An active role for bipolar cells in processing synaptic signals in the retina

How diverse elements of parallel neuronal circuits interact to extract, organize and convey relevant information is a fundamental question in neurobiology. The intricate anatomical and functional organization of multiple parallel synaptic circuits in the CNS makes this investigation a daunting task. For example, in the retina, there are more than 60 neuronal cell types which allow the retina to transduce, process and parse visual images into multiple channels before this information is conveyed to higher visual centres. To this end, transgenic mouse lines in which single types neurons are labelled with fluorescent proteins (FPs), allow one to begin to investigate complex networks more systematically. Here we seek to understand the biophysical mechanisms by which bipolar cells, which bridge the photoreceptors to output ganglion cells, transform simple graded responses of photoreceptors into complex spiking patterns of ganglion cells. Like photoreceptors, bipolar cells also respond to light in a graded fashion. However, in our recent studies indicate that properties intrinsic to the bipolar cells may play an important role in shaping their output properties. Hence, instead of passively conveying information to ganglion cells, bipolar cells process the visual information before they convey it to ganglion cells. To test this idea we will assess the input and output characteristics of the different types of bipolar cells in the mouse retina using state of the art imaging techniques combined with conventional electrophysiological methods. Together, these studies will reveal the properties of the excitatory circuits in retina with unprecedented detail. Such detailed understanding of defined circuits will shed light on how the retina decomposes complex visual images into simple features before they are relayed to higher visual centres.