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D W Tank

Publications and source records attributed to D W Tank.

At least 55 records · Page 3Linked to original sources
PubMed1991

Presynaptic calcium and serotonin-mediated enhancement of transmitter release at crayfish neuromuscular junction.

Fura-2 microfluorometric measurements of calcium concentrations in excitor motor nerve terminals of the first walking leg of crayfish Procambrus clarkii were made during application of serotonin (5-HT) to examine whether changes in residual calcium concentration or calcium influx are responsible for the 5-HT-induced increase in transmitter release at this synapse. Calcium concentrations and EPSPs were monitored simultaneously during 0.5-Hz and moderate-frequency (3-16 Hz) stimulation before, during, and after a 5-min application of 5-HT at concentrations between 5 and 100 microM. We did not observe a significant increase in resting calcium concentration [Ca2+]i in presynaptic terminals during or after application of 5-HT despite simultaneously recorded excitatory junction potential (EJP) enhancement. Injection of the calcium buffer EGTA to concentrations sufficient to reduce significantly the buildup of frequency-dependent facilitation during trains of action potentials did not reduce 5-HT-mediated EJP enhancement. We therefore conclude that 5-HT does not release calcium from intracellular stores to an extent sufficient to overcome calcium buffering and removal systems. Spontaneous release of transmitter quanta was increased by 5-HT to the same extent in normal and increased-osmolarity saline in the absence of measured changes in [Ca2+]i. Thus, changes in residual calcium cannot explain 5-HT-induced synaptic enhancement. Increasing the action-potential-mediated calcium influx by broadening the spike or by increasing extracellular calcium increased evoked transmitter release and increased the accumulation of calcium during trains of action potentials. However, though 5-HT produced a comparable synaptic enhancement, we found no evidence for increased calcium accumulation during trains of action potentials, suggesting that net calcium influx, buffering, and removal are not affected by 5-HT. Therefore, we conclude that 5-HT's action does not result from effects on calcium metabolism and suggest that it acts on the neurosecretory apparatus to increase the effectiveness of calcium for stimulating release. Furthermore, based on its relatively constant effects on facilitated and unfacilitated action-potential-evoked release and spontaneous transmitter release, we conclude that 5-HT actions are independent of the concentration of calcium that is driving release.

Action Potentials↗
PubMed1990

Postsynaptic NMDA receptor-mediated calcium accumulation in hippocampal CA1 pyramidal cell dendrites.

In the CA1 hippocampal region, intracellular calcium is a putative second messenger for the induction of long-term potentiation (LTP), a persistent increase of synaptic transmission produced by high frequency afferent fibre stimulation. Because LTP in this region is blocked by the NMDA (N-methyl-D-aspartate) receptor antagonist AP5 (DL-2-amino-5-phosphonovaleric acid) and the calcium permeability of NMDA receptors is controlled by a voltage-dependent magnesium block, a model has emerged that suggests that the calcium permeability of NMDA receptor-coupled ion channels is the biophysical basis for LTP induction. We have performed microfluorometric measurements in individual CA1 pyramidal cells during stimulus trains that induce LTP. In addition to a widespread component of postsynaptic calcium accumulation previously described, we now report that brief high frequency stimulus trains produce a transient component spatially localized to dendritic areas near activated afferents. This localized component is blocked by the NMDA receptor antagonist AP5. The results directly confirm the calcium rise predicted by NMDA receptor models of LTP induction.

2-Amino-5-phosphonovalerate↗
PubMed1990

Odour-modulated collective network oscillations of olfactory interneurons in a terrestrial mollusc.

Determination of the dynamical structure of neural circuits--the general principles of how neural activity varies with time and manipulates information--is a prerequisite to understanding their computational function. Rhythmically active or oscillating neural circuits are particularly interesting dynamical structures, as rhythms and oscillations are a prominent feature of mammalian central nervous system electrophysiology. Coherent oscillations by networks of interneurons are observed in the vertebrate olfactory system and have recently been described in mammalian visual cortex. These interneuronal networks display oscillations in local field potential (LFP) and probability of producing action potentials that are highly correlated between subcircuits sharing the same stimulus features. Much less is known about the existence and importance of network oscillations in the higher centres of invertebrates. Here we report that a network of olfactory interneurons in the cerebral ganglion of the terrestrial mollusc Limax maximus also displays coherent oscillations in LFP which are modified by odour input. This dynamical structure could be central to the odour recognition and odour learning ability of Limax.

Action Potentials↗
PubMed1990

Brain magnetic resonance imaging with contrast dependent on blood oxygenation.

Paramagnetic deoxyhemoglobin in venous blood is a naturally occurring contrast agent for magnetic resonance imaging (MRI). By accentuating the effects of this agent through the use of gradient-echo techniques in high fields, we demonstrate in vivo images of brain microvasculature with image contrast reflecting the blood oxygen level. This blood oxygenation level-dependent (BOLD) contrast follows blood oxygen changes induced by anesthetics, by insulin-induced hypoglycemia, and by inhaled gas mixtures that alter metabolic demand or blood flow. The results suggest that BOLD contrast can be used to provide in vivo real-time maps of blood oxygenation in the brain under normal physiological conditions. BOLD contrast adds an additional feature to magnetic resonance imaging and complements other techniques that are attempting to provide positron emission tomography-like measurements related to regional neural activity.

Animals↗
PubMed1989

Optical imaging of calcium accumulation in hippocampal pyramidal cells during synaptic activation.

The dynamic response of nerve cells to synaptic activation and the spatial distribution of biochemical processes regulated by ion concentration are critically dependent on the cell-surface distribution of ion channels. In the hippocampus, intracellular calcium-ion concentration is thought to influence the biochemical events associated with kindling, excitotoxicity, and long-term potentiation. Computer models of hippocampal pyramidal cells also indicate that calcium-channel location influences dynamic characteristics such as bursting. Here, we have used in situ microfluorometric imaging in brain slices to directly measure the spatial distribution of calcium accumulation in guinea-pig CA1 pyramidal cells during trains of orthodromic synaptic stimulation. Calcium accumulation is substantial throughout the entire proximal section of the apical and basal dendrites. Most of this accumulation results from influx through non-NMDA (N-methyl-D-aspartate) voltage-gated calcium channels, and in the apical dendrite it drops steeply as the dendrite enters stratum moleculare, the termination zone of perforant path afferents. These results demonstrate a marked segregation of calcium-channel activity and directly show a spatial distribution of calcium accumulation during orthodromic synaptic activation.

Animals↗
PubMed1989

Sealing cultured invertebrate neurons to embedded dish electrodes facilitates long-term stimulation and recording.

Recently it has become possible to form small networks of synaptically connected identified invertebrate neurons in culture. Using conventional saline-filled glass electrodes, it is difficult to simultaneously stimulate and record from more than 2 or 3 cultured neurons and to perform experiments lasting longer than several hours. We demonstrate that it is possible to overcome these limitations by using planar arrays of electrodes embedded in the bottom of a culture dish. The arrays employ conductive leads and insulation that are transparent, making the dishes compatible with voltage-sensitive dyes and inverted microscopy. Identified neurons from leech Hirudo medicinalis, slug Aplysia californica, and snail Helisoma trivolvis, have been grown on these arrays. Due to their large size (soma diameter 40-200 microns) these neurons form seals over the dish electrodes. Individual electrodes can then be used to stimulate and to record action potentials in the associated neuron. With sealing, action potentials have been recorded simultaneously from many neurons for up to two weeks, with signal-to-noise ratios as large as 500:1. We developed and tested a simple model that describes the voltage waveforms measured with array electrodes. Potentials measured from electrodes under cell bodies were primarily derivatives of the intracellular potential, while those measured from electrodes under axon stumps were primarily proportional to local inward Na+ currents. While it is relatively easy to record action potentials, it is difficult to record postsynaptic potentials because of their small size and slow rate of rise.

Action Potentials↗
PubMed1989

Calcium in motor nerve terminals associated with posttetanic potentiation.

We have used fura-2 fluorescence to study the effects of repetitive stimulation producing posttetanic potentiation (PTP) at crayfish neuromuscular junctions on presynaptic calcium concentration. Fura-2 was injected into the preterminal axon of the excitor motor neuron to the claw opener muscle of a walking leg. Pictures of presynaptic terminals on the muscle surface were obtained with a charge-coupled device camera, ratioed, and converted to spatial images of intracellular calcium concentration. Stimulation of the motor nerve for 7-10 min at 20-33 Hz produced potentiation during the tetanus and PTP following the tetanus. Presynaptic calcium levels in terminal boutons and varicosities rose to about 2 microM during the tetanus and decayed at first rapidly and then slowly back to levels near the initial concentration of about 200 nM. The decay rate of potentiated synaptic transmission was the same as the decay rate of the elevated calcium concentration during the posttetanic period dominated by PTP, when facilitation and augmentation had dissipated. A 13-fold potentiation corresponded to a 500 nM elevation of calcium to about 700 nM. The linear dependence we observed is not consistent with the power law formulation of a residual calcium hypothesis for PTP. During the tetanus, the enhancement of synaptic transmission due to facilitation, augmentation, and potentiation exceeded that expected from the correspondence between PTP and posttetanic calcium levels. This may occur because during the tetanus there is insufficient time for calcium to equilibrate spatially between action potentials, and the submembrane calcium will be higher than the volume-average calcium levels that we detect. Following low-frequency trains (typically 8 Hz for about 35 sec), enhanced synaptic transmission and elevated presynaptic calcium decayed rapidly, within a few seconds. Short high-frequency trains (50-100 Hz for 1-2 min) elicited an additional hours-long elevation of presynaptic calcium, corresponding to, and perhaps responsible for, part of the long-term potentiation of transmission that such stimulation produces at this synapse.

Animals↗
PubMed1988

Functional modulation of the nicotinic acetylcholine receptor by tyrosine phosphorylation.

Tyrosine-specific protein phosphorylation has been implicated in the regulation of cell transformation and proliferation. However, recent studies have shown that the expression of protein tyrosine kinases in adult brain is very high, suggesting that tyrosine-specific protein phosphorylation may also have a role in the regulation of neuronal function. Although a number of substrate proteins are phosphorylated on tyrosine residues, the functional alteration of proteins by tyrosine phosphorylation has previously been convincingly demonstrated only for protein tyrosine kinases. The nicotinic acetylcholine receptor, a neurotransmitter-gated ion channel, is phosphorylated by a protein tyrosine kinase in post-synaptic membranes in vitro and in vivo. We demonstrate here that this tyrosine phosphorylation increases the rate of the rapid phase of desensitization of the nicotinic receptor, as measured by single channel recording of purified nicotinic acetylcholine receptor, when reconstituted in lipid vesicles. These data provide direct evidence for the regulation of ion channel properties by tyrosine phosphorylation. The results, which demonstrate a functional role of tyrosine phosphorylation in the nervous system, suggest a widespread role for tyrosine phosphorylation in neuronal signal transduction.

Animals↗
PubMed1988

Spatially resolved calcium dynamics of mammalian Purkinje cells in cerebellar slice.

Microfluorometric imaging was used to study the correlation of intracellular calcium concentration with voltage-dependent electrical activity in guinea pig cerebellar Purkinje cells. The spatiotemporal dynamics of intracellular calcium concentration are demonstrated during spontaneous and evoked activity. The results are in agreement with hypotheses of dendritic segregation of calcium conductances suggested by electrophysiological experiments. These in vitro slice fluorescence imaging methods are applicable to a wide range of problems in central nervous system biochemical and electrophysiological functions.

Animals↗
PubMed1987

Neural computation by concentrating information in time.

An analog model neural network that can solve a general problem of recognizing patterns in a time-dependent signal is presented. The networks use a patterned set of delays to collectively focus stimulus sequence information to a neural state at a future time. The computational capabilities of the circuit are demonstrated on tasks somewhat similar to those necessary for the recognition of words in a continuous stream of speech. The network architecture can be understood from consideration of an energy function that is being minimized as the circuit computes. Neurobiological mechanisms are known for the generation of appropriate delays.

Animals↗
PubMed1986

Computing with neural circuits: a model.

A new conceptual framework and a minimization principle together provide an understanding of computation in model neural circuits. The circuits consist of nonlinear graded-response model neurons organized into networks with effectively symmetric synaptic connections. The neurons represent an approximation to biological neurons in which a simplified set of important computational properties is retained. Complex circuits solving problems similar to those essential in biology can be analyzed and understood without the need to follow the circuit dynamics in detail. Implementation of the model with electronic devices will provide a class of electronic circuits of novel form and function.

Action Potentials↗
PubMed1986

Expression of membrane currents in rat diencephalic neurons in serum-free culture.

The whole-cell gigaseal voltage clamp technique has been used to investigate the timing of expression and type of voltage-dependent ionic currents in dissociated primary cultures of fetal rat (E17) diencephalic neurons grown in a serum-free defined medium. The expression of membrane currents varied among cells at any particular time in culture. Despite this variability, certain characteristics of the appearance of ionic currents emerge from this study. These are: (i) the earliest appearing membrane current is a voltage-dependent outward current carried by K+. In some cells, it is the classical delayed rectifier current, whereas in others it is the transient outward current (IA). (ii) The earliest appearing inward current is carried by Na+. In some cells the channels are first expressed in the neurites and then in or near the cell body. The early neuritic Na+ channels are blocked by cobalt or cadmium as well as by tetrodotoxin (TTX). In others, the early Na+ channels appear in or near the cell body and are only blocked by TTX. (iii) With additional time in culture, a majority of cells exhibit a Ca2+ current at the time of Na+ channel appearance in or near the cell body as well as a transient Ca2+-dependent outward current. The Ca2+ current is only a small fraction of the total inward current. These inward currents show the classical pharmacologic profile. The complex pattern of expression of ionic current may reflect multiple populations of neurons with different developmental sequences resulting from differences in cell age and lineage.

Action Potentials↗
PubMed1985

"Neural" computation of decisions in optimization problems.

Highly-interconnected networks of nonlinear analog neurons are shown to be extremely effective in computing. The networks can rapidly provide a collectively-computed solution (a digital output) to a problem on the basis of analog input information. The problems to be solved must be formulated in terms of desired optima, often subject to constraints. The general principles involved in constructing networks to solve specific problems are discussed. Results of computer simulations of a network designed to solve a difficult but well-defined optimization problem--the Traveling-Salesman Problem--are presented and used to illustrate the computational power of the networks. Good solutions to this problem are collectively computed within an elapsed time of only a few neural time constants. The effectiveness of the computation involves both the nonlinear analog response of the neurons and the large connectivity among them. Dedicated networks of biological or microelectronic neurons could provide the computational capabilities described for a wide class of problems having combinatorial complexity. The power and speed naturally displayed by such collective networks may contribute to the effectiveness of biological information processing.

Animals↗
PubMed1985

Electric field-induced redistribution and postfield relaxation of low density lipoprotein receptors on cultured human fibroblasts.

The lateral mobility of unliganded low density lipoprotein-receptor (LDL-R) on the surface of human fibroblasts has been investigated by studying the generation and relaxation of concentration differences induced by exposure of the cultured cells to steady electric fields. The topographic distribution of receptors was determined by fluorescence microscopy of cells labeled with the intensely fluorescent, biologically active LDL derivative dioctadecylindolcarbocyanine LDL (dil(3)-LDL), or with native LDL and anti-LDL indirect immunofluorescence. Exposure of the LDL-receptor-internalization defective J. D. cells (GM2408A) to an electric field of 10 V/cm for 1 h at 22 degrees C causes greater than 80% of the cells to have an asymmetric distribution of LDL-R; receptors accumulate at the more negative pole of the cell. In contrast, only 20% of LDL-internalization normal GM3348 cells exposed to identical conditions have asymmetrical distributions. Phase micrographs taken during electric-field exposure rule out cell movement as the responsible mechanism for the effect. In both cell types, postfield labeling with the F-actin-specific fluorescent probe nitrobenzoxadiazole-phallacidin shows that no topographic alteration of the actin cytoskeleton accompanies the redistribution of cell surface LDL-Rs, and indirect immunofluorescence labeling of the coat protein clathrin shows that coated pits do not redistribute asymmetrically. Measurements of the postfield relaxation in the percentage of GM2408A cells showing an asymmetric distribution allow an estimate of the effective postfield diffusion coefficient of the unliganded LDL-R. At 37 degrees C, D = 2.0 X 10(-9) cm2/s, decreasing to 1.1 X 10(-9) cm2/s at 22 degrees C, and D = 3.5 X 10(-10) cm2/s at 10 degrees C. These values are substantially larger than those measured by photobleaching methods for the LDL-R complexed with dil(3)-LDL on intact cells, but are comparable to those measured on membrane blebs, and are consistent with diffusion coefficients measured for other unliganded integral membrane receptor proteins by postfield-relaxation methods.

Cell Membrane↗
PubMed1983

Patch-recorded single-channel currents of the purified and reconstituted Torpedo acetylcholine receptor.

Small unilamellar vesicles containing purified and reconstituted nicotinic acetylcholine receptors from Torpedo electroplax have been fused by a simple freeze-thaw procedure to form large liposomes. Giga-seal patch-recording techniques were used to form isolated patches of liposome-membrane and to measure single-channel properties of the reconstituted receptor-ion channel complex. The observed properties are quantitatively similar to those reported for vertebrate muscle nicotinic acetylcholine receptor species recorded in situ. The results demonstrate that the pentameric complex consisting of the alpha 2 beta gamma delta subunits is fully functional. The methods used in these experiments should be useful in studying the effects of chemical alterations on the properties of acetylcholine receptor channels as well as other types of purified and reconstituted ion channels.

Animals↗
PubMed1982

Lateral diffusion of gramicidin C in phospholipid multibilayers. Effects of cholesterol and high gramicidin concentration.

We have measured the lateral diffusion coefficient (D), of active dansyl-labeled gramicidin C (DGC), using the technique of fluorescence photobleaching recovery, under conditions in which the cylindrical dimer channel of DGC predominates. In pure, hydrated, dimyristoylphosphatidylcholine (DMPC) multibilayers (MBL), D decreases from 6 X 10(-8) cm2/s at 40 degrees C to 3 X 10(-8) cm2/s at 25 degrees C, and drops 100-fold at 23 degrees C, the phase transition temperature (Tm) of DMPC. Above Tm, addition of cholesterol decreases D; a threefold stepwise drop occurs between 10 and 20 mol %. Below Tm, increasing cholesterol increases D; a 10-fold increase occurs between 10 and 20 mol % at 21 degrees C, between 20 and 25 mol % at 15 degrees C, and between 25 and 30 mol % at 5 degrees C. In egg phosphatidylcholine (EPC) MBL, D decreases linearly from 5 X 10(-8) cm2/s at 35 degrees C to 2 X 10(-8) cm2/s at 5 degrees C; addition of equimolar cholesterol reduces D by a factor of 2. Thus this transmembrane polypeptide at low membrane concentrations diffuses quite like a lipid molecule. Its diffusivity in lipid mixtures appears to reflect predicted changes of lateral composition. Increasing gramicidin C (GC) in DMPC/GC MBL broadened the phase transition, and the diffusion coefficient of the lipid probe N-4-nitrobenzo-2-diazole phosphatidylethanolamine (NBD-PE) at 30 degrees C decreases from 8 X 10(-8) cm2/s below 5 mol % GC to 2 X 10(-8) cm2/s at 14 mol % GC; D for DGC similarly decreases from 4 X 10(-8) cm2/s at 2 mol % GC to 1.4 X 10(-8) cm2/s at 14 mol % GC. Hence, above Tm, high concentrations of this polypeptide restrict the lateral mobility of membrane components.

Cholesterol↗
PubMed1982

Unconstrained lateral diffusion of concanavalin A receptors on bulbous lymphocytes.

The lateral diffusion coefficient, D, of concanavalin A receptors and receptor complexes on the surface of lymphocytes and RDM4 lymphomas is enhanced by several orders of magnitude to D greater than 5 X 10(-9)cm2/sec by induction of swelling of the cells to bulbous form. Treatments with concanavalin A or 7-nitrobenz-2-oxa-1,3-diazole-phallacidin induce blebs and the bulbous form. The resulting separation of the plasma membrane from most of the F-actin cytoskeleton is accompanied by release of constraints on lateral diffusion of the cell surface receptors, which allows the diffusivity of these glycoproteins to increase nearly to the limit allowed by membrane viscosity.

Actins↗