CHOROIDAL READAPTATION TO GRAVITY IN RATS AFTER SPACEFLIGHT AND HEAD-DOWN TILT

To determine when choroidal structures were restored after readaptatio n to Earth gravity or orthostatic position, fine structure and protein distribution were studied in rat choroid plexus dissected either 6 h [Space Life Sciences-2 (SLS-2) experiments] or 2 days [National Instit utes of Health-Rodent 1 (NIH-R1) experiments] after a spaceflight, or 6 h after head-down tilt (KDT) experiments. Apical alterations were no ted in choroidal cells from SLS-2 and HDT animals, confirming that wei ghtlessness impaired choroidal structures and functions. However, the presence of small apical microvilli and kinocilia and the absence of v esicle accumulations showed that the apical organization began to be r estored rapidly after landing. Very enlarged apical microvilli appeare d after 2 days on Earth, suggesting increased choroidal activity. Howe ver, as distributions of ezrin and carbonic anhydrase II remained alte red in both flight and suspended animals after readaptation to Earth g ravity, it was concluded that choroidal structures and functions were not completely restored, even after 2 days in Earth's gravity.