Rodent retinal microcirculation and visual electrophysiology following simulated microgravity. (May 2020)

• Record Type: Journal Article
• Authors: Dai, Xufeng; Ye, Siming; Chen, Xiaoping; Jiang, Ting; Huang, Haixiao; Li, Wenjiong; Yu, Hongqiang; Bao, Jinhua; Chen, Hao
• Is Part Of: Experimental eye research. Volume 194(2020)
• Publication Date: 2020-05
• Subjects: Microcirculation -- Microgravity -- Oscillatory potentials -- Retina -- Rodent -- Space -- Visual evoked potential; ICP intracranial pressure -- VEP visual evoked potential -- ERGs electroretinograms -- OPs oscillatory potentials -- O2 second OP -- FFA fundus fluorescein angiography -- OCT optical coherence tomography -- TS15D tail-suspended for 15 days -- TS30D tail-suspended for 30 days -- TS30D + R30D tail-suspended for 30 days followed by returning to normal position for 30 days -- HE hematoxylin and eosin -- PBS phosphate buffered saline -- PNA peanut agglutinin -- DAPI 4′, 6-diamidino-2-phenylindole -- DNase I deoxyribonuclease I -- TdT terminal deoxynucleotidyl transferase -- OPL outer plexiform layer -- GCL ganglion cell layer -- IPL inner plexiform layer -- INL inner nuclear layer -- ONL outer nuclear layer -- OS/IS outer/inner segment -- PD papilla diameter -- RPE retinal pigment epithelium; Ophthalmology -- Periodicals; Eye -- Periodicals; Œil -- Périodiques; Ophthalmology; Periodicals; Electronic journals; 612.8405
• DOI: 10.1016/j.exer.2020.108023
• Languages: English
• ISSNs: 0014-4835

Abstract

Abstract: How the absence of gravity affects the physiology of human beings is generating global research interest as space exploration, including missions aboard the International Space Station, continues to push boundaries. Here, we examined changes in retinal microcirculation and visual electrophysiology in mice suspended by their tails to simulate the cephalad movement of blood that occurs under microgravity conditions. Tail suspension was performed with a head-down tilt with a recommended angle of 30°. Mice in the control groups were similarly attached to a tether but could maintain a normal position. Morphologically, the 15-day tail-suspended mice showed retinal microvascular dilation, tortuosity, and a relatively long fluorescence retention; however, the average diameter of the major retinal vessels was not notably changed. In addition, optical coherence tomography showed their optic nerve head had an increased diameter. However, the mice could adapt to the change, with microcirculation and the optic nerve head recovering following 30-day tail suspension. Expression of rhodopsin and cone-opsins was not notably changed, and no retinal apoptotic-positive cells were detected between 15- and 30-day tail suspensions. Moreover, the three experimental groups of suspended mice showed normal retinal layers and thickness. Functionally, following 15-day tail suspension, scotopic electroretinograms showed a decline in the oscillatory potentials (OPs), but not in the b wave; simultaneously, the peak time of flash visual evoked potential component N1 was delayed compared to its baseline and the time-matched control. Following 30-day tail suspension, the OPs (O2) amplitude recovered to approximately 97% of its baseline or 86% of the time-matched control level. By simulating cephalad shifting of blood, short-term tail suspension can affect rodent retinal microcirculation, the optic nerve head, and disturb visual electrophysiology. However, the change is reversible with no permanent injury observed in the retina. The mice could adapt to the short-term change of retinal microcirculation, indicating new conditions that could be combined with, or could enhance, simulated microgravity for further studying the impact of short- or long-term outer space conditions on the retina. Highlights: The effects of simulated microgravity on retinal microcirculation remain unknown. The effect of simulated and real microgravity conditions on the optic nerve head is similar. The changes in the electroretinograms may be related to abnormal retinal microcirculation. However, the changes are reversible with no permanent injury observed in the retina. Retinal changes must be studied under simulated microgravity and other space-like conditions.