DESCRIPTION: (Adapted from the Applicant's Abstract.) This application will examine the hypothesis that during the altered inertial environment of orbital flight, plasticity and adaptive changes take place within the maculae of the vestibular organs. The flight portion of the study will involve electrophysiological recordings from the vestibular nerve of the rat in response to (sinusoidal) linear accelerations along unspecified axes. In parallel, maculas will be harvested from other animals for morphological and anatomical examination, including (a) serial reconstruction of the terminals and receptive fields of selected macular regions using electron-microscopic techniques, (b) changes in glutamate receptor gene expression at macular synapses, (c) changes in glutamate receptor protein in macular hair cells, and (d) changes in the otoconial mass, performed using scanning EM. The results from these experiments will be incorporated into a developing model of the peripheral vestibular system.