Enhanced effect of neuropeptide Y on food intake caused by blockade of the V(1A) vasopressin receptor

Intraperitoneal administration of arginine vasotocin (AVT) induces anorexigenic and anxiogenic actions via the brain V1a receptor-signaling pathway in the tiger puffer, Takifugu rubripes

Arginine vasotocin (AVT) is produced mainly in the hypothalamus and as a neurohypophyseal hormone peripherally regulates water-mineral balance in sub-mammals. In addition, AVT-containing neurons innervate several areas of the brain, and AVT also acts centrally as both an anorexigenic and anxiogenic factor in goldfish. However, it is unclear whether these central effects operate in fish in general. In the present study, therefore, we investigated AVT-like immunoreactivity in the brain of the tiger puffer, a cultured fish with a high market value in Japan and also a representative marine teleost species, focusing particularly on whether AVT affects food intake and psychomotor activity. AVT-like immunoreactivity was distributed higher in the ventral region of the telencephalon, the hypothalamus and midbrain. Intraperitoneal (IP) administration of AVT at 100 pmol g-1 body weight (BW) increased the immunoreactivity of phosphorylated ribosomal proteinS6 (RPS6), a neuronal activation marker, in the telencephalon and diencephalon, decreased food consumption and enhanced thigmotaxis. AVT-induced anorexigenic and anxiogenic actions were blocked by IP co-injection of a V1a receptor (V1aR) antagonist, Manning compound (MC) at 300 pmol g-1 BW. These results suggest that AVT acts as an anorexigenic and anxiogenic factor via the V1aR-signaling pathway in the tiger puffer brain.

Role of linkage between cerebral activity and baroreflex control of heart rate via central vasopressin V1a receptors in food-deprived mice

We previously reported that cerebral activation at the onset of voluntary locomotion suppressed baroreflex control of heart rate (HR) and increased arterial pressure via vasopressin V1a receptors in the brain. Here, we examined whether these responses were associated with food seeking, a motivated behavior, using free-moving wild-type (WT, n=10), V1a receptor knockout (KO, n=9) and wild-type mice locally infused with a V1a receptor antagonist into the nucleus tractus solitarii (BLK, n=10). For 3 consecutive days mice were fed ad libitum (Fed), food deprived (FD), and refed (RF) under a dark/light cycle (19:00/7:00). Food was removed on day2 and restored on day3 at 18:00. Throughout the protocol, cerebral activity was determined from the power density ratio of θ- to δ-wave band (θ/δ) by electroencephalogram every 4sec. Baroreflex was evaluated by the cross-correlation function (R(t)) between changes in HR and arterial pressure every 4sec. The cerebro-baroreflex linkage was then evaluated by the cross-correlation function between θ/δ and R(t). Behavior was recorded with CCD camera. We found that cerebro-baroreflex linkage, enhanced in WT at night after FD (P=0.006), returned to Fed level after RF (P=0.68). Similarly, food-seeking behavior increased after FD to a level twofold higher than during Fed (P=0.004) and returned to Fed level after RF (P=0.74). However, none of these changes occurred in KO or BLK (P>0.11). Thus, the suppression of baroreflex control of HR linked with cerebral activation via V1a receptors might play an important role at the onset of motivated behaviors, such as food seeking induced by FD.

Arginine vasopressin: Direct and indirect action on metabolism

From its identification and isolation in 1954, arginine vasopressin (AVP) has attracted attention, not only for its peripheral functions such as vasoconstriction and reabsorption of water from kidney, but also for its central effects. As there is now considerable evidence that AVP plays a crucial role in feeding behavior and energy balance, it has become a promising therapeutic target for treating obesity or other obesity-related metabolic disorders. However, the underlying mechanisms for AVP regulation of these central processes still remain largely unknown. In this review, we will provide a brief overview of the current knowledge concerning how AVP controls energy balance and feeding behavior, focusing on physiological aspects including the relationship between AVP, circadian rhythmicity, and glucocorticoids.

Chronic Escitalopram Treatment Does Not Alter the Effects of Neonatal Stress on Hippocampal BDNF Levels, 5-HT1A Expression and Emotional Behaviour of Male and Female Adolescent Rats

Early life stress is considered a risk factor for the development of long-term psychiatric disorders. Maternal deprivation (MD) is a useful paradigm to understand the neurobiological underpinnings of early stress-induced changes in neurodevelopment trajectory. The goal of the present study was to examine the effects of a chronic treatment with escitalopram (ESC) on the hippocampal levels of BDNF and neuropeptide Y (NPY), expression of serotonin type 1A receptor (5-HT1A), plasma corticosterone levels and emotional behaviours in male and female adolescent rats submitted to MD at 9 days of life (group DEP9) and challenged with a brief and mild stress (saline injection (SAL)) at the end of MD. Whole litters were kept with mothers (CTL) or submitted to MD (DEP9). Within each group, pups were stress-challenged (CTL-SAL and DEP9-SAL) or not (CTL-NSAL and DEP9-NSAL). ESC or vehicle treatments began at weaning and lasted 24 days, when animals were sacrificed for determination of neurobiological variables or submitted to a battery of tests for evaluation of emotional behaviours. The results showed that BDNF levels were higher in SAL-challenged males and in DEP9-SAL females, whereas 5-HT1A receptor expression was reduced in DEP9 males and in SAL-challenged females. There were no changes in NPY or corticosterone levels. In the forced swim test, SAL-challenged males and DEP9 females displayed less immobility and ESC only increased social motivation in males. The results indicated that neonatal stress led to sex-dependent changes in neurobiology and behaviour and that chronic ESC treatment had minor effects on these parameters.

Estrous Cycle Modulation of Feeding and Relaxin-3/Rxfp3 mRNA Expression: Implications for Estradiol Action

INTRODUCTION

Food intake varies during the ovarian hormone/estrous cycle in humans and rodents, an effect mediated mainly by estradiol. A potential mediator of the central anorectic effects of estradiol is the neuropeptide relaxin-3 (RLN3) synthetized in the nucleus incertus (NI) and acting via the relaxin family peptide-3 receptor (RXFP3).

METHODS

We investigated the relationship between RLN3/RXFP3 signaling and feeding behavior across the female rat estrous cycle. We used in situ hybridization to investigate expression patterns of Rln3 mRNA in NI and Rxfp3 mRNA in the hypothalamic paraventricular nucleus (PVN), lateral hypothalamic area (LHA), medial preoptic area (MPA), and bed nucleus of the stria terminalis (BNST), across the estrous cycle. We identified expression of estrogen receptors (ERs) in the NI using droplet digital PCR and assessed the electrophysiological responsiveness of NI neurons to estradiol in brain slices.

RESULTS

Rln3 mRNA reached the lowest levels in the NI pars compacta during proestrus. Rxfp3 mRNA levels varied across the estrous cycle in a region-specific manner, with changes observed in the perifornical LHA, magnocellular PVN, dorsal BNST, and MPA, but not in the parvocellular PVN or lateral LHA. G protein-coupled estrogen receptor 1 (Gper1) mRNA was the most abundant ER transcript in the NI. Estradiol inhibited 33% of type 1 NI neurons, including RLN3-positive cells.

CONCLUSION

These findings demonstrate that the RLN3/RXFP3 system is modulated by the estrous cycle, and although further studies are required to better elucidate the cellular and molecular mechanisms of estradiol signaling, current results implicate the involvement of the RLN3/RXFP3 system in food intake fluctuations observed across the estrous cycle in female rats.

The influence of post-infarct heart failure and high fat diet on the expression of apelin APJ and vasopressin V1a and V1b receptors

Vasopressin and apelin are reciprocally regulated hormones which are implicated in the pathophysiology of heart failure and the regulation of metabolism; however, little is known about their interactions under pathological conditions. In this study, we determined how post-infarct heart failure (HF) and a high fat diet (HFD) affect expression of the apelin APJ receptor (APJR) and the V1a (V1aR) and V1b (V1bR) vasopressin receptors in the hypothalamus, the heart, and the retroperitoneal adipose tissue. We performed experiments in male 4-week-old Sprague Dawley rats. The animals received either a normal fat diet (NFD) or a HFD for 8 weeks, then they underwent left coronary artery ligation to induce HF or sham surgery (SO), followed by 4 weeks of NFD or HFD. The HF rats showed higher plasma concentration of NT-proBNP and copeptin. The HF reduced the APJR mRNA expression in the hypothalamus. The APJR and V1aR protein levels in the hypothalamus were regulated both by HF and HFD, while the V1bR protein level in the hypothalamus was mainly influenced by HF. APJR mRNA expression in the heart was significantly higher in rats on HFD, and HFD affected the reduction of the APJR protein level in the right ventricle. The regulation of APJR, V1aR and V1bR expression in the heart and the retroperitoneal adipose tissue were affected by both HF and HFD. Our study demonstrates that HF and HFD cause significant changes in the expression of APJR, V1aR and V1bR, which may have an important influence on the cardiovascular system and metabolism.

Arginine vasotocin (AVT)/mesotocin (MT) receptors in chickens: Evidence for the possible involvement of AVT-AVPR1 signaling in the regulation of oviposition and pituitary prolactin expression

Two structurally related peptides, arginine vasotocin (AVT) and mesotocin (MT), are reported to regulate many physiological processes, such as anti-diuresis and oviposition in birds, and their actions are likely mediated by four AVT/MT receptors (AVPR1A, AVPR1B, MTR and AVPR2b), which are orthologous/paralogous to human AVPR1A, AVPR1B, OXTR and AVPR2 respectively. However, our knowledge regarding the functions of these avian AVT/MT receptors has been limited. Here, we examined the functionality and expression of these receptors in chickens and investigated the roles of AVT in the anterior pituitary. Our results showed that 1) AVPR1A, AVPR1B and AVPR2b could be preferentially activated by AVT, monitored by cell-based luciferase reporter assays and/or Western blot, indicating that they are AVT-specific receptors (AVPR1A; AVPR1B) or AVT-preferring receptor (AVPR2b) functionally coupled to intracellular calcium, MAPK/ERK and cAMP/PKA signaling pathways. In contrast, MTR could be activated by AVT and MT with similar potencies, indicating that MTR is a receptor common for both peptides; 2) Using qPCR, differential expression of the four receptors was found in chicken tissues including the oviduct and anterior pituitary. In particular, only AVPR1A is abundantly expressed in the uterus, suggesting its involvement in mediating AVT-induced oviposition. 3) In cultured chick pituitary cells, AVT could stimulate ACTH and PRL expression and secretion, an action likely mediated by AVPR1B and/or AVPR1A abundantly expressed in anterior pituitary. Collectively, our data helps to elucidate the roles of AVT/MT in birds, such as the 'oxytocic action' of AVT, which induces uterine muscle contraction during oviposition.

Intracerebroventricular administration of arginine vasotocin (AVT) induces anorexigenesis and anxiety-like behavior in goldfish

Arginine vasotocin (AVT) is known as a neurohypophyseal hormone that regulates water- and mineral-balance in non-mammalian vertebrates. Recent studies revealed that AVT also exerts central effects on behavior. The goldfish has several merits for evaluation of behavioral changes. However, there is few information on the behavioral action of AVT in this species. Here we examined the effects of AVT on food intake and psychomotor activity. AVT was administered intracerebroventricularly at 1, 5 and 10 pmol g^-1 body weight (BW). Intracerebroventricular (ICV) administration of AVT at 5 and 10 pmol g^-1 BW significantly decreased food intake during 30 min after injection and recovery from anesthesia. The AVT-induced anorexigenic action was attenuated by treatment with the AVT receptor V1aR antagonist Manning compound (MC) at 50 pmol g^-1 BW. As the goldfish tends to prefer the lower to the upper area of a tank, we used this preference behavior for assessing psychomotor activity during a 30-min observation period. ICV administration of AVT at 1, 5 and 10 pmol g^-1 BW significantly prolonged the time spent in the lower area, but did not affect locomotor activity in the tank at any dose. The action of AVT was similar to that of the central-type benzodiazepine receptor inverse agonist FG-7142 at 10 pmol g^-1 BW. AVT-induced anxiety-like behavior was blocked by treatment with MC at 50 pmol g^-1 BW. These results indicate that AVT affects food intake and psychophysiological status, and also induces anorexigenic- and anxiogenic-like actions via the V1aR-signaling pathway in the goldfish brain.

Oxytocin and Vasopressin Systems in Obesity and Metabolic Health: Mechanisms and Perspectives

PURPOSE OF REVIEW

The neurohypophysial endocrine system is identified here as a potential target for therapeutic interventions toward improving obesity-related metabolic dysfunction, given its coinciding pleiotropic effects on psychological, neurological and metabolic systems that are disrupted in obesity.

RECENT FINDINGS

Copeptin, the C-terminal portion of the precursor of arginine-vasopressin, is positively associated with body mass index and risk of type 2 diabetes. Plasma oxytocin is decreased in obesity and several other conditions of abnormal glucose homeostasis. Recent data also show non-classical tissues, such as myocytes, hepatocytes and β-cells, exhibit responses to oxytocin and vasopressin receptor binding that may contribute to alterations in metabolic function. The modulation of anorexigenic and orexigenic pathways appears to be the dominant mechanism underlying the effects of oxytocin and vasopressin on body weight regulation; however, there are apparent limitations associated with their use in direct pharmacological applications. A clearer picture of their wider physiological effects is needed before either system can be considered for therapeutic use.

Inhibition of oxytocin and vasopressin neuron activity in rat hypothalamic paraventricular nucleus by relaxin-3-RXFP3 signalling

KEY POINTS

Relaxin-3 is a stress-responsive neuropeptide that acts at its cognate receptor, RXFP3, to alter behaviours including feeding. In this study, we have demonstrated a direct, RXFP3-dependent, inhibitory action of relaxin-3 on oxytocin and vasopressin paraventricular nucleus (PVN) neuron electrical activity, a putative cellular mechanism of orexigenic actions of relaxin-3. We observed a Gα_i/o -protein-dependent inhibitory influence of selective RXFP3 activation on PVN neuronal activity in vitro and demonstrated a direct action of RXFP3 activation on oxytocin and vasopressin PVN neurons, confirmed by their abundant expression of RXFP3 mRNA. Moreover, we demonstrated that RXFP3 activation induces a cadmium-sensitive outward current, which indicates the involvement of a characteristic magnocellular neuron outward potassium current. Furthermore, we identified an abundance of relaxin-3-immunoreactive axons/fibres originating from the nucleus incertus in close proximity to the PVN, but associated with sparse relaxin-3-containing fibres/terminals within the PVN.

ABSTRACT

The paraventricular nucleus of the hypothalamus (PVN) plays an essential role in the control of food intake and energy expenditure by integrating multiple neural and humoral inputs. Recent studies have demonstrated that intracerebroventricular and intra-PVN injections of the neuropeptide relaxin-3 or selective relaxin-3 receptor (RXFP3) agonists produce robust feeding in satiated rats, but the cellular and molecular mechanisms of action associated with these orexigenic effects have not been identified. In the present studies, using rat brain slices, we demonstrated that relaxin-3, acting through its cognate G-protein-coupled receptor, RXFP3, hyperpolarized a majority of putative magnocellular PVN neurons (88%, 22/25), including cells producing the anorexigenic neuropeptides, oxytocin and vasopressin. Importantly, the action of relaxin-3 persisted in the presence of tetrodotoxin and glutamate/GABA receptor antagonists, indicating its direct action on PVN neurons. Similar inhibitory effects on PVN oxytocin and vasopressin neurons were produced by the RXFP3 agonist, RXFP3-A2 (82%, 80/98 cells). In situ hybridization histochemistry revealed a strong colocalization of RXFP3 mRNA with oxytocin and vasopressin immunoreactivity in rat PVN neurons. A smaller percentage of putative parvocellular PVN neurons was sensitive to RXFP3-A2 (40%, 16/40 cells). These data, along with a demonstration of abundant peri-PVN and sparse intra-PVN relaxin-3-immunoreactive nerve fibres, originating from the nucleus incertus, the major source of relaxin-3 neurons, identify a strong inhibitory influence of relaxin-3-RXFP3 signalling on the electrical activity of PVN oxytocin and vasopressin neurons, consistent with the orexigenic effect of RXFP3 activation observed in vivo.

Diencephalic and septal structures containing the avian vasotocin receptor (V1aR) involved in the regulation of food intake in chickens, Gallus gallus

Recently, it was found that the avian central vasotocin receptor (V1aR) is associated with the regulation of food intake. To identify V1aR-containing brain structures regulating food intake, a selective V1aR antagonist SR-49059 that induced food intake was administrated intracerebroventricularly in male chickens followed by detection of brain structures using FOS immunoreactivity. Particularly, the hypothalamic core region of the paraventricular nucleus, lateral hypothalamic area, dorsomedial hypothalamic nucleus, a subnucleus of the central extended amygdalar complex [dorsolateral bed nucleus of the stria terminalis], medial septal nucleus and caudal brainstem [nucleus of the solitary tract] showed significantly increased FOS-ir cells. On the other hand, the supraoptic nucleus of the preoptic area and the nucleus of the hippocampal commissure of the septum showed suppressed FOS immunoreactivity in the V1aR antagonist treatment group. Further investigation revealed that neuronal activity of arginine vasotocin (AVT-ir) magnocellular neurons in the supraoptic nucleus, preoptic periventricular nucleus, paraventricular nucleus and ventral periventricular hypothalamic nucleus and most likely corticotropin releasing hormone (CRH-ir) neurons in the nucleus of the hippocampal commissure were reduced following the antagonist treatment. Dual immunofluorescence labeling results showed that perikarya of AVT-ir magnocellular neurons in the preoptic area and hypothalamus were colabeled with V1aR. Within the nucleus of the hippocampal commissure, CRH-ir neurons were shown in close contact with V1aR-ir glial cells. Results of the present study suggest that the V1aR plays a role in the regulation of food intake by modulating neurons that synthesize and release anorectic neuropeptides in the avian brain.

Central effect of vasotocin 4 receptor (VT4R/V1aR) antagonists on the stress response and food intake in chicks given neuropeptide Y (NPY)

Previous studies identified SR-49059 as a most effective antagonist of the avian vasotocin 4 receptor (VT4R) compared to other candidate blockers including the Manning compound using in silico 3 dimensional (3D) modeling/docking analysis of the chicken VT4R and an in vitro anterior pituitary cell culture study. The present experiments were designed to validate whether SR-49059 and the Manning compound would likewise be effective in vivo in blocking the VT4R when applied intracerebroventricularly (ICV) to chicks. Two treatments were tested, a stressor (immobilization) and administration of neuropeptide Y (NPY), a potent orexigenic compound. In the first experiment, birds were given the Manning compound, SR-49059 or physiological saline ICV followed by immobilization stress. Blood samples were taken and corticosterone (CORT) was determined by radioimmunoassay. It was hypothesized that both antagonists would reduce the stress response. A second experiment examined the role of the VT4R in food intake regulation. The Manning compound, SR-49059 or physiological saline was administered prior to NPY and food intake was monitored for 1h. It was hypothesized that each of the two antagonists coupled with NPY would augment food intake above the intake resulting from saline plus NPY administration. Related to the second experiment was a third that examined the difference between the effect of central administration of NPY versus SR-49059 in releasing CORT. Results of the first study showed that the Manning compound or SR-49059 prior to stress decreased CORT levels compared to controls while the second experiment showed that SR-49059 or the Manning compound plus NPY, enhanced food intake above that of the experimental group given saline and NPY. The last study showed that NPY increased plasma CORT above birds given SR-49059 centrally or saline administered controls. Taken together, results suggest that the avian VT4R is involved in the central neuroendocrine stress response as well as functions in appetite regulation by mediating an anorexigenic effect similar to what has been reported in mammals for the V1aR. In conclusion, similar to the past in silico and in vitro tests, the current in vivo experiments showed SR-49059 to be a most efficacious avian vasotocin receptor antagonist. Therefore based upon results of functional tests utilizing a highly specific mammalian antagonist, SR-49059, to the mammalian V1aR that likewise was most effective in blocking the avian VT4R and past reported high sequence homology between the mammalian V1aR and the VT4R, it is recommended that the chicken VT4R be renamed the avian V1aR to facilitate better communication among scientists involved in comparative studies.

LMO4 is essential for paraventricular hypothalamic neuronal activity and calcium channel expression to prevent hyperphagia

The dramatic increase in the prevalence of obesity reflects a lack of progress in combating one of the most serious health problems of this century. Recent studies have improved our understanding of the appetitive network by focusing on the paraventricular hypothalamus (PVH), a key region responsible for the homeostatic balance of food intake. Here we show that mice with PVH-specific ablation of LIM domain only 4 (Lmo4) become rapidly obese when fed regular chow due to hyperphagia rather than to reduced energy expenditure. Brain slice recording of LMO4-deficient PVH neurons showed reduced basal cellular excitability together with reduced voltage-activated Ca(2+) currents. Real-time PCR quantification revealed that LMO4 regulates the expression of Ca(2+) channels (Cacna1h, Cacna1e) that underlie neuronal excitability. By increasing neuronal activity using designer receptors exclusively activated by designer drugs technology, we could suppress food intake of PVH-specific LMO4-deficient mice. Together, these results demonstrate that reduced neural activity in LMO4-deficient PVH neurons accounts for hyperphagia. Thus, maintaining PVH activity is important to prevent hyperphagia-induced obesity.

Salivary peptide tyrosine-tyrosine 3-36 modulates ingestive behavior without inducing taste aversion

Hormone peptide tyrosine-tyrosine (PYY) is secreted into circulation from the gut L-endocrine cells in response to food intake, thus inducing satiation during interaction with its preferred receptor, Y2R. Clinical applications of systemically administered PYY for the purpose of reducing body weight were compromised as a result of the common side effect of visceral sickness. We describe here a novel approach of elevating PYY in saliva in mice, which, although reliably inducing strong anorexic responses, does not cause aversive reactions. The augmentation of salivary PYY activated forebrain areas known to mediate feeding, hunger, and satiation while minimally affecting brainstem chemoreceptor zones triggering nausea. By comparing neuronal pathways activated by systemic versus salivary PYY, we identified a metabolic circuit associated with Y2R-positive cells in the oral cavity and extending through brainstem nuclei into hypothalamic satiety centers. The discovery of this alternative circuit that regulates ingestive behavior without inducing taste aversion may open the possibility of a therapeutic application of PYY for the treatment of obesity via direct oral application.

Functional analysis of seven genes linked to body mass index and adiposity by genome-wide association studies: a review

Genome-wide association studies (GWAS) have identified a total of about 40 single nucleotide polymorphisms (SNPs) that show significant linkage to body mass index, a widely utilised surrogate measure of adiposity. However, only 8 of these associations have been confirmed by follow-up GWAS using more sophisticated measures of adiposity (computed tomography). Among these 8, there is a SNP close to the gene FTO which has been the subject of considerable work to diagnose its function. The remaining 7 SNPs are adjacent to, or within, the genes NEGR1, TMEM18, ETV5, FLJ35779, LINGO2, SH2B1 and GIPR, most of which are less well studied than FTO, particularly in the context of obesity. This article reviews the available data on the functions of these genes, including information gleaned from studies in humans and animal models. At present, we have virtually no information on the putative mechanism associating the genes FLJ35779 and LINGO2 to obesity. All of these genes are expressed in the brain, and for 2 of them (SH2B1 and GIPR), a direct link to the appetite regulation system is known. SH2B1 is an enhancer of intracellular signalling in the JAK-STAT pathway, and GIPR is the receptor for an appetite-linked hormone (GIP) produced by the alimentary tract. NEGR1, ETV5 and SH2B1 all have suggested roles in neurite outgrowth, and hence SNPs adjacent to these genes may affect development of the energy balance circuitry. Although the genes have central patterns of gene expression, implying a central neuronal connection to energy balance, for at least 4 of them (NEGR1, TMEM18, SH2B1 and GIPR), there are also significant peripheral functions related to adipose tissue biology. These functions may contribute to their effects on the obese phenotype.

Oxytocin action in the ventral tegmental area affects sucrose intake

Brain oxytocin is known to play a role in the control of food intake, and recent studies suggest that stimulation of central oxytocin receptors selectively suppresses carbohydrate intake. The specific oxytocin projection sites and receptor populations involved in this response are as yet unidentified. We hypothesized that oxytocin receptors in the ventral tegmental area (VTA) may play a role in limiting sucrose intake, because the VTA is known to influence palatable food intake. We first performed a dose response study in which we observed that intra-VTA oxytocin injection significantly suppressed intake of a 10% sucrose solution during a 30-min test session by 13.35-20.5% relative to vehicle treatment. Doses of intra-VTA oxytocin that suppressed sucrose intake had no effect on water intake. Next we examined the effects of two oxytocin receptor antagonists, (d(CH2)5(1),Tyr(Me)(2),Orn(8))-Oxytocin (OVT) and L-368,899. Each of these antagonists significantly increased 10% sucrose intake by 17-20.5% relative to vehicle when delivered directly into the VTA, at doses subthreshold for effect if injected into the cerebral ventricles. Finally, we observed that the effect of intra-VTA oxytocin to suppress 10% sucrose intake was significantly attenuated by pretreatment with L-368,899, supporting the suggestion that the VTA oxytocin treatment suppresses intake through action at oxytocin receptors. These findings support the suggestion that endogenous oxytocin action within the VTA suppresses sucrose intake. We conclude that oxytocin receptors in the VTA play a physiologic role in the control of sucrose ingestion.

Vasopressin V1a and V1b Receptors: From Molecules to Physiological Systems

The neurohypophysial hormone arginine vasopressin (AVP) is essential for a wide range of physiological functions, including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. These and other actions of AVP are mediated by at least three distinct receptor subtypes: V1a, V1b, and V2. Although the antidiuretic action of AVP and V2 receptor in renal distal tubules and collecting ducts is relatively well understood, recent years have seen an increasing understanding of the physiological roles of V1a and V1b receptors. The V1a receptor is originally found in the vascular smooth muscle and the V1b receptor in the anterior pituitary. Deletion of V1a or V1b receptor genes in mice revealed that the contributions of these receptors extend far beyond cardiovascular or hormone-secreting functions. Together with extensively developed pharmacological tools, genetically altered rodent models have advanced the understanding of a variety of AVP systems. Our report reviews the findings in this important field by covering a wide range of research, from the molecular physiology of V1a and V1b receptors to studies on whole animals, including gene knockout/knockdown studies.

An obligate role of oxytocin neurons in diet induced energy expenditure

Oxytocin neurons represent one of the major subsets of neurons in the paraventricular hypothalamus (PVH), a critical brain region for energy homeostasis. Despite substantial evidence supporting a role of oxytocin in body weight regulation, it remains controversial whether oxytocin neurons directly regulate body weight homeostasis, feeding or energy expenditure. Pharmacologic doses of oxytocin suppress feeding through a proposed melanocortin responsive projection from the PVH to the hindbrain. In contrast, deficiency in oxytocin or its receptor leads to reduced energy expenditure without feeding abnormalities. To test the physiological function of oxytocin neurons, we specifically ablated oxytocin neurons in adult mice. Our results show that oxytocin neuron ablation in adult animals has no effect on body weight, food intake or energy expenditure on a regular diet. Interestingly, male mice lacking oxytocin neurons are more sensitive to high fat diet-induced obesity due solely to reduced energy expenditure. In addition, despite a normal food intake, these mice exhibit a blunted food intake response to leptin administration. Thus, our study suggests that oxytocin neurons are required to resist the obesity associated with a high fat diet; but their role in feeding is permissive and can be compensated for by redundant pathways.

Anti-neuropeptide Y plasma immunoglobulins in relation to mood and appetite in depressive disorder

Depression and eating disorders are frequently associated, but the molecular pathways responsible for co-occurrence of altered mood, appetite and body weight are not yet fully understood. Neuropeptide Y (NPY) has potent antidepressant and orexigenic properties and low central NPY levels have been reported in major depression. In the present study, we hypothesized that in patients with major depression alteration of mood, appetite and body weight may be related to NPY-reactive autoantibodies (autoAbs). To test this hypothesis, we compared plasma levels and affinities of NPY-reactive autoAbs between patients with major depression and healthy controls. Then, to evaluate if changes of NPY autoAb properties can be causally related to altered mood and appetite, we developed central and peripheral passive transfer models of human autoAbs in mice and studied depressive-like behavior in forced-swim test and food intake. We found that plasma levels of NPY IgG autoAbs were lower in patients with moderate but not with mild depression correlating negatively with the Montgomery-Åsberg Depression Rating Scale scores and with immobility time of the forced-swim test in mice after peripheral injection of autoAbs. No significant differences in NPY IgG autoAb affinities between patients with depression and controls were found, but higher affinity of IgG autoAbs for NPY was associated with lower body mass index and prevented NPY-induced orexigenic response in mice after their central injection. These data suggest that changes of plasma levels of anti-NPY autoAbs are relevant to altered mood, while changes of their affinity may participate in altered appetite and body weight in patients with depressive disorder.

Central apelin-13 inhibits food intake via the CRF receptor in mice

Apelin, the novel identified peptide, is the endogenous ligand for the APJ. Previous studies have reported the effect of apelin on food intake, however the action of acute central injected apelin on food intake in mice remains unknown. The present study was designed to investigate the mechanism as well as the effect of central apelin-13 on food intake in mice. During the dark period, the cumulative food intake was significantly decreased at 4h after the intracerebroventricular (i.c.v.) injection of 1 and 3μg/mouse apelin-13 and the period food intake was significantly reduced during 2-4h after treatment. In the fasted mice, the cumulative food intake was significantly decreased at 2 and 4h after injection of 3μg/mouse apelin-13. The cumulative water intake was significantly reduced by apelin-13 (3μg/mouse) at 4h after injection in freely feeding and fasted mice. However, during light period, apelin-13 had no influence on food and water intake in freely feeding mice. The APJ receptor antagonist apelin-13(F13A) (6μg/mouse) and the corticotrophin-releasing factor (CRF) receptor antagonist α-helical CRF(9-41) (3μg/mouse) could reverse the inhibitory effect on cumulative food intake/0-4h induced by apelin-13 (3μg/mouse) in freely feeding mice during the dark period, whereas the anorexic effect could not be antagonized by the arginie vasopressin (AVP) receptor antagonist deamino(CH(2))(5)Tyr(Me)AVP (0.5μg/mouse). Taken together, these results suggest that central apelin-13 inhibits food intake in mice and it seems that APJ receptor and CRF receptor, but not AVP receptor, might be involved in this process.