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.     

Electrical activities of a type of electroretinogram recorded from the ocellus of a jellyfish, Polyorchis penicillatus (Hydromedusae)

An electroretinogram (ERG), evoked by light stimuli, was recorded from ocelli of Polyorchis penicillatus (Hydromedusae). The ERG is a polyphasic response with a positive potential change at the onset of illumination followed by a slower biphasic pulse, and a positive deflection at the cessation of illumination which is followed by a series of high-frequency pulses. The most striking features of the initial pulse are its latency-log intensity relation and the gradation of pulse amplitude with respect to the intensity of the light stimulus and to different wavelengths. Maximum spectral sensitivity lies around 530 nm. Response patterns induced by shadowing and repeated stimulation of light- and dark-adapted ocelli are described. Morphological structures which could give rise to the mass response of the ocellus are discussed.     

Visual responses in crayfish 3. Further studies on transmission through the brain

Responses to illumination of the eyes of the crayfish were studied by gross recording from one of the circumesophageal connectives. Two-thirds of the spontaneous activity at this level of the CNS consists of ascending activity, which is eliminated by cutting a connective posterior to the recording electrode. An average of about eight fibers in a connective responded to 1 sec illumination of the homolateral eye. The fibers were of four types: pure-on units, on-sustained units, on-and-off units and pure-off units. The average latency was 74 msec for the on-response and 26 msec for the off-response. The latency of responses to 10 μsec flashes of increasing intensity shortened from 72 to 52 msec. This was demonstrated to be mainly a peripheral effect since ERG latency showed a parallel reduction while the ERG-connective response interval remained more nearly constant at 40–50 msec. ERG amplitude, frequency, and usually the duration of the connective spike discharge increased at greater stimulus intensities, yet the average number of responding fibers was greatest at intermediate intensities. The results indicate minimal processing of response patterns by the brain.     

Electrical activity of the retina in different axial lengths of the eye in humans

In subjects with normal vision, we studied the relationship between the axial length of the eye and the amplitude-temporal characteristics of different types of ganzfield ERG. The amplitude of the ERG had the highest variability in the middle of the range of the axial eye lengths. The variability decreased at both ends of the range. With increasing axial length, the amplitude of the b-wave of all types of ERG decreased, and the latency decreased concurrently. The b-wave reflects the activity of the retinal ON-neurones depolarizing in response to the light stimulus. We assume that the decrease in the amplitude of b-wave may be related to the decreased number of photoreceptors and of neurons in the following retinal levels and/or increased inhibition in proximal retina, as well as an increase in relative activity of retinal OFF-neurones hyperpolarizing in response to the light stimulus.     

Correspondences in the Behavior of the Electroretinogram and of the Potentials Evoked at the Visual Cortex

Electrical potentials from the eye (ERG) and from the contralateral visual cortex were recorded in response to flashes of white and of colored light of various intensities and durations. The evoked potentials were found to parallel the behavior of the ERG in several significant respects. Selective changes in the ERG brought about by increasing the light intensity and by light adaptation led to parallel selective changes in the cortical responses. The dual waves (b₁, b₂) of the ERG were found to have counterparts in two cortical waves (c₁, c₂) which, in respect to changes in light intensity and to light adaptation, behaved analogously to the two retinal components. The responses evoked at high intensity showed only the diphasic c₁-potential. As stimulus intensity was lowered the c₁-wave decreased in magnitude and a delayed c₂-component appeared. The c₂-potential increased in amplitude as light intensity of the flash was further reduced. Eventually the c₂-wave, too, decreased as stimulus reduction continued. There was no wave length specificity in regard to either the duplex b-waves or duplex cortical waves. Both appeared at all wave lengths from 454 mµ to 630 mµ. The two cortical waves evoked by brief flashes of colored light showed all the behavior to changes in stimulus intensity and to light adaptation that occurred with white light.     

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.     

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.     

Quantum Relations of the Rat Electroretinogram

The rat retina is uniform and contains almost exclusively rods. Therefore the rat eye, when uniformly illuminated, produces a gross electroretinogram (ERG) which is simply related to the activity of the individual retinal sources of the ERG. Characteristics of ERG's are shown on an intensity scale of the average number of quanta absorbed per rod per stimulus flash obtained by direct accurate measurement of all quantities involved. An independent check on the accuracy of these measurements is applied to pigment-bleaching data reported by Dowling (1963). When ERG characteristics are placed on this scale it is found that: (a) The b-wave can usually be observed when fewer than one out of two hundred rods absorbs a quantum, the threshold being determined by the noise of the preparation. (b) Near threshold the b-wave amplitude is proportional to intensity. (c) The a-wave appears when there are more than two to four absorptions per rod per flash. (d) The b-wave latency decreases with intensity, and the amplitude becomes proportional to the logarithm of intensity when fewer than one out of ten rods absorbs a quantum. This implies that the b-wave sources must combine excitation from more than one rod (probably more than seven). Therefore the b-wave cannot arise from independent rods or rod-bipolar synapses, but probably reflects activity of entire inner nuclear layer cells.     

Spectral Sensitivity Measured with Electroretinogram Using a Constant Response Method

A new method is presented to determine the retinal spectral sensitivity function S(λ) using the electroretinogram (ERG). S(λ)s were assessed in three different species of myomorph rodents, Gerbils (Meriones unguiculatus), Wistar rats (Ratus norvegicus), and mice (Mus musculus). The method, called AC Constant Method, is based on a computerized automatic feedback system that adjusts light intensity to maintain a constant-response amplitude to a flickering stimulus throughout the spectrum, as it is scanned from 300 to 700 nm, and back. The results are presented as the reciprocal of the intensity at each wavelength required to maintain a constant peak to peak response amplitude. The resulting S(λ) had two peaks in all three rodent species, corresponding to ultraviolet and M cones, respectively: 359 nm and 511 nm for mice, 362 nm and 493 nm for gerbils, and 362 nm and 502 nm for rats. Results for mouse and gerbil were similar to literature reports of S(λ) functions obtained with other methods, confirming that the ERG associated to the AC Constant-Response Method was effective to obtain reliable S(λ) functions. In addition, due to its fast data collection time, the AC Constant Response Method has the advantage of keeping the eye in a constant light adapted state.     

棉铃虫蛾复眼光反应特性

用视网膜电位图(electroretinogram,ERG)技术研究了棉铃虫Helicoverpa armigera蛾暗适应过程中对单色光和白光刺激的光感受性变化。结果显示：(1)依ERG振幅大小(峰-峰值),在340～605 nm波谱内有3个大小不等的峰-主峰位于绿 黄光区562 nm,次峰在蓝光区483 nm,第3个峰在近紫外区400 nm,显示其至少有3种感受器;(2)性别、日龄及暗适应时间长短对其光谱敏感性有影响,低龄时雄蛾对单色光刺激较雌蛾敏感,高日龄时相反;1～5日龄内, 3日龄蛾的视网膜电位(ERP)值最高;随暗适应时间延长,其复眼对近紫外区400 nm敏感性明显增加;(3)一定光强度范围内,随单色光和白光光强度增强该蛾复眼的ERP值增大,初期增加较缓,中期较快,呈近似S型曲线,显示其复眼具有较强的光强度自调节和适应机制。     

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.     

Retinal responses inNautilus

Summary Electrical responses (ERG) were recorded from the retinal surface of the eye ofNautilus pompilius. Brief light flashes and step changes in intensity were used to explore linear and nonlinear response properties. The linear responses could be fitted well with cascaded exponential decay processes and a time delay. Nonlinear phenomena included a saturating amplitude of response with increased light intensity, and shape changes induced by adaptation and by background illumination.This study, of the R/V Alpha Helix Southeastern Asia Expedition, was supported by the National Science Foundation under Grants OFS74-01830 and OCE74-02888 to Scripps Institution of Oceanography. It was also supported by the National Science Foundation Grant BMS75-01149 to Iowa State University. — We would like to thank Walter Schneider for his technical assistance while on shipboard. This work would not have been possible without the help and hospitality of the wonderful people of Bindoy, Negros Oriental, The Republic of the Philippines.     

Oscillations of Potential in the Electroretinogram of the Lobster

The electroretinogram (ERG) evoked in the lobster by a short flash of light consists of a highly damped, slow oscillation of potential, triggered apparently by a single excitatory process. Near the threshold, only one wave may be evident; but as the intensity of stimulus rises, a prior wave appears, and grows so much more rapidly as to become dominant. Simultaneously third and later waves appear, so that at high intensities the response may include five to seven waves. Dark adaptation favors the second and later waves relative to the first; light adaptation tends to suppress them. On turning on a steady light the oscillations are superimposed on the early stages of development of a maintained, steady-state potential (on-response). Turning off the light causes a rapid fluctuation of potential followed by a similarly damped slow oscillation (off-response). These phenomena resemble in part oscillations recently observed in the b wave of the ERG of many vertebrates including man.     

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.     

Distinct responses of cones and melanopsin-expressing retinal ganglion cells in the human electroretinogram

ABSTRACT: BACKGROUND: The discovery of the novel photoreceptor, melanopsin-expressing retinal ganglion cells (mRGCs), has raised researchers' interest in photoreceptive tasks performed by the mRGC, especially in non-image-forming visual functions. In a prior study, we investigated the mRGC response to light stimuli independent of rods and cones with the four-primary illumination system, which modulates stimulus levels to the mRGC and cones independently, and mRGC baseline responses were recorded in the electroretinogram (ERG). METHODS: In the present study, we used the same illumination system to compare independent responses of the mRGC and cones in five subjects (mean +/- SD age, 23.0 +/- 1.7 years). The ERG waveforms were examined as direct measurements of responses of the mRGCs and cones to stimulation (250 msec). Implicit times (the time taken to peaks) and peak values from 30 stimuli given to each subject were analyzed. RESULTS: Two distinct positive peaks appeared in the mRGC response, approximately 80 msec after the onset of the stimuli and 30 msec after their offset, while no such peaks appeared in the cone response. The response to the mRGC stimulus was significantly higher than that to the cone stimulus at ~80 msec (p < 0.05) and tended to be higher than the cone stimulus at ~280 msec (p = 0.08). CONCLUSIONS: Implicit time of the first peak was much longer than that to the b-wave and this delay might reflect mRGC's sluggish responses. This is the first report of amplitudes and implicit time in the ERG from the response of the mRGC that is independent of rods and cones and obtained using the four-primary illumination system.     

Visual responses in teleosts. Electroretinograms, eye movements, and circadian rhythms.

We have recorded ocular potentials in response to brief flashes of light from two teleosts, the white perch (Roccus americana) and the green sunfish (Lepomis cyanellus). The animals were respired and maintained in an alert state for up to 2 d. Responses were recorded with corneal and transcleral electrodes. The responses of green sunfish were composed of electroretinogram (ERG) and eye movement potentials, whereas the responses in white perch contained only the ERG. Injection of curare abolished the sunfish eye movement potentials, unmasking the ERG. Observation under infrared illumination established a direct relationship between eye movements and the fast potentials which could be abolished by curare. We found no evidence of circadian changes in the amplitude of the ERG b-wave of either species. However, our results combined with those of a previous study of sunfish ocular potentials (Dearry, A., and B. Barlow, Jr. 1987. J. Gen. Physiol. 89: 745-770) suggest that the sunfish visual system exhibits rhythmic changes in oculomotor responses, which appear to be controlled by a circadian oscillator.     

Light-induced reduction in excitation efficiency in the trp mutant of Drosophila

In the transient receptor potential (trp) mutant of Drosophila, the receptor potential appears almost normal in response to a flash but quickly decays to baseline during prolonged illumination. Photometric and early receptor potential measurements of the pigment suggest that the pigment is normal and that the decay of the trp response during illumination does not arise from a reduction in the available photopigment molecules. However, there is reduction in pigment concentration with age. Light adaptation cannot account for the decay of the trp response during illumination: in normal Drosophila a dim background light shortens the latency and rise time of the response and also shifts the intensity response function (V-log I curve) to higher levels of light intensity with relatively little reduction in the maximal amplitude (Vmax) of response. In the trp mutant, a dim background light or short, strong adapting light paradoxically lengthens the latency and rise time of the response and substantially reduces Vmax without a pronounced shift of the V-log I curve along the I axis. The effect of adapting light on the latency and V-log I curve seen in trp are associated with a reduction in effective stimulus intensity (reduction in excitation efficiency) rather than with light adaptation. Removing extracellular Ca+2 reduces light adaptation in normal Drosophila, as evidenced by the appearance of "square" responses to strong illumination. In the trp mutant, removing extracellular Ca+2 does not prevent the decay of the response during illumination.     

Reversal of Photoreceptor Polarity Recorded during the Graded Receptor Potential Response to Light in the Eye of Limulus

Intracellular electrodes were inserted into single photoreceptor units of the excised lateral eye of Limulus, and preparations were selected from which graded receptor potentials of relatively large amplitude could be recorded in response to light stimuli. The experimental data indicated that the graded receptor potential does not arise solely from a collapse of the resting membrane potential of the sensory cells of the eye, since a reversal of polarity of the photoreceptor unit could be demonstrated when the eye was stimulated by light. In the recovery period following stimulation, characteristic changes in the so-called resting potential were recorded. It is suggested that these changes in the so-called resting membrane potential are electrical signs of recovery processes occurring in the photoreceptor, because the potential changes were recorded when the eye was in darkness and because the magnitudes of the potential changes were a predictable function of the intensity and duration parameters of the preceding light stimulus.     

Electrophysiological studies on the compound eye of a stalked-eye fly,Cyrtodiopsis dalmanni (Diopsidae,Diptera)

Summary The mass response (ERG) of the compound eye of the Malaysian stalked-eye flyCyrtodiopsis dalmanni was recorded by means of conventional electrophysiological techniques. The ERG consists of a positive on-effect, a sustained negative potential during illumination and a negative off-effect, it resembles that ofCalliphora as described by Autrum (1950). As compared with data derived fromCalliphora under identical conditions the eye ofCyrtodiopsis is more sensitive to weak stimuli and shows considerable adaptation. The spectral response curve reveals peaks at 360 nm, around 450 nm and around 490 nm. Above 550 nm the response curve rises steeply, even with stimuli above 700 nm reactions may be elicited. Most probably this effect is caused by weak absorption of long wavelength radiation in the screening pigments.With simple techniques it is fairly easy to record impulse activity from single units of the optic tract within the eye-stalk. This makesCyrtodiopsis a favorable object for experimental studies on data processing in insect optic centers.The characteristics of the diopsid eye are discussed in context with the environmental conditions in the biotop.I would like to thank the colleagues at the University of Malaya, Kuala Lumpur, Malaysia, for help and hospitality.The investigations were supported by a grant from the Sonderforschungsbereich Vergleichende Sinnes- und Nervenphysiologie at the University of Frankfurt (Main).     

Standardized Full-Field Electroretinography in the Green Monkey (Chlorocebus sabaeus)

Full-field electroretinography is an objective measure of retinal function, serving as an important diagnostic clinical tool in ophthalmology for evaluating the integrity of the retina. Given the similarity between the anatomy and physiology of the human and Green Monkey eyes, this species has increasingly become a favorable non-human primate model for assessing ocular defects in humans. To test this model, we obtained full-field electroretinographic recordings (ERG) and normal values for standard responses required by the International Society for Clinical Electrophysiology of Vision (ISCEV). Photopic and scotopic ERG recordings were obtained by full-field stimulation over a range of 6 log units of intensity in dark-adapted or light-adapted eyes of adult Green Monkeys (Chlorocebus sabaeus). Intensity, duration, and interval of light stimuli were varied separately. Reproducible values of amplitude and latency were obtained for the a- and b-waves, under well-controlled adaptation and stimulus conditions; the i-wave was also easily identifiable and separated from the a-b-wave complex in the photopic ERG. The recordings obtained in the healthy Green Monkey matched very well with those in humans and other non-human primate species (Macaca mulatta and Macaca fascicularis). These results validate the Green Monkey as an excellent non-human primate model, with potential to serve for testing retinal function following various manipulations such as visual deprivation or drug evaluation.