Histological Changes in the Retina Provoked by Lithium Treatment in a Nocturnal Rodent <b><i>(Lagostomus maximus maximus)</i></b>

Abstract

Daily morphological variations have been previously described in the viscacha (Lagostomus maximus maximus) retina. The aim of this work was to determine the effects of lithium administration on the histology of retinas from this nocturnal rodent since lithium is a drug that has been shown to affect different parameters of circadian rhythms. Adult male viscachas were divided into 2 groups, injected daily with lithium chloride or vehicle for 35 days, and sacrificed at 08:00, 16:00, and 24:00 h for light and electron microscopy studies. The following morphometric parameters were analyzed: the thickness of the photoreceptor layer, the rod outer and inner segments, and the outer nuclear layer. The control group displayed a true daily cycle of photoreceptor renewal similar to that previously reported by us for (untreated) viscachas in their normal habitat. In all lithium-treated groups, we did not observe histological changes in the thickness measurement of the retinal layers. In these groups, the retinas presented ultrastructural characteristics similar to those observed in control animals sacrificed at 24:00 h. In conclusion, chronic lithium administration abolished the daily histological rhythm in the viscacha retina, probably via inhibition of the phagocytosis process in pigment epithelial cells.