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At least 973 records · Page 54Linked to original sources
PubMed2004

Light-adaptation attenuates the effects of phosphodiesterase blackade by Zaprinast in the isolated rat retina.

The effect of the type V/VI-selective phosphodiesterase inhibitor, Zaprinast, (200 microM) on the light-evoked extracellular field potential (EFP) in the isolated rat retina was tested under dark- and light-adapted conditions at two different temperatures. Peak enhancement EFP in dark- (344 +/- 70%; mean +/- SEM) and light-adapted (182 +/- 31%) retina at 37 degrees C was reached within 3 min of treatment with Zaprinast (200 microM) followed by a slower decrease to a level of 85 +/- 14 and 26 +/- 7% in dark- and light-adapted retina, respectively. The effect of Zaprinast (20 microM) on the pharmacologically-isolated photoreceptor component of the EFP was lost with increasing levels of background light. This may suggest that there is a slow time scale (minutes) shift in the steady state level of cGMP during light-adaptation.

Adaptation, Ocular↗
PubMed2005

The visual evoked potential in the mouse--origins and response characteristics.

The visual evoked potential (VEP) in the mouse is characterized and compared to responses obtained with the electroretinogram (ERG). The results indicate that: 1, the VEP originates in the visual cortex; 2, the rod and cone pathways contribute separately to the VEP; 3, temporal tuning functions for rod and cone ERGs are low pass and band pass, respectively; VEP tuning functions are both band pass; and 4, VEP acuity is 0.62+/-0.156 cycles/degree. The differences in the spatial and temporal tuning functions obtained from the retina and visual cortex provides a tool to investigate signal processing through the visual system.

Adaptation, Ocular↗
PubMed2005

Recovery of rod-mediated a-wave during light-adaptation in mGluR6-deficient mice.

The purpose of this study was to compare the a-waves of mGluR6-deficient mice (KO) to that of wild-type mice (WT), and to determine whether the light-adapted electroretinogram of the KO mice originate exclusively from cones. Dark-adapted a-waves were recorded under the same conditions from both types of mice. With a 96-cd/m(2) background, the a-wave from both types of mice showed a rapid recovery over a 50-min period. The analysis of the a-waves in KO mice indicated that the recovery was determined mainly by the rod component. The light-adapted b-wave of WT mice showed no corresponding recovery. We conclude that rod contribution must be considered in the analyses of the light-adapted a-waves of KO mice.

Adaptation, Ocular↗
PubMed1999

Sensitivity and dynamics of rod signals in H1 horizontal cells of the macaque monkey retina.

We measured the sensitivity, temporal frequency response, latency, and receptive field diameter of rod input to the H1 horizontal cell type in an in vitro preparation of the macaque retina. The H1 cell has both a cone-connected dendritic tree and a long axon-like process that terminates in a rod-connected arbor. We recorded from the H1 cell body where rod signals were distinguished by sensitivity to short wavelength light after dark adaptation. Receptive fields of rod vs. cone mediated responses were coextensive, indicating that the rod signal is transmitted via rod-cone gap junctions. Sensitivity of the H1 cell rod signal was approximately 1 log unit higher than that of the cone signal. Below cone threshold rod signals were temporally low-pass, with a cutoff frequency below 10 Hz. Rod signals became faster and more transient with increasing light levels. We conclude that the H1 cell rod signal is not sensitive in the low scotopic range and, by comparison with the rod signal recorded directly in cones (Schneeweis & Schnapf (1995) Science, 268, 1053-1056), signal transmission across the cone-H1 synapse does not significantly filter the temporal properties of the rod signal.

Adaptation, Ocular↗
PubMed1997

Changes in NADPH diaphorase reactivity and neuronal nitric oxide synthase in the rat retina following constant illumination.

The distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) reactivity and neuronal nitric oxide synthase immunoreactivity (nNOS-IR) was investigated in the rat retina during photoreceptor regeneration. Photoreceptor damage and the disappearance of a NADPHd reactive/nNOS-IR band corresponding to inner photoreceptor segments were observed after continuous exposure to light irradiation. Both events were reversible after 20 days of total darkness. Also a progressive decrease in the number and in the staining intensity of NADPHd reactivity in amacrine cells were found along the first 3-6 days of darkness stabilizing thereafter in both illuminated and control groups. However, staining intensity in the former group remained more elevated than in the latter one. NOS activity in the retina varies depending on functional and pathological states.

Adaptation, Ocular↗
PubMed1999

Comparable effects of flickering and steady patterns of light adaptation on photomechanical responses of cones in amphibian (Xenopus laevis) retina.

The effects of two distinct patterns of light stimulus, steady and flicker, on cone photomechanical movements (PMMs) in the Xenopus laevis retina were investigated. For both patterns studied, the effects on PMMs were assessed by quantitative analysis of the cone positions in the outer retina. Steady light adaptation was found to be equally effective as flicker in causing cone contractions. This was unlike the situation previously found in the cyprinid fish retina, in which flickering light was significantly more effective than steady. This difference could be related to the light-evoked response characteristics and circuitry of dopaminergic retinal neurones in the two vertebrate classes. The role of dopamine and other possible neuromodulator(s) in light adaptive control of vertebrate retinae is discussed.

Adaptation, Ocular↗
PubMedDate not supplied

NADPH diaphorase activity in mammalian retinas is modulated by the state of visual adaptation.

NADPH diaphorase histochemistry is commonly used to identify cells containing nitric oxide synthase (NOS), the enzyme catalyzing the production of nitric oxide from L-arginine. NADPH diaphorase activity and NOS immunostaining was demonstrated in different cells of the vertebrate retina; photoreceptors, horizontal cells, amacrine cells, ganglion cells, and Müller cells. However, the physiological role of nitric oxide (NO) in the retina has yet to be elucidated. In this study, we tested the assumption that NADPH diaphorase activity in the retinas of rabbits and rats depended on the state of visual adaptation. In the rabbit, light adaptation enhanced NADPH diaphorase activity in amacrine cells and practically eliminated it in horizontal cells. Dark adaptation induced the opposite effects; the NADPH diaphorase activity was reduced in amacrine cells and enhanced in horizontal cells. Retinas from eyes that were injected intravitreally with L-glutamate exhibited a pattern of NADPH diaphorase activity that was similar to that seen in dark-adapted retinas. In rats, the NADPH diaphorase activity of amacrine and horizontal cells exhibited adaptation dependency similar to that of the rabbit retina. But, the most pronounced effect of dark adaptation in the rat's retina was an enhancement of NADPH diaphorase activity in Müller cells, especially of the endfoot region. Assuming that NADPH diaphorase activity is a marker for NOS, these findings suggest that NO production in the mammalian retina is modulated by the level of ambient illumination and support the notion that NO plays a physiological role in the retina.

Adaptation, Ocular↗
PubMed1992

Influence of rod adaptation upon cone responses to light offset in humans: I. Results in normal observers.

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 cone-mediated sensitivity to transient increases or decreases in illumination using sawtooth flicker with rapid-on (ramp-off) or rapid-off (ramp-on) waveforms. In the parafoveal retina, cones alone were stimulated with flicker by spatially superimposing long- and short-wavelength stimuli presented in counterphase and matched in scotopic illuminance. Several different adaptation procedures were used. For higher (greater than 4 Hz) frequencies, sensitivity of cones to both waveforms is nearly identical under any condition of adaptation; sensitivity decreases as rods progressively dark adapt. A considerably different situation exists for slower frequencies (1-4 Hz). Sensitivity of cones to rapid-off flicker is appreciably greater under light-adapted conditions confirming recent observations by Bowen et al. (1989). But as rods progressively dark adapt, sensitivity of cones to rapid-off waveforms decreases considerably while sensitivity to rapid-on waveforms is much less affected; in the totally dark-adapted eye, sensitivity to both waveforms is identical. These results confirm and extend recent physiological observations in amphibian retina (Frumkes & Wu, 1990) suggesting that SRCI specifically involves responses to transient decreases in illumination.

Adaptation, Ocular↗
PubMed1992

Light adaptation, rods, and the human cone flicker ERG.

During the course of light adaptation, the amplitude and implicit time of the human cone ERG change systematically. In the present study, the effect of adapting field luminance on these ERG changes was assessed, and the hypothesis that light adaptation of the rod system is the primary determining factor was evaluated. Cone ERG responses, isolated through the use of 31.1-Hz flicker, were obtained from two visually normal subjects, initially under dark-adapted conditions and then repeatedly for 30 min following the onset of each of a series of ganzfeld adapting fields with luminances that ranged from -1.2 to 2.1 log cd/m2. The increase in flicker ERG amplitude and decrease in implicit time during light adaptation were greatest at the highest adapting field luminances. Photopically equivalent achromatic and long-wavelength adapting fields induced comparable increases in flicker ERG amplitude, while scotopically equivalent adapting fields had considerably different effects. This latter finding demonstrates that the rod system is not a major determinant of the adaptation-induced increase in cone ERG amplitude.

Adaptation, Ocular↗
PubMedDate not supplied

Modulation of transduction gain in light adaptation of retinal rods.

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 background illumination. Background light decreased the saturation period (T) measured at fixed flash intensity (fixed If) and in this respect light-adapted the saturating response. Effects of the background on responses to weak (i.e. subsaturating) and bright flashes were compared with changes in a parameter, phi = e-delta T/TR*, where delta T is the decrease in saturation period, and where TR* is the slope of the line that relates T and ln If in a given state of adaptation. Dark- and light-adapted responses to flash intensities IDf and ILf, respectively, exhibited similar absolute peak photocurrent and falling-phase kinetics when IDf and ILf satisfied the relation, IDf = phi (ILf + IbTR*), where Ib is the background intensity. It is argued that phi approximates the relative PDE*/R* gain of transduction, i.e. the relative peak level of activated cGMP phosphodiesterase (PDE*) produced by a given, small amount of photoactivated visual pigment (R*). Interpreted on this view, the results imply that light adaptation derives largely from a decrease in PDE*/R gain, rather than from the stimulation of guanylate cyclase activity. The data are consistent with the possibility that modulation of the lifetime of PDE* underlies the background dependence of phi.

Adaptation, Ocular↗
PubMedDate not supplied

Serotonin receptors modulate rod signals: a neuropharmacological comparison of light- and dark-adapted retinas.

Previous physiological studies have shown that serotonin (5-HT) reciprocally modulates ON and OFF channels in the mammalian retina. This study was undertaken to determine if the serotoninergic system is exclusively associated with the rod pathway. We tested drugs specific to 5-HT3 receptor, a serotonin-gated ion channel, in both dark- and light-adapted retina. Consistent with previous studies, we demonstrated that 5-HT3 receptors modulate the light-evoked responses of ganglion cells in the dark-adapted state. Moreover, we have extended these prior studies and shown that activation of the 5-HT3 receptor is capable of completely blocking the light-evoked response of OFF-center cells whereas inactivation of the 5-HT3 receptor is capable of completely blocking the light-evoked responses of ON-center cells. In contrast, in light-adapted retinae, serotonin agents failed to have any effect on retinal processing. These data suggest that the serotoninergic system in retina is (1) specifically associated with rod-related pathways; and (2) exerts a powerful modulatory force over information transfer in the retina. Together these observations suggests that serotonin plays an important physiological role in modulating retinal processing.

Adaptation, Ocular↗
PubMed2001

Background light adaptation of the retinal neuronal adaptive system. I. Effect of background light intensity.

The behaviour of the neuronal adaptive retinal mechanisms to environmental light exposures was studied by measuring the oscillatory potentials (OPs) of the electroretinogram. Dark adapted rats were exposed to four levels of background light (BG), starting at a 'low scotopic' level of 1.43x 10(6) cd/m2, increased by steps of two log units, through 'high scotopic' -, 'low mesopic' - and finally the 'high mesopic' BG of 1.43x 10(0) cd/m2. The summed oscillatory response significantly increased as the BG intensity was raised, except at the 'high mesopic' level. The amplitudes of the a- and b-waves reduced as the BG light increased above the 'high scotopic' level. Each OP responded individually to the different BGs. O1 and O2, significantly enhanced at the 'low scotopic' BG. The amplitudes of the three later OPs increased significantly at the 'low mesopic' BG. The adaptational behaviour of the retinal oscillatory response to BG illumination was different to that of the a- and b- waves. The results indicate that the adaptational neuronal system, as reflected by the OPs, seems to be relatively robust and is separate from the slower photochemical adaptive process in the distal retina. The tentative corollary suggests the oscillatory system to play a vision-preserving role, possibly as an alert against undue depletion of the slowly regenerating visual pigment. The enhancement of the oscillatory response at the 'mesopic' illumination levels indicate both scotopic and photopic processes to contribute to neuronal adaptive activity of the retina.

Adaptation, Ocular↗
PubMed2002

Heat shock protein 70 and heat shock protein 90 expression in light- and dark-adapted adult octopus retinas.

Light- and dark-adaptation leads to changes in rhabdom morphology and photopigment distribution in the octopus retina. Molecular chaperones, including heat shock proteins (Hsps), may be involved in specific signaling pathways that cause changes in photoreceptor actin- and tubulin-based cytoskeletons and movement of the photopigments, rhodopsin and retinochrome. In this study, we used immunoblotting, in situ RT-PCR, immunofluorescence and confocal microscopy to localize the inducible form of Hsp70 and the larger Hsp90 in light- and dark-adapted and dorsal and ventral halves of adult octopus retinas. The Hsps showed differences in distribution between the light and dark and in dorsal vs. ventral position in the retina. Double labeling confocal microscopy co-localized Hsp70 with actin and tubulin, and Hsp90 with the photopigment, retinochrome. Our results demonstrate the presence of Hsp70 and Hsp90 in otherwise non-stressed light- and dark-adapted octopus retinas. These Hsps may help stabilize the cytoskeleton, important for rhabdom structure, and are perhaps involved in the redistribution of retinochrome in conditions of light and dark.

Adaptation, Ocular↗