scholarly journals Light Adaptation in Pecten Hyperpolarizing Photoreceptors

1997 ◽  
Vol 109 (3) ◽  
pp. 371-384 ◽  
Author(s):  
Maria del Pilar Gomez ◽  
Enrico Nasi
Keyword(s):  
Light Adaptation ◽  
Light Sensitivity ◽  
Response Amplitude ◽  
Background Intensity ◽  
Sensory Receptor ◽  
Test Flash ◽  
Visual Response ◽  
Modulation Transfer ◽  
Stimulus Response ◽  
Underlying Mechanisms

The ability of scallop hyperpolarizing photoreceptors to respond without attenuation to repetitive flashes, together with their low light sensitivity, lack of resolvable quantum bumps and fast photoresponse kinetics, had prompted the suggestion that these cells may be constitutively in a state akin to light adaptation. We here demonstrate that their photocurrent displays all manifestations of sensory adaptation: (a) The response amplitude to a test flash is decreased in a graded way by background or conditioning lights. This attenuation of the response develops with a time constant of 200–800 ms, inversely related to background intensity. (b) Adapting stimuli shift the stimulus-response curve and reduce the size of the saturating photocurrent. (c) The fall kinetics of the photoresponse are accelerated by light adaptation, and the roll-off of the modulation transfer function is displaced to higher frequencies. This light-induced desensitization exhibits a rapid recovery, on the order of a few seconds. Based on the notion that Ca mediates light adaptation in other cells, we examined the consequences of manipulating this ion. Removal of external Ca reversibly increased the photocurrent amplitude, without affecting light sensitivity, photoresponse kinetics, or susceptibility to background adaptation; the effect, therefore, concerns ion permeation, rather than the regulation of the visual response. Intracellular dialysis with 10 mM BAPTA did not reduce the peak-to-plateau decay of the photocurrent elicited by prolonged light steps, not the background-induced compression of the response amplitude range and the acceleration of its kinetics. Conversely, high levels of buffered free [Ca]i (10 μM) only marginally shifted the sensitivity curve (Δσ = 0.3 log) and spared all manifestations of light adaptation. These results indicate that hyperpolarizing invertebrate photoreceptors adapt to light, but the underlying mechanisms must utilize pathways that are largely independent of changes in cytosolic Ca. The results are discussed in terms of aspects of commonalty to other ciliary sensory receptor cells.

The influence of center-surround antagonism on light adaptation in cones in the retina of the turtle

1995 ◽  
Vol 12 (5) ◽  
pp. 877-885 ◽  
Author(s):  
Dwight A. Burkhardt
Keyword(s):  
Light Adaptation ◽  
Background Field ◽  
Light Sensitivity ◽  
Human Vision ◽  
Background Intensity ◽  
Test Flash ◽  
Cone Photoreceptors ◽  
Background Fields ◽  
Psychophysical Studies ◽  
Large Background

AbstractThe influence of center-surround antagonism on light adaptation in cone photoreceptors was investigated by intracellular recording from red-sensitive cones in the retina of the turtle, Pseudemys scripta elegans. Test flashes of 0.15-mm diameter were applied at the center of background fields of 0.25-mm or 2.2-mm diameter. Immediately upon expanding the background from 0.25 to 2.2 mm, the membrane potential depolarized by about 1–4 mV. The test flash response was enhanced if the depolarization was primarily due to synaptic feedback from horizontal cells, whereas the response was attenuated if the prolonged depolarization, an intrinsic response of the cone, was the dominant source of the depolarization. After several seconds, however, only the synaptic depolarization was maintained so maintained illumination of the large background field produced an enhancement of the cone's incremental sensitivity. The enhancement was examined in detail in steady-state conditions by obtaining amplitude-intensity measurements for centered test flashes on steady background fields over a large range of intensity. The effect of the large background field at any fixed intensity was fairly well described as a vertical (upward) shift of the amplitude-intensity curve obtained on the small field. This operation constitutes a quasi-subtractive mechanism of light adaptation and might provide a basis for the sort of subtractive mechanisms inferred from psychophysical studies of human vision. The enhancement was quantified by measuring the incremental sensitivity over four decades of background illumination. The magnitude of the enhancement increased with background intensity and then tended to stabilize at higher background intensities. The maximum difference in incremental sensitivity obtained on the large vs. small background field averaged 0.46 log unit (±0.12 s.d.). At higher background intensities, incremental sensitivity conformed to Weber's Law behavior about equally well for flashes applied on either small or large background fields. In sum, the present results provide evidence for an additional mechanism of light adaptation in cone photoreceptors by showing that the incremental light sensitivity, initially set by mechanisms in the outer segment, can be modulated some three-fold by synaptic feedback at the inner segment of the cone.

scholarly journals Two light-dependent conductances in Lima rhabdomeric photoreceptors.

1991 ◽  
Vol 97 (1) ◽  
pp. 55-72 ◽  
Author(s):  
E Nasi
Keyword(s):  
Light Adaptation ◽  
Late Phase ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Light Response ◽  
Light Sensitivity ◽  
Resting Potential ◽  
Test Flash ◽  
Ionic Selectivity ◽  
Subsequent Test

Light-dependent membrane currents were recorded from solitary Lima photoreceptors with the whole-cell clamp technique. Light stimulation from a holding voltage near the cell's resting potential evokes a transient inward current graded with light intensity, accompanied by an increase in membrane conductance. While the photocurrent elicited by dim flashes decays smoothly, at higher stimulus intensities two kinetically distinct components become visible. Superfusion with TEA or intracellular perfusion with Cs do not eliminate this phenomenon, indicating that it is not due to the activation of the Ca-sensitive K channels that are present in these cells. The relative amplitude of the late component vs. the early peak of the light response is significantly more pronounced at -60 mV than at -40 mV. At low light intensities the reversal potential of the photocurrent is around 0 mV, but with brighter lights no single reversal potential is found; rather, a biphasic response with an inward and an outward component can be seen within a certain range of membrane voltages. Light adaptation through repetitive stimulation with bright flashes diminishes the amplitude of the early but not the late phase of the photocurrent. These observations can be accounted for by postulating two separate light-dependent conductances with different ionic selectivity, kinetics, and light sensitivity. The light response is also shown to interact with some of the voltage-sensitive conductances: activation of the Ca current by a brief conditioning prepulse is capable of attenuating the photocurrent evoked by a subsequent test flash. Thus, Ca channels in these cells may not only shape the photoresponse, but also participate in the process of light adaptation.

scholarly journals HIGH RESOLUTION CAMERA DESIGN PLANNING THEORETICAL FOUNDATIONS FOR DRIVING SYSTEMS

2021 ◽  
Author(s):  
Viacheslav S. Stadnichuk ◽  
Valentin G. Kolobrodov ◽  
Oleksii O. Mosolab ◽  
Denis Yu. Kondratenko ◽  
Dmytro I. Ryabokon
Keyword(s):  
High Resolution ◽  
Optical Glass ◽  
Light Sensitivity ◽  
Design Parameters ◽  
Optical Parameters ◽  
Functional Requirements ◽  
Modulation Transfer ◽  
Road Signs ◽  
Wide Range ◽  
Camera Design

Background. Analysis of statistical data showed that in most cases the cause of the accident is driver error and, as a consequence, violation of traffic rules. In this regard, over the past 10 years, active developments in the field of recognition of road signs and other obstacles in the path of a car have been actively developing. Car manufacturers offer ready-made built-in systems, mounted behind the interior rearview mirror and connected to the car’s on-board computer, which carries out further control of the car in a critical situation. The main disadvantage of these systems of this class is the low range of recognition of road signs, the dependence of optical parameters on temperature and low light sensitivity. Objective. The purpose of the paper is to model an athermal objective for a high-resolution camera, investigate the characteristics of lenses depending on the ambient temperature. Methods. Analysis and modeling of objectives, lenses, optical glass from different materials. Results. A high-resolution camera objective for all types of cars is proposed. An athermal objective was developed for a high-resolution camera. Conclusions. The optimized athermal design of the visible spectrum objective for long-range car cameras is considered. Car cameras typically have a fixed focus, and forward-facing cameras typically require relatively long focal lengths to provide information about distant objects. The optical system for these cameras should provide high resolution, as well as operate in a wide range of ambient temperatures. The camera design parameters are derived from the functional requirements of road sign recognition at a distance of 200 m. The objective design has five lenses with spherical surfaces. The objective has a relative aperture of f/2 and a modulation transfer function (MTF) of more than 0.5 at 111 l/mm over the entire temperature range.

scholarly journals Evaluation of Motor Neuron Excitability by CMAP Scanning with Electric Modulated Current

2015 ◽  
Vol 2015 ◽  
pp. 1-5 ◽  
Author(s):  
Tiago Araújo ◽  
Rui Candeias ◽  
Neuza Nunes ◽  
Hugo Gamboa
Keyword(s):  
Compound Muscle Action Potential ◽  
Single Pulse ◽  
Response Amplitude ◽  
Stimulus Response ◽  
Response Slope ◽  
Biphasic Pulse ◽  
Muscle Action Potential ◽  
Motor Neuron Excitability ◽  
Peripheral Nerve Excitability ◽  
Pulse Stimulation

Introduction. Compound Muscle Action Potential (CMAP) scan is a noninvasive promissory technique for neurodegenerative pathologies diagnosis. In this work new CMAP scan protocols were implemented to study the influence of electrical pulse waveform on peripheral nerve excitability. Methods. A total of 13 healthy subjects were tested. Stimulation was performed with an increasing intensities range from 4 to 30 mA. The procedure was repeated 4 times per subject, using a different single pulse stimulation waveform: monophasic square and triangular and quadratic and biphasic square. Results. Different waveforms elicit different intensity-response amplitude curves. The square pulse needs less current to generate the same response amplitude regarding the other waves and this effect is gradually decreasing for the triangular, quadratic, and biphasic pulse, respectively. Conclusion. The stimulation waveform has a direct influence on the stimulus-response slope and consequently on the motoneurons excitability. This can be a new prognostic parameter for neurodegenerative disorders.

Center/surround relationships of magnocellular, parvocellular, and koniocellular relay cells in primate lateral geniculate nucleus

1993 ◽  
Vol 10 (2) ◽  
pp. 363-373 ◽  
Author(s):  
Gregg E. Irvin ◽  
Vivien A. Casagrande ◽  
Thomas T. Norton
Keyword(s):  
Contrast Sensitivity ◽  
Lateral Geniculate Nucleus ◽  
Light Adaptation ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Visual Response ◽  
Afferent Pathways ◽  
K Cells ◽  
Lateral Geniculate ◽  
P Cells

AbstractAs in other primates, the lateral geniculate nucleus (LGN) of the prosimian primate, bush baby (Galago crassicaudatus), contains three morphologically and physiologically distinct cell classes [magnocellular (M), parvocellular (P), and koniocellular (K)] (Norton & Casagrande, 1982; Casagrande & Norton, 1991). The present study examined quantitatively the center/surround relationships of cells in all three classes. Estimates of receptive-field center size (Rc) and sensitivity (Kc) and of surround size (Rs) and sensitivity (Ks) were obtained from 47 LGN relay cells by fitting a difference of Gaussians function to contrast-sensitivity data. For M and P cells, center size (Rc) increases with eccentricity but is about two times larger for M than for P cells at a given eccentricity. Surround size (Rs) increases with eccentricity for P but not for M or K cells. The center sensitivity (Kc) is inversely related to center size (Rc) and surround sensitivity (Ks) is inversely related to surround size (Rs) for cells in all classes, a result consistent with the sensitivity regulation that is produced by light adaptation. High spatial-frequency cutoff (acuity) is inversely related to center size (Rc). However, the peak contrast sensitivity is relatively independent of Rc. The ratio of the integrated strength (volume) of the surround to the volume of the center remains relatively constant (median, 0.87) across all three cell classes. This ratio is an excellent predictor of a cell’s rolloff in contrast sensitivity at low spatial frequencies: cells with a low surround/center ratio have less low-frequency rolloff. Although M, P, and K cells generally display similar center/surround relationships, differences in center size and the other parameters between the classes distinguish most M, P, and K cells. These findings demonstrate that both similarities and differences in the visual-response properties of primate LGN cells in these three parallel afferent pathways can be explained by basic center/surround relationships.

Light adaptation and color opponency of horizontal cells in the turtle retina

2003 ◽  
Vol 20 (4) ◽  
pp. 437-452 ◽  
Author(s):  
GILAD TWIG ◽  
HANNA LEVY ◽  
ELITE WEINER ◽  
IDO PERLMAN
Keyword(s):  
Light Adaptation ◽  
Light Sensitivity ◽  
Horizontal Cells ◽  
Background Illumination ◽  
Voltage Range ◽  
Background Adaptation ◽  
Color Opponency ◽  
Light Stimuli ◽  
Type C

Chromaticity-type (C-type) horizontal cells of the turtle retina receive antagonistic inputs from cones of different spectral types, and therefore their response to background illumination is expected to reflect light adaptation of the cones and the interactions between their antagonistic inputs. Our goal was to study the behavior of C-type horizontal cells during background illumination and to evaluate the role of wavelength in background adaptation. The photoresponses of C-type horizontal cells were recorded intracellularly in the everted eyecup preparation of the turtleMauremys caspicaduring chromatic background illuminations. The voltage range of operation was either reduced or augmented, depending upon the wavelengths of the background and of the light stimuli, while the sensitivity to light was decreased by any background. The response–intensity curves were shifted to brighter intensities and became steeper as the background lights were made brighter regardless of wavelength. Comparing the effects of cone iso-luminant backgrounds on the Red/Green C-type horizontal cells indicated that background desensitization in these cells could not solely reflect background adaptation of cones but also depend upon response compression/expansion and changes in synaptic transmission. This leads to wavelength dependency of background adaptation in C-type horizontal cells, that is expressed as increased light sensitivity (smaller threshold elevation) and improved suprathreshold contrast detection when the wavelengths of the background and light stimuli were chosen to exert opponent effects on membrane potential.

M-wave of proximal retina in cat

1986 ◽  
Vol 56 (4) ◽  
pp. 1039-1048 ◽  
Author(s):  
P. A. Sieving ◽  
L. J. Frishman ◽  
R. H. Steinberg
Keyword(s):  
Light Adaptation ◽  
Pattern Electroretinogram ◽  
Stimulus Onset ◽  
Stray Light ◽  
M Wave ◽  
Stimulus Response ◽  
Response Characteristics ◽  
Cat Retina ◽  
Small Spot ◽  
Dc Component

There has been relatively little known about responses from proximal retina in mammals that could contribute to the electroretinogram (ERG). Recently, there has been evidence that the proximal retina is involved in generating the pattern electroretinogram (PERG). In the present work we investigated proximal retinal activity in the intact cat eye during light adaptation. Extracellular potentials evoked in response to circular spots of light, flashed on steady backgrounds, were recorded with microelectrodes placed intraretinally at different depths. Prominent negative responses were found in proximal retina that could be identified as the M-wave previously observed only in cold-blooded retinas. Like the cold-blooded responses, the cat's M-wave consisted of negative-going potentials at stimulus onset and offset that were maximum in amplitude with small spots. By analogy to the cold-blooded data, the cat M-wave is presumed to be the extracellular voltage arising from Muller cell responses to K+ released by proximal retinal neurons. In addition, the cat M-wave only appeared with backgrounds at and above rod saturation and had short latencies (30 ms) at stimulus onset and offset, indicating that it is a cone-driven response. The M-wave could be clearly distinguished from PII (b-wave and DC component) on the basis of its form, depth distribution, and stimulus-response characteristics. For example, photopic PII had its maximum voltage in the distal retinal at 55% retinal depth, whereas the M-wave was maximal in the proximal retina at 25% retinal depth. Also, PII simply increased in amplitude as stimulus spots were enlarged, whereas the M-wave exhibited spatial tuning. Under light-adapted conditions and with small-spot stimuli the M-wave is the largest extracellular voltage in cat retina. By recording the vitreal ERG near the retinal surface with the microelectrode referenced to a silver wire in the vitreous, we found that the M-wave in response to a small spot always had a negative polarity in the vitreous. Thus, unlike PII, the M-wave does not reverse polarity at the vitreo-retinal border. Because of stray-light effects, however, we were not able to assess the amplitude of the M-wave's contribution to the ERG obtained with diffuse retinal illumination. We conclude that the M-wave is present in the cat as a prominent cone-driven response of proximal retina that is separate from the b-wave, and whose significance for electroretinographic recordings remains to be determined.

Light-adaptation properties of the ultraviolet-sensitive cone mechanism in comparison to the other receptor mechanisms of goldfish

1991 ◽  
Vol 6 (4) ◽  
pp. 293-301 ◽  
Author(s):  
Craig W. Hawryshyn
Keyword(s):  
Heart Rate ◽  
Light Adaptation ◽  
Weber Fraction ◽  
Luminance Contrast ◽  
The Other ◽  
Brightness Contrast ◽  
Background Intensity ◽  
Contrast Threshold ◽  
Functional Differences ◽  
Threshold Technique

AbstractThe light-adaptation properties of goldfish photoreceptor mechanisms were examined using Stiles' two-color threshold technique. Threshold vs. background intensity (TVI) curves were determined for isolated cone and rod mechanisms using the heart-rate conditioning technique. The principal aim of this study was to compare the light-adaptation properties of the ultraviolet (UV)-sensitive cone mechanism to the other receptor mechanisms of goldfish. This examination revealed several striking functional differences: (1) The UV-sensitive cone mechanism threshold vs. background intensity (TVI) exhibited a slope of 0.65 (compared to the approximate 1.0 for the other cone mechanisms on a log/log plot) and thus was not in accordance with Weber's law. This may in part be related to the intrusion of the blue-sensitive mechanism at the upper radiance range. (2) The operation of the UV-sensitive cone mechanism was limited to intermediate intensities (i.e. not very dim or bright). (3) The UV-sensitive cone mechanism exhibited a Weber fraction or luminance contrast threshold of 0.316 that was approximately six times larger than the other cone mechanisms but comparable to the rod mechanism. This indicates that the UV-sensitive cone mechanism performs relatively poorly in terms of brightness contrast detection.

scholarly journals Control of the cyclic GMP phosphodiesterase of frog photoreceptor membranes.

1980 ◽  
Vol 76 (5) ◽  
pp. 631-645 ◽  
Author(s):  
P R Robinson ◽  
S Kawamura ◽  
B Abramson ◽  
M D Bownds
Keyword(s):  
Light Intensity ◽  
Cyclic Gmp ◽  
Outer Segment ◽  
Calcium Concentration ◽  
Light Adaptation ◽  
Light Sensitivity ◽  
Change Mechanism ◽  
Outer Segments ◽  
Labile Component ◽  
Photoreceptor Membranes

The light-activated cyclic GMP phosphodiesterase (PDE) of frog photoreceptor membranes has been assayed in isolated outer segments suspended in a low-calcium Ringer's solution. Activation occurs over a range of light intensity that also causes a decrease in the permeability, cyclic GMP levels, and GTP levels of isolated outer segments. At intermediate intensities, PDE activity assumes constant intermediate values determined by the rate of rhodopsin bleaching. Washing causes an increase in maximal enzyme activity. Increasing light intensity from darkness to a level bleaching 5 x 10(3) rhodopsin molecules per outer segment per second shifts the apparent Michaelis constant (Km) from 100 to 900 microM. Maximum enzyme velocity increases at least 10-fold. The component that normally regulates this light-induced increase in the Km of PDE is removed by the customary sucrose flotation procedures. The presence of 10(-3) M Ca++ increases the light sensitivity of PDE, and maximal activation is caused by illumination bleaching only 5 x 10(2) rhodopsin molecules per outer segment per second. Calcium acts by increasing enzyme velocity while having little influence on Km. The effect of calcium appears to require a labile component, sensitive to aging of the outer segment preparation. The decrease in the light sensitivity of PDE that can be observed upon lowering the calcium concentration may be related to the desensitization of the permeability change mechanism that occurs during light adaptation of rod photoreceptors.

scholarly journals Calcium regulates some, but not all, aspects of light adaptation in rod photoreceptors.

1989 ◽  
Vol 94 (2) ◽  
pp. 233-259 ◽  
Author(s):  
G D Nicol ◽  
M D Bownds
Keyword(s):  
Light Adaptation ◽  
Calcium Ionophore ◽  
Absolute Magnitude ◽  
Calcium Ionophore A23187 ◽  
Background Intensity ◽  
Ionophore A23187 ◽  
Background Illumination ◽  
Rod Photoreceptors ◽  
Time To Peak ◽  
Flash Response

The role of calcium as a regulator of light adaptation in rod photoreceptors was examined by manipulation of the intracellular Ca2+ concentration through the use of the calcium ionophore A23187 and external Ca2+ buffers. These studies utilized suspensions of isolated and purified frog rod outer segments that retain their mitochondria-rich inner segments (OS-IS). Three criteria of the dark- and light-adapted flash response were characterized as a function of the Ca2+ concentration: (a) the time to peak, (b) the rate of recovery, and (c) the response amplitude or sensitivity. For all Ca2+ concentrations examined, the time to peak of the flash response was accelerated in the presence of background illumination, suggesting that mechanisms controlling this aspect of adaptation are independent of the Ca2+ concentration. The recovery kinetics of the flash response appeared to depend on the Ca2+ concentration. In 1 mM Ca2+-Ringer's and 300 nM Ca2+-Ringer's + A23187, background illumination enhanced the recovery rate of the response; however, in 10 and 100 nM Ca2+-Ringer's + A23187, the recovery rates were the same for dark- and light-adapted responses. This result implies that a critical level of Ca2+ may be necessary for background illumination to accelerate the recovery of the flash response. The sensitivity of the flash response in darkness (SDF) was dependent on the Ca2+ concentration. In 1 mM Ca2+-Ringer's SDF was 0.481 pA per bleached rhodopsin (Rh*); a background of four Rh*/s decreased SDF by half (Io). At 300 nM Ca2+ + A23187, SDF was reduced to 0.0307 pA/Rh* and Io increased to 60 Rh*/s. At 100 nM Ca2+ + A23187, SDF was reduced further to 0.0025 pA/Rh* and Io increased to 220 Rh*/s. In 10 nM Ca2+ + A23187, SDF was lowered to 0.00045 pA/Rh* and Io raised to 760 RhI/s. Using these values of SDF and Io for each respective Ca2+ concentration, the dependence of the flash sensitivity on background intensity could be described by the Weber-Fechner relation. Under low Ca2+ conditions + A23187, bright background illumination could desensitize the flash response. These results are consistent with the idea that the concentration of Ca2+ may set the absolute magnitude of response sensitivity in darkness, and that there exist mechanisms capable of adapting the photoresponse in the absence of significant changes in cytoplasmic Ca2+ concentration.

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