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PubMed1989

Neural differentiation in the retina of the larval sea lamprey (Petromyzon marinus).

The peripheral retina of the sea lamprey develops in a 5-year-long process in which only certain neurons differentiate each year. The growth of cell layers, the differentiation of the neurons, and the morphology of their dendrites and axons were studied with normal, HRP, and Golgi preparations. Ganglion cells are differentiated in 3-year-old larvae, amacrine and horizontal cells in 4-year-old larvae, photoreceptor cells in stage I transformers, and bipolar cells in stage III transformers. Each new development is expressed as a radial gradient of differentiation. As a result of this protracted and stepped process, lamprey retinal neurons, particularly ganglion cells, differentiate in the absence of other cells to which they will ultimately be connected and may express their individual genetic programs more fully than in other vertebrate retinas. This could account for the unusual relationship of the ganglion cell, inner plexiform, and optic nerve layers and for the very high ratio of displaced to orthotopic ganglion cells.

Animals↗

PubMedDate not supplied

The role of early retinal lateral inhibition: more than maximizing luminance information.

Lateral inhibition is one of the first and most important stages of visual processing. There are at least four theories related to information theory in the literature for the role of early retinal lateral inhibition. They are based on the spatial redundancy in natural images and the advantage of removing this redundancy from the visual code. Here, we contrast these theories with data from the retina's outer plexiform layer. The horizontal cells' lateral-inhibition extent displays a bell-shape behavior as function of background luminance, whereas all the theories show a fall as luminance increases. It is remarkable that different theories predict the same luminance behavior, explaining "half" of the biological data. We argue that the main reason is how these theories deal with photon-absorption noise. At dim light levels, for which this noise is relatively large, large receptive fields would increase the signal-to-noise ratio through averaging. Unfortunately, such an increase at low luminance levels may smooth out basic visual information of natural images. To explain the biological behavior, we describe an alternate hypothesis, which proposes that the role of early visual lateral inhibition is to deal with noise without missing relevant clues from the visual world, most prominently, the occlusion boundaries between objects.

Animals↗

PubMedDate not supplied

Functional dopamine deficits in the senile rat retina.

The activity of the endogenous retinal dopamine (DA) pathway has been examined in the pigmented rat using retinas obtained from normal adult (approximately 3 months) and senile adults (approximately 24 months) using an in vitro electrophysiological approach. By comparing the pharmacological sensitivity of the horizontal cells (HCs) to exogenous DA, a D1 receptor antagonist (SCH 23390) and a DA-transport inhibitor (nomifensine), it is suggested that there is a functional deficit in the endogenous DA activity in the senile retina. Cells recorded from retinae obtained from senile animals are more sensitive to exogenous DA, whilst the senile retina is insensitive to SCH 23390. In addition, nomifensine was effective in potentiating subthreshold DA applications, but only in the normal adult retina. The data may suggest that endogenous DA release upon the HCs and selective re-uptake are suppressed in these retinae. These functional deficits also appear to be associated with changes in the receptive fields of the HCs, suggesting there is a corresponding deficit in spatial processing at the outer plexiform layer (OPL) of the senile rat.

Aging↗

PubMed1991

Dark-induced supersensitivity of dopamine D-1 and D-2 receptors in rat retina.

Light deprivation of rat retina leads to a rapid (within 6 h) development of a state of supersensitivity (upregulation) of dopamine D-1 receptors (positively coupled to adenylate cyclase), which are essentially involved in the modulation by light of the electrical activity and communication between horizontal cells. In contrast, the supersensitivity of D-2 receptors (negatively coupled to cAMP generating system) appears to develop only after 2 days (better after 4 days) of dark adaptation, although these receptors are linked to multiple light-dependent retinal functions. These results suggest the existence of different mechanisms of sensory adaptation for these two subtypes of dopamine receptors.

1-Methyl-3-isobutylxanthine↗

PubMed1996

Postnatal developmental expression of glutamine and related amino acids in the rat retinas.

PURPOSE: To evaluate postnatal developmental changes in the amounts of retinal glutamate, glutamine and GABA, and in the distribution of retinal glutamine in the rat. METHODS: Free amino acids were extracted from rat retinas of different postnatal stages, and the concentrations of glutamate, glutamine and GABA were determined by HPLC. Also, anti-glutamine antibody was raised and an immunocytochemistry was performed with paraffin-embedded retinal sections in parallel with free amino acid analyses. RESULTS: Glutamate occurred in high concentrations at the birth and showed a stable pool, while glutamine and GABA remained low until postnatal day 3 or 5, and gradually increased in the developing rat retinas. Glutamine immunolabeling was observed in the retinal pigment epithelium and in a subpopulation of presumed amacrine cells in the early postnatal days. It was also found in Muller cells and in some ganglion cells or displaced amacrine cells in the ganglion cells layer. Glutamine immunolabeling was transiently observed also in horizontal cells. Finally, the immunolabeling was dominant in the inner and outer plexiform layers in the adult retinas. CONCLUSIONS: Postnatal developmental increase in the levels of glutamine and GABA might be dependent on the maturation of neurons or glial cells that possess the activity of the key enzymes of each amino acid. It was suggested that an expression of glutamine immunolabeling can be a marker of neurons that utilize glutamine as a precursor for glutamate or GABA, and of Müller cell maturations in postnatal early stage of the retina, while it changes to demonstrate the locations of glutamine cycle in the retina with adult characteristics.

Animals↗

PubMed1991

Binocular interaction and signal components of optokinetic responses of climbing fiber afferents in the cerebellar flocculus and nodulus of the pigmented rabbit.

Under anesthesia with N2O (70%) and halothane (2-4%), Purkinje cells were extracellularly recorded in the flocculus and nodulus of immobilized pigmented rabbits, and complex spike responses to optokinetic stimulation (OKS) delivered simultaneously to both the ipsi- and contralateral eyes (binocular OKS) were compared with those to OKS monocularly delivered to the ipsi- or contralateral eye (monocular OKS). The complex spike responses to binocular OKS were an approximate summation of monocular responses to ipsi- and contralateral OKS. The complex spike modulation did not correlate with rhythmical slow and quick nystagmic discharges of the oculomotor nerve evoked by horizontal OKS. This suggests that complex spike responses originate largely from 'retinal slip' signals rather than from 'final motor command' signals represented in the discharges of the oculomotor nerve.

Afferent Pathways↗

PubMed1998

Retinal and lenticular ultrastructure in the aestivating salamanderfish, Lepidogalaxias salamandroides (Galaxiidae, Teleostei) with special reference to a new type of photoreceptor mosaic.

The salamanderfish, Lepidogalaxias salamandroides (Galaxiidae, Teleostei) is endemic to southwestern Australia and inhabits shallow, freshwater pools which evaporate during the hot summer months. Burrowing into the substrate in response to falling water levels allows these fish to aestivate for extended periods of time while encapsulated in a mucous cocoon even when the pools contain no water. Only a few minutes after a major rainfall, these fish emerge into relatively clear water which subsequently becomes laden with tannin, turning the water black and reducing the pH to approximately 4.3. As part of a large study of the visual adaptations of this unique species, the retinal and lenticular morphology of the aestivating salamanderfish is examined at the level of the light and electron microscopes. The inner retina is highly vascularised by a complex system of vitreal blood vessels, while the outer retina receives a blood supply by diffusion from a choriocapillaris. This increased retinal blood supply may be an adaptation for reducing the oxygen tension during critical periods of aestivation. Large numbers of Müller cells traverse the thickness of the retina from the inner to the outer limiting membranes. The ganglion cells are arranged in two ill-defined layers, separated from a thick inner nuclear layer containing two layers of horizontal cells by a soma-free inner plexiform layer. The photoreceptors can be divided into three types typical of many early actinopterygian representatives; equal double cones, small single cones and large rods (2:1:1). These photoreceptors are arranged into a unique regular square mosaic comprising a large rod bordered by four equal double cones with a small single cone located at the corner of each repeating unit. The double cones may optimise perception of mobile prey which it tracks by flexion of its head and "neck" and the large rods may increase sensitivity in the dark tannin-rich waters in which it lives. Each single cone also possesses a dense collection of polysomes and glycogen (a paraboloid) beneath its ellipsoid, the first such finding in teleosts. The retinal pigment epithelium possesses melanosomes, phagocytes and a large number of mitochondria. The anatomy of the retina and the photoreceptor mosaic is discussed in relation to the primitive phylogeny of this species and its unique life history.

Animals↗

PubMed2003

Sensitivity to horizontal and vertical disparity and orientation preference in areas V1 and V2 of the monkey.

It has been suggested that cells are most sensitive to disparities along the axis orthogonal to their orientation preference. To test this assumption we studied the orientation preference of 73 cells sensitive to retinal disparity, 44 from V1 and 29 from V2. Orientation preference and disparity sensitivity were not related in tuned excitatory and tuned inhibitory cells. We found 18 near/far cells with orientation preference. Of these, 10 (56%) had a preferred orientation less than 30% away from the orthogonal to the disparity axis whereas the remaining eight cells (44%) exceeded this value. Our data suggests that the neural mechanisms for encoding retinal disparities present in dynamic random dot stereograms may not be related to the preferred orientation of the cell.

Animals↗

PubMed2000

Three levels of lateral inhibition: A space-time study of the retina of the tiger salamander.

The space-time patterns of activity generated across arrays of retinal neurons can provide a sensitive measurement of the effects of neural interactions underlying retinal activity. We measured the excitatory and inhibitory components associated with these patterns at each cellular level in the retina and further dissected inhibitory components pharmacologically. Using perforated and loose patch recording, we measured the voltages, currents, or spiking at 91 lateral positions covering approximately 2 mm in response to a flashed 300-microm-wide bar. First, we showed how the effect of well known lateral inhibition at the outer retina, mediated by horizontal cells, evolved in time to compress the spatial representation of the stimulus bar at ON and OFF bipolar cell bodies as well as horizontal cells. Second, we showed, for the first time, how GABA(C) receptor mediated amacrine cell feedback to bipolar terminals compresses the spatial representation of the stimulus bar at ON bipolar terminals over time. Third, we showed that a third spatiotemporal compression exists at the ganglion cell layer that is mediated by feedforward amacrine cells via GABA(A) receptors. These three inhibitory mechanisms, via three different receptor types, appear to compensate for the effects of lateral diffusion of activity attributable to dendritic spread and electrical coupling between retinal neurons. As a consequence, the width of the final representation at the ganglion cell level approximates the dimensions of the original stimulus bar.

Action Potentials↗

PubMed1990

Weber and noise adaptation in the retina of the toad Bufo marinus.

Responses to flashes and steps of light were recorded intracellularly from rods and horizontal cells, and extracellularly from ganglion cells, in toad eyecups which were either dark adapted or exposed to various levels of background light. The average background intensities needed to depress the dark-adapted flash sensitivity by half in the three cell types, determined under identical conditions, were 0.9 Rh*s-1 (rods), 0.8 Rh*s-1 (horizontal cells), and 0.17 Rh*s-1 (ganglion cells), where Rh* denotes one isomerization per rod. Thus, there is a range (approximately 0.7 log units) of weak backgrounds where the sensitivity (response amplitude/Rh*) of rods is not significantly affected, but where that of ganglion cells (1/threshold) is substantially reduced, which implies that the gain of the transmission from rods to the ganglion cell output is decreased. In this range, the ganglion cell threshold rises approximately as the square root of background intensity (i.e. in proportion to the quantal noise from the background), while the maintained rate of discharge stays constant. The threshold response of the cell will then signal light deviations (from a mean level) of constant statistical significance. We propose that this type of ganglion cell desensitization under dim backgrounds is due to a post-receptoral gain control driven by quantal fluctuations, and term it noise adaptation in contrast to the Weber adaptation (desensitization proportional to the mean background intensity) of rods, horizontal cells, and ganglion cells at higher background intensities.

Action Potentials↗

PubMed1971

Chromatic sensitivity and spatial organization of cat visual cortical cells: cone-rod interaction.

1. Colour sensitivity and spatial organization were determined for the dominant-eye receptive fields of thirty-eight simple or complex cells in cat primary visual vortex. Receptive fields were all from the cortical area associated with central vision. Each cell was investigated with threshold or suprathreshold monochromatic stimuli, under scotopic, low and high mesopic adaptation.2. The Purkinje shift, well defined for all units, was consistent with dual input from each of only two receptor mechanisms, viz. 556 nm cones and 500 nm rods. With change of adaptation level there was a systematic change in the peak sensitivity of spectral response curves to suprathreshold monochromatic stimuli, equated for quantum flux but of different wave-length. Equally with change of adaptation, the relative shift in threshold between wave-lengths selective for cone or rod activation was in close agreement with the change predicted from the Dartnall nomogram curves for visual pigments 556 and 507 respectively.3. For ganglion cells with concentric fields rod input derives from a spatially larger area than cone input. Rod field centre and rod field surround are substantially larger than the corresponding centre and surround for cones (Andrews & Hammond, 1970b). For cortical cells a conclusive comparable change could only be demonstrated for one simple unit. Its receptive field consisted of a horizontal excitatory stripe with asymmetric inhibitory flanks. When light-adapted the weaker, upper flank was functionally undetectable, indicative of purely rod input to this sideband, and the preference for upward movement was enhanced.4. No difference in receptive field configuration, or in spatial extent of input mediated by cones or by rods, was detected for any other unit. The discrepancy between retinal and cortical findings is discussed. It is inferred that cortical fields are compounded essentially by convergent input from geniculate cell field-centres.

Adaptation, Ocular↗

PubMed1985

The retinal projection to the cat pretectum.

Retinal ganglion cells were labeled retrogradely by localized injections of HRP into different regions of the pretectum, tectum, and optic tract in 26 cats. Retinal projection zones in the pretectum were labeled anterogradely in the same cats by intravitreal injections of 3H-proline. This allowed the HRP injection sites to be located with respect to the retinal termination zones. The form of the projection zones from retina to pretectum was determined from serial reconstructions of either coronal or horizontal sections. The zones are best distinguished in horizontal sections, where they are seen as four roughly parallel strips on either side of the brain. They are more-or-less parallel to the anterior border of the tectum, and appear to traverse the entire width of the retinal projection to the tectum. Each zone is similar in form for the ipsilateral and contralateral projections, although the contralateral projection is thicker and denser. Binocular injections of 3H-proline showed that the projections from the two eyes were in register and did not interdigitate. Cells labeled by HRP injections in the anteromedial end of the pretectum were concentrated in the lower nasal quadrant of the contralateral retina, and the lower temporal quadrant of the ipsilateral retina. Posterolateral injections labeled cells in the upper quadrants. There is thus a rough retinotopic mapping along the elongated axis of the pretectum. When the distributions of ganglion cells labeled by HRP injections to different parts of the pretectum are combined, they show a concentration in both the visual streak and area centralis, and thereby reflect, at least qualitatively, the relative spatial distribution of the entire ganglion-cell population. About 85% of the retinal projection to the pretectum is contralateral. For all of the HRP injections, the spatial density of labeled cells was always low, accounting for no more than 3% of the total spatial density of ganglion cells in any retinal region. Several types of ganglion cells were labeled following injections to most regions of the pretectum; these included alpha, beta, and epsilon cells, as well as small-bodied cells showing a variety of morphologic forms. Alpha cells were labeled mainly from the anterolateral end of the pretectum, but other cell types were labeled from all injected regions. In the peripheral retina, 2% of the labeled cells were alpha cells, 32% were beta cells, 19% were epsilon cells, and the remaining 47% were small cells whose dendrites only occasionally filled to any significant extent.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Combined silicone and fluorosilicone oil tamponade (double filling) in the management of complicated retinal detachment.

We evaluated the use of simultaneous double filling with polydimethylsiloxane (PDMS) and fluorosilicone (FSiO) in the repair of complicated retinal detachment in 12 selected cases. Initial retinal reattachment was achieved in all cases. Proliferative vitreoretinopathy (PVR) recurred in 10 patients (83%), 6 of which showed partial retinal detachment. Inferior and superior postoperative residual free spaces were abolished by this procedure, but a new residual fluid space was created, lying horizontally between the bubbles and expanding in a triangular shape nasally to the optic disk and temporally to the macula. Overall, 9 of 10 eyes with postoperative PVR had proliferation involving these areas. These findings support the concept that 'compartmentalization' is of major importance in determining postoperative cell proliferation.

Adult↗

PubMed1982

Morphological study on the regeneration of the retina in the rainbow trout after ouabain-induced damage: evidence for dedifferentiation of photoreceptors.

The retina of the rainbow trout is capable of marginal regeneration after ouabain-induced degeneration (intraocular injection of 5 microliters 10(-4) M ouabain). In the central area where the pigment epithelium proliferates to a multicellular layer, the neural retina does not regenerate up to 182 days after injection of ouabain. The regeneration process begins in the marginal growth zone with an increase in the mitotic rate; the growth zone itself is not damaged after ouabain administration. The proliferate differentiates with time into a newly layered retina; this portion of the retina is called the paramarginal zone, i.e., the "first" regenerated zone. The paramarginal zone is arranged concentrically to the retinal margin. Cells surviving ouabain administration, located outside, although close to the margin and occurring mostly in the outer nuclear layer, reveal signs of dedifferentiation: loss of the outer segment, amalgamation of the presynaptic terminal with the perikaryal cytoplasm, alteration of cell shape, and mitotic activity. The area in which these dedifferentiation processes are observed is found adjacent and concentric to the paramarginal zone; it is thinner than the latter and incompletely structured ("second" regenerated zone). The third zone adjoins the second zone and is characterized by folds, which were described previously as "rosettes". Extracellular microtubule-like structures, which are found between the horizontal cells in the normal retina of the rainbow trout, regenerate only sparsely in the paramarginal zone, whereas they are lacking in the incompletely regenerated zones.

Animals↗

PubMed1989

Topographic organization of the ganglion cell layer and intraocular vascularization in the retinae of two reef teleosts.

The retinae of two species of teleosts, the rippled blenny Istiblennius edentulus and the blue tusk fish Choerodon albigena are examined in wholemount. The retinal topography of Nissl-stained cells within the ganglion cell layer in each species reveals a temporal (4.32 x 10(4) cells per mm2) and a nasal (3.83 x 10(4) cells per mm2) area centralis in the rippled blenny and two temporal areae centrales (8.30 x 10(4) and 8.00 x 10(4) cells per mm2) and a horizontal streak (5.00 x 10(4) cells per mm2) in the tusk fish. These areas are thought to subserve higher spatial resolution. Transcardial perfusions of indian ink reveal an extensive network of vitreal blood vessels which are supplied by the hyaloid artery and overlie the retina in each species. This rich network of vitreal vessels supplies areas of increased ganglion cell density although areas of maximum cell density are devoid of vessels to preserve the high spatial resolving power of the eye within this region. Unique blood vessel plexuses overlying the optic disc and falciform process in the tusk fish are also described. The diameter of the overlying vitreal vessels is compared to the soma sizes of cells within the ganglion cell layer.

Animals↗

PubMed1996

Nasotemporal overlap at the retinal vertical meridian: investigations with a callosotomy patient.

To evaluate nasotemporal overlap at the retinal vertical midline, we asked a callosotomy patient to compare the orientation of square wave gratings that were presented in his opposing visual fields. The gratings were horizontally or vertically oriented and had spatial frequencies ranging from 1 to 8 cycles per degree (cpd). Retinal stabilization ensured the gratings remained properly lateralized during sustained presentations. In accord with previous investigations, when the gratings were presented for only 200 msec, or their medial edges were 2 from the vertical meridian, performance was generally at chance. However, when presentations lasted 2 sec and the medial edges of the gratings were 1 from the vertical meridian, above chance performance was obtained. Accuracy rates were highest with 2 and 4 cpd gratings, and dropped at 1 and 8 cpd. Unexpectedly, the subject performed significantly better when the gratings were offset vertically from each other than when both were displayed on the horizontal meridian. Since this improvement did not occur when gratings were presented horizontally aligned above or below the horizontal meridian, it must be distributed to the relative offset between the gratings. The data suggest a narrow zone of nasotemporal overlap at the retinal vertical midline where very limited visual information is encoded by crossed temporal and uncrossed nasal retinal ganglion cells. An experiment in which only one grating in a pair was close to the vertical meridian indicates that this zone may be more pronounced in the nasal hemiretina.

Adult↗

PubMed1995

Large optic discs in large eyes, small optic discs in small eyes.

The optic disc area, varying interindividually by a factor of 1:7, is correlated with the count of the retinal ganglion cell axons and photoreceptors. This study evaluated whether the variations in the disc size are additionally correlated with those of the coronary diameters of the globe. Fifty-three normal human donor eyes with a mean age of 54.2 +/- 19.6 years were included in the study. After performing a 16-mm corneoscleral trephination, the globes were fixed and the horizontal and vertical diameters of the globes were measured. We cut the globes into meridional slices sticking together at the posterior fundus region. The areas of the whole retina and the optic disc were planimetrically evaluated on photographs with a millimeter scale aligned. We found that the horizontal and vertical diameters of the globe were correlated with the optic disc size and the retinal surface area. Eyes with long horizontal and vertical diameters had a larger optic disc and a larger retinal surface area than eyes with short diameters. The results suggest the combination of large optic discs in large eyes and of small optic discs in small eyes. Taking into account the relatively low correlation coefficients of 0.3 and 0.4, the study also suggests the existence of other not-evaluated factors influencing the occurrence of large optic discs. The results go along with the reported association between a large optic disc area and a large cornea size.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1997

Modulation of hybrid bass retinal gap junctional channel gating by nitric oxide.

1. To elucidate the role of the nitric oxide (NO) transmitter system in the regulation of gap junctional channel gating, we have examined the effects of the NO donor sodium nitroprusside (SNP) on the electrical synapses of hybrid bass H2-type horizontal cells. 2. SNP reversibly reduced the macroscopic junctional conductance without significantly changing voltage sensitivity. 3. Kinetic analyses showed that SNP made the voltage-dependent decay of junctional currents more rapid. 4. Single-channel data showed that SNP reduced channel open probability by reducing channel open frequency. 5. The action of SNP can be prevented or largely reduced by the NO scavenger, haemoglobin. NO release by SNP solutions was detected directly by a NO sensor. 6. NO appears to modulate the gap junctional conductance by activating the cGMP-cGMP-dependent protein kinase G (PKG) pathway. A membrane-permeable cGMP analogue, 8-Br-cGMP, mimics the action of SNP. A soluble guanylate cyclase inhibitor (LY-83583) and a highly specific cGMP-dependent protein kinase inhibitor (RKRARKE) blocked the action of NO. 3-Isobutyl-1-methylxanthine (IBMX), a non-specific phosphodiesterase inhibitor, potentiated the effect of SNP. 7. [Ca2+]i image studies showed that NO donors did not change [Ca2+]i in horizontal cells, suggesting that the regulation of junctional channels by NO is [Ca2+]i independent.

1-Methyl-3-isobutylxanthine↗