Figure 4.

Morphology and tracer coupling pattern of the G₄,G₅, and G₆ ganglion cells. A: Photomicrograph showing a G₄ ganglion cell (asterisk) with medium-sized dendritic arbor. B: Same frame as in panel A, but with focal depth at the level of the proximal INL. The G₄ cell is tracer coupled to amacrine cells with somata that lay in the INL; primary dendrites are indicated by open arrows. C: Photomicrograph showing a tracer-injected G₅ ganglion cell (asterisk). This G₅ cell displays a dense, bushy dendritic arbor, but shows no evidence of tracer coupling. D: Photomicrograph showing a Neurobiotin-injected G₆ ganglion cell (asterisk). This cell displays heterologous coupling to small (arrowheads) and large (arrows) amacrine cell somata displaced to the GCL. E: Photomicrograph shows the same frame as in D, but with focus on the dendritic processes (arrowhead) of the injected G₆ cell. Arrows point to amacrine cell processes costratifying with dendrites of the injected G₆ cell. F: Photomicrograph of another G₆ cell (asterisk) showing that coupled amacrine cells display both thick dendritic (arrow) and thin axonal (arrowheads) processes. Filled arrow (here and in panel H top) points to the amacrine cell whose dendrite is magnified in panel G and drawn in panel H bottom. G: A selected area of panel F is magnified to show the proximal soma/dendritic region of a coupled amacrine cell (filled arrows in panels F and H top). Angled arrows frame the area where a characteristic dendrite/axon transition occurs. H: Top panel shows a camera-lucida drawing of the G₆ ganglion cell (black) shown in panel F as well as somata and processes of coupled amacrine cells (gray). Lower panel shows the proximal dendritic/ axonal arbor of the coupled amacrine cell marked in panels F,H top (arrow). Note that due to a limited tracer flow into coupled cells this drawing shows only a portion of their arbor. I: AG₆ ganglion cell whose soma is elongated, but otherwise shares all other features of G₆ cells. Arrowheads label injected ganglion cell dendrites, whereas arrows point to dendritic processes of coupled amacrine cells. J: Camera-lucida drawings display cell bodies and proximal dendritic/axonal areas of amacrine cells coupled to elongated G₆ ganglion cells. Soma/ dendritic morphology of these amacrine cells are identical to amacrine cells coupled to other G₆ ganglion cells (see panels D–H). Note that due to a limited tracer flow into coupled cells this drawing shows only a portion of their arbor. a, axonal process. Scale bars = 100 μmin A–E,I–J; 200 μm in F,H; 150 μminG.