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PubMed1997

Light-modulated release of RFamide-like neuropeptides from nervus terminalis axon terminals in the retina of goldfish.

The nervus terminalis of teleosts, a cranial nerve anatomically associated with the olfactory system, projects to visual system targets including retina and optic tectum. It is known to contain gonadotropin-releasing hormone and RFamide-like peptides, but its function remains unknown. We have probed nervus terminalis function in goldfish by measuring peptide content in retina and tectum with a radioimmunoassay for A18Famide (neuropeptide AF; bovine morphine-modulating peptide). We found that retinal peptide content increased in the dark and decreased in the light, whereas tectal peptide content decreased in the dark and increased in the light. In addition, RFamide-like peptide content in the retina was transiently decreased by severing both olfactory tracts, increased in light-adapted eyes treated with a GABAergic agonist (isoguvacine), and decreased in dark-adapted eyes treated with GABAergic antagonists (bicuculline and picrotoxin). We also found that RFamide-like peptide release could be induced in dark-adapted isolated-superfused retinas by exposure to light or a high concentration (102.5 mM) of potassium ions. We interpret the increase and decrease in peptide content as reflecting a decrease and increase, respectively, in rate of peptide release. We propose that the release and accumulation of RFamide-like peptides in axon terminals of nervus terminalis processes in the retina are modulated primarily by neurons intrinsic to the retina and regulated by light. Peptide release appears to be inhibited tonically in the dark by GABA acting through GABAA receptors; light facilitates peptide release by disinhibition due to a reduction in GABA release. In addition, we propose that electrical signals originating outside the retina can override these intrinsic release-modulating influences.

Adaptation, Ocular↗
PubMed1988

[The effect of posterior chamber lenses or YAG laser capsulotomy on sensitivity to glare and twilight vision in comparison to phakic control groups (corrected)].

Patients who had undergone extracapsular cataract extraction with implantation of a posterior chamber intraocular lens, and normal subjects of corresponding age and vision were examined with the mesoptometer and nyktometer to compare their twilight vision and glare sensitivity. All the results were poorer in patients with intraocular lenses. Statistically, some of the differences in the results of examinations performed in the two groups were highly significant. As the controls were strictly matched in age and visual acuity, these results confirm other studies with similar objectives. Additionally, some patients with posterior chamber lenses were examined who had also undergone YAG laser capsulotomy for secondary cataract. Although the number of cases was too small for statistical evaluation, it appeared that in this group twilight vision and glare sensitivity could not be improved in the same way as daylight visual acuity by means of this treatment. These findings indicate that since intraocular lenses are increasingly being implanted in younger patients, special attention should also be paid to scotopic vision and glare sensitivity during examinations for drivers' licenses, particularly in cases of good daylight vision. Special examinations, e.g., with the mesoptometer or nyktometer, should be carried out in all such cases. Increased glare sensitivity in eyes with lens implants should also be taken into consideration with regard to the increasing importance of computer and TV screens.

Adaptation, Ocular↗
PubMed1993

Adaptation of the vestibulo-ocular reflex with the head in different orientations and positions relative to the axis of body rotation.

We investigated the influence of static head orientation and position, relative to the axis of body rotation, upon vestibular adaptation. With the head centered, displaced anterior to the axis of body rotation, or tilted 40 degrees to 45 degrees in roll or pitch, the gain of the vestibulo-ocular reflex (VOR) was trained (to go either up or down) for one hour using artificial manipulation of the visual surround to produce a visual-vestibular mismatch. Before and after each training session, the VOR was measured in darkness with the head in the training as well as in several non-training positions. We found that transfer of VOR adaptation to non-training positions was almost complete when comparing head eccentric versus head-centered rotations. For tilts, however, transfer of VOR learning was far less complete suggesting that static otolith signals provide a strong contextual cue that gates the expression of an adaptive VOR response. Finally, following training to increase the VOR, gain was greater for centripetally than centrifugally directed slow phases. Centripetally directed postsaccadic drift also developed. These findings imply that the gain increase paradigm also leads to abnormal function of the velocity-to-position neural integrator, which holds eccentric positions of gaze.

Adaptation, Physiological↗
PubMed1979

Adaptive modification of the rabbit's horizontal vestibulo-ocular reflex during sustained vestibular and optokinetic stimulation.

Adaptability of the horizontal vestibulo-ocular reflex (HVOR) and the optokinetic response (OKR) was examined in alert albino rabbits during sustained runs lasting 5--12 h under four different stimulus conditions. (1) Sinusoidal rotation of the rabbit in darkness by 5 degrees at 1/10 Hz, or (2) sinusoidal movement of a vertical slit light by 2.5 degrees of 5 degrees at 1/10 Hz around the optical axis of the stationary rabbit, affected the gain of neither the HVOR nor the OKR. (3) Combination of the stimulus as in (1) with the stationary slit light increased the gain of the HVOR gradually. A plateau at about 140% of the initial control was reached in 5 h. (4) Combination of the stimulus as in (1) with the slit light movement by 10 degrees in phase with the turntable decreased the HVOR gain gradually, a plateau being obtained at about 70% of the initial control in 5 h. Changes of the HVOR gain induced in conditions (3) and (4) were not frequency-specific and accompanied by no signficant modification of either the gain or phase of the OKR or the linear property of HVOR-OKR interaction. A small but significant change of the HVOR phase was also detected under the condition (3) but not (4).

Adaptation, Ocular↗
PubMed2006

Removal of ocular artifacts from EEG using adaptive thresholding of wavelet coefficients.

Electroencephalogram (EEG) gives researchers a non-invasive way to record cerebral activity. It is a valuable tool that helps clinicians to diagnose various neurological disorders and brain diseases. Blinking or moving the eyes produces large electrical potential around the eyes known as electrooculogram. It is a non-cortical activity which spreads across the scalp and contaminates the EEG recordings. These contaminating potentials are called ocular artifacts (OAs). Rejecting contaminated trials causes substantial data loss, and restricting eye movements/blinks limits the possible experimental designs and may affect the cognitive processes under investigation. In this paper, a nonlinear time-scale adaptive denoising system based on a wavelet shrinkage scheme has been used for removing OAs from EEG. The time-scale adaptive algorithm is based on Stein's unbiased risk estimate (SURE) and a soft-like thresholding function which searches for optimal thresholds using a gradient based adaptive algorithm is used. Denoising EEG with the proposed algorithm yields better results in terms of ocular artifact reduction and retention of background EEG activity compared to non-adaptive thresholding methods and the JADE algorithm.

Adaptation, Physiological↗
PubMed1997

Characterization of Purkinje cells in the goldfish cerebellum during eye movement and adaptive modification of the vestibulo-ocular reflex.

The discharge characteristics of Purkinje cells were analyzed in the goldfish cerebellum during eye movement and adaptation of the vestibulo-ocular reflex (VOR). Purkinje cells, identified by the simultaneous recording of complex and simple spikes, were recorded in the cerebellar area where electrical microstimulation elicited ipsiversive horizontal eye movements. Simple spikes of Purkinje cells displayed signals related to head and/or eye velocity as determined independently during either VOR suppression or optokinetic stimulation, respectively. Head velocity-only Purkinje cells (12%) increased their firing rate in relationship to ipsilateral head movements. Two types of eye velocity-only Purkinje cells (28%) were found that responded either in phase with ipsi- (16%) or contralateral (12%) eye movement, respectively. Purkinje cells combining both eye and head velocity (60%) were classified into two groups according to their preferred direction for eye movement. Eye velocity signals either added to (18%) or subtracted from (42%) head velocity during all visuo-vestibular interactions. Short term adaptive changes of the VOR were induced by oscillating goldfish in a moving visual surround that modified the ratio of eye to head velocity (gain) from a level of 1.0 (16 degrees/s) towards gains ranging from 2.5 (40 degrees/s) to -1.0 (-16 degrees/s). Simple spike modulation of individual Purkinje cells was shown to correlate well with VOR performance throughout adaptation irrespective of training direction. Purkinje cell behavior always equaled the algebraic summation of eye and head velocity signal sensitivity. Causality of signal generation was addressed by measuring Purkinje cell responses to both eye and head velocity separately throughout the time course of VOR adaptation. The sensitivity of each type of Purkinje cell was found to be independent of the VOR gain state. We therefore conclude that the changes responsible for short term VOR plasticity do not occur in the cerebellum. These observations suggest that Purkinje cells integrate corollary head and eye velocity signals to continuously adjust the set point of brainstem VOR interneurons that embrace the substantive site for adaptive plasticity.

Acclimatization↗
PubMed2000

Effect of melatonin agonists and antagonists on horizontal cell spinule formation and dopamine release in a fish retina.

The crucian carp retina was used to study the effects of the melatonin antagonist p697 (N-pentanoyl 2-benzyltryptamine) and the melatonin agonists [+]- and [-]-AMMTC (N-acetyl-4-aminomethyl-6-methoxy-9-methyl-1,2,3,4-tetrahydrocarbazol e) on horizontal cell spinule formation, an indicator of the state of retinal adaptation. DH97 was capable of both counteracting dark-adaptive spinule degradation and inducing light-adaptive spinule formation at the beginning of the dark phase. Addition of dopamine receptor blockers opposed the action of DH97 on spinules, with SCH 23930, a D1 dopamine receptor antagonist, being more effective than the D2 receptor antagonist sulpiride. DH97 induced a twofold increase in dopamine release. We conclude that melatonin acts as a dark signal within the teleost retina by inhibiting the dopaminergic system. In accordance with this, both enantiomers of AMMTC prevented light-induced spinule formation, and reduced dopamine release to below dark-adaptive baseline levels. We suggest that the suppression of spinule formation by AMMTC may be due to either a direct inhibitory interaction between the melatonin agonist and horizontal cell dopamine D1 receptors, or an inhibitory effect on the activity of the dopamine-releasing interplexiform cells.

Adaptation, Ocular↗
PubMed1996

Does "Touching Four" on the Worth 4-dot test indicate fusion in young children? A computer simulation.

PURPOSE: "Touching four" dots on the Worth 4-dot test is used sometimes as an indication of fusion in young children. The authors examined the reliability of this test. METHODS: A computer simulation of the Worth 4-dot test generated images representing fusion, suppression, and alternate fixation. Sixteen children, ranging in age from 32 to 48 months, were examined using this test. RESULTS: None of the children could accurately describe the images verbally. Alternate fixation could not be distinguished from fusion by asking the subjects to touch the dots. Monocular suppression was identified accurately in all subjects. CONCLUSION: Touching four dots on the Worth 4-dot test does not distinguish fusion from alternate fixation in children with normal ocular alignment. This has important implications regarding the diagnosis of monofixation syndrome and assessment of the response to a prism adaptation trial in young children.

Adaptation, Ocular↗
PubMed2004

A comparison of ERG abnormalities in XLRS and XLCSNB.

Dark and light adapted ERGs were recorded in 19 patients with XLRS and in 15 patients with CSNB. Patients were assigned to clinical groups after identification of mutations in the RS1 (16 patients), NYX (11 patients) and CACNA1F (4 patients) genes causing XLRS, 'complete' CSNB and 'incomplete' CSNB, respectively. ERG responses were compared with those of 26 healthy volunteers. Rod responses were most severely affected in patients in the NYX group but a rod-generated b-wave could be identified in the majority of patients in this group. Rod responses were less severely affected in the CACNA1F and RS1 groups and ERGs did not differ significantly between these two groups. Cone reponses were largely unaffected in the NYX group but were abnormal in the RS1 and especially CACNA1F groups. The ERG results suggest that the RS1 and CACNA1F gene products have comparable functional consequences and that all three genes may affect multiple retinal sites.

Adaptation, Ocular↗
PubMed2002

Effect of melatonin administration on qPer2, qPer3, and qClock gene expression in the suprachiasmatic nucleus of Japanese quail.

Temporal changes of mRNA expression of three clock genes, qPer2, qPer3 and qClock, were studied in the suprachiasmatic nucleus (SCN) of Japanese quail under different light conditions, as well as under the condition of continuous melatonin. In addition, the expression of melatonin receptor genes, Mel1a and Mel1c, in the SCN were also examined. The expression of qPer2 mRNA showed robust oscillation during both light and dark (LD) 12:12 cycles and under constant dark conditions (DD), but did not exhibit circadian rhythmicity in constant light conditions (LL), instead being expressed at a consistently high level. Expression of qPer3 also showed robust oscillation under both LD and DD conditions. Unlike qPer2 however, qPer3 mRNA expression remained rhythmic under LL conditions. Contrary to the findings on the other clock genes, no remarkable rhythmicity was detectable in either light condition. Both Mel1a and Mel1c mRNAs were detected in the SCN, however, Mel1a mRNA levels were higher than Mel1c and showed daily rhythmicity. Although implantation of melatonin tubes caused constant high levels of plasma melatonin and consequently masked the endogenous daily melatonin rhythm, no significant differences in the expression pattern of any of the three clock genes were observed between birds with and without constant melatonin. In addition, a single injection of melatonin did not affect mRNA expression of these clock genes. These results suggest that melatonin does not affect transcription of clock genes, but may act on the mechanism of synchronization among SCN oscillatory cells.

Adaptation, Ocular↗
PubMed2002

Differential induction and localization of mPer1 and mPer2 during advancing and delaying phase shifts.

The mechanism whereby brief light exposure resets the mammalian circadian clock in a phase dependent manner is not known, but is thought to involve Per gene expression. At the behavioural level, a light pulse produces phase delays in early subjective night, phase advances in late subjective night, and no phase shifts in mid-subjective night or subjective day. To understand the relationship between Per gene activity and behavioural phase shifts, we examined light-induced mPer1 and mPer2 expression in the suprachiasmatic nucleus (SCN) of the mouse, in the subjective night, with a view to understanding SCN heterogeneity. In the VIP-containing region of the SCN (termed 'core'), light-induced mPer1 expression occurs at all times of the subjective night, while mPer2 induction is seen only in early subjective night. In the remaining regions of the SCN (termed 'shell'), a phase delaying light pulse produces no mPer1 but significant mPer2 expression, while a phase advancing light pulse produces no mPer2 but substantial mPer1 induction. Moreover, following a light pulse during mid-subjective night, neither mPer1 nor mPer2 are induced in the shell. The results reveal that behavioural phase shifts occur only when light-induced Per gene expression spreads from the core to the shell SCN, with mPer1 expression in shell corresponding to phase advances, and mPer2 corresponding to phase delays. The results indicate that the time course and the localization of light-induced Per gene expression in SCN reveals important aspects of intra-SCN communication.

Adaptation, Ocular↗
PubMed1993

Visual comfort in VDT operation: physiological resting states of the eye.

To recommend a comfortable visual display terminal (VDT) workstation design in an aspect of visual ergonomics, physiological resting states of the eye in 3 visual systems, pupil, vergence, and accommodation, were objectively investigated in 3 experiments. Experiment 1 ascertained a positive display polarity (dark characters on a bright background) and an illumination level of 500 lx to be the most appropriate working conditions, by using pupil analysis and subjective visual comfort in 10 subjects. Dark vergence, in experiment 2, was evaluated to be at a distance of about 50 cm from the eye, as an average in 14 subjects. Dark vergence was found to shift farther with an upward gaze while a nearer shift occurred with a downward gaze. In experiment 3, the average dark focus for 11 subjects was found to be 1.4 diopters (D) or a distance of about 74 cm from the eye. The positive correlation between refractive status of the eye and dark focus was statistically significant (r = 0.602). The ergonomic recommendations for a VDT workstation obtained in this study are a positive display polarity with an appropriate lighting condition, a downward gaze, and a viewing distance between 50 and 70 cm. These recommendations are considered to reduce visual fatigue due to prolonged VDT work and to facilitate visual comfort at work.

Accommodation, Ocular↗