Cafeteria diet increases fat mass and chronically elevates lumbar sympathetic nerve activity in rats

Controversies related to renal artery denervation and devices

PURPOSE OF REVIEW

This review article discusses the controversies, strengths, and limitations of the current literature on renal artery denervation in the management of resistant hypertension, as well as the future directions of this intervention.

RECENT FINDINGS

There have been conflicting data from the different randomized control trials assessing the efficacy of renal artery denervation in the management of resistant hypertension.

SUMMARY

Renal artery denervation is achieved by ablating the sympathetic nerves surrounding the renal arteries using endovascular ultrasound, radiofrequency, or alcohol. Our review article highlights that renal artery denervation is generally effective in improving blood pressure in patients with resistant hypertension. The Food and Drug Administration (FDA) has recently approved the ReCor Medical Paradise system, and the Symplicity Spyral RDN systems for renal artery denervation.

The role of hypertensive status in the preoperative patient selection of TSA

Background

This study investigates the relationship between hypertension and postoperative complications following total shoulder arthroplasty (TSA).

Methods

All patients who underwent TSA between 2015 and 2020 from the American College of Surgeons National Surgical Quality Improvement database were surveyed. The study population was divided into patients with no hypertension and patients with hypertension. Patient demographics, comorbidities, and 30-day postoperative complications were collected. Logistic regression analysis was used to investigate the relationship between hypertension and postoperative complications.

Results

Compared to no hypertension, hypertension was significantly associated with an increased likelihood of experiencing sepsis (P = .021), pneumonia (P = .019), myocardial infarction (P = .038), blood transfusions (P = .006), readmission (P < .001), reoperation (P < .001), non-home discharge (P < .001), and any complication (P < .001). After accounting for significant patient variables, compared to no hypertension, hypertension was independently significantly associated with an increased likelihood of experiencing reoperation (odds ratio 1.48; 95% CI, 1.142-1.905; P = .003) and any complication (odds ratio 1.10; 95% CI, 1.008-1.205; P = .033).

Conclusion

In this study, we identified hypertension as an independent significant predictor for both reoperation and any complication following TSA. This study provides evidence for incorporating a patient's hypertensive status into preoperative screening, aiming to improve surgical candidate selection and surgical outcomes following TSA.

Consumption of a Taiwanese cafeteria diet induces metabolic disorders and fecal flora changes in obese rats

OBJECTIVES

Among diet-induced obesity animal models, the cafeteria diet, which contains human junk food and processed foods, is a popular experimental animal diets in Western countries. Consumption of a cafeteria diet can lead to the development of obesity and non-alcoholic liver disease in as soon as 2 mo, which more accurately reflects human eating patterns. The aim of this study was to establish a Taiwanese cafeteria diet and compare it with a traditional lard-based, 60% high-fat diet in a 12-wk animal model.

METHODS

Six-wk-old male Wistar rats were assigned to the following three groups: control diet (C; LabDiet 5001); high-fat diet (HFD; 60% HFD); and the Taiwanese cafeteria diet (CAF).

RESULTS

At the end of the study, weight gain and steatosis were observed in the HF and CAF groups. Compared with the HFD group, rats in the CAF group showed significantly higher plasma triacylglycerol concentrations and insulin resistance, which may have been correlated with increased inflammatory responses. Significantly lower hepatic sterol regulatory element-binding protein-1c and insulin receptor substrate-1 protein expressions were observed in the CAF group compared with the HFD group. Additionally, disruption of the microbiotic composition followed by increased obesity-related bacteria was observed in the CAF group.

CONCLUSIONS

The present study confirmed that the Taiwanese cafeteria diet-induced rat model provided a potential platform for investigating obesity-related diseases.

Mechanisms and treatment of obesity-related hypertension-Part 1: Mechanisms

The prevalence of obesity has tripled over the past five decades. Obesity, especially visceral obesity, is closely related to hypertension, increasing the risk of primary (essential) hypertension by 65%-75%. Hypertension is a major risk factor for cardiovascular disease, the leading cause of death worldwide, and its prevalence is rapidly increasing following the pandemic rise in obesity. Although the causal relationship between obesity and high blood pressure (BP) is well established, the detailed mechanisms for such association are still under research. For more than 30 years sympathetic nervous system (SNS) and kidney sodium reabsorption activation, secondary to insulin resistance and compensatory hyperinsulinemia, have been considered as primary mediators of elevated BP in obesity. However, experimental and clinical data show that severe insulin resistance and hyperinsulinemia can occur in the absence of elevated BP, challenging the causal relationship between insulin resistance and hyperinsulinemia as the key factor linking obesity to hypertension. The purpose of Part 1 of this review is to summarize the available data on recently emerging mechanisms believed to contribute to obesity-related hypertension through increased sodium reabsorption and volume expansion, such as: physical compression of the kidney by perirenal/intrarenal fat and overactivation of the systemic/renal SNS and the renin-angiotensin-aldosterone system. The role of hyperleptinemia, impaired chemoreceptor and baroreceptor reflexes, and increased perivascular fat is also discussed. Specifically targeting these mechanisms may pave the way for a new therapeutic intervention in the treatment of obesity-related hypertension in the context of 'precision medicine' principles, which will be discussed in Part 2.

Role of the Sympathetic Nervous System in Mild Chronic Inflammatory Diseases: Focus on Osteoarthritis

The sympathetic nervous system (SNS) is a major regulatory mediator connecting the brain and the immune system that influences accordingly inflammatory processes within the entire body. In the periphery, the SNS exerts its effects mainly via its neurotransmitters norepinephrine (NE) and epinephrine (E), which are released by peripheral nerve endings in lymphatic organs and other tissues. Depending on their concentration, NE and E bind to specific α- and β-adrenergic receptor subtypes and can cause both pro- and anti-inflammatory cellular responses. The co-transmitter neuropeptide Y, adenosine triphosphate, or its metabolite adenosine are also mediators of the SNS. Local pro-inflammatory processes due to injury or pathogens lead to an activation of the SNS, which in turn induces several immunoregulatory mechanisms with either pro- or anti-inflammatory effects depending on neurotransmitter concentration or pathological context. In chronic inflammatory diseases, the activity of the SNS is persistently elevated and can trigger detrimental pathological processes. Recently, the sympathetic contribution to mild chronic inflammatory diseases like osteoarthritis (OA) has attracted growing interest. OA is a whole-joint disease and is characterized by mild chronic inflammation in the joint. In this narrative article, we summarize the underlying mechanisms behind the sympathetic influence on inflammation during OA pathogenesis. In addition, OA comorbidities also accompanied by mild chronic inflammation, such as hypertension, obesity, diabetes, and depression, will be reviewed. Finally, the potential of SNS-based therapeutic options for the treatment of OA will be discussed.

Central Nervous System Control of Glucose Homeostasis: A Therapeutic Target for Type 2 Diabetes?

Historically, pancreatic islet beta cells have been viewed as principal regulators of glycemia, with type 2 diabetes (T2D) resulting when insulin secretion fails to compensate for peripheral tissue insulin resistance. However, glycemia is also regulated by insulin-independent mechanisms that are dysregulated in T2D. Based on evidence supporting its role both in adaptive coupling of insulin secretion to changes in insulin sensitivity and in the regulation of insulin-independent glucose disposal, the central nervous system (CNS) has emerged as a fundamental player in glucose homeostasis. Here, we review and expand upon an integrative model wherein the CNS, together with the islet, establishes and maintains the defended level of glycemia. We discuss the implications of this model for understanding both normal glucose homeostasis and T2D pathogenesis and highlight centrally targeted therapeutic approaches with the potential to restore normoglycemia to patients with T2D.

Arterial and Cardiac Remodeling Associated With Extra Weight Gain in an Isolated Abdominal Obesity Cohort

Introduction: This study aims to assess the changes in cardiovascular remodeling attributable to bodyweight gain in a middle-aged abdominal obesity cohort. A remodeling worsening might explain the increase in cardiovascular risk associated with a dynamic of weight gain. Methods: Seventy-five middle-aged subjects (56 ± 5 years, 38 women) with abdominal obesity and no known cardiovascular disease underwent MRI-based examinations at baseline and at a 6.1 ± 1.2-year follow-up to monitor cardiovascular remodeling and hemodynamic variables, most notably the effective arterial elastance (Ea). Ea is a proxy of the arterial load that must be overcome during left ventricular (LV) ejection, with increased EA resulting in concentric LV remodeling. Results: Sixteen obese subjects had significant weight gain (>7%) during follow-up (WG+), whereas the 59 other individuals did not (WG-). WG+ and WG- exhibited significant differences in the baseline to follow-up evolutions of several hemodynamic parameters, notably diastolic and mean blood pressures (for mean blood pressure, WG+: +9.3 ± 10.9 mmHg vs. WG-: +1.7 ± 11.8 mmHg, p = 0.022), heart rate (WG+: +0.6 ± 9.4 min^-1 vs. -8.9 ± 11.5 min^-1, p = 0.003), LV concentric remodeling index (WG: +0.08 ± 0.16 g.mL^-1 vs. WG-: -0.02 ± 0.13 g.mL^-1, p = 0.018) and Ea (WG+: +0.20 ± 0.28 mL mmHg^-1 vs. WG-: +0.01 ± 0.30 mL mmHg^-1, p = 0.021). The evolution of the LV concentric remodeling index and Ea were also strongly correlated in the overall obese population (p < 0.001, R² = 0.31). Conclusions: A weight gain dynamic is accompanied by increases in arterial load and load-related concentric LV remodeling in an isolated abdominal obesity cohort. This remodeling could have a significant impact on cardiovascular risk.

Effects of renal denervation on cardiovascular, metabolic and renal functions in streptozotocin-induced diabetic rats

Diabetes promotes renal sympathetic hyperactivity, autonomic imbalance, and cardiovascular and renal dysfunction. Bilateral renal denervation (BRD) has emerged as a treatment for diabetes; however, the mechanisms that underlie the beneficial effects of BRD are unknown.

AIMS

The present study evaluated the effects of BRD on autonomic, cardiovascular, metabolic, and renal function in streptozotocin-diabetic rats.

MAIN METHODS

Wistar rats were separated into three experimental groups: control (CTR), diabetic (DM), and diabetic that underwent BRD (DM BRD). BRD was performed two weeks after STZ-diabetes induction, the experiments were performed four weeks after DM induction. This study evaluated sympathetic vasomotor nerve activity in different territories (renal, lumbar and splanchnic), arterial baroreceptor reflex, metabolic and renal function.

KEY FINDINGS

BRD significantly reduced glycemia, glycosuria, albuminuria, and SGLT2 gene expression in the kidney in DM rats. Renal sympathetic nerve activity (rSNA) was significantly increased and splanchnic sympathetic nerve activity (sSNA) was significantly decreased in DM rats, without changes in lumbar sympathetic nerve activity (lSNA). BRD was able to normalize sSNA and significantly increase lSNA in DM rats compared to control rats. Additionally, cardiac baroreceptor sensitivity was impaired in DM rats, and BRD significantly improved baroreflex sensitivity.

SIGNIFICANCE

Our data suggest that renal nerves play an important role in autonomic, cardiovascular, and renal dysfunction in STZ-DM rats. Thus, sympathetic renal hyperactivity should be considered a possible therapeutic target in diabetic patients.

Leptin as a Key between Obesity and Cardiovascular Disease

Obesity increases the risk of cardiovascular disease through various influencing factors. Leptin, which is predominantly secreted by adipose tissue, regulates satiety homeostasis and energy balance, and influences cardiovascular functions directly and indirectly. Leptin appears to play a role in heart protection in leptin-deficient and leptin-receptor-deficient rodent model experiments. Hyperleptinemia or leptin resistance in human obesity influences the vascular endothelium, cardiovascular structure and functions, inflammation, and sympathetic activity, which may lead to cardiovascular disease. Leptin is involved in many processes, including signal transduction, vascular endothelial function, and cardiac structural remodeling. However, the dual (positive and negative) regulator effect of leptin and its receptor on cardiovascular disease has not been completely understood. The protective role of leptin signaling in cardiovascular disease could be a promising target for cardiovascular disease prevention in obese patients.

Exploring the Mediators that Promote Carotid Body Dysfunction in Type 2 Diabetes and Obesity Related Syndromes

Carotid bodies (CBs) are peripheral chemoreceptors that sense changes in blood O₂, CO₂, and pH levels. Apart from ventilatory control, these organs are deeply involved in the homeostatic regulation of carbohydrates and lipid metabolism and inflammation. It has been described that CB dysfunction is involved in the genesis of metabolic diseases and that CB overactivation is present in animal models of metabolic disease and in prediabetes patients. Additionally, resection of the CB-sensitive nerve, the carotid sinus nerve (CSN), or CB ablation in animals prevents and reverses diet-induced insulin resistance and glucose intolerance as well as sympathoadrenal overactivity, meaning that the beneficial effects of decreasing CB activity on glucose homeostasis are modulated by target-related efferent sympathetic nerves, through a reflex initiated in the CBs. In agreement with our pre-clinical data, hyperbaric oxygen therapy, which reduces CB activity, improves glucose homeostasis in type 2 diabetes patients. Insulin, leptin, and pro-inflammatory cytokines activate the CB. In this manuscript, we review in a concise manner the putative pathways linking CB chemoreceptor deregulation with the pathogenesis of metabolic diseases and discuss and present new data that highlight the roles of hyperinsulinemia, hyperleptinemia, and chronic inflammation as major factors contributing to CB dysfunction in metabolic disorders.

Cardiac sympathetic drive is increased in cafeteria diet-fed rats independent of impairment in peripheral baroreflex and chemoreflex functions

BACKGROUND AND AIMS

Consumption of a high caloric diet induces autonomic imbalance, which can lead to cardiovascular disease. Impaired arterial baroreflex control is suggested to play an important role in cardiovascular autonomic imbalance, often seen in obesity. We previously demonstrated that cafeteria diets increase the sympathetic drive to white and brown adipose tissue.

METHODS AND RESULTS

After feeding a cafeteria diet to rats for 26 days, we evaluated: (i)heart rate (HR) and arterial pressure (AP); (ii)baroreflex and chemoreflex function; and (iii) autonomic modulation of the heart and vessels, measured through pulse interval (PI) and systolic arterial pressure (SAP) variability analyses and following administration of autonomic blockers. The cafeteria diet increased body fat mass and serum insulin, leptin, triacylglycerol and cholesterol levels. Baseline HR (15%) was also increased, accompanied by increased power in the low frequency band (60%) and in the low frequency/high frequency ratio (104%) in the PI spectra. Nonlinear analysis revealed an increased occurrence of 0V (39%) and decreased occurrence of 2UV (18%) patterns. Following administration of autonomic blockers, we observed an increase in cardiac sympathetic tone (425%) in cafeteria diet-fed rats. The cafeteria diet had no effect on AP, SAP variability, baroreflex and chemoreflex control.

CONCLUSION

Our findings suggest that consumption of a cafeteria diet increases sympathetic drive to the heart but not to the blood vessels, independent of impairment in baroreflex and chemoreflex functions. Other mechanisms may be involved in the increased cardiac sympathetic drive, and compensatory vascular mechanisms may prevent the development of hypertension in this model of obesity.

Comparison of high-fat style diet-induced dysregulation of baroreflex control of renal sympathetic nerve activity in intact and ovariectomized female rats: Renal sympathetic nerve activity in high-fat style diet fed intact and ovariectomized female rats

IMPACT STATEMENT

Over activation of renal sensory nerve in obesity blunts the normal regulation of renal sympathetic nerve activity. To date, there is no investigation that has been carried out on baroreflex regulation of renal sympathetic nerve activity in obese ovarian hormones deprived rat model, and the effect of renal denervation on the baroreflex regulation of renal sympathetic nerve activity. Thus, we investigated the role of renal innervation on baroreflex regulation of renal sympathetic nerve activity in obese intact and ovariectomized female rats. Our data demonstrated that in obese states, the impaired baroreflex control is indistinguishable between ovarian hormones deprived and non-deprived states. This study will be of substantial interest to researchers working on the impact of diet-induced hypertension in pre- and postmenopausal women. This study provides insight into health risks amongst obese women regardless of their ovarian hormonal status and may be integrated in preventive health strategies.

Obesity: sex and sympathetics

Obesity increases sympathetic nerve activity (SNA) in men, but not women. Here, we review current evidence suggesting that sexually dimorphic sympathoexcitatory responses to leptin and insulin may contribute. More specifically, while insulin increases SNA similarly in lean males and females, this response is markedly amplified in obese males, but is abolished in obese females. In lean female rats, leptin increases a subset of sympathetic nerves only during the high estrogen proestrus reproductive phase; thus, in obese females, because reproductive cycling can become impaired, the sporadic nature of leptin-induced sympathoexcitaton could minimize its action, despite elevated leptin levels. In contrast, in males, obesity preserves or enhances the central sympathoexcitatory response to leptin, and current evidence favors leptin’s contribution to the well-established increases in SNA induced by obesity in men. Leptin and insulin increase SNA via receptor binding in the hypothalamic arcuate nucleus and a neuropathway that includes arcuate neuropeptide Y (NPY) and proopiomelanocortin (POMC) projections to the paraventricular nucleus. These metabolic hormones normally suppress sympathoinhibitory NPY neurons and activate sympathoexcitatory POMC neurons. However, obesity appears to alter the ongoing activity and responsiveness of arcuate NPY and POMC neurons in a sexually dimorphic way, such that SNA increases in males but not females. We propose hypotheses to explain these sex differences and suggest areas of future research.

Sympathetic Nervous System Contributions to Hypertension: Updates and Therapeutic Relevance

The sympathetic nervous system plays a pivotal role in the long-term regulation of arterial blood pressure through the ability of the central nervous system to integrate neurohumoral signals and differentially regulate sympathetic neural input to specific end organs. Part 1 of this review will discuss neural mechanisms of salt-sensitive hypertension, obesity-induced hypertension, and the ability of prior experiences to sensitize autonomic networks. Part 2 of this review focuses on new therapeutic advances to treat resistant hypertension including renal denervation and carotid baroactivation. Both advances lower arterial blood pressure by reducing sympathetic outflow. We discuss potential mechanisms and areas of future investigation to target the sympathetic nervous system.

Sites and sources of sympathoexcitation in obese male rats: role of brain insulin

In males, obesity increases sympathetic nerve activity (SNA), but the mechanisms are unclear. Here, we investigate insulin, via an action in the arcuate nucleus (ArcN), and downstream neuropathways, including melanocortin receptor 3/4 (MC3/4R) in the hypothalamic paraventricular nucleus (PVN) and dorsal medial hypothalamus (DMH). We studied conscious and α-chloralose-anesthetized Sprague-Dawley rats fed a high-fat diet, which causes obesity prone (OP) rats to accrue excess fat and obesity-resistant (OR) rats to maintain fat content, similar to rats fed a standard control (CON) diet. Nonspecific blockade of the ArcN with muscimol and specific blockade of ArcN insulin receptors (InsR) decreased lumbar SNA (LSNA), heart rate (HR), and mean arterial pressure (MAP) in OP, but not OR or CON, rats, indicating that insulin supports LSNA in obese males. In conscious rats, intracerebroventricular infusion of insulin increased MAP only in OP rats and also improved HR baroreflex function from subnormal to supranormal. The brain sensitization to insulin may elucidate how insulin can drive central SNA pathways when transport of insulin across the blood-brain barrier may be impaired. Blockade of PVN, but not DMH, MC3/4R with SHU9119 decreased LSNA, HR, and, MAP in OP, but not OR or CON, rats. Interestingly, nanoinjection of the MC3/4R agonist melanotan II (MTII) into the PVN increased LSNA only in OP rats, similar to PVN MTII-induced increases in LSNA in CON rats after blockade of sympathoinhibitory neuropeptide Y Y1 receptors. ArcN InsR expression was not increased in OP rats. Collectively, these data indicate that obesity increases SNA, in part via increased InsR signaling and downstream PVN MC3/4R.

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

Sympathetic Denervation of the Common Hepatic Artery Lessens Glucose Intolerance in the Fat- and Fructose-Fed Dog

This study assessed the effectiveness of surgical sympathetic denervation of the common hepatic artery (CHADN) in improving glucose tolerance. CHADN eliminated norepinephrine content in the liver and partially decreased it in the pancreas and the upper gut. We assessed oral glucose tolerance at baseline and after 4 weeks of high-fat high-fructose (HFHF) feeding. Dogs were then randomized to sham surgery (SHAM) (n = 9) or CHADN surgery (n = 11) and retested 2.5 or 3.5 weeks later while still on the HFHF diet. CHADN improved glucose tolerance by ∼60% in part because of enhanced insulin secretion, as indicated by an increase in the insulinogenic index. In a subset of dogs (SHAM, n = 5; CHADN, n = 6), a hyperinsulinemic-hyperglycemic clamp was used to assess whether CHADN could improve hepatic glucose metabolism independent of a change in insulin release. CHADN reduced the diet-induced defect in net hepatic glucose balance by 37%. In another subset of dogs (SHAM, n = 4; CHADN, n = 5) the HFHF diet was continued for 3 months postsurgery and the improvement in glucose tolerance caused by CHADN continued. In conclusion, CHADN has the potential to enhance postprandial glucose clearance in states of diet-induced glucose intolerance.

Emerging Roles of Sympathetic Nerves and Inflammation in Perivascular Adipose Tissue

Perivascular adipose tissue (PVAT) is no longer recognised as simply a structural support for the vasculature, and we now know that PVAT releases vasoactive factors which modulate vascular function. Since the discovery of this function in 1991, PVAT research is rapidly growing and the importance of PVAT function in disease is becoming increasingly clear. Obesity is associated with a plethora of vascular conditions; therefore, the study of adipocytes and their effects on the vasculature is vital. PVAT contains an adrenergic system including nerves, adrenoceptors and transporters. In obesity, the autonomic nervous system is dysfunctional; therefore, sympathetic innervation of PVAT may be the key mechanistic link between increased adiposity and vascular disease. In addition, not all obese people develop vascular disease, but a common feature amongst those that do appears to be the inflammatory cell population in PVAT. This review will discuss what is known about sympathetic innervation of PVAT, and the links between nerve activation and inflammation in obesity. In addition, we will examine the therapeutic potential of exercise in sympathetic stimulation of adipose tissue.

High-fat diet exacerbates postoperative pain and inflammation in a sex-dependent manner

Obesity is often associated with increased pain, but little is known about the effects of obesity and diet on postoperative pain. In this study, effects of diet and obesity were examined in the paw incision model, a preclinical model of postoperative pain. Long-Evans rats were fed high-fat diet (40% calories from butter fat) or low-fat normal chow. Male rats fed high-fat diet starting 6 weeks before incision (a diet previously shown to induce markers of obesity) had prolonged mechanical hypersensitivity and an overall increase in spontaneous pain in response to paw incision, compared with normal chow controls. Diet effects in females were minor. Removing high-fat diet for 2 weeks before incision reversed the diet effects on pain behaviors, although this was not enough time to reverse high-fat diet-induced weight gain. A shorter (1 week) exposure to high-fat diet before incision also increased pain behaviors in males, albeit to a lesser degree. The 6-week high-fat diet increased macrophage density as examined immunohistochemically in lumbar dorsal root ganglion even before paw incision, especially in males, and sensitized responses of peritoneal macrophages to lipopolysaccharide stimuli in vitro. The nerve regeneration marker growth-associated protein 43 (GAP43) in skin near the incision (day 4) was higher in the high-fat diet group, and wound healing was delayed. In summary, high-fat diet increased postoperative pain particularly in males, but some diet effects did not depend on weight gain. Even short-term dietary manipulations, that do not affect obesity, may enhance postoperative pain.

Deciphering the Neural Control of Sympathetic Nerve Activity: Status Report and Directions for Future Research

Sympathetic nerve activity (SNA) contributes appreciably to the control of physiological function, such that pathological alterations in SNA can lead to a variety of diseases. The goal of this review is to discuss the characteristics of SNA, briefly review the methodology that has been used to assess SNA and its control, and to describe the essential role of neurophysiological studies in conscious animals to provide additional insights into the regulation of SNA. Studies in both humans and animals have shown that SNA is rhythmic or organized into bursts whose frequency varies depending on experimental conditions and the species. These rhythms are generated by brainstem neurons, and conveyed to sympathetic preganglionic neurons through several pathways, including those emanating from the rostral ventrolateral medulla. Although rhythmic SNA is present in decerebrate animals (indicating that neurons in the brainstem and spinal cord are adequate to generate this activity), there is considerable evidence that a variety of supratentorial structures including the insular and prefrontal cortices, amygdala, and hypothalamic subnuclei provide inputs to the brainstem regions that regulate SNA. It is also known that the characteristics of SNA are altered during stress and particular behaviors such as the defense response and exercise. While it is a certainty that supratentorial structures contribute to changes in SNA during these behaviors, the neural underpinnings of the responses are yet to be established. Understanding how SNA is modified during affective responses and particular behaviors will require neurophysiological studies in awake, behaving animals, including those that entail recording activity from neurons that generate SNA. Recent studies have shown that responses of neurons in the central nervous system to most sensory inputs are context-specific. Future neurophysiological studies in conscious animals should also ascertain whether this general rule also applies to sensory signals that modify SNA.

Chronic interfacing with the autonomic nervous system using carbon nanotube (CNT) yarn electrodes

The ability to reliably and safely communicate chronically with small diameter (100–300 µm) autonomic nerves could have a significant impact in fundamental biomedical research and clinical applications. However, this ability has remained elusive with existing neural interface technologies. Here we show a new chronic nerve interface using highly flexible materials with axon-like dimensions. The interface was implemented with carbon nanotube (CNT) yarn electrodes to chronically record neural activity from two separate autonomic nerves: the glossopharyngeal and vagus nerves. The recorded neural signals maintain a high signal-to-noise ratio (>10 dB) in chronic implant models. We further demonstrate the ability to process the neural activity to detect hypoxic and gastric extension events from the glossopharyngeal and vagus nerves, respectively. These results establish a novel, chronic platform neural interfacing technique with the autonomic nervous system and demonstrate the possibility of regulating internal organ function, leading to new bioelectronic therapies and patient health monitoring.

In rats fed high-energy diets, taste, rather than fat content, is the key factor increasing food intake: a comparison of a cafeteria and a lipid-supplemented standard diet

Background

Food selection and ingestion both in humans and rodents, often is a critical factor in determining excess energy intake and its related disorders.

Methods

Two different concepts of high-fat diets were tested for their obesogenic effects in rats; in both cases, lipids constituted about 40% of their energy intake. The main difference with controls fed standard lab chow, was, precisely, the lipid content. Cafeteria diets (K) were self-selected diets devised to be desirable to the rats, mainly because of its diverse mix of tastes, particularly salty and sweet. This diet was compared with another, more classical high-fat (HF) diet, devised not to be as tasty as K, and prepared by supplementing standard chow pellets with fat. We also analysed the influence of sex on the effects of the diets.

Results

K rats grew faster because of a high lipid, sugar and protein intake, especially the males, while females showed lower weight but higher proportion of body lipid. In contrast, the weight of HF groups were not different from controls. Individual nutrient’s intake were analysed, and we found that K rats ingested large amounts of both disaccharides and salt, with scant differences of other nutrients’ proportion between the three groups. The results suggest that the key differential factor of the diet eliciting excess energy intake was the massive presence of sweet and salty tasting food.

Conclusions

The significant presence of sugar and salt appears as a powerful inducer of excess food intake, more effective than a simple (albeit large) increase in the diet’s lipid content. These effects appeared already after a relatively short treatment. The differential effects of sex agree with their different hedonic and obesogenic response to diet.

Recent Advances in Neurogenic Hypertension: Dietary Salt, Obesity, and Inflammation

Neurally-mediated hypertension results from a dysregulation of sympathetic and/or neuroendocrine mechanisms to increase ABP. Multiple factors may exert multiple central effects to alter neural circuits and produce unique sympathetic signatures and elevate ABP. In this brief review, we have discussed novel observations regarding three contributing factors: dietary salt intake, obesity, and inflammation. However, the interaction among these and other factors is likely much more complex; recent studies suggest a prior exposure to one stimulus may sensitize the response to a subsequent hypertensive stimulus. Insight into the central mechanisms by which these factors selectively alter SNA or cooperatively interact to impact hypertension may represent a platform for novel therapeutic treatment strategies.

The Spleen: A Hub Connecting Nervous and Immune Systems in Cardiovascular and Metabolic Diseases

Metabolic disorders have been identified as major health problems affecting a large portion of the world population. In addition, obesity and insulin resistance are principal risk factors for the development of cardiovascular diseases. Altered immune responses are common features of both hypertension and obesity and, moreover, the involvement of the nervous system in the modulation of immune system is gaining even more attention in both pathophysiological contexts. For these reasons, during the last decades, researches focused their efforts on the comprehension of the molecular mechanisms connecting immune system to cardiovascular and metabolic diseases. On the other hand, it has been reported that in these pathological conditions, central neural pathways modulate the activity of the peripheral nervous system, which is strongly involved in onset and progression of the disease. It is interesting to notice that neural reflex can also participate in the modulation of immune functions. In this scenario, the spleen becomes the crucial hub allowing the interaction of different systems differently involved in metabolic and cardiovascular diseases. Here, we summarize the major findings that dissect the role of the immune system in disorders related to metabolic and cardiovascular dysfunctions, and how this could also be influenced by neural reflexes.

Leptin as a Mediator of Obesity-Induced Hypertension

Hypertension and associated cardiovascular diseases represent the most common health complication of obesity and the leading cause of morbidity and mortality in overweight and obese patients. Emerging evidence suggests a critical role for the central nervous system particularly the brain action of the adipocyte-derived hormone leptin in linking obesity and hypertension. The preserved ability of leptin to cause cardiovascular sympathetic nerve activation despite the resistance to the metabolic actions of the hormone appears essential in this pathological process. This review describes the evidence supporting the neurogenic bases for obesity-associated hypertension with a particular focus on the neuronal and molecular signaling pathways underlying leptin's effects on sympathetic nerve activity and blood pressure.

Sympathetic regulation of blood pressure in normotension and hypertension: when sex matters

NEW FINDINGS

What is the topic of this review? Hypertension is a major problem in Western society. Risk of hypertension increases with age, especially in women, who have lower risk compared with men until menopause. This review outlines the sex differences in the sympathetic control of blood pressure and how these mechanisms change with age. What advances does it highlight? It has recently been recognized that men and women regulate blood pressure by different physiological mechanisms. This is important for both the understanding and the clinical management of individual patients with hypertension. This review summarizes recent advances in understanding how the regulation of blood pressure in hypertension by the sympathetic nervous system differs between men and women. The sympathetic nervous system has a central role in the regulation of arterial blood pressure (BP) and in the development of hypertension in humans. Recent evidence points to differences between the sexes in the integrative mechanisms by which BP is controlled, suggesting that the development of hypertension may follow distinct pathways in women compared with men. An important aspect of sympathetic control of BP is its substantial interindividual variability. In healthy young men, the variability in sympathetic nerve activity (SNA) is balanced by variability in cardiac output and vascular adrenergic responses, such that BP remains similar, and normal, across a severalfold range of resting SNA values. In young women, variability in resting SNA is similar to that seen in men, but the 'balancing' mechanisms are strikingly different; women exhibit greater β-adrenergic vasodilatation compared with men, which minimizes the pressor effects of a given level of SNA. Ageing is associated with increased SNA and a loss of the balancing factors seen in younger people, leading to an increased risk of hypertension in older people. Loss of oestrogen with menopause in women appears to be linked mechanistically with the decrease in β-adrenergic vasodilatation and the increased risk of hypertension in older women. Other important factors contributing to hypertension via sympathetic mechanisms are obesity and arterial stiffening, both of which increase with ageing. We conclude with a discussion of important areas in which more work is needed to understand and manage appropriately the sex-specific mechanisms in the development and maintenance of hypertension.

Renal Denervation Normalizes Arterial Pressure With No Effect on Glucose Metabolism or Renal Inflammation in Obese Hypertensive Mice

Hypertension often occurs in concurrence with obesity and diabetes mellitus, commonly referred to as metabolic syndrome. Renal denervation (RDNx) lowers arterial pressure (AP) and improves glucose metabolism in drug-resistant hypertensive patients with high body mass index. In addition, RDNx has been shown to reduce renal inflammation in the mouse model of angiotensin II hypertension. The present study tested the hypothesis that RDNx reduces AP and renal inflammation and improves glucose metabolism in obesity-induced hypertension. Eight-week-old C57BL/6J mice were fed either a low-fat diet (10 kcal%) or a high-fat diet (45 kcal%) for 10 weeks. Body weight, food intake, fasting blood glucose, and glucose metabolism (glucose tolerance test) were measured. In a parallel study, radiotelemeters were implanted in mice for AP measurement. High fat-fed C57BL/6J mice exhibited an inflammatory and metabolic syndrome phenotype, including increased fat mass, increased AP, and hyperglycemia compared with low-fat diet mice. RDNx, but not Sham surgery, normalized AP in high-fat diet mice (115.8±1.5 mm Hg in sham versus 96.6±6.7 mm Hg in RDNx). RDNx had no significant effect on AP in low-fat diet mice. Also, RDNx had no significant effect on glucose metabolism or renal inflammation as measured by the number of CD8, CD4, and T helper cells or levels of inflammatory cytokines in the kidneys. These results indicate that although renal nerves play a role in obesity-induced hypertension, they do not contribute to impaired glucose metabolism or renal inflammation in this model.

Current Approaches to Quantifying Tonic and Reflex Autonomic Outflows Controlling Cardiovascular Function in Humans and Experimental Animals

The role of the autonomic nervous system in the pathophysiology of human and experimental models of cardiovascular disease is well established. In the recent years, there have been some rapid developments in the diagnostic approaches used to assess and monitor autonomic functions. Although most of these methods are devoted for research purposes in laboratory animals, many have still found their way to routine clinical practice. To name a few, direct long-term telemetry recording of sympathetic nerve activity (SNA) in rodents, single-unit SNA recording using microneurography in human subjects and spectral analysis of blood pressure and heart rate in both humans and animals have recently received an overwhelming attention. In this article, we therefore provide an overview of the methods and techniques used to assess tonic and reflex autonomic functions in humans and experimental animals, highlighting current advances available and procedure description, limitations and usefulness for diagnostic purposes.

Effect of Angiotensin(1-7) on Heart Function in an Experimental Rat Model of Obesity

Aim: Obesity is a risk factor for the development of cardiovascular diseases. Recently it was shown that overexpression of the Mas-receptor antagonist angiotensin(1-7) could prevent from diet-induced obesity. However, it remained unclear whether diet-induced obesity and angiotensin(1-7) overexpression might also have effects on the cardiovascular system in these rats.

Methods:Twenty three male Sprague Dawley rats were fed with standard chow (SD+chow, n = 5) or a cafeteria diet (SD+CD, n = 6) for 5 months. To investigate the effect of angiotensin(1-7) transgenic rats, expressing an angiotensin(1-7)-producing fusion protein in testis were used. These transgenic rats also received a 5 month's feeding period with either chow (TGR+chow, n = 6) or cafeteria diet (TGR+CD, n = 6), respectively. Hemodynamic measurements (pressure-volume loops) were carried out to assess cardiac function and blood pressure. Subsequently, hearts were explanted and investigated according to the Langendorff technique. Furthermore, cardiac remodeling in these animals was investigated histologically.

Results:After 5 months cafeteria diet feeding rats showed a significantly increased body weight, which could be prevented in transgenic rats. However, there was no effect on cardiac performance after cafeteria diet in non-transgenic and transgenic rats. Moreover, overexpression of angiotensin(1-7) deteriorated cardiac contractility as indicated by impaired dp/dt. Furthermore, histological analysis revealed that cafeteria diet led to myocardial fibrosis in both, control and transgenic rats and this was not inhibited by an overproduction of angiotensin(1-7).

Conclusion:These results indicate that an overexpression of circulating angiotensin(1-7) prevents a cafeteria diet-induced increase in body weight, but does not affect cardiac performance in this experimental rat model of obesity. Furthermore, overexpression of angiotensin(1-7) alone resulted in an impairment of cardiac function.

Should the sympathetic nervous system be a target to improve cardiometabolic risk in obesity?

The sympathetic nervous system (SNS) plays a key role in both cardiovascular and metabolic regulation; hence, disturbances in SNS regulation are likely to impact on both cardiovascular and metabolic health. With excess adiposity, in particular when visceral fat accumulation is present, sympathetic activation commonly occurs. Experimental investigations have shown that adipose tissue releases a large number of adipokines, cytokines, and bioactive mediators capable of stimulating the SNS. Activation of the SNS and its interaction with adipose tissue may lead to the development of hypertension and end-organ damage including vascular, cardiac, and renal impairment and in addition lead to metabolic abnormalities, especially insulin resistance. Lifestyle changes such as weight loss and exercise programs considerably improve the cardiovascular and metabolic profile of subjects with obesity and decrease their cardiovascular risk, but unfortunately weight loss is often difficult to achieve and sustain. Pharmacological and device-based approaches to directly or indirectly target the activation of the SNS may offer some benefit in reducing the cardiometabolic consequences of obesity. Preliminary evidence is encouraging, but more trials are needed to investigate whether sympathetic inhibition could be used in obesity to reverse or prevent cardiometabolic disease development. The purpose of this review article is to highlight the current knowledge of the role that SNS plays in obesity and its associated metabolic disorders and to review the potential benefits of sympathoinhibition on metabolic and cardiovascular functions.

Obesity-induced increases in sympathetic nerve activity: sex matters

Abundant evidence obtained largely from male human and animal subjects indicates that obesity increases sympathetic nerve activity (SNA), which contributes to hypertension development. However, recent studies that included women reported that the strong relationships between muscle SNA and waist circumference or body mass index (BMI) found in men are not present in overweight and obese women. A similar sex difference in the association between adiposity and hypertension development has been identified in animal models of obesity. In this brief review, we consider two possible mechanisms for this sex difference. First, visceral adiposity, leptin, insulin, and angiotensin II have been identified as potential culprits in obesity-induced sympathoexcitation in males. We explore if these factors wield the same impact in females. Second, we consider if sex differences in vascular reactivity to sympathetic activation contribute. Our survey of the literature suggests that premenopausal females may be able to resist obesity-induced sympathoexcitation and hypertension in part due to differences in adipose disposition as well as its muted inflammatory response and reduced production of pressor versus depressor components of the renin-angiotensin system. In addition, vascular responsiveness to increased SNA may be reduced. However, more importantly, we identify the urgent need for further study, not only of sex differences per se, but also of the mechanisms that may mediate these differences. This information is required not only to refine treatment options for obese premenopausal women but also to potentially reveal new therapeutic avenues in obese men and women.

Comparison between cafeteria and high-fat diets in the induction of metabolic dysfunction in mice

This study sought to compare the metabolic responses induced by high-fat (HF) diet and cafeteria (CA) diet in mice. Adult male C57BL/6J mice were assigned into groups fed a chow (C, n=13), CA (n=12) or HF (n=11) diet during 12 weeks. Diets did not change body weight, Lee index, inguinal subcutaneous fat, the weight of organs and muscles, resting arterial pressure and heart rate. CA and HF increased visceral fat pad mass compared to C group, but only CA group showed greater adipocyte diameter and food intake compared to the C. Food intake was reduced in HF compared to C group. CA and HF showed hyperglycemia in the 3(rd), 6(th), 9(th) and 12(th) week and all values were higher in CA than HF, except in the 6(th) week. CA group showed glucose intolerance (GI) in the 6(th) week, while HF group did not show GI until the 9(th) week. CA decreased insulin sensitivity compared to C in the 12(th) week (kITT=3.3±0.2%/min vs. 4.2±0.1%/min). CA and HF groups presented higher insulin, leptin, total cholesterol, LDL-C, triglycerides and FFA levels compared to the C group. Total cholesterol and LDL-C in mg/dL were higher in the HF (161.9±7.2 and 57.5±13.4) than the CA (110.5±9.1 and 48.5±11.4), and HDL-C was higher in the HF than in the C and CA groups. In conclusion, the CA diet was more efficient to induce hyperphagia, adipocyte hypertrophy, hyperglycemia, earlier GI and insulin resistance, while the HF diet was more efficient to induce lipid profile changes.

Recording sympathetic nerve activity chronically in rats: surgery techniques, assessment of nerve activity, and quantification

The sympathetic nervous system plays a pivotal role in homeostasis through its direct innervation and functional impact on a variety of end organs. In rats, a number of methods are available to assess sympathetic nervous system function. Traditionally, direct recording of sympathetic nerve activity (SNA) has been restricted to acute, anesthetized preparations or conscious animals within a few days after electrode implantation. However, these approaches provide short-term data in studies designed to investigate changes in SNA during chronic disease states. Over the last several years, chronic SNA recording has been pioneered in rabbits and more recently in rats. The purpose of this article is to provide insights and a "how to" guide for chronic SNA recordings in rats based on experiences from two independent laboratories. We will present common methodologies used to chronically record SNA, characteristics and methods to distinguish sympathetic bursts versus electrical artifacts (and provide corresponding audio clips when available), and provide suggestions for analysis and presentation of data. In many instances, these same guidelines are applicable to acute SNA recordings. Using the surgical approaches described herein, both laboratories have been able to chronically record SNA in >50% of rats for a duration >3 wk. The ability to record SNA over the time course of several weeks will, undoubtedly, greatly impact the field of autonomic and cardiovascular physiology.

Leptin acts in the forebrain to differentially influence baroreflex control of lumbar, renal, and splanchnic sympathetic nerve activity and heart rate

Although leptin is known to increase sympathetic nerve activity (SNA), we tested the hypothesis that leptin also enhances baroreflex control of SNA and heart rate (HR). Using α-chloralose anesthetized male rats, mean arterial pressure (MAP), HR, lumbar SNA (LSNA), splanchnic SNA (SSNA), and renal SNA (RSNA) were recorded before and for 2 hours after lateral cerebroventricular leptin or artificial cerebrospinal fluid administration. Baroreflex function was assessed using a 4-parameter sigmoidal fit of HR and SNA responses to slow ramp (3-5 minutes) changes in MAP, induced by intravenous infusion of nitroprusside and phenylephrine. Leptin (3 μg) increased (P<0.05) basal LSNA, SSNA, RSNA, HR, and MAP, and the LSNA, SSNA, RSNA, and HR baroreflex maxima. Leptin also increased gain of baroreflex control of LSNA and RSNA, but not of SSNA or HR. The elevations in HR were eliminated by pretreatment with methscopalamine, to block parasympathetic nerve activity; however, after cardiac sympathetic blockade with atenolol, leptin still increased basal HR and MAP and the HR baroreflex maximum and minimum. Leptin (1.5 μg) also increased LSNA and enhanced LSNA baroreflex gain and maximum, but did not alter MAP, HR, or the HR baroreflex. Lateral cerebroventricular artificial cerebrospinal fluid had no effects. Finally, to test whether leptin acts in the brain stem, leptin (3 μg) was infused into the 4th ventricle; however, no significant changes were observed. In conclusion, leptin acts in the forebrain to differentially influence baroreflex control of LSNA, RSNA, SSNA, and HR, with the latter action mediated via suppression of parasympathetic nerve activity.

Cardiovascular changes in animal models of metabolic syndrome

Metabolic syndrome has been defined as a group of risk factors that directly contribute to the development of cardiovascular disease and/or type 2 diabetes. Insulin resistance seems to have a fundamental role in the genesis of this syndrome. Over the past years to the present day, basic and translational research has used small animal models to explore the pathophysiology of metabolic syndrome and to develop novel therapies that might slow the progression of this prevalent condition. In this paper we discuss the animal models used for the study of metabolic syndrome, with particular focus on cardiovascular changes, since they are the main cause of death associated with the condition in humans.