The horizontal vestibulo-ocular reflex of hypergravity rat at different gravity levels.

The horizontal vestibulo-ocular reflex (VOR) of two groups of rats was measured. One group was bred and kept under hypergravity (HG; 2.5 g) conditions, the other group lived under normal gravity (NG; 1 g). Eye position was recorded in response to horizontal rotatory stimuli. Measurements were made under NG (1 g), and during parabolic flight (0.0 and 1.8 g). For both groups, the response to a rotatory stimulus during parabolic flight is similar to the response that was observed under 1 g conditions. In general, however, the VOR of HG rats is reduced by 20-50% relative to the response of NG rats and the phase is shifted by -40 degrees. We conjecture that this amplitude reduction and phase shift are the consequence of living in a rotating system.