The vestibular functions of the manganese-deficient rat

Vestibular functions were examined in 25 animals of the second generation of rats raised on a manganese-deficient diet; 9 animals appeared to be normal and 16 showed behavioural abnormalities, characterized by inability to swim and lack of tonic eye deviations. The nystagmic responses elicited by rotatory stimulation appeared to be normal. Histological studies showed that the only defect was the absence of both utricular and saccular otoconia. These rats' swimming disability was similar to that of bilabyrinthectomized rats in normogravic condition and to that of normal rats immersed in water during weightlessness. It is concluded that the observed anomalies must be attributed solely to the lack of normal otolith function.