Photoresponses of the compound eye of the sandhopper Talitrus saltator (Crustacea, Amphipoda) in the ultraviolet-blue range

The semi-terrestrial sandhopper Talitrus saltator uses celestial visual cues to orient along the sea-land axis of the beach. Previous spectral-filtering experiments suggested that it perceives directional information from wavelengths in the ultraviolet (UV)-blue range. Binary choice experiments between dark and UV (380-nm) light carried out on dark-adapted individuals of T. saltator showed photopositive movement to UV. Morphologically, each ommatidium in the eye consists of five retinula cells, four large and one small. In electroretinogram experiments, sensitivity of the dark-adapted eye is dominated by a receptor maximally sensitive at about 390-450 nm and secondarily sensitive at about 500-550 nm. Selective light-adaptation experiments at 580 nm showed the apparent sensitivity decreasing at around the secondary sensitive range, thus disclosing the existence of UV-blue photoreceptor cells. Here the existence of UV-blue detection is confirmed, and evidence is provided that green and UV-blue visual pigments are located in the large and small retinula cells, respectively.

The effects of forward light scattering on the multifocal electroretinogram

PURPOSE

To study the effects of forward light scattering on the multifocal electroretinogram (mfERG).

METHODS

Thirty young normal subjects were recruited for this study. The mfERG was measured under five conditions. (1) no light scattering (stimulus contrast 93%), (2) mild light scattering (stimulus contrast 80%), (3) moderate light scattering (stimulus contrast 50%), (4) no light scattering (stimulus contrast 80%), and (5) no light scattering (stimulus contrast 50%).

RESULTS

The amplitudes of N1 and P1 from the central retina did not change significantly, but the amplitudes of N1 and P1 in the mid peripheral retina increased with the increase of forward light scattering. By comparing conditions 1, 4 and 5, it was shown that the amplitudes of N1 and P1 decreased at all eccentricities when stimulus contrast reduced from 93% to 50%.

CONCLUSIONS

This study suggests that the topography and waveform of the mfERG could be affected by forward light scattering.

Test of the paired-flash electroretinographic method in mice lacking b-waves

Previous studies of rod photoreceptors in vivo have employed a paired-flash electroretinographic (ERG) technique to determine rod response properties. To test whether absence versus presence of the ERG b-wave affects the photoreceptor response derived by the paired-flash method, we examined paired-flash-derived responses obtained from nob mice, a mutant strain with a defect in signal transduction between photoreceptors and ON bipolar cells that causes a lack of the b-wave. Normal littermates of the nob mice served as controls. The normalized amplitude-intensity relation of the derived response determined in nob mice at the near-peak time of 86 ms was similar to that determined for the controls. The full time course of the derived rod response was obtained for test flash strengths ranging from 0.11 to 17.38 scotopic cd s m(-2) (sc cd s m(-2)). Time-course data obtained from nob and control mice exhibited significant but generally modest differences. With saturating test flash strengths, half-recovery times for the derived response of nob versus control mice differed by approximately 60 ms or less about the combined (nob and control) average respective values. Time course data also were obtained before versus after intravitreal injection of L-2-amino-4-phosphonobutyrate (APB) (which blocks transmission from photoreceptors to depolarizing bipolar cells) and of cis 2,3-piperidine dicarboxylic acid (PDA) (which blocks transmission to OFF bipolar cells, and to horizontal, amacrine and ganglion cells). Neither APB nor PDA substantially affected derived responses obtained from nob or control mice. The results provide quantitative information on the effect of b-wave removal on the paired-flash-derived response in mouse. They argue against a substantial skewing effect of the b-wave on the paired-flash-derived response obtained in normal mice and are consistent with the notion that, to good approximation, this derived response represents the isolated flash response of the photoreceptors in both nob and normal mice.

Protective effect of TEMPOL derivatives against light-induced retinal damage in rats

PURPOSE

OT-551 (1-hydroxy-4-cyclopropanecarbonyloxy-2,2,6,6-tetramethylpiperidine hydrochloride), a TEMPOL-H (OT-674) derivative, is a new catalytic antioxidant. In the present study, the efficacy of OT-551 and OT-674 in retinal neuroprotection was tested in a model of light-induced photoreceptor degeneration.

METHODS

Albino rats were intraperitoneally injected with OT-551, OT-674, or water, approximately 30 minutes before a 6-hour exposure to 2700-lux white fluorescent light. Retinal protection was evaluated histologically by measuring the thickness of the outer nuclear layer (ONL) and functionally by electroretinogram (ERG) analysis, 5 to 7 days after exposure to light. Levels of protein modification by 4-hydroxynonenal (4-HNE) and 4-hydroxyhexenal (4-HHE), which are end products of the nonenzymatic oxidation of n-6 and n-3 polyunsaturated fatty acids, respectively, were measured by Western dot blot analysis immediately after exposure to light.

RESULTS

After exposure to light, water-treated animals had a 77% loss of ERG b-wave amplitudes and a 26% and 56% loss of mean ONL thickness in the inferior and superior hemispheres, respectively. Compared with water-treated rats, ERG b-wave amplitudes in light-exposed eyes were significantly higher in 25 (P < 0.05)-, 50 (P < 0.05)-, and 100 (P < 0.001)-mg/kg OT-551-treated rats. Mean ONL thickness in the superior hemisphere was significantly higher in 25 (P < 0.01)-, 50 (P < 0.01)-, and 100 (P < 0.001)-mg/kg OT-551-treated, light-exposed eyes and in 100 mg/kg (P < 0.05) OT-674-treated eyes. No decrease of ONL thickness was observed in the light-protected covered fellow eyes in any animal. Increased levels of 4-HNE- and 4-HHE-protein modifications after exposure to light in water-treated eyes were completely counteracted by 100 mg/kg OT-551.

CONCLUSIONS

Systemic administration of OT-551 and OT-674 provides both functional and morphologic photoreceptor cell protection against acute light-induced damage, most likely by inhibiting lipid peroxidation. The protection by OT-551 was greater than OT-674.

A novel isoform of acetylcholinesterase exacerbates photoreceptors death after photic stress

PURPOSE

To study the involvement of stress-induced acetylcholinesterase (AChE) expression in light-induced retinal damage in albino rats.

METHODS

Adult albino rats were exposed for 24 hours to bright, damaging light. AChE expression was monitored by in situ hybridization, by histochemistry for AChE activity, and by immunocytochemistry. An orphan antisense agent (Monarsen; Ester Neurosciences, Ltd., Herzlia Pituach, Israel) was administered intraperitoneally to minimize light-induced AChE expression. The electroretinogram (ERG) was recorded to assess retinal function.

RESULTS

Twenty-four-hour exposure to bright light caused severe reduction in the ERG responses and augmented expression of mRNA for the "read-through" variant of AChE (AChE-R) in photoreceptor inner segments (IS), bipolar cells, and ganglion cells. AChE activity increased in IS. The expressed AChE protein was a novel variant, characterized by an extended N terminus (N-AChE). Systemic administration of the orphan antisense agent, Monarsen, reduced the photic induction of mRNA for AChE-R, and of the N-AChE protein. Rats exposed to bright, damaging light and treated daily with Monarsen exhibited larger ERG responses, relatively thicker outer nuclear layer (ONL), and more ONL nuclei than did rats exposed to the same damaging light but treated daily with saline.

CONCLUSIONS

The findings indicate that the photic-induced novel variant of AChE (N-AChE-R) may be causally involved with retinal light damage and suggest the use of RNA targeting for limiting such damage.

Prolonged rhodopsin phosphorylation in light-induced retinal degeneration in rat models

PURPOSE

The effects of various light-induced stresses on the retina were examined in the retinal degenerative rat model.

METHODS

Retinal morphology and electroretinograms (ERGs) were analyzed after application of light-induced stress of several intensities (650, 1300, 2500, or 5000 lux). For evaluation of rhodopsin (Rho) function, the kinetics of Rho regeneration and dephosphorylation were studied by spectrophotometric analysis and immunofluorescence labeling with antibodies specifically directed toward the phosphorylated residues (334)Ser and (338)Ser in the C terminus of Rho. Retinal cGMP concentration was determined by ELISA. Expression levels of neurotrophic factors (FGF2, brain-derived neurotrophic factor [BDNF], platelet-derived growth factor [PDGF], and ciliary neurotrophic factor [CNTF]) were evaluated quantitatively by RT-PCR.

RESULTS

Light intensity-dependent deterioration of ERG responses and thinning of the retinal outer nuclear layer were observed in wild-type and Royal College of Surgeons (RCS) rat retinas. Under dark adaptation after light-induced stress, the kinetics of Rho regeneration were not different between wild-type and RCS rat retinas. Rho dephosphorylation at (334)Ser and (338)Ser was extremely delayed in RCS rat retinas compared with wild-type without light-induced stress, but Rho dephosphorylation at those sites became slower in both RCS and wild-type rat retinas. In terms of expression of neurotrophic factors, almost no significant changes were observed between the animals after light-induced stress.

CONCLUSIONS

The present study indicates that light-induced stress causes intensity-dependent deterioration in retinal function and morphology in wild-type and RCS rat retinas. Disruption of the phototransduction cascade resulting from slower kinetics of Rho dephosphorylation appears to be involved in retinal degeneration.

Analysis of the human a-wave ERG component

The a-wave is one of the main issues of research in the field of ocular electrophysiology, since it is strictly connected with early photoreceptoral activities. The present study proposes mathematical methods that analyse this component in human subjects, and supports experimental evidence relating to possible correlations among the responses of photoreceptoral units under a light stimulus. The investigation is organized in two parts: the first part concerns the onset and the initial slope, up to the first minimum (about 10-15 ms), the second part deals with the main portion of the wave, up to about 30 ms. In both cases, the a-waves, recorded at various levels of luminance, have been fitted with a set of appropriate functions representing possible models of physiological behaviour which would take place in the early stages of phototransduction. The statistical nature of the underlying processes is also discussed. The results indicate that correlations occur in the early stages, whereas random processes are set up later.

Retinal Light Damage: Structural and Functional Effects of the Antioxidant Glutathione Peroxidase-1

PURPOSE

The role of the antioxidant enzyme glutathione peroxidase-1 (GPx1) in protecting the retina against photo-oxidative damage was investigated in GPx1-deficient and wild-type mice.

METHOD

Albino GPx1-deficient and age-matched wild-type mice were examined. Baseline electroretinograms (ERGs) were recorded. Thereafter, mice were exposed to intense light for 12 hours. After a 24-hour recovery in darkness, post-light-insult ERGs were recorded and compared with baseline. Structural effects of light insult were evaluated by retinal histology. Antioxidant expression was investigated by quantitative reverse transcription-PCR (qRT-PCR).

RESULTS

Light insult significantly affected ERG responses, with reduced a- and b-wave amplitudes. Structurally, photoreceptor layers were predominantly affected. As expected, GPx1 expression was negligible in GPx1-deficient mice but was upregulated in wild-type mice in response to light insult. Similarly, hemeoxygenase-1 and thioredoxin-1 expression increased significantly in wild-type retinas after light exposure. Catalase, GPx isoforms (GPx2 to -4), peroxiredoxin-6, glutaredoxin-1, and thioredoxin-2 expression was unaffected by GPx1 deficiency and light insult, whereas significant increases in glutaredoxin-2 occurred in non-light-exposed (baseline) GPx1-deficient retinas. Compared with baseline wild-type retinas, lipid peroxidation (TBARS assay), an indicator of oxidative stress, was elevated in baseline GPx1-deficient retinas. Unexpectedly, the light insult induced diminution of retinal function, in terms of ERG amplitude, and structural damage was significantly greater in wild-type than in with GPx1-deficient retinas.

CONCLUSIONS

The data showing increased oxidative damage in baseline GPx-deficient retina give rise to the hypothesis that increased oxidative stress provides a "preconditioning" environment in which protective mechanisms paradoxically render GPx1-deficient retinas less vulnerable to light-induced oxidative damage. This study identified glutaredoxin-2 as a potential candidate.

Ultraviolet‐ and short‐wavelength cone contributions alter the early components of the ERG of young zebrafish

The electroretinogram (ERG) is a commonly used measure to examine retinal processing in both basic and clinical research. The purpose of this study was to determine the retinal mechanisms responsible for the developmental differences found in the zebrafish ERG waveform. The ERG of young zebrafish possesses a voltage-negative response to ultraviolet- and short-wavelength stimuli, but not to middle- and long-wavelength stimuli; the ERG of adult zebrafish does not possess this response component. ERGs were obtained from young zebrafish before and after the introduction of either aspartate, or a combination of APB (DL-2-amino-4-phosphonobutyric acid) and PDA (cis-2,3-piperidinedicarboxylic acid) in order to suppress the responses of various types of retinal neurons. Log irradiance versus response amplitude functions of the ERG response to 200-ms stimuli of various wavelengths at various times following stimulus onset (70 and 120 ms) was derived as well as spectral sensitivity. Aspartate eliminated all voltage-positive responses regardless of stimulus wavelength; irradiance-response functions following aspartate were similar to the early responses of young control fish to ultraviolet- and short-wavelength stimuli. APB + PDA produced similar but not identical results as aspartate, suggesting that the combination of these agents does not completely eliminate all post-receptoral contributions to the ERG. Spectral sensitivity functions derived from aspartate-exposed subjects at various time measurements were dominated by contributions from ultraviolet- and short-wavelength-sensitive cone types. These wavelength-dependent ERG responses are similar to those found in humans with enhanced S-cone syndrome. Finally, ERG waveform differences across stimulus wavelength suggest that the circuitry of ultraviolet- and short-wavelength cone types is different to that of middle- and long-wavelength cone types in young zebrafish.

Acid-sensing ion channel 2 is important for retinal function and protects against light-induced retinal degeneration

pH variations in the retina are thought to be involved in the fine-tuning of visual perception. We show that both photoreceptors and neurons of the mouse retina express the H+-gated cation channel subunits acid-sensing ion channel 2a (ASIC2a) and ASIC2b. Inactivation of the ASIC2 gene in mice leads to an increase in the rod electroretinogram a- and b-waves and thus to an enhanced gain of visual transduction. ASIC2 knock-out mice are also more sensitive to light-induced retinal degeneration. We suggest that ASIC2 is a negative modulator of rod phototransduction, and that functional ASIC2 channels are beneficial for the maintenance of retinal integrity.

Regional variations in local contributions to the primate photopic flash ERG: revealed using the slow-sequence mfERG

PURPOSE

To determine the variations with eccentricity of the primate photopic ERG and to separate contributions by different retinal cells by using intravitreal pharmacologic agents.

METHODS

Slow-sequence multifocal (mf)ERGs were obtained from 19 anesthetized adult rhesus monkeys and 5 normal human subjects. Recordings in monkeys were obtained before and after injections of tetrodotoxin citrate (TTX) to block sodium-dependent spiking; TTX+N-methyl-D-aspartic acid (NMDA)+picrotoxin (PTX) or gamma-aminobutyric acid (GABA) to block all inner retinal activity; L-2 amino-4-phosphonobutyric acid (APB) to block the On-pathway; and cis-2, 3 piperidine dicarboxylic acid (PDA) to block the Off-pathway and the otherwise unblocked inner retinal activity. The stimulus consisted of 103 equal-sized hexagons within 17 degrees of the fovea; every 200 ms (15 frames), each hexagon had a 50% chance of remaining at 20 cd/m(2) or increasing briefly to 4.7 cd-s/m(2). Oscillatory potentials (OPs; 90-300 Hz) were extracted.

RESULTS

The slow-sequence mfERG summed over the stimulated area looked similar to a standard photopic, full-field ERG, with a- and b-waves and OPs. OPs in the foveal and temporal retina were larger than in the nasal retina. This nasotemporal asymmetry was removed by TTX, and the OPs were eliminated, either by blocking inner retina activity or by blocking the On-pathway. The summed mfERG waveform, including OPs, was shaped mainly by the more peripheral retinal regions. The foveal b-wave peak occurred about 5 to 6 ms later than in the periphery, with the depolarizing peak of the On-pathway/bipolar contribution occurring earlier than the depolarizing peak of the Off contribution at all eccentricities. The a-wave was composed of a small photoreceptor contribution and postreceptoral portion originating from hyperpolarizing neurons.

CONCLUSIONS

The variations in the primate photopic ERG with eccentricity are due to spike-driven oscillatory activity that is more prominent in central and temporal retina than in nasal retina and to the slower timing of all responses in the central, compared with the peripheral, retina. The full-field, photopic ERG most closely resembles the mfERG responses to stimulation of peripheral regions.

Stray light-induced multifocal electroretinograms

PURPOSE

To evaluate the characteristics of stray light-induced response in multifocal ERG (mfERG) elicited by the stimulus falling on the disc.

METHODS

A patient with an enlarged optic disc (4 x 4 disc diameters of disc of normal fellow eye) and four normal volunteers served as subjects. The mfERGs elicited by different stimulus intensities (0.67-4.67 cd-sec/m(2)) were recorded from the patient, and the mfERGs obtained with stimuli on the enlarged optic disc. For comparison, full-field pseudorandom ERGs (ffprERGs) were also recorded in all subjects. The first-order kernels (K1) and the second-order kernels (K2.1) were analyzed.

RESULTS

A small and delayed K1 was recorded on the enlarged disc, but K2.1 was flat on the disc at all intensities. The implicit time of K1 at lower intensities was longer than at higher intensities. ffprERGs at very low intensities in the patient and normal subjects were similar to the mfERG on the disc (delayed K1 associated with flat K2.1).

CONCLUSIONS

The responses elicited by stimulating the disc were delayed in K1 and flat in K2.1. Because similar ffprERGs were observed at very low intensities, it is likely that an optic disc with high reflectance scattered the stimulus light to create a weak full-field stimulus. Thus, care must be taken when focal lesions are investigated with mfERGs.

The influence of ambient room lighting on the pattern electroretinogram (PERG)

It has been suggested that low ambient lighting conditions increase the amplitude of the PERG, but no data has been available on this issue. We recorded the transient PERG (0.8 degrees check size) and steady-state PERG (15 rev/s, 0.8 degrees and 16 degrees check size) under three lighting conditions: dark room, only illuminated by the stimulus (resulting in 30 lux), our standard room lighting (windows occluded, one lighted lamp, 200 lux) and fully lit room (full ceiling illumination with eight fluorescent tubes) resulting in rather bright 2300 lux. The stimulus luminance was 50 cd/m2. The sequence of lighting conditions varied for each subject and followed a balanced permutation of an ABCCBA scheme. Results showed a significant effect (P < 0.01) across lighting conditions, with no relevant difference between the 30 and 200 lux conditions, but a reduction down to 70% at the 2300 lux condition. This obtained across all check sizes and temporal conditions. As an example, the transient PERG P50-amplitudes were as follows: dark, 5.6 +/- 0.8 microV; medium, 5.3 +/- 0.6 microV and bright, 3.8 +/- microV (mean +/- SEM). Peak times decreased significantly with illumination (dark, medium or bright): 45.9 +/- 0.9, 43.1 +/- 0.6 or 40.8 +/- 0.8 ms. Contrast measurements quantitatively explained the noticeable reduction of PERG amplitude at the brightest illumination level simply by straylight, which reduced the display contrast. This suggests that bright sunlight should be excluded, and that lighting conditions should be moderately standardized at low or medium luminance levels for reproducible amplitudes and peak times.

The mouse ERG before and after light damage is independent of p53

Death of retinal photoreceptors by apoptosis is observed under many physiological and pathological conditions such as histogenesis, retinal dystrophies and light-induced photoreceptor degeneration. To date, little is known about regulatory mechanisms for apoptosis in the retina. The tumor suppressor gene p53 is a regulator of apoptosis in a number of systems, however, p53-independent apoptosis has also been described. We have therefore investigated whether the lack of p53 influences the dark-adapted ERG in C57BL/6 p53-/- mice compared to p53+/+ control littermates under physiological (regular light-dark cycle) conditions. We also recorded ERGs at 12 to 14 h in darkness following diffuse bright light exposure to 8,000 or 15,000 lux for 2 h. ERG analysis over a range of 6 logarithmic units of light intensity revealed normal and virtually identical a-, b-, c-waves and oscillatory potentials in dark-adapted p53+/+ and p53-/- mice. After exposure to diffuse white fluorescent light strong decreases of all ERG components were found to be very similar in both genotypes. These data support the notion that the p53 protein is neither essential for normal retinal function nor for processes involved in light-induced depression of the ERG in mice.

Light-emitting diodes and cool white fluorescent light similarly suppress pineal gland melatonin and maintain retinal function and morphology in the rat

BACKGROUND AND PURPOSE

A novel light-emitting diode (LED) light source for use in animal-habitat lighting was evaluated.

METHODS

The LED was evaluated by comparing its effectiveness with that of cool white fluorescent light (CWF) in suppressing pineal gland melatonin content and maintaining normal retinal physiology, as evaluated by use of electroretinography (ERG), and morphology.

RESULTS

Pineal melatonin concentration was equally suppressed by LED and CWF light at five light illuminances (100, 40, 10, 1, and 0.1 lux). There were no significant differences in melatonin suppression between LED and CWF light, compared with values for unexposed controls. There were no differences in ERG a-wave implicit times and amplitudes or b-wave implicit times and amplitudes between 100-lux LED-exposed rats and 100-lux CWF-exposed rats. Results of retinal histologic examination indicated no differences in retinal thickness, rod outer segment length, and number of rod nuclei between rats exposed to 100-lux LED and 100-lux CWF for 14 days. Furthermore, in all eyes, the retinal pigmented epithelium was intact and not vacuolated, whereas rod outer segments were of normal thickness.

CONCLUSION

LED light does not cause retinal damage and can suppress pineal melatonin content at intensities similar to CWF light intensities.

[The effect of light intensity and neostigmine on the electroretinogram of Drosophila melanogaster]

In this article is presented the influence upon the electroretinogram, of some external factors acting at different levels of the visual system in the fruit fly, Drosophila melanogaster. The experiments revealed the effects generated by the light intensity modification as well as by the injection of a neuropharmaceutic--the neostigmine. The increase of the light stimuli intensity induced the same change of the rate between the amplitudes of the main electroretinographic components as the neostigmine does. It was used the "flickering" excitation regime, utilizing a data acquisition system adapted to the principal experimental device.

[Phototoxic maculopathy after arc welding: value of multifocal ERG]

BACKGROUND

Phototoxic maculopathy most likely results from longer exposure to light from sources such as the sun, welding arcs, tungsten halogen lamp filaments or operation microscopes. The value of the multifocal ERG for the evaluation of functional defects in this rare entity has not been described to date.

CASES

We describe the case of a 38-year-old male patient who presented to his local ophthalmologist with bilateral loss of vision and acute ocular pain after having worked for two hours at an electric welding arc. A foveal lesion was found in both eyes, resulting in a bilateral reduction of visual acuity. Nine months later, the patient underwent examination and further investigations at the university eye clinic in Tübingen. Visual field defects on both sides could be detected with automatic threshold perimetry. Using the multifocal ERG with a central element of 2 degrees diameter, a central defect was detected only for the right eye.

CONCLUSIONS

In rare cases, a photic maculopathy can result from exposure to light during arc welding. It can be masked in the first days by a phototoxic keratitis. Multifocal ERG and automatic perimetry are useful tools for the detection and quantification of the functional defects.

Light induces peroxidation in retina by activating prostaglandin G/H synthase

Prostaglandin G/H synthase (PGHS) has been shown to generate peroxides to a significant extent in the retina and absorbs light at the lower end of the visible spectrum. We postulated that PGHS could be an important initial source of peroxidation in the retina exposed to light, which would in turn alter retinal function. Exposure of pig eyes (in vivo) to light (350 fc/3770 lx) caused after 3 h a 50% increase and by 5 h a 30% decrease in a- and b-wave amplitudes of the electroretinogram (ERG) which were comparable at 380-650 nm and 380-440 nm but were not observed at wavelengths > 450 nm. These effects of light were prevented by free radical scavengers (dimethylthiourea and high-dose allopurinol) and PGHS inhibitors (naproxen and diclofenac), but stable analogs of prostaglandins did not affect the ERG. Both increases and subsequent decreases in ERG wave amplitudes following light exposure in vivo were associated with increases in retinal prostaglandin and malondialdehyde (peroxidation product) levels, which were inhibited by the nonselective PGHS blockers, naproxen and diclofenac. Similar observations were made in vitro on isolated porcine eyecups as well as on retinal membranes exposed to light (250 fc/ 2700 lx) 380-650 nm and 380-440 nm but not at > 500 nm. Both PGHS-1 and PGHS-2 contributed equivalently to light-induced prostaglandin synthesis, as shown after selective PGHS-2 blockers, but mRNA expression of PGHS-1 and 2 was not affected by light. Finally, light stimulated activities of pure PGHS-1 and PGHS-2 isozymes, and these were also shown to produce superoxide radical (detected with fluorogenic spin trap, proxyl fluorescamine). Taken together, data suggest that PGHS- (1 and 2) is activated by short wavelength visible light, and in the retina is an important source of reactive oxygen species which in turn alter retinal electrophysiological function. PGHS thus seems a likely chromophore in setting forth photic-induced retinal injury. Findings provide an explanation for increased sensitivity of the retina to visible light predominantly at the far blue range of its spectrum.

[The comparative characteristics of the electroretinograms of vertebrates evoked by light and x-ray stimulation under different conditions of adaptation]

Existence of two electrical responses specific for the X-rays and differing from the responses to red or blue light, was confirmed in the electroretinogram of the frog eye during darkness adaptation, monochromatic illumination as well as in response to paired stimuli in different combinations of red and blue light and the X-rays. The data obtained suggest the possibility of using roentgenophosphen as a test for determining of individual radiation sensitivity in humans.

[The effect of prolonged exposure to UV radiation on the state of the ocular media and on the parameters of the electroretinogram in the rabbit]

Rabbits were exposed to vertically directed UV-B radiation (280-320 nm) 5 days a week during 10 months with daily dose 6.5 J/m2 (biological effective daily dose 0.83 J/m2). Within the first week expressed photokeratoconjunctivitis was observed, but to the end of third week state of cornea and conjunctiva became practically normal. Transparency of intra-eye structures was unchanged, functional activity of retina underwent undulatory alterations. Amplitude changes of a- and b-waves of electroretinogram reached 30% of control values during the first, were negligible within the second, and exceed control by 15-20% between 8 and 10-th months of exposure. Critical frequency of flashing was unchanged.

[Acute eye damage from ultraviolet radiation]

The eyes of rabbits were UV-irradiated in a range close to the natural spectrum at a dose of 23.2 kJ/m2 (biologically effective dose 1.3 kJ/m2). The condition of optic media was estimated, as well as the parameters of electroretinogram (ERG) induced by single light stimulus of varying intensity and paired light stimuli with different intervals between them. As a result a distinct photokeratoconjunctivitis developed, the amplitude of the ERG a-wave decreased by 30-50% and that of b-wave by 35%, while the latencies of the both waves and the critical frequency of flashes remained unchanged. The cornea transparency did not decrease markedly even during the period of maximum photokeratoconjunctivitis and the changes in the ERG parameters were mostly due to the retina damage by the indirect effect of UV irradiation.

Specific features of the electroretinogram of vertebrates induced by X-rays

The net electroretinograms of dark-adapted retinas of the common frog in situ were investigated on an automated experimental system with programmed control and electronic differentiation of biopotentials with respect to the first and second derivatives. It was demonstrated that X-rays elicit an electroretinogram consisting of two components, provisionally called the first and second X-ray reactions (X-1 and X-2), which differ with respect to their parameters from electroretinograms elicited under the same conditions by red and blue light. The administration of sodium azide, sodium nitrate, monoiodo-acetate and other substances alter the X-1 and X-2 as well as the photo-induced ERGs in different ways; this indicates their relative independence and different mechanisms of the occurrence and passing of excitation across the structures of the retina, and makes it possible to partially isolate these for individual study. Thus, the assertion of a number of investigators regarding the absence of specific features in the X-ray induced electroretinograms becomes problematical. The discovery of X-ray-specific reactions in the retina makes it possible to hope that the radiological phosphene (the X-ray phosphene) may serve as a test for the determination of the individual radiational excitability of the central nervous 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.

[The specific characteristics of the vertebrate electroretinogram evoked by x-rays]

Summarised electroretinograms (ERGs) of dark-adaptable retina of Rana temporaria were studied in situ with an automated experimental device with programmable control and first and second derivatives electron differentiation. X-rays were shown to induce the ERG composed of two components which were conventionally designated as the first and second roentgen responses (R-1 and R-2). These differ by their parameters from the ERGs induced by red and blue light in the same experiment. Administration of sodium azide, sodium nitrite, monoiodine acetate and other compounds changed the waves of R-1 and R-2 as well as photo-induced ERGs. This suggests their relative independence and different mechanism of initiation, and allows their partial isolation for separate studying.

[The electroretinogram parameters and the state of the cornea in the rabbit following acute exposure of the eye to UV-radiation of different intensities]

The purpose of this study was to investigate wave amplitudes and latencies of electroretinograms (ERG) and to examine the eye cornea of rabbits a month after their eye UV-B-irradiation with a biologically effective dose of 1.3 kJ/m2 at three intensities of 1.62, 0.567 or 0.157 W/m2. It was demonstrated that ERG a- and b-waves decreased significantly 7-20 days after irradiation while latencies remained unchanged. It was also found that during this time period ERG wave amplitudes were dependent on the intensity: at higher intensities amplitudes of both waves diminished to a greater extent. After irradiation with a peak intensity photokeratoconjunctivitis was more severe and prolonged; however, the effect of irradiation with two other intensities was very similar. In view of the fact that the highest intensity of UV-B-radiation was comparable with that beyond the Earth's atmosphere while the lowest intensity was close to that near the Earth's surface, the above findings can be used to solve space biology problems and to assess potential effects of the ozone layer destruction on the eye.

[Effect of UV-B radiation on the parameters of rabbit electroretinogram]

Rabbit's eyes were exposed to UV-B-light (lambda = 280-320 nm) at biologically effective doses of 20 to 1300 J/M2. The amplitudes of a- and b-waves of the ERG were found to decrease during a period of 7-20 days to reach approximately 50% of the initial level at a maximum dose. By day 30 the wave amplitudes returned to the control. The latencies of both ERG waves were invariable throughout the entire period of observation. The postirradiation changes in the ERG wave amplitudes were most pronounced during the attenuating photokeratitis.