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.