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PubMed1996

Horizontal cell spinule dynamics in fish are affected by rearing in monochromatic light.

Blue acaras (Aequidens pulcher, Cichlidae) were reared for 1 yr in white or monochromatic "red", "green" and "blue" lights to study the function and control mechanisms of horizontal cell (HC) spinules in the synaptic pedicles of cones. Ratios of spinules per synaptic ribbon (S/R) were determined in tangential sections in both single and double cones. We found that the S/R ratios in light adapted retinae decreased with decreasing wavelength of the rearing light in all cone types. Conversely, there was an increasing number of incompletely formed spinules with the highest frequency in the blue light group. Dark adaptation resulted in the complete degradation of mature spinules. However, significant numbers of incompletely degraded spinules were observed in the group reared in blue light. Fish reared in blue light which were transferred to white light formed mature spinules when light adapted and still had vestigial spinules when dark adapted. The mechanisms of spinule formation and degradation and the control of spinule dynamics appear to be fully developed in fish reared in monochromatic light. However, long-term chromatic deprivation seems to induce a compensatory modulation of spinule dynamics. A working hypothesis is formulated that interprets the observed effects as manifestations of differences in the activition of dopaminergic interplexiform cells (light adapted) and the sensitivity to glutamate of HCs (dark adapted). Our findings are consistent with the hypothesis that spinules are involved in sign-inverting feedback transmission from HCs to cones.

Adaptation, Ocular↗
PubMed1996

Motion detection in goldfish investigated with the optomotor response is "color blind".

The action spectrum of the optomotor response in goldfish was measured to investigate which of the four cone types involved in color vision contributes to motion detection. In the dark-adapted state, the action spectrum showed a single maximum in the range of 500-520 nm, and resembled the rod spectral sensitivity function. Surprisingly, the action spectrum measured in the light-adapted state also revealed a single maximum only, located in the long wavelength range between 620 and 660 nm. A comparison with spectral sensitivity functions of the four cone types suggests that motion detection is dominated by the L-cone type. Using a two colored, "red-green" cylinder illuminated with two monochromatic lights separately adjustable in intensity, it could be shown that motion vision is "color-blind": the optomotor response disappeared whenever "isoluminant" red and green stripes were offered. Under this condition, calculations revealed that the L-cones were only slightly modulated by the "red-green" stimulus.

Adaptation, Ocular↗
PubMed1997

[3H]raclopride and [3H]spiroperidol binding to retinal membranes of the teleost Eugerres plumieri: effect of light and dark adaptation.

Monoamine and metabolites were determined in the retina of the teleost Eugerres plumieri after dark and light adaptation. Dopamine, homovanillic acid and 3,4-dihydroxyphenylacetic acid increased after light exposure. The results indicate an increase in the turnover rate of dopamine due to light exposure. Dopamine D2 receptors were studied by determining the binding parameters of [3H]spiroperidol and [3H]raclopride to retinal membranes. The results were best fitted to a two-site model, where the high-affinity site may correspond to D2 receptors and the low-affinity site could be D4 receptors, which have been recently described in the retina, although further research is needed to confirm this suggestion. The number of sites labeled with [3H]spiroperidol was lower than with [3H]raclopride. This may indicate the existence of monomer and dimer conformations of D2-like receptors in the retina, as has been shown in the brain. Light exposure increased the number of sites labeled with both ligands. Since D2 receptors are known to modulate the production of melatonin, the augmentation in the capacity of these receptors could contribute to the reduction of melantonin during light exposure.

Adaptation, Ocular↗
PubMed2002

Massive light-driven translocation of transducin between the two major compartments of rod cells: a novel mechanism of light adaptation.

We report a new cellular mechanism of rod photoreceptor adaptation in vivo, which is triggered by daylight levels of illumination. The mechanism involves a massive light-dependent translocation of the photoreceptor-specific G protein, transducin, between the functional compartments of rods. To characterize the mechanism, we developed a novel technique that combines serial tangential cryodissection of the rat retina with Western blot analysis of protein distribution in the sections. Up to 90% of transducin translocates from rod outer segments to other cellular compartments on the time scale of tens of minutes. The reduction in the transducin content of the rod outer segments is accompanied by a corresponding reduction in the amplification of the rod photoresponse, allowing rods to operate in illumination up to 10-fold higher than would otherwise be possible.

Adaptation, Ocular↗
PubMedDate not supplied

Modulation of horizontal cell function by GABA(A) and GABA(C) receptors in dark- and light-adapted tiger salamander retina.

The physiological function of GABA transporters and GABA receptors in retinal horizontal cells (HCs) under dark-and light-adapted conditions were studied by whole-cell voltage clamp and intracellular recording techniques in retinal slices and whole-mounted isolated retinas of the larval tiger salamander. Puff application of GABA in picrotoxin elicited a NO-711 (a potent GABA transporter blocker)-sensitive inward current that did not exhibit a reversal potential in the physiological range, consistent with the idea that these HCs contain electrogenic GABA transporters. Application of GABA in NO-711 elicited a chloride current in HCs; about half of the current was suppressed by bicuculline or I4AA (a GABA(C) receptor antagonist), and the remaining half was suppressed by bicuculline + I4AA or picrotoxin. In whole-mount retinas, NO-711, bicuculline, I4AA, or picrotoxin hyperpolarized the HCs and enhanced the light responses under dark-adapted conditions, and blocked the time-dependent recovery of HC membrane potential and light responses during background illumination. Based on the parallel conductance model, GABA released in darkness mediates a chloride conductance about three times greater than the leak conductance or the glutamate-gated cation conductance. About half of this chloride conductance is mediated by GABA(A) receptors, and the other half is mediated by GABA(C) receptors. These results suggest that GABA released from HCs through the NO-711-sensitive GABA transporters activates GABA(A) and GABA(C) receptors, resulting in chloride conductance increase which leads to a HC depolarization and reduction of the light response. Additionally, GABA transporters also mediate GABA release in background light that is responsible for the recovery of HC membrane potential and light responses.

Adaptation, Ocular↗
PubMed2002

Background adaptation in a rat model of retinopathy of prematurity.

Low dark-adapted, scotopic retinal and visual sensitivity in retinopathy of prematurity (ROP) could be due to disease of the inner retina, or the recently described rod photoreceptor abnormalities. Receptoral disease decreases catch of quanta from both test flashes and steady background lights; increment threshold functions are shifted up and right. In diseases with normal receptors but low retinal sensitivity due to abnormal post receptoral processing, the increment threshold functions are shifted up with no horizontal translation. Herein we test the hypothesis that the rod photoreceptors are the site of ROP disease which causes low dark adapted b-wave sensitivity. The effect of steady background light on the ERG b-wave in a rat model of ROP is studied. ERG stimulus/response functions were obtained using full-field stimuli in the dark-adapted state, and in the presence of a steady background light. In each adaptation condition, log sigma, the test flash intensity that produced a half-maximum b-wave amplitude, was calculated. In pilot experiments, the background light selected had raised log sigma about a log unit in controls. In dark-adapted ROP rats log sigma was significantly higher, 0.35 log unit, than in controls. In the presence of the background light, log sigma in ROP and control rats did not differ significantly indicating a relative shift, up and right, of the increment sensitivity function for the less sensitive ROP rats. The effect of the background light is consistent with receptoral disease causing low dark adapted b-wave sensitivity in ROP rats.

Adaptation, Ocular↗
PubMed2004

An in vivo microdialysis study of light/dark-modulation of vitreal dopamine release in zebrafish.

Dopamine (DA) is an important neuromodulator in the visual system. The release of DA in the retina largely depends on environmental lighting conditions. Most previous studies have assessed the effect of illumination on retinal DA or its metabolites using homogenates or in vitro preparations. This study was designed to investigate the effect of transitions between lighting conditions--from dark to steady or flickering light and vice versa--on retinal DA release in zebrafish using in vivo microdialysis. The transition from dark to flickering light increased DA release, whereas the transition from flickering light to dark decreased it. This latter effect depended on time of day within the light period, e.g., it was strongest in the late afternoon. When using steady light, none of these effects were seen. Our study also demonstrates that in vivo microdialysis can successfully be applied to the investigation of retinal DA release in zebrafish.

Adaptation, Ocular↗
PubMed2000

Taurine blocks spontaneous cone contraction but not horizontal cell dark suppression in isolated goldfish retina.

The objective of this study was to investigate the effects of taurine on cone retinomotor movements and the responses of cone-driven horizontal cells in dark-adapted teleost retina. In isolated goldfish retina preparations maintained in the dark, cones spontaneously contracted, and the responses of horizontal cells were suppressed. Addition of 5 mM taurine to the physiological solution blocked the spontaneous contraction of cones in the dark but did not block the dark-suppression of horizontal cell responses. These results indicate that the mechanism that leads to horizontal cell dark suppression is not sensitive to taurine. Although both cone retinomotor position and horizontal cell responsiveness are known to be modulated by dopamine, the present results do not support the hypothesis that taurine inhibits dopamine release in the dark because only spontaneous cone contraction was affected by taurine. These results also indicate that spontaneous cone contraction in the dark is not the cause of horizontal cell dark suppression because, in the presence of taurine, cones were elongated yet horizontal cell responses were still suppressed. Consequently, these results make it clear that horizontal cell dark suppression is not an artifact produced by incubating isolated teleost retina preparations in taurine-free physiological solution.

Adaptation, Ocular↗
PubMed1985

Changes in the coupling between accommodation and vergence eye movements induced in human subjects by altering the effective interocular separation.

It has usually been thought that the coupling between accommodation and convergence of the eyes is fixed and not modifiable by experience. Experiments are reported which show that the ratio of accommodative vergence to the accommodation stimulus, the stimulus AC/A ratio (one measure of the coupling), is elevated by brief periods (approximately 30 min) of experience of viewing the world through periscopic spectacles which increase the effective interocular separation. Experience of viewing through 'cyclopean' spectacles, which superimpose the line of sight of the two eyes, reduced the stimulus AC/A ratio in one subject and increased it in another, while it remained hardly affected in a third.

Accommodation, Ocular↗
PubMed1975

Intracellular recordings from gecko photoreceptors during light and dark adaptation.

Intracellular recordings were obtained from rods in the Gekko gekko retina and the adaptation characteristics of their responses studied during light and dark adaptation. Steady background illumination induced graded and sustained hyperpolarizing potentials and compressed the incremental voltage range of the receptor. Steady backgrounds also shifted the receptor's voltage-intensity curve along the intensity axis, and bright backgrounds lowered the saturation potential of the receptor. Increment thresholds of single receptors followed Weber's law over a range of about 3.5 log units and then saturated. Most of the receptor sensitivity change in light derived from the shift of the voltage-intensity curve, only little from the voltage compression. Treatment of the eyecup with sodium aspartate at concentrations sufficient to eliminate the beta-wave of the electroretinogram (ERG) abolished initial transients in the receptor response, possibly indicating the removal of horizontal cell feedback. Aspartate treatment, however, did not significantly alter the adaptation characteristics of receptor responses, indicating that they derive from processes intrinsic to the receptors. Dark adaptation after a strongly adapting stimulus was similarly associated with temporary elevation of membrane potential, initial lowering of the saturation potential, and shift of the voltage-intensity curve. Under all conditions of adaptation studied, small amplitude responses were linear with light intensity. Further, there was no unique relation between sensitivity and membrane potential suggesting that receptor sensitivity is controlled at least in part by a step of visual transduction preceding the generation of membrane voltage change.

Adaptation, Ocular↗
PubMed1982

Early visual adaptation in color opponent goldfish ganglion cells.

The initial stages of light and dark adaptation in the human visual system cannot be explained by a simple relation between sensitivity and pigment bleaching. We found changes in sensitivity in the goldfish ganglion cells similar to those seen in humans, and our results from experiments suggest that a change in gain, rather than an overloading of the ganglion cell activity, is responsible for the sensitivity loss. Furthermore, long wavelength background lights selected to stimulate only the long wavelength receptor mechanism produce only the early sensitivity changes in the medium wavelength cone mechanism being monitored at the ganglion cell. This suggests that the early gain changes occur due to neural interaction where different receptor signals merge.

Adaptation, Ocular↗
PubMed1975

Effects of adapting lights on the time course of the receptor potential of the anuran retinal rod.

1. The intracellular receptor potential of the retinal rod cell was recorded in the unperfused, isolated retina of Rana catesbiana and in the perfused, isolated retina of Bufo marinus. Qualitatively, the responses from the two preparations were similar. 2. The rate at which the receptor potential returned to the dark level at the termination of a pulse of light (Voff) was measured at a fixed potential chosen to be about 0-6 of the way from the dark level to the peak of the response. 3. When the light intensity was such that less than about 10-minus 5 of the photopigment was bleached per second, Voff increased as the duration of the pulse was increased, reaching a maximum in 50-100 s. 4. When a brief test flash was presented at various intervals after an adapting pulse lasting about 50 s, Voff for the test flash was greater than the value in the dark adapted state for times up to about 80 s after the adapting pulse. 5. It has been hypothesized that in the vertebrate rod light causes release from the disk sacs of particles which block conducting channels in the surface membrane (Yoshikami & Hagins, 1971, 1973). A modification is proposed in which the blocking particles are converted to an inactive state can be increased by light adaptation. 6. This modified hypothesis will account qualitatively for the further observations that (a) during the response to illumination lasting several seconds the membrane potential recovers part of the way to the dark level and (b) if a second light pulse is superimposed on this background illumination then after the superimposed pulse the depolarization is increased.

Adaptation, Ocular↗
PubMed2003

Interocular amplitude differences of the full field electroretinogram in normal subjects.

AIMS: To determine the interocular amplitude response difference of the electroretinogram (ERG) in normal subjects. METHODS: 79 subjects, without retinal changes of clinical significance, underwent ERG testing. They included 63 men and 16 women, with a mean age of 44 (SD 12) years and range of 18-65 years. Isolated rod, scotopic maximal, dark adapted 30 Hz flicker, photopic single flash, and light adapted 30 Hz flicker responses were recorded in both eyes following the International Society for Clinical Electrophysiology of Vision (ISCEV) standard protocol. The interocular percentage differences of the ERG b-wave amplitudes were calculated and presented as percentiles (25th, 50th, 75th, 95th), means (SD), and medians. RESULTS: The median interocular percentage differences in the b-wave amplitudes for the above ERG stimulus responses were 10%, 8%, 10%, 11%, and 10%, respectively. The mean interocular percentage differences were 11%, 11%, 12%, 13%, and 14%. The 95th percentiles for the interocular percentage differences were 28%, 27%, 36%, 33%, and 35%, respectively. CONCLUSIONS: The interocular percentage differences in the ERG b-wave amplitudes for five different stimulus responses were similar in our cohort of individuals without clinically significant retinal changes and ranged from a median of 8-11% and a 95th percentile of 27-36%. Our findings should be useful for determining sample sizes in future therapeutic trials on retinal diseases with monocular therapeutic strategies and may also have application for the more accurate detection of asymmetric retinal disease.

Adaptation, Ocular↗
PubMed1978

Visual sensitivity.

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Adaptation, Ocular↗
PubMed2003

Occlusable corneas in toadfishes: light transmission, movement and ultrastruture of pigment during light- and dark-adaptation.

The toadfishes Tetractenos hamiltoni and Torquigener pleurogramma (Tetraodontidae) possess occlusable yellow corneas. We examine the light transmission and location of the yellow/orange pigment throughout the cornea, the temporal properties of pigment migration and the ultrastructure of the pigmented processes during light- and dark-adaptation. Each species was dark-adapted during the day and light-adapted during the night and then exposed to either sun illumination or darkness for different lengths of time (0-70 min). Movement of corneal pigment could be induced in both species regardless of time of day or night. The pigment was able to migrate in a dorsal or ventral direction and changed from minimal to maximal pigmentation within 60 min. Three types of transmission curves were found with varying degrees of transmission in the 400-500 nm waveband, indicating that the pigment distribution is not uniform across the cornea; some areas of the cornea transmit near UV light, while others absorb blue light. The gradual change of the transmission characteristics in different areas of the cornea indicates the presence of different concentrations of a single type of pigment. Ultrastructural examination of the corneas showed that the layer containing the pigment is situated within the scleral cornea either surrounding (T. pleurogramma) or abutting (T. hamiltoni) an iridescent layer. Long sheet-like processes or chromatophores extending centrally from dorsal and ventral reservoirs are filled with pigment during the light-adapted state but empty in the dark-adapted state.

Adaptation, Ocular↗
PubMed1977

Adaptive properties of the b-wave and the PIII in the perfused isolated carp retina.

1. Perfusion of isolated carp retina with a pure oxygen saturated standard solution used in this experiment permitted several continuous hours of ERG recordings showing a distinctive b-wave as well as the PIII isolated by sodium aspartate. 2. The dark-adapted threshold for the PIII required an absorption of 5 to 6 quanta per rod. The 'rod-cone break' in the increment threshold curve for the b-wave was induced at a background intensity of about 2.0 X 10(-2) muW/cm2. 3. Both the b-wave and the PIII showed rapid and complete recovery of sensitivity after exposure to dim adapting lights. After bright light adaptation, the sensitivities went through a short 'fast phase' followed by a prolonged 'slow phase' of recovery. The rate of recovery during the fast phase was significantly faster for the PIII than for the b-wave. Neither a lowered temperature (9 degrees C) nor the application of ouabain (10(-6) M) influenced the fast phase. This seems to prove that the visual pigment, photoproducts and the active transport hardly participate in its mechanism, if at all. 4. The prolonged slow phase that followed the fast phase was distinguished by the recovery of the rod activity, even in isolated retinas.

Adaptation, Ocular↗