Access to abstract permanently restricted to Ball State community only. / Access to thesis permanently restricted to Ball State community only. / Department of Educational Psychology

Background: Cryptococcal induced visual loss is common and increasingly becoming a debilitating consequence in survivors of cryptococcal meningitis (CM). Conflicting reports of the optic neuritis and papilloedema models of visual loss have delayed the introduction of effective interventional strategies for prevention and treatment of visual loss in CM. Qualitative and quantitative diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) of the optic nerves have proven useful in the examination of the microstructure of the optic nerve especially in optic neuritis. Its application has been extrapolated to other optic nerve disorders such as ischaemic optic neuropathy and glaucoma. The aim of this study is to elucidate the pathogenesis of cryptococcal-induced visual loss using diffusion imaging of the optic nerve as an investigational tool. Method: Full ethical approval was obtained from the Greys Hospital, Department of Health and University of KwaZulu Natal Ethics Committees. Reliable and reproducible optic nerve diffusion techniques were first developed and optimized on 29 healthy volunteers at Greys Hospital, Neurology and Radiology departments using a Philips 1.5 Tesla Gyroscan. Informed consent was also obtained from 95 patients suffering from CM (≥18 yrs. of age), 14 patients with papilloedema and 14 patients with optic neuritis from other causes, recruited from Greys and Edendale Hospitals. Patients underwent full neuro-ophthalmological assessments, CSF examination, haematological workup, CD4 count, (viral load for some), electrophysiological assessment of vision [Visual evoked potential (VEP) and Humphreys visual fields (HVF)], Magnetic Resonance Imaging (MRI) scan of the brain and orbits and DWI and DTI of the optic nerves. Results and Discussion: Visual loss is common in CM, occurring in 34.6-48%. Optic neuritis was uncommon as evidenced by a lack of signal change and lack of enhancement within the optic nerve in all patients scanned. The peri-optic CSF space was not dilated and the optic nerve diameter was not increased regardless of CSF pressure and visual status. Swollen optic discs occurred in only 25% of patients whereas raised intracranial pressure (> 20cmCSF) was demonstrated in 69-71% of patients. Therefore visual loss could not be explained by papilloedema alone. The VEP P100 latency was shown to be a useful screening test for subclinical optic nerve disease in CM, but HVF was not. The optic nerve diffusion imaging used was reliable and reproducible and produced diffusion parameters equivalent to other investigators in the field. Neither optic nerve movement nor the CSF signal was demonstrated to impact significantly on optic nerve diffusion parameters. Optic nerve diffusion imaging did not demonstrate similarities between CM and papilloedema or optic neuritis regardless of CSF pressure or vision. Conclusion: The rarity of optic neuritis in CM and the disparity between papilloedema and visual loss together with the lack of support from diffusion studies suggest a 3rd mechanism of visual loss viz. the optic nerve compartment syndrome. Good clinical support is provided by a case report for this hypothesis that shows re-opening of the peri-optic CSF space and return of the peri-optic CSF signal on MRI with lowering of intracranial pressure and antifungal treatment. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.

Brain derived neurotrophic factor (BDNF) is a chemokine which levels are regulated by neuronal activity and could act as a sensor in front of distinct physiologic stimulus, activating the transcription of specific group of genes. In this work we show that BDNF induces the expression of BMP7 in neurons through TrkB receptor and MAPK/ERK pathways, an induction mechanism that is mediated in part by the release of the transcriptional repression exerted by p53 family proteins. BMP members in mammals are expressed in the growing nervous system where emerged as crucial regulators of dorsoventral patterning of the neural tube, neural cell fate determination, and cell death as well as terminal neural cell differentiation. In the earlier cerebral cortex development (at embryonic day 13, E13) BMPs predominantly induce cell death and inhibit the proliferation, as a mechanism for the regulation of cell number and phenotype within the developing cortex. Subsequently they exert sequential actions promoting neuronal differentiation at E16 and increasingly with time, they promote astrocytic differentiation and inhibit oligodendrocytes generation. This thesis demonstrates that BMP7 injection at midgestation alters the laminar distribution of pyramidal neurons in the cerebral cortex while GABAergic neurons distribution was not affected. We observed that abnormal high levels of BMP7 during cerebral cortex development induce the premature radial glia maturation into astrocytes impairing the radial migration of upper layers pyramidal neurons that remained accumulated in lower cortical regions. We also observed that altered BMP7 levels during midgestation lead to corpus callosum malformation. Although corpus callosum agenesis can be due to multiple causes, our analysis show that the correct pattern of BMP7 expression is necessary for the proper maturation of intermediate structures such as the glial wedge, the induseum griseum and the subcallosal sling, that provide essential guidepost signals for the proper corpus callosum development. Based on these results, it is proposed a physiologic model where the expression of BDNF induced by the initial electrical activity in the perinatal period would induce in turn, an increase in BMP7 expression. Both chemokines may act co-ordinately maturating neurons and glial cells at the end of neurogenic period. The alteration of BDNF and BMP7 spatio-temporal expression patterns could dramatically affect the proper cerebral cytoarchitecture and consequently the cerebral functioning. Indeed, different traumas occurred during embryonic and perinatal development are associated with an imbalance in BDNF and BMP7 levels. To check this hypothesis we reproduced an embryonic sublethal hypoxia, a pathological condition that can be associated to altered BDNF and BMP7 expression. Moreover, perinatal reduction of oxygen input can dramatically affect the cerebral cortex developmental program. As a result, many behavioural and learning disorders in infants have been associated to this pathological condition. We observed that this condition reduces BMP7 expression and signalling in the cerebral cortex promoting the differentiation of cortical progenitors into the oligodendrocytes in detrimental to the astroglial fate in vitro and in vivo. So, our findings indicate that changes on BMP7 expression in the tightly regulated developmental program of the central nervous system might importantly modify the cellular fate choice of cortical progenitors. When this change occurs during the critic perinatal developmental period, it could compromise the normal brain functionality in the affected individual. / “FUNCIÓN Y REGULACIÓN DE LA PROTEINA MORFOGENÉTICA DE HUESO (BMP7) EN EL DESARROLLO DE LA CORTEZA” TEXTO: "Brain derived neurotrophic factor" (BDNF) es una citoquina regulada por la actividad neuronal y puede actuar como sensor en respuesta a distintos estímulos fisiológicos, activando grupos específicos de genes. En este trabajo demuestro que BDNF induce la expresión de BMP7 en neuronas a través del receptor TrkB y la vía de señalización MAPK/ERK. Un mecanismo de inducción mediado en parte por la liberación de la represión transcripcional ejercida por la familia de proteínas p53. La inyección intraventricular de BMP7 durante la corticogenesis altera la distribución de las neuronas piramidales en la corteza cerebral. BMP7 induce la maduración prematura de la glia radial hacia astrocito alterando la migración radial de las neuronas piramidales de capas altas, que quedan anormalmente acumuladas en capas corticales inferiores. Niveles anormales de BMP7 durante fases gestacionales intermedias provocan malformación del cuerpo calloso (CC). Aunque la agénesis del CC puede ser debida a múltiples causas, nuestros análisis muestran que BMP7 es necesario para la formación de poblaciones de la línea media (glial wedge, induseum griseum y subcallosal sling) que participan en mecanismos de guía axonal necesarios para el desarrollo del CC. Proponemos un modelo fisiológico donde la expresión de BDNF inducida por el aumento de actividad eléctrica perinatal induciría a su vez un aumento de los niveles de BMP7. Ambas citoquinas actuarían conjuntamente madurando de una manera sincrónica las poblaciones neuronales y gliales de la corteza cerebral. La modificación del patrón de expresión espacio-temporal de ambas citoquinas podría afectar la composición celular y por tanto la correcta funcionalidad de la corteza cerebral. De hecho, diferentes traumas producidos durante el desarrollo embrionario y perinatal, donde se observa alteración de los niveles de BDNF y BMP7, están asociados a distintos desordenes neurológicos. En este trabajo reproducimos una hipoxia embrionaria sub-letal y observamos que los niveles de expresión y señalización de BMP7 están reducidos en animales hipóxicos. Esta reducción en los niveles de BMP7 promueve la diferenciación de los progenitores corticales hacia un fenotipo oligodendroglial en detrimento del fenotipo astroglial. Por tanto, BMP7 es vital para la correcta determinación de diferentes progenitores neurales durante el desarrollo cortical.

Thesis (M.Sc.)--York University, 2006. Graduate Programme in Kinesiology & Health Science. / Typescript. Includes bibliographical references (leaves 70-77). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR19733

Thesis (Ph. D.)--Carleton University, 2001. / Includes bibliographical references (p. 165-175). Also available in electronic format on the Internet.

Thesis (M.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 86-97). Also available in electronic format on the Internet.

Thesis (Ph.D.) - Carleton University, 2005. / Includes bibliographical references (p. 175-191). Also available in electronic format on the Internet.

Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 95-108). Also available in electronic format on the Internet.

Thesis (M.A.)--Northern Kentucky University, 2008. / Made available through ProQuest. Publication number: AAT 1450372. ProQuest document ID: 1490083611. Includes bibliographical references (p. 44-46)

Thesis (M. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 94-102). Also available in electronic format on the Internet.