A simple method for simultaneous monitoring of respiratory and cardiac function in mice

[Speaker] Motoshige Sato:1
[Co-author] Nobuyoshi Matsumoto:1, Asako Noguchi:1, Toya Okonogi:1, Takuya Sasaki:1, Yuji Ikegaya:1
1:Laboratory of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, The University of Tokyo, Japan

Normal circulatory and respiratory systems are essential for animals to survive and are regulated by the autonomic nervous system, which is under the control of the central nervous system. However, it still remains unknown whether and how the peripheral systems and individual neuronal activity in the central nervous system interact with each other. To address this question, we developed a simple method that monitors both circulatory and respiratory activity, which can be easily combined with neurophysiological experiments.
We first isolated a low-frequency component from the cardiac rhythms using the fast Fourier transform on the single-lead ECG of anesthetized mice. To validate that the slow oscillatory component corresponded to respiratory rhythms, we recorded ECG simultaneously with side abdominal movement and the local field potentials (LFPs) of the olfactory bulb. We then pharmacologically manipulated the respiratory rate during the simultaneous recording.
We confirmed that all the three signals were synchronously coupled even when the respiratory rate was manipulated by drug injection. Even in awake mice, the respiratory signal could be isolated from ECG while they were immobile or slowly behaved. Finally, we combined ECG recordings with in vivo whole-cell patch-clamp recordings from single hippocampal CA1 neurons of anesthetized mice to investigate the relationship between the respiratory oscillations and membrane potential dynamics. Interestingly, the membrane potentials in some (but not all) CA1 neurons fluctuated with simultaneously recorded respiratory rhythms.
In conclusion, we provided a novel, simple approach to monitor the respiratory function in various physiological and pharmacological experiments. Combined with neurophysiological methods, the method will disclose the interaction of the central nervous system and the peripheral functions including circulation and respiration.

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