Rod and cone signals in S-potentials of the isolated perfused cat eye

Two types ofS-potentials have been identified in the dark-adapted retina of isolated, perfused cat eyes. One type shows the action of rods exclusively, the other shows both rod and cone activity. In all of the latter units the cones make a much larger contribution to the total response than the rods and in some of these units little or no rod response can be detected at all. Although an unusual effect occurs with strong short wavelength stimulation that suggests some antagonistic receptor interaction, the results in the main support hypotheses proposing considerable independence between rod and cone signals at or before the inner nuclear layer of the retina.     

Rod and cone contributions to peripheral colour vision

The changes in chromaticities were measured, in a dark-adapted state, when monochromatic lights were moved from the fovea to 2.5° and 7.5° temporally. In order to analyze the contributions of the rod and cone mechanisms to these changes, the chromaticities were measured during dark adaptation following high light adaptation. For several min during the cone-plateau period, the colourmixture functions remained invariant and the outlines of the test field appeared distinct and clearcut. Just prior to the cone-rod break of the dark-adaptation curve, however, the chromaticities generally started to change and the shape of the test field became somewhat blurred. The evidence is judged to indicate that the chromaticities measured during the period of invariance are due to pure cone activity, while the shift in chromaticities measured during the further stay in the dark is due to the effect of rod intrusion.     

Rod and cone contributions to change in hue with eccentricity

Using an asymmetric colour-matching technique, the sensation of hue of monochromatic lights was measured during the cone-plateau period and after 30 min dark-adaptation at different eccentricities. The measurements were obtained both at photopic and mesopic intensities. Presupposing that the results recorded during the cone-plateau period reflect activities of dark-adapted cone mechanisms, while the changes in hue observed during the rod-phase of the dark-adaptation reflect the effect of rod intrusion, the changes in hue with eccentricity were explained on neural rather than photochemical receptor mechanisms.     

Rod pathways in the retina of the cat

Neurons involved in the transfer of rod signals to the ganglion cells in the retina of the cat have been recorded from and stained with horseradish peroxidase (HRP) and their synaptic connections determined by electron microscopy. The single morphological type of rod bipolar cell responds with a sustained hyperpolarization to light and in turn drives at least five morphologically different types of amacrine cells, each of which has a unique response pattern. Two amacrines respond with either a transient (AII) or a sustained (A17) depolarization to light, while three amacrines give transient (A8) or sustained (A6, A13) hyperpolarizations. Circuitry whereby rod signals reach both on-centre and off-centre ganglion cells is discussed.     

Rod and cone inputs to bipolar and horizontal cells of the Xenopus retina

This report summarizes some recent studies of the Xenopus retina in which intracellular recordings were made from photoreceptors, horizontal and bipolar cells. The studied cells were identified by injection of Lucifer yellow. Rod spectral sensitivity functions conformed to the density spectrum of a 524 nm pigment, those of cones to that of a 612 nm pigment. Horizontal cell responses reflected both these classes of photoreceptor input. Rod input evoked a slow waveform, with Vmax less than or equal to 18 mV, cone input a faster waveform with Vmax = 30-40 mV. In the mesopic state the horizontal response reflected both waveforms. Rod and cone inputs to the horizontal cells appeared not to act independently, in that a steady weak green background greatly enhanced the response to a superimposed red flash, but not the reverse. A third photoreceptor type (blue-sensitive rod, Y lambda max = 445 nm) provided input to a chromatic bipolar cell which was hyperpolarized by blue light and depolarized by red light. Such chromatic bipolars had broad areas of spatial integration and lacked center-surround organization.     

Blue cone function in the retina of the cat

Selective chromatic adaptation revealed the presence of a blue-sensitive mechanism in the cone electroretinogram of the cat. This mechanism λ_max near 460 nm), narrower than a Dartnall nomogram (460 nm), suggests the interaction of at least two cone photoreceptor systems in the pre-ganglion cell retina.     

Rod and cone contribution to adaptation processes in cat retinal ganglion cells

Extracellular ganglion cell responses were recorded to investigate mechanisms of light adaptation. Monochromatic test spots (575 nm) were projected onto the receptive field center of off-center cells and superimposed on a steady blue-green Ganzfeld background (Schott Filter BG 28), the strength of which was increased in steps of 0.5 log units to adapt rods. Response vs. log intensity functions were determined over a range of 7 log units of test light irradiance at each background level. At higher adaptation levels response thresholds followed the typical Weber function. Surprisingly at lower adaptation levels the sensitivity of the cell increased by about 0.7 log units, most markedly in a range of 1 log unit of moderate light adaptation when the background was changed from dark to the dimmest detectable background (10^–5lm/m²). In the dark-adapted state a small off-response of long latency (40–100ms at 10² quanta · s^–1 · m^–2) is observed at low rod stimulating test light irradiances. A transition to a cone-dominated transient response of 2 to 5 ms duration occurred at high intensities (10⁵ quanta · s^–1 · m²). At mesopic levels the two responses seem to cancel each other, rendering a delayed off-response that is probably the result of rod-cone interaction. As in psychophysics, saturation can be observed at very high background intensities (10⁶ quanta · s^–1 m^–2). These data suggest interactions between rods and cones that determine the sensitivity of cat retinal ganglion cells at low levels of adaptation for suprathreshold stimuli.     

Rod and cone contributions to the delayed response of the on-off ganglion cell in the frog

Delayed responses from on-off ganglion cells were further studied. Spectral sensitivity experiments indicate that signals from cones as well as rods contribute to the delayed response. Chromatic pre-adaptation studies showed that a reduction in the sensitivity of rods results in a smaller amplitude of the late response and a slight increase in delay time, while desensitizing the cone system causes a shorter delay time and a greater amplitude in the late response. These results suggest that rod signals are excitatory and cone signals inhibitory and that these signals summate to elicit the delayed response.     

Rod and cone system contributions to oscillatory potentials: an explanation for the conditioning flash effect

The oscillatory potentials (OPs) of the human electroretinogram (ERG) are smaller in response to the initial flash of a series than to subsequent flashes. To investigate a possible rod system contribution to this "conditioning flash effect," we have examined OPs in normals and rod monochromats. The OPs recorded from rod monochromats were similar to those recorded from normals under test conditions that selectively stimulate rods. However, under conditions that in normals stimulate both rods and cones and that result in maximal amplitude of the OPs, the rod monochromats exhibit markedly reduced OPs. This finding suggests that the initial (conditioning) flash operates by adapting the rod system contribution to the OPs, so that the OPs in response to subsequent flashes result primarily from the cone system. In agreement with this hypothesis, the conditioning flash effect did not occur when flashes were presented against a background which eliminated the rod system response nor during the cone plateau phase of dark adaptation.     

Rod and cone disc shedding in the rhesus monkey retina: A quantitative study

Four Rhesus monkeys were maintained for several months on a daily lighting schedule of 12 hr light and 12 hr darkness (12L:12D). The animals were then fixed by intracardiac perfusion at 1 and 5 hr following the onset of light, and at 1 and 5 hr after the offset of light. The number of phagosomes/mm of retinal pigment epithelium (RPE) was counted in the light microscope for both foveal and extrafoveal locations. At extrafoveal sites, phagosomes within the RPE cell bodies and those within the ensheathing processes bordering cone outer segments were counted separately. Counts at foveal and extrafoveal locations suggest that the rate of disc shedding, and therefore the rate of membrane replacement, is probably less for foveal cones than it is for rods. The number of phagosomes above the rod tips 1 hr following light onset and their diminution several hours later suggests that an increase in rod shedding, similar to the “burst” of rod shedding reported for other species, also exists in the monkey retina. The number and location of phagosomes 5 hr after the offset of light indicates that there could be another phase of increased rod shedding somewhere around the middle of the dark period. Phagosome counts in the foveal RPE were highest 5 hr after light offset, however the counts at 1 and 5 hr following light onset were nearly as high. The number of RPE phagosomes at both foveal and extrafoveal locations was lowest 1 hr after light offset. Counts of phagosomes within the sheaths of extrafoveal cones showed that about 20% contained one or more phagosomes within their sheaths. Of those sheaths that did contain phagosomes, approximately 25% had multiple phagosomes. There appears to be a considerable period of time during which extrafoveal cone phagosomes remain within the ensheathing processes, moving from the cone tips toward the apical RPE surface. Rod and cone disc shedding in the monkey retina are probably cyclic processes—although the temporal pattern of shedding may be different than that reported for other species.     

Rod and cone contribution to the EOG ratio

The EOG ratio is an established clinical test of retinal function. Since its development by Arden and coworkers in 1962, it has been thought of as simply a rod-medicated response. Using scotopically matched red and blue lights, we found a 24% larger response to the red light than to the blue light, establishing that a cone contribution exists in the EOG ratio of normal subjects.     

Physiological and morphological identification of L- and C-type S-potentials in the turtle retina

We have recorded the electrical responses to red light and simultaneously marked with procion yellow the cells that give the L- and C-type of S-potential in the turtle retina. The L-type response originates in a horizontal cell with predominantly thick dendrites. The C-type response originates in a horizontal cell with predominantly thin dendrites which are located sclered to those of the L-type response cell. The L- and C-type cells as seen in procion-yellow marking are compared with cells of toluidine-blue stained sections.