Cornelia Leibrock

Electrical properties of a light-addressable microelectrode chip with high electrode density for extracellular stimulation and recording of excitable cells

A light-addressable microelectrode chip with 3600 TiN electrodes was fabricated. Amorphous silicon (a-Si:H) serves as a photo conductor. The electrodes on the chip are addressed by a laser spot and electrical properties of the system are determined. DC measurements show a dark to bright dynamic of 10(6)-10(7). The AC impedance dynamic @ 1 kHz/100 mV and thus the signal-to-noise-ratio is determined to 60. This value is quite sufficient for electrophysiological measurements. For the first time, recordings from cardiac myocytes are reported using the principle of light-addressing. Measurements were done with a standard laser scan microscope (Zeiss LSM 410).

Functional re-establishment of the perforant pathway in organotypic co-cultures on microelectrode arrays.

Co-cultures of entorhinal cortex (EC) and dentate gyrus (DG) explants are a useful model system to study the formation and stabilization of axonal projections. We adapted this model system to EC-DG co-cultures on microelectrode arrays (MEA) for the characterization of axonal projections on a functional level for days and weeks. EC and DG explants were placed on MEA to allow for the reconstitution of perforant pathway projections. Connections formed were characterized by morphological and electrophysiological analyses to verify characteristic features of perforant pathway signal transmission. Morphological analysis reveals proper projection of EC neurons into the molecular layer of the DG. Examination of synaptic transmission after high frequency stimulation imply unidirectional connections that used glutamate receptors of the AMPA/kainate type as main mediators of excitatory signal transmission. The system was evaluated by the introduction of the NCAM binding peptide C3d. In accordance with in vivo and in vitro experiments C3d modulated signal transmission by NCAM-related mechanisms resulting in morphological re-arrangements.

Netzwerkanalyse erregbarer Zellen

Netzwerkanalyse erregbarer Zellen potentiale im Kilohertzbereich oder langsamere, lokale Feldpotentiale (im Bereich von weniger als einem Kilohertz) abgeleitet werden. Bei letzteren handelt es sich um Summenaktivitäten vieler Zellen. Da mit einigen MEA-Meßsystemen Potentialveränderungen mit über20kHz abgetastet werden können, ist die zeitliche Auflösung der Signale sehr gut und weitaus besser als bei den optischen Meßmethoden. Allerdings ist die räumliche Auflösung durch die Anzahl und Dichte der Elektroden begrenzt. Trotzdem ist eine ortsauflösende Analyse der Signalentstehung und auch eine Bestimmung von Ausbreitungsrichtung und Geschwindigkeit des Signal zwi chen Zellgruppen möglich (Fej tl et al. 1998). (Ko FERENZ: SUBSTRATE-INTEGRATED MICROELECfRODE ARRAYS: TECH OLOGY A D APPLICATIONS, 23.-26.6.1998, NMI REUTLI GEN)