Circadian Rhythm in Intrinsic Heart Rate

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dc.contributor.advisorBackx, Peter
dc.contributor.authorBarazi, Nour
dc.date.accessioned2020-11-13T13:56:43Z
dc.date.available2020-11-13T13:56:43Z
dc.date.copyright2020-09
dc.date.issued2020-11-13
dc.date.updated2020-11-13T13:56:43Z
dc.degree.disciplineBiology
dc.degree.levelMaster's
dc.degree.nameMSc - Master of Science
dc.description.abstractHeart rate (HR) as well as adverse cardiac events (i.e. myocardial infarction, arrhythmias, stroke, and sudden cardiac death) show circadian patterns. Circadian HR fluctuations are traditionally thought to be controlled by the autonomic nervous system (ANS). However, recent studies have concluded that diurnal HR variation arise from intrinsic remodeling in SA node. To re-examine the mechanisms controlling circadian HR fluctuations, we performed surface electrocardiographic recordings (sECG) at 4 time points per day (ZT0, ZT6, ZT12 and ZT18) in CD1 mice that had been anesthetized in order to eliminate the potential confounding effects of activity on daily HR variation. We found that unconscious mice still showed diurnal HR fluctuation with peaks of HR in the dark period (ZT 18) and HR troughs in the light period (ZT 6). The amplitude of circadian HR fluctuations was reduced by ~2/3 by blockade of the cardiac parasympathetic nervous activity (PNA) with atropine while being reduced by ~1/3 by blockade of the cardiac sympathetic nerve activity (SNA) with propranolol. Complete ANS block abolished entirely the diurnal HR fluctuations. To assess the contribution of activity to diurnal HR fluctuations we also analyzed HR in telemetrized sedentary mice which showed, unexpectedly, nearly identical amplitudes of HR fluctuations to anesthetized mice. On the other hand, after mice were given access to running wheels for 1 week, the circadian HR amplitudes increased by ~150%. Conclusion: HR fluctuation requires the ANS even in the absence of physical activity with a 2:1 proportion of parasympathetic versus sympathetic control of circadian rhythm in basal HR. These results highlight the importance of taking experimental time of day into consideration when assessing HR responses to treatments and drug administration in anesthetized mice.
dc.identifier.urihttp://hdl.handle.net/10315/37958
dc.languageen
dc.rightsAuthor owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.
dc.subjectMedicine
dc.subject.keywordsBiology
dc.subject.keywordsPhysiology
dc.subject.keywordsCardiac biology
dc.subject.keywordsCardiac physiology
dc.subject.keywordsCircadian rhythm
dc.subject.keywordsHeart
dc.subject.keywordsHR
dc.subject.keywordsIntrinsic
dc.subject.keywordsAutonomic
dc.subject.keywordsExtrinsic
dc.subject.keywordsBasal heart rate
dc.subject.keywordsHeart rate
dc.subject.keywordsIntrinsic heart rate
dc.subject.keywordsResting heart rate
dc.subject.keywordsMice
dc.subject.keywordsCD1 mice
dc.subject.keywordsZeitgeber
dc.subject.keywordsAutonomic nervous system
dc.subject.keywordsParasympathetic nervous system
dc.subject.keywordsSympathetic nervous system
dc.subject.keywordsVagal tone
dc.subject.keywordsCircadian autonomic
dc.subject.keywordsHeart rate fluctuation
dc.subject.keywordsDay and night changes
dc.subject.keywordsCVD
dc.subject.keywordsCardiovascular disease
dc.subject.keywordsArrhythmia
dc.subject.keywordsSudden cardiac death
dc.subject.keywordsSinoatrial node
dc.subject.keywordsSA node
dc.subject.keywordsAnimal study
dc.subject.keywordsHuman physiology
dc.subject.keywordsPacemaker potential
dc.subject.keywordsHeart rate variability
dc.subject.keywordsHRV
dc.subject.keywordsAutonomic remodeling
dc.subject.keywordsAutonomic remodelling
dc.subject.keywordsExercise adaptations
dc.subject.keywordsCardiac adaptations
dc.subject.keywordsCircadian
dc.subject.keywordsRhythm
dc.subject.keywordsHeart rate rhythm
dc.subject.keywordsHeart rhythm
dc.subject.keywordsCircadian biology
dc.subject.keywordsChronobiology
dc.subject.keywordsCircadian medicine
dc.subject.keywordsMethods
dc.subject.keywordsCircadian study
dc.subject.keywordsCircadian research
dc.subject.keywordsCardiovascular
dc.subject.keywordsCardiac
dc.subject.keywordsCardiovascular research
dc.subject.keywordsCardiac research
dc.titleCircadian Rhythm in Intrinsic Heart Rate
dc.typeElectronic Thesis or Dissertation

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