Box 1 Figure I. Cellular and physiological characterization of genetically identified RGC subtypes in mice.

Populations of On-Off DSGCs can be genetically identified using transgenic mouse lines that express fluorescent markers [such as green fluorescent protein (GFP)] under the control of specific promoters. The GFP expressing cells can be targeted for electrophysiological recordings and/or filling with dye. When one or several of the GFP-expressing cells are filled with dye, their morphology and geometric relationship to one another can then be assessed. Their receptive field tuning to specific light stimuli [in this case stimuli moving along different axes of the retina: superior (up), inferior (down), anterior (toward nasal retina) or posterior (toward temporal retina)] can also be determined. The cells shown here are all tuned for posterior motion. These parameters can then be matched to the axonal connectivity of the GFP expressing cells. The example shown here depicts GFP expressing axons from posterior tuned On-Off DSGCs within the visual thalamus. All RGC axons are labeled in magenta. Image of targeted recording provided by Mihai Manu and Steven Baccus and remaining panels reproduced, with permission, from [36].