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Updated: Oct 14, 2025
Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents
Published on: January 24, 2013
Dissecting the Roles of the Autonomic Nervous System and Physical Activity on Circadian Heart Rate Fluctuations in
Nour Barazi1, Nazari Polidovitch1, Ryan Debi1
1Department of Biology, York University, Toronto, ON, Canada.
Insights
The autonomic nervous system (ANS), particularly parasympathetic nervous activity, significantly drives daily heart rate (HR) variations in mice. Physical activity has a minor impact on circadian HR rhythms unless mice engage in wheel running.
Area of Science:
- Cardiovascular Physiology
- Chronobiology
- Neuroscience
Background:
- Circadian rhythms in heart rate (HR), blood pressure, and cardiovascular events are influenced by daily variations in physical activity and the cardiac autonomic nervous system (ANS).
- Understanding the distinct roles of the ANS and physical activity in regulating circadian HR fluctuations is crucial for cardiovascular health research.
Purpose of the Study:
- To differentiate the contributions of the autonomic nervous system (ANS) alone versus physical activity to circadian heart rate (HR) fluctuations.
- To investigate the specific roles of parasympathetic nervous activity (PNA) and sympathetic nerve activity (SNA) in mediating daily HR variations.
Main Methods:
- Measured heart rate (HR) in mice under conditions of immobilization (isoflurane anesthesia) and free movement using telemetry.
- Administered pharmacological blockade of cardiac parasympathetic nervous activity (PNA) with atropine and sympathetic nerve activity (SNA) with propranolol.
- Assessed the impact of voluntary wheel running on circadian HR fluctuations.
Main Results:
- Anesthetized mice exhibited significant circadian HR fluctuations (amplitude ~47 bpm), with higher HR during the active (dark) period.
- Blockade of PNA reduced circadian HR fluctuations by ~70%, while SNA blockade caused <15% decline.
- Complete ANS blockade left small HR fluctuations, and freely moving mice showed only slightly larger fluctuations than anesthetized mice.
- Access to running wheels for one week significantly increased circadian HR fluctuation amplitude to ~103 bpm, correlating with increased oxygen consumption.
Conclusions:
- The ANS is a primary driver of circadian HR variations, with PNA playing a more dominant role than SNA, independent of physical activity.
- Physical activity's impact on daily HR variations is minimal unless mice have access to running wheels, suggesting a threshold effect or adaptation.
Abstract:
Heart rate (HR) and blood pressure as well as adverse cardiovascular events show clear circadian patterns, which are linked to interdependent daily variations in physical activity and cardiac autonomic nerve system (ANS) activity. We set out to assess the relative contributions of the ANS (alone) and physical activity to circadian HR fluctuations. To do so, we measured HR (beats per minute, bpm) in mice that were either immobilized using isoflurane anesthesia or free-moving. Nonlinear fits of HR data to sine functions revealed that anesthetized mice display brisk circadian HR fluctuations with amplitudes of 47.1±7.4bpm with the highest HRs in middle of the dark (active) period (ZT 18: 589±46bpm) and lowest HRs in the middle of the light (rest) period (ZT 6: 497±54bpm). The circadian HR fluctuations were reduced by ~70% following blockade of cardiac parasympathetic nervous activity (PNA) with atropine while declining by <15% following cardiac sympathetic nerve activity (SNA) blockade with propranolol. Small HR fluctuation amplitudes (11.6±5.9bpm) remained after complete cardiac ANS blockade. Remarkably, circadian HR fluctuation amplitudes in freely moving, telemetrized mice were only ~32% larger than in anesthetized mice. However, after gaining access to running wheels for 1week, circadian HR fluctuations increase to 102.9±12.1bpm and this is linked directly to increased O2 consumption during running. We conclude that, independent of physical activity, the ANS is a major determinant of circadian HR variations with PNA playing a dominant role compared to SNA. The effects of physical activity to the daily HR variations are remarkably small unless mice get access to running wheels.
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