FREQUENCY OF THE 22-KHZ CALL OF RATS IS MODULATED BY THE RHYTHM OF THE HEART-RATE

The 22 kHz calls of rats are rhythmically frequency modulated. To test whether these modulations are correlated with the action of the heart, ECG was chronically registered in 16 male Wistar rats. In 11 rats loud acoustic stimuli provoked emission of the long calls or 22 kHz calls. In 10 self-vocalizing rats, we observed small frequency modulations (SFMs) in the constant frequency component of these calls. On the average, 7 ms after the R-peak of the ECG the calf frequency is lowered by 151 Hz. The heart rate and the rate of the SFMs are highly correlated (r = 0.997). Further, we show that the SFMs are produced by a reduction of call amplitude. The comparison with the course of the blood pressure in rats suggests that this change in call amplitude is caused by the blood pressure change during the action of the heart. Measuring SFMs offers a noninvasive way to determine the heart rate in vocalizing rats.