Frequency-dependent baroreflex modulation of blood pressure and heart rate variability in conscious mice

The goal of this study was to determine the baroreflex influence on systolic arterial pressure ( SAP) and pulse interval ( PI) variability in conscious mice. SAP and PI were measured in C57B1/6J mice subjected to sinoaortic deafferentation ( SAD, n = 21) or sham surgery ( n = 20). Average SAP and PI did not differ in SAD or control mice. In contrast, SAP variance was enhanced ( 21 +/- 4 vs. 9.5 +/- 1 mmHg(2)) and PI variance reduced (8.8 +/- 2 vs. 26 +/- 6ms(2)) in SAD vs. control mice. High-frequency (HF: 1-5 Hz) SAP variability quantified by spectral analysis was greater in SAD (8.5 +/- 2.0 mmHg2) compared with control (2.5 +/- 0.2 mmHg(2)) mice, whereas low-frequency (LF: 0.1-1 Hz) SAP variability did not differ between the groups. Conversely, LF PI variability was markedly reduced in SAD mice (0.5 +/- 0.1 vs. 10.8 +/- 3.4 ms(2)). LF oscillations in SAP and PI were coherent in control mice ( coherence = 0.68 +/- 0.05), with changes in SAP leading changes in PI ( phase = -1.41 +/- 0.06 radians), but were not coherent in SAD mice ( coherence = 0.08 +/- 0.03). Blockade of parasympathetic drive with atropine decreased average PI, PI variance, and LF and HF PI variability in control ( n = 10) but had no effect in SAD ( n = 6) mice. In control mice, blockade of sympathetic cardiac receptors with propranolol increased average PI and decreased PI variance and LF PI variability ( n = 6). In SAD mice, propranolol increased average PI ( n = 6). In conclusion, baroreflex modulation of PI contributes to LF, but not HF PI variability, and is mediated by both sympathetic and parasympathetic drives in conscious mice.