Discrete sampling of continuous biological signals: analog-to-digital conversion

An integrated multielectrode electrophysiology system

An integrated system for recording and analyzing electrophysiological data from multiple channels is described. The system uses an MS-DOS microcomputer, a 16-channel amplifier, and multiple-tipped electrode arrays designed for use in intact and slice preparations. The system is designed for applications where the collection and analysis of multiple-channel electrophysiological data is desirable, including the construction of current source density (CSD) profiles from field potential data. The software incorporates on-line averaging, CSD and freeze-frame capabilities to guide the experiment in progress. Additional off-line analyses include multiple unit activity, power spectra, and automatic scans of data files for peak amplitude, area, latency, and slope within user-defined latency windows. All data and analyses can be exported to commercial statistical/graphical programs for the creation of publication-ready figures.

Circadian rhythms in hippocampal responsiveness to perforant path stimulation and their relation to behavioral state

Male rats were chronically implanted with electrodes to record the monosynaptic granule cell response in the dentate gyrus of hippocampus to perforant path stimulation while the animals were unrestrained. Samples of the dentate response were collected every 15 min for up to 14 days under various lighting conditions including constant light (LL) and constant darkness (DD). Circadian rhythms in the slope of evoked population EPSPs were found in all records. EPSP rhythms reached peak values during subjective night. Circadian rhythms in the height of the population spike were found in 8 out of the 12 animals studied. Spike rhythms reached peak values during the subjective day at times when EPSPs were at a daily minimum. Rhythms were confirmed statistically by periodogram. Rhythms followed changes in the LD cycle and persisted under LL or DD. The behavioral state associated with each sample was determined by EEG and video records of 4 animals. Day-night differences in EPSPs were found within the active awake, still alert, slow-wave and paradoxical sleep states. Day-night differences in the spike were detected during the still alert and paradoxical sleep states.

Hippocampal field potential: a microcomputer aided comparison of amplitude and integral

A microcomputer based system is described for the analysis of various aspects of hippocampal field potential response recorded in vitro, either in the dendritic or somatic region. A comparison is made between the average amplitude and the time integral of synaptically evoked population spike at the cell body layer, following various intensities of stimuli delivered to the stratum radiatum. There was a good correlation between the two measures at low and intermediate intensities of stimulation. With stimulus intensities beyond those eliciting the population spike of maximal integral, the amplitude of the population spike further increased while its duration decreased. It is concluded that the integral provides a more accurate estimate of the extent of neuronal firing than the amplitude.

Effects of corticosterone on the electrophysiology of hippocampal CA1 pyramidal cells in vitro

Modulation of CA1 field potential amplitudes by normal and stress concentrations of corticosterone (CT) was observed in hippocampal slice preparations from adrenalectomized rats. Slices exposed to CT levels characteristic of a morning (4 nM) or evening (7 nM) resting state showed increased population spike amplitudes in the CA1 pyramidal cell field within 10 min. A stress concentration (15 nM) also increased spike amplitudes, but only at the higher stimulus intensities. The effects of these doses were essentially the same 10 and 60 min after administration. The hormone facilitated responding more in morning resting concentrations than in concentrations characteristic of the evening resting state. This occurred, however, only for relatively low intensity stimuli. The data provide some support for the suggestion that circadian fluctuations in magnitude of long-term potentiation result from corresponding changes in CT level. The rapid onset of the observed changes is difficult to account for in terms of generally accepted mechanisms of receptor binding.