R-3 Repository :: Browsing by Author "Glantz, Raymon M."

Browsing by Author "Glantz, Raymon M."

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A mathematical model of the vagally driven primary pacemaker cell membrane of the SA node of the heart
(1982) Bristow, David Graham; Clark, John W.; Glantz, Raymon M.; Johnson, Don H.
The study of the electrophyslologlcal activity of the SA node of the heart is currently a subject of considerable Interest In the research community. Information regarding the electrical behavior of the SA node Is by no means complete, yet sufficiently detailed Information Is available In the literature to allow the formulation of a reasonably quantitative model of the primary pacemaker cell membrane, and its vagal Innervation. In this study, the well-known McAlIIster-Noble-Tslen model of cardiac Purklnje fiber Is modified to account for the electrical activity of the SA node. To model the effects of vagal activity on the sinus rhythm a muscarinic channel with dynamics as suggested by Purves and Noma et al. has been added to the basic membrane model. The model mimics the published data quite well and Is capable of characterizing the free running behavior of the SA node, as well as Its response to electrotonic and vagal stimulation.
A mathematical reconstruction of the frog atrial action potential based on voltage clamp data
(1983) Robinson, Keith; Clark, John W.; Glantz, Raymon M.; Johnson, Don H.
Recent advances in cardiac electrophysiology have allowed for the preparation of viable single frog atrial cells. These cells have properties which make them ideal for voltage clamp studies. The ionic currents observed under voltage clamp conditons from single frog atrial cells are analyzed with the use of automatic methods programmed on a computer. From the analyzed data, mathematical models are formed which describe the time and voltage dependence of the various ionic currents observed under voltage clamp conditions. These models are then combined, and a membrane action potential is reconstructed based on the analyzed ionic current data. This membrane action potential is then used as input to a nonlinear least-squares fitting routine in an attempt to accurately fit the model to experimental action potential data.
An analysis of an optomotor reflex using methods from control theory, cross-correlation analysis, and information theory
(2003) Miller, Clyde Steven, Jr; Glantz, Raymon M.
This report describes a novel approach to the question of how spike trains encode information. Traditional methods rely on signal processing techniques based on point process theory and focus on the relationship between stimulus and spike train response. Broadly, these methodologies attempt to either: quantify changes in some set of spike train parameters on the assumption that this set expresses the neural code, or reconstruct the stimulus from the spike train. Both are attempts to read spikes directly. But only the biological decoder can actually read spikes. In this new approach, inferences about the code are made only after simultaneously observing both the spike trains and the responsiveness of the target neuron (i.e., the decoder) to the input spike train. The biological decoder in this study is a set of motoneurons that mediate a compensatory optomotor reflex after decoding visually-elicited spike trains from two classes of neurons that synapse onto them. The reflex consists of eyestalk counterrotation in response to apparent motion of the global visual field. The range of behaviorally relevant stimuli is established by characterizing the ratio of eyestalk movement to angular displacement of the stimulus (gain) as several stimulus dimensions are varied. These same stimuli are employed during electrophysiological studies to elicit spike trains under conditions which cause the behavior. Information theoretic calculations quantify the extent to which the behavior and the neuronal ensemble responses can distinguish stimuli and enable direct comparisons between the two types of response. Information theoretic comparisons show that an ensemble of 6 motoneurons can account for the measured behavior. These comparisons also indicate that other sources of visual input probably participate in the pathway. The motoneurons read a rate code from one class of neuronal inputs and an interval code from the other.
Application of distributed arithmetic to digital signal processing
(1979) Chu, Shuni; Burrus, C. Sidney; Glantz, Raymon M.; Johnson, Don H.
Distributed arithmetic trades memory for logic circuits and speed, it is suitable for some fixed computations like the DFT computation and the filter calculation with fixed coefficients. A prime length N DFT computation can be converted to two length (Nl)/2 real convolutions and distributed arithmetic can be applied to these convolution computations. Since all the computations of a prime factor FFT reside in a few short length DFT computations, we can do all the prime factor FFT computations by distributed arithmetic. When the input to a DFT is read, we can save half of the computations of a prime factor FFT algorithm by computing only half of the output without computing the other half and get the other half by the symmetric relation. Using an input index table and an output index table in a prime factor FFT algorithm, we avoid any index calculations for any dimension transform. The transpose form of filter structures using distributed arithmetic have a different arrangement of memory and accumulators from that of direct structures. In software implementation, the transpose structure has the advantage of less process with the input or output data to get the address to address the table in the memory but with the disadvantage of more accumulations when compared to the direct structure. Altogether, an IIR filter with transpose structure will have a little higher speed than that with direct structure when implemented on a microprocessor. Distributed arithmetic reduces the DFT and filter computations to simple and repeated addressing and accumulating operations which can be done by simple logic. A general, external logic can be designed to do both the DFT and filter calculations with a microprocessor.
Decreased transmitter release conferred by a mutation in the slowpoke-encoded calcium-dependent potassium channel gene at the Drosophila neuromuscular junction
(1995) Hillman, Timothy Mark; Glantz, Raymon M.
Using immunocytochemical and electrophysiological methods, the effects of mutations in the structural gene for a calcium activated potassium channel, slowpoke (slo), in Drosophila melanogaster were studied. Anti-horseradish peroxidase was used to visualize the branching of the nerves innervating the body wall muscles. No differences are observed between slo and normal larvae. Defects in synaptic transmission at the neuromuscular junction were analyzed electrophysiologically. slo mutants show significant reductions in transmitter release. Also, slo mutations paired with hyperexcitable mutants (Shaker, ether a go go) and/or pharmacological agents (4-aminopyridine) significantly decrease the high amounts of transmitter release normally observed in these situations. Significant reductions in transmitter release caused by the slo mutation are only observed at low external calcium concentrations. This decrease in transmitter release may be due to reduced neuronal excitability conferred by the slo mutation.
Functional connections between motion detectors in the optic nerve and connective of the crayfish
(1980) Martel, Michael Lee; Glantz, Raymon M.; Sass, Ronald L.; Troelstra, Arne
Results are reported here from experiments in which single unit neural activity was recorded simultaneously from the optic nerve and connective of the crayfish Procombarus clarkli to study functional connections between units responding to movement in visual space. The single unit data was analyzed through computer generated plots of poststimulus time histograms, interspike interval histograms, autocorrelation plots, joint peristimulus time histograms and normal and shifted crosscorrelation plots. In three experiments, discussed here in detail, evidence was obtained for strong functional connections between optic nerve motion detectors and connective motion detectors. In two other experiments, evidence was obtained for strong functional connections between the connective motion detectors and units in the other two classes of crayfish optic nerve visual units: the sustaining units and the dimming units.
Potential fields from cardiac strands of cylindrical geometry
(1984) Ganapathy, Nirmala; Clark, John W.; Glantz, Raymon M.; Figueiredo, Rui J. P. de
This paper deals with the classical forward and inverse volume conductor field problems associated with the isolated active cardiac strand. The Purkinje fiber and the atrial trabeculum are chosen as specific examples of cardiac tissue that may be well modeled by cylindrical geometry. The electrical behavior of these strands is modeled in terms of the electrical activity of an equivalent single cell, with a representative membrane that separates an anisotropic intracellular medium from an isotropic extracellular medium. The isolated single atrial muscle fiber is also studied as an interesting special case. A Potential theory model is developed for the strand, that is based on a solution of Laplace's equation in the media of interest, subject to appropriate boundary conditions. The solution for potential at an arbitrary point in the extracellular medium is in the form of a Fourier integral; the equation is subsequently reformulated into a more convenient computational form using a discrete Fourier transform (DFT) method. Implementation of this method using a Fast Fourier Transform (FFT) technique, results in a fast and efficient numerical algorithm for the calculation of volume conductor potentials. A benefit of this approach is that the classical forward and inverse problems in electrophysiology may be viewed as equivalent filtering problems. Thus not only can volume conductor field potentials at varions distances from the strand be easily and rapidly computed, but given field potential data, good estimates of the action potential waveform can also be obtained provided the signal to noise ratio is adequate.
The role of calcium in light adaptation of the crayfish photoreceptor
(1992) Son, Edward Mun-Song; Glantz, Raymon M.
As previously shown in many other photoreceptors, during prolonged exposure to light, receptor sensitivity (mv/photon catch) declines and the speed of the response (rate of depolarization and rate of repolarization) increases. The functional significance of internal and external calcium in these changes were examined in the crayfish. We show that the response time characteristics depend significantly on the internal calcium level, whereas sensitivity appears to depend on the extracellular calcium. The effect of BAPTA, a calcium chelator, within the photoreceptor was to slow the response kinetics without changing sensitivity. We also examined the role of potassium channel blockers in accounting for BAPTA's effect. Although these blockers displayed similar effects to that of BAPTA, the data fail to provide irrefutable evidence that calcium works through the activation or the deactivation of K$\sp{+}$ conductances alone. Probably (even exclusively), internal calcium also affects the transduction process that precedes the channels openings.
Visual processing in the crayfish medulla
(1990) Pfeiffer-Linn, Cindy L.; Glantz, Raymon M.
The crayfish visual system consists of a neural network which acts to convey and process sensory information to the brain. One previously established pathway in this network involves a class of visual interneuron known as sustaining fibers. These third order interneurons make a functional connection with oculomotor neurons in the brain which mediate a light elicited behavior known as the dorsal light reflex. This behavior represents one of the few sensory examples where the physiological input and behavioral output are known. However, little is known about what type of information is being conveyed and processed to the sustaining fibers from the photoreceptors. As a result, I have used a neuropharmacological approach in this thesis to verify synaptic connections to the sustaining fibers and to analyze the mechanisms of action for conveying visual information. Each cell type analyzed in this study was found to receive two antagonistic neurotransmitter inputs. In two instances, I discovered rather unconventional mechanisms used by the crayfish to generate the cell's light response. One of these occurs in a class of neurons known as tangential cells. Here, acetylcholine initiates the initial hyperpolarizing phase of the light response, whereas gamma-aminobutryric acid is actively responsible for the repolarizing phase of the response. These two antagonistic neurotransmitters were found to act on the exact same set of chloride channels. A second unconventional mechanism is used by the crayfish to generate the sustaining fiber's light response. In this case, two different glutamate receptors act jointly to shape the light response. One type of glutamate receptor (non-NMDA) mediates the initial transient depolarization of the sustaining fiber light response and the subsequent plateau response may be due to activation of a second class of glutamate receptor (NMDA). The results of this pharmacological study elucidated many of the synaptic connections in the crayfish visual system and illustrated the mechanisms of information transfer. These studies have direct implications for a number of general aspects of visual processing such as contrast and motion detection.

Browsing by Author "Glantz, Raymon M."

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