Bipolar Cells of the Mouse Retina
In the retina, bipolar cells are situated between photoreceptors and ganglion cells. They act, directly or indirectly (via amacrine cells), to transmit signals from the photoreceptors to the ganglion cells. Each bipolar cell can synapse with either rods or cones, but not both (hence the name “bipolar”). There are ten distinct types of cone bipolar cells in the mammalian retina, and only one type of rod bipolar cell (stained red in the image above).
Bipolar cells can be further classified as “ON” or “OFF” based on how they react to changes in the release of glutamate by photoreceptors. When light hits a photoreceptor cell, the photoreceptor hyperpolarizes and releases less glutamate. ON bipolar cells (stained blue in the image above) will respond to this change by depolarizing and OFF bipolar cells will respond by hyperpolarizing.
Image by Luca Della Santina, courtesy of Rachel Wong, University of Washington.