Time course of the hemodynamic responses to aortic depressor nerve stimulation in conscious spontaneously hypertensive rats

Abstract

The time to reach the maximum response of arterial pressure, heart rate and vascular resistance (hindquarter and mesenteric) was measured in conscious male spontaneously hypertensive (SHR) and normotensive control rats (NCR; Wistar; 18-22 weeks) subjected to electrical stimulation of the aortic depressor nerve (ADN). The parameters of stimulation were 1 mA intensity and 2 ms pulse length applied for 5 s, using frequencies of 10, 30, and 90 Hz. The time to reach the hemodynamic responses at different frequencies of ADN stimulation was similar for SHR (N = 15) and NCR (N = 14); hypotension = NCR (4194 ± 336 to 3695 ± 463 ms) vs SHR (3475 ± 354 to 4494 ± 300 ms); bradycardia = NCR (1618 ± 152 to 1358 ± 185 ms) vs SHR (1911 ± 323 to 1852 ± 431 ms), and the fall in hindquarter vascular resistance = NCR (6054 ± 486 to 6550 ± 847 ms) vs SHR (4849 ± 918 to 4926 ± 646 ms); mesenteric = NCR (5574 ± 790 to 5752 ± 539 ms) vs SHR (5638 ± 648 to 6777 ± 624 ms). In addition, ADN stimulation produced baroreflex responses characterized by a faster cardiac effect followed by a vascular effect, which together contributed to the decrease in arterial pressure. Therefore, the results indicate that there is no alteration in the conduction of the electrical impulse after the site of baroreceptor mechanical transduction in the baroreflex pathway (central and/or efferent) in conscious SHR compared to NCR.

Baroreflex activation in conscious rats modulates the joint inflammatory response via sympathetic function

“…Taking into account that anesthesia attenuates baroreflex function (Palmisano et al, 1991;Tanaka and Nishikawa, 1999;Akine et al, 2001;Bassani et al, 2013), our laboratory developed a technique to electrically activate the aortic depressor nerve, an afference of the baroreflex, in conscious rats. We demonstrated that electrical stimulation of the aortic depressor nerve activates the baroreflex promoting bradycardia and hypotension, under physiological (De Paula et al, 1999;Durand et al, 2009) and pathophysiological conditions (Salgado et al, 2007;Durand et al, 2009Durand et al, , 2012, without the undesirable effects of anesthesia. Moreover, electrical stimulation of the aortic depressor nerve in conscious rats shifts the sympathovagal balance toward a parasympathetic predominance (Krieger et al, 1982;Chapleau et al, 1988).…”

Effect of Cardiac-Cycle-Synchronized Selective Vagal Stimulation on Heart Rate and Blood Pressure in Rats

“…In rats, the ADN is a separate fascicle, typically on the surface of the vagal nerve. Once the ADN is surgically freed from its surrounding tissue and detached from the vagal nerve, bipolar electrical stimulation can activate the baroreflex and lower BP by reducing the sympathetic tone [8].…”

Low intensity stimulation of aortic baroreceptor afferent fibers as a potential therapeutic alternative for hypertension treatment

“…However, success of conscious longitudinal baroreflex studies using the ADN in rats is currently low and hampered by (1) inherent anatomical challenges given the small diameter of the nerve and the relative ease to sustain a damage to it during dissection and manipulation; and (2) the use of unrefined electrode design and nerve stimulation protocols that can ensure long-term viability of the nerve. To our knowledge, current studies reporting hemodynamic responses to ADN stimulation in conscious rats are typically run within 24 h after surgical implantation of the electrodes 18 , 29 , 36 . It is therefore possible that reported measures by those studies may, to a great extent, be confounded by issues related to surgical stress and inadequate animal recovery.…”