title: Exposure to hypergravity during the preweaning but not postweaning period reduces vestibular-related stress responses in rats.
abstract: Gravitational forces, including hypergravity or microgravity, induce plasticity of vestibular-related functions. These functions are not easily reversed if exposure to the gravitational forces occurs during vestibular development. In the present study, we hypothesized that vestibular-related stress responses might be suppressed in rats exposed to hypergravity during the vestibular development period. We exposed the rats to 2 g (hypergravity) during the preweaning (BW-HG; embryonic day 14 to postnatal week 3) or postweaning (AW-HG; postnatal weeks 4-6) periods. After recovery for 4 wk at 1 g, we conducted rotarod tests and then exposed the rats to 2 g for 90 min. In BW-HG rats, vestibular-related motor coordination on the rotarod test was partially, but not fully, restored to the level of AW-HG rats or rats raised at 1 g (1-G group). Loading-induced plasma adrenocorticotropic hormone and corticosterone levels were significantly suppressed in BW-HG and in rats with a vestibular lesion compared with AW-HG and 1-G rats. Arginine vasopressin and Fos expression levels in the paraventricular hypothalamic nucleus were also significantly lower in BW-HG and vestibular lesion rats than in AW-HG and 1-G rats. By contrast, there was no difference in the electrical foot shock-induced increase in plasma corticosterone among the experimental groups, suggesting that the nonvestibular-related stress response was not suppressed by exposure to 2 g during preweaning. These results indicated that exposure to hypergravity during preweaning specifically suppressed the vestibular-related stress response, and this suppression did not recover after 4 wk at 1 g.
authors.affiliation: Department of Physiology, Gifu University Graduate School of Medicine, Gifu, Japan;
authors.forename: Chikara
authors.initials: C
authors.lastname: Abe
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ueta
authors.forename: Hironobu
authors.initials: H
authors.lastname: Morita
mesh_terms: D000818:Animals; D001120:Arginine / Q000378:metabolism; D003345:Corticosterone / Q000378:metabolism; D006112:Gravitation; D018471:Hypergravity; D008297:Male; D010286:Paraventricular Hypothalamic Nucleus / Q000502:physiology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D013312:Stress, Physiological / Q000502:physiology*; D014667:Vasopressins / Q000378:metabolism / Q000502:physiology; D014726:Vestibular Nuclei / Q000502:physiology*; D014886:Weaning
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D014667:Vasopressins; D001120:Arginine; D003345:Corticosterone
keywords: Fos; adrenocorticotrophic hormone; corticosterone; green fluorescent protein; vasopressin; vestibular system