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

Nikolay Aseyev,Matvey Roshchin,Pavel M Balaban,Igor S Zakharov,Richard D Boyle,Alia Kh Vinarskaya,Yekaterina Popova,Aleksey Yu Malyshev,Leonid Uroshlev,Alena B Zuzina,Ekaterina Chesnokova,Tatiana A Korshunova,Victor N Ierusalimsky,Maria S Lemak,Artem Kasianov,Svetlana Volkova,Peter Kolosov,Ivan A Novikov

doi:10.3389/fncel.2017.00348

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.

Highlights

Vertebrates and invertebrates sense inertial acceleration and a change in orientation with respect to gravity by mechanoreceptors in the otolith and statolith organs, respectively
There was no significant difference between groups in the count of scanning movements (p = 0.114 by Fisher’s Exact Test with Monte-Carlo simulated p-value based on 99999 replicates); 82 of 88 (93%) snails of all groups turned the body to position the head above the shell in T2 phase
To account for possible environmental and habitat factors of unmanned spaceflights that can affect measured parameters of behavior other than those related to the state of weightlessness, we designed four control groups based on housing, food and water availability, and lighting, and included a landing-like simulation

Summary

Introduction

Vertebrates and invertebrates sense inertial acceleration and a change in orientation with respect to gravity by mechanoreceptors in the otolith and statolith organs, respectively. There is the possibility of longterm circadian changes of responses, as it was shown for the snail lip sensory nerve (Voss et al, 1997); this factor might influence the results because the recordings of PF snails commenced after their arrival to the lab at night. To exclude such a possibility we provide additional experiments with our isolated CNS-statocysts preparations (Figure S5). Results of these technical controls allow us to analyze the data acquired by the main protocol

Methods

Results

Conclusion