Affiliations: [a] Department of Otolaryngology Head and Neck Surgery, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| [b] Department of Otorhinolaryngology Head and Neck Surgery, Osaka University Graduate School of Medicine, Japan
| [c] Department of Otolaryngology Head and Neck Surgery, Nara Medical University, Japan
Correspondence:
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Corresponding author: Arata Horii, MD, PhD, Department of Otolaryngology Head and Neck Surgery, Niigata University Graduate School of Medical and Dental Sciences, 1-757, Asahimachi-dori, Chuo-ku, Niigata City, 951-8510, Japan. Tel.: +81 25 227 2303; Fax: +81 25 227 0787; E-mail: ahorii@med.niigata-u.ac.jp.
Abstract: BACKGROUND:Due to spatial disorientation reported in space, spatial memory and navigation performances could be more largely impaired by gravity changes. Hippocampus, a key structure for spatial memory, receives inputs from gravity-sensing otolith organs. OBJECTIVE:To determine the key molecules in the rat hippocampus that contribute to an adaptation to altered gravity in terms of spatial memory performance. METHODS:Gene expression of hippocampus and spatial memory after continuous two-weeks exposure to 2 G hypergravity (HG) were examined using a microarray analysis followed by real-time PCR methods and radial arm maze testing, respectively. Serum cortisol levels during HG load were measured as a stress marker. RESULTS:Accuracy to enter the correct arms in HG rats was significantly lower than that of controls, indicating an impaired spatial memory due to gravity changes. Microarray analysis followed by real-time PCR confirmed an upregulation of insulin like growth factor binding protein 2 (IGFBP2) gene. Serum cortisol level was the same level as controls at the last day of hypergravity, suggesting the adaptation to HG-induced stress. CONCLUSIONS:Given that the IGF systems are involved in neurotrophic and synaptic plasticity mechanisms, IGF system might contribute to the adaptation to altered gravity in terms of spatial memory.
