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

Abstract

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(-5) lm/m2). In the dark-adapted state a small off-response of long latency (40-100 ms at 10(2) quanta.s-1.microns-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 (10(5) quanta.s-1.microns-2). 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 (10(6) quanta.s-1 microns-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.

Glycinergic and GABAergic control of intensity-response function of frog ERG waves under different conditions of light stimulation

“…Thus we might suggest that although it is not solely responsible for this phenomenon both the inhibitory systems play a role in its generation. Suppression of the OFF responses of ganglion cells mediated by rods in the same intensity range (2.5±3 log units above threshold) has been demonstrated in cat (Gunther & Zrenner 1990) and tiger salamander retina (Hensley et al 1993). However suppression of ganglion cells ON responses has not been found which is in accordance with our observation for the ERG b-wave.…”

ERG OFF response in frog retina: light adaptation and effect of 2‐amino‐4‐phosphonobutyrate

“…The descendent part of the first component, obtained with stimulus intensities about 2.5 log units above the b-wave threshold, might be related to the much slower rate of recovery of rods hyperpolarization after brighter stimuli (Norman & Werblin 1974, Wu 1987. Suppression of the offset responses of ganglion cells mediated by rods in the same intensity range (2.5-3 log units above threshold) has been demonstrated in cat (Olsen et al 1986, Gunther & Zrenner 1990) and tiger salamander retina (Hansley et al 1993). However, suppression of the responses of ONand ON-OFF ganglion cells to light onset has not been found.…”