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At least 1,243 records · Page 69Linked to original sources
PubMed1971

Spectral sensitivity studies on the visual system of the praying mantis, Tenodera sinensis.

In these studies a constant ERG response was used as a measure of visual sensitivity to different wavelengths of light. The dark-adapted compound eye of Tenodera sinensis is dominated by a single class of photoreceptors. with a major peak of sensitivity at about 510-520 nm, and with a minor peak of sensitivity in the near-ultraviolet region at about 370 nm. The dark-adapted dorsal ocellus does not contain a homogeneous population of sensory receptors. The sensitivity function of the dark-adapted ocellus to longer wavelength light (yellow and red) is determined by a single receptor with a major peak of sensitivity in the green at 510-520 nm with some sensitivity in the near-ultraviolet. Sensitivity at shorter wavelengths (near-ultraviolet and blue), however, involves the stimulation of both this and a near-ultraviolet-sensitive receptor with a maximum sensitivity at about 370 nm. Anatomically, the sensory cells of the dorsal ocellus of Tenodera were determined histologically to be grouped into two distinct regions, each group making its own separate contribution to the ocellar nerve. This may represent the separation of two different photoreceptor types in the ocellus of the mantis.

Adaptation, Ocular↗
PubMed1973

Adaptation in the ventral eye of Limulus is functionally independent of the photochemical cycle, membrane potential, and membrane resistance.

The early receptor potential (ERP), membrane potential, membrane resistance, and sensitivity were measured during light and/or dark adaptation in the ventral eye of Limulus. After a bright flash, the ERP amplitude recovered with a time constant of 100 ms, whereas the sensitivity recovered with an initial time constant of 20 s. When a strong adapting light was turned off, the recovery of membrane potential and of membrane resistance had time-courses similar to each other, and both recovered more rapidly than the sensitivity. The receptor depolarization was compared during dark adaptation after strong illumination and during light adaptation with weaker illumination; at equal sensitivities the cell was more depolarized during light adaptation than during dark adaptation. Finally, the waveforms of responses to flashes were compared during dark adaptation after strong illumination and during light adaptation with weaker illumination. At equal sensitivities (equal amplitude responses for identical flashes), the responses during light adaptation had faster time-courses than the responses during dark adaptation. Thus neither the photochemical cycle nor the membrane potential nor the membrane resistance is related to sensitivity changes during dark adaptation in the photoreceptors of the ventral eye. By elimination, these results imply that there are (unknown) intermediate process(es) responsible for adaptation interposed between the photochemical cycle and the electrical properties of the photoreceptor.

Action Potentials↗
PubMed1973

Early receptor potential evidence for the existence of two thermally stable states in the barnacle visual pigment.

The early receptor potential (ERP) in the barnacle photoreceptor is shown by intracellular recording to exhibit a strong dependence on the color of the stimulus and of the preceding adaptation. The adaptation effects appear to be stable for at least 3 h in the dark. Most strikingly, the ERP is positive after red adaptation and mainly negative after blue adaptation. The simplest hypothesis which accounts for these observations is that two thermally stable pigment states with different absorption spectra contribute to the ERP. All ERP responses appear to be consistent with the sums of different ratios of the ERP's of the two pure states. The relative populations of the two states are shown to vary reciprocally, suggesting that the two are states of the same closed pigment cycle. Both states have approximately Dartnall nomogram-shaped absorption spectra, one peaked near 495 nm, and the other near 532 nm.

Adaptation, Ocular↗
PubMed1974

Independence of location of light absorption and discrete wave latency distribution in Limulus ventral nerve photoreceptors.

Discrete waves of depolarization evoked by dim pulses of light in dark-adapted ventral nerve photoreceptors in Limulus show fluctuation in their latency. To a resolution of 5-10 microm the latency distribution function appears to be independent of where in the receptor light is absorbed. Also, there is apparent local adaptation to bright light pulses.

Adaptation, Ocular↗
PubMed1975

Properties of visual cells in the lateral eye of Limulus in situ.

Excitatory properties of visual cells in the lateral eye of Limulus, investigated by optic nerve recordings in situ, differ significantly from the properties of cells in the classical, excised eye preparation. The differences suggest the possibility that two receptor mechanisms function in the eye in situ: one mechanism encodes low light intensities and the other responds to high intensities. The two mechanisms enable each ommatidium to respond over an intensity range of approximately 10 log units. This hypothesis was tested by measuring the increment threshold and the spectral sensitivity, by studying light and dark adaptation, and by analyzing the variability of the impulse discharge. Although the results do not conclusively identify two receptor mechanisms, they indicate that a process or a part of a process that functions in the eye in situ is abolished by excising the eye or cutting off its blood supply.

Action Potentials↗
PubMed1975

Light-induced changes of sensitivity in Limulus ventral photoreceptors.

The responses of Limulus ventral photoreceptors to brief test flashes and to longer adapting lights were measured under voltage clamp conditions. When the cell was dark adapted, there was a range of energy of the test flashes over which the peak amplitude of the responses (light-induced currents) was directly proportional to the flash energy. This was also true when test flashes were superposed on adapting stimuli but the proportionality constant (termed peak currently/photon) was reduced. The peak current/photon was attenuated more by brighter adapting stimuli than by less bright adapting stimuli. The peak current/photon is a measure of the sensitivity of the conductance-increase mechanism underlying the light response of the photo-receptor. The response elicited by an adapting stimulus had a large initial transient which declined to a smaller plateau. The peak current/photon decreased sharply during the declining phase of the transient and was relatively stable during the plateau. This indicates that the onset of light adaptation is delayed with respect to the onset of the response to the adapting stimulus. If the adaptational state just before the onset of each of a series of adapting stimuli was constant, the amplitude of the transient was a nearly linear function of intensity. When the total intensity was rapidly doubled (or halved) during a plateau response, the total current approximately doubled (or halved). We argue that the transition from transient to plateau, light-elicited changes of threshold, and the nonlinear function relating the plateau response to stimulus intensity all reflect changes of the responsiveness of the conductance-increase mechanism.

Adaptation, Ocular↗
PubMed1975

Local adaptation in the ventral photoreceptors of Limulus.

Local adaptation was demonstrated in the ventral photoreceptors of Lumulus using either flashes or continuous illumination. Spots of light locally desensitized the region of the photoreceptor on which they were focused. In dark-adapted photoreceptors where "quantum bumps" were clearly discernible, local adaptation of the quantum bumps was observed. Local adaptation could induce differences of threshold of 1 decade over distances of 50-80 mum. With continuous local illumination these gradients could be maintained from 2 s to 30 min. In addition, the decrease in time scale associated with light adaptation was also found to be localized to the region of illumination.

Adaptation, Ocular↗
PubMed1991

Physiological roles of Na+/Ca2+ exchange in Limulus ventral photoreceptors.

In previous work we have presented evidence for electrogenic Na+/Ca2+ exchange in Limulus ventral photoreceptors (1989. J. Gen. Physiol. 93:473-492). This article assesses the contributions to photoreceptor physiology from Na+/Ca2+ exchange. Four separate physiological processes were considered: maintenance of resting sensitivity, light-induced excitation, light adaptation, and dark adaptation. (a) Resting sensitivity: reduction of [Na+]o caused a [Ca2+]o-dependent reduction in light sensitivity and a speeding of the time courses of the responses to individual test flashes; this effect was dependent on the final value to which [Na+]o was reduced. The desensitization caused by Na+ reduction was dependent on the initial sensitivity of the photoreceptor; in fully dark-adapted conditions no desensitization was observed; in light-adapted conditions, extensive desensitization was observed. (b) Excitation: Na+ reduction in fully dark-adapted conditions caused a Ca2+o-dependent depolarizing phase in the receptor potential that persisted beyond the stimulus duration and was evoked by a bright adapting flash. (c) Light adaptation: the degree of desensitization induced by a bright adapting flash was Na+o dependent, being larger with lower [Na+]o. Na+ reduction enhanced light adaptation only at intensities brighter than 4 x 10(-6) W/cm2. In addition to being Na+o dependent, light adaptation was Ca2+o dependent, being greater at higher [Ca2+]o. (d) Dark adaptation: the recovery of light sensitivity after adapting illumination was Na+o dependent. Dark adaptation after bright illumination in voltage-clamped and in unclamped conditions was faster in normal-Na+ saline than in reduced Na+ saline. The final sensitivity to which photoreceptors recovered was lower in reduced-Na+ saline when bright adapting illumination was used. The results suggest the involvement of Na+/Ca2+ exchange in each of these physiological processes. Na+/Ca2+ exchange may contribute to these processes by counteracting normal elevations in [Ca2+]i.

Adaptation, Ocular↗
PubMed1997

Retinal control of scleral precursor synthesis.

There is a light-dependent diurnal rhythm in scleral precursor synthesis (SPS). In form-deprivation myopia (FDM) there is an increase in SPS. Daily periods of normal vision prevent FDM, but light intensities that maintain the retinal dark-light switch in its dark state do not, implicating melatonin, dopamine, enkephalin, neurotensin and somatostatin in the control of SPS. FDM is also prevented by pirenzepine, a cholinergic muscarinic antagonist To test if these compounds control the rate of SPS, agonists and antagonists were applied directly to the sclera, but the only effects detected were at very high concentrations, making them physiologically insignificant.

Adaptation, Ocular↗
PubMed1996

Spectral plasticity of H1 horizontal cells in carp retina: independent modulation by dopamine and light-adaptation.

It was shown previously that the spectral sensitivity of luminosity/H1-type horizontal cells (HCs) in carp retinae reflects the absorption spectrum of red-sensitive cones for long wavelengths but can appear highly variable and "truncated' in the short-wavelength region of the spectrum. We have found that light-adaptation sharpened the red-sensitive spectral peak and decreased the blue/red response amplitude ratio (B/R ratio), mainly by decreasing the response to short-wavelength stimuli. The adaptation effect was more pronounced for red background light than for blue. During dark adaptation, the B/R ratio increased steadily. Exogenous dopamine (DA; 5 microM) changed the spectral response profile in a similar way to light-adaptation. However, the effect of light-adaptation in reducing the B/R ratio was still seen in retinae bathed in 5 microM DA. This effect of background adaptation was also recorded in retinae bathed in 37 microM haloperidol, as well as in retinae pretreated with 6-hydroxydopamine (i.e. DA-depleted). The results suggest that (i) short-wavelength-sensitive cones play a dynamic role in determining the spectral response profile of H1 HCs and (ii) spectral response characteristics are modulated independently by exogenous DA and an unknown endogenous neuromodulator which is activated by light-adaptation.

Adaptation, Ocular↗
PubMed1999

Light adaptation and dark adaptation of human rod photoreceptors measured from the a-wave of the electroretinogram.

1. We recorded the a-wave of the human electroretinogram from subjects with normal vision, using a corneal electrode and ganzfeld (full-field) light stimulation. From analysis of the rising phase of rod-isolated flash responses we determined the maximum size (amax) of the a-wave, a measure of the massed circulating current of the rods, and the amplification constant (A) of transduction within the rod photoreceptors. 2. During light adaptation by steady backgrounds the maximal response was reduced, as reported previously. amax declined approximately as I0/(I0 + IB), where IB is retinal illuminance and I0 is a constant. In different subjects I0 ranged from 40 to 100 trolands, with a mean of 70 trolands, corresponding to about 600 photoisomerizations s-1 per rod. (1 troland is the retinal illuminance that results when a surface luminance of 1 cd m-2 is viewed through a pupil area of 1 mm2.) The amplification constant A decreased only slightly in the presence of steady backgrounds. 3. Following a full bleach amax recovered along an S-shaped curve over a period of 30 min. There was no detectable response for the first 5 min, and half-maximal recovery took 13-17 min. 4. The apparent amplification constant decreased at early times after large bleaches. However, upon correction for reduced light absorption due to loss of pigment, with regeneration of rhodopsin occurring with a time constant of 9-15 min in different subjects, it appeared that the true value of A was probably unchanged by bleaching. 5. The recovery of amax following a bleach could be converted into recovery of equivalent background intensity, using a 'Crawford transformation' derived from the light adaptation results. Following bleaches ranging from 10 to > 99 %, the equivalent background intensity decayed approximately exponentially, with a time constant of about 3 min. 6. The time taken for amax to recover to a fixed proportion of its original level increased approximately linearly (rather than logarithmically) with fractional bleach, with a slope of about 12 min per 100 % bleach. Similar behaviour has previously been seen in psychophysical dark adaptation experiments, for the dependence of the 'second component' of recovery on the level of bleaching.

Adaptation, Ocular↗
PubMed1995

ERG OFF response in frog retina: light adaptation and effect of 2-amino-4-phosphonobutyrate.

The intensity-response (V/log I) function of ERG OFF response (d-wave) in dark and light adapted superfused frog eyecups was investigated before and after blockade of the retinal ON channel by 2-amino-4-phosphonobutyrate (APB). The V/log I function of the dark adapted d-wave had two distinct components, each of them consisting of an ascendent and descendent part. In eyes adapted to mesopic or photopic background the V/log I function had only one component. It was shifted to the right along the intensity axis, had a steeper slope and a higher maximal response amplitude compared with the two components of the dark-adapted V/log I curve. Perfusion with 200 mumol APB markedly increased the d-wave amplitude at all stimulus intensities except for the threshold ones in both dark and light adapted eyes. The position of the V/log I curve was shifted slightly to the left along the intensity axis in dark adapted eyes, but was not changed in light adapted eyes. Thus the adaptational mechanism responsible for changes in the decremental sensitivity with increased background illumination was not altered by APB. The effect of APB was studied also in chromatically adapted eyes, in which the responses were predominantly mediated by one photoreceptor type. The results showed that the potentiating effect of APB on d-wave did not depend on photoreceptor input.

Adaptation, Ocular↗
PubMed1982

Evaluation of pupillary function in thyroid disease.

Employing the technique of infrared television pupillography, the pupil area in darkness, pupillary unrest, and various parameters of the light response were measured in 5 patients with clinical and biochemical overt thyrotoxicosis and in 2 patients with longstanding severe primary myxoedema. The patients were studied before and after medical treatment. The treatments did not induce significant alterations in any of the parameters measured. Thus pupillary measurements are not a convenient method for recording of peripheral thyroid hormone action.

Adaptation, Ocular↗
PubMed1971

The Purkinje shift in cat: extent of the mesopic range.

1. The mesopic range, defined for cats with fully dilated pupils, extends from -1.0 to +1.4 log cd/m(2). The technique employed involves measurement of the relative shift in threshold with adaptation level, between two wave-lengths respectively selective for cones and rods at threshold. The magnitude of this shift is compared with that predicted from the Dartnall nomogram for visual pigments 556 and 507 (the in situ cone and rod absorption maxima).2. The result is based on monochromatic increment threshold determinations for 149 on-centre or off-centre fibres, isolated in the optic tract posterior to the chiasma, under a variety of adaptation levels. All units included receive dual input - from 500 nm rods and from a single class of cones with maximum sensitivity at 556 nm. No units receive input from 450 nm cones; six units with input mediated purely by rods are excluded from the sample.

Adaptation, Ocular↗
PubMed1973

Scotopic and photopic components of the rat electroetinogram.

1. Increment thresholds were measured on the albino rat retina using the e.r.g. as an indicator of visual sensitivity.2. Light adaptation produces a change in b-wave spectral sensitivity independently of whether brief or steady adapting backgrounds are used. This shows that the changed spectral sensitivity is not directly associated with the bleaching of visual pigment.3. Light adaptation does not appear to alter the spectral sensitivity of the ordinary a-wave. Consequently, after light adaptation a- and b-waves have different spectral sensitivities.4. B-wave increments determined with a blue test stimulus on a red adaptive background show rod saturation. Background levels which saturate the rods cause the a-wave mechanism to cease responding to incremental stimuli.5. A background intense enough to saturate the rods evokes a maximum a-wave response. If a light is sufficiently bright to saturate the rods then the isolated a-wave fails to signal the termination of the stimulus.6. Scotopically equated blue and orange stimuli produce equal early receptor potentials.

Adaptation, Ocular↗