Motion Detection Pathway Search: Investigation of ON Bipolar Cell Subtypes that provide Synaptic Inputs to Starburst Amacrine Cells in the Mouse Retina
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The visual system utilizes parallel processing to simultaneously process multiple aspects – shape, color, textures, motion, etc. – of an external target by means of different pathways. Bipolar cells (BC) – transmit information from photoreceptors to amacrine cells and ganglion cells in the retina – are integral to parallel processing in all vertebrate visual systems. Since parallel processing in the retina is complex, further investigation is required. The purpose of this study is to elucidate the significance of XBC, Type 6, and Type 7 BCs for perceiving motion within mice retinas. Immunohistochemistry was performed to visualize C-terminal binding protein 2 (CtBP2) and the three bipolar cells at the 2nd choline acetyltransferase (ChAT) band – band of starburst amacrine cells’ dendrites that are crucial to computing direction selectivity. The fluorescent antibody markers for the BCs, CtBP2, and ChAT bands were then viewed and photographed under a confocal microscope. The images were analyzed on ImageJ with Manders colocalization coefficients to determine the number of colocalized puncta near ChAT. The colocalized puncta near ChAT were counted in order to estimate an average percent of inputs received by ChAT from the three bipolar cells: ChAT was estimated to receive about 20%, less than 1%, and 18% of XBC, Type 6, and Type 7 BCs outputs, respectively. Nonetheless the sample size of the BCs was small, thus the values indicated may not be accurate. In conclusion, this study found that Type 7 and XBC BCs may have important inputs to the ChAT band, while Type 6 BCs may have little to no inputs to processes occurring at the ChAT band.