Retinal mechanisms of visual adaptation in the skate.

Abstract

Electrical potentials were recorded from different levels within the skate retina. Comparing the adaptive properties of the various responses revealed that the isolated receptor potential and the S-potential always exhibited similar changes in sensitivity, and that the b-wave and ganglion-cell thresholds acted in concert. However, the two sets of responses behaved differently under certain conditions. For example, a dimly illuminated background that had no measurable effect on the sensitivities of either of the distal responses, raised significantly the thresholds of both the b-wave and the ganglion cell responses. In addition, the rate of recovery during the early, "neural" phase of dark adaptation was significantly faster for the receptor and S-potentials than for the b-wave or ganglion cell discharge. These results indicate that there is an adaptive ("network") mechanism in the retina which can influence significantly b-wave and ganglion cell activity and which behaves independently of the receptors and horizontal cells. We conclude that visual adaptation in the skate retina is regulated by a combination of receptoral and network mechanisms.

Ambient Light Regulates Sodium Channel Activity to Dynamically Control Retinal Signaling

“…The retina adapts by adjusting its sensitivity to mean light intensity and contrast. Adaptation to mean light intensity occurs in both photoreceptors and the retinal network, whereas contrast adaptation only occurs in the retinal network (Green et al, 1975;Naka et al, 1979;Green and Powers, 1982 of network adaptation to both mean light intensity and contrast (Green et al, 1975;Naka et al, 1979;Shapley and Enroth-Cugell, 1984;Smirnakis et al, 1997;Rieke, 2001;Baccus and Meister, 2002;Page-McCaw et al, 2004); however, the cellular mechanisms that mediate these forms of adaptation are poorly understood. Our findings suggest that sodium channels, found in a subset of bipolar cells, regulate network adaptation by increasing retinal sensitivity to both mean intensity and contrast in dimlight conditions but not in bright conditions when they were inactivated by light-evoked dopamine release.…”

“…Adaptation to the mean intensity of ambient light occurs in rod and cone photoreceptors (Pugh et al, 1999;Fain et al, 2001) and at sites in the retinal network postsynaptic to photoreceptors ( Fig. 1) (Green et al, 1975;Naka et al, 1979;Green and Powers, 1982;Shapley and Enroth-Cugell, 1984;Page-McCaw et al, 2004;Dunn and Rieke, 2006). Contrast adaptation occurs in the retinal network but not in photoreceptors (Shapley and Enroth-Cugell, 1984;Smirnakis et al, 1997;Dunn and Rieke, 2006).…”

“…In the retina, sodium channels in a subset of bipolar cells boost light-evoked EPSPs (L-EPSPs) in dim-light conditions and amplify the excitatory drive to ganglion cells (Ichinose et al, 2005). Because bipolar cells have been implicated as sites of network adaptation (Green et al, 1975;Naka et al, 1979;Shapley and Enroth-Cugell, 1984;Smirnakis et al, 1997;Rieke, 2001;Baccus and Meister, 2002;PageMcCaw et al, 2004), the voltage-gated sodium channels in bipolar cells may regulate network adaptation by increasing retinal sensitivity in dim-light conditions (Fig. 1, left).…”

Signal transmission from rods to ganglion cells in rat retina after bleaching a portion of the receptive field.

“…Following weaker exposures two factors would tend to make the differences smaller. On the exposed side pigment regeneration would proceed more rapidly (Perlman, 1978) and the desensitizing effects of bleached pigment, which vary logarithmically, would be less prominent (Dowling, 1960;Rushton, 1961;Green, Dowling, Siegel & Ripps, 1975). Thus, one would expect that recovery on both sides would be neurally controlled to a larger extent.…”

ADAPTIVE PROPERTIES OF THE b-WAVE AND THE PIII IN THE PERFUSED ISOLATED CARP RETINA

“…The initial fast and subsequent slow retinal adaptation has been known for many years.The fast`neural adaptation'was considered by some researchers to be related to the activity in the neural network,while the slow`photochemical adaptation'was related to the regeneration of the visual pigment (DOWLING,1963(DOWLING, , 1967BROWN and WATANABE,1965).However,recent investigations seem to prove that at least part of the fast process of dark adaptation occurs at the photoreceptors (FRANK,1971;DOWLING and RIPPS,1972;HOOD et al,1973;GREEN et al,1975),and that substantial slow recovery of sensitivity is observed even in isolated retinas,which should have little or no rhodopsin regeneration (ERNST and KEMP,1972;HOOD et al,1973). GRABOWSKI and PAK(1975),in their study on the axolotl rod responses,divided the course of dark adaptation into a fast processes have not been fully studied in the isolated retina of carp,which is one of the common materials for retina research,the present study was designed 1)to produce prolonged recordings of stable electroretinograms(ERGs)from the isolated carp retina by using the perfusion method,2)to explore the properties of carp ERGs during light and dark adaptation,3)to try to find out whether the fast and/or slow adaptation occurs at the photoreceptors,and 4)to elucidate the adaptive properties of the photoreceptors in case the fast and/or slow adaptation should occur in them.…”