Circadian rhythms in the green sunfish retina

We investigated the occurrence of circadian rhythms in retinomotor movements and retinal sensitivity in the green sunfish, Lepomis cyanellus. When green sunfish were kept in constant darkness, cone photoreceptors exhibited circadian retinomotor movements; rod photoreceptors and retinal pigment epithelium (RPE) pigment granules did not. Cones elongated during subjective night and contracted during subjective day. These results corroborate those of Burnside and Ackland (1984. Investigative Ophthalmology and Visual Science. 25:539-545). Electroretinograms (ERGs) recorded in constant darkness in response to dim flashes (lambda = 640 nm) exhibited a greater amplitude during subjective night than during subjective day. The nighttime increase in the ERG amplitude corresponded to a 3-10-fold increase in retinal sensitivity. The rhythmic changes in the ERG amplitude continued in constant darkness with a period of approximately 24 h, which indicates that the rhythm is generated by a circadian oscillator. The spectral sensitivity of the ERG recorded in constant darkness suggests that cones contribute to retinal responses during both day and night. Thus, the elongation of cone myoids during the night does not abolish the response of the cones. To examine the role of retinal efferents in generating retinal circadian rhythms, we cut the optic nerve. This procedure did not abolish the rhythms of retinomotor movement or of the ERG amplitude, but it did reduce the magnitude of the nighttime phases of both rhythms. Our results suggest that more than one endogenous oscillator regulates the retinal circadian rhythms in green sunfish. Circadian signals controlling the rhythms may be either generated within the eye or transferred to the eye via a humoral pathway.     

Cerebroid Ganglion is the Presumptive Pacemaker of the Circadian Rhythm of Electrical Response to Light in the Crayfish

One of the most widely studied circadian rhythms in invertebrates is that of light responsiveness whose underlying mechanisms seem to involve different groups of oscillators which act as pacemakers. Although, in crayfish, there are clear circadian rhythms in the electroretinogram (ERG) amplitude, the precise location of the pacemaker system driving this rhythm is uncertain. Some data suggest that the circadian pacemaker could be located in a group of neurosecretory cells of the supraesophageal ganglion (the cerebroid ganglion or brain) and that the sinus gland plays a determinant role in the generation and expression of this rhythm through periodic release of pigment-dispersing hormone (PDH). The aim of this work is to examine the role of the brain in the expression of the ERG circadian activity. The hypothesis we test is that the electrical activity at the brain level has a circadian behavior in the firing pattern of spontaneous multiunit activity (MUA) and in visual evoked potentials (VEPs). The results indicate that there are robust circadian rhythms in both MUA, recorded from several regions of the brain, and in the averaged VEPs recorded from the protocerebrum area. These rhythms are 180° out of phase to one another. The rhythm of VEPs showed a main peak at midnight which was in close phase relationship with the ERG amplitude rhythm.     

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.     

Sodium Iodate Selectively Injuries the Posterior Pole of the Retina in a Dose-Dependent Manner: Morphological and Electrophysiological Study

Sequential morphological and functional features of retinal damage in mice exposed to different doses (40 vs. 20 mg/kg) of sodium iodate (NaIO₃) were analyzed. Retinal morphology, apoptosis (TUNEL assay), and function (electroretinography; ERG) were examined at several time points after NaIO₃ administration. The higher dose of NaIO₃ caused progressive degeneration of the whole retinal area and total suppression of scotopic and photopic ERG. In contrast, the lower dose induced much less severe degeneration in peripheral part of retina along with a moderate decline of b- and a-wave amplitudes in ERG, corroborating the presence of regions within retina that retain their function. The peak of photoreceptor apoptosis was found on the 3rd day, but the lower dose induced more intense reaction within the central retina than in its peripheral region. In conclusion, these results indicate that peripheral area of the retina reveals better resistance to NaIO₃ injury than its central part.     

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.     

Electrophysiological consequences of leukotrienes applied on isolated rat retina

Scotopic vision is the result of a cascade of light-dependent biochemical events in rod outer segments (ROS) involving mainly a cGMP-modulation of sodium current. This modification of ionic currents induces changes of membrane potential which generates electroretinographic (ERG) waves. As (i) ERG disturbances are commonly recorded in hypoxic and inflammatory retinal diseases (ii) leukotrienes (LTs), a very potent mediators of inflammation, disturb ionic exchanges in several artificial or natural membrane systems, we undertook the investigation of the effects of LTs on ERG record in mammalian isolated retina. LTB4, LTC4 and LTD4, all induced a dose-dependent marked reduction of the b wave amplitude of ERG. This effect is correlated with a significant decrease in the survival time of the retina. The analysis of the modification of ERG indicates that LTs exhibit a real toxic effect since b wave is mainly affected while P III wave is unchanged. Comparatively with other nervous cells, this phenomenon may be attributed to an increase in Na+ permeability of ROS. It is suggested that LTs may be involved in the development of inflammatory or ischemic retinal diseases.     

Analysis of the retina via suprafusion electroretinography.

Electroretinographic (ERG) transient responses elicited in monkeys by abrupt changes in the periodicity of a rapidly intermittent (suprafusion) luminance stimulus were studied experimentally, and analyzed and interpreted through a theory of dynamic retinal responses. The suprafusion ERG transients are confirmed to behave in accord with theoretical expectation, as elemental responses (retinal Green's functions). By aid of the theory the ERG wave-forms can be reduced to two significant elements. One element, accounting for approximately two-thirds of the total ERG variance, is strictly linear, and correlates well with simultaneously evoked cortical (VEP) transients which were previously related to suprafusion perception in humans. The other element, comprising approximately one-third the ERG transient, is a rectification, with properties indicating that it may arise from a specific layer of retinal neurons (amacrine cells); on this assumption the theory demonstrates that high-frequency nonlinear ERG flicker can isolate activities proximal and distal to the rectifying (amacrine) layer. Thus, the hypothesis of an amacrine origin for the rectifying element entails the possibility that suprafusion ERG studies could accomplish in vivo "dissection" of the human retina.     

Circadian rhythm of active amino acid transport in rat liver

Abstract

The circadian change of the encephalic photosensitivity of quail has been demonstrated. In this study the diurnal variation of the retinal photosensitivity was investigated by the electroretinogram (ERG) to explore the phase relation between the retinal and encephalic systems. The b‐wave, a major component of the ERG, was used as a measure of retinal photosensitivity.

1. In the bird maintained in LD12:12 the b‐wave amplitude of the ERG stayed at a high level for the first 10 h of the light period, and decreased abruptly around the time of light‐off. The decreased level continued until midnight. Thenceforth the b‐wave amplitude recovered progressively to the daytime level before the time of next light on.

2. In the bird maintained in LD16:8, the decrease of the retinal sensitivity in the light phase was initiated prior to the time of expected light‐off, and the onset time of decreasing tendency was advanced by 2 h, with dark adaptation for 30 min given immediately before the ERG measurement. Upon continuous light exposure, the b‐wave amplitude always remained at low level.

3. Periodic changes in retinal sensitivity persisted when the environmental dark phase was temporarily extended for 19 to 30 h.

These observations suggest that the diurnal rhythm of the neural retina in quail might be generated endogenously and appears to control the encephalic photosensitive system.     

Involvement of PAF (Platelet-Activating Factor) in chloroquine-induced retinopathy]

Chloroquine retinopathy is a severe toxic retinal impairment which may result in loss of vision by alterations of the pigmentary epithelium and photoreceptors. Currently, there is no specific treatment for this retinopathy. In order to test the possible involvement of Platelet-Activating Factor (PAF) in chloroquine-induced retinopathy and the use of PAF antagonists for prevention of this condition, we have examined the effect of these substances on the electroretinogram (ERG) of isolated rat retina. When retinas from normal rats were perfused with chloroquine (10(-6) M), a marked and rapid decrease in ERG b-wave amplitude was observed. In contrast, chloroquine had no effect on the ERG of retina isolated from animals pretreated with the PAF antagonist, BN 50730 (30 mg/kg/day i.p., 5 days). The results obtained indicate that (i) chloroquine is a toxic drug for retinal function, (ii) PAF plays a key role in chloroquine retinopathy and (iii) PAF antagonists may constitute valuable agents for the treatment of this retinal impairment.     

Electrophysiological consequences of leukotrienes applied on isolated rat retina

Scotopic vision is the result of a cascade of light-dependent biochemical events in rod outer segments (ROS) involving mainly a cGMP-modulation of sodium current. This modification of ionic currents induces changes of membrane potential which generates electroretinographic (ERG) waves. As (i) ERG disturbances are commonly recorded in hypoxic and inflammatory retinal diseases (ii) leukotrienes (LTs), a very potent mediators of inflammation, disturb ionic exchanges several artificial or natural membrane systems, we undertook the investigation of the effects of LTs on ERG record in mammalian isolated retina. LTB₄, LTC₄ and LTD₄, all induced a dose-dependent marked reduction of the b wave amplitude of ERG. This effect is correlated with a significant decrease in the survival time of the retina. The analysis of the modification of ERG indicates that LTs exhibit a real toxic effect since b wave is mainly affected while P III wave is unchanged. Comparatively with other nervous cells, this phenomenon may be attributed to an increase in Na⁺ permeability of ROS. It is suggested that LTs may be involved in the development of inflammatory or ischemic retinal diseases.     

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.     

Carboxypeptidase E is required for normal synaptic transmission from photoreceptors to the inner retina

Defects in the gene encoding carboxypeptidase E (CPE) in either mouse or human lead to multiple endocrine disorders, including obesity and diabetes. Recent studies on Cpe-/- mice indicated neurological deficits in these animals. As a model system to study the potential role of CPE in neurophysiology, we carried out electroretinography (ERG) and retinal morphological studies on Cpe-/- and Cpe fat/fat mutant mice. Normal retinal morphology was observed by light microscopy in both Cpe-/- and Cpe(fat/fat) mice. However, with increasing age, abnormal retinal function was revealed by ERG. Both Cpe-/- and Cpe fat/fat animals had progressively reduced ERG response sensitivity, decreased b-wave amplitude and delayed implicit time with age, while maintaining a normal a-wave amplitude. Immunohistochemical staining showed specific localization of CPE in photoreceptor synaptic terminals in wild-type (WT) mice, but in both Cpe-/- and Cpe fat/fat mice, CPE was absent in this layer. Bipolar cell morphology and distribution were normal in these mutant mice. Electron microscopy of retinas from Cpe fat/fat mice revealed significantly reduced spherule size, but normal synaptic ribbons and synaptic vesicle density, implicating a reduction in total number of vesicles per synapse in the photoreceptors of these animals. These results suggest that CPE is required for normal-sized photoreceptor synaptic terminal and normal signal transmission to the inner retina.     

Pigment dispersing hormone generates a circadian response to light in the crayfish, Procambarus clarkii

Photoreceptor cells have been identified as important structures in the organization of the circadian system responsible for the generation and expression of the electroretinogram (ERG) circadian rhythm. They are the structures where the circadian periodicity is expressed (effectors) and which transform information from external light signals to be conducted to the pacemaker in order to induce adjustments of the rhythm (synchronizers). After isolation, eyestalks perfused in a pigment dispersing hormone (PDH) solution, show significant changes in receptor potential (RP) amplitude and duration. Exogenous PDH injected into intact crayfish induces a migration of retinal shielding pigments to a light-adapted state. A single dose of PDH produces advances or delays in the circadian rhythm of response to light of visual photoreceptors. All these effects depend on the circadian phase of PDH application. Consequently, the determination of the action of exogenous PDH on photoreceptor cells proved to be very helpful in understanding some mechanisms underlying the circadian organization of crayfish.     

Effects of 3,4-methylenedioxymethamphetamine administration on retinal physiology in the rat

3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) is known to produce euphoric states, but may also cause adverse consequences in humans, such as hyperthermia and neurocognitive deficits. Although MDMA consumption has been associated with visual problems, the effects of this recreational drug in retinal physiology have not been addressed hitherto. In this work, we evaluated the effect of a single MDMA administration in the rat electroretinogram (ERG). Wistar rats were administered MDMA (15 mg/kg) or saline and ERGs were recorded before (Baseline ERG), and 3 h, 24 h, and 7 days after treatment. A high temperature (HT) saline-treated control group was also included. Overall, significantly augmented and shorter latency ERG responses were found in MDMA and HT groups 3 h after treatment when compared to Baseline. Twenty-four hours after treatment some of the alterations found at 3 h, mainly characterized by shorter latency, tended to return to Baseline values. However, MDMA-treated animals still presented increased scotopic a-wave and b-wave amplitudes compared to Baseline ERGs, which were independent of temperature elevation though the latter might underlie the acute ERG alterations observed 3 h after MDMA administration. Seven days after MDMA administration recovery from these effects had occurred. The effects seem to stem from specific changes observed at the a-wave level, which indicates that MDMA affects subacutely (at 24 h) retinal physiology at the outer retinal (photoreceptor/bipolar) layers. In conclusion, we have found direct evidence that MDMA causes subacute enhancement of the outer retinal responses (most prominent in the a-wave), though ERG alterations resume within one week. These changes in photoreceptor/bipolar cell physiology may have implications for the understanding of the subacute visual manifestations induced by MDMA in humans.     

RETINAL CIRCADIAN RHYTHMS IN HUMANS *

Circadian rhythms in the retina may reflect intrinsic rhythms in the eye. Previous reports on circadian variability in electrophysiological human retinal measures have been scanty, and the results have been somewhat inconsistent. We studied the circadian variation of the electrooculography (EOG), electroretinography (ERG), and visual threshold (VTH) in subjects undergoing a 36h testing period. We used an ultrashort sleep-wake cycle to balance effects of sleep and light-dark across circadian cycles. Twelve healthy volunteers (10 males, 2 females; mean age 26.3 years, standard deviation [SD] 8.0 years, range 19-40 years) participated in the study. The retinal functions and oral temperature were measured every 90 min. The EOG was measured in the light, whereas the ERG and the VTH were measured in the dark. Sleep was inferred from activity detected by an Actillume monitor. The EOG peak-to-peak responses followed a circadian rhythm, with the peak occurring late in the morning (acrophase 12:22). The ERG b-wave implicit time peaked in the early morning (acrophase 06:46). No statistically significant circadian rhythms could be demonstrated in the ERG a-wave implicit time or peak-to-peak amplitude. The VTH rhythm peaked in the early morning (acrophases 07:59 for blue and 07:32 for red stimuli). All retinal rhythms showed less-consistent acrophases than the temperature and sleep rhythms. This study demonstrated several different circadian rhythms in retinal electrophysiological and psychophysical measures of healthy subjects. As the retinal rhythms had much poorer signal-to-noise ratios than the temperature rhythm, these measures cannot be recommended as circadian markers. (Chronobiology International, 18(6), 957-971, 2001)     

The electroretinogram in multiple sclerosis and demyelinating optic neuritis

The electroretinogram (ERG) to flashes of white light presented under photopic conditions and the pattern reversal visual evoked potentials (PR-VEPs) from both eyes were recorded from 14 patients with multiple sclerosis (MS) with monocular demyelinating optic neuritis (DON) and from 11 patients soon after presenting with monocular demyelinating optic neuritis alone. Fifteen and 10 normal subjects, matched for age and sex, were used as controls for each group of patients respectively. In the DON group of patients and controls the flicker following ERG (FF-ERG) to white flashes of light at 40 Hz was also recorded. Skin electrodes and averaging procedures were used for all the recordings. The PR-VEP elicited with stimulation of the affected eye was absent or abnormally delayed, and the amplitude of the ‘b’ wave of ERG of the affected eye was diminished in all patients. The ‘b’ wave latency, however, was similar in both affected and non-affected eyes and the controls. There was no difference in ‘a’ wave amplitude and latency between eyes of patients and normal subjects. The FF-ERG in 8 out of 10 patients with satisfactory recordings was diminished in the affected eye. These results provide neurophysiological evidence that retinal damage is not due to loss of myelin but is an early feature of demyelinating optic neuritis. This damage preferentially affects the retinal elements associated with the generation of the ‘b’ wave of the ERG, probably the glial cells of Müller.     

正常猕猴与人的视网膜电图比较

目的比较正常猕猴与人视网膜电图异同,为进一步利用猕猴建立动物模型研究视网膜疾病打下基础。方法健康成年猕猴7只（14只眼）与8例（16只眼）正常人进行视网膜电图检测,对两者Rod-ERG中的b波,Max-ERG的a、b波,Cone-ERG的b波峰时值及波幅和OPs的O2值,Flicker-ERG的P值进行统计学检验。结果猕猴与人的视网膜电图波形结果较为相似,各指标与人的结果相比,潜伏期短,幅值低,但Cone-ERG和Flicker-ERG两者幅值差异不具有统计学意义。结论视网膜电图检测从功能上证明猕猴较其他常用实验动物更接近人,尤其表现在视锥细胞及黄斑区功能,可用作人类视网膜疾病尤其是黄斑区病变的良好动物模型。     

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

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

Ba2+ unmasks K+ modulation of the Na+-K+ pump in the frog retinal pigment epithelium

This paper presents electrophysiological evidence that small changes in [K+]o modulate the activity of the Na+-K+ pump on the apical membrane of the frog retinal pigment epithelium (RPE). This membrane also has a large relative K+ conductance so that lowering [K+]o hyperpolarizes it and therefore increases the transepithelial potential (TEP). Ba2+, a K+ channel blocker, eliminated these normal K+-evoked responses; in their place, lowering [K+]o evoked an apical depolarization and TEP decrease that were blocked by apical ouabain or strophanthidin. These data indicate that Ba2+ blocked the major K+ conductance(s) of the RPE apical membrane and unmasked a slowing of the normally hyperpolarizing electrogenic Na+-K+ pump caused by lowering [K+]o. Evidence is also presented that [K+]o modulates the pump in the isolated RPE under physiological conditions (i.e., without Ba2+). In the intact retina, light decreases subretinal [K+]o and produces the vitreal-positive c-wave of the electroretinogram (ERG) that originates primarily in the RPE from a hyperpolarization of the apical membrane and TEP increase. When Ba2+ was present in the retinal perfusate, the apical membrane depolarized in response to light and the TEP decreased so that the ERG c-wave inverted. The retinal component of the c-wave, slow PIII, was abolished by Ba2+. The effects of Ba2+ were completely reversible. We conclude that Ba2+ unmasks a slowing of the RPE Na+-K+ pump by the light-evoked decrease in [K+]o. Such a response would reduce the amplitude of the normal ERG c-wave.     

RETINAL CIRCADIAN RHYTHMS IN HUMANS*

Circadian rhythms in the retina may reflect intrinsic rhythms in the eye. Previous reports on circadian variability in electrophysiological human retinal measures have been scanty, and the results have been somewhat inconsistent. We studied the circadian variation of the electrooculography (EOG), electroretinography (ERG), and visual threshold (VTH) in subjects undergoing a 36h testing period. We used an ultrashort sleep-wake cycle to balance effects of sleep and light-dark across circadian cycles. Twelve healthy volunteers (10 males, 2 females; mean age 26.3 years, standard deviation [SD] 8.0 years, range 19–40 years) participated in the study. The retinal functions and oral temperature were measured every 90 min. The EOG was measured in the light, whereas the ERG and the VTH were measured in the dark. Sleep was inferred from activity detected by an Actillume monitor. The EOG peak-to-peak responses followed a circadian rhythm, with the peak occurring late in the morning (acrophase 12:22). The ERG b-wave implicit time peaked in the early morning (acrophase 06:46). No statistically significant circadian rhythms could be demonstrated in the ERG a-wave implicit time or peak-to-peak amplitude. The VTH rhythm peaked in the early morning (acrophases 07:59 for blue and 07:32 for red stimuli). All retinal rhythms showed less-consistent acrophases than the temperature and sleep rhythms. This study demonstrated several different circadian rhythms in retinal electrophysiological and psychophysical measures of healthy subjects. As the retinal rhythms had much poorer signal-to-noise ratios than the temperature rhythm, these measures cannot be recommended as circadian markers. (Chronobiology International, 18(6), 957–971, 2001)