No abstract

No abstract

We investigated the effect of prolonged hypergravity on the otoconial layer of the maculae utriculi and the maculae sacculi in hamsters. The animals were placed in a centrifuge under conditions of 2.5 G, and remained there for 6 months. We then determined the calcium contents of the otoconia with energy dispersive X-ray element analysis, and recorded the size, shape and distribution of the otoconia. Scanning electron microscopy was used to make photos to determine the effects of hypergravity on the shape and size of the otoconia, and on the distribution of smaller and larger otoconia. No differences were found in the calcium content, shape, size or distribution of otoconia between centrifuged hamsters and control animals. Our findings indicate that structural adaptation to hypergravity does not take place at the otoconial level, at least not in animals subjected to hypergravity after the vestibular system was fully matured.

We studied the functional adaptation process in 40 hamsters subjected to either prolonged hypergravity to normal gravity. Subadult golden hamsters (n = 20) exposed to a hypergravity condition of 2.5 G for 6 months were tested to investigate the effect of hyper gravity on the perceptive motor skills and compared with control hamsters (n = 20). The motor coordination of the hypergravity hamsters hardly changed; locomotion was normal and swimming was possible. Equilibrium maintenance was disturbed during the first 3 months as was shown by the higher crossing time (p < 0.001) and higher fall frequency (p < 0.001) for the hypergravity group. Significant differences were also found in orientation during swimming (p = 0.007) and turning behaviour in the rotation task (p < 0.001) and in the no-rotation task (p = 0.029). After 6 months, 10 hamsters of both groups were tested for another 4 months, also the hypergravity hamsters were living at 1 G. Differences in orientation in the two groups did not change during swimming and turning behaviour during the rotation task (p = 0.026). Based on our findings, we conclude that the hamsters functionally adapted to hypergravity, which led to an altered performance of several tasks. The condition continued after 4 months of normal gravity.