Comparative study of the rod and cone contributions to the generation of b-wave ERG and tectal evoked potential in the dark-adapted carp

Amplitudes and peak latencies as functions of wave length and monochromatic light intensity were investigated for b-wave ERG and tectal evoked potentials (EP) in the dark-adapted carp (Cyprinus carpio L). It was found, that independently of light intensity b-wave action spectra had one maximum in the medium wave band, corresponding to rod sensitivity area. For tectal EP, similar action spectra with maximum in the middle-wave were seen at low light intensity only. The b-wave amplitude growth was significant for the whole band of light intensities, and these changes were accompanied with a slight decrease in peak latency (to 50-100 ms). Tectal EP amplitude increased when low-intensity light was changed for medium intensity light and did not considerably increase to brighter light stimuli. However, tectal EP time latency significantly decreased (to 100-200 ms) during light intensity increasing. This differences show that retinal rod system, which in responsible for ERG b-wave in darkness, is not a key factor in the generation of tectal EP.     

Effect of spatial frequency on simultaneous recorded steady-state pattern electroretinograms and visual evoked potentials

Pattern electroretinograms (P-ERGs) and visual evoked potentials (VEPs) to 4 Hz alternating square-wave gratings were simultaneously recorded in 23 subjects. Responses were Fourier analyzed and amplitude and phase of the 2nd and 4th temporal harmonics were measured.The spatial frequency-amplitude function of the P-ERG 2nd harmonic component displayed either a bandpass tuning behavior, or a low-pass behavior. The peak amplitude for subjects with bandpass tuning was at 1.5 c/deg. The phase of the P-ERG 2nd harmonic decreased monotonically as spatial frequency increased. The VEP 2nd harmonic had a bimodal spatial frequency function with a peak at 3 c/deg and a second increase at spatial frequencies below 1 c/deg, regardless of the P-ERG characteristics. The phase of VEP 2nd and 4th harmonic had an inverted U-shaped function with peak at 3 c/deg and 1.5 c/deg respectively.Comparison of simultaneously recorded P-ERG and VEP spatial frequency functions demonstrated different tuning behavior for cortical and retinal responses. It is concluded that the proposed technique permits the separate analysis of retinal and cortical processing of visual information. The 2nd and 4th harmonic components of VEP behave independently of each other suggesting they may be generated by different subsystems.     

Aspects of color vision in bluegill sunfish (Lepomis macrochirus): ecological and evolutionary relevance

Summary Spectral sensitivity curves were measured for bluegills using a heart-rate conditioning technique. A mean spectral sensitivity curve (n=3) determined using a white background exhibited two main peaks, indicating the possible presence of two cone photoreceptors mechanisms. Chromatic adaptation was used to separate the contribution of the cone mechanisms to sensitivity. Peak sensitivities were located at 540 and 640 nm against red and blue-green backgrounds, respectively.Light adaptation curves were measured for each cone mechanism indicating that these cone mechanisms have their greatest contrast sensitivity at higher background intensities. Spatial summation properties were also measured for each cone mechanism revealing a critical diameter (summation area) of 5° for both mechanisms.Microspectrophotometric (MSP) measurements were made on individuals from the same group of bluegills used in the above experiments. The results showed the presence of two cone types: single green-sensitive cones with an average _max of 536 nm (SD±1.8nm,n=11) and twin redsensitive cones with an average _max of 620 nm (SD ±1.9 nm,n=11).The correlation between the visual pigment absorption spectra and action spectra of the two cone mechanisms indicate a sound physiological basis for sensitivity. The functional properties of the two cone mechanisms, will be discussed in relation to the ecological and behavioral aspects of bluegills.Abbreviation TVI threshold vs intensity     

Dynamics of chromatic adaptation in cones of freshwater turtle

The closer the wavelength of a steady background of monochromatic light is to the peak sensitivity of a cone that is being illuminated, the stronger is the desensitization of that cone; this is chromatic adaptation. A model of the freshwater turtle retina with the neural components of chromatic adaptation via negative feedback circuits is used to simulate and study various aspects of chromatic adaptation. An internal negative feedback circuit resides solely within the cone pedicle and thereby, its adaptive effects are relatively specific, so that univariance is maintained. The cone-L-horizontal cell circuit is an external negative feedback circuit and its adaptive effects are less specific since all 3 chromatic cone types are involved, so that univariance is violated. Chromatic adaptation is the result of the decrease in the cone gain due to the dependency of the gains of the negative feedback circuits on the mean illuminance level. The results of the model are consistent with von Kries law, but the changes in gains of the cones due to chromatic adaptation are dependent on wavelength, intensity of the adapting light and size.     

The Electroretinogram of a Diurnal Gecko

Using the electroretinogram as the criterion of retinal activity the flicker fusion frequency, course of dark adaptation, and spectral sensitivity of the pure cone retina of the diurnal gecko, Phelsuma inunguis, were investigated. Both the curve relating flicker fusion frequency to stimulus intensity and that relating the amplitude of the flicker response to stimulus intensity showed a break as the intensity was increased. The dark adaptation curve was that typical of cone retinae; there was no break, adaptation was relatively rapid, and there was a total increase of sensitivity of only about 3 log units. The spectral sensitivity curve showed two maxima, a major one at about 560 mµ and another at about 460 mµ. Chromatic adaptation with red and blue lights demonstrated the presence of two independent mechanisms. Although red adaptation could not have had a direct effect on the pigment responsible for the "blue" mechanism the sensitivity of this mechanism was depressed by red adaptation. The possible relationships of the two mechanisms are discussed.     

Dim light adaptation attenuates acute melatonin suppression in humans

Abstract Studies in rodents with retinal degeneration indicated that neither the rod nor the cone photoreceptors obligatorily participate in circadian responses to light, including melatonin suppression and photoperiodic response. Yet there is a residual phase-shifting response in melanopsin knockout mice, which suggests an alternate or redundant means for light input to the SCN of the hypothalamus. The findings of Aggelopoulos and Meissl suggest a complex, dynamic interrelationship between the classic visual photoreceptors and SCN cell sensitivity to light stimuli, relative to various adaptive lighting conditions. These studies raised the possibility that the phototransductive physiology of the retinohypothalamic tract in humans might be modulated by the visual rod and cone photoreceptors. The aim of the following two-part study was to test the hypothesis that dim light adaptation will dampen the subsequent suppression of melatonin by monochromatic light in healthy human subjects. Each experiment included 5 female and 3 male human subjects between the ages of 18 and 30 years, with normal color vision. Dim white light and darkness adaptation exposures occurred between midnight and 0200 h, and a full-field 460-nm light exposure subsequently occurred between 0200 and 0330-h for each adaptation condition, at 2 different intensities. Plasma samples were drawn following the 2-h adaptation, as well as after the 460-nm monochromatic light exposure, and melatonin was measured by radioimmunoassay. Comparison of melatonin suppression responses to monochromatic light in both studies revealed a loss of significant suppression after dim white light adaptation compared with dark adaptation (p < 0.04 and p < 0.01). These findings indicate that the activity of the novel circadian photoreceptive system in humans is subject to subthreshold modulation of its sensitivity to subsequent monochromatic light exposure, varying with the conditions of light adaptation prior to exposure.     

Pattern-reversal visual evoked potentials in photosensitive epilepsy

VEPs to checkerboard pattern-reversal were recorded from 18 epileptic patients who had EEG photoparoxysmal responses to stroboscopic light. Patients were grouped according to whether seizures were precipitated by environmental light stimuli, or television viewing. Longitudinal studies were conducted on 8 patients treated with valproic acid. We concluded the following: (1) Latency of the major positive peak (P2) of the pattern-reversal VEP was shorter among photosensitive patients than among normal controls. This was especially true of television-sensitive patients. (2) Valproic acid, when effective in controlling seizures, lengthened the P2 latency and decreased VEP amplitude. Studies of drug effects on VEPs may help to elucidate neurochemical mechanisms of the visual cortex. (3) Because of overlap of values with normals, VEP measurements are not at present very sensitive in the diagnosis of photosensitivity. However, longitudinal studies in individuals parallel clinical changes and may be useful as objective measures of improvement.     

Dynamic characteristics of the receptive field of L-cells for monochromatic lights

We applied the Wiener theory to analyse receptive field responses of L-cells in the carp and studied some dynamic properties of the receptive field of L-cells for monochromatic light stimuli. The L-cells were stimulated by each monochromatic light modulated in white-noise fashion. They responded almost linearly to all the monochromatic light stimuli. The impulse responses of the L-cells became larger in amplitude and faster in latency, peak response time, and repolarising phase as a spot of monochromatic light was enlarged. The L-cells seem to respond like a lowpass filter and the cutoff frequency of their gain characteristics increases with the enlargement of the monochromatic light spot. The relation between shift of cutoff frequency and spot diameter was monotonic increasing for each monochromatic light.     

Photomorphogenic responses to UV radiation IV: a comparative study of UVB effects on growth and pigment accumulation in etiolated and de-etiolated hypocotyls of wild-type and aurea mutant of tomato Lycopersicon esculentum Mill)

ABSTRACT

The question of how de-etiolation of tomato seedling under continuous monochromatic yellow light exerts an influence on UV radiation-induced responses has been studied. Hypocotyl extension and the accumulation of anthocyanins and UV-absorbing compounds was compared in the aurea mutant of tomato and its isogenic wild type. The data of the present paper provide evidence that, during de-etiolation of tomato seedlings, yellow light exerts its effects over seedlings responsiveness to subsequent UV irradiation through several mechanisms: 1) a significant enhancement of shorter UVB wavelength efficiency in both the genotypes; 2) the abolition of UVA -blue light-induced accumulation of UV-absorbing compounds that does not involve pnyA; 3) the disappearance of UVA-blue light-induced hypocotyl growth inhibition that does not involve phyA; 4) higher anthocyanin accumulation rate in response to UV radiation mediated by phyA. Yellow light-induced growth inhibition and accumulation of UV-absorbing compound both mediated by phyA and present only in wild type tomato, appear to be completely separate from the action of UV radiation on the same responses.     

Opponent and nonopponent contributions to the zebrafish electroretinogram using heterochromatic flicker photometry

While some lower vertebrates, such as zebrafish, do not appear to possess anatomically separate pathways of processing visual information (such as M-pathways and P-pathways), it is believed that separate processing of the visual stimulus (such as luminance and chromatic processing) is a basic requirement of vertebrate vision. In this study, spectral sensitivity functions were obtained from electroretinogram responses to heterochromatic flicker photometry stimuli at several flicker rates, including a low flicker rate (2 Hz), in an attempt to predominantly stimulate chromatic processes and a high flicker rate (16 Hz), in an attempt to predominantly stimulate luminance processes. In addition, chromatic adaptation was used to isolate and examine the temporal properties of the different cone-type contributions to the electroretinogram response. Spectral sensitivity functions based on responses to heterochromatic stimuli of a low flicker rate appeared to receive both opponent and nonopponent contributions; however, when the stimulus flicker rate was high, spectral sensitivity appeared to be a function of only nonopponent mechanisms. Also, the differences in cone contributions to the spectral sensitivity functions across the different flicker rates appear to be related to the temporal properties of the cone contributions to the electroretinogram response.     

The Spectral Sensitivity of Crayfish and Lobster Vision

(1) The spectral sensitivity function for the compound eye of the crayfish has been determined by recording the retinal action potentials elicited by monochromatic stimuli. Its peak lies at approximately 570 mµ. (2) Similar measurements made on lobster eyes yield functions with maxima in the region of 520 to 525 mµ, which agree well with the absorption spectrum of lobster rhodopsin if minor allowances are made for distortion by known screening pigments. (3) The crayfish sensitivity function, since it is unaffected by selective monochromatic light adaptation, must be determined by a single photosensitive pigment. The absorption maximum of this pigment may be inferred with reasonable accuracy from the sensitivity data. (4) The visual pigment of the crayfish thus has its maximum absorption displaced by 50 to 60 mµ towards the red end of the spectrum from that of the lobster and other marine crustacea. This shift parallels that found in both rod and cone pigments between fresh water and marine vertebrates. In the crayfish, however, an altered protein is responsible for the shift and not a new carotenoid chromophore as in the vertebrates. (5) The existence of this situation in a new group of animals (with photoreceptors which have been evolved independently from those of vertebrates) strengthens the view that there may be strong selection for long wavelength visual sensitivity in fresh water.     

Responses of the infrared sensilla of Melanophila acuminata (Coleoptera: Buprestidae) to monochromatic infrared stimulation

The pit organs of the beetle Melanophilaacuminata were stimulated with monochromatic infrared radiation using a continuous wave CO overtone infrared laser. Best sensitivity was in the wavelength range 2.8–3.5 μm. In this range a stimulus intensity of 14.7 mW cm⁻² was sufficient to generate single action potentials. At a wavelength of 5 μm receptor performance significantly decreased. An increase in stimulus intensity caused a decrease in response latency and an increase in the number of action potentials elicited. At a given wavelength (3.4 μm) the dynamic amplitude range of action potential responses covered 12 dB. At high stimulus intensities (94.2 mW cm⁻²) a stimulus duration of 4 ms was sufficient to generate one to two action potentials and a stimulus duration of 60 ms already caused response saturation (with up to nine action potentials). In a repetitive stimulus regime distinct receptor potentials were visible up to a frequency of 600 Hz. Accepted: 18 March 2000     

Intracellular recordings from gecko photoreceptors during light and dark adaptation

Intracellular recordings were obtained from rods in the Gekko gekko retina and the adaptation characteristics of their responses studied during light and dark adaptation. Steady background illumination induced graded and sustained hyperpolarizing potentials and compressed the incremental voltage range of the receptor. Steady backgrounds also shifted the receptor's voltage-intensity curve along the intensity axis, and bright backgrounds lowered the saturation potential of the receptor. Increment thresholds of single receptors followed Weber's law over a range of about 3.5 log units and then saturated. Most of the receptor sensitivity change in light derived from the shift of the voltage-intensity curve, only little from the voltage compression. Treatment of the eyecup with sodium aspartate at concentrations sufficient to eliminate the beta-wave of the electroretinogram (ERG) abolished initial transients in the receptor response, possibly indicating the removal of horizontal cell feedback. Aspartate treatment, however, did not significantly alter the adaptation characteristics of receptor responses, indicating that they derive from processes intrinsic to the receptors. Dark adaptation after a strongly adapting stimulus was similarly associated with temporary elevation of membrane potential, initial lowering of the saturation potential, and shift of the voltage-intensity curve. Under all conditions of adaptation studied, small amplitude responses were linear with light intensity. Further, there was no unique relation between sensitivity and membrane potential suggesting that receptor sensitivity is controlled at least in part by a step of visual transduction preceding the generation of membrane voltage change.     

The contribution of single and double cones to spectral sensitivity in budgerigars during changing light conditions

Bird colour vision is mediated by single cones, while double cones and rods mediate luminance vision in bright and dim light, respectively. In daylight conditions, birds use colour vision to discriminate large objects such as fruit and plumage patches, and luminance vision to detect fine spatial detail and motion. However, decreasing light intensity favours achromatic mechanisms and eventually, in dim light, luminance vision outperforms colour vision in all visual tasks. We have used behavioural tests in budgerigars (Melopsittacus undulatus) to investigate how single cones, double cones and rods contribute to spectral sensitivity for large (3.4°) static monochromatic stimuli at light intensities ranging from 0.08 to 63.5 cd/m². We found no influences of rods at any intensity level. Single cones dominate the spectral sensitivity function at intensities above 1.1 cd/m², as predicted by a receptor noise-limited colour discrimination model. Below 1.1 cd/m², spectral sensitivity is lower than expected at all wavelengths except 575 nm, which corresponds to double cone function. We suggest that luminance vision mediated by double cones restores visual sensitivity when single cone sensitivity quickly decreases at light intensities close to the absolute threshold of colour vision.     

Scalp-recorded oscillatory potentials evoked by transient pattern-reversal visual stimulation in man

Replicable oscillatory potentials, time-locked to pattern stimuli (9.0° central; counterphase reversal at 2.13 Hz) were dissociated from conventional, broad-band VEPs recorded in healthy volunteers at occipital scalp locations by high-pass digital filtering at 17.0–20.0 Hz. Nine consecutive wavelets were identified with a 56.4 ± 8.4 msec mean latency of the first replicable wavelet and mean peak-to-peak amplitude varying between 0.9 and 2.0 μV. The first 2 wavelets had significantly shorter latencies than wave N70 of unfiltered VEP, whereas the last 2 wavelets had longer latencies than N145. Latency and amplitude values varied as a function of contrast and spatial frequency of the stimulus, with shorter latencies and larger amplitudes at 60–90% contrast level and tuning of amplitude at 5.0 c/deg. All wavelets were correlated with wave P100 of unfiltered VEP, while a correlation with N70 of VEP was observed only for those wavelets with latencies in the range of wave P100. Two patients with documented brain lesions involving the visual system are described as examples of oscillatory responses occurring irrespective of filter bandpass and instead of the expected conventional VEP when the generation of these is interfered with by brain pathology. A substantial cortical contribution to the origin of the oscillatory response is conceivable. It is suggested that the oscillatory response to pattern-reversal stimulation reflects events in the visual system that are parallel to, and partly independent of, the conventional VEP, with potential application in research or for clinical purposes.     

P300, stimulus intensity,and modality

Auditory and visual stimulus intensity levels were manipulated systematically in separate conditions to assess the influence of these variables on the P300 event-related brain potential (ERP). Increases in stimulus intensity produced increases in P300 amplitude and decreases in peak latency for both modalities, although the latency effects were stronger for visual stimulation. Similar, somewhat weaker stimulus intensity effects also were observed for the N100, P200, and N200 components. The findings suggest that stimulus intensity contributes to both P300 amplitude and latency measures in important ways and are discussed in relation to the use of ERPs in applied contexts.     

The Electrical Response of the Planarian Ocellus

The planarian ocellar potential (OP), an action potential evoked from the planarian ocellus by a light flash, was recorded with microelectrodes. OP amplitude, latency, and peak delay varied as a function of stimulus intensity and state of adaptation in a manner similar to the responses of other photoreceptors. Changes in the OP that occurred with different directions of incident light are described and attributed to screening effects of the ocellar pigment cells. The temperature coefficient (Q₁₀) of OP latency was 1.5; latency decreased continuously as temperature was increased to destructive levels. The energy of activation of the rate of OP formation was calculated to approximate 10 kcal. These findings suggest dependence of OP latency on ionic diffusion and of OP formation on a biocatalytic process.     

Delayed visual evoked potentials are independent of pattern orientation in macular disease

Visual evoked potentials (VEPs) and contrast sensitivity (CS) were studied in patients affected by maculopathy. VEP delays and CS reduction were demonstrated in each affected eye. In distinction to patients affected by multiple sclerosis (MS), in maculopathy patients VEP latency is independent of the orientation of the grating stimulus. It is proposed that stimulating with more than one pattern orientation is useful in the differential diagnostic use of VEPs.     

Human visual evoked potentials to bars and cross-like figures

Temporal and amplitude characteristics of averaged visual evoked potentials to presentation of lines, corners and crosses with different orientation recorded in 19 adult healthy subjects were compared in 34 derivations. In all subjects, the latencies of P1, N2, and P3 were shorter while their amplitudes were higher for crosses than for lines. The effect of lengthening of P1 peak latency from occipital to temporal cortex was mostly pronounced for EPs to a bar, whereas as increase in the P1 amplitude was most evident for a cross-like figure. Correlation of these data with: i) greater magnitude and shorter latencies of responses to crosses vs. bars in a half of cat striate neurons, ii) sensitivity of cells in monkey inferior temporal cortex to star-like figures, and iii) relatively better human recognition of figures with comers than with lines, as well as significance of the effects obtained for detection of image features in different areas of the human visual cortex is discussed.     

Effects of chlorpromazine on pattern and flash ERGs and VEPs compared to oxazepam and to placebo in normal subjects

Antidopaminergic drugs delay the pattern-reversal VEP (P-VEP) and the flash VEP (F-VEP) and, in separate studies, reductions in the amplitude and increases in the latencies of scotopic ERGs have been reported. This study investigated the effects of chlorpromazine (CPZ) on the pattern ERG (P-ERG), P-VEP, flash ERGs and VEPs and oscillatory potentials (OPs). Normal volunteers (N = 15) were administered a placebo, or a single dose of CPZ 100 mg or oxazepam (OZP) 15 mg at weekly intervals, in a double-blind crossover design. A gold foil-ipsilateral ear derivation and an Oz′-Fz derivation were used for the ERG and VEP recordings, respectively. The latencies of ‘mixed’ and cone ERGs were significantly prolonged after CPZ compared to both placebo and to OZP. Amplitudes of rod- and cone-dominated ERGs were reduced following CPZ administration. All components of the OPs were significantly delayed after CPZ administration. No significant intertreatment differences were found in the F-VEP results. The P-ERG P50 peak and the P-VEP N70 and P100 peaks were significantly delayed after CPZ in the case of 28′ checks but not 55′ checks. Retinocortical times and P-ERG and P-VEP amplitudes were not significantly affected. In contrast to CPZ, the administration of OZP had virtually no significant effects compared to placebo. These findings suggest that the antidopaminergic CPZ has a primary effect on retinal electrophysiology. Similar findings have been reported in Parkinson's disease and in animal models.