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1000
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Abstract/Summary
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Birds have an excellent visual system, which they depend on in many life situations such as finding food or mating partners. The retina in the eye contains photoreceptors, which can be subdivided into cones and rods active at either high or low light intensities. Among other species, birds have the highest diversity of cones, because in addition to red, green and blue-sensitive cones, also found in the human retina, they can also sense ultraviolet light and possess a so-called double cone, which consists of two subunits and whose function is still unclear. However, how does the eye extract information such as colour, high-resolution details or our own movement from these light signals? To answer this question, we need to understand how the information from the individual photoreceptors is processed within the retina before it is transmitted to the brain.The aim of this project was to provide deeper insights into the neuronal connectivity in the avian retina and to reveal species-specific but also regional differences (central vs peripheral retina). The European robin has a fovea (site of sharpest vision) and therefore offers the opportunity to gain insights into the signal transmission of all the above-mentioned information. Using a multi-beam scanning electron microscope, we were able to generate two high-resolution (nanometre scale) data sets of the European robin retina located in two different regions enabling us to analyse the connectivity of various retinal neurons. A comparison with previous results from the chicken identified for example a high similarity between bipolar cell types but substantial differences in their individual connectivity to cones, which might reflect an adaptation to their different lifestyles. The majority of these bipolar cell types but also half of the analysed horizontal cell types predominantly contacted double cones, sometimes even highly selective only one of its subunits. A comparison with already functionally characterized retinas such as the turtle retina might lead to the speculation that double cones are responsible for the transmission of non-colour-specific information such as movement or highly detailed information whereas colour vision is processed through the individual single cones.The results of this project provide important insights into visual information processing in the avian retina and a comprehensive comparison with other vertebrates will provide important insights into evolutionary developments of the retina. Detailed functional analysis of the avian retina are urgently needed to link the identified circuits to specific visual information and also to further characterize the role of double cones in the retina.
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