Autonomic Regulation of Glucose Homeostasis: a Specific Role for Sympathetic Nervous System Activation

The bone-muscle unit: from mechanical coupling to soluble factors-mediated signaling

Skeletal muscles (SKM) and bones form a morpho-functional unit, interconnected throughout life primarily through biomechanical coupling. This relationship serves as a key reciprocal stimulus, but they also interact via various hormones, such as sex steroids, growth hormone-insulin-like growth factor 1 (GH-IGF1) axis hormones, and adipokines like leptin and adiponectin. Additionally, myokines (released by muscles) and osteokines (released by bones) facilitate dense crosstalk, influencing each other's activity. Key myokines include interleukin (IL)-6, IL-7, IL-15, and myostatin, while osteocalcin (OC) and sclerostin are crucial bone-derived mediators affecting SKM cells. Moreover, miRNAs act as endocrine-like regulators, contributing to a complex network. This review covers the current understanding of bone-muscle crosstalk, which is essential for grasping the musculoskeletal apparatus's role in disease pathogenesis and may inform therapeutic development.

Regenerative failure of sympathetic axons contributes to deficits in functional recovery after nerve injury

Renewed scientific interest in sympathetic modulation of muscle and neuromuscular junctions has spurred a flurry of new discoveries with major implications for motor diseases. However, the role sympathetic axons play in the persistent dysfunction that occurs after nerve injuries remains to be explored. Peripheral nerve injuries are common and lead to motor, sensory, and autonomic deficits that result in lifelong disabilities. Given the importance of sympathetic signaling in muscle metabolic health and maintaining bodily homeostasis, it is imperative to understand the regenerative capacity of sympathetic axons after injury. Therefore, we tested sympathetic axon regeneration and functional reinnervation of skin and muscle, both acute and long-term, using a battery of anatomical, pharmacological, chemogenetic, cell culture, analytical chemistry, and electrophysiological techniques. We employed several established growth-enhancing interventions, including electrical stimulation and conditioning lesion, as well as an innovative tool called bioluminescent optogenetics. Our results indicate that sympathetic regeneration is not enhanced by any of these treatments and may even be detrimental to sympathetic regeneration. Despite the complete return of motor reinnervation after sciatic nerve injury, gastrocnemius muscle atrophy and deficits in muscle cellular energy charge, as measured by relative ATP, ADP, and AMP concentrations, persisted long after injury, even with electrical stimulation. We suggest that these long-term deficits in muscle energy charge and atrophy are related to the deficiency in sympathetic axon regeneration. New studies are needed to better understand the mechanisms underlying sympathetic regeneration to develop therapeutics that can enhance the regeneration of all axon types.

Conditioning Electrical Stimulation Fails to Enhance Sympathetic Axon Regeneration

BACKGROUND

Peripheral nerve injuries are common, and there is a critical need for the development of novel treatments to complement surgical repair. Conditioning electrical stimulation (ES; CES) is a novel variation of the well-studied perioperative ES treatment paradigm. CES is a clinically attractive alternative because of its ability to be performed at the bedside prior to a scheduled nerve repair surgery.

OBJECTIVES

Although 60 minutes of CES has been shown to enhance motor and sensory axon regeneration, the effects of CES on sympathetic regeneration are unknown. We investigated how 2 clinically relevant CES paradigms (10 and 60 minutes) impact sympathetic axon regeneration and distal target reinnervation.

RESULTS

Our results indicate that the growth of sympathetic axons is inhibited by CES at acute time points, and at a longer survival time point post-injury, there is no difference between sham CES and the CES groups. Furthermore, 10-minute CES did not enhance motor and sensory regeneration with a direct repair, and neither 60-minute nor 10-minute CES enhanced motor and sensory regeneration through a graft.

CONCLUSION

We conclude sympathetic axons may retain some regenerative ability, but no enhancement is exhibited after CES, which may be accounted for by the inability of the ES paradigm to recruit the small-caliber sympathetic axons into activity. Further studies will be needed to optimize ES parameters to enhance the regeneration of all neuron types.

Scaffold-free endocrine tissue engineering: role of islet organization and implications in type 1 diabetes

Type 1 diabetes (T1D) is a chronic hyperglycemia disorder emerging from beta-cell (insulin secreting cells of the pancreas) targeted autoimmunity. As the blood glucose levels significantly increase and the insulin secretion is gradually lost, the entire body suffers from the complications. Although various advances in the insulin analogs, blood glucose monitoring and insulin application practices have been achieved in the last few decades, a cure for the disease is not obtained. Alternatively, pancreas/islet transplantation is an attractive therapeutic approach based on the patient prognosis, yet this treatment is also limited mainly by donor shortage, life-long use of immunosuppressive drugs and risk of disease transmission. In research and clinics, such drawbacks are addressed by the endocrine tissue engineering of the pancreas. One arm of this engineering is scaffold-free models which often utilize highly developed cell-cell junctions, soluble factors and 3D arrangement of islets with the cellular heterogeneity to prepare the transplant formulations. In this review, taking T1D as a model autoimmune disease, techniques to produce so-called pseudoislets and their applications are studied in detail with the aim of understanding the role of mimicry and pointing out the promising efforts which can be translated from benchside to bedside to achieve exogenous insulin-free patient treatment. Likewise, these developments in the pseudoislet formation are tools for the research to elucidate underlying mechanisms in pancreas (patho)biology, as platforms to screen drugs and to introduce immunoisolation barrier-based hybrid strategies.

Dapagliflozin increased pancreatic beta cell proliferation and insulinogenic index in mice fed a high-fat and high-sodium chloride diet

People in Eastern Asia, including Japan, traditionally consume higher amounts of sodium chloride than in the United States and Western Europe, and it is common knowledge that impaired insulin secretion-rather than insulin resistance-is highly prevalent in Asian people who have diabetes mellitus. We previously reported that mice fed a high-fat and high-sodium chloride (HFHS) diet had a relatively lower degree of obesity than mice fed a high-fat diet, but had a comparatively impaired insulin secretion. Sodium-glucose cotransporter-2 (SGLT2) inhibitors have been shown to dampen down the sympathetic nervous system, which reportedly is activated by a high-sodium chloride diet. In this study, we examined the effects of dapagliflozin, a SGLT2 inhibitor, on glucose metabolism and insulin secretion in mice fed a HFHS diet. C57BL6/J mice were fed a HFHS diet for 6 weeks and subsequently divided into two treatment groups fed: (1) a HFHS diet mixed with dapagliflozin for up to 3 weeks (HFHS + Da) and (2) a HFHS diet without dapagliflozin (HFHS). Dapagliflozin improved glucose tolerance and the insulinogenic index accompanied by increased pancreatic beta cell proliferation. Furthermore, dapagliflozin decreased both the tyrosine hydroxylase-positive area in pancreatic islets and catecholamine excretion in urine. Our results suggest that dapagliflozin improved insulin secretion by suppressing sympathetic nerve activation in mice fed a HFHS diet.

The Acute Effects of a Fast-Food Meal Versus a Mediterranean Food Meal on the Autonomic Nervous System, Lung Function, and Airway Inflammation: A Randomized Crossover Trial

BACKGROUND/OBJECTIVES

This study aimed to assess the acute effects of two isoenergetic but micronutrient-diverse meals-a Mediterranean-like meal (MdM) and a fast food-like meal (FFM)-on the autonomic nervous system (ANS), lung function, and airway inflammation response.

METHODS

Forty-six participants were enrolled in a randomized crossover clinical trial, consuming two isoenergetic meals: FFM (burger, fries, and sugar-sweetened drink) and MdM (vegetable soup, whole-wheat pasta, salad, olive oil, sardines, fruit, and water). Pupillometry assessed parasympathetic (MaxD, MinD, Con, ACV, MCV) and sympathetic (ADV, T75) nervous system outcomes. Lung function and airway inflammation were measured before and after each meal through spirometry and fractional exhaled nitric oxide (FeNO), respectively.

RESULTS

Mixed-effects model analysis showed that the MdM was associated with a hegemony of parasympathetic responses, with a significant increase of MaxD associated with a faster constriction velocity (ACV and MCV); on the other side, the FFM was associated with changes in the sympathetic response, showing a quicker redilation velocity (a decrease in T75). After adjusting for confounders, the mixed-effects models revealed that the FFM significantly decreased T75. Regarding lung function, a meal negatively impacted FVC (ae = -0.079, p < 0.001) and FEV1 (ae = -0.04, p = 0.017); however, FeNO increased, although after adjusting, no difference between meals was seen.

CONCLUSIONS

Our study showed that the FFM counteracted the parasympathetic activity of a meal, while a meal, irrespective of the type, decreased lung function and increased airway inflammation.

A subset of neurons in the paraventricular nucleus of the hypothalamus directly project to liver-related premotor neurons in the ventrolateral medulla

Sympathetic circuits including pre-sympathetic neurons in the ventrolateral medulla (VLM) and in the paraventricular nucleus (PVN) of the hypothalamus play an important role in the regulation of hepatic glucose metabolism. Despite the importance of central regulatory pathways, specific information regarding the circuits of liver-related neurons is limited. Here, we tested the hypothesis that PVN neurons are directly connected to spinally-projecting liver-related neurons in the VLM of mice. Pseudorabies virus (PRV) was used to identify liver-related neurons and time-dependent analyses revealed the location and distribution of neurons in the PVN and ventral brainstem. Four days following PRV injection, most liver-related neurons were found in the VLM and consist of both catecholaminergic (CA) and non-CA neurons. Furthermore, in addition to PRV inoculation, a monosynaptic viral tracer was used to identify VLM-projecting PVN neurons to specifically dissect PVN-VLM connections within the liver pathway. Five days following PRV inoculation, our anatomical findings revealed that a small population of liver-related PVN neurons projected to the VLM. In addition, photo-stimulation of axonal projections from SIM1-expressing PVN neurons resulted in evoked excitatory postsynaptic currents in a subset of spinally projecting liver-related neurons in the VLM. In summary, our data demonstrate the existence of monosynaptic, glutamatergic connections between PVN neurons and pre-sympathetic liver-related neurons in the VLM. These new findings regarding the central circuits involved in the sympathetic regulation of the liver provide further information necessary for developing new strategies to improve glucose homeostasis via modulation of the autonomic nerves.

L-type calcium channel blockade worsens glucose tolerance and β-cell function in C57BL6/J mice exposed to intermittent hypoxia

Intermittent hypoxemia (IH), a pathophysiologic consequence of obstructive sleep apnea (OSA), adversely affects insulin sensitivity, insulin secretion, and glucose tolerance. Nifedipine, an L-type calcium channel blocker frequently used for the treatment of hypertension, can also impair insulin sensitivity and secretion. However, the cumulative and interactive repercussions of IH and nifedipine on glucose homeostasis have not been previously investigated. Adult male C57BL6/J mice were exposed to either nifedipine or vehicle concurrently with IH or intermittent air (IA) over 5 days. IH exposure entailed cycling fractional-inspired oxygen levels between 0.21 and 0.055 at a rate of 60 events/h. Nifedipine (20 mg/kg/day) or vehicle was administered via subcutaneous osmotic pumps resulting in four groups of mice: IA-vehicle (control), IA-nifedipine, IH-vehicle, and IH-nifedipine. Compared with IA (control), IH increased fasting glucose (mean Δ: 33.0 mg/dL; P < 0.001) and insulin (mean Δ: 0.53 ng/mL; P < 0.001) with nifedipine having no independent effect. Furthermore, glucose tolerance was worse with nifedipine alone, and IH further exacerbated the impairment in glucose disposal (P = 0.013 for interaction). Nifedipine also decreased glucose-stimulated insulin secretion and the insulinogenic index, with addition of IH attenuating those measures further. There were no discernible alterations in insulin biosynthesis/processing, insulin content, or islet morphology. These findings underscore the detrimental impact of IH on insulin sensitivity and glucose tolerance while highlighting that nifedipine exacerbates these disturbances through impaired β-cell function. Consequently, cautious use of L-type calcium channel blockers is warranted in patients with OSA, particularly in those at risk for type 2 diabetes.NEW & NOTEWORTHY The results of this study demonstrate the interaction between intermittent hypoxemia (IH) and nifedipine in a murine model. IH raises fasting glucose and insulin levels, with nifedipine exacerbating these disturbances. Glucose tolerance worsens when nifedipine is administered alone, and IH magnifies the impairment in glucose disposal. These findings raise the possibility of potential deleterious effects of L-type calcium channel blockers in patients with obstructive sleep apnea (OSA).

Targeting the sympathetic nervous system with the selective imidazoline receptor agonist moxonidine for the management of hypertension: an international position statement

Hypertension is often linked with metabolic risk factors that share common pathophysiological pathways. Despite wide-spread availability of multiple drug classes, optimal blood pressure (BP) control remains challenging. Increased central sympathetic outflow is frequently neglected as a critical regulator of both circulatory and metabolic pathways and often remains unopposed therapeutically. Selective imidazoline receptor agonists (SIRAs) effectively reduce BP with a favorable side effect profile compared with older centrally acting antihypertensive drugs. Hard outcome data in hypertension, such as prevention of stroke, heart and kidney diseases, are not available with SIRAs. However, in direct comparisons, SIRAs were as effective as angiotensin-converting enzyme inhibitors, β-blockers, calcium channel blockers, and diuretics in lowering BP. Other beneficial effects on metabolic parameters in hypertensive patients with concomitant overweight and obesity have been documented with SIRAs. Here we review the existing evidence on the safety and efficacy of moxonidine, a widely available SIRA, compared with common antihypertensive agents and provide a consensus position statement based on inputs from 12 experts from Europe and Australia on SIRAs in hypertension management.

Noninvasive Blood Glucose Monitoring Using Spatiotemporal ECG and PPG Feature Fusion and Weight-Based Choquet Integral Multimodel Approach

change of blood glucose (BG) level stimulates the autonomic nervous system leading to variation in both human's electrocardiogram (ECG) and photoplethysmogram (PPG). In this article, we aimed to construct a novel multimodal framework based on ECG and PPG signal fusion to establish a universal BG monitoring model. This is proposed as a spatiotemporal decision fusion strategy that uses weight-based Choquet integral for BG monitoring. Specifically, the multimodal framework performs three-level fusion. First, ECG and PPG signals are collected and coupled into different pools. Second, the temporal statistical features and spatial morphological features in the ECG and PPG signals are extracted through numerical analysis and residual networks, respectively. Furthermore, the suitable temporal statistical features are determined with three feature selection techniques, and the spatial morphological features are compressed by deep neural networks (DNNs). Lastly, weight-based Choquet integral multimodel fusion is integrated for coupling different BG monitoring algorithms based on the temporal statistical features and spatial morphological features. To verify the feasibility of the model, a total of 103 days of ECG and PPG signals encompassing 21 participants were collected in this article. The BG levels of participants ranged between 2.2 and 21.8 mmol/L. The results obtained show that the proposed model has excellent BG monitoring performance with a root-mean-square error (RMSE) of 1.49 mmol/L, mean absolute relative difference (MARD) of 13.42%, and Zone A + B of 99.49% in tenfold cross-validation. Therefore, we conclude that the proposed fusion approach for BG monitoring has potentials in practical applications of diabetes management.

The relationship between glycated haemoglobin and blood glucose-lowering treatment trajectories in type 2 diabetes: The Fremantle Diabetes Study Phase II

AIMS

To examine the relationships between glycaemia and treatment complexity over 6 years in well-characterized community-based people with type 2 diabetes.

MATERIALS AND METHODS

Fremantle Diabetes Study Phase II participants who had type 2 diabetes with glycated haemoglobin (HbA1c) and blood glucose-lowering therapy (BGLT) data over 6 years were included. Group-based multi-trajectory modelling identified combined HbA1c/BGLT trajectory subgroups for diabetes durations of ≤1.0 year (Group 1; n = 160), >1.0 to 10.0 years (Group 2; n = 382;) and >10.0 years (Group 3; n = 357). Multinomial regression was used to identify baseline associates of subgroup membership.

RESULTS

The optimum numbers of trajectory subgroups were three in Group 1 (low, medium, high) and four in Groups 2 and 3 (low, low/high medium, high). Each low trajectory subgroup maintained a mean HbA1c concentration of <53 mmol/mol (<7.0%) on lifestyle measures, or monotherapy (Group 3). All five medium subgroups had stable HbA1c trajectories at <58 mmol/mol (<7.5%) but required increasing oral BGLT, or insulin (Group 3, high medium). The Group 1 high subgroup showed a falling then increasing HbA1c with steady progression to insulin. The high subgroups in Groups 2 and 3 showed stable HbA1c profiles at means of approximately 64 mmol/mol (8.0%) and 86 mmol/L (10.0%), respectively, on insulin. Non-Anglo Celt ethnicity, central obesity and hypertriglyceridaemia were strongly associated with Group 1 high subgroup membership. Younger age at diagnosis and central obesity were independent associates of the most adverse HbA1c trajectories in Groups 2 and 3.

CONCLUSIONS

These data demonstrate diabetes duration-dependent heterogeneity in glycaemic and treatment profiles and related clinical and laboratory variables, which have implications for management.

Sympathetic circuits regulating hepatic glucose metabolism: where we stand

The prevalence of metabolic disorders, including type 2 diabetes mellitus, continues to increase worldwide. Although newer and more advanced therapies are available, current treatments are still inadequate and the search for solutions remains. The regulation of energy homeostasis, including glucose metabolism, involves an exchange of information between the nervous systems and peripheral organs and tissues; therefore, developing treatments to alter central and/or peripheral neural pathways could be an alternative solution to modulate whole body metabolism. Liver glucose production and storage are major mechanisms controlling glycemia, and the autonomic nervous system plays an important role in the regulation of hepatic functions. Autonomic nervous system imbalance contributes to excessive hepatic glucose production and thus to the development and progression of type 2 diabetes mellitus. At cellular levels, change in neuronal activity is one of the underlying mechanisms of autonomic imbalance; therefore, modulation of the excitability of neurons involved in autonomic outflow governance has the potential to improve glycemic status. Tissue-specific subsets of preautonomic neurons differentially control autonomic outflow; therefore, detailed information about neural circuits and properties of liver-related neurons is necessary for the development of strategies to regulate liver functions via the autonomic nerves. This review provides an overview of our current understanding of the hypothalamus-ventral brainstem-liver pathway involved in the sympathetic regulation of the liver, outlines strategies to identify organ-related neurons, and summarizes neuronal plasticity during diabetic conditions with a particular focus on liver-related neurons in the paraventricular nucleus.

Effects of continuous positive airway pressure therapy on glucose metabolism in patients with obstructive sleep apnoea and type 2 diabetes: a systematic review and meta-analysis

Obstructive sleep apnoea is a highly prevalent chronic disorder and has been shown to be associated with disturbed glucose metabolism and type 2 diabetes. However, the evidence from individual clinical trials on the effect of continuous positive airway pressure (CPAP) treatment on glycaemic control in patients with co-existing obstructive sleep apnoea and type 2 diabetes remains controversial. A systematic review of randomised controlled trials assessing the effect of CPAP on glycaemic control in patients with obstructive sleep apnoea and type 2 diabetes was conducted using the databases MEDLINE, Embase, Cochrane and Scopus up to December 2022. Meta-analysis using a random-effect model was performed for outcomes that were reported in at least two randomised controlled trials. From 3031 records screened, 11 RCTs with a total of 964 patients were included for analysis. CPAP treatment led to a significant reduction in haemoglobin A1c (HbA1c) (mean difference -0.24%, 95% CI -0.43- -0.06%, p=0.001) compared to inactive control groups. Meta-regression showed a significant association between reduction in HbA1c and hours of nightly CPAP usage. CPAP therapy seems to significantly improve HbA1c and thus long-term glycaemic control in patients with type 2 diabetes and obstructive sleep apnoea. The amount of improvement is dependent on the hours of usage of CPAP and thus optimal adherence to CPAP should be a primary goal in these patients.

Brain Dopamine-Clock Interactions Regulate Cardiometabolic Physiology: Mechanisms of the Observed Cardioprotective Effects of Circadian-Timed Bromocriptine-QR Therapy in Type 2 Diabetes Subjects

Despite enormous global efforts within clinical research and medical practice to reduce cardiovascular disease(s) (CVD), it still remains the leading cause of death worldwide. While genetic factors clearly contribute to CVD etiology, the preponderance of epidemiological data indicate that a major common denominator among diverse ethnic populations from around the world contributing to CVD is the composite of Western lifestyle cofactors, particularly Western diets (high saturated fat/simple sugar [particularly high fructose and sucrose and to a lesser extent glucose] diets), psychosocial stress, depression, and altered sleep/wake architecture. Such Western lifestyle cofactors are potent drivers for the increased risk of metabolic syndrome and its attendant downstream CVD. The central nervous system (CNS) evolved to respond to and anticipate changes in the external (and internal) environment to adapt survival mechanisms to perceived stresses (challenges to normal biological function), including the aforementioned Western lifestyle cofactors. Within the CNS of vertebrates in the wild, the biological clock circuitry surveils the environment and has evolved mechanisms for the induction of the obese, insulin-resistant state as a survival mechanism against an anticipated ensuing season of low/no food availability. The peripheral tissues utilize fat as an energy source under muscle insulin resistance, while increased hepatic insulin resistance more readily supplies glucose to the brain. This neural clock function also orchestrates the reversal of the obese, insulin-resistant condition when the low food availability season ends. The circadian neural network that produces these seasonal shifts in metabolism is also responsive to Western lifestyle stressors that drive the CNS clock into survival mode. A major component of this natural or Western lifestyle stressor-induced CNS clock neurophysiological shift potentiating the obese, insulin-resistant state is a diminution of the circadian peak of dopaminergic input activity to the pacemaker clock center, suprachiasmatic nucleus. Pharmacologically preventing this loss of circadian peak dopaminergic activity both prevents and reverses existing metabolic syndrome in a wide variety of animal models of the disorder, including high fat-fed animals. Clinically, across a variety of different study designs, circadian-timed bromocriptine-QR (quick release) (a unique formulation of micronized bromocriptine-a dopamine D2 receptor agonist) therapy of type 2 diabetes subjects improved hyperglycemia, hyperlipidemia, hypertension, immune sterile inflammation, and/or adverse cardiovascular event rate. The present review details the seminal circadian science investigations delineating important roles for CNS circadian peak dopaminergic activity in the regulation of peripheral fuel metabolism and cardiovascular biology and also summarizes the clinical study findings of bromocriptine-QR therapy on cardiometabolic outcomes in type 2 diabetes subjects.

Frequency-coded patterns of sympathetic vasomotor activity are differentially evoked by the paraventricular nucleus of the hypothalamus in the Goldblatt hypertension model

Introduction

The paraventricular nucleus of the hypothalamus (PVN) contains premotor neurons involved in the control of sympathetic vasomotor activity. It is known that the stimulation of specific areas of the PVN can lead to distinct response patterns at different target territories. The underlying mechanisms, however, are still unclear. Recent evidence from sympathetic nerve recording suggests that relevant information is coded in the power distribution of the signal along the frequency range. In the present study, we addressed the hypothesis that the PVN is capable of organizing specific spectral patterns of sympathetic vasomotor activation to distinct territories in both normal and hypertensive animals.

Methods

To test it, we investigated the territorially differential changes in the frequency parameters of the renal and splanchnic sympathetic nerve activity (rSNA and sSNA, respectively), before and after disinhibition of the PVN by bicuculline microinjection. Subjects were control and Goldblatt rats, a sympathetic overactivity-characterized model of neurogenic hypertension (2K1C). Additionally, considering the importance of angiotensin II type 1 receptors (AT1) in the sympathetic responses triggered by bicuculline in the PVN, we also investigated the impact of angiotensin AT1 receptors blockade in the spectral features of the rSNA and sSNA activity.

Results

The results revealed that each nerve activity (renal and splanchnic) presents its own electrophysiological pattern of frequency-coded rhythm in each group (control, 2K1C, and 2K1C treated with AT1 antagonist losartan) in basal condition and after bicuculline microinjection, but with no significant differences regarding total power comparison among groups. Additionally, the losartan 2K1C treated group showed no decrease in the hypertensive response triggered by bicuculline when compared to the non-treated 2K1C group. However, their spectral patterns of sympathetic nerve activity were different from the other two groups (control and 2K1C), suggesting that the blockade of AT1 receptors does not totally recover the basal levels of neither the autonomic responses nor the electrophysiological patterns in Goldblatt rats, but act on their spectral frequency distribution.

Discussion

The results suggest that the differential responses evoked by the PVN were preferentially coded in frequency, but not in the global power of the vasomotor sympathetic responses, indicating that the PVN is able to independently control the frequency and the power of sympathetic discharges to different territories.

Sex differences in particulate air pollution-related cardiovascular diseases: A review of human and animal evidence

Cardiovascular disease (CVD) is the leading cause of mortality globally. In the past several decades, researchers have raised significant awareness about the sex differences in CVD and the importance of heart disease in women. Besides physiological disparities, many lifestyles and environmental factors such as smoking and diet may affect CVD in a sex-dependent manner. Air pollution is a well-recognized environmental risk factor for CVD. However, the sex differences in air pollution-related CVD have been largely neglected. A majority of the previously completed studies have either evaluated only one sex (generally male) as study subjects or did not compare the sex differences. Some epidemiological and animal studies have shown that there are sex differences in the sensitivity to particulate air pollution as evidenced by the different morbidity and mortality rates of CVD induced by particulate air pollution, although this was not conclusive. In this review, we attempt to evaluate the sex differences in air pollution-related CVD and the underlying mechanisms by reviewing both epidemiological and animal studies. This review may provide a better understanding of the sex differences in environmental health research, enabling improved prevention and therapeutic strategies for human health in the future.

Correlation among Poincare plot and traditional heart rate variability indices in adults with different risk levels of metabolic syndrome: a cross-sectional approach from Southern India

OBJECTIVES

Heart rate variability (HRV) is an important marker of cardiac autonomic modulation. Metabolic syndrome (MetS) can alter cardiac autonomic modulation, raising the risk of cardiovascular disease (CVD). Poincaré plot analysis (PPA) is a robust scatter plot-based depiction of HRV and carries similar information to the traditional HRV measures. However, no prior studies have examined the relationship between PPA and traditional HRV measures among different risk levels of MetS. We evaluated the association between the Poincare plot and traditional heart rate variability indices among adults with different risk levels of MetS.

METHODS

We measured anthropometric data and collected fasting blood samples to diagnose MetS. The MetS risk was assessed in 223 participants based on the number of MetS components and was classified as control (n=64), pre-MetS (n=49), MetS (n=56), and severe MetS (n=54). We calculated the Poincaré plot (PP) and traditional HRV measures from a 5 min HRV recording.

RESULTS

Besides the traditional HRV measures, we found that various HRV indices of PPA showed significant differences among the groups. The severe MetS group had significantly lower S (total HRV), SD1 (short-term HRV), SD2 (long-term HRV), and higher SD2/SD1. The values of S, SD1, SD2, and SD2/SD1 were significantly correlated with most traditional HRV measures.

CONCLUSIONS

We found gradual changes in HRV patterns as lower parasympathetic and higher sympathetic activity alongside the rising number of MetS components. The HRV indices of PPA integrating the benefits of traditional HRV indices distinguish successfully between different risk levels of MetS and control subjects.

Association between metabolic syndrome components and cardiac autonomic modulation in southern Indian adults with pre-metabolic syndrome: hyperglycemia is the major contributing factor

Metabolic syndrome (MetS) involves multi-factorial conditions linked to an elevated risk of type 2 diabetes mellitus and cardiovascular disease. Pre-metabolic syndrome (pre-MetS) possesses two MetS components but does not meet the MetS diagnostic criteria. Although cardiac autonomic derangements are evident in MetS, there is little information on their status in pre-MetS subjects. In this study, we sought to examine cardiac autonomic functions in pre-MetS and to determine which MetS component is more responsible for impaired cardiac autonomic functions. A total of 182 subjects were recruited and divided into healthy controls (n=89) and pre-MetS subjects (n=93) based on inclusion and exclusion criteria. We performed biochemical profiles on fasting blood samples to detect pre-MetS. Using standardized protocols, we evaluated anthropometric data, body composition, baroreflex sensitivity (BRS), heart rate variability (HRV), and autonomic function tests (AFTs). We further examined these parameters in pre-MetS subjects for each MetS component. Compared to healthy controls, we observed a significant cardiac autonomic dysfunction (CAD) through reduced BRS, lower overall HRV, and altered AFT parameters in pre-MetS subjects, accompanied by markedly varied anthropometric, clinical and biochemical parameters. Furthermore, all examined BRS, HRV, and AFT parameters exhibited an abnormal trend and significant correlation toward hyperglycemia. This study demonstrates CAD in pre-MetS subjects with reduced BRS, lower overall HRV, and altered AFT parameters. Hyperglycemia was considered an independent determinant of alterations in all the examined BRS, HRV, and AFT parameters. Thus, hyperglycemia may contribute to CAD in pre-MetS subjects before progressing to MetS.

Metabolic associated fatty liver disease is a disease related to sympathetic nervous system activation

Strong evidence from animal and human studies shows that sympathetic nervous system (SNS) activation is a key factor in the development of metabolic associated fatty liver disease (MAFLD). Activation of the sympathetic nervous system plays an important role in the pathogenesis of obesity, metabolic syndrome, diabetes, hypertension, and MAFLD. When genetically susceptible subjects are exposed to a variety of epigenetic changes, their liver damage may develop into MAFLD. Thus, the pathogenesis of MAFLD is complex, involving the complex interaction of insulin resistance, abnormal hormone secretion, obesity, diet, genetic factors, immune activation, gut microbiota, and other factors. In these processes, the role of sympathetic nerves cannot be underestimated. Notably, SNS has been proposed as a therapeutic target for MAFLD by inhibiting sympathetic nerves. It is worthy of further discussion and research.

How exposure to chronic stress contributes to the development of type 2 diabetes: A complexity science approach

Chronic stress contributes to the onset of type 2 diabetes (T2D), yet the underlying etiological mechanisms are not fully understood. Responses to stress are influenced by earlier experiences, sex, emotions and cognition, and involve a complex network of neurotransmitters and hormones, that affect multiple biological systems. In addition, the systems activated by stress can be altered by behavioral, metabolic and environmental factors. The impact of stress on metabolic health can thus be considered an emergent process, involving different types of interactions between multiple variables, that are driven by non-linear dynamics at different spatiotemporal scales. To obtain a more comprehensive picture of the links between chronic stress and T2D, we followed a complexity science approach to build a causal loop diagram (CLD) connecting the various mediators and processes involved in stress responses relevant for T2D pathogenesis. This CLD could help develop novel computational models and formulate new hypotheses regarding disease etiology.

Social Nervous Exercise Intervention and Its Association with Fasting Blood Glucose on Diabetes Mellitus Gestational

BACKGROUND: Gestational diabetes mellitus (GDM) has been identified as a major complication of pregnancies and has remained a major cause of perinatal morbidity and mortality, in both mother and child. Exercise can be used as a strategy to reduce hyperglycemia experienced during GDM. Regular exercise is important for a healthy pregnancy and can lower the risk of developing GDM. For women with GDM. Exercise is safe and can affect the pregnancy outcomes beneficially. The role of exercise about increases skeletal muscle glucose uptake and minimizing hyperglycemia. Social nervous (SaSo) exercise is a moderate-intensity exercise intervention that plays a role in controlling blood glucose through autonomic nervous stimulation so that it has an effect on glucose homeostasis. Social nervous exercise can stimulate the parasympathetic or myelinated vagus nerves. The social nerve or the social nervous system is the vagus nerve nc-X which is supported by cranial nerves, namely, nerves V, VII, IX, and XI centered in the nucleus ambiguous. AIM: The aim of the study is to determine the impact of a social nervous (SaSo) exercise training program consisting of warm-up, core (prayer movements), and cooling exercises on glucose homeostasis parameters in pregnant women diagnosed with GDM. METHODS: Thirty-seven pregnant women diagnosed with GDM at 24–28 weeks of gestation were allocated into two groups, thats the experimental group (n=19) with the SaSo program being regularly monitored and the control group (n=18) receiving only standard antenatal care for GDM. The Saso program started from the time diabetes was diagnosed until 6 weeks of intervention. Interventions were performed twice per week and sessions lasted 40–45 min. RESULTS: The baseline results for the experimental and control groups were homogeneous, without differences in the baseline variables (p > 0.05). Social nervous exercise the experimental group significantly reduced fasting blood glucose levels (p < 0.001) compared to the control group. CONCLUSIONS: A social nervous exercise program has a beneficial effect on fasting blood glucose levels in late pregnancy.

Systematisation of biological protectors for managing the metabolic syndrome development

BACKGROUND

Metabolic syndrome (MS) is becoming a major health risk in the world. Disorders of homeostasis are a trigger for MS and subsequent cardiometabolic diseases (CMDs). Its physiological role can be supported by biological protectors (BP). The purpose of this study is to develop a BP system for managing the MS development.

METHODS

Within the framework of the case-control study, 3000 participants aged 20-60 years formed 2 groups: the main group and the control group.

RESULTS

The study compared traditional markers of oxidative stress, chronic inflammation, and insulin resistance, which reflect the state of homeostasis. The BP system, proposed based on the concept of maintaining homeostasis, offers the following points for investigating the possibilities of therapeutic intervention: confronting dysregulation of homeostasis, resisting chronic inflammation and oxidative stress, resisting the consequences of disturbed homeostasis. This approach not only contributed to the understanding of general biological processes, but also provided a targeted search and development of BP to maintain the stability of homeostasis with MS.

CONCLUSIONS

The study results provided insight into new opportunities in the MS management.

Endovascular denervation (EDN): From Hypertension to Non-Hypertension Diseases

Recently, the use of endovascular denervation (EDN) to treat resistant hypertension has gained significant attention. In addition to reducing sympathetic activity, EDN might also have beneficial effects on pulmonary arterial hypertension, insulin resistance, chronic kidney disease, atrial fibrillation, heart failure, obstructive sleep apnea syndrome, loin pain hematuria syndrome, cancer pain and so on. In this article we will summarize the progress of EDN in clinical research.

Update on the Relationship Between Depression and Neuroendocrine Metabolism

Through the past decade of research, the correlation between depression and metabolic diseases has been noticed. More and more studies have confirmed that depression is comorbid with a variety of metabolic diseases, such as obesity, diabetes, metabolic syndrome and so on. Studies showed that the underlying mechanisms of both depression and metabolic diseases include chronic inflammatory state, which is significantly related to the severity. In addition, they also involve endocrine, immune systems. At present, the effects of clinical treatments of depression is limited. Therefore, exploring the co-disease mechanism of depression and metabolic diseases is helpful to find a new clinical therapeutic intervention strategy. Herein, focusing on the relationship between depression and metabolic diseases, this manuscript aims to provide an overview of the comorbidity of depression and metabolic.

Non-invasive Monitoring of Three Glucose Ranges Based On ECG By Using DBSCAN-CNN

Autonomic nervous system (ANS) can maintain homeostasis through the coordination of different organs including heart. The change of blood glucose (BG) level can stimulate the ANS, which will lead to the variation of Electrocardiogram (ECG). Considering that the monitoring of different BG ranges is significant for diabetes care, in this paper, an ECG-based technique was proposed to achieve non-invasive monitoring with three BG ranges: low glucose level, moderate glucose level, and high glucose level. For this purpose, multiple experiments that included fasting tests and oral glucose tolerance tests were conducted, and the ECG signals from 21 adults were recorded continuously. Furthermore, an approach of fusing density-based spatial clustering of applications with noise and convolution neural networks (DBSCAN-CNN) was presented for ECG preprocessing of outliers and classification of BG ranges based ECG. Also, ECG's important information, which was related to different BG ranges, was graphically visualized. The result showed that the percentages of accurate classification were 87.94% in low glucose level, 69.36% in moderate glucose level, and 86.39% in high glucose level. Moreover, the visualization results revealed that the highlights of ECG for the different BG ranges were different. In addition, the sensitivity of prediabetes/diabetes screening based on ECG was up to 98.48%, and the specificity was 76.75%. Therefore, we conclude that the proposed approach for BG range monitoring and prediabetes/diabetes screening has potentials in practical applications.

Activation of nucleus accumbens μ-opioid receptors enhances the response to a glycaemic challenge

Opioids are known to affect blood glucose levels but their exact role in the physiological control of glucose metabolism remains unclear. Although there are numerous studies investigating the peripheral effects of opioid stimulation, little is known about how central opioids control blood glucose and which brain areas are involved. One brain area possibly involved is the nucleus accumbens because, as well as being a key site for opioid effects on food intake, it has also been implicated in the control of blood glucose levels. Within the nucleus accumbens, μ-opioid receptors are most abundantly expressed. Therefore, in the present study, we investigated the role of μ-opioid receptors in the nucleus accumbens in the control of glucose metabolism. We show that infusion of the μ-opioid receptor agonist [d-Ala2 , N-MePhe4 , Gly-ol]-enkephalin (DAMGO) in the nucleus accumbens by itself does not affect blood glucose levels, but it enhances the glycaemic response after both an insulin tolerance test, as well as a glucose tolerance test. These findings indicate that the nucleus accumbens plays a role in the central effects of opioids on glucose metabolism, and highlight the possibility of nucleus accumbens μ-opioid receptors as a therapeutic target for enhancing the counter-regulatory response.

Autonomic nervous system activity changes in patients with hypertension and overweight: role and therapeutic implications

The incidence and prevalence of hypertension is increasing worldwide, with approximately 1.13 billion of people currently affected by the disease, often in association with other diseases such as diabetes mellitus, chronic kidney disease, dyslipidemia/hypercholesterolemia, and obesity. The autonomic nervous system has been implicated in the pathophysiology of hypertension, and treatments targeting the sympathetic nervous system (SNS), a key component of the autonomic nervous system, have been developed; however, current recommendations provide little guidance on their use. This review discusses the etiology of hypertension, and more specifically the role of the SNS in the pathophysiology of hypertension and its associated disorders. In addition, the effects of current antihypertensive management strategies, including pharmacotherapies, on the SNS are examined, with a focus on imidazoline receptor agonists.

A ganglionic blocker and adrenoceptor ligands modify clozapine-induced insulin resistance

Clozapine is a second generation antipsychotic drug that has proven to be helpful in the management of patients with psychotic disorders that are resistant to other medications. Unfortunately, the majority of patients treated with clozapine develop metabolic dysregulation, including weight gain and insulin resistance. There are few treatments available to effectively counter these side-effects. The goal of the present study was to use an established animal model to better understand the nature of these metabolic side-effects and determine whether existing drugs could be used to alleviate metabolic changes. Adult female rats were treated with a range of doses of clozapine (2, 10 and 20 mg/kg) and subjected to the hyperinsulinemic-euglycemic clamp, to measure whole-body insulin resistance. Clozapine dose-dependently decreased the glucose infusion rate, reflecting pronounced insulin resistance. To reverse the insulin resistance, rats were co-treated with the ganglionic blocker mecamylamine (0.1, 1.0 and 5.0 mg/kg) which dose-dependently reversed the effects of 10 mg/kg clozapine. A 1.0 mg/kg dose of mecamylamine independently reversed the large increase in peripheral epinephrine caused by treatment with clozapine. To study the influence of specific adrenoceptors, rats were treated with multiple doses of α₁ (prazosin), α₂ (idazoxan), β₁ (atenolol) and β₂ (butoxamine) adrenoceptor antagonists after the onset of clozapine-induced insulin resistance. Both beta blockers were effective in attenuating the effects of clozapine, while idazoxan had a smaller effect; no change was seen with prazosin. The current results indicate that peripheral catecholamines may play a role in clozapine's metabolic effects and be a target for future treatments.

The role of selective imidazoline receptor agonists in modern hypertension management: an international real-world survey (STRAIGHT)

BACKGROUND

Multiple pharmacologic strategies are currently available to lower blood pressure (BP). Renin-angiotensin system (RAS)-inhibitors, calcium channel blockers and diuretics are widely recommended as first line therapies. Sympathetic activation is an important contributor to BP elevation but remains unopposed or is even increased by some of these drug classes. Selective imidazoline receptor agonists (SIRAs) reduce increased central sympathetic outflow and are considered as add-on therapy in most guidelines. We conducted an international survey to evaluate contemporary hypertension management strategies in countries with high prescription rates of SIRAs to better understand the rationale and practical indications for their use in a real-world setting.

METHODS

Physicians from seven countries (India, Jordan, Lebanon, Russia, Saudi Arabia, South Africa, United Arab Emirates) were asked to complete a web-based questionnaire and comment on clinical case scenarios to provide information on their current practice regarding antihypertension strategies, underlying rationale for their choices, and adherence to relevant guidelines.

RESULTS

281 physicians completed the questionnaire including mainly cardiologists (35%) and general practitioners (32%). 96% reported using European (60%) or local (56%) guidelines in their daily practices. The majority of responding physicians (83%) had knowledge of SIRAs and 70% prescribed SIRAs regularly typically as a third line antihypertensive strategy (63%). The preferred combination partners for SIRAs were RAS-inhibitors (72%).

CONCLUSIONS

Contemporary hypertension management varies between countries and therapeutic approaches in a real-world setting are not always in line with recommendations from available guidelines. In the countries selected for this survey prescription of SIRAs was common and appeared to be guided predominantly by considerations relating to the underlying pathophysiologic mechanism of sympathetic inhibition.

Renal denervation improves vascular endothelial dysfunction by inducing autophagy via AMPK/mTOR signaling activation in a rat model of type 2 diabetes mellitus with insulin resistance

BACKGROUND

Recent clinical and animal studies have shown that renal denervation (RDN) improves insulin sensitivity and endothelial dysfunction. However, the specific mechanism remains incompletely understood. The purpose of this study is to investigate the effects of RDN on endothelial dysfunction of type 2 diabetes mellitus (T₂DM) rat models with insulin resistance and to explore the underlying molecular mechanisms.

METHODS

Male Sprague-Dawley rats were fed with or without high-fat diet allocated in different groups, combined with low-dose streptozotocin which induces a rat model to develop T₂DM with insulin resistance. RDN was conducted 1 week after the rat models fully developed T₂DM. The animals were sub-divided into four groups randomly: control group (CON, n = 6), diabetic group (T₂DM, n = 6), diabetic with sham surgery group (Sham, n = 6) and diabetic with RDN group (RDN, n = 6). Rats in all groups were studied at baseline, both preoperatively and 4 weeks after RDN, respectively. Western blot was used to detect the expression of angiotensin-converting enzyme 2 (ACE2) protein and the expression of autophagy-related proteins Beclin1, LC3 and p62 and autophagy signaling pathway AMPK/mTOR proteins and apoptosis-related protein caspase-3 in the aorta endothelial cells. In addition, the effects of ACE2 on autophagy of human umbilical vein insulin resistance endothelial cell culture in vitro were also studied.

RESULTS

RDN decreased plasma and renal tissue norepinephrine levels. The Von Willebrand factor level was also decreased, while the plasma level of nitric oxide (NO) was significantly increased after RDN. Compared with the T₂DM group and the Sham group, the endothelium-dependent and endothelium-independent diastolic function of the RDN group was improved significantly, the expression of Beclin1, LC3, ACE2 and eNOS proteins was higher, and the level of p62 protein was decreased. Furthermore, we found that RDN can activate the expression of p-AMPK and inhibit the expression of p-mTOR. In cell culture experiment, ACE2 activated p-AMPK and inhibited p-mTOR, thus promoting autophagy.

CONCLUSIONS

RDN may not only increase the expression of ACE2 in the vascular endothelium, but also can via ACE2 activate p-AMPK and inhibit p-mTOR, thus promoting autophagy and improving endothelial dysfunction.

Chronic vagus nerve stimulation for drug-resistant epilepsy may influence fasting blood glucose concentration

Background

Cervical vagus nerve stimulation (VNS) has been widely accepted as adjunctive therapy for drug-resistant epilepsy and major depression. Its effects on glycemic control in humans were however poorly understood. The aim of our study was to investigate the potential effects of VNS on fasting blood glucose (FBG) in patients with drug-resistant epilepsy.

Methods

Patients with drug-resistant epilepsy who had received VNS implants at the same hospital were retrospectively studied. Effects on FBG, weight, body mass index and blood pressure were evaluated at 4, 8 and 12 months of follow-up.

Results

32 subjects (11 females/21 males, 19 ± 9 years, body mass index 22.2 ± 4.0 kg/m²) completed 12-month follow-up. At the 4 months, there were no significant changes in FBG concentrations from baseline to follow-up in both Sham-VNS (4.89 ± 0.54 vs. 4.56 ± 0.54 mmol/L, N = 13, p = 0.101) and VNS (4.80 ± 0.54 vs. 4.50 ± 0.56 mmol/L, N = 19, p = 0.117) groups. However, after 8 (4.90 ± 0.42 mmol/L, N = 32, p = 0.001) and 12 (4.86 ± 0.40 mmol/L, N = 32, p = 0.002) months of VNS, FBG levels significantly increased compared to baseline values (4.52 ± 0.54 mmol/L, N = 32). Changes in FBG concentrations at both 8 (R² = 0.502, N = 32, p < 0.001) and 12 (R² = 0.572, N = 32, p < 0.001) months were negatively correlated with baseline FBG levels.

Conclusions

Our study suggests that chronic cervical VNS elevates FBG levels with commonly used stimulation parameters in patients with epilepsy.

Trial registration VNSRE, NCT02378792. Registered 4 March 2015—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT02378792

Both Prediabetes and Type 2 Diabetes Are Associated With Lower Heart Rate Variability: The Maastricht Study

OBJECTIVE

Low heart rate variability (HRV), a marker for cardiac autonomic dysfunction, is a known feature of type 2 diabetes, but it remains incompletely understood whether this also applies to prediabetes or across the whole glycemic spectrum. Therefore, we investigated the association among prediabetes, type 2 diabetes, and measures of glycemia and HRV.

RESEARCH DESIGN AND METHODS

In the population-based Maastricht Study (n = 2,107; mean ± SD age 59 ± 8 years; 52% men; normal glucose metabolism [n = 1,226], prediabetes [n = 331], and type 2 diabetes [n = 550, oversampled]), we determined 24-h electrocardiogram-derived HRV in time and frequency domains (individual z-scores, based upon seven and six variables, respectively). We used linear regression with adjustments for age, sex, and major cardiovascular risk factors.

RESULTS

After adjustments, both time and frequency domain HRV were lower in prediabetes and type 2 diabetes as compared with normal glucose metabolism (standardized β [95% CI] for time domain: -0.15 [-0.27; -0.03] and -0.34 [-0.46; -0.22], respectively, P for trend <0.001; for frequency domain: -0.14 [-0.26; -0.02] and -0.31 [-0.43; -0.19], respectively, P for trend <0.001). In addition, 1-SD higher glycated hemoglobin, fasting plasma glucose, and 2-h postload glucose were associated with lower HRV in both domains (time domain: -0.16 [-0.21; -0.12], -0.16 [-0.21; -0.12], and -0.15 [-0.20; -0.10], respectively; frequency domain: -0.14 [-0.19; -0.10], -0.14 [-0.18; -0.09], and -0.13 [-0.18; -0.08], respectively).

CONCLUSIONS

Both prediabetes and type 2 diabetes were independently associated with lower HRV. This is further substantiated by independent continuous associations between measures of hyperglycemia and lower HRV. These data strongly suggest that cardiac autonomic dysfunction is already present in prediabetes.

The neuronal (pro)renin receptor and astrocyte inflammation in the central regulation of blood pressure and blood glucose in mice fed a high-fat diet

We report here that the neuronal (pro)renin receptor (PRR), a key component of the brain renin-angiotensin system (RAS), plays a critical role in the central regulation of high-fat-diet (HFD)-induced metabolic pathophysiology. The neuronal PRR is known to mediate formation of the majority of angiotensin (ANG) II, a key bioactive peptide of the RAS, in the central nervous system and to regulate blood pressure and cardiovascular function. However, little is known about neuronal PRR function in overnutrition-related metabolic physiology. Here, we show that PRR deletion in neurons reduces blood pressure, neurogenic pressor activity, and fasting blood glucose and improves glucose tolerance without affecting food intake or body weight following a 16-wk HFD. Mechanistically, we found that a HFD increases levels of the PRR ligand (pro)renin in the circulation and hypothalamus and of ANG II in the hypothalamus, indicating activation of the brain RAS. Importantly, PRR deletion in neurons reduced astrogliosis and activation of the astrocytic NF-κB p65 (RelA) in the arcuate nucleus and the ventromedial nucleus of the hypothalamus. Collectively, our findings indicate that the neuronal PRR plays essential roles in overnutrition-related metabolic pathophysiology.

Neuromodulation of metabolic functions: from pharmaceuticals to bioelectronics to biocircuits

Neuromodulation of central and peripheral neural circuitry brings together neurobiologists and neural engineers to develop advanced neural interfaces to decode and recapitulate the information encoded in the nervous system. Dysfunctional neuronal networks contribute not only to the pathophysiology of neurological diseases, but also to numerous metabolic disorders. Many regions of the central nervous system (CNS), especially within the hypothalamus, regulate metabolism. Recent evidence has linked obesity and diabetes to hyperactive or dysregulated autonomic nervous system (ANS) activity. Neural regulation of metabolic functions provides access to control pathology through neuromodulation. Metabolism is defined as cellular events that involve catabolic and/or anabolic processes, including control of systemic metabolic functions, as well as cellular signaling pathways, such as cytokine release by immune cells. Therefore, neuromodulation to control metabolic functions can be used to target metabolic diseases, such as diabetes and chronic inflammatory diseases. Better understanding of neurometabolic circuitry will allow for targeted stimulation to modulate metabolic functions. Within the broad category of metabolic functions, cellular signaling, including the production and release of cytokines and other immunological processes, is regulated by both the CNS and ANS. Neural innervations of metabolic (e.g. pancreas) and immunologic (e.g. spleen) organs have been understood for over a century, however, it is only now becoming possible to decode the neuronal information to enable exogenous controls of these systems. Future interventions taking advantage of this progress will enable scientists, engineering and medical doctors to more effectively treat metabolic diseases.

Stress and obesity: The ghrelin connection

Ghrelin is a hormone associated with feeding and energy balance. Not surprisingly, this hormone is secreted in response to acute stressors and it is chronically elevated after exposure to chronic stress in tandem with a number of metabolic changes aimed at attaining homeostatic balance. In the present review, we propose that ghrelin plays a key role in these stress-induced homeostatic processes. Ghrelin targets the hypothalamus and brain stem nuclei that are part of the sympathetic nervous system to increase appetite and energy expenditure and promote the use of carbohydrates as a source of fuel at the same time as sparing fat. Ghrelin also targets mesolimbic brain regions such as the ventral segmental area and the hippocampus to modulate reward processes, to protect against damage associated with chronic stress, as well as to potentially increase resilience to stress. In all, these data support the notion that ghrelin, similar to corticosterone, is a critical metabolic hormone that is essential for the stress response.