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P B Manis

Publications and source records attributed to P B Manis.

9 recordsLinked to original sources
PubMed1992

The parameter identification problem for the somatic shunt model.

The somatic shunt model, a generalized version of the Rall equivalent cylinder model, is used commonly to describe the passive electrotonic properties of neurons. Procedures for determining the parameters of the somatic shunt model that best describe a given neuron typically rely on the response of the cell to a small step of hyperpolarizing current injected by an intrasomatic recording electrode. In this study it is shown that the problem of estimating model parameters for the somatic shunt model using physiological data is ill-posed, in that very small errors in measured data can lead to large and unpredictable errors in parameter estimates. If the somatic shunt is assumed to be a real property of the intact neuron, the effects of these errors are not severe when predicting EPSP waveshapes resulting from synaptic input at a given location. However, if the somatic shunt is assumed to be a consequence of a leakage pathway around the recording electrode, and a correction for the shunt is applied, then the instability of the inverse problem can introduce large errors in estimates of EPSP waveshape as a function of synaptic location in the intact cell. Morphological constraints can be used to improve the accuracy of the inversion procedure in terms of both parameter estimates and predicted EPSP responses.

Mathematics↗
PubMed1991

Outward currents in isolated ventral cochlear nucleus neurons.

Neurons of the ventral cochlear nucleus (VCN) perform diverse information processing tasks on incoming activity from the auditory nerve. We have investigated the cellular basis for functional diversity in VCN cells by characterizing the outward membrane conductances of acutely isolated cells using whole-cell, tight-seal, current- and voltage-clamp techniques. The electrical responses of isolated cells fall into two broad categories. Type 1 cells respond to small depolarizations with a regular train of action potentials. Under voltage clamp, these cells exhibit a noninactivating outward current for voltage steps positive to -35 mV. Analysis of tail currents reveals two exponentially decaying components with slightly different voltage dependence. These currents reverse at -73 mV, near the potassium equilibrium potential of -84 mV, and are blocked by tetraethylammonium (TEA). The major outward current in Type I cells thus appears to be mediated by potassium channels. In contrast to Type I cells, Type II cells respond to small depolarizations with only one to three short-latency action potentials and exhibit strong rectification around -70 mV. Under voltage clamp, these cells exhibit a noninactivating outward current with a threshold near -70 mV. Analysis of tail currents reveals two components with different voltage sensitivity and kinetics. A low-threshold current with slow kinetics is partly activated at rest. This current reverses at -77 mV and is blocked by 4-aminopyridine (4-AP) but is only partly affected by TEA. The other component is a high-threshold current activated by steps positive to -35 mV. This current is blocked by TEA, but not by 4-AP. A simple model based on the voltage dependence and kinetics of the slow low-threshold outward current in Type II cells was developed. The model produces current- and voltage-clamp responses that resemble those recorded experimentally. Our results indicate that the two major classes of acoustic response properties of VCN neurons are in part attributable to the types of outward (potassium) conductances present in these cells. The low-threshold conductance in the Type II (bushy) cells probably plays a role in the preservation of information about the acoustic stimulus phase from the auditory nerve to central auditory nuclei involved in low-frequency sound localization.

4-Aminopyridine↗
PubMed1990

Membrane properties and discharge characteristics of guinea pig dorsal cochlear nucleus neurons studied in vitro.

Intracellular recordings were made from neurons of the guinea pig dorsal cochlear nucleus in an in vitro brain slice preparation. The membrane properties of the cells were studied, and the membrane potentials were manipulated by current injection to determine how intrinsic conductances might alter the cell discharge patterns. Eleven cells were marked with Lucifer yellow. Ten of these cells were identified as the large pyramidal cells of layer 2 of this nucleus, and 1 cell was identified as a "vertical" cell in layer 3. Two kinds of action potentials were observed: simple spikes and complex spikes. This report discusses only cells with simple spikes. Simple spiking cells (60/72 recorded cells; all stained cells were simple spiking cells) discharged in a regular fashion with depolarization, and had linear frequency-current relationships up to 2 nA with a mean slope of 116 Hz/nA. The discharge rate was approximately constant throughout the current pulse. Responses of simple spiking cells to depolarizing current steps superimposed on a steady-state membrane hyperpolarization were studied. When the membrane has been held hyperpolarized, small current pulses produce a long-latency regular train of action potentials. Larger current pulses superimposed on membrane hyperpolarization can produce a short-latency action potential followed by a long silent interval (i.e., a long first interspike interval), and finally a regular train of spikes. It is concluded that the membrane conductances of DCN pyramidal cells are capable of generating at least 3 discharge patterns (regular firing, long first spike latency, and long first interspike interval) depending on the state of the membrane potential prior to a depolarizing current step. These responses are similar to the "chopper," "buildup," and "pauser" discharge patterns reported for these cells in vivo in response to tone bursts. The modulation of the intrinsic membrane conductances by membrane polarization and the possible contribution of these conductances to the generation of DCN discharge patterns provide new insights into the mechanisms underlying the responses of DCN cells to acoustic stimuli.

Animals↗
PubMed1989

A fast, high precision and inexpensive analog to digital board for PC-AT or compatible.

We describe a simple and inexpensive circuit for analog data acquisition with high speed and high resolution, for use in an IBM PC-AT or compatible. The circuit is suitable for a wide range of applications in electrophysiology. Features of the circuit include multichannel reading, programmable sampling rate, and direct memory access controlled dual buffering for continuous recording. A program written in the C programming language for control of data acquisition is also given.

Computers↗
PubMed1989

Responses to parallel fiber stimulation in the guinea pig dorsal cochlear nucleus in vitro.

1. Parallel fibers of the guinea pig dorsal cochlear nucleus (DCN) were electrically stimulated at the pial surface of the nucleus in a brain-slice preparation. Extracellular field potentials produced by the parallel fibers and postsynaptic cells, and the response of single units were identified and characterized. Responses were compared with those reported for stimulation of parallel fibers in the cerebellum and to those seen with electrical stimulation of the auditory nerve. 2. Stimulation of the DCN parallel fibers generates a consistent set of extracellular field potentials. In layer 1 of the DCN, a short-latency triphasic wave (P1(1)-N1(1)-P2(1)) is followed by a slower negative wave (N2(1)). The onset phase of the N2(1) often exhibits a small positive notch (P2a1). In layer 2, an initial triphasic wave (P1(2)-N1(2)-P2(2)) is followed by a short-latency negative wave (N2(2)) and a slower positive wave (P3(2)). The N1(2) is approximately coincident with the N1(1), whereas the P3(2) is coincident with N2(1). The falling phase of the P3(2) is sometimes interrupted by a brief negative deflection (N3(2)). These field potentials are similar, but not identical to those reported for parallel fiber stimulation in the cerebellum in vivo (15). These responses differ substantially from those produced in the DCN by electrical stimulation of the auditory nerve (50). 3. Low-calcium solutions and pharmacologic manipulations were used to separate pre- and postsynaptic response components in the field potential records. When the slice is bathed in a low-calcium solution the P2a1, N2(1), N2(2), P3(2), and the brief late deflections are abolished. However, the P1(1)-N1(1)-P2(1) and P1(2)-N1(2)-P2(2) remain unaffected. A similar separation of pre- and postsynaptic components can be achieved with 100 microM adenosine or 0.5 mM kynurenic acid. It is concluded that the P1(1)-M1(1)-P2(1) wave is the compound action potential of the unmyelinated parallel fibers, whereas the longer-latency field potential components are generated postsynaptically. 4. The conduction velocity of the parallel fiber volley was measured to be 0.30 m/s at the pial surface, in a line approximately parallel to the strial axis of the nucleus. Mapping experiments reveal that the spread of the P1(1)-N1(1)-P2(1) is greatest along the strial axis, and more limited in the orthogonal direction. 5. Single units were recorded in layer 2. At a distance of 500-700 microns from the stimulating electrode, the latencies of single-unit discharges fall between 2.5 and 4 ms, at the time of the N2(2).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Goldfish retinotectal transmission in vitro: component current sink-source pairs isolated by varying calcium and magnesium levels.

Field potentials and radial current source-densities (CSDs) evoked by optic tract stimulation were observed in goldfish tectum in vitro. The effects of different concentrations of calcium and magnesium were studied to improve understanding of component events in retinotectal transmission and interpretations of effects of pharmacological agents. Responses were of 3 forms: 'non-synaptic', 'subthreshold', and 'complex.' Subthreshold responses occurred when amplitudes were less than 40% of their maximal levels. They consisted of a sink-source pair with the sink in the superficial optic neuropil and the source 100-150 micron deeper. They were monophasic, rising in 1-2 ms and decaying as simple exponentials with time constants between 3.3 and 4.5 ms. Several other conditions which reduce amplitudes (besides low [Ca2+] and/or high [Mg2+]) produce responses of the subthreshold form. Complex responses, observed when amplitudes were 40-100% of maximal, were characterized by more rapid rise and decay and included, in the most extreme cases, a late, long, low-amplitude sink-source pair of opposite polarity. We propose that the time course of decay of subthreshold responses is determined by the passive cable properties of bi- or multistratified neurons with one dendritic arbor in the optic neuropil and a second arbor 100-250 micron deeper. Complex responses probably include recurrent inhibition to depolarized dendrites of the optic neuropil, latent by 4 ms to the monosynaptic excitation. Pharmacological assessments of retinotectal transmission may be made more precise by using low [Ca2+]/high [Mg2+] media to isolate monosynaptic activity.

Animals↗
PubMed1985

Steady growth cone currents revealed by a novel circularly vibrating probe: a possible mechanism underlying neurite growth.

The rate and direction of neurite growth have been shown in a number of studies to be determined by the distribution of adhesive sites on the growth cone. Recent evidence showing that the application of extrinsic electric fields can redistribute membrane molecules and alter both the rate and direction of neurite growth have raised the question whether endogenous electric fields might be produced by steady currents in growth cones. To investigate this question, we have devised a novel circularly vibrating microprobe capable of measuring current densities in the range of 5 nA/cm2 (near the theorectical limit of sensitivity), with a spatial resolution of 2 micron. The design of this device and the development of a novel algorithm for computing current vectors on-line is described. Using this probe we have found that cultured goldfish retinal ganglion cell growth cones generate steady inward currents at their tips. The measured currents, in the range of 10-100 nA/cm2, appear to flow into the filopodia at their tips and back outward near the junctures of the filopodia and the growth cone. The currents appear to be produced only during active growth. Ion substitution experiments support the conclusion that the majority of this current is carried by Ca2+ ions, which we postulate flow through a population of activated voltage-sensitive Ca2+ channels located on the filopodial tips. Calculation of the transmembrane current density (4 X 10(-6) nA/cm2) leads to an estimate of channel density (10 channels/micron2) in close agreement with the measured density of Ca2+ channels in other systems. The assumption that calcium channel proteins are conveyed to nerve terminals by active transport, whereas sodium channel proteins are conveyed passively by a slower somatofugal diffusion process [Strichartz et al, 1984], would explain why developing neurons tend to display Ca2+-sensitive electrogenesis at their growing tips, and Na+-sensitive action potentials later in development. In order to gain some insight into the possible role of these steady growth currents, we estimated the membrane depolarization and axial voltage gradient they produce. It is likely that the currents produce sufficient membrane depolarization (approximately equal to 4 mV) to cause autogenous activation of ion channel permeabilities. Similarly, the axial voltage gradient (approximately equal to 4 mV/cm) would be expected to move intracytoplasmic vesicles by electrophoresis at a rate (20-40 microns/hr) very close to that at which the filopodia are observed to grow.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1977

Magnification in striate cortex and retinal ganglion cell layer of owl monkey: a quantitative comparison.

Magnification, the relative size of the neural representation of a portion of the visual field, decreases more rapidly with increasing visual field eccentricity in striate cortex than in the retinal ganglion cell layer of the owl monkey (Aotus trivirgatus); the proportion of the cells in striate cortex devoted to central vision is much larger than the comparable proportion of retinal ganglion cells. Magnification in striate cortex is a power function of magnification in the retinal ganglion cell layer. A formula for convergence (ganglion cells to cortical neurons) follows from this relationship.

Animals↗