Adaptation, the ability of the eye to adjust its sensitivity to match the available light, is a very important aspect of normal healthy vision. When the eye does not adapt properly it becomes impossible to see in both dim and bright light. One of the difficulties of dealing with visual problems of this sort is the fact that the whole process of adaptation is rather poorly understood. From studies of cellular responses in cold- blooded vertebrates we know that exposure to light modifies the response properties of both photoreceptors and second order cells. Studies on fish, frogs and turtles show that rod and cone photoreceptors are strongly adapted by background light. However, an increasing body of evidence indicates that in the eyes of mammals photoreceptor adaptation is of limited importance in controlling the sensitivity of rod and possibly also cone driven responses. One of the objectives of this proposal is understanding how these latter network mechanisms cause thresholds to elevate, responses to speed-up, and dynamic range to be modified. The present grant proposes using the isolated retina of the rat to study these processes. By making intraretinal recordings the following questions about adaptation will be addressed: a) How do the photoreceptors and proximal retina light and dark adapt in the isolated rat retina? b) Where are the sites at which backgrounds and bleaches modify retinal sensitivity? c) Is it possible to evoke responses from the isolated retina by polarizing the rod synaptic terminals with transretinal current? d) What types of cells are stimulated by transretinal currents? e) Might the gain of synaptic transmission from photoreceptors to bipolar cells be strongly dependent on photoreceptor hyperpolarization in such a way that the hyperpolarization caused by a bleach or a background would greatly reduce the transmission of signal to the second order cells and so cause postreceptor adaptation? f) What does the isolated mouse retina reveal about the physiological abnormalities in MDX CV3 mice and other transgenic mice? We believe that such studies can contribute to our understanding of the synaptic mechanisms controlling retinal sensitivity in the mammalian retina. From such understanding can come a better basis for trying to treat diseases in which rod photoreceptors and adaptational mechanisms are compromised.
| Winkler, B S; Kapousta-Bruneau, N; Arnold, M J et al. (1999) Effects of inhibiting glutamine synthetase and blocking glutamate uptake on b-wave generation in the isolated rat retina. Vis Neurosci 16:345-53 |
