Ultrasonic analysis of tremorine and cold tremor activity in unanesthetized rats

In order to quantify the tremorine and cold tremor activity in unanesthetized rats, a new ultrasonic motion transducer method was used. Both kinds of activity are reported as vibratory body motion that occurred between 18-32 Hz as determined by spectral analysis. The recorded signal was analyzed and its power spectrum was obtained through a fast Fourier transform operation. It was found that a negative linear relation occurs between shiver amplitude and ambient temperature (r = 0.999). A negative linear relation also occurs between metabolic rate and ambient temperature (r = 0.997). In addition, a positive linear relation between metabolic rate and cold shiver exists (r = 0.999). Both tremorine (30 mg/kg, i.p.) and cold tremor (Ta = 2-22 degrees C) activity monitored by the ultrasonic method were completely abolished by premedication with 1 mg/kg atropine. Thus, it appears that the advantages of this tremor detection method are that is non-invasive and non-contact. Therefore, the ultrasonic method provides a good choice for quantifying tremorine and cold tremor activity in unanesthetized animals during studies of thermoregulatory physiology or motor disorders.