Activation of reciprocal pathways between arcuate nucleus and ventrolateral periaqueductal gray during electroacupuncture: involvement of VGLUT3

Arcuate Nucleus of the Hypothalamus: Anatomy, Physiology, and Diseases

The hypothalamus is part of the diencephalon and has several nuclei, one of which is the arcuate nucleus. The arcuate nucleus of hypothalamus (ARH) consists of neuroendocrine neurons and centrally-projecting neurons. The ARH is the center where the homeostasis of nutrition/metabolism and reproduction are maintained. As such, dysfunction of the ARH can lead to disorders of nutrition/metabolism and reproduction. Here, we review various types of neurons in the ARH and several genetic disorders caused by mutations in the ARH.

The autonomic nervous system: A potential link to the efficacy of acupuncture

The autonomic nervous system (ANS) is a diffuse network that regulates physiological systems to maintain body homeostasis by integrating inputs from the internal and external environment, including the sympathetic, parasympathetic, and enteric nervous systems (ENS). Recent evidence suggests that ANS is one of the key neural pathways for acupuncture signal transduction, which has attracted worldwide attention in the acupuncture field. Here, we reviewed the basic and clinical research published in PubMed over the past 20 years on the effects of acupuncture on ANS regulation and homeostasis maintenance. It was found that acupuncture effectively alleviates ANS dysfunction-associated symptoms in its indications, such as migraine, depression, insomnia, functional dyspepsia, functional constipation. Acupuncture stimulation on some specific acupoints activates sensory nerve fibers, the spinal cord, and the brain. Using information integration and efferents from a complex network of autonomic nuclei of the brain, such as the insular cortex (IC), prefrontal cortex, anterior cingulate cortex (ACC), amygdala (AMG), hypothalamus, periaqueductal gray (PAG), nucleus tractus solitarius (NTS), ventrolateral medulla (VLM), nucleus ambiguus (AMB), acupuncture alleviates visceral dysfunction, inflammation via efferent autonomic nerves, and relieves pain and pain affect. The modulating pattern of sympathetic and parasympathetic nerves is associated with acupuncture stimulation on specific acupoints, intervention parameters, and disease models, and the relationships among them require further exploration. In conclusion, ANS is one of the therapeutic targets for acupuncture and mediates acupuncture's actions, which restores homeostasis. A systemic study is needed to determine the rules and mechanisms underlying the effects of acupoint stimulation on corresponding organs mediated by specific central nervous networks and the efferent ANS.

The effects of frequency-specific, non-invasive, median nerve stimulation on food-related attention and appetite

Median nerve stimulation (MNS) in the existing literature has been used for treating gastrointestinal disorders and amelioration of nausea and vomiting. Recently, studies have shown that MNS can also exert effects on olfactory performances and corresponding anatomical regions through the activation of vagal pathways. This study aimed to test effects of specific frequencies of MNS on food-related attention and appetite. The experiment used an odourised, dot probe task for testing food-related attention and a combination of behavioural (i.e., visual analogue scales; VAS) and physiological approaches (i.e., electrocardiograph; ECG - root mean square of successive differences between normal heartbeats-RMSSD: parasympathetic nervous system activation (RMSSD), stress index-SI: sympathetic nervous system activation) for measuring hunger, appetite, and satiation. Twenty-four healthy, male adults completed a VAS and dot probe task before and after receiving either 40 Hz-, 80 Hz-, 120 Hz MNS or sham (control) across four different sessions with continuous ECG recording throughout each session. Data from the dot probe task were analysed using repeated-measures ANOVA, while pair-wise tests were used for ECG recordings and VAS. Improvements on the dot probe task, not specific to odour-food congruence were found after 40 Hz MNS (p-value = 0.048; strong effect size (0.308 partial eta squared)) while increased ratings of hunger (VAS) (p-value = 0.03, small effect size (0.47 Cohen-D)) and RMSSD scores (p-value < 0.001; medium effect size (0.76 Cohen-D)) were found after 120 Hz MNS. These findings implore further testing of MNS frequency parameters on improving RMSSD, a characteristic marker of measuring parasympathetic/autonomic nervous system activation pertaining to the vagal network. Furthermore, improving sympathovagal balance is associated with cardiovascular benefits in numerous health-related conditions such as obesity, hypertension and diabetes.

Peripheral ERK modulates acupuncture-induced brain neural activity and its functional connectivity

Acupuncture has been widely used as a therapeutic intervention, and the brain network plays a crucial role in its neural mechanism. This study aimed to investigate the acupuncture mechanism from peripheral to central by identifying how the peripheral molecular signals induced by acupuncture affect the brain neural responses and its functional connectivity. We confirmed that peripheral ERK activation by acupuncture plays a role in initiating acupuncture-induced peripheral proteomic changes in mice. The brain neural activities in the neocortex, hippocampus, thalamus, hypothalamus, periaqueductal grey, and nucleus of the solitary tract (Sol) were significantly changed after acupuncture, and these were altered by peripheral MEK/MAPK inhibition. The arcuate nucleus and lateral hypothalamus were the most affected by acupuncture and peripheral MEK/MAPK inhibition. The hypothalamic area was the most contributing brain region in contrast task PLS analysis. Acupuncture provoked extensive changes in brain functional connectivity, and the posterior hypothalamus showed the highest betweenness centrality after acupuncture. After brain hub identification, the Sol and cingulate cortex were selected as hub regions that reflect both degree and betweenness centrality after acupuncture. These results suggest that acupuncture activates brain functional connectivity and that peripheral ERK induced by acupuncture plays a role in initiating brain neural activation and its functional connectivity.

The Hypotensive Role of Acupuncture in Hypertension: Clinical Study and Mechanistic Study

As a component of traditional Chinese medicine (TCM), acupuncture has the potential to lower blood pressure (BP) in patients with hypertension. Emerging evidence indicates that the acupuncture-induced inhibition of high BP occurs through the activation of the pathway in the afferent, central, and efferent pathways. An increasing number of studies have demonstrated that acupuncture not only activates distinct brain regions under conditions of hypertension caused by an imbalance between the sympathetic and parasympathetic systems but also modulates neurotransmitters in related brain regions to alleviate the autonomic response. The activity of these pathways can be assessed by injecting agonists or inhibitors or by performing neurotomy. This review focuses on the clinical and mechanistic studies of acupuncture in modulating BP, which might provide a neurobiological foundation for the effects of acupuncture. Although many mechanisms underlying the effects of acupuncture on cardiovascular function have been identified, further investigation is warranted.

Acupuncture activates a direct pathway from the nucleus tractus solitarii to the rostral ventrolateral medulla

Our previous studies have shown that electroacupuncture (EA) at the Jianshi-Neiguan acupoints (P5-6, overlying the median nerve) attenuates sympathoexcitatory responses through its influence on neuronal activity in the rostral ventrolateral medulla (rVLM). The nucleus tractus solitarii (NTS) receives input from somatic nerve stimulation. Connections between the NTS and the rVLM during EA stimulation have not been investigated and thus were the focus of the present study. Seven to ten days after unilateral microinjection of a rhodamine-conjugated microsphere retrograde tracer (100 nl) into the rVLM, rats were subjected to EA or sham-EA without electrical stimulation. EA was performed for 30 min at the P5-6 acupoints bilaterally. Perikarya containing the microsphere tracer were found in the NTS of both groups. Compared to controls (needle placement without electrical stimulation, n = 7), c-Fos immunoreactivity and neurons double-labeled with c-Fos, an immediate early gene, and the tracer were significantly increased in the NTS of EA-treated rats (all P < 0.05; n = 8), particularly, in the medial and lateral subdivisions of NTS at subpostremal and obex levels. These results suggest that EA at the P5-6 acupoints activates NTS neurons. Furthermore, EA-activated NTS neurons directly project to the rVLM and likely influence the rVLM activity.

Median nerve stimulation induces analgesia via orexin-initiated endocannabinoid disinhibition in the periaqueductal gray

Adequate pain management remains an unmet medical need. We previously revealed an opioid-independent analgesic mechanism mediated by orexin 1 receptor (OX1R)-initiated 2-arachidonoylglycerol (2-AG) signaling in the ventrolateral periaqueductal gray (vlPAG). Here, we found that low-frequency median nerve stimulation (MNS) through acupuncture needles at the PC6 (Neiguan) acupoint (MNS-PC6) induced an antinociceptive effect that engaged this mechanism. In mice, MNS-PC6 reduced acute thermal nociceptive responses and neuropathy-induced mechanical allodynia, increased the number of c-Fos-immunoreactive hypothalamic orexin neurons, and led to higher orexin A and lower GABA levels in the vlPAG. Such responses were not seen in mice with PC6 needle insertion only or electrical stimulation of the lateral deltoid, a nonmedian nerve-innervated location. Directly stimulating the surgically exposed median nerve also increased vlPAG orexin A levels. MNS-PC6-induced antinociception (MNS-PC6-IA) was prevented by proximal block of the median nerve with lidocaine as well as by systemic or intravlPAG injection of an antagonist of OX1Rs or cannabinoid 1 receptors (CB1Rs) but not by opioid receptor antagonists. Systemic blockade of OX1Rs or CB1Rs also restored vlPAG GABA levels after MNS-PC6. A cannabinoid (2-AG)-dependent mechanism was also implicated by the observations that MNS-PC6-IA was prevented by intravlPAG inhibition of 2-AG synthesis and was attenuated in Cnr1 ^-/- mice. These findings suggest that PC6-targeting low-frequency MNS activates hypothalamic orexin neurons, releasing orexins to induce analgesia through a CB1R-dependent cascade mediated by OX1R-initiated 2-AG retrograde disinhibition in the vlPAG. The opioid-independent characteristic of MNS-PC6-induced analgesia may provide a strategy for pain management in opioid-tolerant patients.

Acupuncture with reinforcing and reducing twirling manipulation inhibits hippocampal neuronal apoptosis in spontaneously hypertensive rats

To observe the effects of different acupuncture manipulations on blood pressure and target organ damage in spontaneously hypertensive rats (SHRs), this study used the reinforcing twirling method (1.5–2-mm depth; rotating needle clockwise for 360° and then counter clockwise for 360°, with the thumb moving heavily forward and gently backward, 60 times per minute for 1 minute, and retaining needle for 9 minutes), the reducing twirling method (1.5–2-mm depth; rotating needle counter clockwise for 360° and then clockwise for 360°, with the thumb moving heavily backward and gently forward, 60 times per minute for 1 minute, and retaining needle for 9 minutes), and the needle retaining method (1.5–2-mm depth and retaining the needle for 10 minutes). Bilateral Taichong (LR3) was treated by acupuncture using different manipulations and manual stimulation. Reinforcing twirling, reducing twirling, and needle retaining resulted in a decreased number of apoptotic cells, reduced Bax mRNA and protein expression, and an increased Bcl-2/Bax ratio in the hippocampus compared with the SHR group. Among these groups, the Bcl-2/Bax protein ratio was highest in the reducing twirling group, and the Bcl-2/Bax mRNA ratio was highest in the needle retaining group. These results suggest that reinforcing twirling, reducing twirling, and needle retaining methods all improve blood pressure and prevent target organ damage by increasing the hippocampal Bcl-2/Bax ratio and inhibiting cell apoptosis in the hippocampus in SHR.

What do we understand from clinical and mechanistic studies on acupuncture treatment for hypertension?

The outcome of acupuncture on hypertension treatment is inconclusive. This study aims to evaluate the influence of acupuncture on hypertension, based on findings from mechanistic studies over the course of decades particularly those conducted at the University of California, Irvine. Low-current and low-frequency electroacupuncture (EA) at P5-6 (overlying the median nerve) and S36-37 (overlying the deep peroneal nerve) reduced high blood pressure in a subset of patients (~70 %) with mild-to-moderate hypertension, in a slow-onset (4-8 weeks) but long-lasting (1-2 months) manner. EA inhibited cardiovascular sympathoexcitatory neurons through activation of neurons in the arcuate nucleus of the hypothalamus, the ventrolateral periaqueductal gray in the midbrain and the nucleus raphe pallidus in the medulla, through inhibiting the activity of premotor sympathetic neurons in the rostral ventrolateral medulla (rVLM). Several neurotransmitters such as glutamate, acetylcholine, opioids, GABA, nociceptin, serotonin and endocannabinoids were involved in this EA-induced hypotensive response. The long-lasting inhibition of hypertension induced by EA was related to opioids and GABA in the rVLM, neural circuitry between the arcuate and ventrolateral periaqueductal gray, and prolongation of the increase in preproenkephalin mRNA levels and enkephalin levels in the rVLM and arcuate. Moreover, the long-lasting inhibition of sympathetic activity by EA was confirmed in EA-treated hypertensive patients with decreased levels of norepinephrine, renin and aldosterone.

The effects of beta-endorphin: state change modification

Beta-endorphin (β-END) is an opioid neuropeptide which has an important role in the development of hypotheses concerning the non-synaptic or paracrine communication of brain messages. This kind of communication between neurons has been designated volume transmission (VT) to differentiate it clearly from synaptic communication. VT occurs over short as well as long distances via the extracellular space in the brain, as well as via the cerebrospinal fluid (CSF) flowing through the ventricular spaces inside the brain and the arachnoid space surrounding the central nervous system (CNS). To understand how β-END can have specific behavioral effects, we use the notion behavioral state, inspired by the concept of machine state, coming from Turing (Proc London Math Soc, Series 2,42:230-265, 1937). In section 1.4 the sequential organization of male rat behavior is explained showing that an animal is not free to switch into another state at any given moment. Funneling-constraints restrict the number of possible behavioral transitions in specific phases while at other moments in the sequence the transition to other behavioral states is almost completely open. The effects of β-END on behaviors like food intake and sexual behavior, and the mechanisms involved in reward, meditation and pain control are discussed in detail. The effects on the sequential organization of behavior and on state transitions dominate the description of these effects.

GABA in nucleus tractus solitarius participates in electroacupuncture modulation of cardiopulmonary bradycardia reflex

Phenylbiguanide (PBG) stimulates cardiopulmonary receptors and cardiovascular reflex responses, including decreases in blood pressure and heart rate mediated by the brain stem parasympathetic cardiac neurons in the nucleus ambiguus and nucleus tractus solitarius (NTS). Electroacupuncture (EA) at P5-6 stimulates sensory fibers in the median nerve and modulates these reflex responses. Stimulation of median nerves reverses bradycardia through action of γ-aminobutyric acid (GABA) in the nucleus ambiguus, important in the regulation of heart rate. We do not know whether the NTS or the neurotransmitter mechanisms in this nucleus participate in these modulatory actions by acupuncture. We hypothesized that somatic nerve stimulation during EA (P5-6) modulates cardiopulmonary inhibitory responses through a GABAergic mechanism in the NTS. Anesthetized and ventilated cats were examined during either PBG or direct vagal afferent stimulation while 30 min of EA was applied at P5-6. Reflex heart rate and blood pressure responses and NTS-evoked discharge were recorded. EA reduced the PBG-induced depressor and bradycardia reflexes by 67% and 60%, respectively. Blockade of GABAA receptors in the NTS reversed EA modulation of bradycardia but not the depressor response. During EA, gabazine reversed the vagally evoked discharge activity of cardiovascular NTS neurons. EA modulated the vagal-evoked cardiovascular NTS cellular activity for 60 min. Immunohistochemistry using triple labeling showed GABA immunoreactive fibers juxtaposed to glutamatergic nucleus ambiguus-projecting NTS neurons in rats. These glutamatergic neurons expressed GABAA receptors. These findings suggest that EA inhibits PBG-evoked bradycardia and vagally evoked NTS activity through a GABAergic mechanism, likely involving glutamatergic nucleus ambiguus-projecting NTS neurons.

From peripheral to central: the role of ERK signaling pathway in acupuncture analgesia

Despite accumulating evidence of the clinical effectiveness of acupuncture, its mechanism remains largely unclear. We assume that molecular signaling around the acupuncture needled area is essential for initiating the effect of acupuncture. To determine possible bio-candidates involved in the mechanisms of acupuncture and investigate the role of such bio-candidates in the analgesic effects of acupuncture, we conducted 2 stepwise experiments. First, a genome-wide microarray of the isolated skin layer at the GB34-equivalent acupoint of C57BL/6 mice 1 hour after acupuncture found that a total of 236 genes had changed and that extracellular signal-regulated kinase (ERK) activation was the most prominent bio-candidate. Second, in mouse pain models using formalin and complete Freund adjuvant, we found that acupuncture attenuated the nociceptive behavior and the mechanical allodynia; these effects were blocked when ERK cascade was interrupted by the mitogen-activated protein kinase kinase (MEK)/mitogen-activated protein kinase (MAPK) inhibitor U0126 (.8 μg/μL). Based on these results, we suggest that ERK phosphorylation following acupuncture needling is a biochemical hallmark initiating the effect of acupuncture including analgesia.

PERSPECTIVE

This article presents the novel evidence of the local molecular signaling in acupuncture analgesia by demonstrating that ERK activation in the skin layer contributes to the analgesic effect of acupuncture in a mouse pain model. This work improves our understanding of the scientific basis underlying acupuncture analgesia.

Acupuncture effect and central autonomic regulation

Acupuncture is a therapeutic technique and part of traditional Chinese medicine (TCM). Acupuncture has clinical efficacy on various autonomic nerve-related disorders, such as cardiovascular diseases, epilepsy, anxiety and nervousness, circadian rhythm disorders, polycystic ovary syndrome (PCOS) and subfertility. An increasing number of studies have demonstrated that acupuncture can control autonomic nerve system (ANS) functions including blood pressure, pupil size, skin conductance, skin temperature, muscle sympathetic nerve activities, heart rate and/or pulse rate, and heart rate variability. Emerging evidence indicates that acupuncture treatment not only activates distinct brain regions in different kinds of diseases caused by imbalance between the sympathetic and parasympathetic activities, but also modulates adaptive neurotransmitter in related brain regions to alleviate autonomic response. This review focused on the central mechanism of acupuncture in modulating various autonomic responses, which might provide neurobiological foundations for acupuncture effects.

Acupuncture's Cardiovascular Actions: A Mechanistic Perspective

Over the last several decades, there has been an explosion of articles on acupuncture, including studies that have begun to explore mechanisms underlying its analgesic and cardiovascular actions. Modulation of cardiovascular function is most effective during manual and low-frequency, low-intensity electroacupuncture (EA) at a select set of acupoints situated along meridians located over deep somatic nerves on the upper and lower extremities. Stimulation at these acupoints activates underlying sensory neural pathways that project to a number of regions in the central nervous system (CNS) that ultimately regulate autonomic outflow and hence cardiovascular function. A long-loop pathway involving the hypothalamus, midbrain, and medulla underlies EA modulation of reflex increases in blood pressure (BP). Actions of excitatory and inhibitory neurotransmitters in the supraspinal CNS underlie processing of the somatic input and adjustment of autonomic outflow during EA. Acupuncture also decreases elevated blood pressure through actions in the thoracic spinal cord. Reflexes that lower BP likewise are modulated by EA through its actions on sympathetic and parasympathetic nuclei in the medulla. The autonomic influence of acupuncture is slow in onset but prolonged in duration, typically lasting beyond the period of stimulation. Clinical studies suggest that acupuncture can be used to treat cardiac diseases, such as myocardial ischemia and hypertension, associated with overactivity of the sympathetic nervous system.

Medullary GABAergic mechanisms contribute to electroacupuncture modulation of cardiovascular depressor responses during gastric distention in rats

Electroacupuncture (EA) at P5-P6 acupoints overlying the median nerves typically reduces sympathoexcitatory blood pressure (BP) reflex responses in eucapnic rats. Gastric distention in hypercapnic acidotic rats, by activating both vagal and sympathetic afferents, decreases heart rate (HR) and BP through actions in the rostral ventrolateral medulla (rVLM) and nucleus ambiguus (NAmb), leading to sympathetic withdrawal and parasympathetic activation, respectively. A GABAA mechanism in the rVLM mediates the decreased sympathetic outflow. The present study investigated the hypothesis that EA modulates gastric distention-induced hemodynamic depressor and bradycardia responses through nuclei that process parasympathetic and sympathetic outflow. Anesthetized hypercapnic acidotic rats manifested repeatable decreases in BP and HR with gastric distention every 10 min. Bilateral EA at P5-P6 for 30 min reversed the hypotensive response from -26 ± 3 to -6 ± 1 mmHg and the bradycardia from -35 ± 11 to -10 ± 3 beats/min for a period that lasted more than 70 min. Immunohistochemistry and in situ hybridization to detect c-Fos protein and GAD 67 mRNA expression showed that GABAergic caudal ventral lateral medulla (cVLM) neurons were activated by EA. Glutamatergic antagonism of cVLM neurons with kynurenic acid reversed the actions of EA. Gabazine used to block GABAA receptors microinjected into the rVLM or cVLM reversed EA's action on both the reflex depressor and bradycardia responses. EA modulation of the decreased HR was inhibited by microinjection of gabazine into the NAmb. Thus, EA through GABAA receptor mechanisms in the rVLM, cVLM, and NAmb modulates gastric distention-induced reflex sympathoinhibition and vagal excitation.

Acupuncture regulation of blood pressure: two decades of research

Although mechanisms underlying acupuncture regulation of pain have been studied by a number of laboratories in many countries, much less is known about its ability to modulate cardiovascular function. In the last two decades, our laboratory has systematically investigated the peripheral and central neural mechanisms underlying acupuncture regulation of blood pressure. These observations account for acupuncture's distant actions and, to some extent, its local actions, with respect to the site of needling. Four fundamental findings have advanced our knowledge. First, point-specific effects of acupuncture underlie its cardiovascular actions. Second, variable regions in the supraspinal and spinal central nervous system that receive input from somatic afferent stimulation account for acupuncture's ability to modulate blood pressure. Thus, depending on the underlying situation, for example, high or low blood pressure, acupuncture modifies autonomic outflow by reducing activity in brain stem nuclei that participate in the primary response. Third, repetitive acupuncture through a molecular mechanism can cause prolonged cardiovascular effects that far outlast acupuncture stimulation. Fourth, there is a range of cardiovascular responsiveness to acupuncture that depends, at least in part, on interactions between neural modulators that synaptically regulate autonomic function in the brain stem. Thus, acupuncture has the capability of profoundly regulating cardiovascular function in patients with disease, for example, hypertension, and the experimental laboratory is directing best approaches to study its actions in humans.

Electroacupuncture frequency-related transcriptional response in rat arcuate nucleus revealed region-distinctive changes in response to low- and high-frequency electroacupuncture

Electroacupuncture (EA) has been clinically applied for treating different medical conditions, such as pain, strain, and immune diseases. Low- and high-frequency EAs have distinct therapeutic effects in clinical practice and experimental studies. However, the molecular mechanism of this difference remains obscure. The arcuate nucleus (Arc) is a critical region of the hypothalamus and is responsible for the effect of EA stimulation to remote acupoints. Gene expression profiling provides a powerful tool with which to explore the basis of physiopathological responses to external stimulus. In this study, using cDNA microarray, we investigated gene expressions in the rat Arc region induced by low-frequency (2-Hz) and high-frequency (100-Hz) EAs to two remote acupoints, zusanli (ST36) and sanyinjiao (SP6). We have found that more genes were differentially regulated by 2-Hz EA than 100-Hz EA (154 vs. 66 regulated genes/ESTs) in Arc, especially those related to neurogenesis, which was confirmed by qRT-PCR. These results demonstrate that the expression level of genes in the Arc region could be effectively regulated by low-frequency EA, compared with high-frequency EA, helping to uncover the mechanisms of the therapeutic effects of the low-frequency EA. Our results also indicate different-frequency EAs are spatially specific.

Cardioprotection of electroacupuncture against myocardial ischemia-reperfusion injury by modulation of cardiac norepinephrine release

Augmentation of cardiac sympathetic tone during myocardial ischemia has been shown to increase myocardial O(2) demand and infarct size as well as induce arrhythmias. We have previously demonstrated that electroacupuncture (EA) inhibits the visceral sympathoexcitatory cardiovascular reflex. The purpose of this study was to determine the effects of EA on left ventricular (LV) function, O(2) demand, infarct size, arrhythmogenesis, and in vivo cardiac norepinephrine (NE) release in a myocardial ischemia-reperfusion model. Anesthetized rabbits (n = 36) underwent 30 min of left anterior descending coronary artery occlusion followed by 90 min of reperfusion. We evaluated myocardial O(2) demand, infarct size, ventricular arrhythmias, and myocardial NE release using microdialysis under the following experimental conditions: 1) untreated, 2) EA at P5-6 acupoints, 3) sham acupuncture, 4) EA with pretreatment with naloxone (a nonselective opioid receptor antagonist), 5) EA with pretreatment with chelerythrine (a nonselective PKC inhibitor), and 6) EA with pretreatment with both naloxone and chelerythrine. Compared with the untreated and sham acupuncture groups, EA resulted in decreased O(2) demand, myocardial NE concentration, and infarct size. Furthermore, the degree of ST segment elevation and severity of LV dysfunction and ventricular arrhythmias were all significantly decreased (P < 0.05). The cardioprotective effects of EA were partially blocked by pretreatment with naloxone or chelerythrine alone and completely blocked by pretreatment with both naloxone and chelerythrine. These results suggest that the cardioprotective effects of EA against myocardial ischemia-reperfusion are mediated through inhibition of the cardiac sympathetic nervous system as well as opioid and PKC-dependent pathways.

Control and physiological determinants of sympathetically mediated brown adipose tissue thermogenesis

Brown adipose tissue (BAT) represents a remarkable heat-producing tissue. The thermogenic potential of BAT is conferred by uncoupling protein 1, a protein found uniquely in brown adipocytes. BAT activity and capacity is controlled by the sympathetic nervous system (SNS), which densely innervates brown fat depots. SNS-mediated BAT thermogenesis is essentially governed by hypothalamic and brainstem neurons. BAT activity is also modulated by brain energy balance pathways including the very significant brain melanocortin system, suggesting a genuine involvement of SNS-mediated BAT thermogenesis in energy homeostasis. The use of positron emission tomography/computed tomography scanning has revealed the presence of well-defined BAT depots in the cervical, clavicular, and paraspinal areas in adult humans. The prevalence of these depots is higher in subjects exposed to low temperature and is also higher in women compared to men. Moreover, the prevalence of BAT decreases with age and body fat mass, suggesting that BAT could be involved in energy balance regulation and obesity in humans. This short review summarizes recent progress made in our understanding of the control of SNS-mediated BAT thermogenesis and of the determinants of BAT prevalence or detection in humans.