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First published online July 20, 2006
Journal of Experimental Biology 209, 2847-2858 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02298

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Microgravity-induced modifications of the vestibuloocular reflex in Xenopus laevis tadpoles are related to development and the occurrence of tail lordosis

Eberhard R. Horn

Gravitational Physiology, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany

View larger version (174K): [in a new window]   Fig. 1. Tail lordosis induced by microgravity. Lordotic body shapes of tadpoles exposed to microgravity during a spaceflight (MM, CM) or to simulated 1g-condition by centrifugation (CC) during a spaceflight. CM differs from MM because these tadpoles were centrifuged at 1g for 4 days, and thereafter exposed to microgravity for 5 days, while MM tadpoles were exposed to microgravity for 9.2 days (observations from the STS-84 mission in 1997). The numbers indicate the lordosis score with 1 weak, 2 medium, and 3 strong. 0 indicates normal body shape.

View larger version (56K): [in a new window]   Fig. 2. The roll-induced vestibuloocular reflex in Xenopus tadpoles. (A) Schematic presentation of the frontal view of an animal that indicates the direction (arrow) and extent (°) of eye movement during a right and left roll, respectively. R, reference line that is constant with respect to the animal; E, eye cup margin that is used as recording line. (B) Typical rVOR characteristic obtained during a 360° lateral roll. Definitions of the rVOR amplitude and those parameters used for the calculation of the rVOR gain (see arrows at the left side of the characteristic) are included. (C,D) Original video picture of the eyes of a tadpole in a frontal view in the horizontal (C) and 90° lateral (D) position. Because the camera is moved with the stimulation machine, only the eyes change their position. With respect to the frontal view, the animal is rotated to the left; with respect to the animal's body, to the right. The dotted line corresponds to line R.

View larger version (27K): [in a new window]   Fig. 3. The amplitude of the roll-induced static vestibuloocular reflex (rVOR) in Xenopus laevis tadpoles with lordotic tail. Observations after the 9.2-day SMM-06 Shuttle-to-Mir mission 06 (STS-84, 1997). At the onset of the mission, embryos had reached the developmental stages 25-28. For the recordings after landing, tadpoles were grouped according to the development of tail lordosis (L, filled circles) or normally developed tails (N, open circles). rVOR amplitude = maximal angular roll of the eyes during a 360° lateral body roll. MM, tadpoles that were exposed to microgravity throughout the 9.2-day mission; CM, tadpoles exposed to in-flight 1g-simulation for the first 4 days (93 h) and thereafter to microgravity until the end of the mission; MC, tadpoles exposed to microgravity for the first 4 days (93 h) and thereafter to in-flight 1g-simulation until deactivation of the centrifuge, 12 h before the end of the mission; CC, tadpoles exposed to microgravity throughout the 9-day mission except the time between launch and activation of the centrifuge and after deactivation of the 1g-centrifuge; GG, tadpoles from the 1g-ground control. Observation periods are defined below the lowest plot; pF, days after fertilization; post-LD, days after landing of the spacecraft. Each filled and open circle represents an individual animal. Numbers at the bottom of each plot give the numbers of tadpoles; levels of statistical significances in bold italic letters indicate differences between normal and lordotic animals of the respective observation period; NS, not significant. Numbers above brackets indicate differences between samples of the two observation periods.

View larger version (26K): [in a new window]   Fig. 4. The gain of the roll-induced static vestibuloocular reflex (rVOR) in Xenopus laevis tadpoles with lordotic tail. Post-flight observations about the rVOR gain from tadpoles that flew on the 9.2-day SMM-06 mission compared to their ground-reared siblings. Same animals as in Fig. 3. rVOR gain30 = ratio between the angular eye movement and the lateral roll of 30° from the horizontal to the inclined position. For further explanations, see Fig. 3.

View larger version (23K): [in a new window]   Fig. 5. The static vestibuloocular reflex (rVOR) in Xenopus laevis tadpoles with lordotic tail compared to 1g-controls in stage-matched samples. Tadpoles are grouped according to their developmental stages 47 and 48 at the time of the rVOR recording. Note the depressed rVOR in lordotic tadpoles within each stage group, in particular for the MM-group, and also that in this group lordotic stage 48 tadpoles have a weaker rVOR than the normal stage 47 tadpoles. For further explanations, see Fig. 3.

View larger version (24K): [in a new window]   Fig. 6. Post-flight observations of the rVOR amplitude (A,B) and rVOR gain (C,D) from tadpoles that flew on the 10-day German D-2 mission (STS-55, 1993) compared to their ground-reared siblings. At the onset of the mission, tadpoles had reached the developmental stages 33-36. Observations were from post-flight days 2-6 (A,C) and 9-12 (B,D). During each period, animals were tested once. rVOR amplitude and rVOR gain30, cf. Fig. 2. Filled circles, microgravity tadpoles (0g); 0g-animals were grouped according to the development of lordosis or normal development. Open circles, 1g-animals from the in-flight control (F1g) and from the ground control (G1g). Numbers at the abscissa indicate sample size. Groups that differ significantly are connected by brackets; levels of significance (P) are shown.

View larger version (26K): [in a new window]   Fig. 7. Post-flight observations of the rVOR amplitude (A,C) and rVOR gain (B,D) from tadpoles that flew on the 10-day French Soyuz taxi flight Andromède to the International Space Station (2001) compared to their ground-reared siblings. At onset of the mission, tadpoles had reached developmental stages 26-27 (A,B) or stage 45 (C,D). Observations were from the post-flight days 2-4. Each animal was tested only once. rVOR amplitude and rVOR gain30, cf. Fig. 1. Filled circles, microgravity tadpoles (0g); 0g-animals were grouped according to the development of lordosis or normal development. Open circles, animals from the ground control (1g). Numbers at the abscissa indicate sample size. Groups that differ significantly are connected by brackets; levels of significances are shown. Note the increase of the rVOR in the old group with normal tails.