Possible cues driving context-specific adaptation of optocollic reflex in pigeons (Columba livia)

2012 ◽  
Vol 107 (2) ◽  
pp. 704-717 ◽  
Author(s):  
Henri Gioanni ◽  
Pierre-Paul Vidal
Keyword(s):  
Columba Livia ◽  
Motor Command ◽  
Slow Phase ◽  
Gaze Stabilization ◽  
Specific Adaptation ◽  
Body Vibration ◽  
Fast Phase ◽  
Context Specific ◽  
Context Cues

Context-specific adaptation (Shelhamer M, Clendaniel R. Neurosci Lett 332: 200–204, 2002) explains that reflexive responses can be maintained with different “calibrations” for different situations (contexts). Which context cues are crucial and how they combine to evoke context-specific adaptation is not fully understood. Gaze stabilization in birds is a nice model with which to tackle that question. Previous data showed that when pigeons ( Columba livia) were hung in a harness and subjected to a frontal airstream provoking a flying posture (“flying condition”), the working range of the optokinetic head response [optocollic reflex (OCR)] extended toward higher velocities compared with the “resting condition.” The present study was aimed at identifying which context cues are instrumental in recalibrating the OCR. We investigated that question by using vibrating stimuli delivered during the OCR provoked by rotating the visual surroundings at different velocities. The OCR gain increase and the boost of the fast phase velocity observed during the “flying condition” were mimicked by body vibration. On the other hand, the newly emerged relationship between the fast-phase and slow-phase velocities in the “flying condition” was mimicked by head vibration. Spinal cord lesion at the lumbosacral level decreased the effects of body vibration, whereas lesions of the lumbosacral apparatus had no effect. Our data suggest a major role of muscular proprioception in the context-specific adaptation of the stabilizing behavior, while the vestibular system could contribute to the context-specific adaptation of the orienting behavior. Participation of an efferent copy of the motor command driving the flight cannot be excluded.

scholarly journals Angular vestibuloocular reflex responses in Otop1 mice. I. Otolith sensor input is essential for gravity context-specific adaptation

2019 ◽  
Vol 121 (6) ◽  
pp. 2291-2299 ◽  
Author(s):  
Serajul I. Khan ◽  
Charles C. Della Santina ◽  
Americo A. Migliaccio
Keyword(s):  
Semicircular Canals ◽  
Vertical Axis ◽  
Neural Circuitry ◽  
Vestibuloocular Reflex ◽  
Training Context ◽  
Specific Adaptation ◽  
Axis Parallel ◽  
Vor Adaptation ◽  
Context Specific

The role of the otoliths in mammals in the angular vestibuloocular reflex (VOR) has been difficult to determine because there is no surgical technique that can reliably ablate them without damaging the semicircular canals. The Otopetrin1 (Otop1) mouse lacks functioning otoliths because of failure to develop otoconia but seems to have otherwise normal peripheral anatomy and neural circuitry. By using these animals we sought to determine the role of the otoliths in angular VOR baseline function and adaptation. In six Otop1 mice and six control littermates we measured baseline ocular countertilt about the three primary axes in head coordinates; baseline horizontal (rotation about an Earth-vertical axis parallel to the dorsal-ventral axis) and vertical (rotation about an Earth-vertical axis parallel to the interaural axis) sinusoidal (0.2–10 Hz, 20–100°/s) VOR gain (= eye/head velocity); and the horizontal and vertical VOR after gain-increase (1.5×) and gain-decrease (0.5×) adaptation training. Countertilt responses were significantly reduced in Otop1 mice. Baseline horizontal and vertical VOR gains were similar between mouse types, and so was horizontal VOR adaptation. For control mice, vertical VOR adaptation was evident when the testing context, left ear down (LED) or right ear down (RED), was the same as the training context (LED or RED). For Otop1 mice, VOR adaptation was evident regardless of context. Our results suggest that the otolith translational signal does not contribute to the baseline angular VOR, probably because the mouse VOR is highly compensatory, and does not alter the magnitude of adaptation. However, we show that the otoliths are important for gravity context-specific angular VOR adaptation. NEW & NOTEWORTHY This is the first study examining the role of the otoliths (defined here as the utricle and saccule) in adaptation of the angular vestibuloocular reflex (VOR) in an animal model in which the otoliths are reliably inactivated and the semicircular canals preserved. We show that they do not contribute to adaptation of the normal angular VOR. However, the otoliths provide the main cue for gravity context-specific VOR adaptation.

Fast-phase transvascular fluid flux and the Fahraeus effect

1987 ◽  
Vol 62 (4) ◽  
pp. 1513-1520 ◽  
Author(s):  
W. N. Richardson ◽  
D. Bilan ◽  
M. Hoppensack ◽  
L. Oppenheimer
Keyword(s):  
Mechanical Properties ◽  
Slow Rate ◽  
Time Course ◽  
Rate Of Change ◽  
Distributed Model ◽  
Slow Phase ◽  
Fluid Flux ◽  
Fast Phase ◽  
Constant Rate ◽  
Fahraeus Effect

Transvascular fluid flux was induced in six isolated blood-perfused canine lobes by increasing and decreasing hydrostatic inflow pressure (Pi). Fluid flux was followed against the change in concentration of an impermeable tracer (Blue Dextran) measured directly with a colorimetric device. The time course of fluid flux was biphasic with an initial fast transient followed by a slow phase. Hematocrit changes unrelated to fluid flux occurred due to the Fahraeus effect, and their contribution to the total color signal was subtracted to determine the rate of fast fluid flux (Qf). Qf was related to Pi to derive fast-phase conductance (Kf). Slow-phase Kf was calculated from the constant rate of change of lobe weight. For a mean change in Pi of 7 cmH2O, 40% of the color signal was due to fluid flux. Fast- and slow-phase Kf's were 0.86 +/- 0.15 and 0.27 +/- 0.05 ml X min-1. cmH2O–1 X 100 g dry wt-1. The fast-phase Kf is smaller than that reported for plasma-perfused lobes. Possible explanations discussed are the nature of the perfusate, the mechanical properties of the interstitium, and the slow rate of rise of the driving pressure at the filtration site on the basis of a distributed model of pulmonary vascular compliance.

scholarly journals Mechanism of retraction of the trailing edge during fibroblast movement.

1981 ◽  
Vol 90 (1) ◽  
pp. 187-200 ◽  
Author(s):  
W T Chen
Keyword(s):  
Slow Component ◽  
Fast Component ◽  
Slow Phase ◽  
Main Body ◽  
Elastic Recoil ◽  
Forward Movement ◽  
Trailing Edge ◽  
Fast Phase ◽  
Focal Contacts

Retraction of the taut, trailing portion of a moving chick heart fibroblast in vitro is an abrupt dynamic process. Upon retraction, the fibroblast tail always ruptures, leaving a small amount of itself attached to the substratum by focal contacts. Time-lapse cinemicrography shows that retraction produces a sudden, massive movement of both surface and cytoplasmic material toward a cluster of focal contacts near the main body of the cell. The appearance of folds on the upper cell surface at this time and the absence of endocytotic vesicles are consistent with this forward movement. Retraction of the trailing edge, either occurring naturally or produced artificially with a microneedle, consists of an initial fast component followed and overlapped by a slow component. Upon artificial detachment in the presence of iodoacetate, dinitrophenol, and sodium fluoride, and at 4 degrees C, the slow component is strongly inhibited and the fast one only slightly inhibited. Moreover of the bundles of microfilaments oriented parallel to the long axis of the tail seen in TEM. Most of the birefringence is lost during the fast phase and the rest during the slow phase of retraction. Concurrently, the bundles of microfilaments disappear during the fast phase of retraction and are replaced by a microfilament meshwork. All of these results are consistent with the hypothesis that the initial fast component of retraction is a passive elastic recoil, associated with the oriented bundles of microfilaments, and that the slow component of retraction is an active contraction, associated with a meshwork of microfilaments.

scholarly journals The assembly of microtubule protein in vitro. The kinetic role in microtubule elongation of oligomeric fragments containing microtubule-associated proteins

1985 ◽  
Vol 227 (2) ◽  
pp. 439-455 ◽  
Author(s):  
P M Bayley ◽  
F M M Butler ◽  
D C Clark ◽  
E J Manser ◽  
S R Martin
Keyword(s):  
Self Assembly ◽  
Protein Concentration ◽  
Wavelength Dependence ◽  
Electrophoretic Analysis ◽  
Slow Phase ◽  
Condensation Polymerization ◽  
Fast Phase ◽  
Microtubule Protein ◽  
Kinetics Of

The kinetics of assembly were studied for bovine and pig microtubule protein in vitro over a range of conditions of pH, temperature, nucleotide and protein concentration. The kinetics are in general biphasic with two major processes of similar amplitude but separated in rate by one order of magnitude. Rates and amplitudes are complex functions of solution conditions. The rates of the fast phase and the slow phase attain limiting values as a function of increasing protein concentration, and are more stringently limited at pH 6.5 than pH 6.95. Such behaviour indicates that mechanisms other than the condensation polymerization of tubulin dimer become rate-limiting at higher protein concentration. The constancy of the wavelength-dependence of light-scattering and ultrastructural criteria indicate that microtubules of normal morphology are formed in both phases of the assembly process. Electrophoretic analysis of assembling microtubule protein shows that MAP- (microtubule-associated-protein-)rich microtubules are formed during the fast phase. The rate of dissociation of oligomeric species on dilution of microtubule protein closely parallels the fast-phase rate in magnitude and temperature-dependence. We propose that the rate of this process constitutes an upper limit to the rate of the fast phase of assembly. The kinetics of redistribution of MAPs from MAP-rich microtubules may be a factor limiting the slow-phase rate. A working model is derived for the self-assembly of microtubule protein incorporating the dissociation and redistribution mechanisms that impose upper limits to the rates of assembly attainable by bimolecular addition reactions. Key roles are assigned to MAP-containing fragments in both phases of microtubule elongation. Variations in kinetic behaviour with solution conditions are inferred to derive from the nature and properties of fragments formed from oligomeric species after the rapid temperature jump. The model accounts for the limiting rate behaviour and indicates experimental criteria to be applied in evaluating the relative contributions of alternative pathways.

scholarly journals Children coping with COVID-19: Intersectional understandings of film and media access in a crisis

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Justine Atkinson ◽  
Firdoze Bulbulia
Keyword(s):  
South Africa ◽  
The Netherlands ◽  
Case Studies ◽  
Media Access ◽  
Specific Focus ◽  
Film Education ◽  
The World ◽  
Context Specific ◽  
The Impact

As a result of the global COVID-19 pandemic and resulting lockdowns across the world, digital access has become paramount, as most aspects of education have moved online. Drawing together five case studies located in South Africa, Argentina, the Netherlands, India and Ethiopia, this article assesses the role of film education during the COVID-19 pandemic, with a specific focus on the impacts of digital access. We examine multimodal forms of film education, and how these were used to inform, entertain and educate children during the crisis by the varying work undertaken by the organizations. Applying theories of intersectionality, we address the need for context-specific approaches to film education, focusing upon the impact that the societal and individual contexts had on the dissemination of film education in each country.

scholarly journals Complexities and Context: Women's Peace-Building in Conflict and Post-Conflict Bougainville

2021 ◽  
Author(s):  
◽  
Dylan Page
Keyword(s):  
Peace Process ◽  
United Nations Security Council ◽  
Peace Building ◽  
Peace Negotiations ◽  
Peace Processes ◽  
Post Conflict ◽  
Peace And Conflict Studies ◽  
The Pacific ◽  
Context Specific

<p>The potential role of women in conflict and post-conflict environments has been the subject of much debate in the field of peace and conflict studies. In 2000 the United Nations Security Council passed Resolution 1325, which called for a greater involvement of women and acknowledgement of gender issues in conflict and post-conflict environments, and this has led to further discussion about what this might mean and how it might be implemented. Despite this women are continually under-represented in nearly all peace processes and there is no universally agreed upon way to ensure this situation does not come about. The barriers women face range from cultural to logistical and economic, and surmounting them can be hard to achieve.  One case where women have been involved at all levels in the peace process with substantial success is the Pacific island of Bougainville, where a conflict over mining issues and secession from Papua New Guinea was waged from 1988-1997. Women were active in attempts to bring all parties to negotiations during the conflict and have also been heavily involved in the continuing reconciliation and healing processes. For cultural reasons Bougainvillean women were well placed to perform the role of peace-builders but that is not to say that they did not face challenges and barriers to their involvement. This thesis examines the involvement of women in both the immediate peace negotiations and the longer-term aspects of the peace process in Bougainville in order explain how and why they enjoyed these successes and what lessons can be learnt from this case in regards to the potential roles of women in other post-conflict environments. Four factors will be identified as key to women's involvement in the peace process: the history of Bougainville up to and including the conflict; the grassroots mobilisation and organisation of women; the traditional cultural roles of women in Bougainville; and the identification of women with motherhood and its associated traits.  These factors indicate that the involvement of women in peace processes is highly context-specific and although there are policies which can be pursued to encourage their participation the potential barriers to this are imposing.</p>

Role of slow phase separation in assessing the equilibrium phase behaviour of PC-PMMA blends

Polymer ◽  
1991 ◽  
Vol 32 (2) ◽  
pp. 272-278 ◽  
Author(s):  
M. Nishimoto ◽  
H. Keskkula ◽  
D.R. Paul
Keyword(s):  
Phase Separation ◽  
Equilibrium Phase ◽  
Phase Behaviour ◽  
Slow Phase ◽  
Pmma Blends
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