Lateral spread of light adaptation in the rat retina

SUMMARY1. Adaptation by weak backgrounds and the spatial spread of desensitization between rods was studied in the snapping turtle retina, Chelydra serpentine. Intracellular membrane potentials were recorded from these photoreceptors in an eyecup preparation.2. The kinetics and sensitivity of rod responses were changed significantly by large, very dim backgrounds. For the twenty-five most sensitive rods where the dark-adapted flash sensitivity, SD, was greater than 1D0 mV/Rh*, Rh* being the number of effective photo-isomerizations per rod, the background intensity required to halve the amplitude of the linear range response averaged 0-21 Rh* s'l. The time-to-peak of the test responses was reduced up to 50 % by these dim backgrounds.3. The desensitizing effects of full field backgrounds of various intensities on the responses to large test spots were measured. The dependence of incremental flash sensitivity, SF, on background intensity, IB, followed the formwhere Io is the background intensity which halved SD. The same intensity dependence held for slit-shaped background fields that desensitized responses to small test spots.4. The desensitizing effects of large, very dim flashed and continuous backgrounds took several seconds to appear and decay to dark levels. This in conjunction with the sparsity of photons suggests, that the desensitization from a single photoisomerization can persist for several seconds.5. A comparison of the desensitizing effects of spot and annular backgrounds revealed that small spot backgrounds superimposed on the centred test spots desensitized rods more effectively than annular fields. This finding held true even when annular patterns produced a greater maintained hyperpolarization in the rods. Thus, there was no unique relationship between desensitization and the steady maintained hyperpolarization evoked by a background field.6. The dependence of adaptation on distance from the impaled rod was determined with slit-shaped background fields placed at different positions across the rod's receptive field. 6PHY 369 D. R. COPENHAGEN AND D. G. GREEN 7. The desensitizing effect of displaced slit stimuli was found to decline much more rapidly with distance than excitation. Displacing the slit by 20 ,um from the centre reduced its desensitizing effect by more than 1 log unit. In contrast, excitation fell to about 80 % at the same distance (A ranging from 50 to 70 ,sm).8. The fall off of desensitization with distance matched the calculated fall off with distance of light scatter from a slit. 9. No difference was noted in the kinetics of test responses in the presence of equally desensitizing, superimposed and displaced slits.10. It is concluded that there is little spread of desensitization between rods. Thus, adaptation appears to be accounted for primarily on the basis of local photoisomerizations in each rod outer segment.11. The exceedingly low rates of photo-isomerizations required to halve sensitivity leads to the conclusion that a single photo-isomerization produces profound changes that...

Section: Introductionmentioning

confidence: 99%

The absence of spread of adaptation between rod photoreceptors in turtle retina.

Copenhagen¹,

Green²

1985

“…We have shown previously that the desensitizing effect of illuminating a small area of the receptive field of a ganglion cell is not confined to the illuminated area but spreads laterally (Green, Tong & Cicerone, 1977), although not uniformly (Cicerone & Green, 1980) throughout the field centre. Locations near the illuminated area suffer a greater sensitivity loss than locations further from illumination.…”

Section: Introductionmentioning

confidence: 99%

Dark adaptation within the receptive field centre of rat retinal ganglion cells.

Cicerone¹,

Green

1980

SUMMARY1. Recordings from single axons of retinal ganglion cells in the rat's optic tract were used to determine whether bleaching a small area of the receptive field reduced sensitivity globally or locally, near the bleached photoreceptors.2. When a suprathreshold test spot was alternated between two equally sensitive positions, the ganglion cell gave an approximately balanced response. The balance was upset if a small-spot bleach was selectively applied to one position. Recovery of the balanced condition was rapid.3. Varying the duration of a constant illuminance bleach varied the duration of the imbalance following the bleach.4. The recovery of sensitivity after small-spot bleaches was measured both at the location of the bleach and also at another location, initially equally sensitive. The recovery at the bleached location lagged recovery at the unbleached location; but even in the bleached location, the return of sensitivity was rapid.5. Recovery of sensitivity after half-field bleaches was measured in the bleached and unbleached halves of the receptive field. Recovery in the bleached half lagged that in the unbleached half.6. A comparison between the effects of a small-spot bleach and a half-field bleach of the same strength show that the duration of dark adaptation depends on the area of the bleach.

“…B. BONDS AND C. ENROTH-CUGELL .adaptation'; Rushton, 1965a), the receptive field centre sums laterally adaptive effects, although such summation is rarely perfect (Green, Tong & Cicerone, 1977;Harding, 1977). Here we present experiments designed to reveal lateral adaptive interactions within retinal ganglion cell receptive field centres as a result of bleaching.…”

Section: Introductionmentioning

confidence: 99%

Spatial consequences of bleaching adaptation in cat retinal ganglion cells.

Bonds¹,

Enroth‐Cugell²

1981

SUMMARY1. Experiments were conducted to study the effects of localized bleaching on the centre responses of rod-driven cat retinal ganglion cells.2. Stimulation as far as 20 from the bleaching site yielded responses which were reduced nearly as much as those generated at the bleaching site. Bleaching in the receptive field middle reduced responsiveness at a site 10 peripheral more than bleaching at that peripheral site itself.3. The effectiveness of a bleach in reducing centre responsiveness is related to the sensitivity of the region in which the bleach is applied.4. Response reduction after a 0.20 bleach followed the same temporal pattern for concentric test spots of from 0-2 to 1.80 in diameter, implying a substantially uniform spread of adaptation within these bounds.5. A linear trade-off between fraction of rhodopsin and area bleached over a range of 8: 1 yields the same pattern of response reduction, implying that the non-linear nature of bleaching adaptation is a property of the adaptation pool rather than independent photoreceptors.