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K D Harris

Publications and source records attributed to K D Harris.

14 recordsLinked to original sources
PubMed2003

Hippocampal network patterns of activity in the mouse.

Genetic engineering of the mouse brain allows investigators to address novel hypotheses in vivo. Because of the paucity of information on the network patterns of the mouse hippocampus, we investigated the electrical patterns in the behaving animal using multisite silicon probes and wire tetrodes. Theta (6-9 Hz) and gamma (40-100 Hz) oscillations were present during exploration and rapid eye movement sleep. Gamma power and theta power were comodulated and gamma power varied as a function of the theta cycle. Pyramidal cells and putative interneurons were phase-locked to theta oscillations. During immobility, consummatory behaviors and slow-wave sleep, sharp waves were present in cornu ammonis region CA1 of the hippocampus stratum radiatum associated with 140-200-Hz "ripples" in the pyramidal cell layer and population burst of CA1 neurons. In the hilus, large-amplitude "dentate spikes" occurred in association with increased discharge of hilar neurons. The amplitude of field patterns was larger in the mouse than in the rat, likely reflecting the higher neuron density in a smaller brain. We suggest that the main hippocampal network patterns are mediated by similar pathways and mechanisms in mouse and rat.

Animals↗
PubMed2001

Temporal interaction between single spikes and complex spike bursts in hippocampal pyramidal cells.

Cortical pyramidal cells fire single spikes and complex spike bursts. However, neither the conditions necessary for triggering complex spikes, nor their computational function are well understood. CA1 pyramidal cell burst activity was examined in behaving rats. The fraction of bursts was not reliably higher in place field centers, but rather in places where discharge frequency was 6-7 Hz. Burst probability was lower and bursts were shorter after recent spiking activity than after prolonged periods of silence (100 ms-1 s). Burst initiation probability and burst length were correlated with extracellular spike amplitude and with intracellular action potential rising slope. We suggest that bursts may function as "conditional synchrony detectors," signaling strong afferent synchrony after neuronal silence, and that single spikes triggered by a weak input may suppress bursts evoked by a subsequent strong input.

Action Potentials↗
PubMed2001

Introducing telemedicine technology to rural physicians and settings.

OBJECTIVE: The researchers investigated rural health providers' perceptions of telemedicine, developed a framework for assessing their readiness to adopt this type of technology, and offered a guide for its implementation. STUDY DESIGN: Qualitative data were collected from semistructured interviews with thematic analysis. POPULATION: The study population included physicians, nurses, and administrative personnel located in 10 health care practices in 4 communities in 3 rural Missouri counties. OUTCOMES MEASURED: The researchers measured how often health providers used telemedicine technology and their perceptions of the advantages, disadvantages, barriers, and facilitators involved in adopting it. RESULTS: Participants varied widely in their perceptions of telemedicine. Providers in practices affiliated with the university's tertiary center were more likely to use it than were those in private practice. Interviews and other data yielded 6 themes related to a provider's receptivity to technological change: These themes were turf, efficacy, practice context, apprehension, time to learn, and ownership. Each theme applies to the computer and videoconferencing components of telemedicine, and each may operate as a perceived barrier or facilitator of change. CONCLUSIONS: Care providers and administrators consider a range of factors, including economic ramifications, efficacy, social pressure, and apprehension, when deciding whether and how fast to adopt telemedicine. Since adopting this technology can be a major change, agencies trying to introduce it into rural areas should take all these factors into account in their approach to health care providers, staff, and communities.

Adult↗
PubMed2000

Intracellular features predicted by extracellular recordings in the hippocampus in vivo.

Multichannel tetrode array recording in awake behaving animals provides a powerful method to record the activity of large numbers of neurons. The power of this method could be extended if further information concerning the intracellular state of the neurons could be extracted from the extracellularly recorded signals. Toward this end, we have simultaneously recorded intracellular and extracellular signals from hippocampal CA1 pyramidal cells and interneurons in the anesthetized rat. We found that several intracellular parameters can be deduced from extracellular spike waveforms. The width of the intracellular action potential is defined precisely by distinct points on the extracellular spike. Amplitude changes of the intracellular action potential are reflected by changes in the amplitude of the initial negative phase of the extracellular spike, and these amplitude changes are dependent on the state of the network. In addition, intracellular recordings from dendrites with simultaneous extracellular recordings from the soma indicate that, on average, action potentials are initiated in the perisomatic region and propagate to the dendrites at 1.68 m/s. Finally we determined that a tetrode in hippocampal area CA1 theoretically should be able to record electrical signals from approximately 1, 000 neurons. Of these, 60-100 neurons should generate spikes of sufficient amplitude to be detectable from the noise and to allow for their separation using current spatial clustering methods. This theoretical maximum is in contrast to the approximately six units that are usually detected per tetrode. From this, we conclude that a large percentage of hippocampal CA1 pyramidal cells are silent in any given behavioral condition.

Action Potentials↗
PubMed2000

Accuracy of tetrode spike separation as determined by simultaneous intracellular and extracellular measurements.

Simultaneous recording from large numbers of neurons is a prerequisite for understanding their cooperative behavior. Various recording techniques and spike separation methods are being used toward this goal. However, the error rates involved in spike separation have not yet been quantified. We studied the separation reliability of "tetrode" (4-wire electrode)-recorded spikes by monitoring simultaneously from the same cell intracellularly with a glass pipette and extracellularly with a tetrode. With manual spike sorting, we found a trade-off between Type I and Type II errors, with errors typically ranging from 0 to 30% depending on the amplitude and firing pattern of the cell, the similarity of the waveshapes of neighboring neurons, and the experience of the operator. Performance using only a single wire was markedly lower, indicating the advantages of multiple-site monitoring techniques over single-wire recordings. For tetrode recordings, error rates were increased by burst activity and during periods of cellular synchrony. The lowest possible separation error rates were estimated by a search for the best ellipsoidal cluster shape. Human operator performance was significantly below the estimated optimum. Investigation of error distributions indicated that suboptimal performance was caused by inability of the operators to mark cluster boundaries accurately in a high-dimensional feature space. We therefore hypothesized that automatic spike-sorting algorithms have the potential to significantly lower error rates. Implementation of a semi-automatic classification system confirms this suggestion, reducing errors close to the estimated optimum, in the range 0-8%.

Action Potentials↗
PubMed1999

Peroxynitrite irreversibly decreases diastolic and systolic function in cardiac muscle.

Much of the damaging action of nitric oxide in heart may be due to its diffusion-limited reaction with superoxide to form peroxynitrite. Direct infusion of peroxynitrite into isolated perfused hearts fails to model the effects of in situ formation because the bulk of peroxynitrite decomposes before reaching the myocytes. To examine the direct effects of peroxynitrite on the contractile apparatus of the heart, we exposed intact and skinned rat papillary muscles to a steady state concentration of 4-microM peroxynitrite for 5 min, followed by a 30-min recovery period to monitor irreversible effects. In intact muscles developed force fell immediately to 26% of initial force, recovering to 43% by 30 min. Resting tension increased by 600% immediately, and was still elevated 500% by 30 min. Nitrotyrosine immunochemistry showed that peroxynitrite can induce tyrosine nitration at low concentrations and is capable of penetrating 200-380 microm into the papillary muscle after a 5-min infusion. Decomposed peroxynitrite had no effect on either intact or skinned muscle developed force or resting tension. Our results show that peroxynitrite directly damages both developed force and resting tension of isolated heart muscle, which can be extrapolated to systolic and diastolic injury in intact hearts.

Animals↗
PubMed1998

Precision in estimating the frequency separation between spectral lines.

It is common to estimate the frequency separation between peaks in a digitized frequency-domain spectrum by fitting an appropriate function to the experimental spectrum using least-squares procedures. In this paper, we assess from first principles the precision associated with such measurements of frequency separation. In addition to the frequency separation between the peaks, other parameters involved in fitting the spectrum are the peak widths, the lineshape functions (Gaussian, Lorentzian, etc.) for the peaks, and the peak amplitudes. The precision also depends on the signal-to-noise ratio and the spacing between adjacent data points in the digitized spectrum. It is assumed that the residuals considered in the least-squares fitting procedure are the differences between the intensities of corresponding digitized data points in the experimental and fitted spectra. Under these conditions, analytical expressions for the precision in peak separation are derived for the following cases: (i) when the amplitudes of two peaks are known and the two peaks have known equal widths; (ii) when the ratio of the amplitudes of two peaks is known, and the widths of the two peaks are known to be equal, but the actual value of the peak width is not known. In each case, the situation with two Gaussian peaks and the situation with two Lorentzian peaks are considered. In all cases, the absolute precision P(eta) in the estimated frequency separation eta between the two peaks is approximated by an equation of the type P(eta) approximately F(eta/Delta, alpha)SK, where Delta is the peak width, alpha is the ratio A2/A1 of amplitudes of the two peaks, S is the signal-to-noise ratio, and K is the density of data points in the frequency-domain spectrum. The form of the function F(eta/Delta, alpha) depends on the type of lineshape (Gaussian or Lorentzian), and depends on which of the parameters A1, A2, and Delta are known independently of the fitting procedure. Attempts to extend our first-principles approach to assess the precision in least-squares estimates of frequency separation between peaks in more complex situations than those discussed above generally lead to analytical expressions that are formidably complicated. In such cases, numerical approaches based on the theoretical framework developed here may be employed to assess the precision in estimating the frequency separation.

Magnetic Resonance Spectroscopy↗
PubMed1997

MDL-28170, a membrane-permeant calpain inhibitor, attenuates stunning and PKC epsilon proteolysis in reperfused ferret hearts.

OBJECTIVES: This paper tests the hypothesis that calpains are activated in the ischemic (I)/reperfused (R) heart and contribute to myocardial stunning. METHODS: Isolated ferret hearts were Langendorff perfused isovolumically, and subjected to 20 min of global I followed by 30 min of R in the presence or absence of 0.2 microM MDL-28170, a membrane-permeant calpain inhibitor. Right trabeculae then were isolated from these hearts, skinned chemically, and pCa(2+)-force curves obtained. Samples of left ventricle were extracted subjected to SDS-PAGE, and Western analyzed for PKC epsilon and PKM epsilon. RESULTS: Perfused ferret hearts exhibit a 43% decline in left ventricular developed pressure during R. Pre-treatment of hearts with MDL-28170 prior to I significantly improves function during R. Trabecular myofilaments from normal hearts have a KD for Ca2+ of 6.27 +/- 0.06; I/R decreased the KD to 6.09 +/- 0.04; trabeculae from I/R hearts pre-treated with MDL-28170 have a KD of 6.28 +/- 0.04. Western analysis shows ferret hearts to contain a single approximately equal to 96 kDa species of PKC epsilon. I/R hearts contain the native PKC epsilon and a approximately equal to 25 kDa smaller species of PKC epsilon which corresponds to PKM epsilon, the calpain proteolyzed form of PKC epsilon. Pre-treatment of I/R hearts with MDL-28170 markedly diminishes PKM epsilon in reperfused hearts. CONCLUSIONS: Mechanical stunning during R is sensitive to MDL-28170. Depressed mechanical function is reflected in a hyposensitization of trabecular myofilaments to Ca2+. Western analysis shows that PKM epsilon is present in R hearts.

Animals↗
PubMed1996

Memory for places: a navigational model in support of Marr's theory of hippocampal function.

In this report we describe a model that applies Marr's theory of hippocampal function to the problem of map-based navigation. Like many others we attribute a spatial memory function to the hippocampus, but we suggest that the additional functional components required for map-based navigation are located elsewhere in the brain. One of the key functional components in this model is an egocentric map of space, located in the neocortex, that is continuously updated using ideothetic (self-motion) information. The hippocampus stores snapshots of this egocentric map. The modeled activity pattern of head direction cells is used to set the best egocentric map rotation to match the snapshots stored in the hippocampus, resulting in place cells with a nondirectional firing pattern. We describe an evaluation of this model using a mobile robot and demonstrate that with this model the robot can recognize an environment and find a hidden goal. This model is discussed in the context of prior experiments that were designed to discover the map-based spatial processing of animals. We also predict the results of further experiments.

Animals↗
PubMed1995

PCR-based analysis of voltage-gated K+ channels in vascular smooth muscle.

Irregularities in K+ currents form the basis of several cardiovascular dysfunctions, among which are arrhythmias and vasospasms. The developmental regulation of voltage-gated K+ channels, however, has been difficult to study. A novel approach was therefore employed to examine these channels in muscle tissue. Primers for a PCR-based analysis were designed using published nucleic acid sequences for voltage-gated K+ channels. Final selection of the primer pairs was based on the homology present in the S4 and H5 transmembrane domains. A specific band was amplified with these primers using RNA isolated from both rat A10 vascular smooth muscle cells and rat heart tissue.

Animals↗
PubMed1995

Representing and understanding geometric features of one-dimensional tunnel structures in solid inclusion compounds.

A computational method is presented for probing geometric, topological, and structural characteristics of one-dimensional tunnel structures in solid inclusion compounds. The method is illustrated for the urea and thiourea inclusion compounds, highlighting important structural differences between the urea and thiourea tunnel structures, and potential areas of application of the methodology are discussed.

Crystallization↗