The cellular mechanism underlying the directional selectivity of retinal ganglion cells in many species is as yet poorly understood. A hypothesis postulates that this directionality is due to a spatially-asymmetric inhibitory input onto the ganglion cells. This asymmetric input would prevent responses to motions in the null-direction, but would not prevent preferred-direction responses. An alternative hypothesis assumes that preferred-null discrimination occurs in the dendrites of amacrine cells, which then relay this information to ganglion cells. These dendrites would provide a spatially asymmetric excitatory input onto the ganglion cell. Nonlinear processes in the dendrites would produce null-direction inhibition and facilitation of the responses to preferred-direction motions. The neurotransmitter GABA is believed to mediate the inhibition in both hypotheses. This grant proposal describes three experiments that will scrutinize these two hypotheses. The experiments will use ON-OFF directionally selective ganglion cells of turtles and rabbits. 1) The first experiment will test whether GABAergic inhibition via GABA-A receptors is necessary for directional selectivity. 2) The second experiment will test whether direct ganglion-cell inhibition is necessary for directional selectivity. 3) The third experiment will determine whether the excitatory receptive field reflects the spatial asymmetry necessary for directional selectivity. This project should contribute to the understanding of how biophysical mechanisms underlie directional selectivity. Furthermore, the study of retinal directional selectivity will have an impact on the understanding of eye-movement control.
| Segovia, Yolanda; Perez, Rosa María; Grzywacz, Norberto Mauricio et al. (2012) Does Müller Cell Differentiation Occur Prior to the Emergence of Synapses in Embryonic Turtle Retina? J Life Sci (Libertyville) 2012:1200-1205 |
| Cao, Xiwu; Merwine, David K; Grzywacz, Norberto M (2011) Dependence of the retinal Ganglion cell's responses on local textures of natural scenes. J Vis 11: |
| Ray, Aditi; Sun, Gerald J; Chan, Leanne et al. (2010) Morphological alterations in retinal neurons in the S334ter-line3 transgenic rat. Cell Tissue Res 339:481-91 |
| Barraza, Jose F; Grzywacz, Norberto M (2008) Speed adaptation as Kalman filtering. Vision Res 48:2485-91 |
| Lee, Eun-Jin; Padilla, Monica; Merwine, David K et al. (2008) Developmental regulation of the morphology of mouse retinal horizontal cells by visual experience. Eur J Neurosci 27:1423-31 |
| Chatterjee, Susmita; Merwine, David K; Amthor, Franklin R et al. (2007) Properties of stimulus-dependent synchrony in retinal ganglion cells. Vis Neurosci 24:827-43 |
| Grzywacz, Norberto M; Amthor, Franklin R (2007) Robust directional computation in on-off directionally selective ganglion cells of rabbit retina. Vis Neurosci 24:647-61 |
| Lee, Eun-Jin; Merwine, David K; Padilla, Monica et al. (2007) Choline acetyltransferase-immunoreactive neurons in the retina of normal and dark-reared turtle. J Comp Neurol 503:768-78 |
| Liu, Fan; Merwine, David K; Grzywacz, Norberto M (2006) Statistically robust detection of spontaneous, non-stereotypical neural signals. J Neurosci Methods 153:299-311 |
| Grzywacz, Norberto M; Zucker, Charles L (2006) Modeling Starburst cells' GABA(B) receptors and their putative role in motion sensitivity. Biophys J 91:473-86 |
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