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

Area of Science:

• Vestibular Neuroscience
• Gravitational Physiology
• Oculomotor Control

Background:

• The vestibulo-ocular reflex (VOR) stabilizes gaze during head movements.
• Understanding VOR adaptation to altered gravity is crucial for spaceflight and understanding sensory compensation.
• Previous research has explored short-term effects of gravity changes on VOR.

Purpose of the Study:

• To investigate the long-term effects of hypergravity (HG) on the horizontal vestibulo-ocular reflex (VOR) in rats.
• To compare VOR function in rats bred and raised under HG (2.5 g) versus normal gravity (NG; 1 g).
• To assess VOR responses under varying gravitational conditions, including normal gravity and parabolic flight.

Main Methods:

• Horizontal VOR was measured in two groups of rats: HG (2.5 g) and NG (1 g).
• Eye position was recorded during horizontal rotatory stimuli.
• Measurements were conducted under 1 g and during parabolic flight (0.0 and 1.8 g).

Main Results:

• The VOR of HG rats exhibited a 20-50% amplitude reduction compared to NG rats.
• A phase shift of -40 degrees was observed in the VOR of HG rats.
• VOR responses during parabolic flight were similar to 1 g conditions for both groups.

Conclusions:

• Prolonged exposure to hypergravity significantly alters the horizontal VOR in rats.
• The observed VOR amplitude reduction and phase shift in HG rats are likely consequences of adaptation to a rotating system.
• These findings highlight the plasticity of the vestibular system and its adaptation to sustained altered gravitational environments.