Purpose: In the mammalian retina, signals from rod photoreceptors can reach the ganglion cells only through the cone bipolar cells. Under scotopic conditions, these bipolar cells are thought to receive tonic transmitter release from the partially depolarized cones. Here we test the effects of removing the glutamatergic cone input by monitoring the rod-driven response of retinal ganglion cells in a transgenic mouse that lacks nearly all cone photoreceptors. Methods: Coneless transgenics were generated by linking a cone-specific promoter to the gene for an attenuated diphtheria toxin. The cones die upon differentiation and are absent in the adult except for a few cells at the retinal margin. Ganglion cell signals were recorded from isolated transgenic and wild-type retinae with an extracellular multi-electrode array. Their spatial, temporal, and chromatic response properties were determined by reverse correlation to a flickering checkerboard stimulus. Results: At low mean intensities (520 Φ500nm/μm2/s) the visual responses of coneless and wild-type retinae were very similar. Spatio-temporal response properties from 40 transgenic ganglion cells fell into several functional classes and matched quantitatively the counterparts in the wild-type retina. With increasing light levels, ganglion cells in the transgenic retina retained the rod's spectral sensitivity, confirming the lack of cone input. At a mean intensity of 19,000 Φ500nm/μm2/s most of the cells failed to respond, even to a strong periodic flash, presumably due to rod photoreceptor saturation. Conclusion: Given that the rod signal flows through the cone pathway, it is remarkable that the coneless retina transmits rod responses in essentially the same way as the normal retina. This could be explained if the cone bipolar cell used an adaptation mechanism by which its response becomes independent of the steady rate of glutamatergic input. The results also argue against dramatic developmental aberrations resulting from the early cone ablation. Acute cone ablation experiments will test this possibility further.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience