Cat Retina Research Articles

Light-evoked increases in [K+]o in proximal portion of the dark-adapted cat retina.

1. The scotopic threshold response (STR) and slow negative response are negative-going potentials in the dark-adapted electroretinogram (ERG) of the cat eye that originate proximal to the photoreceptors and are present at threshold and with dim illuminations. The present paper examines the hypothesis that these events are associated with Müller cell responses to potassium released by proximal retinal neurons by measuring light-dependent changes in extracellular K+ concentration [( K+]o, in proximal retina. 2. Extracellular field potentials and changes in [K+]o, evoked in response to diffuse illumination of the dark-adapted retina, were recorded with a double-barreled K+-sensitive microelectrode placed in the retina at different depths. The vitreal ERG was recorded at the same time. 3. The dynamic range of the light-evoked increases in [K+]o, recorded in proximal retina from threshold to saturation, was strikingly similar to that of the STR and slow negative response. The threshold for the [K+]o increase was near that of the most sensitive ganglion cells, and the response saturated approximately 2.4 log units below rod saturation. Also, onset latencies and rates of rise for the increases in [K+]o and the field potentials in proximal retina followed similar functions of intensity. 4. The depth distribution of the light-evoked [K+]o increases resembled that of the STR. The increases in [K+]o were largest and fastest in proximal retina where the STR was largest. This was true both for very low intensity stimuli, below the threshold for PII (DC-component and b-wave) in distal retina, and for stimulus intensities near STR saturation, where PII (DC-component) was present. For stimuli of intensities near rod saturation, when the b-wave was present in distal retina, there was a small fast increase in [K+]o at light onset in distal retina and a slower increase in proximal retina. Both increases were truncated by spread of the large light-evoked decrease in [K+]o in subretinal space that is known to cause the c-wave in the ERG and slow PIII in neural retina. 5. The duration of the increases in [K+]o in proximal retina was more sustained than the proximal field potentials. In response to stimuli of 2-4 s, the field potential began to recover toward base line after about 300 ms, whereas the increases in [K+]o remained at maximal levels until stimulus offset.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of GABA immunoreactivity in the cat retina: A light- and electron-microscopic study

The distribution of GABA-like immunoreactivity in the cat retina was studied through the use of preembedding immunocytochemistry for light microscopy and by postembedding immunogold techniques for electron microscopy. Staining was observed in both inner and outer plexiform layers. Approximately 30% of the somata in the amacrine portion of the inner nuclear layer were immunoreactive and included amacrine and interplexiform cells. Horizontal cells and a subpopulation of cone bipolar cells were also stained. In the ganglion cell layer, staining was observed in both small- and medium-sized neurons. GABA-labeled amacrine cells were presynaptic to somata of amacrine cells and to dendrites of amacrine, bipolar, and ganglion cells. Bipolar cells were a major target, receiving more than 60% of all labeled synapses in the inner plexiform layer. Many of these contacts were reciprocal synapses. These findings support a major role for GABA-labeled amacrines in providing feedback inhibition to bipolar cells in the inner retina.

The quinoxalinediones antagonise the visual firing of sustained retinal ganglion cells

The non N-methyl-D-aspartate (NMDA) receptor antagonists dinitroquinoxaline-2,3-dione (DNQX) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), both inhibit the visually driven response of sustained ganglion cells in the cat retina in vivo. In contrast to these findings, the potent NMDA receptor antagonists 3-((±)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CCP) has no effect. Thus, the endogenous excitatory amino acid released onto these cells on visual stimulation acts at non-NMDA receptors.

Benzodiazepines and the mammalian retina. III. Postnatal development

Iontophoretic effects of the benzodiazepine receptor agonist, flurazepam, and antagonist, flumazepil (RO-15-1788) on the retinal ganglion cells of kittens (7–9 weeks of age) have been compared with those of adult cats (18–22 weeks of age). In the adult retina, flurazepam decreased and flumazepil increased the visually evoked and spontaneous firing of ON-, but produced no effects on the response of OFF-retinal ganglion cells. However, in the kittens retina, in which ON-cells' selectivity to GABA is not fully developed 3, both the visually evoked and spontaneous activities of ON- and OFF-cells were inhibited by flurazepam and enhanced by flumazepil. This suggests that postnatal development of benzodiazepine action parallels that of GABA action at the retinal ganglion cells in the cat retina.

Analysis of cat retina for dopamine, dihydroxyphenylacetic acid, 3-methoxytyramine and homovanillic acid.

Twenty retinas from 10 cats were evaluated for dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT) and homovanillic acid (HVA) by high pressure liquid chromatography and electrochemical detection. Dopamine was present in all 20 retinas at a mean concentration of 3.00 +/- 0.54 ng/mg protein. Dihydroxyphenylacetic acid, 3-MT and HVA were detected in 16, 14 and 9 retinas respectively. In retinas in which these metabolites were detectable, they were present in the following mean concentrations: DOPAC, 1.07 +/- 0.21 ng/mg protein; 3-MT, 3.44 +/- 0.97 ng/mg protein and HVA, 4.54 +/- 1.05 ng/mg protein. Significantly higher concentrations of 3-MT (p = 0.0108, paired t test) and HVA (p = 0.0166, paired t test) than DOPAC were present in cat retina. Linear correlation analysis between DA and its metabolites indicated that the 3-MT and DOPAC concentrations correlated well with each other and with the amount of DA in cat retina. The concentrations of the end product metabolite, HVA, had poor correlations with the concentrations of 3-MT, DOPAC or DA. These data indicated that once DA is released in cat retina it can be metabolized to 3-MT, DOPAC and HVA.

A model for spatiotemporal frequency responses in the X cell pathway of the cat's retina

A linear model is described for the cat eye's signal-processing pathway, from the visual stimulus at the cornea, to cones, to X-type ganglion cells. The model contains elements representing the eye's optics, phototransduction, gain control, spatiotemporal processing by cell layers, and pure delay. Centresurround antagonism in the model arises through the presence of a centre element producing a small spatial spread of signals, and an antagonistic element producing a larger spread. Two arrangements were tried, feedforward and feedback, in which the antagonistic element's output was subtracted from the centre element's output, and input, respectively. The model was fitted to empirical spatial and temporal frequency responses collected by Frishman et al. (1987), and accounted qualitatively for these data in the feedback, but not the feedforward, arrangement. The model's centre pathway comprises a cascade of low-pass spatial filters, as does the surround pathway. As a consequence, the spatial frequency responses for these two pathways closely approximate Gaussian functions of spatial frequency, and the spatial frequency response of the complete model at low temporal frequency closely matches that of the difference of Gaussians model.

The spike generating mechanism of cat retinal ganglion cells

The spike generating mechanism (SGM) of sustained and transient-type ganglion cells has been investigated from intracellular recordings in the cat retina. The relationship between the generator potential and the impulse pattern, which are respectively the input and the output of the SGM, has been studied after separating one component from the other. Comparison of averaged generator potentials and the corresponding PSTHs showed that the spike generator is highly sensitive to changes of the generator potential. It proved to be relatively indifferent to the prevailing average levels of depolarization. During sustained parts of the responses the SGM exhibits a stochastic nature. At higher light flicker frequencies, during spike bursts, on the other hand spike generation is very regular and phase locked to the stimulus. The averaged generator potentials were also used to develop and test a set of minimal, computer simulated models of the spike generator. A slow threshold adaptation (time constant about 50 msec) is absolutely necessary in addition to the faster refractory recovery in order to produce spike patterns similar to those measured during the corresponding response periods. The developed model accounts completely for the observed characteristics of ganglion cell spike generation under a wide variety of light stimulus regimes and both for the sustained and for the transient type of ganglion cell.

Fractal analysis of ganglion cell dendritic branching patterns of the rat and cat retinae.

Fractal analysis of ganglion cell dendritic branching patterns of the rat and cat retinae.

Properties of excitatory amino acid receptors on sustained ganglion cells in the cat retina

Iontophoretic effects of N-methyl- d-aspartate , quisqualate and kainate and a variety of excitatory amino acid receptor antagonists, on retinal ganglion cells, were studied in optically intact eyes of barbiturate anaesthetized cats. All three agonists raised the spontaneous firing of both ON- and OFF-sustained retinal ganglion cells, with the potency order of kainate > quisqualate > N-methyl- d-aspartate . However, the excitatory amino acid analogues readily saturated the receptors and reduced the visually driven firing of cells with high spontaneous firing, but mimicked an increase in endogenous excitatory amino acid release and raised the visually induced response in cells with low spontaneous firing. The quinoxaline compounds, 6-cyano-2,3 dihydroxy-7-nitroquinoxaline and 6-7-dinitroquinoxaline-2, 3-dione, blocked the visually driven firing and the kainate- and quisqualate-induced excitation, whilst 3((±)-2-car☐ypiperazin-4-yl)propyl-1-phosphonate, antagonized the N-methyl- d-aspartate-induced excitation, but failed to block visually driven firing of the retinal ganglion cells. The broadband excitatory amino acid receptor antagonists, such as kynurenate, were also effective in antagonizing the visually driven response and also blocked the N-methyl- d-aspartate -as well as kainate- and quisqualate-induced responses. These results suggest that the receptors at the bipolar/ganglion cell synapse are of the non- N-methyl- d-aspartate type, but that N-methyl- d-aspartate receptors are also present on ganglion cells although their physiological role is unclear.

GABA-like immunoreactivity in the cat retina: light microscopy.

Semithin sections of the cat retina were stained with antibodies against GABA conjugated to bovine serum albumin with glutaraldehyde. Labelled cells were visualized by means of the peroxidase-antiperoxidase method. In the outer plexiform layer both A- and B-type horizontal cells and the B-type axon terminal system expressed GABA-like immunoreactivity. Approximately 25-30% of all amacrine cells and the whole inner plexiform layer were heavily labelled. Two types of putative GABA-ergic interplexiform cells could be distinguished. One of them also expressed tyrosine-hydroxylase-like immunoreactivity. A few bipolar cells were also GABA-immunolabelled. GABA-like immunoreactivity and 3H-muscimol uptake were colocalized in 90% of the amacrine cells labelled. However, horizontal cells did not accumulate 3H-muscimol.

GABA-like immunoreactivity in the cat retina: electron microscopy.

The synaptic organization of the cat retina was studied with antibodies against the GABA-GA (glutaraldehyde)-BSA (bovine serum albumin) complex. The postembedding technique combined with immunogold labelling ensured ultrastructural preservation and made identification of synapses possible. The most common putative GABA-ergic synapses in the inner plexiform layer were amacrine-to-bipolar-cell synapses followed by amacrine-to-ganglion-cell and amacrine-to-amacrine-cell synapses. GABA-immunoreactive amacrine cells received most of their synaptic input from bipolar cells followed by other amacrine cells. Synapses between two labelled amacrine cells were common. Rod bipolar cells were the predominant input source and also the preferred output target of GABA-labelled amacrine cells. OFF- and ON-ganglion cells received putative GABA-ergic synapses at their dendrites in laminas a and b, respectively, and also at their somata. In the outer plexiform layer, synapses of interplexiform cells onto bipolar cell dendrites expressed GABA-like immunoreactivity. In both the cone pedicles and the rod spherules, GABA-like immunoreactivity was observed in horizontal cell processes.

Neurofibrillar long-range amacrine cells in mammalian retinae.

A distinct population of wide-field, unistratified amacrine cells are shown to be selectively stained by using neurofibrillar methods in rabbit and cat retinae. Their cell bodies may be located in the inner nuclear, inner plexiform or ganglion cell layers and they branch predominantly in stratum 2 of the inner plexiform layer. Characteristically, each cell has two or more long-range distal processes which extend for 2-3 mm beyond a more symmetrical, proximal dendritic field of 0.6-0.8 mm diameter. Although the neurofibrillar long-range amacrines account for less than 1 amacrine in 500, they achieve effective coverage of the retina by both the proximal and distal dendrites.

An immunocytochemical comparison of Müller cells and astrocytes in the cat retina

Immunocytochemical localization, at the light and electron microscopic levels, of five different known glial proteins was used to compare Müller cells with astrocytes in the adult cat retina. Retina from two different areas of the eye was examined. A region of retina on the border of the optic nerve was used because of its large population of astrocytes, and a region away from the optic nerve was used to examine Müller cells (astrocytes are sparse in this region). Antibodies to cellular retinaldehyde binding protein and glutamine synthetase labeled the Müller cells but not the astrocytes, while labeling with anti-carbonic anhydrase C, anti-alpha crystallin and anti-glial fibrillary acidic protein was found in both Müller cells and astrocytes.

An immunocytochemical study of cat retinal Müller cells in culture

Müller cells, the specialized radial glia found in vertebrate retinas, were enzymatically dissociated from adult cat retinas and grown in culture. The cells were processed for immunofluorescence microscopy at times ranging from 4 hr to 3 months in culture. Labeling with antibodies specific to glial fibrillary acidic protein, cellular retinaldehyde binding protein, glutamine synthetase, carbonic anhydrase C and alpha crystallin, all proteins known to be found in Müller cells, was detected in the cultured cells. Immunoblot analysis of the cultured cells showed single protein bands corresponding to the appropriate molecular weights of the antigens.

Colocalization of [ 3H]muscimol uptake and choline acetyltransferase immunoreactivity in amacrine cells of the cat retina

High affinity uptake of [ 3H]muscimol, a γ-aminobutyric acid (GABA) analogue, followed by autoradiography, labelled practically all amacrine cells which expressed GABA-like immunoreactivity. Hence it is a good marker for putative GABAergic amacrine cells. All amacrine cells, which were stained with antibodies against choline acetyltransferase, a marker for cholinergic neurones, also accumulated [ 3H]muscimol. This makes it likely that cholinergic amacrine cells of the cat retina are a subpopulation of putative GABAergic amacrine cells.

The development of astrocytes in the cat retina: evidence of migration from the optic nerve

To test recent ideas of the origin of retinal astrocytes we have studied the distribution of astrocytes, identified by anti-GFAP antibodies, in the developing retina of the cat. GFAP + cells first appeared at the optic disc at E53 (embryonic day 53). At subsequent ages, GFAP + cells covered successively larger regions surrounding the optic disc, and were found at the edge of the retina by P35 (postnatal day 35). During development, the GFAP + cells near the optic disc were strongly related to blood vessels and axon bundles; in a more peripheral zone they were closely associated with the immature capillary net; while the most peripheral GFAP + cells appeared to extend exploratory processes towards the margin of the retina. The velocity at which the ‘front’ of GFAP + cells spread over the retina was estimated at 170–240 μm/day. At no time during development were GFAP + cells observed in the area centralis. Except at the area centralis, the spread of GFAP + cells preceded the formation of capillaries, by a small but distinct margin. GFAP + cells also extended for a short distance from the optic disc along the proximal part of the hyaloid artery. These results support the view that retinal astrocytes migrate into the retina from the optic disc, in close association with the formation of retinal vasculature.

Time course of stratification of the dendritic fields of ganglion cells in the retina of the cat

The inner plexiform layer (IPL) of the retina has been shown by previous workers to comprise a number of sublayers (sublaminae or strata), each containing a distinct component of its circuitry. Using horseradish peroxidase applied to cultured whole retinas, we have observed the segregation of the dendrites of ganglion cells of the cat retina into two sublayers of the IPL. These sublayers appear to correspond to the a and b sublaminae described in studies of the adult IPL. As the dendritic fields of ganglion cells form, in mid-gestation, they are diffuse, spreading through the ganglion cell and inner plexiform layers. A few weeks before birth the dendrites become restricted to the IPL, but it is not until after birth, between P(postnatal day)2 and P5, that they segregate into inner and outer sublayers of the IPL. The process of segregation may involve the loss or ‘pruning’ of excess dendrites formed in ‘wrong’ sublayers. The segregation of dendrites into sublayers occurs concurrently with the formation of synapses by bipolar cells and may be induced by contacts made by bipolar cells onto the dendrites of ganglion cells.

Visual adaptation is highly localized in the cat's retina.

1. The aim of this study was to determine how the spatial pattern of steady light in a visual stimulus affects the state of adaptation of the retina. 2. Impulse rate was recorded from single X and Y ganglion cells in the cat's retina. The luminance of a narrow bar of light centred over the receptive field was modulated sinusoidally in time about a steady background, and a cell's contrast gain was measured as the ratio of impulse rate modulation to bar contrast. 3. The contrast gain of a cell was set by the background, a fixed luminance level about which luminance varied in the form of a grating; grating luminance varied sinusoidally with distance but did not vary in time. When the spatial frequency of the grating was low, contrast gain was increased by a grating with a trough centred over the receptive field, and decreased by a peak-centred grating. 4. As the spatial frequency of the grating increased, its effect on contrast gain disappeared. For cells around 10 deg from the central area, this change occurred at spatial frequencies close to 1 cycle deg-1. 5. For each cell the effect on contrast gain of the background's spatial frequency was compared with the spatial frequency response to a time-varying grating. It was found that the summation area for adapting light in both X and Y cells is very close in size to an X cell centre mechanism, and that the summation area for adapting light in Y cells is therefore considerably smaller than a Y cell centre. 6. From this and other evidence it was shown that sub-areas of the Y cell centre mechanism can be independently adapted. 7. A background grating with a trough centred over the receptive field raised contrast gain more at mid-range spatial frequencies than at low frequencies, producing a hump in the contrast gain versus frequency curve. A peak-centred grating reduced contrast gain more at mid-range frequencies than at low, producing a dip. 8. The dip in the contrast gain versus frequency curve for a peak-centred grating was always greater than the hump for a trough-centred grating. 9. These humps and dips were interpreted in terms of a model containing two antagonistic pathways. One pathway had a smaller summation area for adapting light than the other.(ABSTRACT TRUNCATED AT 400 WORDS)

Intraretinal axons of ganglion cells in the Japanese monkey ( Macaca fuscata): conduction velocity and diameter distribution

In anesthetized and immobilized Japanese monkeys ( Macaca fuscata), intraretinal conduction velocities of the ganglion cell axons were measured. The field potentials elicited by optic chiasm shocks consisted of fast and slow components with estimated conduction velocities of 1.19 and 0.72 m/s in recordings from the optic nerve fiber layer, and 1.65 and 1.00 m/s in recordings from the ganglion cell layer. Single cell recordings verified that the time course of the fast component corresponded to the antidromic spike latencies of Y-like cells, whereas that of the slow component covered the latency range of both X-like and W-like cells. In an electron microscopic study of the cross-sections of the intraretinal optic nerve fiber bundles, the axon diameter histograms of large samples (n = 3000−6000) all showed a unimodal distribution with a sharp peak at 0.3–0.6 μm and a long tail extending to 2–3 μm. The mean diameter was largest in the ventral and nasal bundles, smallest in the papillomacular bundle and intermediate in the dorsal, upper arcuate and lower arcuate bundles. However, diameter histograms of a small number of regional axons (n = 255−300) showed a broad tail distinct from the peak at 0.3–0.6 μm, enabling us to segregate a group of larger axons from the medium-sized to small axons. From such regional axon diameter histograms we estimated the mean relative occurrences of the larger axons (7.1–11.3%) and their mean diameters (0.9–1.3 μm). We further applied this relative frequency to the unimodal distribution of the histograms with larger samples in the upper and lower arcuate bundles and estimated the mean axon diameter of the large axons (1.1 μm) and that of the medium-sized to small axons (slightly below 0.5 μm). Finally, in studying the relation between axon diameter and conduction velocity in the two arcuate fiber bundles, we found it to be somewhat different from that previously reported for the cat retina.

Substance P‐like immunoreactive amacrine cells in the cat retina

Substance P-like immunoreactivity was localized by immunocytochemical techniques to two subpopulations of amacrine cells in the cat retina. One cell was a unistratified amacrine with processes ramifying within stratum 4 of the inner plexiform layer. The other cell type was a bistratified cell with processes in both stratum 1 (s1) and stratum 4 (s4). Both cell types were seen with their somas displaced to the ganglion cell layer as well as in the conventional amacrine location in the inner nuclear layer. Substance P cells were present in the greatest density within the area centralis and decreased in number toward the periphery. The ratio of amacrine to displaced amacrine cells also decreased peripherally. However, the coverage by immunoreactive fibers in s4 remained three times that seen in s1. Computer-assisted analysis confirmed the location of substance P-containing processes at 5-15% (s1) and 50-70% (s4) depth levels in the inner plexiform layer. A comparison of substance P-like immunoreactivity in light- and dark-adapted cat retinas showed no apparent differences in the distribution of immunoreactivity due to lighting conditions.