Electroretinogram Components Research Articles

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.

Response linearity and kinetics of the cat retina: the bipolar cell component of the dark-adapted electroretinogram.

The electroretinogram (ERG) of the dark-adapted cat eye in response to brief ganzfeld flashes of a wide range of intensities was recorded after intravitreal injection of n-methyl DL aspartate (NMDLA, cumulative intravitreal concentration of 1.3-3.9 mM) to suppress inner-retinal components, and after intravitreal DL or L-2-amino-4-phosphonobutyric acid (DL-APB, 1-3 mM; L-APB, 1.2 mM) and 6-cyano-7-nitroquinoxaline-2,3 dione (CNQX, 40-60 microM), to suppress all post-receptoral neuronal responses. Rod PII, the ERG component arising from rod bipolar cells, was derived by subtracting records obtained after APB and CNQX from post-NMDLA records. When we measured the derived response at fixed times after the stimulus, we found that PII initially increased in proportion to stimulus intensity without any sign of a threshold. The leading edge of PII at early times after the stimulus, when the response was still small, was well described by V(t) = kI(t-td)5 where k is a constant, I is the intensity of the stimulus, and td is a brief delay of about 3 ms. Correspondingly, the time for the response to rise to an arbitrary small criterion voltage Vcrit was adequately fitted by tcrit = td + (Vcrit/kI)1/5. The time course of the leading edge of the PII response can be interpreted to indicate that the mechanism generating PII introduces three stages of temporal integration in addition to the three stages that are provided by the mechanism of the rod photoreceptors. This finding is consistent with the operation within the rod bipolar cell of a G-protein cascade similar to that in the rods.

Temporal adaptations in visual systems of deep-sea crustaceans

The temporal characteristics of the visual systems of deep-sea crustaceans were examined at varying light levels. Experimental organisms were collected off Hawaii and southern California in 1991 and 1992, and continually maintained in the dark. At the University of California Santa Barbara Marine Laboratory, the temporal components of both visual interneuron activity and electroretinograms (ERGs) of adult Gnathophausia ingens were tested at threshold and with background light levels up to 6 log units above threshold. To compare these responses with those of mid-water organisms inhabiting shallower depths, the temporal characteristics of the ERGs of Oplophorus spinosus and juvenile G. ingens were assessed. Adults of both species showed little or no change in the time components of their responses when light-adapted, except for the response latency. There was also no evidence of a circadian rhythm in visual sensitivity. O. spinosus, a vertical migrator, and juvenile G. ingens, which inhabit a shallower depth than the adults, exhibited more rapid responses than adult G. ingens. These varying responses are considered adaptations to the differences in light levels at the characteristic depths of the organisms.

Push-pull model of the primate photopic electroretinogram: a role for hyperpolarizing neurons in shaping the b-wave.

Existing models of the primate photopic electroretinogram (ERG) attribute the light-adapted b-wave to activity of depolarizing bipolar cells (DBCs), mediated through a release of potassium that is monitored by Müller cells. However, possible ERG contributions from OFF-bipolar cells (HBCs) and horizontal cells (HzCs) have not been explored. We examined the contribution of these hyperpolarizing second-order retinal cells to the photopic ERG of monkey by applying glutamate analogs to suppress photoreceptor transmission selectively to HBC/HzCs vs. DBCs. ERGs of Macaca monkeys were recorded at the cornea before and after intravitreal injection of drugs. Photopic responses were elicited by bright 200-220 ms flashes on a steady background of 3.3 log scotopic troland to suppress rod ERG components. 2-amino-4-phosphonobutyric acid (APB), which blocks DBC light responses, abolished the photopic b-wave and indicated that DBC activity is requisite for photopic b-wave production. However, applying cis-2,3-piperidine dicarboxylic acid (PDA) and kynurenic acid (KYN), to suppress HBCs/HzCs and third-order neurons, revealed a novel ERG response that was entirely positive and was sustained for the duration of the flash. The normally phasic b-wave was subsumed into this new response. Applying n-methyl-dl-aspartate (NMA) did not replicate the PDA+KYN effect, indicating that third-order retinal cells are not involved. This suggests that HBC/HzC activity is critical for shaping the phasic b-wave. Components attributable to depolarizing vs. hyperpolarizing cells were separated by subtracting waveforms after each drug from responses immediately before. This analysis indicated that DBCs and HBC/HzCs each can produce large but opposing field potentials that nearly cancel and that normally leave only the residual phasic b-wave response in the photopic ERG. Latency of the DBC component was 5-9 ms slower than the HBC/HzC component. However, once activated, the DBC component had a steeper slope. This resembles properties known for the two types of cone synapses in lower species, in which the sign-preserving HBC/HzC synapse has faster kinetics but probably lower gain than the slower sign-inverting G-protein coupled DBC synapse. A human patient with "unilateral cone dystrophy" was found to have a positive and sustained ERG that mimicked the monkey ERG after PDA+KYN, indicating that these novel positive photopic responses can occur naturally even without drug application. These results demonstrate that hyperpolarizing second-order neurons are important for the primate photopic ERG.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopaminergic modulation of rod pathway signals does not affect the scotopic ERG of cat at dark-adapted threshold.

1. Two rod-driven electroretinogram (ERG) components were recorded to monitor scotopic retinal signals during experimental manipulation of dopamine and gamma-aminobutyric acid (GABA) in normal cat eyes and in eyes pretreated with 6-hydroxydopamine (6-OHDA). The scotopic threshold response (STR) was elicited near absolute threshold to monitor signals traversing the rod pathway near quantal threshold; scotopic PII, which normally begins approximately 2 log units higher, was also monitored. Responses were evaluated by V-log I curves and criterion amplitudes after intravitreal drug injections into intact eyes in vivo. The depletion of dopaminergic cells by pretreating with 6-OHDA was confirmed histologically by immunocytochemical methods. 2. Dopamine abolished the STR and markedly decreased PII in the normal eye. Both 6-OHDA pretreatment and application of the dopamine antagonist, haloperidol, increased the STR amplitudes, but only for stimuli beginning 2 log units above threshold; PII amplitude also was increased. However, neither 6-OHDA pretreatment nor haloperidol affected the STR near absolute threshold. 3. Both GABA and bicuculline suppressed the STR in the normal eye. However, when applied to eyes pretreated with 6-OHDA or concurrent with haloperidol, bicuculline enhanced the STR. GABA enhanced the PII amplitude in the normal eye but had no effect in eyes pretreated with 6-OHDA or in the presence of haloperidol. 4. These results suggest that 1) dopaminergic activity modulates signals in the rod pathway at higher stimulus intensities but not near absolute threshold and 2) GABA can affect the scotopic PII component by acting through dopaminergic cells in the dark-adapted retina.

Circadian rhythm in the visual system of the lizard Anolis carolinensis.

The electroretinogram (ERG) was recorded from free-moving Anolis lizards once per hour for 5 days. As in our previous work, the b-wave, but not the a-wave, showed a reliable circadian rhythm (CR) in amplitude, with an acrophase near projected noon. Both the a- and b-waves showed a CR in peak time (implicit time, or IT), with the a-wave IT being longest near midnight, and the b-wave IT at midday. Acrophases were shifted when animals were housed on a phase-shifted light-dark cycle. The ERG CR was unaffected by removal of the parietal organ, but it was virtually abolished by removal of the pineal gland, thus suggesting that pineal output (probably melatonin) modulates retinal responses. In addition to the ERG, the tectal light-evoked potential exhibited a CR--a finding compatible with a circadian variation in retinal output. Lastly, the amplitude of the ERG component waveforms showed a seasonal variation, but the ERG CR was constant across the year.

Effects of Calcitonin gene-related peptide on the rabbit electroretinogram

In order to better understand the role of Calcitonin gene-related peptide (CGRP) in mammalian retina, the dose related effects of human CGRP (hCGRP) on rabbit electroretinogram (ERG) were examined in the present study. CGRP was administered intraocularly in doses of 0.1, 1.0 and 10.0 μg. ERG A- and B-wave as well as oscillatory potentials (P1, P2, P3 and P4) were recorded. The highest dose of CGRP (10.0 μg) significantly increased the amplitudes of the A-wave and OP components (P1, P2, P3 and P4) produced by relatively high stimulus intensity. The same dose of the peptide also enhanced B-wave amplitude at all intensities studied. The effects of the intermediate dose of CGRP (1.0 μg) on the B-wave amplitudes were dependent on stimulus intensities. B-wave amplitudes at high stimulus intensities were not affected by 1.0 μg of CGRP but were significantly increased with relatively lower stimulus intensities. The amplitudes of P3, one of OP components, were significantly increased. However, amplitudes of A-wave and other OP components (P1, P2 and P4) were not affected by 1.0 μg CGRP. The lowest dose of the peptide (0.1 μg) did not affect any amplitudes of ERG components. Implicit times of A-wave, B-wave and OP components were not significantly affected by the different doses of CGRP. Taken together, these results indicate that CGRP may play a functional role in modulating retinal responses to photic stimulation.

An investigation of ophthalmic function in winter seasonal affective disorder

AbstractTo evaluate the possibility that abnormalities in visual functioning may be of importance in winter seasonal affective disorder (SAD), we compared various ophthalmological function tests by drawing subsets of a group of 61 patients and 61 normal controls. We measured dark adaptation with a Goldmann‐Weekers dark adept meter in winter and summer. In winter we also measured intraocular pressure with an applanation tonometer while ‘off’ and “on” light therapy, pupillary size by measuring pupillaryphotos, color vision with a Nagelanomaloscope and the Farnsworth‐Munsell 100 Hue test, and determined b‐wave components of pattern electroretinograms and P100 components of pattern visual evoked potentials. We found no significant differences between patients and controls. These observations have direct implications upon different theories linking SAD to abnormal ophthalmic junction. This body of work provides little evidence to link SAD to an intrinsic ophthalmic defect in the electrophysiological and neurological pathways studied. Depression 1:29–37 (1993). Published 1993 by Wiley‐Liss, inc.

The electroretinogram sensitivity in patients with diabetes.

Electroretinograms (ERGs) were measured in 65 patients with diabetes and 10 control subjects. The single flash ERGs were recorded as a function of the stimulus intensity. A Naka-Rushton-type function was fit to b-wave amplitudes, measured as a function of stimulus intensity, to evaluate changes in ERG amplitude and sensitivity. We also measured the temporal aspects of the ERG b-waves. The ERG sensitivity tended to decrease as the retinopathy progressed. An average sensitivity loss in eyes with diabetic retinopathy was statistically significant. However, the eyes of diabetic patients without visible retinopathy did not show significant ERG sensitivity loss. There was less variability in temporal compared with amplitude measurements of ERG components, and significantly prolonged b-wave implicit times were found in all stages of retinopathy and in eyes of diabetic patients without retinopathy.

Light-emitting diodes and half-cell electrodes in experimental recording of electroretinogram c-wave.

A method of electroretinogram c-wave recording in the rat was developed that uses a contact lens electrode connected through a saline bridge with a silver-silver chloride half-cell. A cluster of light-emitting diodes, regulated by an electronic light-emitting diode stimulator, was used as a light source. The method enables recordings of c-waves of 0.4-1.6 mV amplitude as well as other electroretinogram components in narrow limits of variation. The two main sources of response variability are voltage shunting and eyeball protrusion.

M-wave of the toad electroretinogram

1. In the retina, two distinct, light-evoked releases of K+ have been described. One takes place in the outer plexiform layer (OPL) and is termed the "distal K+ increase." The other takes place in the inner plexiform layer (IPL) and is termed the "proximal K+ increase." Although the distal K+ increase generates the electroretinogram (ERG) b-wave, the contribution of the much larger proximal K+ increase to the ERG is less well understood. In this paper we detail our investigation of the proximal K+ increase and its contribution to the ERG. We describe an ERG component, the M-wave, which had not heretofore been observed in the diffuse-flash, vitreal ERG. 2. We studied the proximal K+ increase and the ERG M-wave in the isolated retina preparation of the toad, Bufo marinus. We used K(+)-sensitive microelectrodes, as well as conventional intra- and extracellular microelectrodes, to record K+ changes, the local (or intraretinal) ERG, the vitreal ERG, and Müller cell responses. 3. As in earlier studies of the amphibian and cat M-wave, we readily observed an M-wave in the intraretinal, or local, ERG (LERG). The M-wave we studied had characteristics similar to those of M-waves that were previously described. Specifically, we found that the M-wave was generated by a Müller cell response to the proximal K+ increase and that both the proximal K+ increase and the LERG M-wave were spatially tuned. 4. We used the aspartate receptor agonist, N-methyl-DL-aspartate (NMA), to reveal that an M-wave is present in the vitreal ERG. Researchers who previously investigated the M-wave were unable to identify an M-wave in the vitreal ERG. We found that the toad ERG M-wave was a small, positive potential that was partially obscured by the much larger b-wave and slow PIII components. 5. We observed that picrotoxin (PTX) had an excitatory effect on inner retina, as evidenced by an enhanced proximal K+ increase and an enhanced M-wave. This result indicates that it is likely that GABAergic inhibition in inner retina plays an important role in retinal processing in the toad. 6. At threshold, we found that the ERG consisted mainly of an M-wave, indicating that the amphibian threshold ERG is driven by proximal retina. This result is analogous to previous observations of the threshold ERG in cat. However, in cat, the M-wave and threshold response have been described as distinct ERG components.(ABSTRACT TRUNCATED AT 400 WORDS)

EOG and ERG modifications induced in the chicken eye after blockade of catecholamine and 5-hydroxytryptamine biosynthesis

The involvement of catecholaminergic and indoleaminergic systems in the modulation of the standing potential of the eye was tested in chickens by means of an indirect electrooculography method and direct current electroretinogram recordings. D,L alpha-monofluoromethyl dopa (MFMD), 50 and 100 nmol), a highly specific inactivator of aromatic L-amino acid decarboxylase, was injected intravitreally. This treatment is known to induce a selective and irreversible blockade of dopamine and 5-hydroxytryptamine biosynthesis. Five hours after drug injection an important increase in the standing potential appeared. The light peak was delayed by about 5 min but its amplitude was unchanged. The return of the standing potential to basal value during maintained illumination was delayed by 5-10 min. The time course of the dark trough was not modified. The intensity-voltage functions were also studied for the various electroretinogram components, 5 hr after MFMD. The voltage of the b-wave was reduced (by 65% with the highest intensity), while the other components were little affected. Substantial reduction in dopamine and 5-hydroxytryptamine concentrations were found in treated retinas. These data, together with previous results, suggest that the standing potential of the chicken eye may be modulated by a balance between catecholamine and indoleamine systems.

The effect of acute trichloroethylene exposure on electroretinogram components

The effects of acute exposure to trichloroethylene (TCE) on the electroretinogram (ERG) and oscillatory potentials (OPs) were studied on adult New Zealand rabbits anesthetized with urethane. The ERG and OPs were recorded under photopic conditions with a speculum electrode, with pupils fully dilated and the cornea anesthetized. Emulsified (Intralipid) TCE was given intravenously in three consecutive injections of equal volume for a total dose varying between 24 and 85 mg/kg. Averaged ERG and OPs (50 sweeps) were taken up to 250 minutes after the last TCE injection. Our results indicated that, irrespective of the dose used, there was a significant ( p<0.001) reduction (average: 50%) in the amplitude of the b-wave of the ERG following TCE injection. In contrast, the OPs showed a differential effect. At low doses, OP4 showed a significant ( p<0.001) reduction resulting in some cases to its complete extinction, while at higher dose there is a marked increase in amplitude. Our results would suggest that the OPs are a better retinal potential to assess the level of TCE toxicity than is the b-wave of the ERG.

Electrooculographic and electroretinographic study in the chicken after dopamine and haloperidol

The implication of dopamine in the modulation of the standing potential of the eye was tested in the chicken through an indirect electrooculographic method and direct current electroretinogram (ERG) recording after haloperidol, a mixed D1-D2 antagonist. The standing potential of the eye was reduced within 15 min after intravitreal injection of the antagonist (150 micrograms). This effect is rapidly reversed by an application of dopamine. The fast oscillation was preserved but the light peak was either strongly reduced or abolished. The dark trough showed an apparently normal time course. The intensity-voltage function was studied for the various ERG components. After haloperidol the b-wave and the c-wave were strongly reduced, whereas the a-wave was little affected. Together with previous data obtained with intraocular injections of dopamine, our data suggest the involvement of dopamine in the modulation of the standing potential. They also support the hypothesis that the light peak, which is generated by a photoreceptor-pigment epithelium interaction, is influenced by dopamine or by a related substance. The modulatory effect could also be due to a balance between several neurotransmitter systems.

The human focal electroretinogram as a function of stimulus area

Focal electroretinograms to on-off luminance modulation (2.7 Hz) of uniform fields with a different area (144-2.25 deg2) centered on the fovea were recorded in two young normal subjects. The electroretinogram responses typically consisted of an a-wave, a b-wave, a PIII component and a d-wave. The concentric reduction of the test field size caused progressive amplitude decrement of all components, while their response density increased. The spatial summation properties of the b-wave differed from those of the a-wave, PIII component and d-wave so that the relative contribution of the b-wave to the electroretinogram waveform depended on the stimulus area. For a critically small field size, the electroretinogram was dominated by the PIII and d-wave components. Only these two electroretinogram components displayed a density profile that could be compared with that of cone distribution.

Visual Function Deficits in Glaucoma

The pattern electroretinogram is abnormal in glaucoma. Part of the pattern electroretinogram may be attributed to the summation of responses to luminance increases and decreases (nonlinear luminance responses). We conducted a study to investigate the effect of glaucoma on the pattern electroretinogram component waves and to determine if the flicker electroretinogram nonlinear components are abnormal in glaucoma. We tested 35 subjects in two replications of four conditions: 10- and 20-Hz flicker, and 4- and 10-Hz pattern reversal. Only the even harmonics were recorded. The patients with glaucoma had reduced electroretinogram amplitudes for all measures relative to the normal subjects. Electroretinogram amplitudes of those suspected of having glaucoma were intermediate. The greatest amplitude reductions were for the 10-Hz flicker electroretinogram and the 4-Hz pattern electroretinogram. These results confirm pattern electroretinogram abnormalities and reveal flicker electroretinogram abnormalities in glaucoma.

Oscillatory potentials of local macular ERG in diabetic retinopathy

The oscillatory potentials (OPs) in electroretinogram (ERG) have clinical values in measuring retinal functions of the early stage of diabetic retinopathy. However, OPs have, until now, been evaluated as components of total ERG recorded with a full field stimulus over the entire retina. Therefore, little information could be obtained about the macular condition (diabetic retinopathy). Using focal stimuli, we successfully recorded OPs in the human macular region. We modified our previously reported system for recording local macular ERG under the fundus monitor with an infrared television fundus camera. We evaluated macular OPs with simultaneously recorded a- and b-waves in many patients with diabetic retinopathy. In some kinds of early diabetic maculopathy, the macular OPs were selectively reduced, leaving the a- and b-waves intact. The macular OPs can be a valuable indicator in assessing the macular function in diabetic maculopathy.

Retinitis pigmentosa and inner retina. Functional study by means of oscillatory potentials of the electroretinogram.

The alterations of the inner retina in retinitis pigmentosa have been described in previous papers less often than the external retina alterations, both from the electrophysiological and morphological point of view. The oscillatory potentials (OPs) of the electroretinogram (ERG) are a good tool to investigate the inner part of the retina because of the deep anatomical location of their generators. We studied the photopic OPs in a group of 25 subjects affected with retinitis pigmentosa and compared them with other ERG components to obtain information about the functional damage of the inner retina. The OPs were recordable in 9 patients. No analogies were found with the inheritance modes. No relationship was found between OPs and 20 Hz ERG photopic response which was still present in a consistent number of eyes when OPs were no longer recordable. Such finding can be interpreted as an expression of inner retinal damage paralleling the photoreceptors and retinal pigment epithelium impairment.

Intraretinal analysis of the threshold dark-adapted ERG of cat retina.

1. The dark-adapted electroretinogram (ERG) obtained with 4-s flashes near threshold and at low intensities has three clear negative components: 1) a fast negative response at stimulus onset, 2) a slow negative response that increases in amplitude for about 2 s, and 3) a negative-going OFF response. The fast negative response was previously shown to originate from the scotopic threshold response (STR) arising in the proximal portion of neural retina. We investigated the intraretinal origins of the other two negative components and found that they also have origins in neural retina proximal to the photoreceptors. 2. In this study the ERG evoked in response to diffuse illumination of the dark-adapted cat retina was recorded between a chlorided silver wire in the vitreous and a plate behind the eye. Extracellular field potentials were recorded simultaneously with a microelectrode placed intraretinally at different retinal depths. In some cases light-dependent changes in extracellular K+ concentration ([K+]o) were recorded with the K+-selective barrel of a double-barreled microelectrode. 3. The three negative-going ERG potentials increased in amplitude from threshold up to approximately 6.0 log q.deg-2.s-1. The potential during illumination then became nearly flat, and the negative OFF response was exaggerated. At higher intensities, positive-going PII (DC-component and b-wave) and the c-wave emerged, whereas the a-wave (negative-going) was usually below threshold. 4. The slow negative ERG response was generated in neural retina, rather than by the retinal pigment epithelium. The response was positive-going in the transretinal recordings obtained in subretinal space. It was not, however, related to two positive-going responses from distal retina previously described as contributing negative components to the ERG: the neural retina component of the c-wave, termed slow PIII, and the rod-receptor potential. The slow negative response had a slower time course and lower threshold than slow PIII, and, more importantly, it was present in the absence of the [K+]o decrease in subretinal space that causes slow PIII. Furthermore, APB (1.2 mM vitreal concentration) blocked the entire negative-going ERG, whereas at higher intensities it blocked PII but not the c-wave in the ERG or slow PIII in transretinal recordings. These results indicate that the negative-going ERG components near threshold and at low intensities all originated proximal to the photoreceptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensitivity of ERG components from dark-adapted goldfish retinas treated with APB

The electroretinogram (ERG) of the dark-adapted goldfish was examined before and after intravitreal injection of DL-2-amino-4-phosphonobutyric acid (APB). APB abolished the b-wave and decreased absolute sensitivity of the remaining waveform, which was composed of a vitreal-negative component followed by a vitreal-positive component. The sensitivity, time course and amplitude of these components differed from ERGs obtained from animals treated with sodium aspartate. Spectral sensitivity of both post-APB components closely resembled that of the normal dark-adapted b-wave. The results suggest that APB does not act selectively on any particular class of photoreceptors or photoreceptor pathways in the dark-adapted goldfish retina.