Electron microscopic analysis of amacrine and bipolar cell inputs on Y-, X-, and W-cells in the cat retina

In the cat retina, bipolar and amacrine cell inputs were analyzed electron microscopically in 5 ganglion cells (two Y-cells, two X-cells and one W-cell) that were well-isolated and had clear morphological features. For Y- and X-cells, subtypes of a and b were further identified according to the sublamina of the inner plexiform layer in which their dendrites extended. Y-a and Y-b ganglion cells had large somas, thick axons, and several thick dendrites that branched extensively with a large dendritic field. X-a and X-b cells had medium-sized somas, medium-sized axons and extremely narrow dendritic fields. The W-cell studied had a medium-sized soma, a medium-sized axon, and extremely thin dendrites that extended widely. For each of the 5 ganglion cells, ultrathin serial sections were made to study relative occurrence of amacrine and bipolar synapses in whole length of dendrites. About 50% of the terminals were bipolar in the Y-a and Y-b cell dendrites, 36-38% in the X-a and X-b cell dendrites, whereas only 19.7% were bipolar in the W cell dendrites. Bipolar terminals tended to make synaptic contacts with the distal dendrites of Y- and W-cells.