c-fos mRNA Expression in the Vestibular System following Hypergravity Stimulation in Rats

Altered environmental gravity, including both hypo- and hypergravity, may result in space adaptation syndrome. To explore the characteristics of this adaptive plasticity, the expression of immediate early gene c-fos mRNA in the vestibular related tissues following an exposure to hypergravity stimulus was determined in rats. The animals were subjected to a force of 2 g (twice earth's gravity) for 1, 3, or 12 h, and were examined poststimulus at 0, 2, 6, 12, and 24 h. RT-PCR (reverse transcription polymerase chain reaction) and real-time quantitative RT-PCR were adopted to analyze temporal changes in the expression of c-fos mRNA. The hypergravity stimulus increased the expression of c-fos mRNA in the vestibular ganglion, medial vestibular nucleus, inferior vestibular nucleus, hippocampus, cerebellum, and cortex. The peak expression occurred at 0 h poststimulation in animals stimulated with hypergravity for 1 h, and at 6 h poststimulus in those stimulated for 3 h. In contrast, those stimulated for 12 h exhibited dual peaks at 0 and 12 h poststimulus. Bilateral labyrinthectomy markedly attenuated the degree of c-fos mRNA expression. Glutamate receptor antagonist also dramatically attenuated the degree of c-fos mRNA expression. These results indicate that expression of c-fos mRNA in response to hypergravity occurs in the vestibular related tissues of the central nervous system, in which peripheral vestibular receptors and glutamate receptors play an important role. The temporal pattern of c-fos mRNA expression depended on the duration of the hypergravity stimulus.

Role of the Peripheral Vestibular System on Neuroplasticity Induced by Hypergravity Stimulation

BACKGROUND AND OBJECTIVES: Altered environmental gravity, including both hypo- and hypergravity, may result in space adaptation syndrome. To explore the characteristics of this adaptive plasticity, the expression of immediate early gene c-fos mRNA in the vestibular system following an exposure to hypergravity stimulus was determined in rats. MATERIALS AND METHOD: The animals were subjected to 2 G force (two-fold earth's gravity) stimulus for 3 hours, and were examined at post-stimulus hours 0, 2, 6, 12, and 24. Real time reverse transcription-polymerase chain reaction (RT-PCR) was adopted to analyze temporal changes in the expression of c-fos mRNA. RESULTS: The hypergravity stimulation produced the expression of c-fos mRNA in the vestibular ganglion, medial vestibular nucleus, inferior vestibular nucleus, hippocampus, vestibulocerebellum, and vestibular cortex. The peak expression occurred at hour 6 in the animals hypergravity-stimulated for 3 hours. Bilateral labyrinthectomy significantly attenuated the degree of up-regulation in c-fos mRNA expression. MK-801, an NMDA receptor antagonist, also significantly attenuated the degree of up-regulation in c-fos mRNA expression. CONCLUSION: These results indicate that the adaptive neuroplasticity in response to an altered gravity occurs in the vestibular-related organs in the central nervous system, in which peripheral vestibular receptors and NMDA receptors play an important role.

Mareo de vuelo: consideraciones fisiológicas y fisiopatológicas / Motion sickness: physiological and physiopathologic considerations

La experiencia del vuelo requiere de una adecuada interacción de las aferencias vestibulares, visuales y propioceptivas en los núcleos vestibulares, moduladas por la actividad del flóculo del cerebelo. Durante el vuelo se presentan situaciones de alta complejidad dinámica, determinadas por aceleraciones angulares y lineales sobre los ejes corporales. La orientación espacial dinámica implica que los mecanismos descritos a nivel del tronco cerebral tengan un comando de análisis supranuclear, ubicado en la corteza cerebral, en constante reanálisis de las eferencias de respuesta durante el vuelo. Experiencias clínicas y experimentales, en condiciones de gravedad terrestre, microgravedad en vuelos parabólicos e ingravidez en vuelos orbitales y permanencias prolongadas en transbordadores espaciales, sugieren fuertemente que una disfunción de las aferencias vestibulares puede generar mareo de vuelo y desorientación espacial. Un estudio realizado en veinte cadetes de la Escuela de Aviación, en el inicio de su período de instrucción y que presentaron mareo de vuelo, demuestra una significativa paresia vestibular periférica y modificaciones optokinéticas en el estudio otoneurológico-electronistagmográfico. La consecuencia de estos déficits en el proceso de interacción visual-vestibular y en el control oculo-motor determinan fallas en el proceso de adaptación del sistema nerviso central frente a estimulación no fisiológicas