Edge Detection and Center-Surround Receptive Fields

ON and OFF responses of bipolar cells result from the presence of different glutamate receptors in the two cell types. OFF bipolar cells possess KA and AMPA-type ionotropic glutamate receptors, but not NMDA receptors (Thoreson and Witkovsky, 1999). Thus, like horizontal cells, the synapse from cones to OFF bipolar cells is sign-conserving, that is, light-evoked hyperpolarization of the cone reduces the depolarizing influence of AMPA/KA receptors thereby causing the OFF bipolar cell to hyperpolarize. 

Many amacrine cells have relatively dedicated functions. Some examples include  

radially symmetric starburst amacrine cells help create directional selectivity in directionally selective ganglion cells (Taylor and Vaney, 2003). 

Dopaminergic amacrine cells with widespread dendritic arborizations increase release of dopamine in response to increases in global illumination. Dopamine diffuses throughout the retina to influence cells as far away as the RPE. The increased release of dopamine by light modifies cell function to optimize retinal responses in dayhght (Witkovsky, 2004). 

All amacrine cells transfer rod signals from rod bipolar cells to ganglion cells (Bloomfield and Dacheux, 2001). 

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Edge Detection and Center-Surround Receptive Fields... 

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