Heart Rate and Body Temperature Monitoring in Pair-Housed Mice Using Star-Oddi Micro-HRT Biologgers

Background: Chronic stress-related disorders (ie., PTSD) are associated with elevated cardiovascular disease (CVD) risk. Improved methods however are needed to examine longitudinal cardiovascular changes and physiological adaptations in chronic stress mouse models, taking into account group-housed settings that consider environmental and social factors. Objective: To address this, we pilot tested the use of Star-Oddi micro-HRT biologgers for circadian and thermoregulatory monitoring of heart rate (HR) and body temperature (BT) in pair-housed mice during and after chronic stress exposure, combined with our custom software and video monitoring behavioral analysis system. Methods: 10–12-week-old C57BL/6 (n=4) were implanted with the micro-HRT biologgers to continuously record HR and BT at 773 Hz over a 7-day period. Mice were pair-housed under a 12:12-hour light cycle. Chronic stress was introduced through a Pavlovian fear conditioning paradigm (CS/US pairing) using a conditioned stimuli (CS) auditory cue to evoke a conditioned cardiovascular arousal state. Control non-stressed mice received the CS only. Two variations of ECG amplification and bandwidth were tested. The quality of the recordings was assessed using raw ECG data and manual annotation, compared to on-board HR calculations and their associated quality index (QI) ranging from 0 (Best) to 3 (Worst). Amplification and bandwidth of the ECG signal was also assessed using power spectral density (PSD) analysis and at the end of the study, a 1 mg/kg isoproterenol injection was administered to elicit a maximum HR response. In addition, deep learning-based tracking, circadian-dependent freezing and locomotion behaviors were analyzed alongside HR and BT data. Results: Both ECG bandwidth variations provided high-quality recordings, but the higher bandwidth setting yielded more consistent HR readings with a lower QI due to higher frequency content of the QRS waveform in mice. The on-board HR calculations correlated strongly with the raw ECG data, especially during rest, with a maximum HR of 804bpm, minimum HR 329bpm and average HR of 548±105bpm. The subcutaneous body temperature had a maximum of 36.93°C, minimum of 34.03°C and an average of 35.41±0.69°C. Moreover, the CS-evoked changes in HR and BT successfully tracked longitudinally stress-induced arousal states across day-night cycles. Conclusions: Star-Oddi micro-HRT biologgers effectively recorded normal longitudinal circadian patterns HR, ECG and BT, and corresponding stress-induced cardiovascular arousal states in pair-housed mice. This pilot study demonstrates the feasibility of using these biologgers for minimally invasive, high-resolution physiological monitoring in pair-housed mice, enabling the analysis of integrated circadian and stress-related cardiovascular outcomes. Congressionally Directed Medical Research Programs (CDMRP) PR210574 and NIH-NIA 1R21AG086859-01 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.