Selective denervation of the aortic and carotid baroreceptors in rats

Inflammation of some visceral sensory systems and autonomic dysfunction in cardiovascular disease

The sensitization and hypertonicity of visceral afferents are highly relevant to the development and progression of cardiovascular and respiratory disease states. In this review, we described the evidence that the inflammatory process regulates visceral afferent sensitivity and tonicity, affecting the control of the cardiovascular and respiratory system. Some inflammatory mediators like nitric oxide, angiotensin II, endothelin-1, and arginine vasopressin may inhibit baroreceptor afferents and contribute to the baroreflex impairment observed in cardiovascular diseases. Cytokines may act directly on peripheral afferent terminals that transmit information to the central nervous system (CNS). TLR-4 receptors, which recognize lipopolysaccharide, were identified in the nodose and petrosal ganglion and have been implicated in disrupting the blood-brain barrier, which can potentiate the inflammatory process. For example, cytokines may cross the blood-brain barrier to access the CNS. Additionally, pro-inflammatory cytokines such as IL-1β, IL-6, TNF-α and some of their receptors have been identified in the nodose ganglion and carotid body. These pro-inflammatory cytokines also sensitize the dorsal root ganglion or are released in the nucleus of the solitary tract. In cardiovascular disease, pro-inflammatory mediators increase in the brain, heart, vessels, and plasma and may act locally or systemically to activate/sensitize afferent nervous terminals. Recent evidence demonstrated that the carotid body chemoreceptor cells might sense systemic pro-inflammatory molecules, supporting the novel proposal that the carotid body is part of the afferent pathway in the central anti-inflammatory reflexes. The exact mechanisms of how pro-inflammatory mediators affects visceral afferent signals and contribute to the pathophysiology of cardiovascular diseases awaits future research.

Autonomic Regulation of Inflammation in Conscious Animals

Bioelectronic medicine is a novel field in modern medicine based on the specific neuronal stimulation to control organ function, cardiovascular, and immune homeostasis. However, most studies addressing neuromodulation of the immune system have been conducted on anesthetized animals, which can affect the nervous system and neuromodulation. Here, we review recent studies involving conscious experimental rodents (rats and mice) to better understand the functional organization of neural control of immune homeostasis. We highlight typical experimental models of cardiovascular regulation, such as electrical activation of the aortic depressor nerve or the carotid sinus nerve, bilateral carotid occlusion, the Bezold-Jarisch reflex, and intravenous administration of the bacterial endotoxin lipopolysaccharide. These models have been used to investigate the relationship between neuromodulation of the cardiovascular and immune systems in conscious rodents (rats and mice). These studies provide critical information about the neuromodulation of the immune system, particularly the role of the autonomic nervous system, i.e., the sympathetic and parasympathetic branches acting both centrally (hypothalamus, nucleus ambiguus, nucleus tractus solitarius, caudal ventrolateral medulla, and rostral ventrolateral medulla), and peripherally (particularly spleen and adrenal medulla). Overall, the studies in conscious experimental models have certainly highlighted to the reader how the methodological approaches used to investigate cardiovascular reflexes in conscious rodents (rats and mice) can also be valuable for investigating the neural mechanisms involved in inflammatory responses. The reviewed studies have clinical implications for future therapeutic approaches of bioelectronic modulation of the nervous system to control organ function and physiological homeostasis in conscious physiology.

P2X3 receptor antagonism attenuates the progression of heart failure

Despite advances in the treatment of heart failure, prognosis is poor, mortality high and there remains no cure. Heart failure is associated with reduced cardiac pump function, autonomic dysregulation, systemic inflammation and sleep-disordered breathing; these morbidities are exacerbated by peripheral chemoreceptor dysfunction. We reveal that in heart failure the carotid body generates spontaneous, episodic burst discharges coincident with the onset of disordered breathing in male rats. Purinergic (P2X3) receptors were upregulated two-fold in peripheral chemosensory afferents in heart failure, and when antagonized abolished these episodic discharges, normalized both peripheral chemoreceptor sensitivity and the breathing pattern, reinstated autonomic balance, improved cardiac function, and reduced both inflammation and biomarkers of cardiac failure. Aberrant ATP transmission in the carotid body triggers episodic discharges that via P2X3 receptors play a crucial role in the progression of heart failure and as such offer a distinct therapeutic angle to reverse multiple components of its pathogenesis.

Physiological Sympathetic Activation Reduces Systemic Inflammation: Role of Baroreflex and Chemoreflex

Baroreflex and chemoreflex act through the autonomic nervous system, which is involved with the neural regulation of inflammation. The present study reports the effects of reflex physiological sympathetic activation in endotoxemic rats using bilateral carotid occlusion (BCO), a physiological approach involving the baroreflex and chemoreflex mechanisms and the influence of the baroreceptors and peripheral chemoreceptors in the cardiovascular and systemic inflammatory responses. After lipopolysaccharide (LPS) administration, the arterial pressure was recorded during 360 min in unanesthetized rats, and serial blood samples were collected to analyze the plasma cytokine levels. BCO elicited the reflex activation of the sympathetic nervous system, providing the following outcomes: (I) increased the power of the low-frequency band in the spectrum of the systolic arterial pressure during the BCO period; (II) reduced the levels of pro-inflammatory cytokines in plasma, including the tumor necrosis factor (TNF) and the interleukin (IL)-1β; (III) increased the plasma levels of anti-inflammatory cytokine IL-10, 90 min after LPS administration. Moreover, selective baroreceptor or chemoreceptor denervation deactivated mechanosensitive and chemical sensors, respectively, and decreased the release of the LPS-induced cytokine but did not alter the BCO modulatory effects. These results show, for the first time, that physiological reflex activation of the sympathetic circuit decreases the inflammatory response in endotoxemic rats and suggest a novel function for the baroreceptors as immunosensors during the systemic inflammation.

Electrical stimulation of the carotid sinus lowers arterial pressure and improves heart rate variability in L-NAME hypertensive conscious rats

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.