S-Potentials in the Skate Retina : Intracellular recordings during light and dark adaptation

The S-potentials recorded intracellularly from the all-rod retina of the skate probably arise from the large horizontal cells situated directly below the layer of receptors. These cells hyperpolarize in response to light, irrespective of stimulus wavelength, and the responses in photopic as well as scotopic conditions were found to be subserved by a single photopigment with λ_max = 500 nm. The process of adaptation was studied by recording simultaneously the threshold responses and membrane potentials of S-units during both light and dark adaptation. The findings indicate that the sensitivity of S-units, whether measured upon steady background fields or in the course of dark adaptation, exhibits changes similar to those demonstrated previously for the ERG b-wave and ganglion cell discharge. However, the membrane potential level of the S-unit and its sensitivity to photic stimulation varied independently for all the adapting conditions tested. It appears, therefore, that visual adaptation in the skate retina occurs before the S-unit is reached, i.e., at the receptors themselves.     

Visual Adaptation in the Retina of the Skate

The electroretinogram (ERG) and single-unit ganglion cell activity were recorded from the eyecup of the skate (Raja erinacea and R. oscellata), and the adaptation properties of both types of response compared with in situ rhodopsin measurements obtained by fundus reflectometry. Under all conditions tested, the b-wave of the ERG and the ganglion cell discharge showed identical adaptation properties. For example, after flash adaptation that bleached 80% of the rhodopsin, neither ganglion cell nor b-wave activity could be elicited for 10–15 min. Following this unresponsive period, thresholds fell rapidly; by 20 min after the flash, sensitivity was within 3 log units of the dark-adapted level. Further recovery of threshold was slow, requiring an additional 70–90 min to reach absolute threshold. Measurements of rhodopsin levels showed a close correlation with the slow recovery of threshold that occurred between 20 and 120 min of dark adaptation; there is a linear relation between rhodopsin concentration and log threshold. Other experiments dealt with the initial unresponsive period induced by light adaptation. The duration of this unresponsive period depended on the brightness of the adapting field; with bright backgrounds, suppression of retinal activity lasted 20–25 min, but sensitivity subsequently returned and thresholds fell to a steady-state value. At all background levels tested, increment thresholds were linearly related to background luminance.     

Rhodopsin photoproducts and rod sensitivity in the skate retina

The late photoproducts that result from the isomerization of rhodopsin have been identified in the isolated all-rod retina of the skate by means of rapid spectrophotometry. The sequence in which these intermediates form and decay could be described by a scheme that incorporates two pathways for the degradation of metarhodopsin II (MII) to retinol: one via metarhodopsin III (MIII) and the other (which bypasses MIII) through retinal. Computer simulation of the model yielded rate constants and spectral absorbance coefficients for the late photoproducts which fit experimental data obtained at temperatures ranging from 7 degrees C to 27 degrees C. Comparing the kinetics of the thermal reactions with the changes in rod threshold that occur during dark adaptation indicated that the decay of MII and the fall in receptor thresholds exhibit similarities with regard to their temperature dependence. However, the addition of 2 mM hydroxylamine to a perfusate bathing the retina greatly accelerated the photochemical reactions, but had no significant effect on the rate of recovery of rod sensitivity. It appears, therefore, that the late bleaching intermediates do not control the sensitivities of skate rods during dark adaptation.     

The time course of dark adaptation in the bee: a phototactic and electrophysiological investigation

ABSTRACT. The time course of dark adaptation in Apis melifera L. was investigated by analyses of phototactic behaviour and electroretinogram (ERG). The behavioural results give a function for dark adaptation showing that in the dark after strong light adaptation the sensitivity increases exponentially with a time constant of 3 min. The sensitivity changes c. 2.4 log units during the time span of 5–720 s. The electrophysiological results indicate a smaller change in sensitivity at the level of the photoreceptors. Within a time span between 20 and 720 s the sensitivity increases during dark adaptation by a factor of 4.3 on a linear scale.     

Neural and Photochemical Mechanisms of Visual Adaptation in the Rat

The effects of light adaptation on the increment threshold, rhodopsin content, and dark adaptation have been studied in the rat eye over a wide range of intensities. The electroretinogram threshold was used as a measure of eye sensitivity. With adapting intensities greater than 1.5 log units above the absolute ERG threshold, the increment threshold rises linearly with increasing adapting intensity. With 5 minutes of light adaptation, the rhodopsin content of the eye is not measurably reduced until the adapting intensity is greater than 5 log units above the ERG threshold. Dark adaptation is rapid (i.e., completed in 5 to 10 minutes) until the eye is adapted to lights strong enough to bleach a measurable fraction of the rhodopsin. After brighter light adaptations, dark adaptation consists of two parts, an initial rapid phase followed by a slow component. The extent of slow adaptation depends on the fraction of rhodopsin bleached. If all the rhodopsin in the eye is bleached, the slow fall of threshold extends over 5 log units and takes 2 to 3 hours to complete. The fall of ERG threshold during the slow phase of adaptation occurs in parallel with the regeneration of rhodopsin. The slow component of dark adaptation is related to the bleaching and resynthesis of rhodopsin; the fast component of adaptation is considered to be neural adaptation.     

中华通草蛉复眼光感受性

运用视网膜电位（Electroretinogram,ERG）技术,对中华通草蛉Chrysopa sinica Tjedar成虫复眼在暗适应过程中对单色光和白光刺激的光感受变化进行了测定。结果表明：（1）在340～605 nm光谱范围内该草蛉的光反应表现3个峰,其中最高峰位于562 nm,次峰在524 nm,第3峰在460 nm;（2）一定光强度（LogI=4.5～0）范围内,其复眼ERG值随光强度的增强而增大,呈近线性增长式样;（3）暗适应时间影响其复眼的ERG值大小,在暗适应100 min时其ERG值达到稳定;（4）中华通草蛉复眼ERG的波形由4个部分组成：开光反应、正相电位、持续负电位和闭光反应。     

Visual pigment,dark adaptation and rhodopsin renewal in the eye of Pontoporeia affinis (Crustacea,Amphipoda)

The benthic amphipod Pontoporeia affinis lives in the Baltic sea and in northern European lakes in an environment where very little light is available for vision. The eyes, consisting of 40–50 ommatidia, are correspondingly modified. Microspectrophotometric recordings on isolated eyes show the presence of at least two kinds of screening pigments in the ommatidia with maxima at 540–580 nm and 460–500 nm. Difference spectra obtained from the rhabdoms after exposure to red and blue light, respectively, give evidence of a single rhodopsin with its maximum at 548 nm and a 500-nm metarhodopsin. In ERG recordings sensitivity in the dark-adapted state, after saturating exposures to blue and to red light, stabilizes at levels determined by the rhodopsin concentration. No change is observed during 10–14 h after the beginning of dark adaptation. However, using animals pre-exposed with a strong red light and then kept in darkness, it is found that after a delay of 20–40 h sensitivity of the dark-adapted eye begins to increase and finally, after 5–6 days reaches a level corresponding to 100% rhodopsin. Thus, a slow renewal of rhodopsin appears to occur in darkness, where a photoisomerization of metarhodopsin is excluded.Abbreviations ERG electroretinogram - IR infrared - MSP microspectrophotometry     

The Rat Electroretinogram : I. Contrasting effects of adaptation on the amplitude and latency of the b-wave

Characteristics of the electroretinogram (ERG) produced by the essentially all rod eye of the rat are presented as functions of the number of quanta absorbed by each rod per stimulus flash. The ERG's were obtained with 1.5 msec. stimulus flashes and uniform illumination of the entire retina. Under these conditions, distortions in the ERG due to stray light are minimized, and the ERG more accurately reflects the activity of its retinal sources. The effects of background light and two forms of dark adaptation were studied and compared. The results, especially for the b-wave, permit an interpretation in terms of two distinct processes. One process appears to determine the b-wave latency. This process is almost independent of the state of adaptation of the retina. The other process does not affect the latency, but determines the b-wave threshold and amplitude. This process strongly depends upon the state of adaptation. Moreover, the effects of dark adaptation on this amplitude-determining process are almost identical with the effects of background light.     

Adaptation in Skate Photoreceptors

Receptor potentials were recorded extracellularly from the all-rod retina of the skate after the application of sodium aspartate. This agent suppresses the responses of proximal elements, but leaves relatively unaffected the electrical activity of the photoreceptors (a-wave) and pigment epithelium (c-wave). Since the latter develops too slowly to interfere with the receptor response, it was possible to isolate receptor potentials and to compare their behavior in light and dark adaptation with earlier observations on the S-potential, b-wave, and ganglion cell discharge. The results show that the photoreceptors display the full complement of adaptational changes exhibited by cells proximal to the receptors. Thus, it appears that visual adaptation in the skate is governed primarily by the photoreceptors themselves. Of particular interest was the recovery of sensitivity in the presence of background fields that initially saturate the receptor potential. Analysis of this recovery phase indicates that a gain-control mechanism operates within the receptors, at a distal stage of the visual process.     

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.     

Pharmacology of the skate electroretinogram indicates independent ON and OFF bipolar cell pathways

Organization of afferent information into parallel ON and OFF pathways is a critical feature of the vertebrate visual system. All afferent visual information in the vertebrate retina reaches the inner plexiform layer (IPL) via bipolar cells. It is at the bipolar cell level that separation of ON and OFF information first appears for afferent information from cones. This may also hold true for the rod pathway of cold-blooded vertebrates, but not for mammals. The all-rod retina of the skate presents an opportunity to examine such pathways in a retina having but a single class of photoreceptor. Immunocytochemical evidence suggests that both ON and OFF bipolar cells are present in the skate retina. We examined the pharmacology of the skate electroretinogram (ERG) to test the hypothesis that independent ON and OFF bipolar cell pathways are functional as rod afferent pathways from outer to inner plexiform layer in the skate. 100 microM 2-amino-4-phosphonobutyric acid (APB) reversibly blocked the skate ERG b-wave. A small d-wave-like OFF component of the ERG revealed by DC recording of response to a prolonged (10 s) flash of light was reduced or blocked by 5 mM kynurenic acid (KYN). We found that addition of 200 microM picrotoxin to the Ringer''s solution revealed prominent ON and OFF components of the skate ERG while reducing the c-wave. These ON and OFF components were reversibly blocked by 100 microM APB and 5 mM KYN, respectively. Reversible block of the OFF component by KYN was also accomplished in the presence of 500 microM N-methyl-DL-aspartate. From these findings, we conclude that ON and OFF bipolar cells are likely to be functional as parallel afferent interplexiform pathways in the all-rod retina of the skate.     

Transient Fluctuation of Serum Melatonin Rhythm is Suppressed Centrally by Vitamin B

Vitamin B₁₂ has been reported to improve sleep-wake rhythm disorders. Although the mechanism is still unclear, a change in the sensitivity of the circadian clock system to photic input is thought to be a possible mechanism of the effect. In this study, the effect of the vitamin B₁₂ on the circadian aspect of the electroretinogram (ERG) and serum melatonin level was analyzed in rats. Vitamin B₁₂, α-(5,6-dimethylbenzimidazolyl)-co-methyl-cobamide was daily administrated subcutaneously for 8 weeks to adult male Wister rats in the experimental group, and saline was given to the control group. The ERGs were recorded under dark adaptation during the night and day, and under light adaptation (0.1 lux) during the night. Blood was drawn before and after ERG recording. The amplitudes of the a-wave, fc-wave, and trough-to-peak of both waves and latencies of ERG were analyzed following various exposures to stimuli of light intensity. These parameters in the group treated with vitamin B₁₂ showed similar characteristics to the control group, and no significant difference was observed between the two groups. The melatonin levels of both groups before the measurement of ERG were similar under each measurement condition. The elevated serum melatonin concentration in the control group under dark adaptation at night was suppressed after the series of 10-msec light stimuli used for measurement of ERG. However, this suppressing effect of light pulses on melatonin level was significantly inhibited in the group treated with vitamin B₁₂. Under light adaptation during the night and under dark adaptation during the day, melatonin levels after the measurement of ERG were not different between the groups. From these results, it is suggested that vitamin B₁₂ is effective in suppressing melatonin rhythm disturbances introduced by transient light stimulation, and it affects the site more central than the retinal level. (Chronobiology International, 14(6), 549–560, 1997)     

Comparison of Stimulus Energies Required to Elicit the ERG in Response to X-Rays and to Light

The retina of Rana pipiens, the leopard frog or grass frog, is shown to be an extremely sensitive detector of x-rays. Its sensitivity to x-rays equals in some respects its sensitivity to visible light. The energy required for the response to visible light is so low that the reaction has long been known as one of the most sensitive in biological systems. An exact comparison is made of the amount of energy required in the stimulus to elicit an electroretinogram (ERG) in response to x-rays and in response to light. ERG's from threshold responses to maximal responses obtainable with x-rays and with light are reproduced. The rods of the retina are shown to be responsible for the production of the ERG. The actual amount of energy absorbed in the rhodopsin from x-ray and from light stimulation over a wide range of intensities and durations has been determined and has been related to the amplitude of the ERG. To the question whether light or x-rays are more efficient in eliciting an ERG, no simple or unequivocal answer can be given. The three dimensional relationship of amplitude of response, intensity of stimulus, and duration of stimulus shows rather unexpectedly that in certain regions light is more efficient while in other regions x-rays are more efficient.     

Out of the blue: the spectral sensitivity of hummingbird hawkmoths

The European hummingbird hawkmoth Macroglossum stellatarum is a diurnal nectar forager like the honeybee, and we expect similarities in their sensory ecology. Using behavioural tests and electroretinograms (ERGs), we studied the spectral sensitivity of M. stellatarum. By measuring ERGs in the dark-adapted eye and after adaptation to green light, we determined that M. stellatarum has ultraviolet (UV), blue and green receptors maximally sensitive at 349, 440 and 521 nm, and confirmed that green receptors are most frequent in the retina. To determine the behavioural spectral sensitivity (action spectrum) of foraging moths, we trained animals to associate a disk illuminated with spectral light, with a food reward, and a dark disk with no reward. While the spectral positions of sensitivity maxima found in behavioural tests agree with model predictions based on the ERG data, the sensitivity to blue light was 30 times higher than expected. This is different from the honeybee but similar to earlier findings in the crepuscular hawkmoth Manduca sexta. It may indicate that the action spectrum of foraging hawkmoths does not represent their general sensory capacity. We suggest that the elevated sensitivity to blue light is related to the innate preference of hawkmoths for blue flowers.     

Visual sensitivity and the state of adaptation in the antAtta sexdens (Hymenoptera: Formicoidea)

In the worker ant,Atta sexdens, the ERG is cornea negative, shows two phasic and one tonic component and never presents an initial positive deflection. Dark adaptation was found to be complete within 10 min even with the longest pre-adapting duration used. Circadian variations were observed on continuous records, showing a tenfold sensitivity increase of the ERG during the night. Effects of light adaptation were also studied. The ERG amplitude can increase after light exposure. The possible role that pigment migration might play in the described sensitivity changes is discussed.     

An effect of tricaine methanesulfonate on the electroretinogram of Taricha granulosa.

MS-222 is an anesthetic that is widely used for cold-blooded animals. The present study uses contact circum-corneal electrodes and conventional recording equipment to determine the effect of this anesthetic on the electroretinogram (ERG) of the rough-skinned newt ($\text{Taricha granulosa}$). When applied prior to retinal bleach, MS-222 retarded the rate of subsequent dark adaptation. This retardation was evidenced by a decreased sensitivity to light during the adaptation process, and by a higher threshold for induction of an ERG response after bleach.     

Electrophysiological evidence for rod and cone-based vision in the nocturnal flying squirrel

Summary The flying squirrel (Glaucomys volans) is a strongly nocturnal rodent. Previous anatomical observations suggested that the retina of this animal contains some cone-like receptors in addition to large numbers of rods. Evidence for duplicity of function in this visual system was obtained from an examination of three indices of visual activity: the electroretinogram (ERG), the isolated PIII retinal response, and the visually evoked cortical potential (VECP). The spectral sensitivity of the dark-adapted flying squirrel is similar to that of other mammals — it has a 500 nm peak (Figs. 3, 8). Responses of the ERG and isolated PIII to flickering light indicate the operation of two processes (Figs. 4, 7), one of which is unable to follow flickering light at repetition rates above 10–15 Hz. Spectral sensitivity measurements reveal that these two processes have different spectral sensitivities. The photopic mechanism in the flying squirrel visual system has peak sensitivity at about 520 nm (Figs. 5, 7, 9). The effects of steady light adaptation are much more obvious in the cortical potentials than they are in the retinal potentials.We thank David Birch for his advice and assistance. This research was supported by a Grant from the National Eye Institute (EY-00105).     

Sensitivity facilitation in the insect eye

Summary ERG amplitude facilitation, observed in the eye ofAtta sexdens after light adaptation, was studied as a function of duration and intensity of adaptation, of dark interval between adapting and test stimuli, and of level of steady background illumination. Results show that sensitivity facilitation in this eye cannot be regarded as a minor effect since it covers a 2 log unit range, the same as that obtained for conditions that produce sensitivity reduction. Maximum facilitation occurs with short and intense light adaptation. The time span of the effect is close to 2 min, and its maximum amplitude may be attained up to 20 s after light adaptation. Increase in background illumination gradually erases facilitation. However, the facilitated response is less sensitive to background illumination than the dark adapted response. Long durations of light adaptation cause ERG decrease, or inhibition. A comparison of these two end results of light adaptation suggests that they arise from different processes, perhaps with distinct origins.Supported by a grant from Fundação de Amparo à Pesquisa do Estado de São Paulo, to the senior author (Contract n 71/1141)With a Fellowship from Fundação de Amparo à Pesquisa do Estado de São Paulo (N 74/388)We wish to express our appreciation to Henrique Fix for his editorial assistance, and to Celia Jablonka for laboratory help.     

Effect of 2-amino-4-phosphonobutyrate on the OFF responses of frog retinal ganglion cells and local ERG after glycinergic blockade

Perfusion with the ON channel blocker 2-amino-4-phosphonobutyrate (APB) of dark adapted frog eyecups not only abolished the ganglion cells' (GC) ON responses and the ERG b-wave, but markedly potentiated the OFF responses of ON-OFF and phasic OFF-GCs and the d-wave amplitude of simultaneously recorded local ERG. Glycinergic blockade by strychnine prevented this potentiating effect in 31 out of 69 GCs, but did not change it at all in the other cells. At the same time the d-wave potentiation was preserved during the glycinergic blockade in all eyecups. The results indicate that glycinergic transmission is involved in the inhibition exerted from ON upon OFF channel in some but not all frog retinal GCs.     

Wavelength dependence of dark adaptation in Phycomyces phototropism

The wavelength dependence of phototropic dark adaptation in Phycomyces was studied between 347 and 545 nm. Dark adaptation kinetics were measured for wavelengths of 383, 409, 477, and 507 nm in the intensity range from 6.2 X 10(-2) to 2 X 10(-7) W X m-2. At these wavelengths, dark adaptation follows a biexponential decay as found previously with broadband blue light (Russo, V. E. A., and P. Galland, 1980, Struct. Bonding., 41:71; Lipson, E. D., and S. M. Block, 1983, J. Gen. Physiol., 81:845). We have found that the time constants of the fast and slow components depend critically on the wavelength. At 507 nm, dark adaptation kinetics were found to be monophasic. The phototropic latency after a step down by a factor of 500 was measured for 19 different wavelengths. Maximal latencies were found at 383, 477, and 530 nm; minimal latencies were found at 409 and 507 nm. With irradiation programs that employ different wavelengths before and after the step down, the dark adaptation kinetics depend critically on the sequence in which the two wavelengths are given. We have found too that not only do the adaptation kinetics vary with wavelength, but so also do the phototropic bending rate and the phototropic latencies in experiments without intensity change. The results imply that more than one photoreceptor is mediating phototropism in Phycomyces and that sensory adaptation is regulated by these photoreceptors.