The main objective of this thesis is to investigate the intrinsic optical signals (IOSs) with an ultra-high resolution optical coherence tomography system (UHROCT). In order to study the retinal IOSs evoked by visible light, an UHROCT and an Electroretinogram (ERG) system was combined. An animal model (chicken retina) based on its retinal avascularity and cone dominance, was selected. Imaging the chicken retina with OCT resulted in high contrast, high resolution (~3μm axial and ~5 μm lateral resolution) 2D and 3D volumetric tomograms, in which all retina layers were clearly distinguishable. Using the combined UHROCT and ERG system to image IOSs from the chicken retina exposed to visible light (7ms green flash) resulted in highly reproducible IOS recordings from all retinal layers for the first time. All inner retinal layers showed an initial increase and subsequently a decrease in the intensity of the backreflected imaging light within the first 100 ms after the onset of the stimulus. Outer segments of the photoreceptors also showed a decrease in the backreflected imaging light within 100 ms after the onset of the flash. All retinal layers showed a strong decrease in the backreflected light within 150 to 175 ms after the onset of the flash. Imaging the pupil dynamics of the chicken with a modified combined UHROCT and ERG system showed that part of the strong negative IOSs observed in all retinal layers resulted from the vignetting of the imaging beam due to the light induced pupil constriction. Thorough analysis of the pupil dynamics acquired with UHROCT showed a time dependent effect of the anesthesia agent on pupil constriction. Further experiments to investigate an anesthesia effects on retinal function showed significant changes in ERG components. Statistical analysis showed that Isoflurane anesthesia severely affects the inner retinal response. In conclusion, it was hypothesized that the fast IOSs within ~50-100 ms after the onset of the visual stimulus originated from the neuronal tissue in the retina and are related to tissue optical property changes as a result of the electrical signal propagation in the light activated retina. Longer term decreases in backreflected light are likely due to pupil changes.

The main objective of this thesis is to investigate the intrinsic optical signals (IOSs) with an ultra-high resolution optical coherence tomography system (UHROCT). In order to study the retinal IOSs evoked by visible light, an UHROCT and an Electroretinogram (ERG) system was combined. An animal model (chicken retina) based on its retinal avascularity and cone dominance, was selected. Imaging the chicken retina with OCT resulted in high contrast, high resolution (~3μm axial and ~5 μm lateral resolution) 2D and 3D volumetric tomograms, in which all retina layers were clearly distinguishable. Using the combined UHROCT and ERG system to image IOSs from the chicken retina exposed to visible light (7ms green flash) resulted in highly reproducible IOS recordings from all retinal layers for the first time. All inner retinal layers showed an initial increase and subsequently a decrease in the intensity of the backreflected imaging light within the first 100 ms after the onset of the stimulus. Outer segments of the photoreceptors also showed a decrease in the backreflected imaging light within 100 ms after the onset of the flash. All retinal layers showed a strong decrease in the backreflected light within 150 to 175 ms after the onset of the flash. Imaging the pupil dynamics of the chicken with a modified combined UHROCT and ERG system showed that part of the strong negative IOSs observed in all retinal layers resulted from the vignetting of the imaging beam due to the light induced pupil constriction. Thorough analysis of the pupil dynamics acquired with UHROCT showed a time dependent effect of the anesthesia agent on pupil constriction. Further experiments to investigate an anesthesia effects on retinal function showed significant changes in ERG components. Statistical analysis showed that Isoflurane anesthesia severely affects the inner retinal response. In conclusion, it was hypothesized that the fast IOSs within ~50-100 ms after the onset of the visual stimulus originated from the neuronal tissue in the retina and are related to tissue optical property changes as a result of the electrical signal propagation in the light activated retina. Longer term decreases in backreflected light are likely due to pupil changes.

No description available.

Eine wichtige Folge des Status epilepticus ist die Entwicklung einer chronischen Epilepsie. Die genauen Mechanismen und die Kinetik der Epileptogenese sind weitestgehend unklar. Ziel der vorliegenden Arbeit war ein besseres Verständnis des Prozesses durch die In-vitro-Analyse von Lokalisation und Kinetik funktioneller Folgen des Status epilepticus in vivo. In kombinierten Hippokampus-entorhinaler Kortex Hirnschnittpräparaten von Wistar-Ratten nach elektrisch induziertem selbsterhaltendem Status epilepticus (self-sustaining status epilepticus, SSSE) wurden im Niedrig-Magnesium-Modell anfallsartige Ereignisse (AE) ausgelöst und untersucht. Die In-vitro-Analyse der AE wurde eine, vier und acht Wochen nach SSSE durchgeführt. Um das räumliche Verhalten der epileptischen Aktivität beurteilen zu können, wurde die Messung des extrazellulären Feldpotenzials mit der Analyse intrinsischer optischer Signale kombiniert. Im Verlauf nach SSSE kam es zu einer Latenzverkürzung bis zum Auftreten epileptischer Aktivität und zu einer Zunahme der AE-Frequenz. Vier und acht Wochen nach SSSE stieg der Anteil der AE mit großflächigem Ursprung signifikant an. Im Verlauf nach SSSE wurden außerdem zunehmend diskontinuierliche Ausbreitungsmuster der Anfallsaktivität beobachtet. Acht Wochen nach SSSE zeigten 50% der Präparate zudem eine zeitlich und räumlich von den AE unabhängige, hochfrequente Aktivität im Gyrus dentatus. Zusammenfassend wurden eine Latenzverkürzung und eine Zunahme der AE-Frequenz als Hinweise für eine gesteigerte Exzitabilität des Hirngewebes nach SSSE gesehen. Neben dem großflächigen Ursprung deutet auch die Zunahme diskontinuierlicher Ausbreitungsmuster auf eine gesteigerte Synchronizität des neuronalen Netzwerkes nach SSSE hin. Die autonome Aktivität im Gyrus dentatus spricht dafür, dass die in vorangegangenen Studien beschriebenen strukturellen Änderungen in dieser Region mit einer veränderten Funktionalität einhergehen. / The development of chronic epilepsy is a serious consequence of Status epilepticus. Little is known about the mechanisms and kinetic of the epileptogenic process. The aim of this md-thesis was the analysis of localisation and kinetic of functional deficits in vitro after Status epilepticus in vivo. Using the Low-Magnesium-Model, seizure-like events (SLE) were induced in combined hippocampal-entorhinal cortex slices of wistar rats after electrically induced self-sustaining Status epilepticus (SSSE). One, four and eight weeks after SSSE the in-vitro-analysis of SLE was performed. In order to determine onset and spread-pattern of epileptic activity, the measurement of the extracellular field-potential was combined with the imaging of intrinsic optical signals (IOS). In the time course after SSSE there was a reduction of the latency to onset of seizure activity and an increase of the SLE-frequency. Four and eight weeks after SSSE a significant increase of SLE with regional onset was found. In Addition, there was an increase of non-contiguous propagation of seizure activity. Eight weeks after SSSE 50% of the brain-slices showed autonomous high-frequent activity in the dentate gyrus. In conclusion a reduction of the latency to onset of seizure activity and an increase of the SLE-frequency were found. These changes are indicators of increased excitability after SSSE. Other than the regional onset, the non-contiguous spread-pattern also indicates increased synchronicity of the neuronal network after SSSE. The autonomous activity in the dentate Gyrus shows, that the previously described structural changes in this region lead to functional deficits.

No description available.