Orally active vasopressin V1a receptor antagonist, SRX251, selectively blocks aggressive behavior

Distinct correlations of vasopressin release within the lateral septum and the bed nucleus of the stria terminalis with the display of intermale aggression

Arginine vasopressin (AVP) has been implicated in a wide variety of social behaviors ranging from affiliation to aggression. However, the precise functional involvement of AVP in intermale aggression is still a matter of debate. In fact, very little is known about AVP release patterns within distinct brain regions during the display of intermale aggression and, in turn, the behavioral consequences of such release. We used intracerebral microdialysis to monitor local AVP release within the lateral septum (LS) and the bed nucleus of the stria terminalis (BST) of adult male Wistar rats during the resident-intruder (RI) test. Resident males were cohabitated with a female prior to the RI test to stimulate intermale aggression toward the intruder male. AVP release within the LS correlated positively with intermale aggression. The specific AVP V1a receptor antagonist d(CH(2))(5)Tyr(Me)AVP (10 microg/ml) administered via retrodialysis (3.3 microl/min, 30 min) into the LS of high-aggressive rats prior to the second RI test, prevented an increase in aggression in the second compared with the first RI test as seen in vehicle-treated high-aggressive rats. In contrast to the LS, AVP release within the BST correlated negatively with intermale aggression. Moreover, retrodialysis of synthetic AVP (1 microg/ml) administered into the BST of high-aggressive rats significantly reduced the display of aggression during the second RI test. These data reveal that AVP can both promote and inhibit intermale aggression, depending upon the brain region in which AVP is released. Although challenging the general view that central AVP release enhances intermale aggression in rodents, our data support a model in which AVP coordinates a range of social behaviors by eliciting region-specific effects.

Neuroendocrinology of coping styles: towards understanding the biology of individual variation

Individual variation in behavior and physiology is a widespread and ecologically functional phenomenon in nature in virtually all vertebrate species. Due to domestication of laboratory animals, studies may suffer from a strong selection bias. This paper summarizes behavioral, neuroendocrine and neurobiological studies using the natural individual variation in rats and mice. Individual behavioral characteristics appear to be consistent over time and across situations. The individual variation has at least two dimensions in which the quality of the response to a challenging condition (coping style) is independent from the quantity of that response (stress reactivity). The neurobiology reveals important differences in the homeostatic control of the serotonergic neuron and the neuropeptides vasopressin and oxytocin in relation to coping style. It is argued that a careful exploitation of the broad natural and biologically functional individual variation in behavior and physiology may help in developing better animal models for understanding individual disease vulnerability.

Social dominance in male vasopressin 1b receptor knockout mice

We have previously reported that mice with a targeted disruption of their vasopressin 1b receptor gene, Avpr1b, have mild impairments in social recognition and reduced aggression. The reductions in aggression are limited to social forms of aggression, i.e., maternal and inter-male aggression, while predatory aggression remains unaffected. To further clarify the role of the Avpr1b in the regulation of social behavior we first examined anxiety-like and depression-like behaviors in Avpr1b knockout (Avpr1b -/-) mice. We then went on to test the ability of Avpr1b -/- mice to form dominance hierarchies. No major differences were found between Avpr1b -/- and wildtype mice in anxiety-like behaviors, as measured using an elevated plus maze and an open field test, or depression-like behaviors, as measured using a forced swim test. In the social dominance study we found that Avpr1b -/- mice are able to form dominance hierarchies, though in early hierarchy formation dominant Avpr1b -/- mice display significantly more mounting behavior on Day 1 of testing compared to wildtype controls. Further, non-socially dominant Avpr1b -/- mice spend less time engaged in attack behavior than wildtype controls. These findings suggest that while Avpr1b -/- mice may be able to form dominance hierarchies they appear to employ alternate strategies.

Vasopressin modulates medial prefrontal cortex-amygdala circuitry during emotion processing in humans

The neuropeptide vasopressin is a modulator of mammalian social behavior and emotion, particularly fear, aggression, and anxiety. In humans, the neural circuitry underlying behavioral effects of vasopressin is unknown. Using a double-blind crossover administration of 40 IU of vasopressin or placebo and functional MRI during processing of facial emotions in healthy male volunteers, we show that vasopressin specifically reduces differential activation in the subgenual cingulate cortex. Structural equation modeling of a previously evaluated circuit between amygdala, subgenual cingulate, and supragenual cingulate revealed altered effective connectivity between subgenual and supragenual cingulate under vasopressin. Our data demonstrate an impact of vasopressin on activity and connectivity in the cortical component of a medial prefrontal cortex-amygdala circuit implicated in emotional regulation, providing the first data on the neural basis for the effects of vasopressin on social behavior in humans with potential therapeutic significance for mood and anxiety disorders.

Aggression and anxiety: social context and neurobiological links

Psychopathologies such as anxiety- and depression-related disorders are often characterized by impaired social behaviours including excessive aggression and violence. Excessive aggression and violence likely develop as a consequence of generally disturbed emotional regulation, such as abnormally high or low levels of anxiety. This suggests an overlap between brain circuitries and neurochemical systems regulating aggression and anxiety. In this review, we will discuss different forms of male aggression, rodent models of excessive aggression, and neurobiological mechanisms underlying male aggression in the context of anxiety. We will summarize our attempts to establish an animal model of high and abnormal aggression using rats selected for high (HAB) vs. low (LAB) anxiety-related behaviour. Briefly, male LAB rats and, to a lesser extent, male HAB rats show high and abnormal forms of aggression compared with non-selected (NAB) rats, making them a suitable animal model for studying excessive aggression in the context of extremes in innate anxiety. In addition, we will discuss differences in the activity of the hypothalamic–pituitary–adrenal axis, brain arginine vasopressin, and the serotonin systems, among others, which contribute to the distinct behavioural phenotypes related to aggression and anxiety. Further investigation of the neurobiological systems in animals with distinct anxiety phenotypes might provide valuable information about the link between excessive aggression and disturbed emotional regulation, which is essential for understanding the social and emotional deficits that are characteristic of many human psychiatric disorders.

Influence of dietary sodium on the blood pressure and renal sympathetic nerve activity responses to intracerebroventricular angiotensin II and angiotensin III in anaesthetized rats

The regulation of blood pressure and sympathetic outflow by the brain renin-angiotensin system in animals subjected to raised or lowered dietary Na(+) intake is unclear. This study compared the mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) responses to intracerebroventricular (i.c.v.) infusion of angiotensin II (AngII) and III (AngIII) before and after peripheral V(1) receptor blockade (V(1)B) in alpha-chloralose-urethane-anaesthetized rats fed a low (0.03%, LNa(+)), normal (0.3%, NNa(+)) or high Na(+) diet (3.0%, HNa(+)) from 4 to 11 weeks of age. The rise in MAP 2 min post AngII i.c.v. was greater in HNa(+) (14 +/- 3 mmHg) versus LNa(+) (8 +/- 1 mmHg, P < 0.05) and after AngIII i.c.v. in HNa(+) (14 +/- 3 mmHg) versus NNa(+) (6 +/- 1 mmHg, P < 0.05) and LNa(+) (7 +/- 1 mmHg, P < 0.05). The MAP responses to AngII and AngIII i.c.v. were abolished after V(1)B in LNa(+), but were only attenuated in HNa(+). In NNa(+), V(1)B blunted the MAP responses to AngII and abolished those to AngIII. The MAP remained elevated 30 min after AngII in all groups, but returned to baseline levels 15 min after AngIII in NNa(+) and HNa(+) (P < 0.01). Twenty minutes after i.c.v. AngII, RSNA rose above baseline in HNa(+) (112 +/- 1%), a response not observed in the LNa(+) and NNa(+) groups. Twenty minutes post AngIII i.c.v., RSNA was elevated in both HNa (109 +/- 2%) and NNa(+) (109 +/- 2%). After V(1)B, RSNA rose only in the HNa(+) group 15 min post AngIII infusion (109 +/- 1%). Together, these findings: (1) suggest that HNa(+) intake augments the MAP and RSNA responses to i.c.v. AngII and AngIII; (2) highlight an important role for peripheral V(1) receptors during these responses; and (3) differentiate the effects of AngII and AngIII on blood pressure and RSNA.

Early life stress, the development of aggression and neuroendocrine and neurobiological correlates: what can we learn from animal models?

Early life stress (child and adolescent abuse, neglect and trauma) induces robust alterations in emotional and social functioning resulting in enhanced risk for the development of psychopathologies such as mood and aggressive disorders. Here, an overview is given on recent findings in primate and rodent models of early life stress, demonstrating that chronic deprivation of early maternal care as well as chronic deprivation of early physical interactions with peers are profound risk factors for the development of inappropriate aggressive behaviors. Alterations in the hypothalamic-pituitary-adrenocortical (HPA), vasopressin and serotonin systems and their relevance for the regulation of aggression are discussed. Data suggest that social deprivation-induced inappropriate forms of aggression are associated with high or low HPA axis (re)activity and a generally lower functioning of the serotonin system in adulthood. Moreover, genetic and epigenetic modifications in HPA and serotonin systems influence the outcome of early life stress and may even moderate adverse effects of early social deprivation on aggression. A more comprehensive study of aggression, neuroendocrine, neurobiological and (epi)genetic correlates of early life stress using animal models is necessary to provide a better understanding of the invasive aggressive deficits observed in humans exposed to child maltreatment.

Oxytocin, vasopressin, and human social behavior

There is substantial evidence from animal research indicating a key role of the neuropeptides oxytocin (OT) and arginine vasopressin (AVP) in the regulation of complex social cognition and behavior. As social interaction permeates the whole of human society, and the fundamental ability to form attachment is indispensable for social relationships, studies are beginning to dissect the roles of OT and AVP in human social behavior. New experimental paradigms and technologies in human research allow a more nuanced investigation of the molecular basis of social behavior. In addition, a better understanding of the neurobiology and neurogenetics of human social cognition and behavior has important implications for the current development of novel clinical approaches for mental disorders that are associated with social deficits (e.g., autism spectrum disorder, social anxiety disorder, and borderline personality disorder). This review focuses on our recent knowledge of the behavioral, endocrine, genetic, and neural effects of OT and AVP in humans and provides a synthesis of recent advances made in the effort to implicate the oxytocinergic system in the treatment of psychopathological states.

Depression and antidepressants: molecular and cellular aspects

Clinical depression is viewed as a physical and psychic disease process having a neuropathological basis, although a clear understanding of its ethiopathology is still missing. The observation that depressive symptoms are influenced by pharmacological manipulation of monoamines led to the hypothesis that depression results from reduced availability or functional deficiency of monoaminergic transmitters in some cerebral regions. However, there are limitations to current monoamine theories related to mood disorders. Recently, a growing body of experimental data has showed that other classes of endogenous compounds, such as neuropeptides and amino acids, may play a significant role in the pathophysiology of affective disorders. With the development of neuroscience, neuronal networks and intracellular pathways have been identified and characterized, describing the existence of the interaction between monoamines and receptors in turn able to modulate the expression of intracellular proteins and neurotrophic factors, suggesting that depression/antidepressants may be intermingled with neurogenesis/neurodegenerative processes.

Persistence of reduced aggression in vasopressin 1b receptor knockout mice on a more "wild" background

It has been previously reported that vasopressin 1b receptor knockout (Avpr1b(-/-)) mice have reduced levels of aggressive behavior compared to wildtype littermates. However, as the background of the mice was always a mixture of 129/SvJ and C57BL/6, we wanted to determine if the phenotype persisted when our laboratory line was crossed with a wild-derived sub-species of house mice. To this end, we crossed our Avpr1b(-/-) mice with Mus musculus castaneus, one of the few sub-species that will breed with laboratory strains. Subsequent F(2) offspring were tested in a resident-intruder behavioral test to assess aggressive behavior. We found that even on this more "wild" background, Avpr1b(-/-) mice continued to demonstrate longer attack latencies and fewer attacks in a resident-intruder test than wildtype littermates. These findings are consistent with previous reports of reduced aggressive behavior in Avpr1b(-/-) mice and show that the deficit does persist on a different background strain. Further, these findings confirm the importance of the Avpr1b to normal displays of social forms of aggressive behavior.

Imaging the neural circuitry and chemical control of aggressive motivation

BACKGROUND

With the advent of functional magnetic resonance imaging (fMRI) in awake animals it is possible to resolve patterns of neuronal activity across the entire brain with high spatial and temporal resolution. Synchronized changes in neuronal activity across multiple brain areas can be viewed as functional neuroanatomical circuits coordinating the thoughts, memories and emotions for particular behaviors. To this end, fMRI in conscious rats combined with 3D computational analysis was used to identifying the putative distributed neural circuit involved in aggressive motivation and how this circuit is affected by drugs that block aggressive behavior.

RESULTS

To trigger aggressive motivation, male rats were presented with their female cage mate plus a novel male intruder in the bore of the magnet during image acquisition. As expected, brain areas previously identified as critical in the organization and expression of aggressive behavior were activated, e.g., lateral hypothalamus, medial basal amygdala. Unexpected was the intense activation of the forebrain cortex and anterior thalamic nuclei. Oral administration of a selective vasopressin V1a receptor antagonist SRX251 or the selective serotonin reuptake inhibitor fluoxetine, drugs that block aggressive behavior, both caused a general suppression of the distributed neural circuit involved in aggressive motivation. However, the effect of SRX251, but not fluoxetine, was specific to aggression as brain activation in response to a novel sexually receptive female was unaffected.

CONCLUSION

The putative neural circuit of aggressive motivation identified with fMRI includes neural substrates contributing to emotional expression (i.e. cortical and medial amygdala, BNST, lateral hypothalamus), emotional experience (i.e. hippocampus, forebrain cortex, anterior cingulate, retrosplenial cortex) and the anterior thalamic nuclei that bridge the motor and cognitive components of aggressive responding. Drugs that block vasopressin neurotransmission or enhance serotonin activity suppress activity in this putative neural circuit of aggressive motivation, particularly the anterior thalamic nuclei.

Vasopressin increases locomotion through a V1a receptor in orexin/hypocretin neurons: implications for water homeostasis

Water homeostasis is a critical challenge to survival for land mammals. Mice display increased locomotor activity when dehydrated, a behavior that improves the likelihood of locating new sources of water and simultaneously places additional demands on compromised hydration levels. The neurophysiology underlying this well known behavior has not been previously elucidated. We report that the anti-diuretic hormone arginine-vasopressin (AVP) is involved in this response. AVP and oxytocin directly induced depolarization and an inward current in orexin/hypocretin neurons. AVP-induced activation of orexin neurons was inhibited by a V1a receptor (V1aR)-selective antagonist and was not observed in V1aR knock-out mice, suggesting an involvement of V1aR. Subsequently activation of phospholipase Cbeta triggers an increase in intracellular calcium by both calcium influx through nonselective cation channels and calcium release from calcium stores in orexin neurons. Intracerebroventricular injection of AVP or water deprivation increased locomotor activity in wild-type mice, but not in transgenic mice lacking orexin neurons. V1aR knock-out mice were less active than wild-type mice. These results suggest that the activation of orexin neurons by AVP or oxytocin has an important role in the regulation of spontaneous locomotor activity in mice. This system appears to play a key role in water deprivation-induced hyperlocomotor activity, a response to dehydration that increases the chance of locating water in nature.

Conopressin-T from Conus tulipa reveals an antagonist switch in vasopressin-like peptides

We report the discovery of conopressin-T, a novel bioactive peptide isolated from Conus tulipa venom. Conopressin-T belongs to the vasopressin-like peptide family and displays high sequence homology to the mammalian hormone oxytocin (OT) and to vasotocin, the endogenous vasopressin analogue found in teleost fish, the cone snail's prey. Conopressin-T was found to act as a selective antagonist at the human V 1a receptor. All peptides in this family contain two conserved amino acids within the exocyclic tripeptide (Pro7 and Gly9), which are replaced with Leu7 and Val9 in conopressin-T. Whereas conopressin-T binds only to OT and V 1a receptors, an L7P analogue had increased affinity for the V 1a receptor and weak V2 receptor binding. Surprisingly, replacing Gly9 with Val9 in OT and vasopressin revealed that this position can function as an agonist/antagonist switch at the V 1a receptor. NMR structures of both conopressin-T and L7P analogue revealed a marked difference in the orientation of the exocyclic tripeptide that may serve as templates for the design of novel ligands with enhanced affinity for the V 1a receptor.

Vasopressin: behavioral roles of an "original" neuropeptide

Vasopressin (Avp) is mainly synthesized in the magnocellular cells of the hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) whose axons project to the posterior pituitary. Avp is then released into the blood stream upon appropriate stimulation (e.g., hemorrhage or dehydration) to act at the kidneys and blood vessels. The brain also contains several populations of smaller, parvocellular neurons whose projections remain within the brain. These populations are located within the PVN, bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and suprachiasmatic nucleus (SCN). Since the 1950s, research examining the roles of Avp in the brain and periphery has intensified. The development of specific agonists and antagonists for Avp receptors has allowed for a better elucidation of its contributions to physiology and behavior. Anatomical, pharmacological and transgenic, including "knockout," animal studies have implicated Avp in the regulation of various social behaviors across species. Avp plays a prominent role in the regulation of aggression, generally of facilitating or promoting it. Affiliation and certain aspects of pair-bonding are also influenced by Avp. Memory, one of the first brain functions of Avp that was investigated, has been implicated especially strongly in social recognition. The roles of Avp in stress, anxiety, and depressive states are areas of active exploration. In this review, we concentrate on the scientific progress that has been made in understanding the role of Avp in regulating these and other behaviors across species. We also discuss the implications for human behavior.

Reduced ultrasonic vocalizations in vasopressin 1b knockout mice

The neuropeptides oxytocin and vasopressin have been implicated in rodent social and affiliative behaviors, including social bonding, parental care, social recognition, social memory, vocalizations, territoriality, and aggression, as well as components of human social behaviors and the etiology of autism. Previous investigations of mice with various manipulations of the oxytocin and vasopressin systems reported unusual levels of ultrasonic vocalizations in social settings. We employed a vasopressin 1b receptor (Avpr1b) knockout mouse to evaluate the role of the vasopressin 1b receptor subtype in the emission of ultrasonic vocalizations in adult and infant mice. Avpr1b null mutant female mice emitted fewer ultrasonic vocalizations, and their vocalizations were generally at lower frequencies, during a resident-intruder test. Avpr1b null mutant pups emitted ultrasonic vocalizations similar to heterozygote and wildtype littermates when separated from the nest on postnatal days 3, 6, 9, and 12. However, maternal potentiation of ultrasonic vocalizations in Avpr1b null and heterozygote mutants was absent, when tested at postnatal day 9. These results indicate that Avpr1b null mutant mice are impaired in the modulation of ultrasonic vocalizations within different social contexts at infant and adult ages.

Vasopressin 1a receptor knockout mice have a subtle olfactory deficit but normal aggression

Two receptors for vasopressin (Avp) are expressed in the brain, the Avp 1a receptor (Avpr1a) and the Avp 1b receptor (Avpr1b). To investigate the role of Avpr1a in behaviors in mice more extensively, we generated a line of mice lacking a functional Avpr1a (knockout, Avpr1a(-/-)). We first performed a baseline phenotypic screen of the Avpr1a knockouts followed by a more detailed analysis of their circadian rhythms and olfactory function. When free-running in constant darkness, the Avpr1a(-/-) mice have a longer circadian tau than the wild types. There are also subtle olfactory deficits in Avpr1a(-/-) mice as measured in an olfactory habituation/dishabituation test and in the discrimination of female urine from male urine using an operant testing paradigm. An extensive body of research has shown that manipulation of the Avpr1a alters behavior, including aggression and social recognition. Therefore, we expected profound behavioral deficits in mice lacking the Avpr1a gene. Contrary to our expectations, social aggression, anxiety-like behavior and social recognition are unaffected in this line of Avpr1a knockout mice. These data suggest either that the Avpr1a is not as critical as we thought for social behavior in mice or, more likely, that the neural circuitry underlying aggression and other social behaviors compensates for the life-long loss of the Avpr1a. However, the olfactory deficits observed in the Avpr1a(-/-) mice suggest that Avp and Avpr1a drugs may affect behavior, in part, by modulation of chemosensory systems.

[Some neurological and psychiatric complications of the disorders of the hypothalamo-hypophyseal system]

Connection between the central nervous system and the endocrine system is extremely complex. The hypothalamus serves as a crucial centre for the integration and coordination of autonomic functions by neuronal and hormonal pathways. It plays a central role in the homeostatic regulation of internal physiological conditions. It controls growth and reproduction, stress reactions, and determines rhythmicity, periodicity and timing of physiological processes. Beside its well-known functions, antidiuretic hormone has a role in social behavior as it enhances aggression via vasopressin receptor 1A. Oxitocin is affected in the formation of maternal behavior, and in other social interactions, like the pair bounding, as well as in analgesia and pain modulation. The corticotrop-releasing hormone acts as a neurotransmitter, it has a special role in stress-behavior, anxiety, and depression, and it blocks deep sleeping. Among the neurotransmitters and neuropeptids of the hypothalamus, serotonin, norepinephrine, GABA, cholecystokinin, neuropeptide-Y, Agouti-related protein, alpha-MSH and ghrelin have essential importance in the eating disorders. The levels of leptin and galanin determine whether formation of anabolic or catabolic neurotransmitters should take place. In the thermoregulation the central thermoreceptors play role, and suprachiasmatic nucleus is responsible for circadian rhythm, through "timing genes". The diseases of the hypothalamus cause most frequently bulimia or anorexia, hypersomnia, impotency, and attacks of anxiety. The most common expansive process of the hypothalamus is craniopharyngioma. The lack or diminution of vasopressin causes diabetes insipidus, while inappropriate antidiuretic hormone secretion induces Schwartz-Barter syndrome. Fröhlich-, Kleine-Levin- or Prader-Willi syndromes have characteristic neuropsychiatric features. The main psychiatric symptom of hypopituitarism is a combination of dementia and delirium. The most characteristic neurological sign of pituitary adenoma is the visual field defect. Carpal tunnel syndrome, obstructive sleeping apnoe and headache are typical neurological features in somatotrop adenomas.