The retina of the nine-banded armadillo (Dasypus novemcinctus)

Abstract

The retina of the nine-banded armadillo is described using light microscopy and transmission electron microscopy. In general the retina of the nine-banded armadillo is similar in structure to the retinas of other mammals. No identifiable cone type photoreceptors are present. In some armadillos there are tubular inclusions in the nuclei of many of the retinal pigment epithelial cells. Many nuclear inclusions have an associated vacuole, which is observable with the light microscope. The incidence of vacuolated retinal pigment epithelial cell nuclei is similar in the dorsal and ventral, nasal and temporal retina and in both eyes of an individual. Subretinal visual cells are present in the eyes of all nine-banded armadillos. The number of subretinal visual cells present varies between individuals, but is similar in different retinal locations and in both eyes of an animal. Ectopic synaptic ribbons are very common in the photoreceptor terminals of the nine-banded armadillo, and the amount of synaptic ribbon material in each photoreceptor terminal varies considerably. Some armadillos were maintained in constant light for five days, constant dark for five days, or constant dark for five days followed by exposure to light for two hours. The incidence of vacuolated retinal pigment epithelial cell nuclei and of subretinal visual cells, and the number and length of synaptic ribbons in the photoreceptor terminals did not change noticeably in the eyes of armadillos maintained under any of these conditions.