P28 The role of the otoliths in vestibulo-ocular reflex adaptation
Khan SI & Migliaccio AA
The aim of this study was to determine the role of the otoliths in vestibulo-ocular reflex (VOR) adaptation. Until recently the role of the otoliths has been difficult to determine because there is no surgical or chemical technique that can selectively ablate the otoliths without damaging the semicircular canals. The tilted mouse (Otop 1) lacks functioning otoliths, but has normal semicircular canals(Hurle et al 2003). In 4 Otop 1 mice and 4 control littermates we measured: 1) baseline ocular counter-tilt about the 3 primary axes; 2) baseline horizontal sinusoidal VOR gain 3) baseline vertical sinusoidal VOR; 4) horizontal VOR after adaptation training; 5) vertical VOR after adaptation training to one side. Counter-tilt responses in tilted mice were significantly reduced compared to controls, confirming that tilted mice had minimal otolith function. Baseline horizontal and vertical VOR gains were similar between the two mouse types, confirming that the semicircular canals in titled mice were similar to normal. Horizontal VOR adaptation was similar between both mouse types, suggesting that otoliths played a minor role during horizontal VOR adaptation. However, there was a significant difference in vertical VOR adaptation between both mouse types. For the control mouse, adaptation of the VOR gain was most evident when the testing context was same as training context, i.e., they showed context-specific adaptation. Whereas context specific adaptation was absent in tilted mouse. Our results suggest that context-specific VOR gain adaptation is almost entirely reliant on otolith input and not to other contextual cues, e.g., proprioceptive signals.
- Hurle B, Ignatova E, Massironi SM, Mashimo T, Rios X, Thalmann R, and Ornitz DM. Non-syndromic vestibular disorder with otoconial agensis in tilted mice cased by mutatios in Otopertrin1. Hum Mol Genet 2003, 12:777-789