Dynamic characteristics of baroreflex neural and peripheral arcs are preserved in spontaneously hypertensive rats

2011 ◽  
Vol 300 (1) ◽  
pp. R155-R165 ◽  
Author(s):  
Toru Kawada ◽  
Shuji Shimizu ◽  
Atsunori Kamiya ◽  
Yusuke Sata ◽  
Kazunori Uemura ◽  
...  
Keyword(s):  
Transfer Function ◽  
Dynamic Characteristics ◽  
Spontaneously Hypertensive Rats ◽  
Transfer Functions ◽  
Carotid Sinus ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Carotid Sinus Baroreflex ◽  
Low Pass ◽  
Dynamic Gain

Although baroreceptors are known to reset to operate in a higher pressure range in spontaneously hypertensive rats (SHR), the total profile of dynamic arterial pressure (AP) regulation remains to be clarified. We estimated open-loop transfer functions of the carotid sinus baroreflex in SHR and Wistar Kyoto (WKY) rats. Mean input pressures were set at 120 (WKY120 and SHR120) and 160 mmHg (SHR160). The neural arc transfer function from carotid sinus pressure to efferent splanchnic sympathetic nerve activity (SNA) revealed derivative characteristics in both WKY and SHR. The slope of dynamic gain (in decibels per decade) between 0.1 and 1 Hz was not different between WKY120 (10.1 ± 1.0) and SHR120 (10.4 ± 1.1) but was significantly greater in SHR160 (13.2 ± 0.8, P < 0.05 with Bonferroni correction) than in SHR120. The peripheral arc transfer function from SNA to AP showed low-pass characteristics. The slope of dynamic gain (in decibels per decade) did not differ between WKY120 (−34.0 ± 1.2) and SHR120 (−31.4 ± 1.0) or between SHR120 and SHR160 (−32.8 ± 1.3). The total baroreflex showed low-pass characteristics and the dynamic gain at 0.01 Hz did not differ between WKY120 (0.91 ± 0.08) and SHR120 (0.84 ± 0.13) or between SHR120 and SHR160 (0.83 ± 0.11). In both WKY and SHR, the declining slope of dynamic gain was significantly gentler for the total baroreflex than for the peripheral arc, suggesting improved dynamic AP response in the total baroreflex. In conclusion, the dynamic characteristics of AP regulation by the carotid sinus baroreflex were well preserved in SHR despite significantly higher mean AP.

scholarly journals Aortic depressor nerve stimulation does not impede the dynamic characteristics of the carotid sinus baroreflex in normotensive or spontaneously hypertensive rats

2017 ◽  
Vol 312 (5) ◽  
pp. R787-R796 ◽  
Author(s):  
Toru Kawada ◽  
Michael J. Turner ◽  
Shuji Shimizu ◽  
Masafumi Fukumitsu ◽  
Atsunori Kamiya ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Sympathetic Nerve ◽  
Spontaneously Hypertensive Rats ◽  
Sympathetic Nerve Activity ◽  
Carotid Sinus ◽  
Hypertensive Rats ◽  
Nerve Activity ◽  
Spontaneously Hypertensive ◽  
Aortic Depressor Nerve ◽  
Carotid Sinus Baroreflex

Recent clinical trials in patients with drug-resistant hypertension indicate that electrical activation of the carotid sinus baroreflex can reduce arterial pressure (AP) for more than a year. To examine whether the electrical stimulation from one baroreflex system impedes normal short-term AP regulation via another unstimulated baroreflex system, we electrically stimulated the left aortic depressor nerve (ADN) while estimating the dynamic characteristics of the carotid sinus baroreflex in anesthetized normotensive Wistar-Kyoto (WKY; n = 8) rats and spontaneously hypertensive rats (SHR; n = 7). Isolated carotid sinus regions were perturbed for 20 min using a Gaussian white noise signal with a mean of 120 mmHg for WKY and 160 mmHg for SHR. Tonic ADN stimulation (2 Hz, 10 V, and 0.1-ms pulse width) decreased mean sympathetic nerve activity (73.4 ± 14.0 vs. 51.6 ± 11.3 arbitrary units in WKY, P = 0.012; and 248.7 ± 33.9 vs. 181.1 ± 16.6 arbitrary units in SHR, P = 0.018) and mean AP (90.8 ± 6.6 vs. 81.2 ± 5.4 mmHg in WKY, P = 0.004; and 128.6 ± 9.8 vs. 114.7 ± 10.3 mmHg in SHR, P = 0.009). The slope of dynamic gain in the neural arc transfer function from carotid sinus pressure to sympathetic nerve activity was not different between trials with and without the ADN stimulation (12.55 ± 0.93 vs. 13.03 ± 1.28 dB/decade in WKY, P = 0.542; and 17.37 ± 1.01 vs. 17.47 ± 1.64 dB/decade in SHR, P = 0.946). These results indicate that the tonic ADN stimulation does not significantly modify the dynamic characteristics of the carotid sinus baroreflex.

scholarly journals Differences in the dynamic baroreflex characteristics of unmyelinated and myelinated central pathways are less evident in spontaneously hypertensive rats

2015 ◽  
Vol 309 (11) ◽  
pp. R1397-R1405 ◽  
Author(s):  
Michael J. Turner ◽  
Toru Kawada ◽  
Shuji Shimizu ◽  
Masafumi Fukumitsu ◽  
Masaru Sugimachi
Keyword(s):  
Transfer Function ◽  
Spontaneously Hypertensive Rats ◽  
Modulation Frequency ◽  
Frequency Range ◽  
Hypertensive Rats ◽  
Baroreflex Control ◽  
Spontaneously Hypertensive ◽  
C Fibers ◽  
C Fiber ◽  
Dynamic Gain

The aim of the study was to identify the contribution of myelinated (A-fiber) and unmyelinated (C-fiber) baroreceptor central pathways to the baroreflex control of sympathetic nerve activity (SNA) and arterial pressure (AP) in anesthetized Wistar-Kyoto (WKY; n = 8) and spontaneously hypertensive rats (SHR; n = 8). The left aortic depressor nerve (ADN) was electrically stimulated with two types of binary white noise signals designed to preferentially activate A-fibers (A-BRx protocol) or C-fibers (C-BRx protocol). In WKY, the central arc transfer function from ADN stimulation to SNA estimated by A-BRx showed strong derivative characteristics with the slope of dynamic gain between 0.1 and 1 Hz ( Gslope) of 14.63 ± 0.89 dB/decade. In contrast, the central arc transfer function estimated by C-BRx exhibited nonderivative characteristics with Gslope of 0.64 ± 1.13 dB/decade. This indicates that A-fibers are important for rapid baroreflex regulation, whereas C-fibers are likely important for more sustained regulation of SNA and AP. In SHR, the central arc transfer function estimated by A-BRx showed higher Gslope (18.46 ± 0.75 dB/decade, P < 0.01) and that estimated by C-BRx showed higher Gslope (8.62 ± 0.64 dB/decade, P < 0.001) with significantly lower dynamic gain at 0.01 Hz (6.29 ± 0.48 vs. 2.80 ± 0.36%/Hz, P < 0.001) compared with WKY. In conclusion, the dynamic characteristics of the A-fiber central pathway are enhanced in the high-modulation frequency range (0.1–1 Hz) and those of the C-fiber central pathway are attenuated in the low-modulation frequency range (0.01–0.1 Hz) in SHR.

Effects of tempol on baroreflex neural arc versus peripheral arc in normotensive and spontaneously hypertensive rats

2015 ◽  
Vol 308 (11) ◽  
pp. R957-R964 ◽  
Author(s):  
Toru Kawada ◽  
Yusuke Sata ◽  
Shuji Shimizu ◽  
Michael J. Turner ◽  
Masafumi Fukumitsu ◽  
...  
Keyword(s):  
Spontaneously Hypertensive Rats ◽  
Carotid Sinus ◽  
Dominant Role ◽  
Regression Line ◽  
Redox Signaling ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Carotid Sinus Baroreflex ◽  
Wistar Kyoto

Although oxidative redox signaling affects arterial pressure (AP) regulation via modulation of vascular tone and sympathetic nerve activity (SNA), it remains unknown which effect plays a dominant role in the determination of AP in vivo. Open-loop systems analysis of the carotid sinus baroreflex was conducted to separately quantify characteristics of the neural arc from baroreceptor pressure input to SNA and the peripheral arc from SNA to AP in normotensive Wistar-Kyoto (WKY; n = 8) and spontaneously hypertensive rats (SHR; n = 8). Responses in SNA and AP to a staircase-wise increase in carotid sinus pressure were examined before and during intravenous administration of the membrane-permeable superoxide dismutase mimetic tempol (30 mg/kg bolus followed by 30 mg·kg−1·h−1). Two-way ANOVA indicated that tempol significantly decreased the response range of SNA (from 89.1 ± 2.4% to 60.7 ± 2.5% in WKY and from 77.5 ± 3.2% to 56.9 ± 7.3% in SHR, P < 0.001) without affecting the lower plateau of SNA (from 12.5 ± 2.4% to 9.5 ± 2.5% in WKY, and from 28.8 ± 2.8% to 30.4 ± 5.7% in SHR, P = 0.800) in the neural arc. While tempol did not affect the peripheral arc characteristics in WKY, it yielded a downward change in the regression line of AP vs. SNA in SHR. In conclusion, oxidative redox signaling plays an important role, not only in the pathological AP elevation, but also in the baroreflex-mediated physiological AP regulation. The effect of modulating oxidative redox signaling on the peripheral arc contributed to the determination of AP in SHR but not in WKY.

791 CAROTID SINUS NERVE ABLATION IN ADULT SPONTANEOUSLY HYPERTENSIVE RATS (SHR) IS CHRONICALLY ANTI-HYPERTENSIVE

2012 ◽  
Vol 30 ◽  
pp. e229
Author(s):  
Fiona D. McBryde ◽  
Ana P.L. Abdala ◽  
Alex V. Gourine ◽  
Nepthali Marina ◽  
Emma B. Hendy ◽  
...  
Keyword(s):  
Spontaneously Hypertensive Rats ◽  
Carotid Sinus ◽  
Carotid Sinus Nerve ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive

scholarly journals Contrasting open-loop dynamic characteristics of sympathetic and vagal systems during baroreflex-mediated heart rate control in rats

2019 ◽  
Vol 317 (6) ◽  
pp. R879-R890 ◽  
Author(s):  
Toru Kawada ◽  
Hiromi Yamamoto ◽  
Yohsuke Hayama ◽  
Takuya Nishikawa ◽  
Kunihiko Tanaka ◽  
...  
Keyword(s):  
Heart Rate ◽  
Transfer Function ◽  
Dynamic Characteristics ◽  
Carotid Sinus ◽  
Gaussian White Noise ◽  
Open Loop ◽  
Model Parameters ◽  
Before And After ◽  
Dynamic Gain ◽  
Sinus Pressure

Although heart rate (HR) is governed by the sympathetic and parasympathetic nervous systems, a head-to-head comparison of the open-loop dynamic characteristics of the total arc from a baroreceptor pressure input to the HR response has yet to be performed. We estimated the transfer function from carotid sinus pressure input to the HR response ( HCSP→HR) before and after bilateral vagotomy ( n = 7) as well as before and after the administration of a β-blocker propranolol ( n = 8) in anesthetized male Wistar-Kyoto rats. The carotid sinus pressure was perturbed according to a Gaussian white noise signal so that the input power spectra were relatively flat between 0.01 and 1 Hz. The gain plot of HCSP→HR was V-shaped. Vagotomy reduced the dynamic gain at 1 Hz (0.0598 ± 0.0065 to 0.0025 ± 0.0004 beats·min−1·mmHg−1, P < 0.001) but not at 0.01 or 0.1 Hz. β-Blockade reduced the dynamic gain at 0.01 Hz (0.247 ± 0.069 to 0.077 ± 0.017 beats·min−1·mmHg−1, P = 0.020) but not at 0.1 or 1 Hz. We also estimated the efferent limb transfer function from electrical vagal efferent stimulation to the HR response ( HVN→HR) under β-blockade conditions. We associated the model parameters of HVN→HR with the mean HR and the standard deviation of HR so that HVN→HR could be estimated based only on the HR data. We finally estimated the neural arc transfer function from a pressure input to efferent vagal nerve activity by dividing HCSP→HR by HVN→HR. The mathematically determined vagal neural arc showed derivative characteristics with its phase near zero radians at the lowest frequency.

scholarly journals Electrical Stimulation of Carotid Sinus in Conscious Normotensive and Spontaneously Hypertensive Rats

2015 ◽  
Vol 29 (S1) ◽  
Author(s):  
Gean Domingos ◽  
Fernanda Santos‐Almeida ◽  
Luiz Eduardo Silva ◽  
Daniel Dias ◽  
Carlos Alberto Silva ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Spontaneously Hypertensive Rats ◽  
Carotid Sinus ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Stimulation Of

Arterial baroreflex dynamics in normotensive and spontaneously hypertensive rats

1992 ◽  
Vol 263 (3) ◽  
pp. R524-R528 ◽  
Author(s):  
S. Harada ◽  
T. Imaizumi ◽  
S. Ando ◽  
Y. Hirooka ◽  
K. Sunagawa ◽  
...  
Keyword(s):  
Transfer Function ◽  
Sympathetic Nerve ◽  
Spontaneously Hypertensive Rats ◽  
Sympathetic Nerve Activity ◽  
Arterial Baroreflex ◽  
Frequency Range ◽  
Hypertensive Rats ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Spontaneously Hypertensive

To investigate dynamic or frequency-dependent characteristics of arterial baroreflex control of efferent sympathetic nerve activity in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY), we assessed the transfer function from aortic pressure (AP) to renal sympathetic nerve activity (RSNA) using a “white-noise technique.” In pentobarbital sodium-anesthetized rats, we recorded RSNA as the output, while AP was randomly perturbed to impose input pressure changes with broad frequencies. We calculated the transfer function from AP to RSNA over the frequency range of 0.01-5 Hz through the spectral analysis of the input and output. The results indicated that the gain, phase shift, and coherence of the transfer function for SHR and for WKY were similar and statistically indistinguishable. The gain was relatively constant below 0.05 Hz but increased steadily by fivefold as frequency increased in the frequency range of 0.05-0.8 Hz. The phase was out of phase where coherence was high. The coherence was high (greater than 0.5) in the frequency range of 0.04-0.8 and 1.00-1.03 Hz but was low in other frequencies. These results suggest that dynamic or frequency-dependent characteristics of arterial baroreflex control of RSNA were not altered in SHR as compared with WKY.

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