The prion protein is required for normal responses to light stimuli by photoreceptors and bipolar cells.

The prion protein, PrP, is well known as an essential susceptibility factor for neurodegenerative prion diseases, yet its function in normal, healthy cells remains uncertain. A role in synaptic function has been proposed for PrP, supported by its cell surface expression in neurons and glia. Here, in mouse retina, we localized PrP to the junctions between photoreceptors and bipolar cells using synaptic proteins EAAT5, CtBP2, and PSD-95. PrP localized most densely with bipolar cell dendrites synapsing with cone photoreceptors. In two coisogenic mouse strains, deletion of the gene encoding PrP, , significantly altered the scotopic and/or photopic electroretinographic (ERG) responses of photoreceptors and bipolar cells. Cone-dominant pathways showed the most significant ERG changes. Retinal thickness, quantitated by high-resolution optical coherence tomography (OCT), and ribbon synapse morphology were not altered upon deletion of PrP, suggesting that the ERG changes were driven by functional rather than structural alterations.