The vasopressin Avpr1b receptor: molecular and pharmacological studies

Regulation of the hypothalamic-pituitary-adrenal axis by neuropeptides

The major endocrine response to stress occurs via activation of the hypothalamic-pituitary-adrenal (HPA) axis, leading ultimately to increases in circulating glucocorticoids, which are essential for the metabolic adaptation to stress. The major players in the HPA axis are the hypothalamic neuropeptide, corticotropin releasing hormone (CRH), the pituitary hormone adrenocorticotropic hormone, and the negative feedback effects of adrenal glucocorticoids. In addition, a number of other neuropeptides, including vasopressin (VP), angiotensin II, oxytocin, pituitary adenylate cyclase activating peptide, orexin and cholecystokinin, and nesfatin can affect HPA axis activity by influencing the expression and secretion of CRH, and also by modulating pituitary corticotroph function or adrenal steroidogenesis. Of these peptides, VP co-secreted with CRH from axonal terminals in the external zone of the median eminence plays a prominent role by potentiating the stimulatory effect of CRH and by increasing the number of pituitary corticotrophs during chronic challenge. Although the precise role and significance of many of these neuropeptides in regulating HPA axis activity requires further investigation, it is likely that they are part of a multifactorial system mediating the fine tuning of HPA axis activity during adaptation to a variety of physiological and stressful conditions.

Hypothalamic-pituitary-adrenal axis function during perinatal depression

Abnormal function of the hypothalamic-pituitary-adrenal (HPA) axis is an important pathological finding in pregnant women exhibiting major depressive disorder. They show high levels of cortisol pro-inflammatory cytokines, hypothalamic-pituitary peptide hormones and catecholamines, along with low dehydroepiandrosterone levels in plasma. During pregnancy, the TH2 balance together with the immune system and placental factors play crucial roles in the development of the fetal allograft to full term. These factors, when altered, may generate a persistent dysfunction of the HPA axis that may lead to an overt transfer of cortisol and toxicity to the fetus at the expense of reduced activity of placental 11β-hydroxysteroid dehydrogenase type 2. Epigenetic modifications also may contribute to the dysregulation of the HPA axis. Affective disorders in pregnant women should be taken seriously, and therapies focused on preventing the deleterious effects of stressors should be implemented to promote the welfare of both mother and baby.

Individual differences in gene expression of vasopressin, D2 receptor, POMC and orexin: vulnerability to relapse to heroin-seeking in rats

Individual vulnerability to stress-induced relapse during abstinence from chronic heroin exposure is a key feature of opiate addiction, with limited studies on this topic. Arginine vasopressin (AVP) and its V1b receptor, components of the brain stress responsive systems, play a role in heroin-seeking behavior triggered by foot shock (FS) stress in rats. In this study, we tested whether individual differences in the FS-induced heroin-seeking were associated with alterations of AVP and V1b, as well as other stress responsive systems, including pro-opiomelanocortin (POMC), orexin, plasma ACTH and corticosterone, as well as dopamine D2 receptor (D2) and plasma prolactin. Sprague-Dawley rats were subjected to 3-hour intravenous heroin self-administration (SA) and then tested in extinction, and FS-induced and heroin priming-induced reinstatements. The rats that self-administered heroin were divided into high and low reinstatement responders induced by FS (H-RI; L-RI). Over SA sessions, both the H-RI and L-RI displayed similar active lever responding, heroin infusion and total heroin intake. Compared to the L-RI, however, the H-RI showed greater active lever responses during stress-induced reinstatement, with higher AVP mRNA levels in medial/basolateral amygdala and lower D2 mRNA levels in caudate putamen. However, heroin priming resulted in similar reinstatement in both groups and produced similarly low POMC and high orexin mRNA levels in hypothalamus. Our results indicate that: 1) enhanced amygdalar AVP and reduced striatal D2 expression may be related to individual vulnerability to stress-induced reinstatement of heroin- seeking; and 2) heroin abstinence-associated alterations of hypothalamic orexin and POMC expression may be involved in drug priming-induced heroin-seeking.

Vasopressin Proves Es-sense-tial: Vasopressin and the Modulation of Sensory Processing in Mammals

As mammals develop, they encounter increasing social complexity in the surrounding world. In order to survive, mammals must show appropriate behaviors toward their mates, offspring, and same-sex conspecifics. Although the behavioral effects of the neuropeptide arginine vasopressin (AVP) have been studied in a variety of social contexts, the effects of this neuropeptide on multimodal sensory processing have received less attention. AVP is widely distributed through sensory regions of the brain and has been demonstrated to modulate olfactory, auditory, gustatory, and visual processing. Here, we review the evidence linking AVP to the processing of social stimuli in sensory regions of the brain and explore how sensory processing can shape behavioral responses to these stimuli. In addition, we address the interplay between hormonal and neural AVP in regulating sensory processing of social cues. Because AVP pathways show plasticity during development, early life experiences may shape life-long processing of sensory information. Furthermore, disorders of social behavior such as autism and schizophrenia that have been linked with AVP also have been linked with dysfunctions in sensory processing. Together, these studies suggest that AVP's diversity of effects on social behavior across a variety of mammalian species may result from the effects of this neuropeptide on sensory processing.

The influence of psychological stress on arginine vasopressin concentration in the human plasma and cerebrospinal fluid

Psychological stress is strain affecting the intangible self, caused by problems in adaptation, perception, and emotions. Previous studies have demonstrated that arginine vasopressin (AVP) plays an important role in psychological stress. The goal of present study was to investigate the interaction between AVP release and cardiovascular functions by measuring AVP concentration and recording blood pressure or heart rate during psychological stress in human. The results showed that (1) psychological stress not only increased the systolic blood pressure, diastolic blood pressure and heart rate, but also elevated the cortisol and AVP concentration in both plasma and CSF in a stress level-dependent manner; (2) there was a positive relationship between plasma AVP concentration and systolic blood pressure, diastolic blood pressure, heart rate or plasma cortisol concentration; (3) there was also a positive relationship between AVP concentrations in plasma and CSF AVP. The data suggested that plasma AVP, which might come from the central nervous system, might influence the cardiovascular functions during psychological stress in human.

Alcohol: a stimulant activating brain stress responsive systems with persistent neuroadaptation

Addictive diseases, including addiction to alcohol, opiates or cocaine, pose massive public health costs. Addictions are chronic relapsing brain diseases, caused by drug-induced direct effects and persistent neuroadaptations at the molecular, cellular and behavioral levels. These drug-type specific neuroadapations are mainly contributed by three factors: environment, including stress, the direct reinforcing effects of the drug on the CNS, and genetics. Results from animal models and basic clinical research (including human genetic study) have shown important interactions between the stress responsive systems and alcohol abuse. In this review we will discuss the involvement of the dysregulation of the stress responsive hypothalamic-pituitary-adrenal (HPA) axis in alcohol addiction (Section I). Addictions to specific drugs such as alcohol, psychostimulants and opiates (e.g., heroin) have some common direct or downstream effects on several brain stress-responsive systems, including vasopressin and its receptor system (Section II), POMC and mu opioid receptor system (Section III) and dynorphin and kappa opioid receptor systems (Section IV). Further understanding of these systems, through laboratory-based and translational studies, have the potential to optimize early interventions and to discover new treatment targets for the therapy of alcoholism. This article is part of the Special Issue entitled 'CNS Stimulants'.

A novel experimental strategy to assess the metabolic effects of selective activation of a G(q)-coupled receptor in hepatocytes in vivo

Increased hepatic glucose production is a key pathophysiological feature of type 2 diabetes. Like all other cell types, hepatocytes express many G protein-coupled receptors (GPCRs) that are linked to different functional classes of heterotrimeric G proteins. The important physiological functions mediated by G(s)-coupled hepatic glucagon receptors are well-documented. In contrast, little is known about the in vivo physiological roles of hepatocyte GPCRs that are linked to G proteins of the G(q) family. To address this issue, we established a transgenic mouse line (Hep-Rq mice) that expressed a G(q)-linked designer receptor (Rq) in a hepatocyte-selective fashion. Importantly, Rq could no longer bind endogenous ligands but could be selectively activated by a synthetic drug, clozapine-N-oxide. Clozapine-N-oxide treatment of Hep-Rq mice enabled us to determine the metabolic consequences caused by selective activation of a G(q)-coupled GPCR in hepatocytes in vivo. We found that acute Rq activation in vivo led to pronounced increases in blood glucose levels, resulting from increased rates of glycogen breakdown and gluconeogenesis. We also demonstrated that the expression of the V(1b) vasopressin receptor, a G(q)-coupled receptor expressed by hepatocytes, was drastically increased in livers of ob/ob mice, a mouse model of diabetes. Strikingly, treatment of ob/ob mice with a selective V(1b) receptor antagonist led to reduced glucose excursions in a pyruvate challenge test. Taken together, these findings underscore the importance of G(q)-coupled receptors in regulating hepatic glucose fluxes and suggest novel receptor targets for the treatment of type 2 diabetes.

Central CRF neurons are not created equal: phenotypic differences in CRF-containing neurons of the rat paraventricular hypothalamus and the bed nucleus of the stria terminalis

Corticotrophin-releasing factor (CRF) plays a key role in initiating many of the endocrine, autonomic, and behavioral responses to stress. CRF-containing neurons of the paraventricular nucleus of the hypothalamus (PVN) are classically involved in regulating endocrine function through activation of the stress axis. However, CRF is also thought to play a critical role in mediating anxiety-like responses to environmental stressors, and dysfunction of the CRF system in extra-hypothalamic brain regions, like the bed nucleus of stria terminalis (BNST), has been linked to the etiology of many psychiatric disorders including anxiety and depression. Thus, although CRF neurons of the PVN and BNST share a common neuropeptide phenotype, they may represent two functionally diverse neuronal populations. Here, we employed dual-immunofluorescence, single-cell RT-PCR, and electrophysiological techniques to further examine this question and report that CRF neurons of the PVN and BNST are fundamentally different such that PVN CRF neurons are glutamatergic, whereas BNST CRF neurons are GABAergic. Moreover, these two neuronal populations can be further distinguished based on their electrophysiological properties, their co-expression of peptide neurotransmitters such as oxytocin and arginine-vasopressin, and their cognate receptors. Our results suggest that CRF neurons in the PVN and the BNST would not only differ in their response to local neurotransmitter release, but also in their action on downstream target structures.

Vasotocin analogues with selective natriuretic, kaliuretic and antidiuretic effects in rats

The aim of the present study was an investigation of mechanisms mediating selective effect of vasotocin analogues on water, sodium, and potassium excretion. We tested vasotocin analogues: Mpa(1)-vasotocin (dAVT), Mpa(1)-Arg(4)-vasotocin (dAAVT) and Mpa(1)-DArg(8)-vasotocin (dDAVT). The effects on water, sodium, and potassium transport were evaluated in experiments using normal and water-loaded Wistar rats. It was shown that all tested peptides exerted antidiuretic activity. Vasotocin and dAVT induced natriuresis and kaliuresis in rats. V1a agonist (Phe(2)-Ile(3)-Orn(8)-vasopressin) reproduced the renal effects of dAVT on sodium and potassium excretion but not on water reabsorption. dAAVT, dDAVT and V2 agonist (desmopressin) induced kaliuresis without any effect on sodium excretion. Natriuresis was associated with increase in cGMP excretion, whereas kaliuresis was correlated with rise of cAMP excretion. V1a antagonist (Pmp(1)-Tyr(Me)(2)-vasopressin) significantly reduced the dAVT-stimulated natriuresis and did not influence on urinary potassium excretion. V2 antagonist (Pmp(1)-DIle(2)-Ile(4)-vasopressin) significantly reduced the dAVT- and dAAVT-induced kaliuresis. It is assumed that effects of the nonapeptides on sodium and potassium transport are independent of their antidiuretic activity and mediated by different subtypes of V receptors (the V1a or V1a-like receptor for natriuretic effect and V2 or V2-like one for kaliuretic). In accordance to the data obtained, there is a possibility of selective regulation of renal water reabsorption and urinary sodium and potassium excretion with involvement of neurohypophysial hormones.

Family-based study of AVPR1B association and interaction with stressful life events on depression and anxiety in suicide attempts

The cortisol response to psychosocial stress may become dysregulated in stress-related disorders. It is potentiated by pituitary secretion of adrenocorticotropic hormone (ACTH), which is, in part, regulated by arginine vasopressin receptor-1B (AVPR1B). AVPR1B variants were previously reported to associate with mood and anxiety disorders. This study aims, for the first time, to investigate association of AVPR1B genetic variants with mood and anxiety outcomes in suicidal behavior.Using a family-based study design of 660 complete nuclear family trios with offspring who have made a suicide attempt (SA), we tested the direct association and linkage of AVPR1B single nucleotide polymorphisms (SNPs) with SA, as well as with depression and anxiety in SA. Main findings were the association and linkage of AVPR1B exon 1 SNP rs33990840 and a major 6-SNP haplotype representative of all common AVPR1B-SNPs, on the outcome of high Beck Depression Inventory scores in SA. By contrast, genetic associations with lifetime diagnoses of depression and anxiety in SA or gene-environment interactions between AVPR1B variants and stressful life events (SLEs) were not significant. An exploratory screen of interactions between AVPR1B and CRHR1 (corticotropin-releasing hormone receptor-1), the principal pituitary regulator of ACTH secretion, showed no support for gene-gene interactions on the studied outcomes. The results suggest that AVPR1B genetic variation, eg, non-synonymous SNP rs33990840 mediating putative consequences on ligand binding, has a role in SA etiology characterized by elevated depression symptoms, without involving AVPR1B-moderation of SLEs.

Stress responsiveness of the hypothalamic-pituitary-adrenal axis: age-related features of the vasopressinergic regulation

The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in adaptation to environmental stresses. Parvicellular neurons of the hypothalamic paraventricular nucleus secrete corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) into pituitary portal system; CRH and AVP stimulate adrenocorticotropic hormone (ACTH) release through specific G-protein-coupled membrane receptors on pituitary corticotrophs, CRHR1 for CRH and V1b for AVP; the adrenal gland cortex secretes glucocorticoids in response to ACTH. The glucocorticoids activate specific receptors in brain and peripheral tissues thereby triggering the necessary metabolic, immune, neuromodulatory, and behavioral changes to resist stress. While importance of CRH, as a key hypothalamic factor of HPA axis regulation in basal and stress conditions in most species, is generally recognized, role of AVP remains to be clarified. This review focuses on the role of AVP in the regulation of stress responsiveness of the HPA axis with emphasis on the effects of aging on vasopressinergic regulation of HPA axis stress responsiveness. Under most of the known stressors, AVP is necessary for acute ACTH secretion but in a context-specific manner. The current data on the AVP role in regulation of HPA responsiveness to chronic stress in adulthood are rather contradictory. The importance of the vasopressinergic regulation of the HPA stress responsiveness is greatest during fetal development, in neonatal period, and in the lactating adult. Aging associated with increased variability in several parameters of HPA function including basal state, responsiveness to stressors, and special testing. Reports on the possible role of the AVP/V1b receptor system in the increase of HPA axis hyperactivity with aging are contradictory and requires further research. Many contradictory results may be due to age and species differences in the HPA function of rodents and primates.

Neuroendocrine aspects of Tourette syndrome

There is sparse evidence suggesting the participation of neuroendocrine mechanisms, mainly involving sex and stress steroid hormones, to the pathophysiology of neurodevelopmental disorders such as Tourette syndrome (TS) and obsessive-compulsive disorder (OCD). Patients with TS exhibit a sex-specific variability in gender distribution (male/female ratio=3-4/1) and in its natural history, with a severity peak in the period around puberty. The administration of exogenous androgens may worsen tics in males with TS, whereas drugs counteracting the action of testosterone might show some antitic efficacy. This suggests a higher susceptibility of patients with TS to androgen steroids. There are insufficient data on the regulation of the hypothalamic-pituitary-gonadal (HPG) axis in TS. However, preliminary evidence suggests that a subgroup of women with TS might be more sensitive to the premenstrual trough of estrogen levels. Patients with TS exhibit differences in a number of behavioral, cognitive, and anatomical traits that appear to be sex related. There is a body of evidence supporting, albeit indirectly, the hypothesis of an increased exposure to androgenic steroids during the very early phases of neural development. Animal models in rodents suggest a complex role of gonadal hormones upon the modulation of anxiety-related and stereotyped behaviors during adult life. Patients with TS exhibit an enhanced reactivity of the hypothalamic-pituitary-adrenal axis to external stressors, despite a preserved diurnal cortisol rhythm and a normal restoration of the baseline activity of the axis following the acute stress response. Preliminary evidence suggests the possible implication of oxytocin (OT) in disorders related to the TS spectrum, especially non-tic-related OCD. The injection of OT in the amygdala of rodents was shown to be able to induce hypergrooming, suggesting the possible involvement of this neuropeptide in the pathophysiology of complex, stereotyped behaviors. In contrast, there is anecdotal clinical evidence that tics improve following periods of affectionate touch and sexual intercourse.

Stress-dependent and gender-specific neuroregulatory roles of the apelin receptor in the hypothalamic-pituitary-adrenal axis response to acute stress

The neuropeptide apelin is expressed in hypothalamic paraventricular and supraoptic nuclei and mediates its effects via activation of the apelin receptor (APJ). Evidence suggests a role for apelin and APJ in mediating the neuroendocrine response to stress. To understand the physiological role of APJ in regulation of the hypothalamic-pituitary-adrenal (HPA) axis, we measured ACTH and corticosterone (CORT) plasma levels in male and female mice lacking APJ (APJ knockout, APJ KO) and in wild-type controls, in response to a variety of acute stressors. Exposure to mild restraint, systemic injection of lipopolysaccharide (LPS), insulin-induced hypoglycaemia and forced swim (FS) stressors, elevated plasma ACTH and CORT levels in wild-type mice. Acute mild restraint significantly increased plasma ACTH and CORT to a similar level in APJ KO mice as in wild-type mice. However, an intact APJ was required for a conventional ACTH, but not CORT, response to LPS administration in male mice and to insulin-induced hypoglycaemia in male and female mice. In contrast, APJ KO mice displayed an impaired CORT response to acute FS stress, regardless of gender. These data indicate that APJ has a role in regulation of the HPA axis response to some acute stressors and has a gender-specific function in peripheral immune activation of the HPA axis.

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.

[The syndrome of inappropriate antidiuresis]

The syndrome of inappropriate antidiuresis (SIAD; formerly the syndrome of inappropriate secretion of antidiuretic hormone) is the most frequent cause of hyponatremia. A strong association exists between mortality and hyponatremia, which reflects the severity of the underlying disease. In SIAD, hyponatremia is associated with normovolaemia but the assessment of extracellular volume can be difficult. Clinical features are mainly neurological and can lead to death but mechanisms of adaptation can limit cerebral oedema. The notion of mild asymptomatic hyponatremia was questioned by the observation of subclinical neurocognitive impairment, a greater risk of falls and fractures. Aetiologies are classified into six groups: neurologic disorders, infections mainly cerebral, meningeal and pulmonary, drugs in particular antidepressants, tumors, genetic causes, and idiopathic. Symptomatic acute hyponatremia is a therapeutic emergency that is not specific of SIAD. When hyponatremia is asymptomatic, fluid restriction with salt intake is generally sufficient but urea can be an alternative. In chronic SIAD, there is currently no recommendation. Fluid restriction is not always feasible; urea has proved its efficacy, its good tolerance and its long-term harmlessness. Vaptans have demonstrated their good tolerance and their efficacy on the correction of hyponatremia from SIAD in studies subgroups, for moderate hyponatremia and asymptomatic patients. In the only study having compared vaptans and urea, efficacy and tolerance were similar. Because of the cost difference between vaptans and urea and while waiting for follow-up studies, urea appears at present as the first-line treatment of hyponatremia in SIAD.

Neuropeptide receptor ligands as drugs for psychiatric diseases: the end of the beginning?

The search for novel drugs for treating psychiatric disorders is driven by the growing medical need to improve on the effectiveness and side-effect profile of currently available therapies. Given the wealth of preclinical data supporting the role of neuropeptides in modulating behaviour, pharmaceutical companies have been attempting to target neuropeptide receptors for over two decades. However, clinical studies with synthetic neuropeptide ligands have been unable to confirm the promise predicted by studies in animal models. Here, we analyse preclinical and clinical results for neuropeptide receptor ligands that have been studied in clinical trials for psychiatric diseases, including agents that target the receptors for tachykinins, corticotropin-releasing factor, vasopressin and neurotensin, and suggest new ways to exploit the full potential of these candidate drugs.

Oxytocin and vasopressin agonists and antagonists as research tools and potential therapeutics

We recently reviewed the status of peptide and nonpeptide agonists and antagonists for the V(1a), V(1b) and V(2) receptors for arginine vasopressin (AVP) and the oxytocin receptor for oxytocin (OT). In the present review, we update the status of peptides and nonpeptides as: (i) research tools and (ii) therapeutic agents. We also present our recent findings on the design of fluorescent ligands for V(1b) receptor localisation and for OT receptor dimerisation. We note the exciting discoveries regarding two novel naturally occurring analogues of OT. Recent reports of a selective VP V(1a) agonist and a selective OT agonist point to the continued therapeutic potential of peptides in this field. To date, only two nonpeptides, the V(2) /V(1a) antagonist, conivaptan and the V(2) antagonist tolvaptan have received Food and Drug Administration approval for clinical use. The development of nonpeptide AVP V(1a), V(1b) and V(2) antagonists and OT agonists and antagonists has recently been abandoned by Merck, Sanofi and Pfizer. A promising OT antagonist, Retosiban, developed at Glaxo SmithKline is currently in a Phase II clinical trial for the prevention of premature labour. A number of the nonpeptide ligands that were not successful in clinical trials are proving to be valuable as research tools. Peptide agonists and antagonists continue to be very widely used as research tools in this field. In this regard, we present receptor data on some of the most widely used peptide and nonpeptide ligands, as a guide for their use, especially with regard to receptor selectivity and species differences.

The contributions of oxytocin and vasopressin pathway genes to human behavior

Arginine vasopressin (AVP) and oxytocin (OXT) are social hormones and mediate affiliative behaviors in mammals and as recently demonstrated, also in humans. There is intense interest in how these simple nonapeptides mediate normal and abnormal behavior, especially regarding disorders of the social brain such as autism that are characterized by deficits in social communication and social skills. The current review examines in detail the behavioral genetics of the first level of human AVP-OXT pathway genes including arginine vasopressin 1a receptor (AVPR1a), oxytocin receptor (OXTR), AVP (AVP-neurophysin II [NPII]) and OXT (OXT neurophysin I [NPI]), oxytocinase/vasopressinase (LNPEP), ADP-ribosyl cyclase (CD38) and arginine vasopressin 1b receptor (AVPR1b). Wherever possible we discuss evidence from a variety of research tracks including molecular genetics, imaging genomics, pharmacology and endocrinology that support the conclusions drawn from association studies of social phenotypes and detail how common polymorphisms in AVP-OXT pathway genes contribute to the behavioral hard wiring that enables individual Homo sapiens to interact successfully with conspecifics. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Stress and the HPA axis: role of glucocorticoids in alcohol dependence

Stress has long been suggested to be an important correlate of uncontrolled drinking and relapse. An important hormonal response system to stress-the hypothalamic-pituitary-adrenal (HPA) axis-may be involved in this process, particularly stress hormones known as glucocorticoids and primarily cortisol. The actions of this hormone system normally are tightly regulated to ensure that the body can respond quickly to stressful events and return to a normal state just as rapidly. The main determinants of HPA axis activity are genetic background, early-life environment, and current life stress. Alterations in HPA axis regulation are associated with problematic alcohol use and dependence; however, the nature of this dysregulation appears to vary with respect to stage of alcohol dependence. Much of this research has focused specifically on the role of cortisol in the risk for, development of, and relapse to chronic alcohol use. These studies found that cortisol can interact with the brain's reward system, which may contribute to alcohol's reinforcing effects. Cortisol also can influence a person's cognitive processes, promoting habit-based learning, which may contribute to habit formation and risk of relapse. Finally, cortisol levels during abstinence may be useful clinical indicators of relapse vulnerability in alcohol-dependent people.

G protein-coupled receptors in the hypothalamic paraventricular and supraoptic nuclei--serpentine gateways to neuroendocrine homeostasis

G protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors in the mammalian genome. They are activated by a multitude of different ligands that elicit rapid intracellular responses to regulate cell function. Unsurprisingly, a large proportion of therapeutic agents target these receptors. The paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus are important mediators in homeostatic control. Many modulators of PVN/SON activity, including neurotransmitters and hormones act via GPCRs--in fact over 100 non-chemosensory GPCRs have been detected in either the PVN or SON. This review provides a comprehensive summary of the expression of GPCRs within the PVN/SON, including data from recent transcriptomic studies that potentially expand the repertoire of GPCRs that may have functional roles in these hypothalamic nuclei. We also present some aspects of the regulation and known roles of GPCRs in PVN/SON, which are likely complemented by the activity of 'orphan' GPCRs.

The molecular physiology of CRH neurons

Corticotropin releasing hormone (CRH) is essential for stress adaptation by mediating hypothalamic-pituitary-adrenal (HPA) axis, behavioral and autonomic responses to stress. Activation of CRH neurons depends on neural afferents from the brain stem and limbic system, leading to sequential CRH release and synthesis. CRH transcription is required to restore mRNA and peptide levels, but termination of the response is essential to prevent pathology associated with chronic elevations of CRH and HPA axis activity. Inhibitory feedback mediated by glucocorticoids and intracellular production of the repressor, Inducible Cyclic AMP Early Repressor (ICER), limit the magnitude and duration of CRH neuronal activation. Induction of CRH transcription is mediated by the cyclic AMP/protein kinase A/cyclic AMP responsive element binding protein (CREB)-dependent pathways, and requires cyclic AMP-dependent nuclear translocation of the CREB co-activator, Transducer of Regulated CREB activity (TORC). This article reviews current knowledge on the mechanisms regulating CRH neuron activity.

Oxytocin, vasopressin and estrogen receptor gene expression in relation to social recognition in female mice

Inter- and intra-species differences in social behavior and recognition-related hormones and receptors suggest that different distribution and/or expression patterns may relate to social recognition. We used qRT-PCR to investigate naturally occurring differences in expression of estrogen receptor-alpha (ERα), ER-beta (ERβ), progesterone receptor (PR), oxytocin (OT) and receptor, and vasopressin (AVP) and receptors in proestrous female mice. Following four 5 min exposures to the same two conspecifics, one was replaced with a novel mouse in the final trial (T5). Gene expression was examined in mice showing high (85-100%) and low (40-60%) social recognition scores (i.e., preferential novel mouse investigation in T5) in eight socially-relevant brain regions. Results supported OT and AVP involvement in social recognition, and suggest that in the medial preoptic area, increased OT and AVP mRNA, together with ERα and ERβ gene activation, relate to improved social recognition. Initial social investigation correlated with ERs, PR and OTR in the dorsolateral septum, suggesting that these receptors may modulate social interest without affecting social recognition. Finally, increased lateral amygdala gene activation in the LR mice may be associated with general learning impairments, while decreased lateral amygdala activity may indicate more efficient cognitive mechanisms in the HR mice.

Persistent increase in hypothalamic arginine vasopressin gene expression during protracted withdrawal from chronic escalating-dose cocaine in rodents

Arginine vasopressin (AVP) from the paraventricular nucleus (PVN) of hypothalamus has important roles in regulation of the hypothalamic-pituitary-adrenal (HPA) axis and stress-related behaviors during chronic stress. It is unknown, however, whether AVP in the PVN is involved in the modulation of HPA activity after chronic cocaine exposure. Here, we examined the gene expression alterations of AVP in the hypothalamus, and V1b receptor and pro-opiomelanocortin (POMC) in the anterior pituitary, as well as HPA hormonal changes, in Fischer rats after chronic cocaine and withdrawal, using two different chronic (14-day) 'binge' pattern administration regimens: steady-dose cocaine (SDC, 45 mg/kg/day) and escalating-dose cocaine (EDC, 45 up to 90 mg/kg/day). There was a significant (7-fold) plasma adrenocorticotropic hormone (ACTH) elevation after chronic EDC (but not SDC), coupled with increased V1b and POMC mRNA levels in the anterior pituitary. From acute (1-day) to protracted (14-day) withdrawal from chronic EDC (but not from SDC), we found persistent elevations of both plasma ACTH and corticosterone levels and AVP mRNA levels in the PVN. Selective V1b antagonist SSR149415 (5 mg/kg) attenuated acute withdrawal-induced HPA activation after EDC. To study potential roles of endogenous opioids in modulating the AVP gene, we administered naloxone (1 mg/kg); we found that opioid receptor antagonism increased AVP mRNA levels in cocaine-naive rats, but not in cocaine-withdrawn rats, suggesting less tonic opioid inhibition of PVN AVP neurons after chronic EDC. To assess the effects of cocaine withdrawal on sub-populations of PVN AVP neurons, we utilized AVP-enhanced green fluorescent protein (EGFP) promoter transgenic mice and found that acute withdrawal following chronic EDC increased the number of AVP-EGFP neurons in the parvocellular PVN (pPVN). These results suggest that during protracted withdrawal, enhanced pPVN AVP gene expression is associated with persistent elevations of basal HPA activity; a hyposensitivity of PVN AVP gene expression to naloxone is indicative of reduced opioidergic tone. Our studies indicate that the AVP and its V1b receptor system may be a potential therapeutic target for treating anxiety and depressive symptoms associated with cocaine addiction.

Oxytocin and vasopressin in the human brain: social neuropeptides for translational medicine

The neuropeptides oxytocin (OXT) and arginine vasopressin (AVP) are evolutionarily highly conserved mediators in the regulation of complex social cognition and behaviour. Recent studies have investigated the effects of OXT and AVP on human social interaction, the genetic mechanisms of inter-individual variation in social neuropeptide signalling and the actions of OXT and AVP in the human brain as revealed by neuroimaging. These data have advanced our understanding of the mechanisms by which these neuropeptides contribute to human social behaviour. OXT and AVP are emerging as targets for novel treatment approaches--particularly in synergistic combination with psychotherapy--for mental disorders characterized by social dysfunction, such as autism, social anxiety disorder, borderline personality disorder and schizophrenia.

Genetic influences on social cognition

Human social behavior develops under the influence of genetic, environmental, and cultural factors. Social cognition comprises our ability to understand and respond appropriately to other people's social approaches or responses. The concept embraces self-knowledge and theory of mind, or the ability to think about emotions and behavior from the perspective of another person. The neuropeptides oxytocin (OT) and vasopressin (AVP) are now known to play an important role, affecting individual differences in parenting behavior, social recognition, and affiliative behaviors. The processes of social cognition are also supported by reward circuitry, underpinned by the dopaminergic neurotransmitter system. Reward processes build social relationships, in parenting and pair-bonding, and influence social interactions that require trust, or display altruism. The impact of emotional regulation upon social behavior, including mood and anxiety, is also mediated through the serotonergic system. Variation in activity of serotonergic networks in the brain influences emotional responsivity, including subjective feelings, physiological responses, emotional expressions, and the tendency to become engaged in action as a consequence of a feeling state. Genetic variation in the receptors associated with OT, AVP, dopamine, and serotonin has been intensively studied in humans and animal models. Recent findings are building an increasingly coherent picture of regulatory mechanisms.