Universiẗat, Diss., 2007--Giessen.

Zugl.: Giessen, Univ., Diss., 2007

Universiẗat, Diss.--München, 1995.

Tübingen, Univ., Diss., 2007.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 105-120).

Frankfurt (Main), Univ., Diss., 2001.

Universiẗat, Diss., 2003--Kiel.

abstract: Patients with Alzheimer's disease (AD) exhibit a significantly higher incidence of unprovoked seizures compared to age-matched non-AD controls, and animal models of AD (i.e., transgenic human amyloid precursor protein, hAPP mice) display neural hyper-excitation and epileptic seizures. Hyperexcitation is particularly important because it contributes to the high incidence of epilepsy in AD patients as well as AD-related synaptic deficits and neurodegeneration. Given that there is significant amyloid-β (Aβ) accumulation and deposition in AD brain, Aβ exposure ultimately may be responsible for neural hyper-excitation in both AD patients and animal models. Emerging evidence indicates that α7 nicotinic acetylcholine receptors (α7-nAChR) are involved in AD pathology, because synaptic impairment and learning and memory deficits in a hAPPα7-/- mouse model are decreased by nAChR α7 subunit gene deletion. Given that Aβ potently modulates α7-nAChR function, that α7-nAChR expression is significantly enhanced in both AD patients and animal models, and that α7-nAChR play an important role in regulating neuronal excitability, it is reasonable that α7-nAChRs may contribute to Aβ-induced neural hyperexcitation. We hypothesize that increased α7-nAChR expression and function as a consequence of Aβ exposure is important in Aβ-induced neural hyperexcitation. In this project, we found that exposure of Aβ aggregates at a nanomolar range induces neuronal hyperexcitation and toxicity via an upregulation of α7-nAChR in cultured hippocampus pyramidal neurons. Aβ up-regulates α7-nAChRs function and expression through a post translational mechanism. α7-nAChR up-regulation occurs prior to Aβ-induced neuronal hyperexcitation and toxicity. Moreover, inhibition of α7-nAChR or deletion of α7-nAChR prevented Aβ induced neuronal hyperexcitation and toxicity, which suggests that α7-nAChRs are required for Aβ induced neuronal hyperexcitation and toxicity. These results reveal a profound role for α7-nAChR in mediating Aβ-induced neuronal hyperexcitation and toxicity and predict that Aβ-induced up-regulation of α7-nAChR could be an early and critical event in AD etiopathogenesis. Drugs targeting α7-nAChR or seizure activity could be viable therapies for AD treatment. / Dissertation/Thesis / Ph.D. Neuroscience 2011

Introduction: Beat-to-beat variability in cycle length exists in spontaneously beating cardiac preparations of varying complexities from the level of the isolated whole heart to the single sinoatrial nodal cell (SANC). The nature of this variability is poorly characterised as are its fundamental physiological origins. Methods: Recordings of spontaneous electrical activity were made from hearts in vivo, during Langendorff-perfusion, and from single SANC. Heart rate variability (HRV) was calculated in the time- and frequency-domains at baseline and in response to pharmacological mediators that interfered with critical processes involved in automaticity (catecholamines, carbachol, ivabradine, zatebradine, ryanodine and thapsigargin). In addition, a novel 2D technique for imaging Ca2+ fluorescence in spontaneously beating, fluo4-AM loaded, patched single sinoatrial nodal cells was developed to investigate the biophysical behaviour of Ca2+ during pacemaking to see if variability in this was responsible for SANC HRV. Results: Under baseline, temperature-stable conditions, levels of HRV were greatest in vivo (human > rat). SANC exhibited slightly lower levels of HRV, whereas HRV levels expressed by Langendorff-perfused hearts were the least (rabbit > rat), although still comprised a significant proportion of the variability witnessed in vivo. Anaesthetising in vivo rabbits decreased HRV to levels similar to those seen in the Langendorff-perfused heart. HRV was decreased by catecholamines and by ryanodine/thapsigargin in the Langendorff heart. Conversely, HRV was increased by carbachol, ivabradine, zatebradine and ryanodine in SANC. Heart rate changes had a marked effect on levels of HRV. 2D Ca2+ imaging of SANC showed that diastolic local Ca2+ releases (LCRs) occurred earlier than previously thought, with early LCRs having characteristics that were distinct from later LCRs. Mean time of occurrence of all the LCRs within a given diastole closely predicted the duration of the cycle. The rate of restitution of the whole cell Ca2+ transient (used as a surrogate for the pumping function of SERCA) in turn closely predicted the mean time of occurrence of LCRs. Tight synchronisation of the electrical activity of the cell with the biophysical behaviour of Ca2+ appeared to predict shorter cycle lengths. Isoprenaline increased LCR amplitude, though did not increase LCR number, size or duration. Isoprenaline caused LCRs to occur earlier, and synchronised their occurrence and the rate of pumping of Ca2+ back into the sarcoplasmic reticulum. Finally, LCRs were found to preferentially recur in certain regions of the cell, dubbed hotspots. Isoprenaline favoured hotspot production. Conclusion: Whilst greatest in vivo, significant HRV exists in spontaneously beating cardiac preparations devoid of a functioning autonomic nervous system. Studies in SANC indicate that the origin of this is likely to be variability in release of LCRs from the SR via ryanodine receptors. This in turn is controlled by SR refilling kinetics via SR Ca2+ pumping. The coupled system of membrane- and Ca2+-pacemaker clocks are so heavily intertwined that myriad factors will come to bear on generating such variability, including the amount of Ca2+ available for pumping and the phosphorylation state of key proteins, to the extent that variability in no one process can take the credit for generating such HRV.

abstract: Following a traumatic brain injury (TBI) 5-50% of patients will develop post traumatic epilepsy (PTE). Pediatric patients are most susceptible with the highest incidence of PTE. Currently, we cannot prevent the development of PTE and knowledge of basic mechanisms are unknown. This has led to several shortcomings to the treatment of PTE, one of which is the use of anticonvulsant medication to the population of TBI patients that are not likely to develop PTE. The complication of identifying the two populations has been hindered by the ability to find a marker to the pathogenesis of PTE. The central hypothesis of this dissertation is that following TBI, the cortex undergoes distinct cellular and synaptic reorganization that facilitates cortical excitability and promotes seizure development. Chapter 2 of this dissertation details excitatory and inhibitory changes in the rat cortex after severe TBI. This dissertation aims to identify cortical changes to a single cell level after severe TBI using whole cell patch clamp and electroencephalogram electrophysiology. The work of this dissertation concluded that excitatory and inhibitory synaptic activity in cortical controlled impact (CCI) animals showed the development of distinct burst discharges that were not present in control animals. The results suggest that CCI induces early "silent" seizures that are detectable on EEG and correlate with changes to the synaptic excitability in the cortex. The synaptic changes and development of burst discharges may play an important role in synchronizing the network and promoting the development of PTE. / Dissertation/Thesis / Masters Thesis Biology 2014