Persistence of tight junctions and changes in apical structures and protein expression in choroid plexus epithelium of rats after short-term head-down tilt.
Major alterations of choroidal cell polarity and protein expression were previously shown to be induced in rats by long-term adaptation to space flight (14 days aboard a space shuttle) or anti-orthostatic suspension (14 and 28 days) performed by tilting rats head-down (i.e. using a ground-based model known to simulate several effects of weightlessness). In rabbits, it was hypothesized that the blood-CSF barrier was opened in choroid plexus, after a short head-down suspension. To understand the early responses to fluid shifts induced by head-down tilts and evaluate the tightness of the choroidal junctions, we have investigated the effects of acute adaptations to anti-orthostatic restraints, using hindlimb-suspended Sprague-Dawley and Wistar rats. Ultrastructural and immunocytochemical studies were performed on choroid plexuses from lateral, third and fourth ventricles, after 30, 90 and 180 minutes of head-down tilt. Alterations were not perceptible at the level of choroidal tight junctions, as shown by freeze-fracture, claudin-1 and ZO-1 immunolocalizations and conventional electron microscopy, after intravenous injection of cytochrome C. The apical surface of choroidal cells was clearly more affected. Microvilli were longer and thinner and ezrin was over-expressed during all the periods of time considered, showing an early cytoskeletal response. Several proteins involved in the choroidal production of cerebrospinal fluid (sodium-potassium ATPase, carbonic anhydrase II, aquaporin 1) appeared first increased (30 minutes after the tilt), and then, returned to the control level or were lowered (after a 3-hour head-down suspension). Although head-down tilts do not seem to damage the blood-cerebrospinal fluid barrier in choroid plexus, it seemed that the expression of several apical proteins is affected very early.
Masseguin
C
C
Neurobiologie des Signaux Intercellulaires, UMR 7101 CNRS, Université Pierre et Marie Curie, Paris VI, F-75252 Paris cédex 05, France.
Mani-Ponset
L
L
Herbuté
S
S
Tixier-Vidal
A
A
Gabrion
J
J
D000818:Animals; D002831:Choroid Plexus / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure*; D004848:Epithelium / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D018475:Head-Down Tilt / Q000009:adverse effects / Q000502:physiology*; D008297:Male; D014176:Protein Biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D019108:Tight Junctions / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure*