title: Differences in the dynamic baroreflex characteristics of unmyelinated and myelinated central pathways are less evident in spontaneously hypertensive rats.
abstract: 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.
authors.affiliation: Department of Cardiovascular Dynamics, National Cerebral and Cardiovascular Center, Osaka, Japan; and michaeljturner@icloud.com.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Turner
authors.affiliation: Department of Cardiovascular Dynamics, National Cerebral and Cardiovascular Center, Osaka, Japan; and.
authors.forename: Toru
authors.initials: T
authors.lastname: Kawada
authors.affiliation: Department of Cardiovascular Dynamics, National Cerebral and Cardiovascular Center, Osaka, Japan; and.
authors.forename: Shuji
authors.initials: S
authors.lastname: Shimizu
authors.affiliation: Department of Cardiovascular Dynamics, National Cerebral and Cardiovascular Center, Osaka, Japan; and Department of Artificial Organ Medicine, Faculty of Medicine, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Fukumitsu
authors.affiliation: Department of Cardiovascular Dynamics, National Cerebral and Cardiovascular Center, Osaka, Japan; and Department of Artificial Organ Medicine, Faculty of Medicine, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Sugimachi
mesh_terms: D000818:Animals; D062186:Arterial Pressure; D017704:Baroreflex; D004195:Disease Models, Animal; D004558:Electric Stimulation; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D009413:Nerve Fibers, Myelinated; D036421:Nerve Fibers, Unmyelinated; D011311:Pressoreceptors / Q000503:physiopathology*; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D013997:Time Factors
keywords: baroreceptor; baroreflex; hypertension; sympathetic nerve activity