A new planar multielectrode array: recording from a rat auditory cortex.

In the study of the spatiotemporal properties of the cortex, a demand often arises for recording local field evoked potentials (LFEP) and neural spikes from a quantity of points at close range from each other. In such a situation a device composed of a lot of electrodes assembled in a single bunch would be suitable. Such circumstances gave us the impetus to create the device described in this paper, namely a new planar electrode array for in vivo multisite extracellular recording. The device is made of plastic and includes platinum electrodes 50 microm in diameter. The array of 64 incorporated microelectrodes is placed on the surface of the cortex of anesthetized rats. Recordings could be made through all electrodes for more than 1 h without damage to the cortex. The inter-polar distance is approximately 100 microm so that each individual electrode can record activity from a separate population of neurons near the cortical surface. The recording system described here is highly useful for visualizing spatiotemporal structure of the cortical activities and for imaging dynamic neuronal assemblies.

Chronic multichannel recordings from organotypic hippocampal slice cultures: protection from excitotoxic effects of NMDA by non-competitive NMDA antagonists.

In vitro neuronal damage has traditionally been evaluated by biochemical or anatomical but not by electrophysiological techniques. In the present study, we combined two newly developed technologies, an 8 x 8 multi-electrode array (MED-64) and cultured hippocampal slices, to demonstrate the potential use of electrophysiological measures as index of neuronal damage. We first demonstrated the stability of electrophysiological recordings over prolonged periods of time (up to 14 days) in field CA1 of cultured hippocampal slices following electrical stimulation of the Schaffer collateral pathway. We then assessed the neurotoxic properties of NMDA and AMPA and determined that the time-course, potency, and efficacy of these two neurotoxins were similar to those assessed by other experimental approaches. We also compared the efficacy and potency of two non-competitive NMDA receptor antagonists to protect against NMDA-mediated neurotoxicity. Again, the results matched well with the results obtained from traditional techniques. Thus, this new technology might provide a new and powerful method to study the chronic effects of drugs or other experimental manipulations in an in vitro preparation.

Asymmetrical distribution of the Schaffer projections within the apical dendrites of hippocampal field CA1.

Continuous current source densities were calculated in two dimensions (proximo-distal vs. medio-lateral) from slices of hippocampal field CA1 placed on a 64-electrode array in the presence of GABA blockers. The synaptic sink generated by stimulation of the Schaffer-commissural fibers spread across the extent of field CA1 within the same sublamina of the stratum radiatum as the stimulation electrode. The size and shape of the current sink varied according to the proximo-distal position of the stimulation site. Sinks generated by stimulation close to the cell body layer were more compact when compared to those produced by stimulation near the top of stratum radiatum which were broad and skewed in the proximal direction. These distributions were obtained with stimulation at either the CA3 or the subicular border of CA1. Induction of LTP increased the intensity of the current field but did not notably affect its distribution. It is concluded that (1) axons remain at the same proximo-distal level as they traverse stratum radiatum of CA1 and (2) generate proximally directed collaterals. Because of this, fibers that enter CA1 stratum radiatum immediately above the pyramidal cell bodies form compact synaptic fields while those entering CA1 at the top of the lamina form much broader and asymmetrical distributed fields.

Long-term recording of LTP in cultured hippocampal slices.

Long-term potentiation (LTP) was elicited by high frequency stimulation in hippocampal slices cultured on multi-electrode arrays. LTP lasting more than 1 h was recorded in 75% of slices, and a significant number of slices exhibited a non-decaying LTP that lasted more than 48 h. LTP induction was completely and reversibly blocked by an antagonist of the NMDA receptor, APV. Our results suggest the possibility of using chronic recording in hippocampal slices cultured on multi-electrode arrays to study the mechanisms underlying LTP maintenance and stabilization.