Intensity-response Curves Research Articles

Physiological properties of retinal ganglion cells of 3-week-old kittens

The physiological properties of the retinal ganglion cells of barbiturate-anesthetized, 3-weekold kittens (21–24 days of age) were studied. The antagonistic, center-surround organization of the receptive field is present. The angular size of the receptive field center is twice as large in kittens but the linear size of the centers on the retina is approximately the same in kittens and adults. The responses elicited by different stimulus intensities are significantly weaker, and the intensity-response curve is flatter in kittens. A higher stimulus intensity is required to elicit a criterion firing rate in kittens. The temporal resolving property of the ganglion cells is poorer in kittens. The response of the kitten's ganglion cells has a longer latency but does not tend to fatigue or to respond in a sluggish manner to a strong stimulus. Thus the ganglion cells of the 3-week-old kitten have some properties which are adult-like and others which are significantly different. We conclude that the kitten enters the critical developmental period with an immature retina.

Effects of intracellular injection of calcium buffers on light adaptation in Limulus ventral photoreceptors.

The calcium sequestering agent, EGTA, was injected into Limulus ventral photoreceptors. Before injection, the inward membrane current induced by a long stimulus had a large initial transient which declined to a smaller plateau. Iontophoretic injection of EGTA tended to prevent the decline from transient to plateau. Before injection the plateau response was a nonlinear function of light intensity. After EGTA injection the response-intensity curves tended to become linear. Before injection, bright lights lowered the sensitivity as determined with subsequent test flashes. EGTA injection decreased the light-induced changes in sensitivity. Ca-EGTA buffers having different levels of free calcium were pressure-injected into ventral photoreceptors; the higher the level of free calcium, the lower the sensitivity measured after injection. The effects of inotophoretic injection of EGTA were not mimicked by injection or similar amounts of sulfate and the effects of pressure injection of EGTA buffer solutions were not mimicked by injection of similar volumes of pH buffer or mannitol. The data are consistent with the hypothesis that light adaptation is mediated by a rise of the intracellular free calcium concentration.

Action spectra and chromatic mechanisms of cells in the median ocelli of dragonflies.

Spectral sensitivities were recorded intracellulary in median ocelli of Anax junius, Aeschnatuberculifera, and Libellulapulcella. All cells had peak sensitivities at 360 and 500 nm while UV-blue+green cells found only in Anax had a third peak sensitivity at 440 nm. Ratios of UV-to-green sensitivities varied from cell to cell in each ocellus, but no UV-only or green-only cells were recorded. Half of the cells tested had a reverse Purkinje shift: They were more sensitive in the green at low illuminations but more sensitive in the UV at high illuminations; their intensity-response curves at 370 and 520 nm crossed but became parallel for large responses. Wave-lengths 420 nm and shorter elicited a family of low intensity-response curves with one slope; wavelengths 440 nm and longer elicities a family of curves with another slope. Orange-adapting lights selectively adapted sensitivity in the green, but UV-adapting lights had little selective effect. Amounts of log-selective adaptation were proportional to log orange-adapting intensity. It is concluded that two spectral mechanisms can be recorded from each cell, possibly by coupling of UV and green cells or possibly because each cell contains two visual pigments. Selective chromatic adaptations may provide the ocellus with a kind of "authomatic color control," while the reverse Purkinje shift could extend the ocellus' sensitivity to prevailing skylight.

Rod late receptor potential and rhodopsin concentration of an isolated frog retina.

The relation of the threshold of the late receptor potential (late RP) and ERG b-wave with the rhodopsin concentration in the rod outer segments of an isolated bullfrog retina were studied by simultaneous recordings of electrical responses and spectral change. The curve indicating log threshold rise of the late RP with the decrease of rhodopsin showed two phases separated by a kink, which was found at 50% rhodopsin concentration; the b-wave threshold, however, was linearly related to rhodopsin concentration. From the intensity response curves (IR curves) at various rhodopsin concentrations, the amplitude decrease of both waves following bleaching light adaptation was compared and the mode of the conversion from the late RP to the b-wave was discussed.

Spectral sensitivity of the system controlling visual pigment composition in tadpole eyes

Rana clamitans tadpoles were kept in incubators in complete darkness or illuminated with different intensities of light of dominant wavelengths 482, 564 and 690 nm. At various times batches of tadpoles were taken from each incubator, dark-adapted and their visual pigments analyzed. While in the dark there was a steady drift of porphyropsin proportion down to about 30 per cent; in the light the visual pigment composition stabilized at various porphyropsin percentages above this value, increasing with increasing intensity of illumination of a given color. Hence a series of curves relating porphyropsin percentage to intensity could be plotted, and selection of several “criterion levels” (between 65 and 77 per cent) permitted direct comparison of the sensitivity of the system to each of the three wavelengths. Blue light was most effective in maintaining high levels of porphyropsin, the sensitivity lying about 3.4 log units above the red. The yellow-green was about 2.7 log units above the red. Tadpoles were transferred from two intensities of red light to two intensities of blue light approx 3 log units lower. No change of visual pigment composition occurred over a 6-day period, confirming the “matching values” deduced from the intensity-response curves. Since the red sensitivity is approx 2.5 log units below the published photopic luminosity curve for tadpoles containing 70 % porphyropsin, the participation of cones is unlikely. There is tolerable agreement with the scotopic sensitivity curve, which is fitted within ±0.2 log units, and it is concluded that the maintenance of porphyropsin in the tadpole eye is most probably mediated by light absorbed in the rods.

E-vector discrimination by the goldfish optic tectum

1. Because behavioral evidence indicates that fishes can perceivee-vector direction in plane polarized light, intracellular recordings were made on bipolar cells, ganglion cells, amacrine cells and horizontal cells in the goldfish retina. In flattened retinal fragments stimulated with polarized flashes no evidence for significante-vector sensitivities was found. 2. Dichroism could not be demonstrated in the cornea, lens or other dioptric elements of this fish eye. 3. Finally extracellular spike recordings of single units in the goldfish optic tectum were made to determine whethere-vector discrimination could be measured in the output of the intact eye in the living fish. 500 msec test flashes were presented to the retina with narrow band spectral red, green and blue light (quantum equalized) as well as with white light over a 4–5 log unit range of intensities. 4. Practically all tectal cells of the 47 successfully recorded showed some sensitivity toe-vector direction. The response function was roughly sinusoidal with maxima and minima 90° apart. Maximal responses to polarization plane orientation were found in all sixe-vector directions tested. Consequently an analyzer without discrete channels for particular polarization planes must be present quite different from that present in many rhabdom bearing eyes. 5. E-vector direction influenced various parameters of the tectal responses (on, off, sustained, etc.) in some cases in the same direction and in other cases in the opposite direction. Both excitatory and inhibitory components, as well as color coded ones, were affected. 6. Intensity response curves indicate polarized light sensitivity ratios ranging from 1.4 to 31.7, with a mean of 8.2 for 13 cases.

E-vector sensitivity patterns in the goldfish optic tectum

1. Spike responses of single optic tectal units to plane polarized light have been recorded with extracellular electrodes in the goldfish. Responses to a series of eight 500 msec flashes were summed and the quantitative effects ofe-vector direction studied over 4–5 log units of intensity with white light and narrow spectral bands of equal quantal content at 460, 540 and 620 nm. 2. As previously reported all or nearly all tectal cells tested (115) were sensitive to the direction of the stimulus' polarization plane. Control experiments with a thin high order birefringent retarder next to the cornea and acting as a pseudo depolarizer provided further proof that thee-vector discrimination found in the optic tectum (as well as the previously reported oriented behavior to polarized light in fish) depends on an intraocular analyzer. 3. Systematic study of tectal cells has been made at various depths and in all directly accessible areas. No localized or differential effects of recording depth one-vector discrimination have been found. However, both directions of maximum response and degree of polarized light sensitivity (PLS) show distinctive patterns over the tectal area. 4. On the basis of established tectal projection maps these data show that preferred retinale-vector directions are tangentially arranged around the eye axis when the stimulus is axial. Distribution of this angular sensitivity seems continuous without discrete channels favoring particular polarization planes. 5. Sensitivity (determined from intensity response curves) is minimal in the center of the retina for an axial stimulus and increases peripherally out to 50–60° or more off axis. Sensitivity ratios of 4–6 are common and much larger ones have been occasionally recorded. 6. Shifting the direction of stimulus from axial to 45° and 60° upward from the axis proved that retinal patterns of preferrede-vector directions and sensitivities are symmetrical relative to the beam axis rather than the anatomical eye axis. Therefore individual tectal cells and before them their retinal receptor elements show different directions ofe-vector preference and different PLS ratios depending on the stimulus configuration. 7. Intensity response curves determined with the red, green and blue narrow spectral bands were essentially superimposable. Therefore, we have no evidence that there is any special interaction of λ and PLS. 8. The effects of stimulus intensity and retinal adaptation on the IR curves do not indicate any particular selective effects. Substantial polarized light sensitivity was present in both the light adapted and dark adapted state. PLS ratios in various cases were (1) about the same at different intensity levels or (2) greater at low than high intensities or (3) greater at high than low intensities. 9. We conclude that linearly polarized light evokes a large entoptic image in the goldfish eye. Two opposite light sectors perpendicular to thee-vector alternate with two dark sectors parallel to thee-vector. Both Haidinger's brushes and Boehm's brushes in human vision show some similarities but also some important differences. The goldfish PL image is achromatic, weak or absent axially and strong peripherally. Also the contrast between the sectors does not depend on movement of the stimulus on the retina to prevent fading as it does in both of the other phenomena. 10. The most likely mechanism for the observed PLS in the goldfish eye is either differential scattering intraocularly or oblique entry of light into the receptor outer segments. Yet present data prevent a firm choice between them.

Intensity-response functions of visually deprived lgn neurons of cats

The responses elicited by different stimulus intensities and sizes were recorded from visually deprived LGN neurons of cats. These data were compared with similar data collected from normal cats ( Winters and Hamasaki, 1972) . Approximately 60 per cent of the visually deprived units were classified as abnormal. These units were characterized by (1) lower firing rates, (2) longer latency, (3) absence of a rise in threshold with targets which overlap the peripheral region of the RFC and (4) flatter intensity-response curves. These properties are similar to those found in an earlier study of visually deprived LGN neurons ( Winters, Hamasaki et al., 1972) .

Electroretinographic intensity-response curves in central retinal.

Electroretinographic studies were carried out in ten patients suffering from unilateral occlusion of the central retinal artery by using twin light flashes (interval of 500 msec), the intensity of which varied within a range of 5 log units. The pathologic conditions in the affected eyes caused a characteristic flattening of the intensity-response curves predominantly in the scotopic part of the curve. The shape changes of the intensity-response curves due to the relative refractory period following the first retinal responses are of a different nature. The procedure enables the quantitative analysis of the wide range of retinal intensity functions.