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Biomedical subjects

B C Wheeler

Publications and source records attributed to B C Wheeler.

11 recordsLinked to original sources
PubMed1992

A flexible perforated microelectrode array for extended neural recordings.

A flexible and perforated 32-element planar microelectrode array has been fabricated and used to measure evoked potentials in brain slices. Electrodes are spaced 200 microns apart in a 4 x 8 array and are sandwiched between layers of insulating polyimide. The polyimide sandwich is lifted off its substrate, making it flexible so that it could shape to contoured tissues. Prior to lift off, holes are etched to expose recording sites 15 microns in diameter and to create perforations which allow increased circulation of artificial cerebrospinal fluid to the recording surface of the tissue and, hence, increased viability. Comparisons of evoked potentials measured over time showed an average increase of 10 h to the viability of the slice while using the perforated versus nonperforated arrays.

Animals↗
PubMed1991

Compliance of hippocampal neurons to patterned substrate networks.

Neuronal growth can be controlled in vitro by plating cells at low density and by differential adhesion between the cell and substrate. Primary cultures of rat hippocampal neurons were grown in serum-free culture on polylysine-coated glass coverslips patterned by selective laser ablation so as to leave grids of polylysine with varying linewidths (3, 5, and 10 microns), intersection distance (80, 120, and 160 microns), and nodal (intersection) diameter (5, 10, and 20 microns). Not only did somae strongly prefer the unablated polylysine areas, but they also migrated to loci where the local area of unablated polylysine was higher. These loci were the nodes, as opposed to the narrow connecting paths, and larger nodes, as compared with smaller nodes. Maximum migration to nodes of 88% occurred for a combination of 5-microns path width, 20-microns node diameter, and 80-microns path length. Daily observations indicated active migration to larger adhesive areas, which explains the differential compliance.

Animals↗
PubMed1991

Urinary protein/creatinine ratio before and during pregnancy in women with diabetes mellitus.

Quantitation of urinary protein excretion has traditionally involved collection of a 24-hour urine specimen. Recent reports have suggested that the ratio of protein to creatinine in a single-voided urine specimen may be used as a screening test of proteinuria, obviating the need for a 24-hour urine collection. This study was undertaken to determine whether the urinary protein/creatinine ratio was correlated with 24-hour protein excretion in women with diabetes, to determine whether pregnancy had any effect on the correlation, and to test the accuracy of estimates of 24-hour protein excretion on the basis of the protein/creatinine ratio. We studied 329 24-hour urine specimens from 133 women with classes B through RF diabetes. The protein/creatinine ratio was highly correlated with total protein excretion (r = 0.977, p less than 0.0001). The correlation was not affected by pregnancy, trimester, or preeclampsia. Three methods were used to predict protein excretion on the basis of the ratio. Compared with actual protein excretion, predicted values had mean errors of 19% to 27%; 6% to 13% of predictions were in error by greater than or equal to 50%. Because of these large errors, we conclude that this method of estimating protein excretion has limited value in pregnant women with diabetes.

Creatinine↗
PubMed1989

Two-dimensional current source density analysis of propagation delays for components of epileptiform bursts in rat hippocampal slices.

Recordings of epileptiform burst activity in the CA1 region of the transverse rat hippocampal slices were made with a 32-channel surface electrode array. The 200 microns interelectrode resolution, the simultaneity of the data, and the use of a two-dimensional current source density analysis allowed accurate measurement of population spike peak times. Differences were found in the apparent propagation delays among 3 burst components: the compound action potential (CAP) along the Schaffer collaterals, the first population spike directly driven by the CAP, and the second (and succeeding) population spikes representing the bursting, epileptiform component. Delay measurements were applied to epileptiform bursts recorded in slices treated with picrotoxin (PTX), pentylenetetrazol (PTZ), and 0-Mg2+ medium. In 0-Mg2+ medium all components propagate at nearly the same velocity. In the PTZ and PTX media the second population spike propagated more slowly than the CAP. The first population spike propagated at the same velocity as the CAP for orthodromic Schaffer collateral stimulation. The first population spike propagated at the same, slower velocity as the second spike for antidromic Schaffer collateral stimulation.

Animals↗
PubMed1989

A high-speed multichannel neural data acquisition system for IBM PC compatibles.

An inexpensive 32-channel data acquisition system has been constructed for use in acquiring neuroelectric data from a multiple element electrode array. Direct memory access (DMA) techniques allowed a maximum aggregate sampling rate of 652 ksamples/s, or 20.4 ksamples/s on 32 channels. The 8-bit analog-to-digital (A/D) conversion circuitry lies on a single plug-in card installed in an IBM PC-compatible AT & T 6300 Plus personal computer, although the card may be used in an IBM PC with no reduction in sampling performance. Data have been taken from 32 points on the surface of the rat hippocampal slice preparation. Assembly language graphics routines permitted rapid display of raw and processed data. Signal processing routines can be executed and results can be displayed to provide rapid feedback to an experimenter.

Action Potentials↗
PubMed1988

High-resolution alignment of action potential waveforms using cubic spline interpolation.

A cubic spline interpolation technique is applied to the problem of aligning action potential waveforms. Interpolation is an attractive alternative to sampling at many times the Nyquist rate in order to reduce errors caused by asynchronous sampling of rapidly changing waveforms. Alignment is achieved by locating the peak of the interpolated waveform, which can be found by solving a quadratic equation. The waveform is then reconstructed for comparison with existing templates. The technique was tested using simulated noisy, randomly arriving waveforms, the interpolated signal and alignment time errors being computed as functions of the signal/noise ratio. The spline technique is superior in accuracy to sampling at eight-times the Nyquist rate and is comparable to a Fourier-transform-based interpolation algorithm. It is computationally efficient, requiring approximately five multiplications per sample point. The interpolation concept is extended to the principal component technique for separation of action potential waveforms. The energy function is interpolated and used to align the waveforms, after which the interpolated coefficients can be used for high speed classification. The technique shows an improvement in both alignment error and effective signal/noise ratio in comparison with sampling or interpolation to a voltage peak.

Action Potentials↗
PubMed1988

Multisite hippocampal slice recording and stimulation using a 32 element microelectrode array.

A technique has been developed in which a planar array of 32 microelectrodes, arranged in a 4 by 8 pattern with 200 micron separation, is used to record from and stimulate the hippocampal slice preparation at multiple sites. Control of media flow past the tissue is critical to observe signals and preserve viability. Active suppression circuitry is used to prevent device saturation due to large stimulation artifacts. The field potentials recorded are spatially unique and provide a 2-dimensional description of the underlying population activity in the various pyramidal strata and subpopulations. Multisite stimulation is also possible with the array, permitting the experimenter to quickly stimulate and record from brain slices in many spatial patterns.

Animals↗