title: The effect of clinorotation on vestibular compensation in upside-down swimming catfish.
abstract: Upside-down swimming catfish Synodontis nigriventris can keep upside-down swimming posture stably under pseudo-microgravity generated by clinostat. When the vestibular organ is unilaterally ablated, the operated S. nigriventris shows disturbed swimming postures under the clinorotation condition. However, about 1 month after the operation, unilateral vestibular organ-ablated S. nigriventris shows stable upside-down swimming posture under the condition (vestibular compensation). In contrast, a closely related upside-up swimming catfish Synodontis multipunctatus belonging to same Synodontis family can not keep stable swimming postures under the clinorotation conditions. In this study, we examined the effect of continuous clinorotation on vestibular compensation in intact and unilateral vestibular organ-ablated Synodontis nigriventris and Synodontis multipunctatus. After the exposure to continuous clinorotation, the postures of the catfish were observed under microgravity provided by parabolic flights of an aircraft. Unilateral vestibular organ-ablated S. nigriventris which had been exposed to continuous clinorotation showed stable swimming postures and did not show dorsal light reaction (DLR) under microgravity. This postural control pattern of the operated catfish was similar to that of intact catfish. Intact and unilateral vestibular organ-ablated S. multipunctatus showed DLR during microgravity. Our results confirmed that S. nigriventris has a novel balance sensation which is not affected by microgravity. DLR seems not to play an important role in postural control. It remains unclear that the continuous clinorotation effects on vestibular compensation because we could not keep used unilateral vestibular organ-ablated fish alive under continuous clinorotation for uninterrupted 25 days. This study suggests that space flight experiments are required to explore whether gravity information is essential for vestibular compensation.
authors.affiliation: Department of Biology, Nara Medical University, Nara, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Ohnishi
authors.forename: Noritomo
authors.initials: N
authors.lastname: Okamoto
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Yamanaka
authors.forename: Akihisa
authors.initials: A
authors.lastname: Takahashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hosoi
authors.forename: Takeo
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D002397:Catfishes; D006112:Gravitation; D010775:Photic Stimulation; D011187:Posture / Q000502:physiology; D012399:Rotation; D013026:Space Flight; D013550:Swimming; D013997:Time Factors; D014722:Vestibule, Labyrinth / Q000502:physiology / Q000601:surgery; D014893:Weightlessness; D018474:Weightlessness Simulation