Adaptive Changes in the Vestibular System of Land Snail to a 30-Day Spaceflight and Readaptation on Return to Earth

Abstract

The vestibular system receives a permanent influence from gravity and reflexively controls equilibrium. If we assume gravity has remained constant during the species' evolution, will its sensory system adapt to abrupt loss of that force? We address this question in the land snail Helix lucorum exposed to 30 days of near weightlessness aboard the Bion-M1 satellite, and studied geotactic behavior of postflight snails, differential gene expressions in statocyst transcriptome, and electrophysiological responses of mechanoreceptors to applied tilts. Each approach revealed plastic changes in the snail's vestibular system assumed in response to spaceflight. Absence of light during the mission also affected statocyst physiology, as revealed by comparison to dark-conditioned control groups. Readaptation to normal tilt responses occurred at ~20 h following return to Earth. Despite the permanence of gravity, the snail responded in a compensatory manner to its loss and readapted once gravity was restored.

Influence of Magnitude and Duration of Altered Gravity and Readaptation to 1 g on the Structure and Function of the Utricle in Toadfish, Opsanus tau

“…Time course of return to normal sensitivity in toadfish afferents paralleled the reported decrease in vestibular disorientation in astronauts after return from shuttle missions ( Reschke et al, 1994 ). Although belonging to a distinct group of animals, recordings taken directly from gravitoreceptors of the land snail (phylum Mollusca), and thus no intervening synapse as in afferent recordings, after exposures of 12–16 ( Balaban et al, 2011 ) and 30 ( Aseyev et al, 2017 ) days in space also showed a pronounced response hypersensitivity to tilt. In a complimentary study in tilapia the gain of an otolith-related vestibuloocular reflex was significantly increased within the first postflight week, and returned to control levels in the second postflight week, of space missions ( Sebastian et al, 2001 ).…”

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