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In JoVE (1)
Other Publications (4)
Articles by Mark Pottek in JoVE
JoVE Neuroscience
Electrophysiological Characterization of GFP-Expressing Cell Populations in the Intact Retina
Department of Neurobiology, University of Oldenburg
This article depicts the recording of individual cells from fluorescently tagged neuronal populations in the intact mouse retina. By using two-photon infrared excitation transgenetically labeled cells were targeted for patch-clamp recording to study their light responses, receptive field properties, and morphology.
Other articles by Mark Pottek on PubMed
Contribution of Connexin26 to Electrical Feedback Inhibition in the Turtle Retina
The first synaptic integration in the neuronal cascade of vision in vertebrates includes a feedback from horizontal cells to cones by a mechanism yet not fully understood. Recent observations in teleosts suggested an electrical feedback mechanism mediated by connexin26 (Cx26) hemichannels at the terminal dendrites of horizontal cells. By using reverse transcription-polymerase chain reaction and immunoblotting from retinal homogenate, we detected Cx26 mRNA transcripts in the turtle retina and demonstrated that they were translated into protein. Cx26 immunoreactivity was especially prominent in the outer plexiform layer. Subcellularly, immunoreactivity was located mainly between horizontal cell axon terminals and in horizontal cell dendrites forming the lateral elements at the ribbon synaptic complex of the cone pedicle. The label was confined to the horizontal cell membrane flanking the ribbon and was not found on the opposing photoreceptor membrane. No gap junctions at this location are known, so immunosignaling suggested the presence of hemichannels. Their relevance to the feedback mechanism was investigated by intracellular recordings from horizontal cells during application of the hemichannel blocker carbenoxolone. Carbenoxolone hyperpolarized the dark membrane potential by about 25 mV, decreased the amplitudes of responses to full-field light flashes, and suppressed the feedback-induced depolarizing inflexion in the response profile. These physiological findings are compatible with the involvement of hemichannels in the feedback between horizontal cells and cones and support the anatomical findings. Together, these data suggest the presence of an electrical feedback mechanism in the turtle retina, which therefore might be a common mechanism at the first visual synapse in vertebrates.
Triangular Neuronal Networks on Microelectrode Arrays: an Approach to Improve the Properties of Low-density Networks for Extracellular Recording
Multi-unit recording from neuronal networks cultured on microelectrode arrays (MEAs) is a widely used approach to achieve basic understanding of network properties, as well as the realization of cell-based biosensors. However, network formation is random under primary culture conditions, and the cellular arrangement often performs an insufficient fit to the electrode positions. This results in the successful recording of only a small fraction of cells. One possible approach to overcome this limitation is to raise the number of cells on the MEA, thereby accepting an increased complexity of the network. In this study, we followed an alternative strategy to increase the portion of neurons located at the electrodes by designing a network in confined geometries. Guided settlement and outgrowth of neurons is accomplished by taking control over the adhesive properties of the MEA surface. Using microcontact printing a triangular two-dimensional pattern of the adhesion promoter poly-D-lysine was applied to the MEA offering a meshwork that at the same time provides adhesion points for cell bodies matching the electrode positions and gives frequent branching points for dendrites and axons. Low density neocortical networks cultivated under this condition displayed similar properties to random networks with respect to the cellular morphology but had a threefold higher electrode coverage. Electrical activity was dominated by periodic burst firing that could pharmacologically be modulated. Geometry of the network and electrical properties of the patterned cultures were reproducible and displayed long-term stability making the combination of surface structuring and multi-site recording a promising tool for biosensor applications.
3D Winding Number: Theory and Application to Medical Imaging
We develop a new formulation, mathematically elegant, to detect critical points of 3D scalar images. It is based on a topological number, which is the generalization to three dimensions of the 2D winding number. We illustrate our method by considering three different biomedical applications, namely, detection and counting of ovarian follicles and neuronal cells and estimation of cardiac motion from tagged MR images. Qualitative and quantitative evaluation emphasizes the reliability of the results.
