A comparative study of neuropeptide Y-immunoreactivity in the retina of dolphin and several other mammalian species

The immunoreactivity of an antibody to neuropeptide Y (NPY) in the retina o f striped (Stenella coeruleoalba) and Fraser (Lagenodelphis hosei) dolphins and several other species was studied and compared. In dolphin retina, mod erate to intense immunostaining was observed primarily in the giant retinal ganglion cells and their dendrite-like processes, while ganglion cells wit h smaller somata were only weakly immunoreactive. In contrast, NPY immunore active cell bodies are mainly located in cells with small somata in the gan glion cell layer and cells resembling amacrine cells in the inner nuclear l ayer in rat retina. Positive immunostaining was also observed in the inner and outer plexiform layers of rat retina, a feature that was not found in d olphin retina; Interestingly, the overall pattern of NPY expression in the retina of dolphin is similar to that in dog but not in rat, or other mammal ian species described previously. One possible explanation is that dolphin and dog are more active by day as compared with rat and cat which are consi dered to be nocturnal. The variable pattern of distribution of NPY observed in different species suggests that NPY plays a unique functional role, for instance; in the demand for higher levels of blood supply for visual conne ctions through the influence of NPV, in the retinal system in a species-dep endent manner probably related to animals' visual behaviors and environment s.