Neuron–transistor coupling: interpretation of individual extracellular recorded signals
The electrical coupling of randomly migrating neurons from rat explant brain-stem slice cultures to the gates of non-metallized field-effect transistors (FETs) has been investigated. The objective of our work is the precise interpretation of extracellular recorded signal shapes in comparison to the usual patch-clamp protocols to evaluate the possible use of the extracellular recording technique in electrophysiology. The neurons from our explant cultures exhibited strong voltage-gated potassium currents through the plasma membrane. With an improved noise level of the FET set-up, it was possible to record individual extracellular responses without any signal averaging. Cells were attached by patch-clamp pipettes in voltage-clamp mode and stimulated by voltage step pulses. The point contact model, which is the basic model used to describe electrical contact between cell and transistor, has been implemented in the electrical simulation program PSpice. Voltage and current recordings and compensation values from the patch-clamp measurement have been used as input data for the simulation circuit. Extracellular responses were identified as composed of capacitive current and active potassium current inputs into the adhesion region between the cell and transistor gate. We evaluated the extracellular signal shapes by comparing the capacitive and the slower potassium signal amplitudes. Differences in amplitudes were found, which were interpreted in previous work as enhanced conductance of the attached membrane compared to the average value of the cellular membrane. Our results suggest rather that additional effects like electrodiffusion, ion sensitivity of the sensors or more detailed electronic models for the small cleft between the cell and transistor should be included in the coupling model.
KeywordsElectrophysiology Extracellular recording Neurons Patch clamp Voltage clamp
We acknowledge Prof Dr W. Knoll (Max-Planck-Institute for Polymer Research, Mainz), in whose group this project was initiated. We thank Prof Dr A. Maelicke (Johannes Gutenberg University of Mainz, Germany) and his group for the use of their animal facility, and Mr Lacher, Drs T. Zetterer and W. Staab from the Institute for Microtechnique, Mainz, for the support during fabrication of the FET sensors. We acknowledge the excellent technical support of Mr Müller and Mr Richter and the other members of the electronic laboratory, and Mr Gerstenberg and Mr Christ from the mechanical workshop of the MPI for Polymer Research. This work was funded by the Ministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF), German Ministry of Science and Technologie (project no. 0310895). We thank Dr C. Sprössler for his work in the field of extracellular recording using FET devices and for fruitful discussions during the project.
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