Microgravity-induced modifications of the vestibuloocular reflex inXenopus laevistadpoles are related to development and the occurrence of tail lordosis

Abstract

SUMMARY During space flights, tadpoles of the clawed toad Xenopus laevisoccasionally develop upward bended tails (tail lordosis). The tail lordosis disappears after re-entry to 1g within a couple of days. The mechanisms responsible for the induction of the tail lordosis are unknown;physical conditions such as weight de-loading or physiological factors such as decreased vestibular activity in microgravity might contribute. Microgravity(μg) also exerts significant effects on the roll-induced vestibuloocular reflex (rVOR). The rVOR was used to clarify whether tail lordosis is caused by physiological factors, by correlating the occurrence ofμ g-induced tail lordosis with the extent of μg-induced rVOR modifications. Post-flight recordings from three space flights (D-2 Spacelab mission,STS-55 in 1993; Shuttle-to-Mir mission SMM-06, STS-84 in 1997; French Soyuz taxi flight Andromède to ISS in 2001) were analyzed in these experiments. At onset of microgravity, tadpoles were at stages 25-28, 33-36 or 45. Parameters tested were rVOR gain (ratio between the angular eye movement and the lateral 30° roll) and rVOR amplitude (maximal angular postural change of the eyes during a 360° lateral roll). A ratio of 22-84% of tadpoles developed lordotic tails, depending on the space flight. The overall observation was that the rVOR of tadpoles with normal tails was either not affected by microgravity, or it was enhanced. In contrast, the rVOR of lordotic animals always revealed a depression. In particular, during post-flight days 1-11, tadpoles with lordotic tails from all three groups (25-28, 33-36 and 45) showed a lower rVOR gain and amplitude than the 1g-controls. The rVOR gain and amplitude of tadpoles from the groups 25-28 and 33-36 that developed normal tails was not affected by microgravity while the rVOR of μg-tadpoles from the stage-45 group with normal tails revealed a significant rVOR augmentation. In conclusion: (1)the vestibular system of tadpoles with lordotic tails is developmentally retarded by microgravity; (2) after a critical status of vestibular maturation obtained during the appearance of first swimming, microgravity activates an adaptation mechanism that causes a sensitization of the vestibular system.

Simulated microgravity induce glutathione antioxidant pathwayin Xenopus laevis embryos

“…Tail lordosis has been observed in tadpoles (Snetkova et al, 1995;Sebastian et al, 1996), but not when eggs were fertilized under microgravity condition and when a 1g condition was simulated during space flight. Tail lordosis could be related to a more general effect of microgravity on growth factors production, which affects axis, vestibule-ocular reflex, and tail development (Horn, 2006). Our finding, in agreement with data from experiments carried out on space flights, validate the RPM as a simulator of microgravity.…”

“…Since space flights began many species have been studied in microgravity conditions to increase our knowledge of the effects of gravity deprivation and reducing human space flight risks. Tadpoles, during space flights, suffered behavioural and morphological modifications such as: swimming abnormalities and hyperextension of the tail (lordosis); which persisted for some days after grounding, as observed in X. laevis tadpoles launched before hatching (Horn, 2006).…”

Simulated microgravity induce glutathione antioxidant pathwayin Xenopus laevis embryos

“…Tail lordosis has been observed in tadpoles (Snetkova et al, 1995;Sebastian et al, 1996), but not when eggs were fertilized under microgravity condition and when a 1g condition was simulated during space flight. Tail lordosis could be related to a more general effect of microgravity on growth factors production, which affects axis, vestibule-ocular reflex, and tail development (Horn, 2006). Our finding, in agreement with data from experiments carried out on space flights, validate the RPM as a simulator of microgravity.…”

“…Since space flights began many species have been studied in microgravity conditions to increase our knowledge of the effects of gravity deprivation and reducing human space flight risks. Tadpoles, during space flights, suffered behavioural and morphological modifications such as: swimming abnormalities and hyperextension of the tail (lordosis); which persisted for some days after grounding, as observed in X. laevis tadpoles launched before hatching (Horn, 2006).…”

Gravity‐related critical periods in vestibular and tail development of Xenopus laevis

“…In contrast to rVOR recordings after microgravity exposure with tadpoles that had reached developmental stages between DS25 and DS45 at launch of the spacecraft (Horn, 2006), the recent postflight recordings of the rVOR revealed no significant difference between the normally developed tadpoles with microgravity experience and their 1g‐ground control siblings, independent of whether they were launched at the early hindlimb (DS47) or forelimb (DS50) bud stages. In addition, a stage‐dependent effect on the formation of tail lordosis was observed.…”

“…The significance of the results of the recent spaceflight experiment becomes obvious when combined and compared with observations obtained from younger tadpoles (Vinnikov et al, '83; Snetkova et al, '95; Souza et al, '95; Horn, 2006). The combined data on rVOR development demonstrate that there is a narrow time window ( = critical period) during vestibular development when rVOR development is sensitive to microgravity, i.e., to gravity deprivation.…”

Xenopus development from late gastrulation to feeding tadpole in simulated microgravity

“…The tadpoles, launched at the early tailbud stage (approximately one day old), exhibited caudal lordosis (also noted in a study by Horn, 2006), disproportionately long tails and short bodies, a failure to inflate their lungs, and a reduced, misshapen branchial apparatus (Snetkova et al, 1995). The acceleration and vibration of the launch and the sudden onset of μG may have caused or contributed to these irregularities.…”

Simulated microgravity induce glutathione antioxidant pathwayin Xenopus laevis embryos

“…Tail lordosis has been observed in tadpoles (Snetkova et al, 1995;Sebastian et al, 1996), but not when eggs were fertilized under microgravity condition and when a 1g condition was simulated during space flight. Tail lordosis could be related to a more general effect of microgravity on growth factors production, which affects axis, vestibule-ocular reflex, and tail development (Horn, 2006). Our finding, in agreement with data from experiments carried out on space flights, validate the RPM as a simulator of microgravity.…”

“…Since space flights began many species have been studied in microgravity conditions to increase our knowledge of the effects of gravity deprivation and reducing human space flight risks. Tadpoles, during space flights, suffered behavioural and morphological modifications such as: swimming abnormalities and hyperextension of the tail (lordosis); which persisted for some days after grounding, as observed in X. laevis tadpoles launched before hatching (Horn, 2006).…”

Gravity‐related critical periods in vestibular and tail development of Xenopus laevis

“…In contrast to rVOR recordings after microgravity exposure with tadpoles that had reached developmental stages between DS25 and DS45 at launch of the spacecraft (Horn, 2006), the recent postflight recordings of the rVOR revealed no significant difference between the normally developed tadpoles with microgravity experience and their 1g‐ground control siblings, independent of whether they were launched at the early hindlimb (DS47) or forelimb (DS50) bud stages. In addition, a stage‐dependent effect on the formation of tail lordosis was observed.…”

“…The significance of the results of the recent spaceflight experiment becomes obvious when combined and compared with observations obtained from younger tadpoles (Vinnikov et al, '83; Snetkova et al, '95; Souza et al, '95; Horn, 2006). The combined data on rVOR development demonstrate that there is a narrow time window ( = critical period) during vestibular development when rVOR development is sensitive to microgravity, i.e., to gravity deprivation.…”

Xenopus development from late gastrulation to feeding tadpole in simulated microgravity

“…The tadpoles, launched at the early tailbud stage (approximately one day old), exhibited caudal lordosis (also noted in a study by Horn, 2006), disproportionately long tails and short bodies, a failure to inflate their lungs, and a reduced, misshapen branchial apparatus (Snetkova et al, 1995). The acceleration and vibration of the launch and the sudden onset of μG may have caused or contributed to these irregularities.…”

Simulated microgravity induce glutathione antioxidant pathwayin Xenopus laevis embryos

“…Tail lordosis has been observed in tadpoles (Snetkova et al, 1995;Sebastian et al, 1996), but not when eggs were fertilized under microgravity condition and when a 1g condition was simulated during space flight. Tail lordosis could be related to a more general effect of microgravity on growth factors production, which affects axis, vestibule-ocular reflex, and tail development (Horn, 2006). Our finding, in agreement with data from experiments carried out on space flights, validate the RPM as a simulator of microgravity.…”

“…Since space flights began many species have been studied in microgravity conditions to increase our knowledge of the effects of gravity deprivation and reducing human space flight risks. Tadpoles, during space flights, suffered behavioural and morphological modifications such as: swimming abnormalities and hyperextension of the tail (lordosis); which persisted for some days after grounding, as observed in X. laevis tadpoles launched before hatching (Horn, 2006).…”

Gravity‐related critical periods in vestibular and tail development of Xenopus laevis

“…In contrast to rVOR recordings after microgravity exposure with tadpoles that had reached developmental stages between DS25 and DS45 at launch of the spacecraft (Horn, 2006), the recent postflight recordings of the rVOR revealed no significant difference between the normally developed tadpoles with microgravity experience and their 1g‐ground control siblings, independent of whether they were launched at the early hindlimb (DS47) or forelimb (DS50) bud stages. In addition, a stage‐dependent effect on the formation of tail lordosis was observed.…”

“…The significance of the results of the recent spaceflight experiment becomes obvious when combined and compared with observations obtained from younger tadpoles (Vinnikov et al, '83; Snetkova et al, '95; Souza et al, '95; Horn, 2006). The combined data on rVOR development demonstrate that there is a narrow time window ( = critical period) during vestibular development when rVOR development is sensitive to microgravity, i.e., to gravity deprivation.…”

Xenopus development from late gastrulation to feeding tadpole in simulated microgravity

“…The tadpoles, launched at the early tailbud stage (approximately one day old), exhibited caudal lordosis (also noted in a study by Horn, 2006), disproportionately long tails and short bodies, a failure to inflate their lungs, and a reduced, misshapen branchial apparatus (Snetkova et al, 1995). The acceleration and vibration of the launch and the sudden onset of μG may have caused or contributed to these irregularities.…”