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PubMed1973

Adaptation and dynamics of cat retinal ganglion cells.

1. The impulse/quantum (I/Q) ratio was measured as a function of background illumination for rod-dominated, pure central, linear square-wave responses of retinal ganglion cells in the cat.2. The I/Q ratio was constant at low backgrounds (dark adapted state) and inversely proportional to the 0.9 power of the background at high backgrounds (the light adapted state). There was an abrupt transition from the dark-adapted state to the light-adapted state.3. It was possible to define the adaptation level at a particular background as the ratio (I/Q ratio at that background)/(dark adapted I/Q ratio).4. The time course of the square-wave response was correlated with the adaptation level. The response was sustained in the dark-adapted state, partially transient at the transition level, and progressively more transient the lower the impulse/quantum ratio of the ganglion cell became. This was true both for on-centre and off-centre cells.5. The frequency response of the central response mechanism at different adaptation levels was measured. It was a low-pass characteristic in the dark-adapted state and became progressively more of a bandpass characteristic as the cell became more light-adapted.6. The rapidity of onset of adaptation was measured with a time-varying adapting light. The impulse/quantum ratio is reset within 100 msec of the onset of the conditioning light, and is kept at the new value throughout the time the conditioning light is on.7. These results can be explained by a nonlinear feedback model. In the model, it is postulated that the exponential function of the horizontal cell potential controls transmission from rods to bipolars. This model has an abrupt transition from dark- to light-adapted states, and its response dynamics are correlated with adaptation level.

Action Potentials↗
PubMed1973

Flux, not retinal illumination, is what cat retinal ganglion cells really care about.

1. Evidence was obtained that the impulse/quantum (I/Q) ratio of the central response mechanism of retinal ganglion cells in the cat is controlled by the steady effective retinal flux of the background.2. One experiment revealed that the I/Q ratio was decreased as the area of an adapting spot, of constant illumination, was increased. The curve relating the I/Q ratio to background flux was the same regardless of the size of the adapting spot.3. The effective central summing area of many retinal ganglion cells was determined. For the same cells, the transition level (Enroth-Cugell & Shapley, 1973) of the impulse/quantum curve was also measured. Diffuse illumination at the transition level was inversely proportional to the effective summing area, when variation in dark-adapted sensitivity between cells was taken into account.4. Therefore, retinal ganglion cells with large central summing areas are more light-adapted by any given diffuse background than cells with small centres.

Action Potentials↗
PubMed1975

Spectral correlates of a quasi-stable depolarization in barnacle photoreceptor following red light.

1. Illumination of B. eburneus photoreceptors with intense red light produces a membrane depolarization that persists in darkness. This quasistable depolarization (latch-up) can be terminated with green light. The phenomenon was investigated with electrophysiological, spectrochemical, and microspectrophotometric techniques. 2. Latch-up was associated with a stable inward current in cells with the membrane potential voltage-clamped at the resting potential in darkness. The stable current could only be elicited at wave-lengths greater than 580 nm. 3. Light-induced current (LIC) was measured at various wave-lengths in dark-adapted photoreceptors with the membrane voltage-clamped to the resting potential. The minimum number of photons required to elicit a fixed amount of LIC occurred at 540 nm, indicating that the photoreceptor is maximally sensitive to this wave-length of light. The photoreceptor was also sensitive to wave-lengths in the near-U.V. region of the spectrum (380-420 nm). 4. Steady red adapting light reduced the magnitude of the LIC uniformly at all wave-lengths except in the near-U.V. region of the spectrum; sensitivity was reduced less in this region. 5. The spectrum for termination of the stable inward current following or during red light was shifted to the blue (peak about 510 nm) compared to the peak for LIC (peak about 540 nm). 6. Absorbance of single cells prepared under bright, red light decreased maximally at 480 nm following exposure to wave-lengths of light longer than 540 nm. 7. A pigment extract of 1000 barnacle ocelli prepared under dim, red light had a maximum absorbance change at 480 nm when bleached with blue-gree light. 8. There was no evidence in the latter two experiments of photointerconversion of pigments with absorbance maxima at 480 and 540 nm. Rather, the maximum absorption of the bleaching products seemed to occur at wave-lengths shorter than 420 nm. 9. Since latch-up induction occurs at wave-lengths longer than 580 nm, it may depend on the 540 pigment or on an undetected red absorbing pigment. 10. A photolabile pigment at 480 nm correlated most closely with termination of the stable inward current associated with latch-up.

Adaptation, Ocular↗
PubMed1982

The influence of temporal frequency and adaptation level on receptive field organization of retinal ganglion cells in cat.

1. The discharges of single X and Y ganglion cells (distinguished by a test of linearity of spatial summation) were recorded in the optic tract of anaesthetized, paralysed cats.2. Fourier techniques were used to analyse the distribution of amplitudes of several component temporal frequencies in the maintained discharge. X and Y cells were distinguished by their mean rates, but not by the amplitude or variability of other component frequencies.3. Sensitivities to moving sinusoidal gratings were measured by an automatic procedure in which stimulus contrast was adjusted to give the smallest modulation of discharge that reliably exceeded that of the relevant component frequency in the maintained discharge.4. Spatial contrast sensitivity curves of X cells and of on-centre Y cells could be described by a model of the receptive field as two concentric Gaussian sensitivity profiles representing the centre and the antagonistic surround.5. Changes in temporal frequency altered the shapes of the spatial contrast sensitivity curves of most units. For X cells sensitivity at the optimum spatial frequency was greater at a temporal frequency of 10.4 Hz than at lower or higher temporal frequencies. The relative sensitivity to low spatial frequencies improved as temporal frequency was raised from 0.16 to 20.8 Hz. The shapes of the contrast sensitivity functions of Y cells were less affected by changes in temporal frequency: at all spatial frequencies sensitivity was greater at 2.6 Hz than at lower or higher frequencies.6. The effect of temporal frequency upon the shape of the spatial contrast sensitivity curve could be explained by assuming that the centre and surround changed their sensitivities without changing their characteristic radii. A simple model, using a temporal R-C filter in the surround pathway, predicted qualitatively similar changes in the shape of contrast sensitivity curves but failed to provide acceptable fits to the observations. A second model, which assumed that surround signals are delayed by a fixed amount before being combined with those from the centre, fitted the observations of most, but not all, X cells.7. Dark adaptation produced changes in the shape of the spatial contrast sensitivity curve consistent with a reduction in the relative sensitivity of the surround, but did not bring about systematic changes in the space constants of the best-fitting theoretical curves.8. The effects of adaptation level upon contrast sensitivity were expressed as plots of increment-threshold against mean illumination. The shallowest of these curves, obtained for the optimum spatial stimulus moving at about 10 Hz, had slopes averaging 0.77. Decreases in spatial or temporal frequency increased the slopes of the curves.

Action Potentials↗
PubMed1978

Directional selectivity in hamster superior colliculus is modified by strobe-rearing but not by dark-rearing.

Visual response properties of superior collicular neurons of normal hamsters were compared with those of animals reared from birth to adulthood in either total darkness or with stroboscopic illumination. Directional selectivity was markedly reduced only in the strobe-reared animals, thus demonstrating visual plasticity in a system that develops apparently normally without visual experience.

Action Potentials↗
PubMed1977

Interactions between rod and cone systems in the goldfish retina.

Signals from both the rod and the cone receptor systems converge upon the same retinal ganglion cell, but only one or the other of these systems appears to be effective at any particular level of adaptation. In this report we provide evidence that the change from one receptor system to the other is not simply due to the two systems having nonoverlapping dynamic ranges; rather, there is a distance-dependent interaction between the two systems.

Adaptation, Ocular↗
PubMed1990

Origin of negative potentials in the light-adapted ERG of cat retina.

1. The light-adapted diffuse-flash electroretinogram (ERG) in the cat exhibits two prominent negative components: a sustained negative potential during illumination and a negative-going OFF response. We investigated their intraretinal origins and found that the sustained component originates from the rod photoreceptors, whereas the OFF response represents a combination of the return to base line of the rod-receptor potential, the offset of PII (rod and cone), and a cone-dependent OFF response originating proximal to the photoreceptors at very high background levels. 2. The ERG, evoked in response to diffuse illumination of the light- and dark-adapted cat retina, was recorded between a chlorided silver wire in the vitreous and a plate behind the eye. Extracellular field potentials were recorded simultaneously with a microelectrode placed intraretinally at different retinal depths. 3. The sustained negative potential and the negative OFF response were not the M-wave ON and OFF responses of proximal retina, despite an overall resemblance in form and time course: 1) the M-wave was spatially tuned, whereas the ERG components were not; 2) tetrodotoxin (TTX) (3.8-microM vitreal concentration) did not alter the M-wave, but it reduced the ERG OFF response; 3) picrotoxin (0.14 mM, after TTX) enhanced the M-wave but did not affect the negative ERG; and 4) 2-amino-4-phosphonobutyric acid (APB; 0.95 mM) removed the M-wave ON response, and aspartate (43 mM) removed the M-wave OFF response, in addition, while the sustained negative potential persisted. 4. The sustained negative potential was not slow PIII, the neural retinal component of the c-wave, a Müller cell response to the photoreceptor-dependent light-evoked decrease in subretinal extracellular K+ concentration [( K+]o). Although Ba2+ (repeated injections of 4-5 mM), a K+ conductance blocker, eliminated slow PIII, it did not remove the sustained negative potential. We concluded that the sustained negative potential was a photoreceptor potential, and the spectral sensitivity of the response indicated that it arose from rods. 5. The contribution of the rod-receptor potential to the ERG depended on background illumination. It was a sustained potential for a range of backgrounds near and 1 or 2 log units above the illumination that saturates rod-driven responses in cat (8.2 log quanta.deg-2.s-1). At lower background intensities, it appeared only as a dip between the b- and c-waves, the b-wave trough, which also was present in fully dark-adapted responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗
PubMed1980

Extrafoveal spectral sensitivity during dark adaptation.

The extrafoveal spectral sensitivity function was measured during dark adaptation at different intensity levels above the cone plateau of the long-term dark-adaptation curve using both flicker and heterochromatic brightness-matching techniques. During most of the cone-plateau period, the spectral sensitivity function was found to be photopic in form at all the intensity levels employed. In the dark-adapted state, the two psychophysical techniques appeared to measure different processes. Thus, the flicker technique yielded a spectral sensitivity function which was basically scotopic in form at all the intensity levels employed while the spectral sensitivity function obtained with the brightness technique was basically photopic in form. It is suggested that, in a dark-adapted state, both rods and cones contribute to the brightness response at each wavelength over the major portion of the spectrum for a long transitional intensity range when the brightness technique is used. The flicker technique, on the other hand, appears to single out the rod activity.

Adaptation, Ocular↗
PubMedDate not supplied

Visual function after pan-retinal photocoagulation: a survey.

Thirty-five diabetic patients who had undergone pan-retinal photocoagulation were surveyed to determine the frequency and severity of visual difficulties they experience. Among the most frequent problems were difficulty adjusting to dim lighting, difficulty adjusting to bright lighting, and trouble in sorting dark colors. Judging distances, negotiating stairways, and avoiding obstacles were identified as having become more difficult since the laser treatment. According to a correlation analysis, the difficulties encountered in some important tasks, such as driving in the daytime, were highly related to visual acuity. However, many of the problems reported most frequently, and many of the problems whose frequency had increased the most since the laser therapy, were not related to acuity. Despite their many visual complaints, the patients expressed very positive attitudes toward the photocoagulation treatment.

Adaptation, Ocular↗
PubMed1995

Anti-arrestin immunoreactivity in the human retina: difference between light- and dark-adaptation.

Differences in arrestin (Arr) immunolocalization between light(LA)- and dark(DA)-adapted retinae have been described in various species. We have for the first time studied 5 LA and 5 DA human retinae from surgically enucleated eyes, each group comprising 1 exenteration specimen and globes with malignant melanoma or 2 degrees glaucoma. To examine the distribution of Arr, immunohistochemistry was performed on paraffin sections using three different antibodies to Arr: a48k, 3D1.2, and 5c6.47. Immunoreactivity (IR) was tested using the avidin-biotin method, and results were visualized with diaminobenzidine. With both a48k and 5c6.47, labeling was most intense in the photoreceptor layer. When comparing LA and DA retinae, IR of photoreceptor outer segments (OS) was clearly different with very little IR in OS of DA but distinct positivity in OS of LA retina. This was most obvious in melanoma eyes where retinal morphology was well-preserved while in glaucomatous eyes with retinal degeneration this pattern was less apparent. 3D1.2 did not react in any of the specimens. Although there was some variation within each group, we demonstrated a distinct difference in anti-Arr IR between LA and DA specimens. Thus Arr-IR might now be used as a promising tool to further study retinal diseases on human surgical specimens involving photoreceptor degeneration.

Adaptation, Ocular↗
PubMed1995

Light adaptation of bovine retinas in situ stimulates phosphatidylinositol synthesis in rod outer segments in vitro.

Light-stimulated phosphoinositide turnover has been reported in both vertebrate retina and isolated rod outer segments (ROS). In the current investigation, we examined the incorporation of [3H]-inositol in vitro in bovine ROS isolated from dark adapted (DROS) or bleached (BROS) retinas. Incorporation of [3H]-inositol into phosphoinositides in BROS was 3-5 fold higher than in DROS. The majority (approximately 90%) of [3H]-inositol was found in phosphatidylinositol (PI), whereas phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) accounted for 7-8% of the label. The enhanced labelling of PI was only observed when bovine retinas were light-adapted prior to ROS preparation, suggesting the requirement for an intact photoreceptor for the observed effect. Our data strongly suggest that bleaching of bovine retina in situ stimulates PI synthesis in isolated ROS in vitro.

Adaptation, Ocular↗
PubMed1979

[Brightness power function and equal brightness contour for dark- and light-adapted eye in the peripheral visual field (author's transl)].

To test whether the equal brightness contour at supra-threshold runs parallel with the contour at threshold, magnitude estimation and the staircase procedure were employed for estimating brightness power function under dark- and light-adaptation. The luminance was changed from 43 to 83 dB re 10(-6) cd/m2 with the light adapting luminance at 53 dB. The retinal loci tested were 0 degrees to 70 degrees periphery in steps of 10 degrees. The exponent of the power function gradually increased from .37 to .73 as eccentricity and adapting luminance increased. The equal brightness contour decreased for dark-adaptation and increased for light-adaptation as eccentricity increased at supra-threshold but at threshold did not follow the parallel hypothesis for both adapting conditions.

Adaptation, Ocular↗
PubMed1975

[Melatonin biosynthesis in the mammalian retina in dependence of light adaptation (author's transl)].

1. The biosynthesis of melatonin was investigated in retinaextracts of bovine eyes in dependence of light adaptation of the animals. S-adenososyl (Methyl-14C) methionin and acetylserotonin were used as substrates. A higher melatonin-biosynthesis was found in the retina from animals which were adapted to lower illumination. 2. The effect of triamterene on the biosynthesis of melatonin in the retina was examined. An increase of melatonin was found in the presence of the diureticum, which is a pteridine compound, when retinas of animals which were kept under low illumination were investigated. The role of melatoninsynthesis in dark adaptation is discussed and it is pointed to a possible danger of blinding in patients which used triamterene. Furthermore it is suggested that triamterene also increases the melatoninsynthesis in the pineal gland and that this may possibly contribute to an understanding of the effect of the diurecticum.

5-Hydroxytryptophan↗
PubMed1975

Experimentally determined optical properties of goldfish cones and rods.

The optical properties of goldfish photoreceptors were evaluated using the special microscope-microspectrophotometer divice. Mode patterns transmitted were identified for both natural and reverse path illumination. Photomechanical changes with adaptive state could be identified. Complex mode interactive phenomena and cross-coupling of energy were observed. These are related to the fact that there are double cones and apposition or near apposition of neighboring receptors in this species. The directionality of individual cones and rods was quantified by making use of the principle of reversibility of light path. Radiation patterns were recorded and analyzed on a computer controlled microdensitometer. Individual cones and rods were shown to exhibit marked directionality. Light collection properites of cones were strikingly evident.

Adaptation, Ocular↗