Ionotropic glutamate receptors in paraventricular nucleus mediate adipose afferent reflex and regulate sympathetic outflow in rats

Chemerin in caudal division of nucleus tractus solitarius increases sympathetic activity and blood pressure

Chemerin is an adipokine that contributes to metabolism regulation. Nucleus tractus solitarius (NTS) is the first relay station in the brain for accepting various visceral afferent activities for regulating cardiovascular activity. However, the roles of chemerin in the NTS in regulating sympathetic activity and blood pressure are almost unknown. This study aimed to determine the role and potential mechanism of chemerin in the NTS in modulating sympathetic outflow and blood pressure. Bilateral NTS microinjections were performed in anaesthetized adult male Sprague-Dawley rats. Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were continuously recorded. Chemerin and its receptor chemokine-like receptor 1 (CMKLR1) were highly expressed in caudal NTS (cNTS). Microinjection of chemerin-9 to the cNTS increased RSNA, MAP and HR, which were prevented by CMKLR1 antagonist α-NETA, superoxide scavenger tempol or N-acetyl cysteine, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors diphenyleneiodonium or apocynin. Chemerin-9 increased superoxide production and NADPH oxidase activity in the cNTS. The increased superoxide production induced by chemerin-9 was inhibited by α-NETA. The effects of cNTS microinjection of chemerin-9 on the RSNA, MAP and HR were attenuated by the pretreatment with paraventricular nucleus (PVN) microinjection of NMDA receptor antagonist MK-801 rather than AMPA/kainate receptor antagonist CNQX. These results indicate that chemerin-9 in the NTS increases sympathetic outflow, blood pressure and HR via CMKLR1-mediated NADPH oxidase activation and subsequent superoxide production in anaesthetized normotensive rats. Glutamatergic inputs in the PVN are needed for the chemerin-9-induced responses.

Neural Circuits Underlying Reciprocal Cardiometabolic Crosstalk: 2023 Arthur C. Corcoran Memorial Lecture

The interplay of various body systems, encompassing those that govern cardiovascular and metabolic functions, has evolved alongside the development of multicellular organisms. This evolutionary process is essential for the coordination and maintenance of homeostasis and overall health by facilitating the adaptation of the organism to internal and external cues. Disruption of these complex interactions contributes to the development and progression of pathologies that involve multiple organs. Obesity-associated cardiovascular risks, such as hypertension, highlight the significant influence that metabolic processes exert on the cardiovascular system. This cardiometabolic communication is reciprocal, as indicated by substantial evidence pointing to the ability of the cardiovascular system to affect metabolic processes, with pathophysiological implications in disease conditions. In this review, I outline the bidirectional nature of the cardiometabolic interaction, with special emphasis on the impact that metabolic organs have on the cardiovascular system. I also discuss the contribution of the neural circuits and autonomic nervous system in mediating the crosstalk between cardiovascular and metabolic functions in health and disease, along with the molecular mechanisms involved.

The metabolic and functional roles of sensory nerves in adipose tissues

Homeostatic regulation of adipose tissue is critical for the maintenance of energy balance and whole-body metabolism. The peripheral nervous system provides bidirectional neural communication between the brain and adipose tissue, thereby providing homeostatic control. Most research on adipose innervation and nerve functions has been limited to the sympathetic nerves and their neurotransmitter norepinephrine. In recent years, more work has focused on adipose sensory nerves, but the contributions of subsets of sensory nerves to metabolism and the specific roles contributed by sensory neuropeptides are still understudied. Advances in imaging of adipose innervation and newer tissue denervation techniques have confirmed that sensory nerves contribute to the regulation of adipose functions, including lipolysis and browning. Here, we summarize the historical and latest findings on the regulation, function and plasticity of adipose tissue sensory nerves that contribute to metabolically important processes such as lipolysis, vascular control and sympathetic axis cross-talk.

Adrenomedullin in paraventricular nucleus attenuates adipose afferent reflex and sympathoexcitation via receptors mediated nitric oxide-gamma-aminobutyric acid A type receptor pathway in rats with obesity-related hypertension

BACKGROUND

Hypothalamic paraventricular nucleus (PVN) is an important central site for the control of the adipose afferent reflex (AAR) that increases sympathetic outflow and blood pressure in obesity-related hypertension (OH).

METHOD

In this study, we investigated the effects of nitric oxide (NO) and cardiovascular bioactive polypeptide adrenomedullin (ADM) in the PVN on AAR and sympathetic nerve activity (SNA) in OH rats induced by a high-fat diet.

RESULTS

The results showed that ADM, total neuronal NO synthase (nNOS) and phosphorylated-nNOS protein expression levels in the PVN of the OH rats were down-regulated compared to the control rats. The enhanced AAR in OH rats was attenuated by PVN acute application of NO donor sodium nitroprusside (SNP), but was strengthened by the nNOS inhibitor nNOS-I, guanylyl cyclase inhibitor (1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one, ODQ) and gamma-aminobutyric acid A type receptor (GABAA) antagonist Bicuculline. Moreover, PVN ADM microinjection not only decreased basal SNA but also attenuated the enhanced AAR in OH rats, which were effectively inhibited by ADM receptor antagonist ADM22-52, nNOS-I, ODQ or Bicuculline pretreatment. Bilateral PVN acute microinjection of ADM also caused greater increases in NO and cyclic guanosine monophosphate (cGMP) levels, and nNOS phosphorylation. Adeno-associated virus vectors encoding ADM (AAV-ADM) transfection in the PVN of OH rats not only decreased the elevated AAR, basal SNA and blood pressure (BP), but also increased the expression and activation of nNOS. Furthermore, AAV-ADM transfection improved vascular remodeling in OH rats.

CONCLUSION

Taken together, our data highlight the roles of ADM in improving sympathetic overactivation, enhanced AAR and hypertension, and its related mechanisms associated with receptors mediated NO-cGMP-GABAA pathway in OH condition.

A Pilot Study of Gene Expression Analysis in Peripheral Blood Mononuclear Cells in Response to a Hypocaloric Mediterranean Diet

Background

Few studies have examined gene expression in peripheral blood mononuclear cells (PBMCs) after a dietary intervention.

Objective

Our study is aimed at evaluating in a pilot study the peripheral blood gene expression in obese patients after weight loss secondary to a hypocaloric Mediterranean diet.

Design

A sample of 11 obese subjects without metabolic syndrome was enrolled. Biochemical, anthropometric parameters and microarray analysis were performed at baseline and after 6 months of dietary intervention.

Results

The mean age was 43.1 ± 6.3 years, and the mean body mass index (BMI) was 38.6 ± 8.1 kg/m². All the next improvements were statistically significant: body weight −7.4 ± 1.9 kg, BMI -2.5 ± 0.2 kg, fat mass −5.7 ± 1.2 kg, waist circumference −5.8 ± 1.2 cm, triglycerides −17.4 ± 6.5 mg/dl, C-reactive protein −3.1 ± 1.5 mg/dL, insulin −2.1 ± 1.0 mUI/L, and HOMA-IR −0.7 ± 0.2 units. We identified 634 differentially expressed genes: 262 genes with relative higher expression levels and 372 with lower expression levels. Cluster analysis showed 35 genes in nutritional disease and 17 genes in endocrine system. The most relevant gene was thyroid peroxidase (TPO), and this gene was overexpressed, and the next genes carbonic anhydrase VI (CA6), caveolin protein 1 (CAV1) and solute carrier family type 12 (SLLC12A3), soluble carrier family type 12 (SLLC12A3), beta 3 receptor (ADRB3), and glutamate receptor ionotropic N methyl D aspartate 2 A (GRIN2A) were all underexpressed.

Conclusion

In PBMC from obese patients after a diet with a Mediterranean pattern, the expression of 634 genes, of the endocrine system and of nutritional disease, is modified.

Retroperitoneal adipose tissue denervation improves cardiometabolic and autonomic dysfunction in a high fat diet model

Sympathetic vasomotor overactivity is a major feature leading to the cardiovascular dysfunction related to obesity. Considering that the retroperitoneal white adipose tissue (rWAT) is an important fat visceral depot and receives intense sympathetic and afferent innervations, the present study aimed to evaluate the effects evoked by bilateral rWAT denervation in obese rats. Male Wistar rats were fed with HFD for 8 consecutive weeks and rWAT denervation was performed at the 6th week. Arterial pressure, splanchnic and renal sympathetic vasomotor nerve activities were assessed and inflammation and the components of the renin -angiotensin system were evaluated in different white adipose tissue depots. HFD animals presented higher serum levels of leptin and glucose, an increase in arterial pressure and splanchnic sympathetic nerve activity; rWAT denervation, normalized these parameters. Pro-inflammatory cytokines levels were significantly increased, as well as RAAS gene expression in WAT of HFD animals; rWAT denervation significantly attenuated these changes. In conclusion, HFD promotes vasomotor sympathetic overactivation and inflammation with repercussions on the cardiovascular system. In conclusion, the neural communication between WAT and the brain is fundamental to trigger sympathetic vasomotor activation and this pathway is a possible new therapeutic target to treat obesity-associated cardiovascular dysfunction.

Angiotensin Type 1 Receptors and Superoxide Anion Production in Hypothalamic Paraventricular Nucleus Contribute to Capsaicin-Induced Excitatory Renal Reflex and Sympathetic Activation

Chemical stimulation of the kidney increases sympathetic activity and blood pressure in rats. The hypothalamic paraventricular nucleus (PVN) is important in mediating the excitatory renal reflex (ERR). In this study, we examined the role of molecular signaling in the PVN in mediating the capsaicin-induced ERR and sympathetic activation. Bilateral PVN microinjections were performed in rats under anesthesia. The ERR was elicited by infusion of capsaicin into the cortico-medullary border of the right kidney. The reflex was evaluated as the capsaicin-induced changes in left renal sympathetic nerve activity and mean arterial pressure. Blockade of angiotensin type 1 receptors with losartan or inhibition of angiotensin-converting enzyme with captopril in the PVN abolished the capsaicin-induced ERR. Renal infusion of capsaicin significantly increased NAD(P)H oxidase activity and superoxide anion production in the PVN, which were prevented by ipsilateral renal denervation or microinjection of losartan into the PVN. Furthermore, either scavenging of superoxide anions or inhibition of NAD(P)H oxidase in the PVN abolished the capsaicin-induced ERR. We conclude that the ERR induced by renal infusion of capsaicin is mediated by angiotensin type 1 receptor-related NAD(P)H oxidase activation and superoxide anion production within the PVN.

Sensory signals mediating high blood pressure via sympathetic activation: role of adipose afferent reflex

Blood pressure regulation in health and disease involves a balance between afferent and efferent signals from multiple organs and tissues. Although there are numerous reviews focused on the role of sympathetic nerves in different models of hypertension, few have revised the contribution of afferent nerves innervating adipose tissue and their role in the development of obesity-induced hypertension. Both clinical and basic research support the beneficial effects of bilateral renal denervation in lowering blood pressure. However, recent studies revealed that afferent signals from adipose tissue, in an adipose-brain-peripheral pathway, could contribute to the increased sympathetic activation and blood pressure during obesity. This review focuses on the role of adipose tissue afferent reflexes and briefly describes a number of other afferent reflexes modulating blood pressure. A comprehensive understanding of how multiple afferent reflexes contribute to the pathophysiology of essential and/or obesity-induced hypertension may provide significant insights into improving antihypertensive therapeutic approaches.

Obesity and Cancer: Existing and New Hypotheses for a Causal Connection

Existing explanations of obesity-associated cancer emphasise direct mutagenic effects of dietary components or hormonal imbalance. Some of these hypotheses are reviewed briefly, but recent evidence suggests a major role for chronic inflammation in cancer risk, possibly involving dietary content. These ideas include the inflammation-induced activation of the kynurenine pathway and its role in feeding and metabolism by activation of the aryl hydrocarbon receptor (AHR) and by modulating synaptic transmission in the brain. Evidence for a role of the kynurenine pathway in carcinogenesis then provides a potentially major link between obesity and cancer. A second new hypothesis is based on evidence that serine proteases can deplete cells of the tumour suppressors Deleted in Colorectal Cancer (DCC) and neogenin. These enzymes include mammalian chymotryptic proteases released by pro-inflammatory neutrophils and macrophages. Blood levels of chymotrypsin itself increase in parallel with food intake. The mechanistically similar bacterial enzyme subtilisin is widespread in the environment, animal probiotics, meat processing and cleaning products. Simple public health schemes in these areas, with selective serine protease inhibitors and AHR antagonists and could prevent a range of intestinal and other cancers.

c-Jun N-terminal Kinase mediates prostaglandin-induced sympathoexcitation in rats with chronic heart failure by reducing GAD1 and GABRA1 expression

AIM

Prostaglandin E2 mediates sympathoexcitation in chronic heart failure (CHF) through EP3 receptors (PTGER3) in the paraventricular nucleus (PVN). The aim of this study was to investigate the role of c-Jun N-terminal kinase (JNK) in expressional regulation of gamma-aminobutyric acid signalling in PVN in CHF rats.

METHODS

Chronic heart failure was induced by left coronary ligation in Wistar rats. Renal sympathetic nerve discharge (RSND) and mean arterial pressure (MAP) responses to the PVN infusion were determined in anaesthetized rats. Osmotic minipumps were used for chronic PVN infusion. PTGER3 expression was examined with immunofluorescence staining, quantitative real-time PCR and Western blot.

RESULTS

Chronic heart failure rats had increased JNK activation and decreased glutamate decarboxylase 1 (GAD1) and GABA_A receptor alpha 1 subunit (GABRA1) expression in the PVN. PVN infusion of the PTGER3 agonist SC-46275 caused sympathoexcitation in sham-operated control (Sham) rats and increased it further in CHF. The PTGER3 antagonist L798106 reduced sympathoexcitation and cardiac dysfunction in CHF. PVN infusion of EP1 receptor antagonist SC-19220, EP2 receptor antagonist AH6809 or EP4 receptor antagonist L-161982 had no effect on sympathoexcitation. The JNK inhibitor SP600125 normalized sympathoexcitation and GAD1 and GABRA1 expression in PVN in CHF rats. Both the p44/42 and p38 mitogen-activated protein kinase inhibitors PD98059 and SB203580 could not prevent the downregulation of GAD1 and GABRA1 expression in PVN in CHF. PTGER3 agonist activated JNK but downregulated GAD1 and GABRA1 expression in NG108 neuronal cells.

CONCLUSION

Prostaglandin signalling through upregulated PTGER3 activates JNK which reduces GAD1 and GABRA1 expression in the PVN, and contributes to sympathoexcitation in CHF.

Reduced lipolysis response to adipose afferent reflex involved in impaired activation of adrenoceptor-cAMP-PKA-hormone sensitive lipase pathway in obesity

Chemical stimulation of white adipose tissue (WAT) causes adipose afferent reflex (AAR) and sympathetic activation. This study is to investigate the effects of AAR on lipolysis and the mechanisms of attenuated lipolysis response to enhanced AAR in obesity. Obesity was caused by high-fat diet for 12 weeks in rats. AAR was induced by injection of capsaicin into inguinal WAT or electrical stimulation of epididymal WAT afferent nerve. AAR caused sympathetic activation, which was enhanced in obesity rats. AAR increased cAMP levels and PKA activity, promoted hormone sensitive lipase (HSL) and perilipin phosphorylation, and increased lipolysis in WAT, which were attenuated in obesity rats. PKA activity, cAMP, perilipin and β-adrenoceptor levels were reduced, while HSL was upregulated in adipocytes from obesity rats. In primary adipocytes, isoproterenol increased cAMP levels and PKA activity, promoted HSL and perilipin phosphorylation, and increased lipolysis, which were attenuated in obesity rats. The attenuated effects of isoproterenol in adipocytes from obesity rats were prevented by a cAMP analogue dbcAMP. The results indicate that reduced lipolysis response to enhanced AAR in obesity is attributed to the impaired activation of β-adrenoceptor-cAMP-PKA-HSL pathway. Increased cAMP level in adipocytes rectifies the attenuated lipolysis in obesity.

Paraventricular nucleus is involved in the central pathway of adipose afferent reflex in rats

Increasing evidence indicates a link between sympathetic nervous system activation and obesity, but the underlying mechanisms remain elusive. The adipose afferent reflex (AAR) is a sympathoexcitatory reflex that is activated by afferent neurotransmission from the white adipose tissue (WAT). This study aimed to investigate whether the hypothalamic paraventricular nucleus (PVH) is an important component of the central neurocircuitry of the AAR. In anesthetized rats, the discharge activity of individual PVH neurons was recorded in vivo. Activation of WAT afferents was initiated by capsaicin injection, and the AAR was evaluated by monitoring renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses. The responses of PVH neurons to activation of WAT afferents were evaluated by c-fos immunoreactivity and the discharge activity of individual PVH neurons, which was recorded using extracellular single-unit recording. After activation of WAT afferents, both individual PVH neuron discharge activity and c-fos immunoreactivity increased. Bilateral selective lesions of the neurons in the PVH with kainic acid abolished the AAR. These results indicate that PVH is an important component of the central neurocircuitry of the AAR.

Slow-pressor angiotensin II hypertension and concomitant dendritic NMDA receptor trafficking in estrogen receptor β-containing neurons of the mouse hypothalamic paraventricular nucleus are sex and age dependent

The incidence of hypertension increases after menopause. Similar to humans, "slow-pressor" doses of angiotensin II (AngII) increase blood pressure in young males, but not in young female mice. However, AngII increases blood pressure in aged female mice, paralleling reproductive hormonal changes. These changes could influence receptor trafficking in central cardiovascular circuits and contribute to hypertension. Increased postsynaptic N-methyl-D-aspartate (NMDA) receptor activity in the hypothalamic paraventricular nucleus (PVN) is crucial for the sympathoexcitation driving AngII hypertension. Estrogen receptors β (ERβs) are present in PVN neurons. We tested the hypothesis that changes in ovarian hormones with age promote susceptibility to AngII hypertension, and influence NMDA receptor NR1 subunit trafficking in ERβ-containing PVN neurons. Transgenic mice expressing enhanced green fluorescent protein (EGFP) in ERβ-containing cells were implanted with osmotic minipumps delivering AngII (600 ng/kg/min) or saline for 2 weeks. AngII increased blood pressure in 2-month-old males and 18-month-old females, but not in 2-month-old females. By electron microscopy, NR1-silver-intensified immunogold (SIG) was mainly in ERβ-EGFP dendrites. At baseline, NR1-SIG density was greater in 2-month-old females than in 2-month-old males or 18-month-old females. After AngII infusion, NR1-SIG density was decreased in 2-month-old females, but increased in 2-month-old males and 18-month-old females. These findings suggest that, in young female mice, NR1 density is decreased in ERβ-PVN dendrites thus reducing NMDA receptor activity and preventing hypertension. Conversely, in young males and aged females, NR1 density is upregulated in ERβ-PVN dendrites and ultimately leads to the neurohumoral dysfunction driving hypertension.

GABA in Paraventricular Nucleus Regulates Adipose Afferent Reflex in Rats

BACKGROUND

Chemical stimulation of white adipose tissue (WAT) induces adipose afferent reflex (AAR), and thereby causes a general sympathetic activation. Paraventricular nucleus (PVN) is important in control of sympathetic outflow. This study was designed to investigate the role of γ-aminobutyric acid (GABA) in PVN in regulating the AAR.

METHODOLOGY/PRINCIPAL FINDINGS

Experiments were carried out in anesthetized rats. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were continuously recorded. AAR was evaluated by the RSNA and MAP responses to electrical stimulation of the right epididymal WAT (eWAT) afferent nerve. Electrical stimulation of eWAT afferent nerve increase RSNA. Bilateral microinjection of the GABAA receptor agonist isoguvacine or the GABAB receptor agonist baclofen attenuated the AAR. The effect of isoguvacine on the AAR was greater than that of baclofen. The GABAA receptor antagonist gabazine enhanced the AAR, while the GABAB receptor antagonist CGP-35348 had no significant effect on the AAR. Bilateral PVN microinjection of vigabatrin, a selective GABA-transaminase inhibitor, to increase endogenous GABA levels in the PVN abolished the AAR. The inhibitory effect of vigabatrin on the AAR was attenuated by the pretreatment with gabazine or CGP-35348. Pretreatment with combined gabazine and CGP-35348 abolished the effects of vigabatrin.

CONCLUSIONS

Activation of GABAA or GABAB receptors in the PVN inhibits the AAR. Blockade of GABAA receptors in the PVN enhances the AAR. Endogenous GABA in the PVN plays an important role in regulating the AAR.

Adipose afferent reflex response to insulin is mediated by melanocortin 4 type receptors in the paraventricular nucleus in insulin resistance rats

BACKGROUND

Adipose afferent reflex (AAR) contributes to sympathetic activation and hypertension. Paraventricular nucleus (PVN) plays an important role in AAR and sympathetic outflow. The aim of the present study was to determine whether PVN mediates AAR response to insulin in a rat model of insulin resistance (IR).

METHODS

Male Sprague-Dawley rats were randomly divided into Control and IR groups. Insulin resistance was induced by supplementing fructose (125 g L(-1) , 12 weeks) in the drinking water. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in anesthetized rats. AAR was evaluated by the RSNA and MAP responses to injection of capsaicin into four sites of right inguinal white adipose tissue.

RESULTS

Rats in IR group showed a rise in plasma noradrenaline (NE), glucose, insulin and triglyceride levels, left ventricular weight, systolic blood pressure, homeostasis model assessment of insulin resistance (HOMA-IR) and PVN glucose and insulin levels, melanocortin 4 type receptors (MC4Rs) protein expression, but not MC3Rs and insulin receptors. Compared with Control group, AAR in IR group was significantly enhanced, which contributed to the elevation of NE level; and insulin microinjection into the PVN or the third ventricle significantly strengthened AAR, which was attenuated by pre-treatment with MC4Rs antagonist HS024 and anti-insulin affibody, respectively, but not insulin receptors antagonist S961.

CONCLUSION

The enhanced AAR participates in sympathetic activation in IR, which can be strengthened by PVN insulin. PVN MC4Rs mediate the AAR response to insulin in IR, but not MC3Rs and insulin receptors.

Cardiac sympathetic afferent reflex and its implications for sympathetic activation in chronic heart failure and hypertension

Persistent excessive sympathetic activation greatly contributes to the pathogenesis of chronic heart failure (CHF) and hypertension. Cardiac sympathetic afferent reflex (CSAR) is a sympathoexcitatory reflex with positive feedback characteristics. Humoral factors such as bradykinin, adenosine and reactive oxygen species produced in myocardium due to myocardial ischaemia stimulate cardiac sympathetic afferents and thereby reflexly increase sympathetic activity and blood pressure. The CSAR is enhanced in myocardial ischaemia, CHF and hypertension. The enhanced CSAR at least partially contributes to the sympathetic activation and pathogenesis of these diseases. Nucleus of the solitary tract (NTS), hypothalamic paraventricular nucleus (PVN) and rostral ventrolateral medulla are the most important central sites involved in the modulation and integration of the CSAR. Angiotensin II, AT1 receptors and NAD(P)H oxidase-derived superoxide anions pathway in the PVN are mainly responsible for the enhanced CSAR in CHF and hypertension. Central angiotensin-(1-7), nitric oxide, endothelin, intermedin, hydrogen peroxide and several other signal molecules are involved in regulating CSAR. Blockade of the CSAR shows beneficial effects in CHF and hypertension. This review focuses on the anatomical and physiological basis of the CSAR, the interaction of CSAR with baroreflex and chemoreflex, and the role of enhanced CSAR in the pathogenesis of CHF and hypertension.

Apelin-13 and APJ in paraventricular nucleus contribute to hypertension via sympathetic activation and vasopressin release in spontaneously hypertensive rats

AIMS

Apelin is a specific endogenous ligand of orphan G protein-coupled receptor APJ. This study was designed to determine the roles and mechanisms of apelin-13 and APJ in paraventricular nucleus (PVN) in renal sympathetic nerve activity (RSNA), arginine vasopressin (AVP) release and mean arterial pressure (MAP) in spontaneously hypertensive rats (SHR).

METHOD

Acute experiment was carried out in 13-week-old male SHR and Wistar-Kyoto rats (WKY) under anaesthesia. RSNA and MAP responses to the PVN microinjection were determined. Apelin and APJ expressions were examined with quantitative real-time PCR and Western blot. AVP and noradrenaline were determined with ELISA. Osmotic minipumps were used for chronic PVN infusion in conscious WKY.

RESULTS

Apelin and APJ in the PVN were up-regulated in SHR. The PVN microinjection of apelin-13 increased, but APJ antagonist F13A decreased the RSNA, MAP, plasma noradrenaline and AVP levels in SHR. N-methyl-D-aspartate receptor (NMDAR) antagonist plus non-NMDAR antagonist abolished the apelin-13-induced sympathetic activation rather than AVP release. NMDAR antagonist or non-NMDAR antagonist alone attenuated the apelin-13-induced sympathetic activation. Chronic infusion of apelin-13 into the PVN in normotensive rats induced hypertension, increased plasma noradrenaline and AVP levels and promoted myocardial atrial natriuretic peptide and beta-myosin heavy chain mRNA expressions, two indicative markers of cardiac hypertrophy.

CONCLUSION

Apelin-13 and APJ in the PVN contribute to hypertension via sympathetic activation and AVP release in SHR. The sympatho-excitatory effect of apeline-13 is mediated by both NMDAR and non-NMDAR in the PVN. Persistent activation of APJ in the PVN induces hypertension.

Short and long sympathetic-sensory feedback loops in white fat

We previously demonstrated white adipose tissue (WAT) innervation using the established WAT retrograde sympathetic nervous system (SNS)-specific transneuronal viral tract tracer pseudorabies virus (PRV152) and showed its role in the control of lipolysis. Conversely, we demonstrated WAT sensory innervation using the established anterograde sensory system (SS)-specific transneuronal viral tracer, the H129 strain of herpes simplex virus-1, with sensory nerves showing responsiveness with increases in WAT SNS drive. Several brain areas were part of the SNS outflow to and SS inflow from WAT between these studies suggesting SNS-SS feedback loops. Therefore, we injected both PRV152 and H129 into inguinal WAT (IWAT) of Siberian hamsters. Animals were perfused on days 5 and 6 postinoculation after H129 and PRV152 injections, respectively, and brains, spinal cords, sympathetic, and dorsal root ganglia (DRG) were processed for immunohistochemical detection of each virus across the neuroaxis. The presence of H129+PRV152-colocalized neurons (~50%) in the spinal segments innervating IWAT suggested short SNS-SS loops with significant coinfections (>60%) in discrete brain regions, signifying long SNS-SS loops. Notably, the most highly populated sites with the double-infected neurons were the medial part of medial preoptic nucleus, medial preoptic area, hypothalamic paraventricular nucleus, lateral hypothalamus, periaqueductal gray, oral part of the pontine reticular nucleus, and the nucleus of the solitary tract. Collectively, these results strongly indicate the neuroanatomical reality of the central SNS-SS feedback loops with short loops in the spinal cord and long loops in the brain, both likely involved in the control of lipolysis or other WAT pad-specific functions.

Adipose afferent reflex: sympathetic activation and obesity hypertension

Excessive sympathetic activity contributes to the pathogenesis of hypertension and the progression of the related organ damage. Adipose afferent reflex (AAR) is a sympatho-excitatory reflex that the afferent activity from white adipose tissue (WAT) increases sympathetic outflow and blood pressure. Hypothalamic paraventricular nucleus (PVN or PVH) is one of the central sites in the control of the AAR, and ionotropic glutamate receptors in the nucleus mediate the AAR. The AAR is enhanced in obesity and obesity hypertension. Enhanced WAT afferent activity and AAR contribute to the excessive sympathetic activation and hypertension in obesity. Blockage of the AAR attenuates the excessive sympathetic activity and hypertension. Leptin may be one of sensors in the WAT for the AAR, and is involved in the enhanced AAR in obesity and hypertension. This review focuses on the neuroanatomical basis and physiological functions of the AAR, and the important role of the enhanced AAR in the pathogenesis of obesity hypertension.

Superoxide anions involved in sympathoexcitation and pressor effects of salusin-β in paraventricular nucleus in hypertensive rats

AIMS

Salusin-β in paraventricular nucleus (PVN) increases renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), heart rate (HR) and arginine vasopressin (AVP) release in hypertensive rats but not in normal rats. The present study was designed to investigate the downstream molecular mechanism of salusin-β in the PVN in hypertension.

METHOD

Renovascular hypertension was induced by two-kidney, one-clip (2K1C) in male SD rats. Acute experiments were carried out 4 weeks after 2K1C or sham operation under anaesthesia.

RESULTS

MrgA1 mRNA expression and salusin-β level in the PVN as well as plasma salusin-β level were increased in 2K1C rats. Bilateral PVN microinjection of salusin-β increased the RSNA, MAP and HR in 2K1C rats, which were abolished by the pre-treatment with polyethylene glycol-superoxide dismutase (PEG-SOD), the superoxide anion scavenger tempol, the NAD(P)H oxidase inhibitor apocynin or the protein kinase C (PKC) inhibitor chelerythrine chloride (CLC), but not affected by the AT1 receptor antagonist losartan, the Mas receptor antagonist A-779, the NOS inhibitor L-NAME or the GABAA and GABAB receptor antagonists gabazine+CGP-35348. Salusin-β-induced increases in superoxide anion level and NAD(P)H oxidase activity in the PVN were abolished by the PVN pre-treatment with CLC. Salusin-β increased AVP levels in rostral ventrolateral medulla and plasma, which were prevented by the pre-treatment with PEG-SOD, apocynin or CLC in 2K1C rats. Salusin-β augmented the enhanced activity of PKC in the PVN in 2K1C rats.

CONCLUSION

Protein kinase C-NAD(P)H oxidase-superoxide anions pathway in the PVN is involved in salusin-β-induced sympathetic activation, pressor response and AVP release in renovascular hypertension.

Superoxide anions in paraventricular nucleus modulate adipose afferent reflex and sympathetic activity in rats

Background

Adipose afferent reflex (AAR) is a sympatho-excitatory reflex induced by chemical stimulation of white adipose tissue (WAT). Ionotropic glutamate receptors including NMDA receptors (NMDAR) and non-NMDA receptors (non-NMDAR) in paraventricular nucleus (PVN) mediate the AAR. Enhanced AAR contributes to sympathetic activation and hypertension in obesity rats. This study was designed to investigate the role and mechanism of superoxide anions in PVN in modulating the AAR.

Methodology/Principal Findings

Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded in anesthetized rats. AAR was evaluated by the RSNA and MAP responses to injections of capsaicin into four sites of right inguinal WAT (8.0 nmol in 8.0 µl for each site). Microinjection of polyethylene glycol-superoxide dismutase (PEG-SOD), the superoxide anion scavenger tempol or the NAD(P)H oxidase inhibitor apocynin into the PVN decreased the baseline RSNA and MAP, and attenuated the AAR. Unilateral WAT injection of capsaicin increased superoxide anions in bilateral PVN, which was prevented by the WAT denervation. WAT injection of capsaicin increased superoxide anion level and NAD(P)H oxidase activity in the PVN, which was abolished by the PVN pretreatment with the combined NMDAR antagonist AP5 and non-NMDAR antagonist CNQX. Microinjection of the NMDAR agonist NMDA or the non-NMDAR agonist AMPA increased superoxide anion level and NAD(P)H oxidase activity in the PVN.

Conclusions

NAD(P)H oxidase-derived superoxide anions in the PVN contributes to the tonic modulation of AAR. Activation of ionotropic glutamate receptors in the PVN is involved in the AAR-induced production of superoxide anions in the PVN.