Development of neuropeptide Y immunoreactive amacrine and ganglion cells in the pre- and postnatal cat retina.

In the adult cat, neuropeptide Y (NPY) immunoreactivity (IR) is found within a subgroup of gamma-type ganglion cells and a large group of regularly arrayed amacrine cells. To examine the development of these two cell groups, we charted the appearance and maturation of neuropeptide Y immunoreactivity in the pre- and post-natal cat retina. Neuropeptide Y immunoreactivity is first observed at the central retina within the ganglion cell layer on embryonic day 46, and immunoreactivity within amacrine cells of the inner plexiform layer is present by E50. The number of immunoreactive profiles reaches the adult level in the amacrine population first (around P7), while the ganglion cell population shows a protracted development, with new cells being added until the third postnatal week. NPY-immunoreactive profiles in the ganglion cell layer were confirmed to be ganglion cells by retrograde labeling in both pre- and post-natal animals. Thus, neuropeptide Y-immunoreactive ganglion cells and amacrine cells attain their mature state with very different timecourses, although both cell groups initially follow a central to peripheral pattern of development. Interestingly, NPY expression within the ganglion cell population is temporally correlated with retinal synaptogenesis in the inner plexiform layer. As in the adult cat, NPY-immunoreactive ganglion cells never show a regular distribution during development, while NPY-IR amacrine cells are always distributed regularly even at the earliest ages. The prenatal presence of a regular distribution of NPY-IR amacrine cells suggests that these cells may participate in establishing the ganglion cell mosaics that appear during postnatal development.