The topography of cytogenesis in the developing retina of the cat

We have studied the pattern of cytogenesis in the developing retina of the cat, by observing mitotic cells in sections and whole mounts of the retinae of animals between the ages of E (embryonic day) 29 and P (postnatal day) 20. The whole mounts were prepared with the mitotic or ventricular layer uppermost; all of the mitotic cells in this layer could then be surveyed. In retinae from animals up to E46, mitotic cells were present in the ventricular layer at densities of 1000 to 3000 cells/mm2, and their density did not vary consistently with position in the retina. Thus cell division occurs throughout the retina at these ages, with an approximately constant spatial density. By E50, cytogenesis begins to cease and there is a significant pattern to the cessation. Initially, mitotic activity ceases over a small region of retina at the site of the developing area centralis. The nonmitotic area then increases with age, comprising the central 30 to 50% of the retina at birth and the whole of the retina by P10. The pattern of cessation of cytogenesis is closely coincident in space and time with the development of the outer plexiform layer and the maturation of the ganglion cell layer described in previous studies. These patterns presumably contribute to the regional variations in structure apparent in the adult retina.