Long-term scotopic (rod-mediated) visual deficits following developmental lead exposure occur in monkeys and hooded rats. This report describes and summarizes previous ERG and biochemical findings, presents new biochemical data aimed at determining the mechanism of inhibition of lead on rod cGMP-PDE, presents an integratory framework for understanding the ERG and ...

BACKGROUND: Prolongation in recovery of rod thresholds has been demonstrated in Stargardt's dystrophy. One possible explanation for this finding includes an impairment of vitamin A transport by the retinal pigment epithelium (RPE). By delivering an increased amount of vitamin A to the RPE, it might be possible to overcome a ...

Following bright flashes, rod photoreceptors exhibit a period of photocurrent saturation that increases linearly with the logarithm of flash intensity. In a recent report, Pepperberg et al. (1992) presented evidence that the slope of the function relating the saturation period (T) to the natural logarithm of flash intensity (ln If) ...

A study is reported of human binocular rivalry and fusion over a range of luminances from scotopic to photopic. At scotopic light levels, rivalry alternations were very slow and complete. Suppression spread over much larger areas of the visual field than at photopic light levels. As luminances decreased from photopic ...

The effect of light adaptation on the period of photocurrent saturation induced by a bright stimulating flash was examined in rod photoreceptors of the larval-stage tiger salamander (Ambystoma tigrinum). Using suction electrodes, photocurrent responses to brief flashes were recorded from single, isolated rods in the presence and absence of steady ...

1. Membrane photocurrents were recorded from outer segments of isolated retinal rods of pigeons (Columba livia), the first such measurements on the photoreceptors of a bird. The amplitude of the response to 20 ms flashes of narrow wavelength bands of light increases linearly with intensity at low photon fluxes and ...

The field-adaptation properties of two scotopic (rod) mechanisms, pi 0 and pi 0', were measured to test a two-pathway model that associates the fast temporal properties of pi 0' with the processing of rod signals by early cone pathways, possibly including cone photoreceptors, and the sluggish temporal properties of pi ...

Amphibians are unusual among vertebrates in having two spectral classes of rod photoreceptors, unique amphibian "green" rods and typical vertebrate "red" rods. Although amphibians have been the subject of extensive research on visual function, it is not known whether possession of two classes of rods is a general feature of ...

The human rod receptors can be studied by measuring the leading edge of the rod a-wave of the ERG. Computational models, previously shown to fit the recordings from single rods, are fitted to dark-adapted a-wave responses. A model proposed by Lamb and Pugh [(1992) Journal of Physiology, 499, 719-758] fits ...

In vertebrate photoreceptors, light induces hydrolysis of cGMP by activating cGMP phosphodiesterase (PDE), which results in closure of the cGMP-activated cation channel. During light adaptation, the cytoplasmic Ca2+ concentration decreases, and this decrease is one of the underlying mechanisms of light adaptation. Sensitivity-modulating protein (S-modulin) is a Ca(2+)-binding protein involved ...

Rod photoreceptors in the retinas of teleost fish undergo changes in cell length in response to changing ambient light intensities. In the dark rods shorten and in the light rods elongate. These movements are mediated by actin-dependent processes which occur in the ellipsoid and myoid of the inner segment. As ...

1. Properties of a new preparation for studying the physiology and biochemistry of phototransduction in retinal rods are described. Whole-cell voltage clamp was used to record the generation, maintenance and light-sensitivity of dark current in rod outer segments that had been isolated from the rest of the receptor cell by ...

OBJECTIVE: To determine possible distinct phenotypic subtypes of cone-rod dystrophy. PATIENTS: Thirty-three patients with cone-rod dystrophy (from 25 families) were assessed prospectively on electroretinography, visual field testing, psychophysical threshold profiles, and fundus features. The clinical records of an additional 150 patients with cone-rod dystrophy were examined retrospectively in terms of ...

1. The relative contribution of rod and cone inputs to bipolar and ganglion cells were studied by comparing the response-irradiance relations, spectral sensitivities, and response waveforms of these neurons recorded from the isolated, flat-mounted tiger salamander retina under dark-adapted conditions. 2. Bipolar cells could be differentiated both on the basis ...

1. Photocurrents were recorded with suction electrodes from rod photoreceptors of seven humans. 2. Brief flashes of light evoked transient outward currents of up to 20 pA. With increasing light intensity the peak response amplitude increased along an exponential saturation function. A half-saturating peak response was evoked by approximately sixty-five ...

1. Response properties of on- and off-centre retinal ganglion cells were investigated in cats. The stimulus parameters were selected so as to demonstrate interactions between the rod and the cone systems. 2. Response versus log stimulus intensity (R-log I) functions were determined for the receptive field centres while both test ...

1. The absolute sensitivity of vision was studied as a function of temperature in two species of frog (Rana temporaria, 9-21 degrees C, and Rana pipiens, 13-28 degrees C). 2. Log behavioural threshold (measured as the lowest light intensity by which frogs trying to escape from a dark box were ...

The retinal photoreceptors of the tiger salamander (Ambystoma tigrinum) have been studied by light and electron microscopy in both light- and dark-adaptation. Rods and cones are present in this duplex retina in a ratio of about 20:1. As in other urodele species these photoreceptors are very large cells. The rod ...

1. Absolute and increment thresholds were measured in a retinal region 12 deg temporal from the fovea with 520 nm targets of varying size and duration. Measurements were made under rod-isolation conditions in two normal observers and in a typical, complete achromat observer who has no cone-mediated vision. The purpose ...

Six OFF-alpha ganglion cells and a single OFF-beta ganglion cell were penetrated with intracellular microelectrodes and marked with horseradish peroxidase (HRP) in a perfused cat eyecup. Gaussian center radii (Rc) ranging from 40 to 217 microns were measured for receptive fields mapped with slits, values in agreement with previous extracellular ...

Using a laser interferometer we can create grating patterns of high optical contrast (interference fringes) directly on the retina. With coarse fringe patterns, the alternating light and dark bars of the pattern can be seen, but the bars of the finest fringes are not subjectively resolved. We report here that ...

Effects of intracellularly applied L-arginine and nicotinamide adenine dinucleotide phosphate (NADPH) on the dark voltage and light responses of retinal rods were studied by means of the whole-cell patch-clamp technique. In this mode an exchange of substances by diffusion between cytosol and pipette medium occurs (Pflügers Arch., 411 (1988) 204-211). ...

A 28-year-old man with multiple evanescent white dot syndrome (MEWDS) in the left eye was examined with a scanning laser densitometer. The first measurements were taken in the acute stage, and repeat examinations were performed during the process of recovery. Fundus pictures were obtained from a 20 degrees retinal field, ...

In previous experiments we established that a light flash reduced cGMP levels of toad rod outer segments within the transduction time interval, but that recovery of the dark level of cGMP occurred more slowly than reported electrophysiological recovery of membrane potential. We now report that a second light flash accelerates ...

Using a Wright colorimeter, absolute threshold, absolute form threshold and specific form threshold were measured during long-term dark adaptation in the extrafoveal retina. The specific form threshold was found to fall markedly at about the cone-rod break but thereafter rose steeply. Furthermore, during the rod phase of the dark adaptation ...

The accuracy of toad snapping towards moving worm dummies under various levels of dim illumination (from absolute threshold to "moonlight") was video-recorded and related to spike responses of retinal ganglion cells exposed to equivalent stimuli. Some toads (at ca. 16 degrees C) successfully snapped at dummies that produced only one ...

Although synaptic transmission in the retina has been assumed to be static, it appears that the voltage gains of the synapses between photoreceptors and second-order cells can be enhanced by light. Voltage gains of the synapses between rods and bipolar (or horizontal) cells are about 10 times higher in the ...

Cyclic GMP is the second messenger in the phototransduction mechanism in rod photoreceptors. Light-induced activation of cGMP phosphodiesterase (PDE), the hydrolyzing enzyme of cGMP, reduces cytoplasmic cGMP concentration to close the cGMP-activated channel and thereby causes a hyperpolarizing light response. Ca2+ concentration decreases during light-adaptation and this decrease is thought ...

We examined how several characteristics of cat retinal ganglion cells--receptive field size, spatial resolution, and centre-surround antagonism--change with background illumination. Spectral sensitivity was also measured to see how these changes depend on the rod-cone shift. The radius of the centre mechanism changed very little across the mesopic range. The absence ...

Changes in electroretinographic b-wave in the presence of background lights of increasing intensity were examined in isolated, superfused carp retinas. Within a certain range of ambient illumination b-waves elicited by red (695 nm) test flashes against dimmer background lights were smaller in size than against brighter ones. Accordingly, incremental thresholds ...

The glucose concentration (gl) in mammalian serum incorporates a normal range of variation of several millimoles. We studied the effects of such variations on light-evoked electrical signals in the in vitro arterially perfused cat eye, avoiding extraocular regulatory mechanisms that might confound data interpretation. Changes in gl from the nominal ...

Dark voltage and light responses of isolated retinal rods of Rana esculenta were investigated by employing the whole-cell patch-clamp technique. When the recording pipette was filled with a medium devoid of nucleotides, a spontaneous hyperpolarization of the dark voltage partly due to a diffusional loss of cGMP and its precursor ...

The time course of dark adaptation was measured in 10 subjects from three families with autosomal dominant sector retinitis pigmentosa (RP) due to mutations in the first exon of the rod opsin gene. In each subject cone adaptation and the early part of the recovery of rod sensitivity followed the ...

Ss wielded an occluded L-shaped rod and attempted to perceive the direction in which the rod was pointing with respect to the hand. The pattern of the rod's different resistances to rotation in different directions, quantified by the inertia tensor, changes systematically with the rod's orientation. Perception of orientation by ...

We recorded pH in the extracellular space surrounding rod photoreceptors in the dark-adapted eye of the cat and during illumination with double-barreled H(+)-selective microelectrodes. A pH of 7.17 was recorded in the vitreous at the retinal surface of the dark-adapted eye and this became more alkaline during light adaptation. In ...

The dark current of single isolated toad rods was monitored by drawing either the inner segment or the outer segment into a suction electrode. The potassium-channel blockers tetraethylammonium (TEA) and 3,4-diaminopyridine (DAP) reduced the amplitude of the dark current when applied to the inner segment. Both drugs were less effective ...

Literature data on light detection by cone and rod vision at absolute threshold are analysed in order (1) to decide whether the threshold performance of dark-adapted cone vision can, like that of rod vision, be consistently explained as limited by noise from a "dark light"; (2) to obtain comparable estimates ...

Under mesopic conditions the contrast sensitivity of the central visual field is reduced as the result of a non-linear interaction between rod- and cone-mediated signals, each of which is capable of higher sensitivity in isolation. The interaction is produced only when the rod-mediated system is driven at flicker rates above ...

Scotopic visual thresholds and time courses for dark adaptation were determined in eight patients with Sorsby's fundus dystrophy. Rhodopsin regeneration also was recorded in two. All patients had poor night vision and a visible yellow deposit at the level of Bruch's membrane that was confluent in the posterior pole. In ...

1. We have undertaken a theoretical analysis of the steps contributing to the phototransduction cascade in vertebrate photoreceptors. We have explicitly considered only the activation steps, i.e. we have not dealt with the inactivation reactions. 2. From the theoretical analysis we conclude that a single photoisomerization leads to activation of ...

We studied rod and cone function in 13 patients from four families with autosomal dominant retinitis pigmentosa and the proline-23-histidine rhodopsin mutation. In patients with early stages of this disease, rod sensitivity was mildly abnormal throughout the retina and cone sensitivity was normal. In more severely affected patients, sensitivity loss ...

In normal observers, sensitivity of cones to rapid sinusoidal flicker decreases by about 0.7 log units as rods progressively dark adapt. However, Arden and Hogg (1985) described a night-vision disorder characterized by normal rod sensitivity but exaggerated suppressive rod-cone interaction (SRCI). We refer to this condition as the exaggerated SRCI ...

Electrophysiological studies have established that lead exposure produces selective rod deficits. The present electroretinographic (ERG) and correlated calcium experiments examined whether low-level or moderate-level developmental lead exposure (peak blood lead of 19 and 59 micrograms/dl, respectively) altered dark adaptation and/or light adaptation. Developmental lead exposure produced long-term dose-response (1) decreases ...

Dark-adapted rods exert a tonic suppressive influence upon cone-mediated sensitivity to rapid flicker, a phenomenon called suppressive rod-cone interaction (SRCI). However, rod dark adaptation has negligible influence upon cone-mediated thresholds measured with more usual psychophysical procedures. The present study separately examined the influences of rod light and dark adaptation upon ...

1. Incremental thresholds were measured in a retinal region 12 deg temporal from the fovea with a target of 200 ms in duration and 6 deg in diameter superimposed on background fields of various intensities and wavelengths. Measurements were made under rod-isolation conditions in five normal observers and in a ...

Using suction electrodes, photocurrent responses to 100-ms saturating flashes were recorded from isolated retinal rods of the larval-stage tiger salamander (Ambystoma tigrinum). The delay period (Tc) that preceded recovery of the dark current by a criterion amount (3 pA) was analyzed in relation to the flash intensity (If), and to ...

Phototransduction mechanisms have been so far investigated mostly in rods, whereas those in cones are much less known. In the present experiment, we investigated phototransduction mechanisms in inside-out patches excised from cone outer segments of the carp. Cyclic GMP-activated channels on the patch became light-sensitive when both GTP and Mg2+ ...

1. The effects of glycine on horizontal cells have been examined by microelectrode recording from superfused retinas isolated from the salamander. 2. Low concentrations of glycine (less than 50 microM) hyperpolarized horizontal cells and increased the magnitude of their light responses. Millimolar concentrations produced the opposite effect of depolarizing these ...

Retinal densitometry is a noninvasive physiologic technique used to examine the visual pigments in living human eyes. To assess possible age-related disturbances of rod photopigment kinetics, retinal densitometry was done in 44 eyes of 44 healthy subjects (age range, 12-78 yr). With progressing age, a significant but small increase in ...

We studied the activation of 3',5'-cyclic guanosine monophosphate (cGMP) phosphodiesterase (PDE) by using a cell-permeant enzyme inhibitor. Rods of Ambystoma tigrinum held in a suction electrode were jumped into a stream of 3-isobutyl-1-methylxanthine (IBMX), 0.01-1 mM. Initial transient light-sensitive currents fit the notion that dark and light-activated forms of PDE ...