| Description |
Due to its unique structural layers, and easy accessibility, the retina provides an excellent model for the study of neuronal circuitry. Light gathered by photoreceptors is neuronally processed through horizontal, amacrine, and bipolar cells (BCs) and is then transmitted to retinal ganglion cells (RGCs), which are the sole source of visual information for the central nervous system. There are ~40 different types of RGCs in the mammalian retina, with each type having different dendritic patterns and synaptic connections, allowing them to select for distinct visual features such as direction, contrast, and color. While it is known that RGCs are postsynaptic to BCs, the types of BCs involved in these circuits are not known. To elucidate the presynaptic inputs of RGCs, our lab uses transgenic mice which have Cre driven by RGC type-specific promoters. We establish that two of these types, known as BD- and J-RGCs, are excellent models for function-specific circuit tracing. We use a dual DNA recombinase system, combined with a protein that crosses synapses, to label the circuits of BD- and J-RGCs fluorescently. Using this, we identified the BC types that provide input into BD- and J-RGCs. During this process, we discovered and characterized a novel BC type. This BC, which we call the Aii-BC, has synaptic inputs and outputs unlike any other BC previously described. Additionally, while all other BCs only release the glutamate, the Aii-BC likely releases both glutamate and glycine. Our lab has previously iv shown that two different proteins are involved in neurite development of RGCs, NMDA receptors, and the T-cell receptor-associated protein CD3ζ. The genetic silencing of either of these genes modifies the BC input to BD- and J-RGCs, while the Aii-BC appears to play a compensatory role following these changes. Additionally, we developed a virtual reality behavior test that can essay a variety of different aspects of visual perception, including color/luminance and motion detection. We found that the quality of their performance is affected by the complexity of the visual target, and their ability to navigate. Importantly, mice retained the memory of the visual target for at least three weeks after the end of their training. |
