| Summary: | Our previous study has shown that the corrected QT (QTc) interval of the electrocardiogram is longer during the dark period than during the light period in telemetered common marmosets. In the present study, we investigated the involvement of sympathetic and parasympathetic nervous activities in the changes of QTc interval associated with the light–dark cycle. Telemetry transmitters were implanted in six common marmosets to continuously record the electrocardiogram. The QT intervals obtained were corrected for the RR interval by applying individual probabilistic QT-rate correction formulae. Power spectral analysis of heart rate variability was performed to quantify each autonomic nervous function. Changes in QTc intervals and autonomic nervous tones were associated with the light–dark cycle. Parasympathetic nervous activity and QTc intervals significantly increased by approximately 10 ms during the dark period. Atropine, a muscarinic receptor antagonist, suppressed the increased parasympathetic tone and QTc prolongation during the dark period. In contrast, propranolol, a β-adrenoceptor antagonist, decreased the sympathetic activity and increased QTc intervals during the light period. These results suggest that the parasympathetic nerve functions prolong QTc intervals during the dark period, while the sympathetic nerve functions shorten them during the light period in common marmosets. Keywords:: common marmoset, autonomic nervous activity, heart rate variability, power spectral analysis, QT interval prolongation
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