Final answer:
Phosphorylation of connexins reduces gap junction communication in retinal neurons, affecting the processing of visual information.
Step-by-step explanation:
The substance that reduces gap junction communication in retinal neurons is d) Phosphorylation of connexins. Gap junctions are specialized connections between cells that allow for the direct transfer of ions and small molecules. They are formed by connexin proteins that span the cell membrane. When connexins are phosphorylated, it can lead to changes in the function and selectivity of the gap junction channels, which can diminish their communicative ability. This process can therefore reduce gap junction communication among retinal neurons, which is crucial for proper vision as gap junctions in the retina help coordinate the activity of neurons responsible for processing visual information.