ASGSB 1999 Annual Meeting Abstracts

EFFECT OF HYPER-G ON MUSCLE AND BODY WEIGHTS IN INTACT AND LABYRINTHECTOMIZED GERBILS. I.V. Polyakov¹, N.G. Daunton, M.L. Corcoran. ¹San Jose State University Foundation, San Jose, CA; NASA Ames Research Center, Moffett Field, CA.

Our previous studies have shown that modifying vestibular input by 30 min of vestibular galvanic stimulation leads to an increase in c-Fos immunoreactivity in CNS areas related to neuromuscular control, and in antigravity muscles. In this work we used chronic centrifugation to increase the level of vestibular input for an extended time period. This treatment is known to increase relative muscle mass in antigravity muscles. We investigated the role of the vestibular system in mediating this effect of centrifugation by comparing the effects of hyperG exposure on animals with and without intact labyrinths. The gerbils were centrifuged at 2G for 2 weeks using the NASA Ames Research Center 24-ft diameter centrifuge. Animals were divided into five groups:  1) stationary control - intact, uncentrifuged;  2) rotation control - intact, centrifuged at only 1.03 G;  3) 2G - intact, centrifuged at 2G;  4) stationary control labx - uncentrifuged, labyrinthectomized; 5) 2G labx - centrifuged, labyrinthectomized. Mean body weight was significantly lower for the 2G intact group compared with the stationary and rotation controls, but the 2G labx animals did not show any difference in mean body weight compared with their stationary control animals. In 2G intact animals mean relative weight of the soleus increased by 30% compared with their controls. However, in the 2G labx group no increase was found in the mean relative weight of the soleus, even though these animals were significantly more active during the early days of centrifugation than the intact animals.  These data suggest that vestibular input plays an important role in the relative muscle hypertrophy seen in intact centrifuged animals, and in the weight loss and inactivity that occur early in adaptation to hyperG in these animals.  These results also indicate that vestibular input can play an important role in maintaining the mass of antigravity muscles.  Further, the lack of stimulation of vestibular gravity receptors during space flight may be a possible cause of the atrophy of antigravity muscles in flight.

(Supported by NASA Task 199-16-12-01)

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