Abstract
Purpose: :
Bipolar cells play major roles in visual signal transmission from photoreceptors to ganglion cells, and can be further subdivided into 9–13 distinct types based on their morphology and physiology. Color pathway has been extensively studied in the primate, but the circuitry for color processing in other mammals is still obscure, especially in the bipolar cell level. This study was aiming to morphologically identify blue cone bipolar cells in the rabbit retina.
Methods: :
For finding the blue cone bipolar cells, Neurobiotin injected bipolar cells in the dorsal side of the whole mount rabbit retina were simultaneously label all cone cells by peanut agglutinin and outer segments of the blue cones by the antibody against S–cone opsin to verify their cone selectivity. Exclusive S cone connecting bipolar cells were identified to be the blue cone bipolar cells.
Results: :
We found that all narrow–field and medium–field types of bipolar cells have no selective cone connection. However, there is one type of wide–field OFF cone bipolar cells with S cone selectivity was identified. This type of cells gives rise 4–5 branchless primary dendrites to specifically contact S cone pedicles. In addition, some C–type like horizontal cells also showed no S cone selectivity.
Conclusions: :
The color encoding bipolar cells in the rabbit retina are apparently different from the ones found in primate and mouse retinas. Therefore, the color information processing pathways in mammalian retinas may not be evolutionary conserved as previously thought.
Keywords: bipolar cells • color vision