 post-ICH. There were no behavioural differences at later time points (day 11 and 32 post-ICH) and no difference in lesion volume (NORMO 14.0 mm3, HYPER: 14.5 mm3). Overall, this study does not support the hypothesis that mild, transient hyperthermia worsens outcome after ICH. Further research is needed to determine if more severe or prolonged hyperthermia worsens outcome, or if the cause of hyperthermia (e.g. infection) is important.

Intracerebral hemorrhage (ICH) is a severe form of stroke, with a high mortality rate and often resulting in irreversible neurological deterioration. Although animal studies have provided insight into the etiology of the disease, many of the causative genes and mechanisms implicated in cerebral-vascular malformations are unknown. Treatment options remain ineffective. With the present models, the pathophysiological consequences of ICH can only be assessed in situ and after histological analysis. Furthermore, common deficiencies of the current models include the heterogeneity, low expression and low reproducibility of the desired phenotype. Hence, there is a requirement for novel approaches to model ICH pathogenesis. Zebrafish (Danio rerio) has gained recognition as a vertebrate model for stroke research. Through a combination of pharmacological blockers, metabolite rescue, genetic approaches, and confocal imaging analysis, I demonstrate a requirement for the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) pathway in regulating developmental cerebral-vascular stabilization. A transient loss in HMGCR function induces ICH, characterised by progressive dilation of blood vessels, vascular permeability and vessel rupture. These effects are likely due to reduced prenylation of Rho GTPases, evidenced by morpholino-mediated blocking of the prenylation pathway and in vivo assessment of endothelial-specific localization of cdc42, a Rho GTPase family protein. These results are in conformity with recent clinical and experimental evidence. I have further shown that this model consistently replicates common pathoghysiological processes associated with ICH. The hemorrhages are associated with the disruption of the blood-brain barrier, vessel disintegration, hematoma expansion and edema into the adjacent brain regions. Also, enhanced apoptosis, activation of inflammatory mediators in the periphery of the hematoma, enriched heme oxygenase 1 (HO-1) expression and localised thrombosis were observed in these embryos. I show that the patterning and distribution of catecholaminergic neurons, response to sensory stimulus and swimming speed were impaired as a consequence of ICH. These results suggest that HMGCR contributes to cerebral-vascular stabilisation through Rho GTPase mediated-signalling and that zebrafish can serve as a powerful paradigm for the systemic analysis of the etiological and pathophysiological underpinnings of ICH and can help establish the basis for future studies into screening for putative therapeutics and elucidating mechanisms aiding functional recovery.

abstract: Intracerebral hemorrhage (ICH) is a devastating type of acute brain injury with high mortality and disability. Acute brain injury swiftly alters the immune reactivity within and outside the brain; however, the mechanisms and influence on neurological outcome remains largely unknown. My dissertation investigated how ICH triggers focal and systemic immune responses and their impact hemorrhagic brain injury. At the focal level, a significant upregulation of interleukin (IL)-15 was identified in astrocytes of brain sections from ICH patients. A transgenic mouse line where the astrocytic IL-15 expression is controlled by a glial fibrillary acidic protein promoter (GFAP-IL-15tg) was generated to investigate its role in ICH. Astrocyte-targeted expression of IL-15 exacerbated brain edema and neurological deficits following ICH. Aggravated ICH injury was accompanied by an accumulation of pro-inflammatory microglia proximal to astrocytes in perihematomal tissues, microglial depletion attenuated the augmented ICH injury in GFAP-IL-15tg mice. These findings suggest that IL-15 mediates the crosstalk between astrocytes and microglia, which worsens ICH injury.Systemic immune response was investigated by leveraging the novel method of obtaining and analyzing bone marrow cells from the cranial bone flaps of ICH patients. A swift increase of hematopoietic stem cell (HSCs) population in the bone marrow was identified, along with a shift towards the myeloid cell lineage. Human findings were mirrored in an ICH mouse model. Fate mapping these HSCs revealed increased genesis of Ly6Clow monocytes in the bone marrow, which transmigrate into the hemorrhagic brain and give rise to alternative activation marker bearing macrophage. Blockade of the β3-adrenergic receptor or inhibition of Cdc42 abolished ICH-induced myeloid bias of HSCs. Importantly, mirabegron, a Food and Drug Administration-approved β3 adrenergic receptor agonist, and a Cdc42 activator, IL-3, enhanced bone marrow generation of Ly6Clow monocytes and improved recovery. These results suggest that brain injury modulates HSC lineage destination to curb distal brain inflammation, implicating the bone marrow as a unique niche for self-protective neuroimmune interactions. Together, these results demonstrate how acute brain injury exerts a profound yet distinct effect on immune responses within and outside the brain and sheds new light on neuroimmune interactions with potential clinical implications. / Dissertation/Thesis / Doctoral Dissertation Neuroscience 2020

Intracerebral hemorrhage defines a category of neurological disease that spans the full range of possible clinical outcomes. At one end of the spectrum is hemorrhagic stroke, an often debilitating neurologic condition with substantial morbidity and mortality while cerebral microhemorrhage at the other end of the spectrum can go completely unnoticed as they are often asymptomatic. Despite the distinct clinical outcomes both conditions share a common risk factor, uncontrolled hypertension. Here we set out to generate a novel mouse model of intracerebral hemorrhage with pressure as the mode of hemorrhage induction. To conduct our studies, we utilize high pressure focused ultrasound in combination with injected microbubbles to cause hemorrhage. We applied this technique at two different pressures resulting in striatal hemorrhage induction with distinct phenotypic outcomes. Following induction at the higher-pressure, mice show evidence of lateral motor deficit and other signs of impairment. Mice with hemorrhage induced at the lower pressure show no behavioral signs of neurological deficit. We employ immunofluorescence and western blotting to understand the cellular responses to intracerebral hemorrhage in these mice. We find evidence of inflammation and cell death following high-pressure induction of intracerebral hemorrhage. Lower pressure induction of intracerebral hemorrhage lacks signs of cell death but shows apparent inflammation. We have created a novel pressure-dependent mouse model of symptomatic and asymptomatic intracerebral hemorrhage by applying high intensity focused ultrasound in combination with circulating microbubbles.

Primary angiitis of the central nervous system (PACNS) is a rare form of vasculitis. It is a diagnosis of exclusion and often diagnosed post mortem on pathologic evaluation. Cerebral angiography can be suggestive, but biopsy is required. Symptoms can vary from headache to focal cranial nerve deficits. On the more severe spectrum, patients can present with ischemic and vary rarely hemorrhagic stroke. We present in this case report key clinical pearls regarding suspected diagnosis. Younger patients with cortical hemorrhages may have PACNS instead of the more common cerebral amyloid angiopathy. Early suspicion may aid in initiating effective treatment as we highlight in the discussion.

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