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Physiological basis of pathophysiological brain rhythms

100%
Witte O. W.
Acta Neurobiologiae Experimentalis
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2000
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vol. 60
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issue 2
289-297
EN
Focal epilepsy may be induced acutely in the brain in vivo by measures which reduce inhibition or enhance excitation. Athough the various models involve different mechanisms causing the epilepsy, their epileptiform discharge patterns vary only little. Intracellular analyses in vivo and in vitro reveal that the cellular hallmark of epileptic discharge, the paroxysmal depolarization shift, is followed by a giant hyperpolarization. The latter is comprised of several, overlapping, components with different durations, including calcium dependent potassium currents and GABA dependent inhibitions. Relative reduction of one inhibitory component is compensated by other inhibitory components. In epilepsy caused by reduction of GABAergic inhibition, the absolute duration and amplitude of GABAergic inhibition may even be increased in comparison to the responses following afferent stimulation under control conditions since the excitatory drive of the paroxysmal discharges on the interneurons is strongly increased. In some interictal discharge patterns, the enhanced inhibitions within the focus determine the refractory periods of the focus. The latter is paced by neurons from the perifocal area which show a shorter inibition associated with the interictal epileptic event. The discharge pattern of the focus may switch to other patterns, either spontaneously, or as entrained by external stimulation. Such changes are caused e.g. by progressive potassium accumulations in the extracellular space with critically small intervals of the epileptic events. It is concluded that the epileptiform discharge patterns reflect intrinsic properties of the brain, and do not very well reflect the mechanism of action of the epileptogenic model. The brain is thus equipped with inherent mechanisms which favor rhythmic epileptiform discharges under certain conditions.
2
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Deterministic brain oscillations in the magnetoencephalogram

63%
Kowalik Z. J., Witte O. W.
Acta Neurobiologiae Experimentalis
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2000
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vol. 60
|
issue 2
195-202
EN
Determinism is a special property of some systems and is defined by its state-space behavior in which the trajectories in time never intersect. Whether or not determinism exists in brain activities is a question that may be resolved by analysis of the dynamical properties of the electroencephalogram (EEG) or magnetoencephalogram (MEG). We will show that even though there are strong nonstationarities in most brain behaviors, small epochs of deterministic dynamics can still be observed. We will also show that the local Lyapunov exponents are measures that can demonstrate smooth transitions into these deterministic states.
3
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Spatiotemporal dynamics of astroglial and microglial responses after photothrombotic stroke in the rat brain

45%
Nowicka D., Rogozinska K., Aleksy M., Witte O. W., Skangiel-Kramska J.
Acta Neurobiologiae Experimentalis
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2008
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vol. 68
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issue 2
155-168
EN
The effects of photothrombotic stroke in primary somatosensory cortex on astroglial and microglial activation in various regions of lesioned brain were examined at different time points, using immunohistochemistry and lectin binding. The increase in GFAP expression was observed exclusively in the ipsilateral hemisphere, both in the perilesional area and cortical regions distant from the infarct. This remote increase was detectable up to sixty days after the infarct. Transient GFAP elevation was also found in the hippocampus one day after photothrombosis, whereas it was more prolonged in amygdala, as demonstrated at four days after lesion. In contrast to a widespread astrocytic activation, the microglial response was shortlasting and local, confined to lesion and perilesional area. Widespread and prolonged activation of astrocytes after stroke may provide factors promoting slowly developing recovery processes in the whole brain, while microglial response seems to be involved in local repair and removal of cellular debris.
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