[The turning reflex, static endurance and structure of the vestibular apparatus receptors in rats exposed to whole-body low-frequency vibration].

Wistar rats were for 2 weeks exposed to vibrations of 18 Hz (acceleration of 2.3 G applied for 5.8 hrs a day for as long as 58 hrs) and 30 Hz (acceleration of 9.6 G applied for 5.1 hrs a day for as long as 56 hrs). The weight gain of experimental animals was less than that of control rats. Static endurance measured in terms of the time, during which the rats stayed on the vertical pole, decreased in the controls as their weight grew. Static endurance of the experimental rats remained essentially unchanged in spite of their growth. This may be associated with the stimulating effect of vibration on the muscle tone. The turning reflex was investigated using a specially designed unit, which allowed stroboscopic photography that was synchronized with the moment, when the animal began to fall down. The angles between the head and torso as related to the horizontal line were calculated and found to be unaltered in both experimental and control animals during 2 weeks. However, after exposure to vibration of both magnitudes the rats began to position the body off the horizontal line. Morphological examinations revealed no distinct structural changes in the utriculus, sacculus or posterior ampulla of the experimental rats when compared with the controls. At the same time it was demonstrated that the exposure produced swelling of cupulate nerve endings in the central compartment of the receptor epithelium of the posterior ampulla. The time course of morphofunctional changes of the vestibular apparatus in response to vibration of different frequencies (from 6 to 50 Hz) was also examined.