Fundamental Studies of Mouse Amacrine Cells

Abstract

Vision begins in the retina where information about the salient features of an image projected on a mosaic of rod and cone photoreceptors is extracted and digitally encoded in neural impulses that are conducted by the axons of the optic nerve to the brain where the message is decoded and interpreted as a visual perception. In spite of the enormity of all that has been learned over the thousands of years that vision has been philosophically contemplated, behaviorally evaluated and experimentally interrogated, the cellular mechanisms that underlie retina function are still not known. An essential step in understanding how any complex machine works is to have a parts list and to understand what each part does. In the case of the amacrine cell family, of its 20 to 30 different subtypes only three have been have been functionally characterized. My research has sought to further our understanding of this diverse and largely unexplored class of retinal cell types by examining the mechanisms that give rise to light-evoked signals in two types of amacrine cells in the mouse retina. One of these is the dopaminergic amacrine cell (DAC), the other is an un-named amacrine cell type that to my knowledge has not been previously identified or examined using electrical recording and will henceforth be referred to as the small bistratified amacrine cell (SBAC). I have succeeded in doing this by utilizing a BAC-transgenic mouse line (GENSAT d2dr-GFP) in which the promoter for dopamine receptor 2 (DR2) drives selective expression of GFP in two populations of amacrine cells (DACs and SBACs) that can be distinguished from each other on the basis of soma size as discussed below. The fluorescently labeled cells were visualized and targeted for whole cell recording using multi-photon laser scanning fluorescence microscopy. The functional properties of the two GFP labeled amacrine cell types were characterized in separate studies described below.