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Role of the Vestibular System in the Regulation of Body Mass in Male and Female Rats.  T.M. Hoban-Higgins and C.A. Fuller.  Section of NPB, University of California, Davis, CA.

   The vestibular macular receptors transduce gravitational and linear acceleration information.  Recent work suggested that they also play a role in the changes seen in body mass regulation at altered G.  This study investigated the role of the vestibular system in the regulation of body mass.  Since there are known gender differences in the regulation of body mass and composition, age-matched male and female rats were used as subjects.  Experimental groups underwent chemical labyrinthectomy (transtympanic injection of sodium arsanilate) to remove vestibular input while control groups experienced the same surgical procedures, but with a saline control injection.  Four subject groups of each gender were established, for a total of eight groups.  These included two experimental groups, one that remained at 1G and one that experienced 8 weeks of 2G produced via centrifugation and two matching control groups.  Body mass and food and water consumption data were collected twice weekly.  Baseline data were collected prior to surgery.  An eight-week recovery period followed surgery to allow for the re-establishment of stable growth curves prior to the onset of centrifugation.  Both male and female rats initially had a decrease in body mass following chemical labyrinthectomy.  However, while regulation at a lower body mass persisted in male rats, body mass of female experimental rats returned to the level of the controls.  Similar results were seen in response to 2G.  Body mass decreased in all 2G groups at the onset of centrifugation, with experimental groups having a smaller response than the controls.  Again, while males continued to regulate body mass at a lower level under 2G, in females body mass returned to levels similar to controls.  Consequently, at the end of the eight week centrifugation period, body mass was similar between all four female groups while differences were evident between male groups.  Male1G animals had a higher body mass than 2G animals and, at each G level, control animals had a higher body mass than labyrinthectomized animals.  (Supported by NASA Grant NNA07CN33G.)