Abstract
Sympathetic and parasympathetic autonomic activities of unrestrained conscious mice were analyzed. The ambient temperature of animals was set to 30°C where significant variability of RR-interval could be recorded. Time series of RR-intervals were obtained from ECG recordings sampled continuously for 40 seconds every 2 minutes. LF (0.025-0.300 Hz) and HF (0.3-4.0 Hz) were calculated as areas of the Fourier amplitude spectrum of RR-intervals. The mean respiratory interval was calculated from the first derivative of ECG baseline fluctuations. The ratio of the mean respiratory interval to the mean RR interval stayed almost constant throughout experiments, which suggested an intimate relationship between the heart rate and the metabolism. After injection of atropine, both LF and HF suddenly decreased, whereas the mean RR-interval was not always significantly decreased. The respiratory-unsynchronized LF that remained in the presence of atropine was eliminated by an additional injection of propranolol, which indicated that the firing rate of pacemaker cells was exclusively determined by classical autonomic neurotransmitters in mice. LF/(LF+ HF) and HF/(LF+ HF) had no significant relationship with the mean RR interval that is presumed to be reflecting the autonomic balance. The possible reasons for this discrepancy will be discussed. [J Physiol Sci. 2006;56 Suppl:S200]
