Limb remote ischemic conditioning (LRIC) provides a physiologic strategy for harnessing the body’s endogenous protective capabilities against injury induced by ischemia–reperfusion in the central nervous system. The aim of the present study was to determine if LRIC played a role in protecting the retina from ischemia–reperfusion injury. A total of 81 adult male Sprague-Dawley rats were randomly assigned to sham and ischemia/reperfusion with or without remote LRIC arms. The retinal ischemic model was generated through right middle cerebral artery occlusion (MCAO) and pterygopalatine artery occlusion for 60 min followed by 1, 3, and 7 days of subsequent reperfusion. LRIC was conducted immediately following MCAO by tightening a tourniquet around the upper thigh and releasing for three cycles. Paraffin sections were stained with hematoxylin and eosin in order to quantify the number of cells in retinal ganglion cells (RGCs) layer throughout the duration of the study. Cellular expression of glial fibrillary acidic protein (GFAP) was detected and examined through immunohistochemistry. Protein expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) was also analyzed by Western blot techniques. Our study demonstrated that the loss of cells in RGC layer was attenuated by LRIC treatment at 3 and 7 days following reperfusion (P < 0.05). Immunohistochemistry studies depicted a gradual increase (P < 0.05) in GFAP levels from day 1 through day 7 following ischemia and subsequent reperfusion, whereas LRIC reduced GFAP levels at 1, 3, and 7 days postreperfusion. In addition, LRIC increased the expression of Nrf2 and HO-1 at day 1 and 3 following ischemia/reperfusion. This particular study is the first remote conditioning study applicable to retinal ischemia. Our results strongly support the position that LRIC may be used as a noninvasive neuroprotective strategy, which provides retinal protection from ischemia–reperfusion injury through the upregulation of antioxidative stress proteins, such as Nrf2 and HO-1.

This study investigated the anatomical consequences of a photoreceptor toxin, iodoacetic acid (IAA), in the rabbit retina. Retinae were examined 2 weeks, 1, 3, and 6 months after systemic IAA injection. The retinae were processed using standard histological methods to assess the gross morphology and topographical distribution of damage, and by immunohistochemistry to examine specific cell populations in the retina. Degeneration was restricted to the photoreceptors and was most common in the ventral retina and visual streak. In damaged regions, the outer nuclear layer was reduced in thickness or eliminated entirely, with a concomitant loss of immunoreactivity for rhodopsin. However, the magnitude of the effect varied between animals with the same IAA dose and survival time, suggesting individual differences in the bioavailability of the toxin. In all eyes, the inner retina remained intact, as judged by the thickness of the inner nuclear layer, and by the pattern of immunoreactivity for protein kinase C-α (rod bipolar cells) and calbindin D-28 (horizontal cells). Müller cell stalks became immunoreactive for glial fibrillary acidic protein (GFAP) even in IAA-treated retinae that had no signs of cell loss, indicating a response of the retina to the toxin. However, no marked hypertrophy or proliferation of Müller cells was observed with either GFAP or vimentin immunohistochemistry. Thus the selective, long lasting damage to the photoreceptors produced by this toxin did not lead to a reorganization of the surviving cells, at least with survival as long as 6 months, in contrast to the remodeling of the inner retina that is observed in inherited retinal degenerations such as retinitis pigmentosa and retinal injuries such as retinal detachment.