Horizontal cells communicate primarily with which retinal elements?

• A. Photoreceptors and bipolar cells
• B. Ganglion cells
• C. Amacrine cells
• D. Muller cells

Answer: (A)

Horizontal cells act as lateral interneurons in the outer retina, mainly in the outer plexiform layer, linking photoreceptors to nearby photoreceptors and bipolar cells to create lateral inhibition. They receive input from multiple photoreceptors and provide inhibitory feedback to neighboring photoreceptors, which modulates the amount of signal passed to bipolar cells. This interaction shapes the center-surround receptive fields and enhances contrast and edge detection. Because of this arrangement, their primary communication is with photoreceptors and bipolar cells. They do not directly interface with retinal ganglion cells, and amacrine cells and Müller glia serve other roles in the inner retina or support functions.