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Biomedical subjects

U Egert

Publications and source records attributed to U Egert.

8 recordsLinked to original sources
PubMed2003

Development of electrical activity in cardiac myocyte aggregates derived from mouse embryonic stem cells.

Embryonic stem cells differentiate into cardiac myocytes, repeating in vitro the structural and molecular changes associated with cardiac development. Currently, it is not clear whether the electrophysiological properties of the multicellular cardiac structure follow cardiac maturation as well. In long-term recordings of extracellular field potentials with microelectrode arrays consisting of 60 substrate-integrated electrodes, we examined the electrophysiological properties during the ongoing differentiation process. The beating frequency of the growing preparations increased from 1 to 5 Hz concomitant to a decrease of the action potential duration and action potential rise time. A developmental increase of the conduction velocity could be attributed to an increased expression of connexin43 gap junction channels. Whereas isoprenalin elicited a positive chronotropic response from the first day of spontaneous beating onward, a concentration-dependent negative chronotropic effect of carbachol only developed after approximately 4 days. The in vitro development of the three-dimensional cardiac preparation thus closely follows the development described for the mouse embryonic heart, making it an ideal model to monitor the differentiation of electrical activity in embryonic cardiomyocytes.

Adrenergic beta-Agonists↗
PubMed2002

MEA-Tools: an open source toolbox for the analysis of multi-electrode data with MATLAB.

Recent advances in electrophysiological techniques have created new tools for the acquisition and storage of neuronal activity recorded simultaneously with numerous electrodes. These techniques support the analysis of the function as well as the structure of individual electrogenic cells in the context of surrounding neuronal or cardiac network. Commercially available tools for the analysis of such data, however, cannot be easily adapted to newly emerging requirements for data analysis and visualization, and cross compatibility between them is limited. In this report we introduce a free open source toolbox called microelectrode array tools (MEA-Tools) for the analysis of multi-electrode data based on the common data analysis environment MATLAB (version 5.3-6.1, The Mathworks, Natick, MA). The toolbox itself is platform independent. The file interface currently supports files recorded with MCRack (Multi Channel Systems, Reutlingen, Germany) under Microsoft Windows 95, 98, NT, and 2000, but can be adapted to other data acquisition systems. Functions are controlled via command line input and graphical user interfaces, and support common requirements for the analysis of local field potentials, extracellular spike activity, and continuous recordings, in addition to supplementary data acquired by additional instruments, e.g. intracellular amplifiers. Data may be processed as continuous recordings or time windows triggered to some event.

Action Potentials↗
PubMed1998

A novel organotypic long-term culture of the rat hippocampus on substrate-integrated multielectrode arrays.

Spatiotemporally coordinated activity of neural networks is crucial for brain functioning. To understand the basis of physiological information processing and pathological states, simultaneous multisite long-term recording is a prerequisite. In a multidisciplinary approach we developed a novel system of organotypically cultured rat hippocampal slices on a planar 60-microelectrode array (MEA). This biohybrid system allowed cultivation for 4 weeks. Methods known from semiconductor production were employed to fabricate and characterize the MEA. Simultaneous extracellular recording of local field potentials (LFPs) and spike activity at 60 sites under sterile conditions allowed the analysis of network activity with high spatiotemporal resolution. To our knowledge this is the first realization of hippocampus cultured organotypically on multi-microelectrode arrays for simultaneous recording and electrical stimulation. This biohybrid system promises to become a powerful tool for drug discovery and for the analysis of neural networks, of synaptic plasticity, and of pathophysiological conditions such as ischemia and epilepsy.

Action Potentials↗
PubMed1994

Extracellular recording in neuronal networks with substrate integrated microelectrode arrays.

A photolithographically produced array of 60 substrate-integrated microelectrodes was used for extracellular recording. Neuronal electrical activity was recorded from chicken retinal ganglion cells with or without stimulation by diffuse light. The retina was removed from chicken embryos of embryonic day 14-18. Only cells recorded from day 18 retina would react to photostimulation, increasing their activity when stimulated, corresponding to the developmental time course of photoreceptor differentiation.

Animals↗
PubMed1993

Graded distribution of the neural 2A10 antigen in the developing chicken retina.

During retinal histogenesis, post-mitotic cells become located in different tissue layers, where they differentiate into distinct cell types. In an attempt to elucidate mechanisms of cell differentiation, we have employed hybridoma technology in conjunction with various in vitro techniques. Here, we present monoclonal antibody 2A10, which binds specifically to the cell surface of neurons and outgrowing neurites. Within the retina 2A10 antigen expression is developmentally regulated being most pronounced during the period of tissue layer formation. Elevated antigen expression is limited to post-mitotic neurons as revealed by labeling with bromodeoxyuridine. Retinal ganglion cells, which are the first neurons to develop, appear not to influence the overall developmental regulation of the antigen in the retina, since elimination of these cells by virtue of optic nerve transection in ovo did not alter the antigen expression. The antigen is distributed in a graded fashion in the radial axis of the retina. Maximal immunoreactivity was found at the inner surface of the retina (optic fiber layer), whereas only minute reactivity was detected in the outermost layer. This graded distribution could possibly be involved in a topographic system providing positional information for differentiating neurons. Operationally, MAb 2A10 is a useful marker for retinal neurons, and provides a tool for establishing pure Müller glia cultures by complement-mediated cytolysis of retinal neurons.

Animals↗
PubMed1992

Crossmodal changes in the somatosensory vibrissa/barrel system of visually deprived animals.

Cats deprived of vision from birth adapt remarkably well to their situation and show little behavioral impairment. They seem to compensate for their lack of vision by relying more on their auditory and tactile senses. We report here that the facial vibrissae, which are most important for tactile orientation in many animals, show supernormal growth in both cats and mice that have been deprived of vision from birth. Furthermore, the whisker representation in the somatosensory cortical barrel field shows a concomitant enlargement in binocularly enucleated mice: individual barrels are expanded in size by up to one-third. The increased use of the vibrissae in visually deprived animals may stimulate both their own growth and, via activation of the respective neural pathways, the expansion of their central representation.

Animals↗
PubMed1990

Effects of NMDA antagonists on developmental plasticity in kitten visual cortex.

The existence of Hebb synapses in the visual cortex of young kittens has long been postulated. A mechanism for the correlation of activity in simultaneously active pre- and postsynaptic neurons could be provided by the properties of the N-methyl-D-aspartate (NMDA) receptor and its associated Ca2+ channel, which opens in a transmitter- and voltage-dependent manner. We have studied the effects on cortical plasticity of blocking NMDA receptors in different ways with competitive and non-competitive NMDA antagonists. In our first approach, the non-competitive NMDA antagonist ketamine, a short-acting dissociative anaesthetic, was injected systemically after each of a series of brief monocular exposures. This procedure prevented the development of an ocular dominance shift towards the experienced eye in the visual cortex. Other short-acting anaesthetics, such as xylazine or methohexital, while providing the same depth of anaesthesia, did not have the same effect on ocular dominance plasticity. We conclude, therefore, that ketamine quite specifically interferes with synaptic consolidation in the visual cortex. In order to establish a role of NMDA receptors for cortical plasticity directly in the visual cortex, we performed another series of experiments: 2-amino-5-phosphono-valerate (APV), a competitive NMDA antagonist, was infused intracortically by means of implanted osmotic minipumps in kittens, which were monocularly deprived for 1-2 weeks. Within a radius of 4-5 mm, the expected ocular dominance shift was prevented or reduced. In addition, however, physiologically determined cell density and responsiveness to visual stimuli were grossly abnormal around the infusion site, and histological cell density was also reduced. Similar effects were found when MK801 (a non-competitive NMDA antagonist) was used in the same type of experiment. The outcome of both experimental approaches makes it very likely that NMDA antagonists somehow interfere with cortical plasticity. Their mode of action, however, remains ambiguous. Although it is quite possible that blocking of the NMDA channel prevents the Hebbian correlative process necessary for synaptic consolidation, more complex effects, such as an interference with a neurotrophic action normally exerted via the NMDA receptor, may have to be taken into account as well.

2-Amino-5-phosphonovalerate↗