Physiological response of the rat to different vibration frequencies.

Vibration (acceleration of 50 m/s2 and frequencies from 30 to 960 Hz) was applied to the tail and hind legs of rats for a 4-h period. The responses of the peripheral circulatory and peripheral nervous systems, muscle function, and the central nervous system were examined. When a tail was exposed to the vibration stimulus, the skin temperature dropped significantly at 30 and 240 Hz; the blood flow decreased significantly at 30, 60, and 480 Hz; and the peripheral nerve conduction velocity was significantly slower at 30, 60, and 120 Hz. After vibration of the hind legs the activity of plasma creatine phosphokinase (CPK) showed significantly high values at 30, 60, 120, and 480 Hz and was especially high at 30 Hz; the content of brain norepinephrine was significantly decreased at 120 Hz in the hypothalamus; dopamine was significantly increased at 60 Hz in the medulla oblongata and pons; and serotonin was significantly increased at 120 Hz in the hypothalamus. Thus the physiological responses of the rat to local vibration depend on, among other variables, the vibration frequency. In the case of the response of plasma CPK it would appear to depend on the amplitude (displacement) of this stimulus.