Adiponectin selectively inhibits oxytocin neurons of the paraventricular nucleus of the hypothalamus

Interplay between the brain and adipose tissue: a metabolic conversation

The central nervous system and adipose tissue interact through complex communication. This bidirectional signaling regulates metabolic functions. The hypothalamus, a key homeostatic brain region, integrates exteroceptive and interoceptive signals to control appetite, energy expenditure, glucose, and lipid metabolism. This regulation is partly achieved via the nervous modulation of white (WAT) and brown (BAT) adipose tissue. In this review, we highlight the roles of sympathetic and parasympathetic innervation in regulating WAT and BAT activities, such as lipolysis and thermogenesis. Adipose tissue, in turn, plays a dual role as an energy reservoir and an endocrine organ, secreting hormones that influence brain function and metabolic health. In addition, this review focuses on recently uncovered communication pathways, including extracellular vesicles and neuro-mesenchymal units, which add new layers of regulation and complexity to the brain-adipose tissue interaction. Finally, we also examine the consequences of disrupted communication between the brain and adipose tissue in metabolic disorders like obesity and type-2 diabetes, emphasizing the potential for new therapeutic strategies targeting these pathways to improve metabolic health.

Increased GABAergic projections in the paraventricular nucleus regulate colonic hypersensitivity via oxytocin in a rat model of irritable bowel syndrome

Irritable bowel syndrome (IBS) is characterized by gastrointestinal dysmotility and visceral hyperalgesia, and the impaired brain-gut axis is accepted as a crucial cause for the onset of IBS. The objective of this study is to investigate the effects of the adaptive changes in the central neural system induced by stress on IBS-like syndromes in rats. Long-term water avoidance stress (WAS) was used to prepare IBS animals. The changes in neuronal excitation and GABA expression were shown by immunohistochemistry. The mRNA and protein expressions of neurotransmitters were detected with Quantitative reverse-transcription PCR (qRT-PCR) and Enzyme-linked immunosorbent assay (ELISA). The intestinal transit time, fecal moisture content, and abdominal withdrawal reflex scores of rats were recorded to monitor intestinal motility and visceral hyperalgesia. In the WAS-treated rats with enhanced intestinal motility and visceral hypersensitivity, more GABAergic projections were found in the paraventricular nucleus (PVN) of the hypothalamus, which inhibited the firing rate of neurons and decreased the expression of oxytocin. Exogenous oxytocin improved gut motility and decreased AWR scores. The inhibition of oxytocin by the adaptive GABAergic projection in the PVN might be an important mediator of IBS, which indicates a potential novel therapeutic target.

Leptin and adiponectin regulate the activity of nuclei involved in sleep-wake cycle in male rats

Epidemiological and experimental evidence recognize a relationship between sleep-wake cycles and adiposity levels, but the mechanisms that link both are not entirely understood. Adipose tissue secretes adiponectin and leptin hormones, mainly involved as indicators of adiposity levels and recently associated to sleep. To understand how two of the main adipose tissue hormones could influence sleep-wake regulation, we evaluated in male rats, the effect of direct administration of adiponectin or leptin in the ventrolateral preoptic nuclei (VLPO), a major area for sleep promotion. The presence of adiponectin (AdipoR1 and AdipoR2) and leptin receptors in VLPO were confirmed by immunohistochemistry. Adiponectin administration increased wakefulness during the rest phase, reduced delta power, and activated wake-promoting neurons, such as the locus coeruleus (LC), tuberomammillary nucleus (TMN) and hypocretin/orexin neurons (OX) within the lateral hypothalamus (LH) and perifornical area (PeF). Conversely, leptin promoted REM and NREM sleep, including increase of delta power during NREM sleep, and induced c-Fos expression in VLPO and melanin concentrating hormone expressing neurons (MCH). In addition, a reduction in wake-promoting neurons activity was found in the TMN, lateral hypothalamus (LH) and perifornical area (PeF), including in the OX neurons. Moreover, leptin administration reduced tyrosine hydroxylase (TH) immunoreactivity in the LC. Our data suggest that adiponectin and leptin act as hormonal mediators between the status of body energy and the regulation of the sleep-wake cycle.

Exploring the New Horizon of AdipoQ in Obesity-Related Alzheimer's Dementia

Alzheimer's disease (AD) is the most common form of dementia, which causes abnormalities in learning, thinking, memory, as well as behavior. Generally, symptoms of AD develop gradually and aggravate over time, and consequently severely interfere with daily activities. Furthermore, obesity is one of the common risk factors for dementia. Dysregulation of adipokine and adipocyte dysfunction are assumed to be accountable for the high risk of obesity in people that develop many related disorders such as AD. Moreover, it has been observed that the dysfunction of adipose is connected with changes in brain metabolism, brain atrophy, cognitive decline, impaired mood, neuroinflammation, impaired insulin signaling, and neuronal dysfunction in people with obesity. Conversely, the pathological mechanisms, as well as the molecular players which are involved in this association, have been unclear until now. In this article, we discuss the impact of adiponectin (AdipoQ) on obesity-related Alzheimer's dementia.

The Novel Perspectives of Adipokines on Brain Health

First seen as a fat-storage tissue, the adipose tissue is considered as a critical player in the endocrine system. Precisely, adipose tissue can produce an array of bioactive factors, including cytokines, lipids, and extracellular vesicles, which target various systemic organ systems to regulate metabolism, homeostasis, and immune response. The global effects of adipokines on metabolic events are well defined, but their impacts on brain function and pathology remain poorly defined. Receptors of adipokines are widely expressed in the brain. Mounting evidence has shown that leptin and adiponectin can cross the blood–brain barrier, while evidence for newly identified adipokines is limited. Significantly, adipocyte secretion is liable to nutritional and metabolic states, where defective circuitry, impaired neuroplasticity, and elevated neuroinflammation are symptomatic. Essentially, neurotrophic and anti-inflammatory properties of adipokines underlie their neuroprotective roles in neurodegenerative diseases. Besides, adipocyte-secreted lipids in the bloodstream can act endocrine on the distant organs. In this article, we have reviewed five adipokines (leptin, adiponectin, chemerin, apelin, visfatin) and two lipokines (palmitoleic acid and lysophosphatidic acid) on their roles involving in eating behavior, neurotrophic and neuroprotective factors in the brain. Understanding and regulating these adipokines can lead to novel therapeutic strategies to counteract metabolic associated eating disorders and neurodegenerative diseases, thus promote brain health.

The Role of Leptin and Adiponectin in Obesity-Associated Cognitive Decline and Alzheimer's Disease

Cross-talk between adipose tissue and central nervous system (CNS) underlies the increased risk of obese people to develop brain diseases such as cognitive and mood disorders. Detailed mechanisms for how peripheral changes caused by adipose tissue accumulation in obesity impact the CNS to cause brain dysfunction are poorly understood. Adipokines are a large group of substances secreted by the white adipose tissue to regulate a wide range of homeostatic processes including, but not limited to, energy metabolism and immunity. Obesity is characterized by a generalized change in the levels of circulating adipokines due to abnormal accumulation and dysfunction of adipose tissue. Altered adipokine levels underlie complications of obesity as well as the increased risk for the development of obesity-related comorbidities such as type 2 diabetes, cardiovascular and neurodegenerative diseases. Here, we review the literature for the role of adipokines as key mediators of the communication between periphery and CNS in health and disease. We will focus on the actions of leptin and adiponectin, two of the most abundant and well studied adipokines, in the brain, with particular emphasis on how altered signaling of these adipokines in obesity may lead to cognitive dysfunction and augmented risk for Alzheimer's disease. A better understanding of adipokine biology in brain disorders may prove of major relevance to diagnostic, prevention and therapy.

[Adiponectin: an endogenous molecule with anti-inflammatory and antidepressant properties?]

Adiponectin (ApN) is a hormone produced by adipose tissue, yet the plasma level of ApN is decreased in overweight and obese people, as well as in people with diabetes. In the periphery, this decrease in circulating levels of ApN induces the establishment of a chronic low-grade inflammatory state and is involved in the development of insulin resistance and atheromas. Conversely, "favorable" living conditions, weight loss and regular physical exercise increase ApN blood concentration. Some forms of ApN can reach the brain parenchyma through the cerebrospinal fluid. In the brain, the increase in ApN exerts powerful antidepressant and anxiolytic effects, in particular by fighting against neuroinflammation.

Adiponectin at physiological level glucose-independently enhances inhibitory postsynaptic current onto NPY neurons in the hypothalamic arcuate nucleus

Adiponectin regulates glucose and lipid metabolism, acting against atherosclerosis and metabolic syndrome. Accumulating evidences suggest that adiponectin acts on the brain including the arcuate nucleus of hypothalamus (ARC). The ARC contains orexigenic neuropeptide Y (NPY)/agouti related peptide (AgRP) neurons and anorexigenic proopiomelanocortin (POMC) neurons, the first order neurons for feeding regulation. We recently reported that intracerebroventricular injection of adiponectin at low glucose level suppressed food intake, while at elevated glucose level it promoted food intake, exhibiting glucose-dependent reciprocal effects. As an underlying neuronal mechanism, physiological level of adiponectin at low glucose activated ARC POMC neurons and at high glucose inactivated them. Now, whether physiological level of adiponectin also affects NPY/AgRP neurons is essential for fully understanding the adiponectin action, but it remains to be clarified. We here report that a physiological dose of adiponectin, in both high and low glucose conditions, attenuated action potential firing without altering resting membrane potential in ARC NPY neurons. This adiponectin effect was abolished by GABA_A receptor blockade. Adiponectin enhanced amplitude but not frequency of inhibitory postsynaptic current (IPSC) onto NPY neurons. These results demonstrate that adiponectin enhances IPSC onto NPY neurons to attenuate action potential firing in NPY neurons in a glucose-independent manner, being contrasted to its glucose-dependent effect on POMC neurons.

Sex-specific differences in cardiovascular and metabolic hormones with integrated signalling in the paraventricular nucleus of the hypothalamus

NEW FINDINGS

What is the topic of this review? We describe roles of crucial signalling molecules in the paraventricular nucleus of the hypothalamus and highlight recent data suggesting sex-specific changes in the expression of crucial signalling molecules and their receptors, which may underlie sex differences in both cardiovascular and metabolic function. What advances does it highlight? This review highlights the integrative capacity of the paraventricular nucleus in mediating cardiovascular and metabolic effects by integrating information from multiple signalling molecules. It also proposes that these signalling molecules have sex-specific differential gene expression, indicating the importance of considering these differences in our ongoing search to understand the female-male differences in the regulation of crucial autonomic systems. Many traditional cardiovascular hormones have been implicated in metabolic function. Conversely, many hormones traditionally involved in metabolic regulation have an effect on cardiovascular function. Many of these signalling molecules exert such effects through specific actions in the paraventricular nucleus, an integrative autonomic control centre located in the hypothalamus. Here, we focus on four cardiovascular/metabolic peptide hormones that signal within the paraventricular nucleus, namely angiotensin II, orexin, adiponectin and nesfatin-1. Each of these hormones has specific electrophysiological effects on paraventricular nucleus neurons that can be related to its physiological actions. In addition, we introduce preliminary transcriptomic data indicating that the genes for some of these hormones and their receptors have sex-specific differential expression.

Adropin acts in the rat paraventricular nucleus to influence neuronal excitability

Adropin is a peptide hormone with cardiovascular and metabolic roles in the periphery, including effects on glucose and lipid homeostasis. Central administration of adropin has been shown to inhibit water intake in rats; however, the site at which central adropin acts has yet to be elucidated. The hypothalamic paraventricular nucleus (PVN), a critical autonomic control center, plays essential roles in the control of fluid balance, energy homeostasis, and cardiovascular regulation, and is, therefore, a potential target for centrally acting adropin. In the present study, we used whole cell patch-clamp techniques to examine the effects of adropin on the excitability of neurons within the PVN. All three neuronal subpopulations (magnocellular, preautonomic, and neuroendocrine) in the PVN were found to be responsive to bath-application of 10 nM adropin, which elicited responses in 68% of cells tested (n = 57/84). The majority of cells (58%) depolarized (5.2 ± 0.3 mV; n = 49) in response to adropin, whereas the remaining responsive cells (10%) hyperpolarized (-3.4 ± 0.5 mV; n = 8), effects that were shown to be concentration-dependent. Additionally, responses were maintained in the presence of 1 μM TTX in 75% of cells tested (n = 9/12), and voltage-clamp analysis revealed that adropin had no effect on the amplitude or frequency of excitatory or inhibitory postsynaptic currents (EPSCs and IPSCs) in PVN neurons, suggesting the peptide exerts direct, postsynaptic actions on these neurons. Collectively, these findings suggest central adropin may exert its physiological effects through direct actions on neurons in the PVN.

Adiponectin potentiates the acute effects of leptin in arcuate Pomc neurons

Objective

Adiponectin receptors (AdipoRs) are located on neurons of the hypothalamus involved in metabolic regulation – including arcuate proopiomelanocortin (Pomc) and Neuropeptide Y/Agouti-related peptide (NPY/AgRP) neurons. AdipoRs play a critical role in regulating glucose and fatty acid metabolism by initiating several signaling cascades overlapping with Leptin receptors (LepRs). However, the mechanism by which adiponectin regulates cellular activity in the brain remains undefined.

Methods

In order to resolve this issue, we utilized neuron-specific transgenic mouse models to identify Pomc and NPY/AgRP neurons which express LepRs for patch-clamp electrophysiology experiments.

Results

We found that leptin and adiponectin synergistically activated melanocortin neurons in the arcuate nucleus. Conversely, NPY/AgRP neurons were inhibited in response to adiponectin. The adiponectin-induced depolarization of arcuate Pomc neurons occurred via activation of Phosphoinositide-3-kinase (PI3K) signaling, independent of 5′ AMP-activated protein kinase (AMPK) activity. Adiponectin also activated melanocortin neurons at various physiological glucose levels.

Conclusions

Our results demonstrate a requirement for PI3K signaling in the acute adiponectin-induced effects on the cellular activity of arcuate melanocortin neurons. Moreover, these data provide evidence for PI3K as a substrate for both leptin and adiponectin to regulate energy balance and glucose metabolism via melanocortin activity.

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Adiponectin activates arcuate Pomc neurons.

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Adiponectin-induced activation of Pomc neurons requires PI3K (independent of AMPK).

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Adiponectin inhibits adjacent NPY/AgRP neurons (disinhibiting arcuate Pomc neurons).

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Leptin potentiates the effects of adiponectin arcuate Pomc neurons.

Glucose level determines excitatory or inhibitory effects of adiponectin on arcuate POMC neuron activity and feeding

Adiponectin regulates glucose and lipid metabolism, acting against metabolic syndrome and atherosclerosis. Accumulating evidence suggest that adiponectin acts on the brain including hypothalamic arcuate nucleus (ARC), where proopiomelanocortin (POMC) neurons play key roles in feeding regulation. Several studies have examined intracerebroventricular (ICV) injection of adiponectin and reported opposite effects, increase or decrease of food intake. These reports used different nutritional states. The present study aimed to clarify whether adiponectin exerts distinct effects on food intake and ARC POMC neurons depending on the glucose concentration. Adiponectin was ICV injected with or without glucose for feeding experiments and administered to ARC slices with high or low glucose for patch clamp experiments. We found that adiponectin at high glucose inhibited POMC neurons and increased food intake while at low glucose it exerted opposite effects. The results demonstrate that glucose level determines excitatory or inhibitory effects of adiponectin on arcuate POMC neuron activity and feeding.

Serum and CSF adiponectin, leptin, and interleukin 6 levels as adipocytokines in Egyptian children with febrile seizures: a cross-sectional study

Background

A febrile seizure (FS) is the most common convulsive disorder in children. Activation of cytokine network is involved in FS pathogenesis. Adiponectin, leptin and IL-6 are the major adipocytokines secreted by fat cells. To date, only a few studies concerned the association of adipocytokines with febrile seizures. In this study, we tried to investigate serum and CSF levels of adiponectin, leptin, and interleukin-6 (IL-6); as adipocytokines, for the first time in Egyptian children with febrile seizures.

Methods

This was a prospective cross-sectional study included one hundred patients with febrile seizure, and matched with age, gender, 100 children with febrile illness without seizures (febrile control, FC) and 100 healthy control group (HC). Serum and cerebrospinal fluid (CSF) levels of adiponectin, leptin, and (IL-6) were measured by enzyme-linked immunosorbent assay (ELISA) method.

Results

Serum adiponectin was significantly higher in children with FS (16.8 ± 3.7 ug/ml) and the FC group (18.3 ± 4.3 ug/ml) compared to the HC group (9.5 ± 2.2 ug/ml); P < 0.05, respectively. Serum leptin was significantly lower in children with FS (0.9 ± 0.3 ng/ml) compared to both the FC group (4.7 ± 1.2 ng/ml) and the HC group (1.8 ± 0.4 ng/ml); P < 0.01, respectively. Children with FS had significantly higher serum IL-6 levels (43.7 ± 11.7 ng/ml) than the FC group (21.9 ± 4.5 ng/ml) and the HC group (6.5 ± 1.8 ng/ml); P < 0.01, respectively. Patients with simple febrile seizures (SFS) had serum and CSF adiponectin levels similar to those with complex febrile seizures (CFS); (P > 0.05). Serum and CSF leptin levels were significantly lower in patients with CFS compared to the SFS group (P < 0.05). Serum and CSF IL-6 levels were significantly higher in patients with CFS compared to the SFS group (P < 0.01). On multivariate logistic regression analysis, the high serum IL-6 levels was the most significant risk factor associated with febrile seizures among studied children (OR: 6.2; 95 % CI: 3.58 –10.57; P = 0.0001).

Conclusion

Our data brought a novel observation that some adipocytokines like leptin and IL-6 could be, at least in part, an aetiopathogenetic factor in the manifestation of febrile seizures in susceptible Egyptian children. Moreover, we observed a significant association between high CSF IL-6 levels and susceptibility to complex febrile seizures as did the low CSF leptin levels.

Secret talk between adipose tissue and central nervous system via secreted factors-an emerging frontier in the neurodegenerative research

First seen as a storage organ, the white adipose tissue (WAT) is now considered as an endocrine organ. WAT can produce an array of bioactive factors known as adipokines acting at physiological level and playing a vital role in energy metabolism as well as in immune response. The global effect of adipokines in metabolic activities is well established, but their impact on the physiology and the pathophysiology of the central nervous system (CNS) remains poorly defined. Adipokines are not only produced by the WAT but can also be expressed in the CNS where receptors for these factors are present. When produced in periphery and to affect the CNS, these factors may either cross the blood brain barrier (BBB) or modify the BBB physiology by acting on cells forming the BBB. Adipokines could regulate neuroinflammation and oxidative stress which are two major physiological processes involved in neurodegeneration and are associated with many chronic neurodegenerative diseases. In this review, we focus on four important adipokines (leptin, resistin, adiponectin, and TNFα) and one lipokine (lysophosphatidic acid-LPA) associated with autotaxin, its producing enzyme. Their potential effects on neurodegeneration and brain repair (neurogenesis) will be discussed. Understanding and regulating these adipokines could be an interesting lead to novel therapeutic strategy in order to counteract neurodegenerative disorders and/or promote brain repair.

Physiological roles for the subfornical organ: a dynamic transcriptome shaped by autonomic state

The subfornical organ (SFO) is a circumventricular organ recognized for its ability to sense and integrate hydromineral and hormonal circulating fluid balance signals, information which is transmitted to central autonomic nuclei to which SFO neurons project. While the role of SFO was once synonymous with physiological responses to osmotic, volumetric and cardiovascular challenge, recent data suggest that SFO neurons also sense and integrate information from circulating signals of metabolic status. Using microarrays, we have confirmed the expression of receptors already described in the SFO, and identified many novel transcripts expressed in this circumventricular organ including receptors for many of the critical circulating energy balance signals such as adiponectin, apelin, endocannabinoids, leptin, insulin and peptide YY. This transcriptome analysis also identified SFO transcripts, the expressions of which are significantly changed by either 72 h dehydration, or 48 h starvation, compared to fed and euhydrated controls. Expression and potential roles for many of these targets are yet to be confirmed and elucidated. Subsequent validation of data for adiponectin and leptin receptors confirmed that receptors for both are expressed in the SFO, that discrete populations of neurons in this tissue are functionally responsive to these adipokines, and that such responsiveness is regulated by physiological state. Thus, transcriptomic analysis offers great promise for understanding the integrative complexity of these physiological systems, especially with development of technologies allowing description of the entire transcriptome of single, carefully phenotyped, SFO neurons. These data will ultimately elucidate mechanisms through which these uniquely positioned neurons respond to and integrate complex circulating signals.

Adiponectin-Mediated Analgesia and Anti-Inflammatory Effects in Rat

The adipose tissue-derived protein, adiponectin, has significant anti-inflammatory properties in a variety of disease conditions. Recent evidence that adiponectin and its receptors (AdipoR1 and AdipoR2) are expressed in central nervous system, suggests that it may also have a central modulatory role in pain and inflammation. This study set out to investigate the effects of exogenously applied recombinant adiponectin (via intrathecal and intraplantar routes; 10–5000 ng) on the development of peripheral inflammation (paw oedema) and pain hypersensitivity in the rat carrageenan model of inflammation. Expression of adiponectin, AdipoR1 and AdipoR2 mRNA and protein was characterised in dorsal spinal cord using real-time polymerase chain reaction (PCR) and Western blotting. AdipoR1 and AdipoR2 mRNA and protein were found to be constitutively expressed in dorsal spinal cord, but no change in mRNA expression levels was detected in response to carrageenan-induced inflammation. Adiponectin mRNA, but not protein, was detected in dorsal spinal cord, although levels were very low. Intrathecal administration of adiponectin, both pre- and 3 hours post-carrageenan, significantly attenuated thermal hyperalgesia and mechanical hypersensitivity. Intrathecal administration of adiponectin post-carrageenan also reduced peripheral inflammation. Intraplantar administration of adiponectin pre-carrageenan dose-dependently reduced thermal hyperalgesia but had no effect on mechanical hypersensitivity and peripheral inflammation. These results show that adiponectin functions both peripherally and centrally at the spinal cord level, likely through activation of AdipoRs to modulate pain and peripheral inflammation. These data suggest that adiponectin receptors may be a novel therapeutic target for pain modulation.

PKA-mediated phosphorylation of Dexras1 suppresses iron trafficking by inhibiting S-nitrosylation

Dexras1 is a small GTPase and plays a central role in neuronal iron trafficking. We have shown that stimulation of glutamate receptors activates neuronal nitric oxide synthase, leading to S-nitrosylation of Dexras1 and a physiological increase in iron uptake. Here we report that Dexras1 is phosphorylated by protein kinase A (PKA) on serine 253, leading to a suppression of iron influx. These effects were directly associated with the levels of S-nitrosylated Dexras1, whereby PKA activation reduced Dexras1 S-nitrosylation in a dose dependent manner. Moreover, we found that adiponectin modulates Dexras1 via PKA. Hence these findings suggest the involvement of the PKA pathway in modulating glutamate-mediated ROS in neurons, and hint to a functional crosstalk between S-nitrosylation and phosphorylation.

Molecular cloning and expression analysis of adiponectin and its receptors (AdipoR1 and AdipoR2) in the hypothalamus of the Huoyan goose during different stages of the egg-laying cycle

BACKGROUND

Adiponectin and its receptors (AdipoR1 and AdipoR2) are novel endocrine systems that act at various levels to regulate metabolic homeostasis and reproductive processes. We cloned and characterized the cDNA of adiponectin and its receptors from the hypothalamus of the Huoyan goose to reveal the influence of these factors on the process of goose egg-laying. We also determined the mRNA and protein expression profiles during different stages of the egg-laying cycle.

METHODS

Hypothalamus tissues were obtained from 36 Huoyan geese in the pre-laying, early-laying, peak-laying, and ceased periods. The cDNA sequences of goose adiponectin and its receptors (AdipoR1 and AdipoR2) were cloned and characterized using the 5'-RACE and 3'-RACE methods. Multiple alignments and phylogenetic analyses of the deduced amino acid sequence were conducted using bioinformatics tools. The expression profiles of mRNA and protein in the hypothalamus during the pre-laying, early-laying, peak-laying and ceased periods were examined using real-time PCR (qRT-PCR) and Western blotting techniques.

RESULTS

The cDNA of adiponectin, AdipoR1 and AdipoR2 consisted of 738, 1131 and 1161 bp open reading frame encoding 245, 376 and 386 amino acids, respectively. The deduced amino acid sequence of goose adiponectin, as well as AdipoR1 and AdipoR2 showed a closer genetic relationship to the avian species than to other mammal species. The expression level of adiponectin mRNA and protein increased from the pre-laying period to the peak-laying period, reached its peak in the peak-laying period, and then decreased during the ceased period. Conversely, the expression levels of AdipoR1 and AdipoR2 mRNA and protein decreased in the early-laying period, peak-laying period, and ceased period compared with the pre-laying period.

CONCLUSIONS

This study is the first to obtain full-length cDNA sequences of goose adiponectin and the genes of its receptors from the hypothalamus, and demonstrate that the egg-laying cycle affects the expression of the goose adiponectin system. Our results suggest the potential role of adiponectin as a key neuromodulator of reproductive functions.

In vitro differentiation between oxytocin- and vasopressin-secreting magnocellular neurons requires more than one experimental criterion

The phenotypic differentiation between oxytocin (OT)- and vasopressin (VP)-secreting magnocellular neurosecretory cells (MNCs) from the supraoptic nucleus is relevant to understanding how several physiological and pharmacological challenges affect their electrical activity. Although the firing patterns of OT and VP neurons, both in vivo and in vitro, may appear different from each other, much is assumed about their characteristics. These assumptions make it practically impossible to obtain a confident phenotypic differentiation based exclusively on the firing patterns. The presence of a sustained outward rectifying potassium current (SOR) and/or an inward rectifying hyperpolarization-activated current (IR), which are presumably present in OT neurons and absent in VP neurons, has been used to distinguish between the two types of MNCs in the past. In this study, we aimed to analyze the accuracy of the phenotypic discrimination of MNCs based on the presence of rectifying currents using comparisons with the molecular phenotype of the cells, as determined by single-cell RT-qPCR and immunohistochemistry. Our results demonstrated that the phenotypes classified according to the electrophysiological protocol in brain slices do not match their molecular counterparts because vasopressinergic and intermediate neurons also exhibit both outward and inward rectifying currents. In addition, we also show that MNCs can change the relative proportion of each cell phenotype when the system is challenged by chronic hypertonicity (70% water restriction for 7 days). We conclude that for in vitro preparations, the combination of mRNA detection and immunohistochemistry seems to be preferable when trying to characterize a single MNC phenotype.

Metabolic influences on reproduction: adiponectin attenuates GnRH neuronal activity in female mice

Metabolic dysfunctions are often linked to reproductive abnormalities. Adiponectin (ADP), a peripheral hormone secreted by white adipose tissue, is important in energy homeostasis and appetite regulation. GnRH neurons are integral components of the reproductive axis, controlling synthesis, and release of gonadotropins. This report examined whether ADP can directly act on GnRH neurons. Double-label immunofluorescence on brain sections from adult female revealed that a subpopulation of GnRH neurons express ADP receptor (AdipoR)2. GnRH/AdipoR2+ cells were distributed throughout the forebrain. To determine the influence of ADP on GnRH neuronal activity and the signal transduction pathway of AdipoR2, GnRH neurons maintained in explants were assayed using whole-cell patch clamping and calcium imaging. This mouse model system circumvents the dispersed distribution of GnRH neurons within the forebrain, making analysis of large numbers of GnRH cells possible. Single-cell PCR analysis and immunocytochemistry confirmed the presence of AdipoR2 in GnRH neurons in explants. Functional analysis revealed 20% of the total GnRH population responded to ADP, exhibiting hyperpolarization or decreased calcium oscillations. Perturbation studies revealed that ADP activates AMP kinase via the protein kinase Cζ/liver kinase B1 pathway. The modulation of GnRH neuronal activity by ADP demonstrated in this report directly links energy balance to neurons controlling reproduction.

Adiponectin enhances the responsiveness of the olfactory system

The peptide hormone adiponectin is secreted by adipose tissue and the circulating concentration is reversely correlated with body fat mass; it is considered as starvation signal. The observation that mature sensory neurons of the main olfactory epithelium express the adiponectin receptor 1 has led to the concept that adiponectin may affect the responsiveness of the olfactory system. In fact, electroolfactogram recordings from olfactory epithelium incubated with exogenous adiponectin resulted in large amplitudes upon odor stimulation. To determine whether the responsiveness of the olfactory sensory neurons was enhanced, we have monitored the odorant-induced expression of the immediate early gene Egr1. It was found that in an olfactory epithelium incubated with nasally applied adiponectin the number of Egr1 positive cells was significantly higher compared to controls, suggesting that adiponectin rendered the olfactory neurons more responsive to an odorant stimulus. To analyze whether the augmented responsiveness of sensory neurons was strong enough to elicit a higher neuronal activity in the olfactory bulb, the number of activated periglomerular cells of a distinct glomerulus was determined by monitoring the stimulus-induced expression of c-fos. The studies were performed using the transgenic mOR256-17-IRES-tauGFP mice which allowed to visualize the corresponding glomerulus and to stimulate with a known ligand. The data indicate that upon exposure to 2,3-hexanedione in adiponectin-treated mice the number of activated periglomerular neurons was significantly increased compared to controls. The results of this study indicate that adiponectin increases the responsiveness of the olfactory system, probably due to a higher responsiveness of olfactory sensory neurons.

Nonsocial functions of hypothalamic oxytocin

Oxytocin (OXT) is a hypothalamic neuropeptide composed of nine amino acids. The functions of OXT cover a variety of social and nonsocial activity/behaviors. Therapeutic effects of OXT on aberrant social behaviors are attracting more attention, such as social memory, attachment, sexual behavior, maternal behavior, aggression, pair bonding, and trust. The nonsocial behaviors/functions of brain OXT have also received renewed attention, which covers brain development, reproduction, sex, endocrine, immune regulation, learning and memory, pain perception, energy balance, and almost all the functions of peripheral organ systems. Coordinating with brain OXT, locally produced OXT also involves the central and peripheral actions of OXT. Disorders in OXT secretion and functions can cause a series of aberrant social behaviors, such as depression, autism, and schizophrenia as well as disturbance of nonsocial behaviors/functions, such as anorexia, obesity, lactation failure, osteoporosis, diabetes, and carcinogenesis. As more and more OXT functions are identified, it is essential to provide a general view of OXT functions in order to explore the therapeutic potentials of OXT. In this review, we will focus on roles of hypothalamic OXT on central and peripheral nonsocial functions.

Expression of adiponectin receptors 1 (AdipoR1) and 2 (AdipoR2) in the porcine pituitary during the oestrous cycle

BACKGROUND

Adiponectin, protein secreted mainly by white adipose tissue, is an important factor linking the regulation of metabolic homeostasis and reproductive processes. The biological activity of the hormone is mediated via two distinct receptors, termed adiponectin receptor 1(AdipoR1) and adiponectin receptor 2 (AdipoR2). The present study analyzed mRNA and protein expression of AdipoR1 and AdipoR2 in the anterior (AP) and posterior (NP) pituitary of cyclic pigs.

METHODS

The total of 20 animals was assigned to one of four experimental groups (n=5 per group) as follows: days 2-3 (early-luteal phase), 10-12 (mid-luteal phase), 14-16 (late-luteal phase), 17-19 (follicular phase) of the oestrous cycle. mRNA and protein expression were analyzed using real-time PCR and Western Blot methods, respectively.

RESULTS

The lowest AdipoR1 gene expression was detected in AP on days 10-12 relative to days 2-3 and 14-16 (p<0.05). In NP, AdipoR1 mRNA levels were elevated on days 10-12 and 14-16 (p<0.05). AdipoR2 gene expression in AP was the lowest on days 10-12, and an expression peak occurred on days 2-3 (p<0.05). In NP, the lowest (p<0.05) expression of AdipoR2 mRNA was noted on days 17-19. The AdipoR1 protein content in AP was the lowest on days 17-19 (p<0.05), while in NP the variations in protein expression levels during the oestrous cycle were negligible. AdipoR2 protein in AP was most abundant on days 10-12, and it reached the lowest level on days 2-3 and 17-19 of the cycle (p<0.05). The presence of AdipoR2 protein in NP was more pronounced on days 10-12 (p<0.05).

CONCLUSIONS

Our study was the first experiment to demonstrate that AdipoR1 and AdipoR2 mRNAs and proteins are present in the porcine pituitary and that adiponectin receptors expression is dependent on endocrine status of the animals.

Increased central and peripheral inflammation and inflammatory hyperalgesia in Zucker rat model of leptin receptor deficiency and genetic obesity

This study investigated whether sensitivity to nociceptive stimuli is altered in obese rats using established models of inflammatory pain, and using real-time PCR, profiled alterations in expression of key adipokine and inflammatory mediator mRNA (adiponectin, tumor necrosis factor-α, interleukin-1β, cyclooxygenase-2, inducible nitric oxide synthase (iNOS)) in spinal cord with obesity. Responses to thermal and mechanical stimulation of the hindpaw and paw oedema were assessed in adult male Zucker fatty rats (fa/fa) and their lean littermates (fa/-; n = 6-9 per group) in the absence of inflammation (acute nociception), then in response to intradermal hindpaw injection of carrageenan (3%; 50 μl) or capsaicin (10 μg; 50 μl) or hindpaw incision. The analgesic potency of morphine (1, 2.5 or 5 mg kg(-1) or vehicle; s.c.) was also assessed. Acute nociception was unaltered in obese animals, but following carrageenan-induced inflammation the obese rats were significantly more sensitive to mechanical and thermal stimulation of the inflamed paw, and displayed greater paw oedema. No difference in the capsaicin- or paw-incision-induced pain sensitivity or in the analgesic potency of morphine was observed between groups. Levels of adiponectin and inducible nitric oxide synthase mRNA were downregulated in spinal cord from obese rats, whereas tumour necrosis factor-α mRNA was upregulated; interleukin-1β and cyclo-oxygenase were unchanged. The increased pain sensitivity and inflammatory response together with changes in spinal adipokine expression in obese rats fit well with the hypothesis that obesity is a chronic low-grade inflammatory disorder, producing a state where responses to subsequent inflammatory challenge are potentiated.

Adiponectin receptor signalling in the brain

Adiponectin is an important adipocyte-derived hormone that regulates metabolism of lipids and glucose, and its receptors (AdipoR1, AdipoR2, T-cadherin) appear to exert actions in peripheral tissues by activating the AMP-activated protein kinase, p38-MAPK, PPARα and NF-kappa B. Adiponectin has been shown to exert a wide range of biological functions that could elicit different effects, depending on the target organ and the biological milieu. There is substantial evidence to suggest that adiponectin receptors are expressed widely in the brain. Their expression has been detected in regions of the mouse hypothalamus, brainstem, cortical neurons and endothelial cells, as well as in whole brain and pituitary extracts. While there is now considerable evidence for the presence of adiponectin and its receptors in the brain, their precise roles in brain diseases still remain unclear. Only a few research studies have looked at this facet of adiponectins in brain disorders. This brief review will describe the evidence for important functions by adiponectin, its structure and known actions, evidence for expression of AdipoRs in the brain, their involvement in brain disorders and the therapeutic potential of agents that could modify AdipoR signalling.

Metabolic dysfunction associated with adiponectin deficiency enhances kainic acid-induced seizure severity

Metabolic syndrome has deleterious effects on the CNS, and recent evidence suggests that obesity rates are higher at presentation in children who develop epilepsy. Adiponectin is secreted by adipose tissue and acts in the brain and peripheral organs to regulate glucose and lipid metabolism. Adiponectin deficiency predisposes toward metabolic syndrome, characterized by obesity, insulin resistance, impaired glucose tolerance, hyperlipidemia, and cardiovascular morbidity. To investigate the relationship between metabolic syndrome and seizures, wild-type C57BL/6J and adiponectin knock-out mice were fed a high-fat diet, followed by treatment with low doses of kainic acid to induce seizures. Adiponectin deficiency in mice fed a high-fat diet resulted in greater fat accumulation, impaired glucose tolerance, hyperlipidemia, increased seizure severity, and increased hippocampal pathology. In contrast, there were no adverse effects of adiponectin deficiency on metabolic phenotype or seizure activity in mice fed a normal (low-fat) chow diet. These findings demonstrate that metabolic syndrome modulates the outcome of seizures and brain injury.

AdipoR1 and 2 are expressed on warm sensitive neurons of the hypothalamic preoptic area and contribute to central hyperthermic effects of adiponectin

Adiponectin can act in the brain to increase energy expenditure and reduce body weight by mechanisms not entirely understood. We found that adiponectin type 1 and type 2 receptors (AdipoR1 and AdipoR2) are expressed in warm sensitive neurons of the hypothalamic preoptic area (POA) which play a critical role in the regulation of core body temperature (CBT) and energy balance. Thus, we tested the ability of adiponectin to influence CBT in wild-type mice and in mice deficient for AdipoR1 or AdipoR2. Local injection of adiponectin into the POA induced prolonged elevation of core body temperature and decreased respiratory exchange ratio (RER) indicating that increased energy expenditure is associated with increased oxidation of fat over carbohydrates. In AdipoR1 deficient mice, the ability of adiponectin to raise CBT was significantly blunted and its ability to decrease RER was completely lost. In AdipoR2 deficient mice, adiponectin had only diminished hyperthermic effects but reduced RER similarly to wild type mice. These results indicate that adiponectin can contribute to energy homeostasis by regulating CBT by direct actions on AdipoR1 and R2 in the POA.

The role of adiponectin in reproduction: from polycystic ovary syndrome to assisted reproduction

OBJECTIVE

To summarize the effects of the adipokine adiponectin on the reproductive endocrine system, from the hypothalamic-pituitary axis to the gonads and target tissues of the reproductive system.

DESIGN

A Medline computer search was performed to identify relevant articles.

SETTING

Research institution.

INTERVENTION(S)

None.

RESULT(S)

Adiponectin is a hormone secreted by adipose tissue that acts to reduce insulin resistance and atherogenic damage, but it also exerts actions in other tissues. Adiponectin mediates its actions in the periphery mainly via two receptors, AdipoR1 and AdipoR2. Adiponectin receptors are present in many reproductive tissues, including the central nervous system, ovaries, oviduct, endometrium, and testes. Adiponectin influences gonadotropin release, normal pregnancy, and assisted reproduction outcomes.

CONCLUSION(S)

Adiponectin, a beneficial adipokine, represents a major link between obesity and reproduction. Higher levels of adiponectin are associated with improved menstrual function and better outcomes in assisted reproductive cycles.

Oxytocin-induced analgesia and scratching are mediated by the vasopressin-1A receptor in the mouse

The neuropeptides oxytocin (OXT) and arginine vasopressin (AVP) contribute to the regulation of diverse cognitive and physiological functions including nociception. Indeed, OXT has been reported to be analgesic when administered directly into the brain, the spinal cord, or systemically. Here, we characterized the phenotype of oxytocin receptor (OTR) and vasopressin-1A receptor (V1AR) null mutant mice in a battery of pain assays. Surprisingly, OTR knock-out mice displayed a pain phenotype identical to their wild-type littermates. Moreover, systemic administration of OXT dose-dependently produced analgesia in both wild-type and OTR knock-out mice in three different assays, the radiant-heat paw withdrawal test, the von Frey test of mechanical sensitivity, and the formalin test of inflammatory nociception. In contrast, OXT-induced analgesia was completely absent in V1AR knock-out mice. In wild-type mice, OXT-induced analgesia could be fully prevented by pretreatment with a V1AR but not an OTR antagonist. Receptor binding studies demonstrated that the distribution of OXT and AVP binding sites in mouse lumbar spinal cord resembles the pattern observed in rat. AVP binding sites diffusely label the lumbar spinal cord, whereas OXT binding sites cluster in the substantia gelatinosa of the dorsal horn. In contrast, quantitative real-time reverse transcription (RT)-PCR revealed that V1AR but not OTR mRNA is abundantly expressed in mouse dorsal root ganglia, where it localizes to small- and medium-diameter cells as shown by single-cell RT-PCR. Hence, V1ARs expressed in dorsal root ganglia might represent a previously unrecognized target for the analgesic action of OXT and AVP.

Adiponectin modulates excitability of rat paraventricular nucleus neurons by differential modulation of potassium currents

The adipocyte-derived hormone adiponectin acts at two seven-transmembrane domain receptors, adiponectin receptor 1 and adiponectin receptor 2, present in the paraventricular nucleus of the hypothalamus to regulate neuronal excitability and endocrine function. Adiponectin depolarizes rat parvocellular preautonomic neurons that secrete either thyrotropin releasing hormone or oxytocin and parvocellular neuroendocrine corticotropin releasing hormone neurons, leading to an increase in plasma adrenocorticotropin hormone concentrations while also hyperpolarizing a subgroup of neurons. In the present study, we investigate the ionic mechanisms responsible for these changes in excitability in parvocellular paraventricular nucleus neurons. Patch clamp recordings of currents elicited from slow voltage ramps and voltage steps indicate that adiponectin inhibits noninactivating delayed rectifier potassium current (I(K)) in a majority of neurons. This inhibition produced a broadening of the action potential in cells that depolarized in the presence of adiponectin. The depolarizing effects of adiponectin were abolished in cells pretreated with tetraethyl ammonium (0/15 cells depolarize). Slow voltage ramps performed during adiponectin-induced hyperpolarization indicate the activation of voltage-independent potassium current. These hyperpolarizing responses were abolished in the presence of glibenclamide [an ATP-sensitive potassium (K(ATP)) channel blocker] (0/12 cells hyperpolarize). The results presented in this study suggest that adiponectin controls neuronal excitability through the modulation of different potassium conductances, effects which contribute to changes in excitability and action potential profiles responsible for peptidergic release into the circulation.

Actions of adiponectin on the excitability of subfornical organ neurons are altered by food deprivation

Adiponectin (ADP) is a peptide produced by adipose tissue, which acts as an insulin sensitizing hormone. Recent studies have shown that adiponectin receptors (AdipoR1 and AdipoR2) are present in the CNS, and although adiponectin does appear in both circulation and the cerebrospinal fluid there is still some debate as to whether or not ADP crosses the blood brain barrier (BBB). Circumventricular organs (CVO) are CNS sites which lack normal BBB, and thus represent sites at which circulating adiponectin may act to directly influence the CNS. The subfornical organ (SFO) is a CVO that has been implicated in the regulation of energy balance as a consequence of the ability of SFO neurons to respond to a number of different circulating satiety signals including amylin, CCK, PYY and ghrelin. Our recent microarray analysis suggested the presence of adiponectin receptors in the SFO. We report here that the SFO shows a high density of mRNA for both adiponectin receptors (AdipoR1 and AdipoR2), and that ADP influences the excitability of dissociated SFO neurons. Separate subpopulations of SFO neurons were either depolarized (8.9+/-0.9 mV, 21 of 97 cells), or hyperpolarized (-8.0+/-0.5 mV, 34 of 97 cells), by bath application of 10nM ADP, effects which were concentration dependent and reversible. Our microarray analysis also suggested that 48 h of food deprivation resulted in specific increases in AdipoR2 mRNA expression (no effect on AdipoR1 mRNA), observations which we confirm here using real-time PCR techniques. The effects of food deprivation also resulted in a change in the responsiveness of SFO neurons to adiponectin with 77% (8/11) of cells tested responding to adiponectin with depolarization, while no hyperpolarizations were observed. These observations support the concept that the SFO may be a key player in sensing circulating ADP and transmitting such information to critical CNS sites involved in the regulation of energy balance.

Adiponectin action from head to toe

Adiponectin, the most abundant protein secreted by white adipose tissue, is known for its involvement in obesity-related disorders such as insulin resistance, type 2 diabetes mellitus and atherosclerosis. Moreover, modulation of the circulating adiponectin concentration is observed in pathologies that are more or less obesity-related, such as cancer and rheumatoid arthritis. The wide distribution of adiponectin receptors in various organs and tissues suggests that adiponectin has pleiotropic effects on numerous physiological processes. Besides its well-known insulin-sensitizing, anti-inflammatory and antiatherosclerotic properties, accumulating evidence suggests that adiponectin may also have anticancer properties and be cardioprotective. A beneficial effect of adiponectin on female reproductive function was also suggested. Since adiponectin has numerous beneficial biological functions, its use as a therapeutic agent has been suggested. However, the use of adiponectin or its receptors as therapeutic targets is complicated by the presence of different adiponectin oligomeric isoforms and production sites, by multiple receptors with differing affinities for adiponectin isoforms, and by cell-type-specific effects in different tissues. In this review, we discuss the known and potential roles of adiponectin in various tissues and pathologies. The therapeutic promise of administration of adiponectin and the use of its circulating levels as a diagnostic biomarker are further discussed based on the latest experimental studies.

Neuropeptide W has cell phenotype-specific effects on the excitability of different subpopulations of paraventricular nucleus neurones

The administration of the neuropeptide W (NPW) and neuropeptide B (NPB) in rodents has been shown to influence the activity of a variety of autonomic and neuroendocrine systems. The paraventricular nucleus (PVN) is a major autonomic and neuroendocrine integration site in the hypothalamus, and neurones within this nucleus express the receptor for these ligands, NPB/W receptor 1 (NPBWR1). In the present study, we used whole cell patch clamp recordings coupled with single-cell reverse transcriptase-polymerase chain reaction to examine the effects of neuropeptide W-23 (NPW-23) on the excitability of identified PVN neurones. Oxytocin, vasopressin and thyrotrophin-releasing hormone neurones were all found to be responsive to 10 nm NPW-23, although both depolarising and hyperpolarising effects were observed in each of these cell groups. By contrast, corticotrophin-releasing hormone cells were unaffected. Further subdivision of chemically phenotyped cell groups into magnocellular, neuroendocrine or pre-autonomic neurones, using their electrophysiological fingerprints, revealed that neurones projecting to medullary and spinal targets were predominantly inhibited by NPW-23, whereas those that projected to median eminence or neural lobe showed almost equivalent numbers of depolarising and hyperpolarising cells. The demonstration of particular phenotypic populations of PVN neurones showing NPW-induced effects on excitability reinforces the importance of the NPB/NPW neuropeptide system as a regulator of autonomic function.

Central adiponectin functions to inhibit arginine vasopressin release in conscious rats

The adipocyte-derived hormone adiponectin plays an important role in modulating energy homeostasis through peripheral tissues and the central nervous system. Several studies have reported that adiponectin exists in cerebrospinal fluid and that adiponectin receptors are expressed in the hypothalamus, including the paraventricular nucleus (PVN), which plays a key role in controlling pituitary hormone secretion. Furthermore, it has been reported that magnocellular arginine vasopressin (AVP) neurones within the PVN express adiponectin receptors. These findings suggest a central role of adiponectin in the modulation of neuroendocrinological functions. In the present study, we investigated the effect of centrally-administered adiponectin on AVP release in conscious rats. Intracerebroventricular (i.c.v.) administration of adiponectin significantly reduced the basal plasma AVP concentration in a dose-dependent manner, with a maximal effect being obtained 10 min after administration. The plasma AVP increase in response to either hyperosmolar or hypovolaemic stimulation was also significantly attenuated by an i.c.v. injection of adiponectin. Treatment with AMP-activated protein kinase (AMPK) inhibitor compound C (100 nmol, i.c.v.) partially reversed the inhibitory effects of adiponectin on AVP release. These findings suggest that central adiponectin plays an inhibitory role in the osmoregulation and baroregulation of AVP release, that the AMPK pathway is at least partly involved in the action of adiponectin, and further suggest a novel physiological or pathophysiological role for central adiponectin in water balance via inhibition of AVP release.

Adiponectin depolarizes parvocellular paraventricular nucleus neurons controlling neuroendocrine and autonomic function

Adiponectin plays important roles in the control of energy homeostasis and autonomic function through peripheral and central nervous system actions. The paraventricular nucleus (PVN) of the hypothalamus is a primary site of neuroendocrine (NE) and autonomic integration, and, thus, a potential target for adiponectin actions. Here, we investigate actions of adiponectin on parvocellular PVN neurons. Adiponectin influenced the majority (65%) of parvocellular PVN neurons, depolarizing 47%, whereas hyperpolarizing 18% of neurons tested. Post hoc identification (single-cell RT-PCR) after recordings revealed that adiponectin depolarizes NE-CRH neurons, whereas intracerebroventricular injections of adiponectin in vivo caused increased plasma ACTH concentrations. Adiponectin also depolarized the majority of TRH neurons, however, NE-TRH neurons were unaffected, in accordance with in vivo experiments showing that intracerebroventricular adiponectin was without effect on plasma TSH. In addition, bath administration of adiponectin also depolarized both preautonomic TRH and oxytocin neurons. These results show that adiponectin acts in the central nervous system to coordinate NE and autonomic function through actions on specific functional groups of PVN neurons.

Adiponectin acts in the nucleus of the solitary tract to decrease blood pressure by modulating the excitability of neuropeptide Y neurons

Adiponectin is an adipocyte derived hormone which acts in the CNS to control autonomic function, energy and cardiovascular homeostasis. Two 7-transmembrane domain receptors, AdipoR1 and AdipoR2, expressed in the hypothalamus and brainstem mediate the actions of adiponectin. The medulla's nucleus of the solitary tract (NTS) is the primary viscerosensory integration site and an important nucleus in the regulation of cardiovascular function. Here we show the localization of both AdipoR1 and AdipoR2 mRNA in the NTS. We have investigated the consequences of receptor activation in response to exogenous application of adiponectin on cardiovascular (blood pressure and heart rate monitoring in vivo), and single neuron (whole cell current-clamp recordings in vitro) function. Microinjection of adiponectin in the medial NTS (mNTS) at the level of the area postrema resulted in a decrease in BP (mean AUC= -2055+/-648.1, n=5, mean maximum effect: -11.7+/-3.6 mm Hg) while similar commissural NTS (cNTS) microinjections were without effect. Patch clamp recordings from NTS neurons in a medullary slice preparation showed rapid (within 200 s of application) reversible (usually within 1000 s following washout) effects of adiponectin on the membrane potential of 62% of mNTS neurons tested (38/61). In 34% (n=21) of mNTS neurons adiponectin induced a depolarization of membrane potential (6.8+/-0.9 mV), while the remainder of mNTS cells influenced by adiponectin (n=17) hyperpolarized in response to this adipokine (-5.4+/-0.7 mV). Post-hoc single cell RT-PCR (ssRT-PCR) analysis of neurons showed that the majority of NPY mRNA positive mNTS neurons were depolarized by adiponectin (7/11), while 4 of these depolarized cells were also GAD67 positive. The results presented in this study suggest adiponectin acts in the NTS to control BP and suggest that such effects may occur as a direct result of the ability of this adipokine to modulate the excitability of discrete groups of neurons in the NTS. These studies identify the mNTS as a new CNS site which adiponectin may act to influence central autonomic processing.

Brain regulation of appetite and satiety

Interest in the control of feeding has increased as a result of the obesity epidemic and rising incidence of metabolic diseases. The brain detects alterations in energy stores and triggers metabolic and behavioral responses designed to maintain energy balance. Energy homeostasis is controlled mainly by neuronal circuits in the hypothalamus and brainstem, whereas reward and motivation aspects of eating behavior are controlled by neurons in limbic regions and the cerebral cortex. This article provides an integrated perspective on how metabolic signals emanating from the gastrointestinal tract, adipose tissue, and other peripheral organs target the brain to regulate feeding, energy expenditure, and hormones. The pathogenesis and treatment of obesity and abnormalities of glucose and lipid metabolism are discussed.

The paraventricular nucleus of the hypothalamus - a potential target for integrative treatment of autonomic dysfunction

BACKGROUND

The paraventricular nucleus of the hypothalamus (PVN) has emerged as one of the most important autonomic control centers in the brain, with neurons playing essential roles in controlling stress, metabolism, growth, reproduction, immune and other more traditional autonomic functions (gastrointestinal, renal and cardiovascular).

OBJECTIVES

Traditionally the PVN was viewed as a nucleus in which afferent inputs from other regions were faithfully translated into changes in single specific outputs, whether neuroendocrine or autonomic. Here we present data which suggest that the PVN plays significant and essential roles in integrating multiple sources of afferent input and sculpting an integrated autonomic output by concurrently modifying the excitability of multiple output pathways. In addition, we highlight recent work that suggests that dysfunction of such intranuclear integrative circuitry contributes to the pathology of conditions such as hypertension and congestive heart failure.

CONCLUSIONS

This review highlights data showing that individual afferent inputs (subfornical organ), signaling molecules (orexins, adiponectin), and interneurons (glutamate/GABA), all have the potential to influence (and thus coordinate) multiple PVN output pathways. We also highlight recent studies showing that modifications in this integrated circuitry may play significant roles in the pathology of diseases such as congestive heart failure and hypertension.

Globular adiponectin inhibits GnRH secretion from GT1-7 hypothalamic GnRH neurons by induction of hyperpolarization of membrane potential

Reproduction is accurately regulated by metabolic states in mammals. Adiponectin regulates luteinizing hormone (LH) secretion in the pituitary and energy homeostasis in the hypothalamus. We further investigated the gonadotropin-releasing hormone (GnRH) secretion regulation by adiponectin and its related molecular and electrophysiological mechanisms. The results showed that adiponectin receptors (AdipR1 and 2) were expressed in GT1-7 cells derived from hypothalamus neurons. GnRH secretion was inhibited via activation of AMP-activated protein kinase (AMPK). Moreover, we revealed that hyperpolarization of plasma membrane potentials and reduction of calcium influx was also caused by adiponectin.

Adipokines and the peripheral and neural control of energy balance

Adipokines are secreted by adipose tissue and control various physiological systems. Low leptin levels during fasting stimulate feeding, reduce energy expenditure, and modulate neuroendocrine and immune function to conserve energy stores. On the other hand, rising leptin levels in the overfed state prevent weight gain by inhibiting food intake and increasing energy expenditure. These actions are mediated by neuronal circuits in the hypothalamus and brainstem. Leptin also controls glucose and lipid metabolism by targeting enzymes such as AMP-activated protein kinase and stearoyl-coenzyme A desaturase-1 in liver and muscle. Likewise, adiponectin and resistin control energy balance and insulin sensitivity via central and peripheral targets. As highlighted in this review, there are distinct as well as common signaling pathways for adipokines. Understanding adipokine signaling in the brain and other organs will provide insights into the pathogenesis and treatment of obesity, diabetes and various metabolic disorders.