Push-pull Manner Research Articles

Columnar neurons support saccadic bar tracking in Drosophila.

Tracking visual objects while maintaining stable gaze is complicated by the different computational requirements for figure-ground discrimination, and the distinct behaviors that these computations coordinate. Drosophila melanogaster uses smooth optomotor head and body movements to stabilize gaze, and impulsive saccades to pursue elongated vertical bars. Directionally selective motion detectors T4 and T5 cells provide inputs to large-field neurons in the lobula plate, which control optomotor gaze stabilization behavior. Here, we hypothesized that an anatomically parallel pathway represented by T3 cells, which provide inputs to the lobula, drives bar tracking body saccades. We combined physiological and behavioral experiments to show that T3 neurons respond omnidirectionally to the same visual stimuli that elicit bar tracking saccades, silencing T3 reduced the frequency of tracking saccades, and optogenetic manipulation of T3 acted on the saccade rate in a push-pull manner. Manipulating T3 did not affect smooth optomotor responses to large-field motion. Our results show that parallel neural pathways coordinate smooth gaze stabilization and saccadic bar tracking behavior during flight.

Understanding Inter-Arm Imbalance in Mach–Zehnder Silicon Optical Modulators: Impact on OMA and Frequency Chirp

Characteristic variations caused by nonuniformities in the fabrication process are inevitable in Mach–Zehnder (MZ) silicon optical modulators. However, it is unknown how inter-arm imbalance in phase shifters that have a voltage dependence impacts device performance with respect to the optical modulation amplitude (OMA) and chirp parameter in a push-pull manner. This paper investigates this issue in carrier-depletion MZ silicon optical modulators. First, a generalized form of the large-signal modulation efficiency (ME) is used to characterize the inter-arm imbalance and quantify its impact on the OMA penalty in terms of the phase shift. This theoretical treatment is then validated experimentally by using a fully-automated wafer-level system to evaluate the extinction ratio (ER) on a 300-mm silicon-on-insulator (SOI) wafer. It is shown that the OMA penalty in terms of the absorption loss can suitably be quantified by using an evaluation methodology that treats the absorption losses in each arm separately. In addition, a generalized form of the chirp parameter is formulated that distinguishes its sources between the nonlinearities in ME and absorption loss and their inter-arm imbalance. The parameter is further evaluated over the entire wafer. The formulation is also applied to the dual-drive regime with an adjustable chirp and the increase in negative chirp at the expense of the OMA penalty is quantitatively discussed.

LLSVPs of primordial origin: Implications for the evolution of plate tectonics

Today's large low shear velocity provinces (LLSVPs) are assumed to be compositionally dense leftovers from the magma-ocean phase that are formed to dense accumulations (piles) by mantle flow. Due to the stabilising effect of dense material on mantle convection, LLSVPs could be of major importance for the evolution of plate tectonics.Here, we examine the influence of dense primordial material using thermochemical mantle convection models with self-consistent plate generation. Our results show that the general evolutionary path from a stagnant lid to an episodic to a permanently mobile stage is almost unaffected by dense LLSVP-like structures. The stabilising effect of a dense basal layer, however, leads to delayed surface mobilisation events. In particular, we find a prolonged episodic stage and a later emergence of continuously moving surface plates. Mobilisation episodes occur when the rigid surface breaks in either a top-down (by downwellings), a bottom-up (by upwellings) or a mixed, push-pull manner. As dense material is constantly entrained by rising currents, the stabilising effect decreases with time. Consequently, we observe a change of the mechanism which triggers a surface mobilisation from top-down to late push-pull, then bottom-up and finally push-pull if the stabilising effect is decreased.Our results suggest that, for LLSVP-like volumes and density contrasts, plate mobilisation is triggered by mantle upwellings, either directly in a bottom-up manner or delayed after a long phase of stagnant lid convection (late push-pull). Generally, a primordial dense layer has a profound impact: continuous plate motion as known today is strongly delayed and early Earth plate tectonics most likely acted in an episodic manner.

Neuronal Circuits That Control Rhythmic Pectoral Fin Movements in Zebrafish.

The most basic form of locomotion in limbed vertebrates consists of alternating activities of the flexor and extensor muscles within each limb coupled with left/right limb alternation. Although larval zebrafish are not limbed, their pectoral fin movements exhibit the following fundamental aspects of this basic movement: abductor/adductor alternation (corresponding to flexor/extensor alternation) and left/right fin alternation. Because of the simplicity of their movements and the compact neural organization of their spinal cords, zebrafish can serve as a good model to identify the neuronal networks of the central pattern generator (CPG) that controls rhythmic appendage movements. Here, we set out to investigate neuronal circuits underlying rhythmic pectoral fin movements in larval zebrafish, using transgenic fish that specifically express GFP in abductor or adductor motor neurons (MNs) and candidate CPG neurons. First, we showed that spiking activities of abductor and adductor MNs were essentially alternating. Second, both abductor and adductor MNs received rhythmic excitatory and inhibitory synaptic inputs in their active and inactive phases, respectively, indicating that the MN spiking activities are controlled in a push-pull manner. Further, we obtained the following evidence that dmrt3a-expressing commissural inhibitory neurons are involved in regulating the activities of abductor MNs: (1) strong inhibitory synaptic connections were found from dmrt3a neurons to abductor MNs; and (2) ablation of dmrt3a neurons shifted the spike timing of abductor MNs. Thus, in this simple system of abductor/adductor alternation, the last-order inhibitory inputs originating from the contralaterally located neurons play an important role in controlling the firing timings of MNs.SIGNIFICANCE STATEMENT Pectoral fin movements in larval zebrafish exhibit fundamental aspects of basic rhythmic appendage movement: alternation of the abductor and adductor (corresponding to flexor-extensor alternation) coupled with left-right alternation. We set out to investigate the neuronal circuits underlying rhythmic pectoral fin movements in larval zebrafish. We showed that both abductor and adductor MNs received rhythmic excitatory and inhibitory synaptic inputs in their active and inactive phases, respectively. This indicates that MN activities are controlled in a push-pull manner. We further obtained evidence that dmrt3a-expressing commissural inhibitory neurons exert an inhibitory effect on abductor MNs. The current study marks the first step toward the identification of central pattern generator organization for rhythmic fin movements.

Activated L-Type Calcium Channels Inhibit Chemosensitized Nematocyst Discharge from Sea Anemone Tentacles.

Because in vivo nematocyst discharge requires extracellular Ca2+, Ca2+ channels have been suspected to be involved; but their identity and role have not been revealed. The majority of nematocysts that discharge from sea anemone tentacles are under the control of sensitizing chemoreceptors for N-acetylated sugars (e.g., N-acetylneuraminic acid). Activated chemoreceptors predispose contact-sensitive mechanoreceptors to trigger discharge. We show that activating L-type Ca2+ channels inhibits N-acetylneuraminic acid-sensitized discharge, contrary to a previous suggestion. In addition, inhibiting L-type channels increases sensitivity to N-acetylneuraminic acid. Specifically, we show that the L-type Ca2+ channel activator (-)-Bay K 8644 dose-dependently inhibits N-acetylneuraminic acid-sensitized discharge, as does raising ambient Ca2+ levels. We also show that lowering extracellular Ca2+ levels or adding any of several selective and chemically distinct L-type Ca2+ channel blockers, including dihydropyridines, dose-dependently increases N-acetylneuraminic acid sensitivity and broadens the dynamic range of N-acetylneuraminic acid sensitization. Consistent with these functional findings, Aiptasia pallida expresses an L-type Ca2+ channel α subunit transcript that encodes a conserved dihydropyridine-binding site. Phylogenetic analysis confirms a close relationship of the Aiptasia Ca2+ channel α subunit sequence between anemones, anthozoans, and cnidarians that extends into protostomal and deuterostomal bilaterians. We conclude that L-type Ca2+ channel activity modulates N-acetylneuraminic acid-sensitized nematocyst discharge in a push-pull manner depending on channel activity state. Our findings suggest that L-type channel activation promotes chemosensory desensitization, and we predict that N-acetylneuraminic acid chemoreceptor signaling will activate L-type channels.

Discovery of a novel ortho-haloacetophenones-specific carbonyl reductase from Bacillus aryabhattai and insight into the molecular basis for its catalytic performance

To exploit robust biocatalysts for chiral 1-(2-halophenyl)ethanols synthesis, an ortho-haloacetophenones-specific carbonyl reductase (BaSDR1) gene from Bacillus aryabhattai was cloned and expressed in Escherichia coli. The impressive properties regarding BaSDR1 application include preference for NADH as coenzyme, noticeable tolerance against high cosubstrate concentration, and remarkable catalytic performance over a broad pH range from 5.0 to 10.0. The optimal temperature was 35 °C, with a half-life of 3.1 h at 35 °C and 0.75 h at 45 °C, respectively. Notably, BaSDR1 displayed excellent catalytic performance toward various ortho-haloacetophenones, providing chiral 1-(2-halophenyl)ethanols with 99% ee for all the substrates tested. Most importantly, the docking results indicated that the enzyme-substrate interactions and the steric hindrance of halogen atoms act in a push-pull manner in regulating enzyme catalytic ability. These results provide valuable clues for the structure-function relationships of BaSDR1 and the role of halogen groups in catalytic performance, and offer important reference for protein engineering and mining of functional compounds.

Design and Analysis of a Dual-Slope Inductance-to-Digital Converter for Differential Reluctance Sensors

A new, simple, and high accuracy dual slope inductance-to-digital converter (DSIDC) suitable for differential reluctance sensors is presented in this paper. Differential reluctance sensors have two inductors that vary in a push-pull manner with respect to measurand. In many such sensors, the relationship between inductance and measurand is nonlinear. It is known that a small linear range can be obtained by taking the difference between the values of the sensor inductances. The proposed DSIDC accepts the sensor inductances having nonlinear characteristics and provides a linear digital output directly proportional to the measurand [without employing a dedicated analog-to-digital converter (ADC)]. The output of the DSIDC is linear for the full range of the sensor. As the output is in digital form, it can be easily stored and processed in a digital system. The DSIDC is based on dual-slope ADC principle and possesses many advantages. The effect of various parameters on the performance of the DSIDC was analyzed, quantified, and presented in this paper. A prototype DSIDC has been built and tested with a differential variable reluctance based displacement transducer. Output from the DSIDC was linear for the full range of input.

Temporal Production Signals in Parietal Cortex

Author SummaryOne advantage of studying sensory systems is that external stimuli can be readily controlled and quantified. Our internal perception of time, however, is not as easily approachable. To address this challenge, we developed a task that leverages our knowledge of the neuronal circuits underlying eye movements. Monkeys were trained to move their eyes consistently at regular time intervals without any external cueing or immediate expectation of reward. The animals were remarkably precise and consistent in their timing. Recordings from individual lateral intraparietal area (LIP) neurons, an area associated with eye movement planning, showed a linear decrease in activity between eye movements. This contrasts with previous studies that have reported increases in LIP activity immediately prior to eye movements and suggests that expectation of reward may have influenced such results. We also found that variations in this decreasing activity were predictive of the animals’ timing. Finally, we demonstrate through a simple model that LIP activity was sufficiently precise to completely explain the timing of the animals' actions. The model demonstrates that a precise internal sense of time can arise by comparing activity across different neuronal populations.

Bang-bang optimality of energy efficient spikes in single neuron models

Event Abstract Back to Event Bang-bang optimality of energy efficient spikes in single neuron models Biswa Sengupta1*, Martin Stemmler2, Jeremy Niven1, Andreas Herz2 and Simon Laughlin1 1 University of Cambridge, United Kingdom 2 LMU Munich , BCCN Munich, Germany About 50-80% of the total energy allocated to the mammalian brain is used for signaling, mainly to drive the $Na^+$/ $K^+$ pump (Attwell & Laughlin, 2001). Due to the substantial contribution of action potentials to the energy consumption, the biophysical properties generating an action potential can be matched to make them energy efficient (Alle et al., 2009). By combining different voltage-dependent ionic conductances with varying biophysical properties, different neurons express a myriad of action potential shapes characterized by varying heights and widths (Bean, 2007). How widespread are energy efficient action potentials and what are the major factors defining the energy efficiency of a single action potential ? The passive electric properties of a neuron, namely its capacitance and input resistance, set a lower bound for the cost of a given action potential. Inward ( $Na^+$) and outward ($K^+$) voltage-dependent currents act in a push-pull manner to change the voltage; these currents will invariably overlap, which can cause the energetic cost to rise to more than eleven-fold the baseline cost. We use seven single compartment models to assess the energy cost of vertebrate (cerebellar granule neurons, cortical interneurons, thalamo-cortical relay neurons and hippocampal interneurons) and invertebrate (squid axons, crab axons and bee kenyon cells) action potentials. We show that the energy consumption of a single action potential is directly dependent on the overlap between the $Na^+$ and $K^+$ currents that generate them. By optimizing the ionic conductance parameters that affect this overlap, we investigate how close each neuron type is to the minimal energy expenditure. Using sensitivity analysis and perturbation theory for periodic systems we show that an optimal model minimizes the overlap between $Na^+$ and $K^+$ currents. Just as in optimal control theory, the ionic conductance parameters allow for a bang-bang control of the underlying $Na^+$ and $K^+$ currents eliciting the action potential. Energy efficient action potentials are neuron-dependent but generally have narrower width, shorter height and exhibit an extremely rapid, explosive onset. Our modeling shows that in some neurons, such as the thalamo-cortical relay neurons, the hippocampal GABAergic interneurons or fast-spiking cortical interneurons, the properties of the currents that minimize the energy cost of the action potential are close to the experimentally measured currents, suggesting selection for reducing the energy costs. The experimentally observed properties of the squid giant axon model however, consumes substantial energy when compared to the optimal model that consumes far lower energy. We suggest that the deviation between the parameters generating the theoretical minimum cost of the action potential and those observed in neurons is dependent upon the function of the neuron. Conference: Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010. Presentation Type: Poster Presentation Topic: Poster session II Citation: Sengupta B, Stemmler M, Niven J, Herz A and Laughlin S (2010). Bang-bang optimality of energy efficient spikes in single neuron models. Front. Neurosci. Conference Abstract: Computational and Systems Neuroscience 2010. doi: 10.3389/conf.fnins.2010.03.00085 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 20 Feb 2010; Published Online: 20 Feb 2010. * Correspondence: Biswa Sengupta, University of Cambridge, Paris, United Kingdom, bs393@cam.ac.uk Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Biswa Sengupta Martin Stemmler Jeremy Niven Andreas Herz Simon Laughlin Google Biswa Sengupta Martin Stemmler Jeremy Niven Andreas Herz Simon Laughlin Google Scholar Biswa Sengupta Martin Stemmler Jeremy Niven Andreas Herz Simon Laughlin PubMed Biswa Sengupta Martin Stemmler Jeremy Niven Andreas Herz Simon Laughlin Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Enhanced Dynamic Range in a Directly Modulated Analog Photonic Link

We demonstrate a directly modulated analog photonic link (APL) capable of a high multioctave spurious-free dynamic range (SFDR). The APL consists of a pair of laser diodes, modulated in a push-pull manner, and a balanced photodetector aiming at suppressing the second-order intermodulation distortion (IMD2). In a wide frequency range of 600 MHz (2.60-3.20 GHz), an IMD2 suppression as high as 23 dB and an improvement of 5-18 dB of the second-order SFDR, relative to a conventional single arm photonic link, have been achieved. In this frequency range, the APL SFDR is in excess of 116 dBmiddotHz2/3 .

The ON–OFF dichotomy in visual processing: From receptors to perception

Vision scientists long ago pointed to black and white as separate sensations and saw confirmation in the fact that in the absence of light, one perceives the visual field as gray against which the negative after-image of a bright light appeared blacker. The first recordings from optic nerve fibers in vertebrates revealed ON and OFF signals, later associated with separate streams, arising already at the synapse between receptors and bipolar cells. These can be identified anatomically and physiologically and remain distinct all the way to the lateral geniculate nucleus, whose fibers form the input to the primary visual cortex. The dichotomy has been probed by electroretinography and analyzed by means of pharmacological agents and dysfunction due to genetic causes. The bi- rather than a unidirectional nature of the retinal output has advantages in allowing small signals to remain prominent over a greater dynamic range. The two streams innervate cortical neurons in a push-pull manner, generating receptive fields with spatial sensitivity profiles featuring ON and OFF subregions. Manifestations of the dichotomy appear in a variety of simple visual discriminations where there are often profound threshold differences in patterns with same polarity as compared with mixed contrast-polarity components. But even at levels in which the spatial, contrast and color attributes have already been securely established and black and white elements participate equally, a categorical difference between blackness and whiteness of a percept persists. It is an opponency, akin to the ones in the color domain, derived from the original ON and OFF signals and subsequently bound with the other attributes to yield a feature's unitary percept.

Aromaticity interplay between quinodimethanes and C(60) in diels-alder reactions: insights from a theoretical study

A theoretical study is performed of the Diels-Alder reactions of various o-quinodimethanes (QDM) with C(60) by the AM1 model and limited ab initio and DFT techniques. All reactions are shown to proceed through a concerted transition state possessing a considerable net aromaticity as evidenced from bond orders and magnetic criteria such as the magnetic susceptibility exhaltations (MSE) and nucleus independent chemical shifts (NICS) and produce different kinds of aromatic stabilized fullerene cycloadducts. Computations show that a strong LUMO-dienophile control of C(60) is realized by the influence of pyramidalization, but its high reactivity over alkene appears to be governed by the global aromaticity on fullerene rather than its strain. The aromatic functionalization occurring in QDM upon cycloaddition drastically increases the reaction rate and exothermicity of all QDM-C(60) reactions as compared to the butadiene-C(60) reaction. In fact, the simultaneously existing aromatic destabilization in fullerene indicates its opposite effect to the resonance stabilization in diene; it is thus fully restricted when the gained aromaticity is transmitted from the nucleophilic QDM to the fullerene electrophile in a push-pull manner. However, the overall aromaticity effect shown by the aromatization as well as the aromaticity of C(60) seems to accelerate these reactions at an increased rate.

Basic Fibroblast Growth Factor (bFGF) and Transforming Growth Factor Beta (TGF-β) Act as Stop and Go Signals to Modulate Postnatal Ocular Growth in the Chick

Occlusion of the eye (form deprivation) during post-natal development leads to ocular enlargement and myopia. The chick model of form deprivation myopia (FDM) has been used to identify candidate factors that underly the control of ocular growth. The major biochemical change associated with eye enlargement is an increase in scleral cartilage proteoglycan production (Rada et al., 1991) which is reduced in recovering eyes. Thus increasing evidence suggests that in the chicken eye, two different signals are involved, one for stop (occluder off) and one for go (occluder on). Because transforming growth factor-beta (TGF-β) and basic fibroblast growth factor (bFGF) are known to act in a push-pull manner in regulating extracellular matrix, their possible roles in FDM were tested. Chicks were occluded monocularly for 8 days, after which axial dimensions were assessed using A-scan ultrasonography, and refractive errors using streak retinoscopy. Under light halothane anesthesia, the control group received daily vehicle injections into both eyes whereas the experimental groups were treated with growth factors in the occluded eye and vehicle in the unoccluded eye.It was shown that: (1) bFGF reduced FDM in a dose-dependent manner, with a 50% effective dose (ED50) of 1·05 and 1·67 ng for subconjunctival and intravitreal delivery, respectively. Both axial eye length and refraction were similarly affected. The effects were mainly confined to a decrease in vitreous chamber depth. The anterior chamber was less deep but only after intravitreal injections, whereas lens thickness was not affected at all. At maximum effect, after subconjunctival applications the bFGF-treated occluded eyes were only 0·09 ± 0·16 mm longer than controls, which corresponded to a refractive error of - 0·67 ± 0·82 diopters (D), whereas after intravitreal applications the difference in axial eye length was - 0·07 ± 0·19 mm, corresponding to - 0·3 ± 0·52 D. (2) This effect could be mimicked by a FGF, but with a potency ∼ 160 times less than that of bFGF. The aFGF rescue effect could only be demonstrated for subconjunctival delivery; high intravitreal doses (≥ 300 ng per injection) induced retinal detachment and photoreceptor degeneration, while doses of aFGF close to the ED50 for bFGP (3 ng per injection) were completely ineffective. (3) TGF-β1 was not found to induce myopia in unoccluded eyes, or to increase myopia in occluded eyes. It was, however, a potent inhibitor of the bFGF rescue effect, if administered together with bFGF in the subconjunctival space. The addition of 50 pg of TGF-β1 resulted in increased axial eye lengths (0·65 ±0·24 mm) and higher myopic refractions (-3·67 ± 2·07 D), compared to eyes treated with bFGF alone (axial eye length: 0·09 ± 016 mm; refractive error: -0·67 ± 0·82 D).The observations show that bFGF and TGF-β1 are candidates for stop and go signals in the control of ocular growth. The possible roles and targets of these factors in the eye are discussed.

Push-pull modulation of ganglion cell responses of carp retina by amacrine cells

The responses of a ganglion and an amacrine cell were recorded simultaneously in the carp retina. Sinusoidal current injected into amacrine cells modulated ganglion cell discharges either in phase (excitation) or in opposite phase (inhibition). ON-center ganglion cells received excitatory inputs and OFF-center ganglion cells received inhibitory inputs from ON-center amacrine cells. They received inputs of opposite polarity from OFF-center amacrine cells. Namely, inputs from ON-center and OFF-center amacrine cells augment the responses of ON-center and OFF-center ganglion cells in a push-pull manner.

Sound reproduction system

A system for reproducing sound, particularly musical sound, giving enhanced pleasure to the listener. The system utilizes a pair of low frequency range speakers (11, 12), a plurality of high frequency range speakers (14) and may employ one or more mid frequency range speakers (13), all of which speakers are of conventional construction. These speakers are, however, disposed in a novel mechanical arrangement and electrically interconnected in a manner to emanate sound in essentially a non-directional manner. The listener thus perceives the sound to be emanating from the dimensional space surrounding the system, rather than from a single point or plane, and experiences the sound much as if he or she were in the same enclosure with live performers, rather than listening to a recording. Achievement of these results is attributable in part to the pair of low frequency range speakers (11, 12) being disposed in a cabinet (16) facing outwardly of opposite faces respectively of the cabinet (16) and being connected to a source of electrical signals in such a manner that the speakers operate in a push-pull manner. The mechanical arrangement of the system is completed by the high frequency range speakers (14) being mounted on the cabinet (16) in a manner to face upwardly of the cabinet (16) and the mid frequency range speaker (13) being mounted on the cabinet (16) to face generally toward the listener.

Apparent opposing effects of cyclic AMP and dibutyryl-cyclic GMP on the neuronal firing of the blowfly chemoreceptors

Cyclic AMP and its dibutyryl derivative inhibit neuronal firing of the labellar sugar sensitive receptor of the blowfly when applied in conjunction with the stimulant sucrose. Furthermore, simultaneous application of aminophylline (phosphodiesterase inhibitor) and sucrose or in combination with cyclic AMP caused a similar depression of the sugar receptors response. In contrast, dibutyryl cyclic GMP elicited an increase in sugar receptor firing when applied with sucrose to the sugar receptor. Either 5′-AMP or 5′-GMP in combination with sucrose had no discernable effect on the sugar receptors response. Different ratio combinations of cyclic AMP and dibutyryl cyclic GMP showed the striking inhibitory effect of cyclic AMP upon the dibutyryl cyclic GMP elicited increases in receptor firing frequency. Therefore, it is suggested that these two nucleotides may be mediating different but complimentary aspects of sugar receptor function in a push-pull manner.