Retinal Anatomy of a Diurnal Laboratory Rodent, the Nile Grass Rat Arvicanthis Niloticus

Abstract

Purpose: : Diurnal animals with cone-dominant vision might better model human retinal diseases involving cone loss than the nocturnal rodents rats and mice (with retinas having >97% rods). This study describes the anatomical features of the retina of this new model, the Nile grass rat, Arvicanthis niloticus.

Methods: : Serial sections (8µm thick) collected from 6 adult, paraffin-embedded Nile grass rat eyes and 6 additional retinas prepared as wholemounts were reacted with a panel of antibodies, classically used for retinal investigations in mammals, and examined by confocal microscopy.

Results: : The Nile grass rat retina covered 42 mm² average area and was only 140 µm thick in the center, thinning even further toward its periphery. The outer nuclear layer was 5 rows thick centrally, and the outermost two rows consisted of cone cell bodies (estimated total number = 1.55x10⁶/retina). Cones accounted for over 40% of the total photoreceptor population. As in other rodents, rods and cones expressed recoverin but not calbindin, calretinin or PKCα. Horizontal cells did not express calretinin, but were positive to calbindin and parvalbumin (as in diurnal gerbilidae, but not rat or mouse). Only rod (PKCα+) and two types of OFF (recoverin+) cones bipolar cells could be defined. PKCα, calbindin, calretinin and GABA antibodies labeled various types of displaced and non-displaced amacrine cells. Parvalbumin+ amacrine cells were non- detectable. Dopaminergic (TH+) and most starburst (ChAT+) amacrine cells were localized in the inner nuclear layer. Antibodies to GFAP and glutamine synthetase respectively labeled astrocytes in the nerve fiber layer and glial Muller cells throughout their full extent.

Conclusions: : Although rod-dominated, the Nile grass rat retina exhibits many morphological features and post-receptoral cell characteristics found in other diurnal rodents (such as guinea pig, gray squirrel and Mongolian gerbil). It is very similar to the near-perifoveal human retina; and might therefore be a suitable model to elucidate various causes of blindness and test potential therapies.

Keywords: retina • anatomy • immunohistochemistry