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L J Frishman

Publications and source records attributed to L J Frishman.

31 records · Page 2Linked to original sources
PubMed1988

Contributions to the electroretinogram of currents originating in proximal retina.

We have investigated responses in proximal retina of the cat that contribute to two kinds of electroretinogram (ERG) recordings: (1) the pattern ERG, a light-adapted response and (2) the threshold and near threshold ERG, a dark-adapted response (Sieving et al., 1986a, 1986b; Sieving & Steinberg, 1985). In intraretinal, extracellular recordings, two negative-going responses were identified that are maximal around the inner plexiform layer, and distinct from PII, which is maximal in distal retina: under light-adapted conditions, a spatially tuned response at light and light offset, the "M-wave" (previously described in cold-blooded animals by Karwoski & Proenza (1977, 1980)), and under dark-adapted conditions, the scotopic threshold response, or "STR," a response at light onset. The results under dark-adapted conditions are examined in more detail here. The STR is a very sensitive response whose threshold is 1.5-2.0 log units below that of the dc-component of PII and therefore well below the threshold of the a-, b-, and c-waves. It saturates about 2.4 log units below rod saturation. The STR contributes a negative-going potential to the dark-adapted ERG that is dominant near threshold; while PII (dc-component and b-wave) contributes a positive-going potential that is dominant at higher intensities (Sieving et al., 1986b). Investigation of the mechanism of the proximal retinal responses that contribute to the ERG supports of K(+)-Müller cell hypothesis of their origin.

Adaptation, Ocular↗
PubMed1987

Interactions between the rod and the cone pathways in the cat retina.

The receptive field centers of 21 on-center X retinal ganglion cells in cat were tested with stimuli designed to detect nonlinear interactions between the rod and the cone systems. One red and one green stimulus light were always present, at a level such that modulation of the red light essentially affected only cones, and that of the green light only rods. The two lights could be superimposed spatially (overlapped configuration) or fall on separate subareas of the receptive field center (nonoverlapped configuration). In most cases, there was less complete summation of the responses to modulation of the lights in the overlapped than in the nonoverlapped configuration, with a corresponding difference in the summation of sensitivities. In 1/6 of the experiments, there was more complete summation of the responses to the lights in the overlapped configuration, with a corresponding difference in the summation of sensitivities. The mean magnitude of the interaction for all experiments was equivalent to an antagonistic interaction between the rod and cone pathways such that the signal in each was diminished by a quantity slightly greater than 30% of the signal in the other.

Animals↗
PubMed1987

Spatiotemporal frequency responses of cat retinal ganglion cells.

Spatiotemporal frequency responses were measured at different levels of light adaptation for cat X and Y retinal ganglion cells. Stationary sinusoidal luminance gratings whose contrast was modulated sinusoidally in time or drifting gratings were used as stimuli. Under photopic illumination, when the spatial frequency was held constant at or above its optimum value, an X cell's responsivity was essentially constant as the temporal frequency was changed from 1.5 to 30 Hz. At lower temporal frequencies, responsivity rolled off gradually, and at higher ones it rolled off rapidly. In contrast, when the spatial frequency was held constant at a low value, an X cell's responsivity increased continuously with temporal frequency from a very low value at 0.1 Hz to substantial values at temporal frequencies higher than 30 Hz, from which responsivity rolled off again. Thus, 0 cycles X deg-1 became the optimal spatial frequency above 30 Hz. For Y cells under photopic illumination, the spatiotemporal interaction was even more complex. When the spatial frequency was held constant at or above its optimal value, the temporal frequency range over which responsivity was constant was shorter than that of X cells. At lower spatial frequencies, this range was not appreciably different. As for X cells, 0 cycles X deg-1 was the optimal spatial frequency above 30 Hz. Temporal resolution (defined as the high temporal frequency at which responsivity had fallen to 10 impulses X s-1) for a uniform field was approximately 95 Hz for X cells and approximately 120 Hz for Y cells under photopic illumination. Temporal resolution was lower at lower adaptation levels. The results were interpreted in terms of a Gaussian center-surround model. For X cells, the surround and center strengths were nearly equal at low and moderate temporal frequencies, but the surround strength exceeded the center strength above 30 Hz. Thus, the response to a spatially uniform stimulus at high temporal frequencies was dominated by the surround. In addition, at temporal frequencies above 30 Hz, the center radius increased.

Action Potentials↗
PubMed1986

M-wave of proximal retina in cat.

There has been relatively little known about responses from proximal retina in mammals that could contribute to the electroretinogram (ERG). Recently, there has been evidence that the proximal retina is involved in generating the pattern electroretinogram (PERG). In the present work we investigated proximal retinal activity in the intact cat eye during light adaptation. Extracellular potentials evoked in response to circular spots of light, flashed on steady backgrounds, were recorded with microelectrodes placed intraretinally at different depths. Prominent negative responses were found in proximal retina that could be identified as the M-wave previously observed only in cold-blooded retinas. Like the cold-blooded responses, the cat's M-wave consisted of negative-going potentials at stimulus onset and offset that were maximum in amplitude with small spots. By analogy to the cold-blooded data, the cat M-wave is presumed to be the extracellular voltage arising from Müller cell responses to K+ released by proximal retinal neurons. In addition, the cat M-wave only appeared with backgrounds at and above rod saturation and had short latencies (30 ms) at stimulus onset and offset, indicating that it is a cone-driven response. The M-wave could be clearly distinguished from PII (b-wave and DC component) on the basis of its form, depth distribution, and stimulus-response characteristics. For example, photopic PII had its maximum voltage in the distal retinal at 55% retinal depth, whereas the M-wave was maximal in the proximal retina at 25% retinal depth. Also, PII simply increased in amplitude as stimulus spots were enlarged, whereas the M-wave exhibited spatial tuning. Under light-adapted conditions and with small-spot stimuli the M-wave is the largest extracellular voltage in cat retina. By recording the vitreal ERG near the retinal surface with the microelectrode referenced to a silver wire in the vitreous, we found that the M-wave in response to a small spot always had a negative polarity in the vitreous. Thus, unlike PII, the M-wave does not reverse polarity at the vitreo-retinal border. Because of stray-light effects, however, we were not able to assess the amplitude of the M-wave's contribution to the ERG obtained with diffuse retinal illumination. We conclude that the M-wave is present in the cat as a prominent cone-driven response of proximal retina that is separate from the b-wave, and whose significance for electroretinographic recordings remains to be determined.

Adaptation, Ocular↗
PubMed1986

Scotopic threshold response of proximal retina in cat.

We describe a new response in proximal retina of cat that is present under scotopic conditions, clearly differs from PII (b-wave and DC component) and contributes a negative potential at threshold to the diffuse electroretinogram (ERG). We have termed this response the scotopic threshold response (STR). Extracellular potentials evoked in response to circular spots of light at dark-adapted threshold, and with dim backgrounds, were recorded with microelectrodes placed intraretinally at different depths. The dark-adapted response of proximal retina (STR) consisted of a graded negative potential to the onset of illumination that maintained amplitude during illumination and decayed back toward the base line at stimulus offset without evidence of a negative-going off response. It thereby differed in form from the photopic M-wave response of proximal retina, which has a negative-going off response. It also did not exhibit spatial tuning, simply increasing in size with stimulus area. In addition, the STR appears to be a rod-driven response whose threshold approximates that of the most sensitive ganglion cells in cat, whereas the M-wave is a much higher threshold cone-driven response. The STR could be clearly distinguished from PII on the basis of its form, depth-distribution, and dynamic range. For example, the STR had its maximum amplitude in the proximal retina at 17% retinal depth, whereas scotopic PII had its maximum in the distal retina at 48% retinal depth. Also, the STR had a lower threshold than PII intraretinally and saturated well below the level of saturation of scotopic PII (rod saturation). By analogy to the PNR and M-wave, the STR is hypothesized to represent either an extracellular voltage arising from proximal retinal neurons or Müller cell responses to K+ released by these neurons. Recording in the vitreous, near the retinal surface, showed that the STR always had a negative polarity. The polarity reversal of the STR at 50-60% retinal depth (from negative, proximal to positive, distal) suggested the presence of a sink proximal to the reversal point and a source distal to it. We also recorded the vitreal ERG in response to diffuse illumination of the dark-adapted retina. The STR could be clearly identified in the scotopic ERG as a threshold negative potential that had been observed previously in the mammalian ERG. The STR differs, therefore, from PII (b-wave and DC component) that is a higher threshold positive component in the diffuse ERG.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Statistics of the maintained discharge of cat retinal ganglion cells.

Action potentials were recorded from single fibres in the optic tracts of anaesthetized cats. Continuous records were obtained at various levels of scotopic and mesopic retinal illumination. In some cases, the light intensity was modulated by a pseudorandom Gaussian white-noise signal. The maintained discharge of on-centre neurones increased while the maintained discharge of off-centre neurons decreased with increased illumination of the receptive field centre. For both cell types, the coefficient of variation declined with increased rate of discharge. There was minimal short-term dependency in the firing patterns, and it was unaffected by the level of retinal illumination. Virtually all of the structure revealed by the normalized autocovariance functions could be attributed to the shape of the interval distributions. The first few coefficients of the serial correlogram were slightly negative. The magnitude of this negativity was not related to illumination. Long-term dependency in the firing pattern was also quite small; the standard deviations of the mean rate in samples of about 1 sec duration were only slightly less than would be predicted from the interval distributions. This dependency tended to increase at higher retinal illuminations. Neural discharges elicited by Gaussian modulation of the light were strikingly different from those elicited by steady light. Modulation caused the first coefficient of the serial correlogram to become more positive, while the next several coefficients became more negative. A corresponding pattern could be seen in the normalized autocovariance functions, and in the differences between the normalized autocovariance and normalized autoconvolution. Long-term dependency also increased dramatically, such that the standard deviations of mean rate were about 60% of what would be expected given the interval distributions observed. These results place a number of constraints upon the ways in which intrinsic noise in the retina may enter the visual processing network. Two alternative models consistent with the data are presented.

Animals↗
PubMed1983

Velocity tuning of cells in dorsal lateral geniculate nucleus and retina of the cat.

Velocity tuning curves were measured for on-center cells in the dorsal lateral geniculate nucleus of the cat using a stimulus approximately the height and one-fourth the width of the hand-plotted receptive-field center. The standard stimulus strength was 1 log unit above the mesopic background luminance. Lateral geniculate Y-cells had significantly higher preferred velocities than geniculate X-cells when cells with receptive fields having the same range of retinal eccentricities were compared. Preferred velocity increased for both classes of cells as a function of retinal eccentricity. For all geniculate cells, preferred velocity increased with stimulus strength, showing an approximately threefold increase in preferred velocity for each log unit of stimulus strength. Preferred velocity was measured for on-center retinal ganglion cells with receptive fields at the same range of retinal eccentricities as the geniculate sample and under the same stimulus conditions. Preferred velocities of retinal ganglion Y-cells were significantly higher than those of ganglion X-cells, and as for geniculate cells, preferred velocities increased with increasing stimulus strength. However, the classes were better separated in the geniculate than in the retina; with geniculate X-cells having lower preferred velocities than retinal X-cells, and the geniculate Y-cells having higher preferred velocities than retinal Y-cells. For retinal ganglion cells, smaller receptive-field center sizes of the X-cells than the Y-cells could account in large part for the lower preferred velocities of the X-cells. However, for geniculate cells, differences in receptive-field center size could not account as well for the differences in preferred velocity between X- and Y-cells. Furthermore, field size differences could not account for the differences in preferred velocity between ganglion and geniculate cells of the same functional class. Experiments comparing responses to moving stimuli and flashed stationary stimuli show that stimuli moving at high velocities are in effect equivalent to brief-duration flashes, and responses are governed by the same laws of temporal summation in both cases. When velocity tuning curves were measured with long bars that enhanced peripheral inhibition, geniculate X- and Y-cells were better separated than ganglion X- and Y-cells, not only with respect to preferred velocity but also, with respect to velocity selectivity (width of the velocity tuning curve) and differential velocity sensitivity (slope of the leg of the velocity tuning curves ascending from low velocities to the peak).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Receptive field properties of x and y cells in the cat retina derived from contrast sensitivity measurements.

The contrast sensitivity to gratings drifting at 2.0 Hz has been measured for X and Y type retinal ganglion cells, and these data have been used to characterize the sizes and peak sensitivities of centers and surrounds. The assumption of Gaussian sensitivity distributions is adequate for both types of cells, but allows a better description of X than of Y cells. The size and peak sensitivity can be specified more precisely, in general, for the center than for the surround. The data also show that for both types of cells (1) center radius increases with eccentricity, but is two to three times larger than Y cells than for X cells at a given eccentricity, (2) spatial resolution is an excellent predictor of center size, (3) the larger the center or surround, the lower its small spot sensitivity at a specific mean lumminance and (4) the surround is nearly as strong as the center for large or diffuse stimuli. X cell surrounds are relatively weaker in the middle of the receptive field than Y cell surrounds, but X cell surrounds are larger relative to their centers.

Action Potentials↗
PubMed1982

Effects of picrotoxin and strychnine on non-linear responses of Y-type cat retinal ganglion cells.

1. The effects of neurotransmitter antagonists on spatially linear and non-linear responses of Y cat retinal ganglion cells were studied. 2. The contrast sensitivity of the spatially linear receptive field centre and surround at mesopic and photopic levels of illumination was affected very little by picrotoxin, but the sensitivity of the non-linear subunits was reduced. 3. Picrotoxin also reduced two other non-linear effects: 'shift responses' and the suppression of the response to a centred test flash caused by movement of a peripheral pattern. 4. In contrast to picrotoxin, strychnine decreased the contrast sensitivity of the receptive field centre, and increased the sensitivity of the subunits. 5. The results support the idea that the non-linear responses may all be generated by similar pathways, which are distinct from those which generate linear responses. Because both picrotoxin and strychnine affect subunit responses, cells using gamma-aminobutyric acid (GABA) and glycine as transmitters are probably involved in subunit pathways.

Action Potentials↗
PubMedDate not supplied

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

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

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMedDate not supplied

Evidence for a ganglion cell contribution to the primate electroretinogram (ERG): effects of TTX on the multifocal ERG in macaque.

To assess the contribution of spiking inner retinal neurons to the multifocal electroretinogram (ERG), recordings were made from four monkeys (Macaca mulatta) before and after intravitreal injections of tetrodotoxin (TTX). TTX blocks all sodium-based action potentials and thus terminates spiking activity of amacrine and ganglion cells. TTX eliminated a large component from the control responses, and this TTX-sensitive component was present as early as 10 ms after the stimulus. Before injection with TTX, the 103 focal ERG responses varied in waveform across the retina. After TTX, the response waveforms were largely independent of retinal position, indicating that it was primarily the TTX-sensitive component of the control response that was dependent upon retinal location. Given that retinal ganglion cells compose a sizable proportion of the retinal elements that produce action potentials, it is likely that part of the TTX-sensitive component is due to the spiking activity of these cells. Further, the systematic change in waveform of the TTX-sensitive component with distance from the optic nerve head suggests that part of the TTX-sensitive component may originate from the activity of the ganglion cell axons. Based on these findings, there is reason to be optimistic that the multifocal technique can be employed to study the effects of glaucoma and other diseases that affect the inner retina.

Action Potentials↗
PubMedDate not supplied

Dissecting the dark-adapted electroretinogram.

Although gross recordings of the ganzfeld flash-evoked electroretinogram (ERG) can potentially provide information about the activity of many, if not all, retinal cell types, it is necessary to dissect the ERG into its components to realize this potential fully. Here we describe various procedures that have been used in intact mammalian eyes to identify and characterize the contributions to the dark-adapted ERG of different cells in the retinal rod pathway. These include (1) examination of the very early part of the response to a flash (believed to reflect directly the photocurrent of rods), (2) application of high-energy probe flashes to provide information about the underlying rod photoreceptor response even when this component is obscured by the responses of other cells, (3) pharmacological suppression of responses of amacrine and ganglion cells to identify the contribution of these cells and to reveal the weaker responses of bipolar cells, (4) use of pharmacological agents that block transmission of signals from rods to more proximal neurons to separate responses of rods from those of later neurons, (5) examination of the ERG changes produced by ganglion-cell degeneration or pharmacological block of nerve-spike generation to identify the contribution of spiking neurons, (6) modeling measured amplitude-energy functions and timecourse of flash responses and (7) using steady backgrounds to obtain differential reductions in sensitivity of different cell types. While some of these procedures can be applied to humans, the results described here have all been obtained in studies of the ERG of anaesthetized cats, or macaque monkeys whose retinas are very similar to those of humans.

Animals↗