Hyper- and hypogravity alter posture in rats compensated on Earth for a vestibular asymmetry

HEAD posture and neck muscle activity (EMGs) were examined in unilateral (U L) and bilateral (BL) vestibularly lesioned rats in hypergravity (1.7 g) an d hypogravity (0 g) during parabolic flights. Compared with BL rats taken a s control, the head and the body of UL deviated toward the lesion side at 0 g and toward the intact side at 1.7 g. Recorded in head fixed condition, l eft and right EMGs remained symmetrical in BL while UL rats displayed an as ymmetry between left and right muscles at 1.7 g, but not at 0 g. These resu lts demonstrate that an experimental otolithic asymmetry, compensated on Ea rth, can become unbalanced in altered gravity. Paradoxically, the utricular system appears to play a major role in that process. NeuroReport 10:669-67 3 (C) 1999 Lippincott Williams & Wilkins.