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We evaluated the effects of long-term (48 h) electrical stimulation of the carotid sinus (CS) in hypertensive rats. L-NAME-treated (10 days) Wistar rats were implanted with a catheter in the femoral artery and a miniaturized electrical stimulator attached to electrodes positioned around the left CS, encompassing the CS nerve. One day after implantation, arterial pressure (AP) was directly recorded in conscious animals for 60 min. Square pulses (1 ms, 3 V, 30 Hz) were applied intermittently (20/20 s ON/OFF) to the CS for 48 h. After the end of stimulation, AP was recorded again. Nonstimulated rats (control group) and rats without electrodes around the CS (sham-operated) were also studied. Next, the animals were decapitated, and segments of mesenteric resistance arteries were removed to study vascular function. After the stimulation period, AP was 16 ± 5 mmHg lower in the stimulated group, whereas sham-operated and control rats showed similar AP between the first and second recording periods. Heart rate variability (HRV) evaluated using time and frequency domain tools and a nonlinear approach (symbolic analysis) suggested that hypertensive rats with electrodes around the CS, stimulated or not, exhibited a shift in cardiac sympathovagal balance towards parasympathetic tone. The relaxation response to acetylcholine in endothelium-intact mesenteric arteries was enhanced in rats that underwent CS stimulation for 48 h. In conclusion, long-term CS stimulation is effective in reducing AP levels, improving HRV and increasing mesenteric vascular relaxation in L-NAME hypertensive rats. Moreover, only the presence of electrodes around the CS is effective in eliciting changes in HRV similar to those observed in stimulated rats.

Baroreflex activation by electric stimulation of the carotid sinus (CS) effectively lowers blood pressure. However, the degree to which differences between stimulation protocols impinge on cardiovascular outcomes has not been defined. To address this, we examined the effects of short- and long-duration (SD and LD) CS stimulation on hemodynamic and vascular function in spontaneously hypertensive rats (SHRs). We fit animals with miniature electrical stimulators coupled to electrodes positioned around the left CS nerve that delivered intermittent 5/25 s ON/OFF (SD) or 20/20 s ON/OFF (LD) square pulses (1 ms, 3 V, 30 Hz) continuously applied for 48 h in conscious animals. A sham-operated control group was also studied. We measured mean arterial pressure (MAP), systolic blood pressure variability (SBPV), heart rate (HR), and heart rate variability (HRV) for 60 min before stimulation, 24 h into the protocol, and 60 min after stimulation had stopped. SD stimulation reversibly lowered MAP and HR during stimulation. LD stimulation evoked a decrease in MAP that was sustained even after stimulation was stopped. Neither SD nor LD had any effect on SBPV or HRV when recorded after stimulation, indicating no adaptation in autonomic activity. Both the contractile response to phenylephrine and the relaxation response to acetylcholine were increased in mesenteric resistance vessels isolated from LD-stimulated rats only. In conclusion, the ability of baroreflex activation to modulate hemodynamics and induce lasting vascular adaptation is critically dependent on the electrical parameters and duration of CS stimulation.

Baroreflex activation by electric stimulation of the carotid sinus (CS) effectively lowers blood pressure. However, the degree to which differences between stimulation protocols impinge on cardiovascular outcomes has not been defined. To address this, we examined the effects of short- and long-duration (SD and LD) CS stimulation on hemodynamic and vascular function in spontaneously hypertensive rats (SHRs). We fit animals with miniature electrical stimulators coupled to electrodes positioned around the left CS nerve that delivered intermittent 5/25 s ON/OFF (SD) or 20/20 s ON/OFF (LD) square pulses (1 ms, 3 V, 30 Hz) continuously applied for 48 h in conscious animals. A sham-operated control group was also studied. We measured mean arterial pressure (MAP), systolic blood pressure variability (SBPV), heart rate (HR), and heart rate variability (HRV) for 60 min before stimulation, 24 h into the protocol, and 60 min after stimulation had stopped. SD stimulation reversibly lowered MAP and HR during stimulation. LD stimulation evoked a decrease in MAP that was sustained even after stimulation was stopped. Neither SD nor LD had any effect on SBPV or HRV when recorded after stimulation, indicating no adaptation in autonomic activity. Both the contractile response to phenylephrine and the relaxation response to acetylcholine were increased in mesenteric resistance vessels isolated from LD-stimulated rats only. In conclusion, the ability of baroreflex activation to modulate hemodynamics and induce lasting vascular adaptation is critically dependent on the electrical parameters and duration of CS stimulation.

We evaluated the effects of long-term (48 h) electrical stimulation of the carotid sinus (CS) in hypertensive rats. L-NAME-treated (10 days) Wistar rats were implanted with a catheter in the femoral artery and a miniaturized electrical stimulator attached to electrodes positioned around the left CS, encompassing the CS nerve. One day after implantation, arterial pressure (AP) was directly recorded in conscious animals for 60 min. Square pulses (1 ms, 3 V, 30 Hz) were applied intermittently (20/20 s ON/OFF) to the CS for 48 h. After the end of stimulation, AP was recorded again. Nonstimulated rats (control group) and rats without electrodes around the CS (sham-operated) were also studied. Next, the animals were decapitated, and segments of mesenteric resistance arteries were removed to study vascular function. After the stimulation period, AP was 16 ± 5 mmHg lower in the stimulated group, whereas sham-operated and control rats showed similar AP between the first and second recording periods. Heart rate variability (HRV) evaluated using time and frequency domain tools and a nonlinear approach (symbolic analysis) suggested that hypertensive rats with electrodes around the CS, stimulated or not, exhibited a shift in cardiac sympathovagal balance towards parasympathetic tone. The relaxation response to acetylcholine in endothelium-intact mesenteric arteries was enhanced in rats that underwent CS stimulation for 48 h. In conclusion, long-term CS stimulation is effective in reducing AP levels, improving HRV and increasing mesenteric vascular relaxation in L-NAME hypertensive rats. Moreover, only the presence of electrodes around the CS is effective in eliciting changes in HRV similar to those observed in stimulated rats.

Made available in DSpace on 2018-12-11T17:27:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-07-01 The activation of GABAergic receptors, GABAA and GABAB, in the lateral parabrachial nucleus (LPBN) increases water and sodium intake in satiated and fluid-depleted rats. The present study investigated the presence of the GABAC receptor in the LPBN, its involvement in water and sodium intake, and its effects on cardiovascular parameters during the acute fluid depletion induced by furosemide combined with captopril (Furo/Cap). One group of male Wistar rats (290-300 g) with bilateral stainless steel LPBN cannulas was used to test the effects of a GABAC receptor agonist and antagonist on the fluid intake and cardiovascular parameters. We investigated the effects of bilateral LPBN injections of trans-4-aminocrotonic acid (TACA) on the intake of water and 0.3 M NaCl induced by acute fluid depletion (subcutaneous injection of Furo/Cap). c-Fos expression increased (P 0.05). Treatment with the GABAC receptor antagonist (Z)-3-[(aminoiminomethyl)thio]prop-2-enoic acid sulfate (ZAPA, 10 nmol) or with ZAPA (10 nmol) plus TACA (160 nmol) did not change the sodium or water intake compared with that for vehicle (saline) (P > 0.05). Bilateral injections of the GABAC agonist in the LPBN of Furo/Cap-treated rats did not affect the mean arterial pressure (MAP) or heart rate (HR). The GABAC receptor expression in the LPBN was confirmed by the presence of a 50 kDa band. Although LPBN neurons might express GABAC receptors, their activation produced no change in water and sodium intake or in the cardiovascular parameters in the acute fluid depletion rats. Therefore, the GABAC receptors in the LPBN might not interfere with fluid and blood pressure regulation. Department of Physiology School of Medicine of Ribeirão Preto University of São Paulo Department of Basic Sciences School of Dentistry UNESP - Universidade Estadual Paulista Rodovia Department of Basic Sciences School of Dentistry UNESP - Universidade Estadual Paulista Rodovia

The baroreflex is an essential regulator of blood pressure (BP); whereby, baroreceptors sense acute changes in BP and convey this information, via the nodose ganglia (NG), to the nucleus of the solitary tract (NTS). Manipulation of the baroreflex may provide a novel strategy in the treatment of hypertension. To that end, our neuroanatomical studies revealed a dense localization of angiotensin type 1a receptor (AT1a)-containing neuronal cell bodies in the NG and terminals in the NTS, thereby positioning them to play a role in the baroreflex. We, therefore, hypothesized that AT1a neurons residing in the NG potently influence cardiovascular function. Male and female mice expressing channelrhodopsin-2 (ChR2) and yellow fluorescent protein (eYFP) specifically in AT1a-expressing neurons (AT1aR-ChR2-eYFP) were used to determine the function of these neurons. In vitro patch clamp electrophysiological recordings from neurons in the NTS receiving axons expressing ChR2-eYFP revealed that optogenetic stimulation (473nm) reliably evoked excitatory postsynaptic currents (EPSCs). In concurrence with studies demonstrating that baroreceptor afferents utilize glutamate in the NTS, these EPSCs were eliminated by the presence of glutamate receptor antagonists. Next, the NG of anesthetized mice were subjected to optogenetic stimulation of varying frequencies (1, 15, 30Hz) for 1 min, and BP and HR responses were assessed. Optogenetic stimulation of these AT1a-expressing neurons led to significant decreases in mean arterial pressure (ΔMAP= -16±3*, -36±4*, -44±7* mmHg) and HR (ΔHR= -13±7, -104±44*, -163±59* bpm) in AT1a-ChR2-eYFP mice (n=6), but there was no effect on control mice harboring only the stop-FLOX-ChR2-eYFP gene (n=5; ΔMAP= 0±2, -2±1, 5±5 mmHg; ΔHR= 4±4, 3±4, -13±21 bpm). Additionally, AT1a-ChR2-eYFP mice rendered hypertensive via DOCA-salt (n=7) exhibited a dampened response to optogenetic stimulation (ΔMAP= -7±1#, -14±3*#, -30±6*# mmHg; ΔHR= -29±34, -71±37*, -178±50* bpm). Collectively, these data suggest that AT1a neurons in the NG are key regulators of the baroreflex, and may serve as a target for antihypertensive therapeutics. (p

It is accepted that activation of angiotensin type 1a receptors (AT1a) within the CNS elevates blood pressure by influencing sympathetic outflow and vasopressin (VP) secretion; however, the neuronal circuits mediating these effects are not completely understood. The present studies characterize the structure and function of AT1a neurons residing in the median preoptic nucleus (MnPO) and the organum vasculosum of the lamina terminalis (OVLT), thereby evaluating their potential role in blood pressure control. Using male mice that express Cre-recombinase prior to the STOP codon of the AT1a gene, initial studies combined genetic reporting with in situ hybridization to reveal that AT1a neurons in the MnPO and OVLT are largely excitatory (87±4% express vesicular glutamate transporter 2). Subsequently, AT1a-Cre mice were delivered a Cre-inducible adeno-associated virus to induce expression of channelrhodopsin-2 (ChR2) and enhanced yellow fluorescent protein (eYFP) specifically within AT1a neurons of the MnPO/OVLT (AAV-ChR2-eYFP; n = 4). Control mice were delivered AAV-eYFP (n = 4). Analysis of eYFP immunofluorescence revealed that neurons within the MnPO/OVLT that express AT1a send projections to the paraventricular nucleus of the hypothalamus (PVN; an area involved in sympathetic outflow and VP secretion) that appear to synapse onto VP synthesizing neurons. To evaluate the functionality of this connection, we optogenetically stimulated AT1a neurons in the region while recording cardiovascular parameters in anesthetized mice. Ten-minutes of optogenetic stimulation (473 nM;15 Hz; 20 ms pulse width; 60 s ON/OFF) robustly elevated systolic blood pressure in AAV-ChR2-eYFP mice relative to AAV-eYFP controls. This effect was rapid in its onset (34 ± 9 vs. -2 ± 4 mmHg at 5 min, p < 0.05) but persisted for the entire 50 min of cardiovascular recording (45 ± 11 vs. -3 ± 7 mmHg at 50 min, p < 0.05). Intriguingly, the optogenetic stimulation also resulted in 62% increase in Fos induction in AVP neurons within the PVN relative to AAV-eYFP controls (86 ± 5 vs. 52 ± 2 %; p

Recent studies demonstrated a critical functional connection between the autonomic (sympathetic and parasympathetic) nervous and the immune systems. The carotid sinus nerve (CSN) conveys electrical signals from the chemoreceptors of the carotid bifurcation to the central nervous system where the stimuli are processed to activate sympathetic and parasympathetic efferent signals. Here, we reported that chemoreflex activation via electrical CSN stimulation, in conscious rats, controls the innate immune response to lipopolysaccharide attenuating the plasma levels of inflammatory cytokines such as tumor necrosis factor (TNF), interleukin 1β (IL-1β) and interleukin 6 (IL-6). By contrast, the chemoreflex stimulation increases the plasma levels of anti-inflammatory cytokine interleukin 10 (IL-10). This chemoreflex anti-inflammatory network was abrogated by carotid chemoreceptor denervation and by pharmacological blockade of either sympathetic - propranolol - or parasympathetic - methylatropine – signals. The chemoreflex stimulation as well as the surgical and pharmacological procedures were confirmed by real-time recording of hemodynamic parameters [pulsatile arterial pressure (PAP) and heart rate (HR)]. These results reveal, in conscious animals, a novel mechanism of neuromodulation mediated by the carotid chemoreceptors and involving both the sympathetic and parasympathetic systems.