The OptoMEA platform: a new tool combining local chemical stimulation with distributed multi-electrode array recordings

We present a novel OptoMEA platform that combines multisite electrical recording with local chemical stimulation. Applying UV light pulses through an array of optical fibres aligned to transparent indium-tin oxide electrodes of an MEA biochip leads to local compound uncaging (e.g. glutamate), thereby stimulating only the tissue/cells around the electrode vicinity. Experimental results obtained using the OptoMEA platform demonstrate its capability to uncage chemical compounds and to locally stimulate neuronal networks, thus providing a significant improvement in spatial control of chemical stimulation. It is expected that this methodology will be useful in facilitating studies of neuronal network systems, and may also find applications in drug screening

OptoMEA: a new tool for combining local optical activation of compounds with distributed MEA recordings

Since their introduction, Micro-Electrode Arrays (MEAs) have been exploited as devices providing distributed information about learning, memory and information processing in a cultured neuronal network, thus changing the field of view from single cell level (glass pipettes) to the scale of the complex network. MEAs represent a growing technology for the study of the functional activity of neuronal networks providing the possibility to gain information about the spatio-temporal dynamics of the network and to allow recordings of electrical activity over periods of time not compatible with conventional electrodes at several sites in parallel. More recently, according to the trend aimed at the reduction of animal tests, MEAs have been exploited as in vitro biosensors to monitor both acute and chronic effects of drugs on neuronal networks in physiological or pathophysiological conditions. On the contrary, the presence of stimulus artefacts and the poorly controlled spread of electrical stimuli in the culture medium limit the applicability of MEAs for neuronal stimulation. Although the problem of artefacts has been recently solved using blanking circuits, the problem of spreading of electrical signals is inherent to the use of electrical stimulations in a conductive volume. Moreover, because neurons are naturally interconnected in complex networks electrical stimuli applied to a region of the network may activate neurons of that region and also fibres of passage coming from neurons of other regions. To overcome these limitations, in addition to electrophysiological techniques, optical methods for the stimulation of neurons have been used for relatively a long time, i.e. by caged compound activation. Here we present the new OptoMEA tool where local light stimulations were obtained switching caged glutamate in the active form by UV light pulses using optical fibres exactly aligned at the MEA electrodes. This tool allows us to activate the network or to deliver other active compounds in specific regions of the network and to monitor their effects on the overall network functioning. This methodology may turn out to be extremely useful for testing the ability of drugs to affect neuronal properties as well as alterations in inter- and intra-neuronal communication

Development and Characterization of PEDOT:PSS/Alginate Soft Microelectrodes for Application in Neuroprosthetics

Reducing the mechanical mismatch between the stiffness of a neural implant and the softness of the neural tissue is still an open challenge in neuroprosthetics. The emergence of conductive hydrogels in the last few years has considerably widened the spectrum of possibilities to tackle this issue. Nevertheless, despite the advancements in this field, further improvements in the fabrication of conductive hydrogel-based electrodes are still required. In this work, we report the fabrication of a conductive hydrogel-based microelectrode array for neural recording using a hybrid material composed of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), and alginate. The mechanical properties of the conductive hydrogel have been investigated using imaging techniques, while the electrode arrays have been electrochemically characterized at each fabrication step, and successfully validated both in vitro and in vivo. The presence of the conductive hydrogel, selectively electrodeposited onto the platinum microelectrodes, allowed achieving superior electrochemical characteristics, leading to a lower electrical noise during recordings. These findings represent an advancement in the design of soft conductive electrodes for neuroprosthetic applications

Spatiotemporal characterization of rhythmic activity in rat spinal cord slice cultures

Rat spinal networks generate a spontaneous rhythmic output directed to motoneurons under conditions of increased excitation or of disinhibition. It is not known whether these differently induced rhythms are produced by a common rhythm generator. To investigate the generation and the propagation of rhythmic activity in spinal networks, recordings need to be made from many neurons simultaneously. Therefore extracellular multisite recording was performed in slice cultures of embryonic rat spinal cords grown on multielectrode arrays. In these organotypic cultures most of the spontaneous neural activity was nearly synchronized. Waves of activity spread from a source to most of the network within 35-85 ms and died out after a further 30-400 ms. Such activity waves induced the contraction of cocultured muscle fibres. Several activity waves could be grouped into aperiodic bursts. Disinhibition with bicuculline and strychnine or increased excitability with high K+ or low Mg2+ solutions could induce periodic bursting with bursts consisting of one or several activity waves. Whilst the duration and period of activity waves were similar for all protocols, the duration and period of bursts were longer during disinhibition than during increased excitation. The sources of bursting activity were mainly situated ventrally on both sides of the central fissure. The pathways of network recruitment from one source were variable between bursts, but they showed on average no systematic differences between the protocols. These spatiotemporal similarities under conditions of increased excitation and of disinhibition suggest a common spinal network for both types of rhythmic activity

Power-law behavior of beat-rate variability in monolayer cultures of neonatal rat ventricular myocytes

It is known that extracardiac factors (nervous, humoral, and hemodynamic) participate in the power-law behavior of heart-rate variability. To assess whether intrinsic properties of cardiac tissue might also be involved, beat- rate variability was studied in spontaneously beating cell cultures devoid of extracardiac influences. Extracellular electrograms were recorded from monolayer cultures of neonatal rat ventricular myocytes under stable incubating conditions for up to 9 hours. The beat-rate time series of these recordings were examined in terms of their Fourier spectra and their Hurst scaling exponents. A non-0 Hurst exponent was found in 21 of 22 preparations (0.39+/-0.09; range, 0.11 to 0.45), indicating the presence of fractal self-similarity in the beat-rate time series. The same preparations exhibited power-law behavior of the power spectra with a power-law exponent of - 1.36+/-0.24 (range, - 1.04 to -1.96) in the frequency range of 0.001 to 1 Hz. Furthermore, it was found that the power-law exponent was nonstationary over time. These results indicate that the power-law behavior of heart-rate variability is determined not only by extracardiac influences but also by components intrinsic to cardiac tissue. Furthermore, the presence of power-law behavior in monolayer cultures of cardiomyocytes suggests that beat-rate variability might be determined by the complex nonlinear dynamics of processes occurring at the level of the cellular network, eg, interactions among a large number of cell oscillators or metabolic regulatory systems

A three-dimensional multi-electrode array for multi-site stimulation and recording in acute brain slices

Several multi-electrode array devices integrating planar metal electrodes were designed in the past 30 years for extracellular stimulation and recording from cultured neuronal cells and organotypic brain slices. However, these devices are not well suited for recordings from acute brain slice preparations due to a dead cell layer at the tissue slice border that appears during the cutting procedure. To overcome this problem, we propose the use of protruding 3D electrodes, i.e. tip-shaped electrodes, allowing tissue penetration in order to get closer to living neurons in the tissue slice. In this paper, we describe the design and fabrication of planar and 3D protruding multi-electrode arrays. The electrical differences between planar and 3D protruding electrode configuration were simulated and verified experimentally. Finally, a comparison between the planar and 3D protruding electrode configuration was realized by stimulation and recording from acute rat hippocampus slices. The results show that larger signal amplitudes in the millivolt range can be obtained with the 3D electrode devices. Spikes corresponding to single cell activity could be monitored in the hippocampus CA3 and CA1 region using 3D electrodes. (C) 2002 Elsevier Science B.V. All rights reserved

Buried microchannels in photopolymer for delivering of solutions to neurons in a network

A simple and efficient technique for the fabrication of buried microfluidic channels is presented. Microchannels made using a contribution of thick liquid and laminated photopolymers are used for the realization of smart microchips for culture, stimulation and recording of neural cell arrays. (C) 1998 Elsevier Science S.A. All rights reserved

Microelectrodes with three-dimensional structures for improved neural interfacing

This paper describes the development of microelectrodes with integrated three-dimensional electrode structures. The integration of three-dimensional structures aims at an improvement of the electrode/tissue interface. Due to the increase in surface area the electrode impedance is reduced, while the density of microelectrodes per area remains the same as with flat electrodes. Two different types of electrodes have been developed: Flexible, implantable microelectrodes with pyramidal, protruding structures and tip-shaped electrode arrays on glass substrates. The protrusion heights of the electrode sites can easily be adjusted depending on the actual application. For the flexible structures we used a polyimide-based process to fabricate microelectrodes with sharp or flat pyramidal tips and with electrode arrangements on front and backside of the devices. The tip-shaped electrode arrays were fabricated from a glass substrate by isotropic wet chemical etching and subsequent metallization and passivation. Data from impedance measurements and acute brain slice recordings indicate a considerable improvement regarding electrode impedance and obtainable signal strength

SpikeOnChip ::a custom embedded platform for neuronal activity recording and analysis

In this paper we present SpikeOnChip, a custom embedded platform for neuronal activity recording and online analysis. The SpikeOnChip platform was developed in the context of automated drug testing and toxicology assessments on neural tissue made from human induced pluripotent stem cells. The system was developed with the following goals: to be small, autonomous and low power, to handle micro-electrode arrays with up to 256 electrodes, to reduce the amount of data generated from the recording, to be able to do computation during acquisition, and to be customizable. This led to the choice of a Field Programmable Gate Array System-On-Chip platform. This paper focuses on the embedded system for acquisition and processing with key features being the ability to record electrophysiological signals from multiple electrodes, detect biological activity on all channels online for recording, and do frequency domain spectral energy analysis online on all channels during acquisition. Development methodologies are also presented. The platform is finally illustrated in a concrete experiment with bicuculline being administered to grown human neuronal tissue through microfluidics, resulting in measurable effects in the spike recordings and activity. The presented platform provides a valuable new experimental instrument that can be further extended thanks to the programmable hardware and software