Social Circuits: Peptidergic Regulation of Mammalian Social Behavior

The clinical manifestation and treatment of Meniere's Disease from the viewpoint of the water homeostasis of the inner ear

Endolymphatic hydrops, a pathological feature of Ménière's disease, has been experimentally and clinically confirmed to be influenced by the blood circulation of vasopressin (VP). VP is a well-known hormonal regulator of water homeostasis. In addition, VP is influenced by various environmental changes, dehydration, fluctuation of atmospheric pressure, pregnancy, and other factors. Furthermore, VP is a key regulator of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis is a major neuroendocrine system that controls reactions to emotional and physical stresses, as well as the sleep/wake cycle (circadian rhythm). Therefore, VP is susceptible to change via the HPA axis. This review considers possible mechanisms of the formation of endolymphatic hydrops from the perspective of the vasopressin-aquaporin 2 system.

Vasotocin receptor gene genotypes moderate the relationship between cortical thickness and sensory processing

Sensory processing is the process by which the central nervous system gathers, interprets, and regulates sensory stimuli in response to environmental cues. However, our understanding of the genetic factors and neuroanatomical correlations that influence sensory processing is limited. The vasotocin system modulates sensory input responsiveness, making it a potential candidate for further investigation. Additionally, human neuroimaging studies have demonstrated that the ability to modulate sensory stimuli is related to neuroanatomical features such as cortical thickness. Therefore, this study aimed to examine the relationship between functional polymorphisms in vasotocin receptor (VTR) genes, sensory profiles, and neuroanatomical correlations. We used structural magnetic resonance imaging (MRI) and the Adolescent/Adult Sensory Profile (AASP) questionnaire in 98 healthy adult participants to assess sensory processing and identified seven single nucleotide polymorphisms. We found that A-allele carriers of rs1042615 in VTR had higher scores for "sensory sensitivity" and "sensation avoiding". Moreover, higher scores for three AASP subscales were associated with decreased cortical thickness in various regions, including the right precentral, paracentral, and fusiform gyri, as well as bilateral inferior temporal gyri. This study sheds light on the potential role of genetic variations in the VTR in modulating sensory processing and correlation with cortical thickness which has future implications for better understanding sensory abnormalities in neurodevelopmental disorders.

Medial prefrontal cortex oxytocin mitigates epilepsy and cognitive impairments induced by traumatic brain injury through reducing neuroinflammation in mice

Traumatic brain injury (TBI) is a major risk factor to develop epilepsy and cognitive impairments. Neuropeptide oxytocin has been previously evidenced to produce antiepileptic effects. However, the involvement of central oxytocin in TBI-induced epileptic status and cognitive dysfunctions is not fully elucidated. In this study, we aim to investigate the role of oxytocin on a TBI model followed by seizure induction to clarify whether the epilepsy and cognitive deficits could be mitigated by oxytocin. TBI was established by weight drop and epileptic behaviors were induced by pentylenetetrazole (PTZ) injection in mice. Moreover, oxytocin was microinjected into the medial prefrontal cortex (mPFC) to observe the effects on the epilepsy and cognition. The blood-brain barrier (BBB) function and the neuroinflammation were measured by Evans Blue staining and enzyme-linked immunosorbent assays, respectively. Mice exposed to TBI demonstrate increased vulnerability to PTZ-mediated seizures and cognitive disturbances with a decrease in peripheral and brain oxytocin levels. Additionally, TBI reduces oxytocin, disrupts the BBB permeability and triggers neuroinflammation in mPFC in PTZ-treated mice. Intra-mPFC oxytocin simultaneously mitigates epilepsy and cognitive impairments. Finally, oxytocin restores BBB integrity and reduces mPFC inflammation in PTZ-treated TBI mice. These findings showed that intra-mPFC oxytocin suppressed the seizure vulnerability and cognitive deficits in TBI mice. The normalization of BBB integrity and inhibition of neuroinflammation may be involved in the antiepileptic and cognition-improved effects of oxytocin, suggesting that targeting inflammatory procedure in mPFC may decrease the risk to develop epilepsy and cognitive impairments in individuals previously experienced TBI.

Ninjinyoeito improves social behavior disorder in neuropeptide Y deficient zebrafish

Sociability is an essential component of the linkage structure in human and other vertebrate communication. Low sociability is defined as a poor social approach, including social withdrawal and apathy, and is implicated in a variety of psychiatric disorders. Ninjinyoeito (NYT), a traditional Japanese herbal medicine, has been used in the medical field. This study aimed to determine the effect of NYT on low sociality in NPY-KO zebrafish. NPY-KO zebrafish were fed a 3% NYT-supplemented diet for 4 days and subjected to behavioral tests. In the mirror test, NPY-KO zebrafish fed a control diet showed avoidance behavior toward their mirror counterparts. In contrast, the treatment of NPY-KO zebrafish with NYT significantly increased their interaction with their counterparts in the mirror. In addition, a 3-chambers test was conducted to confirm the effect of NYT on the low sociality of NPY-KO zebrafish. NPY-KO zebrafish fed the control diet showed less interaction with fish chambers, while NYT treatment increased the interaction. Phosphorylation of ERK, a marker of neuronal activity, was significantly reduced in the whole brain of NYT-fed NPY-KO zebrafish, compared to the control diet. NYT treatment significantly suppressed hypothalamic-pituitary-adrenal-related genes (gr, pomc, and crh) and sympathetic-adrenal-medullary-related genes (th1, th2, and cck) in NPY-KO zebrafish. NYT administration significantly reduced mRNA levels of gad1b compared to the control diet, suggesting the involvement of GABAergic neurons in NYT-induced improvement of low sociability. Furthermore, the expression of CREB was suppressed when NPY-KO zebrafish were fed NYT. Next, we attempted to identify the effective herb responsible for the NYT-induced improvement of low sociability. NPY-KO zebrafish were fed an experimental diet containing the target herb for 4 days, and its effect on sociability was evaluated using the 3-chambers test. Results showed that Cinnamon Bark and Polygala Root treatments significantly increased time spent in the fish tank area compared to the control diet, while the other 10 herbs did not. We confirmed that these two herbs suppressed the activity of HPA-, SAM-, and GABAergic neurons, as well as NYT-treated zebrafish, accompanied by downregulation of CREB signaling. This study suggests the potential use of NYT as a drug for sociability disorders.

The Role of OXT, OXTR, AVP, and AVPR1a Gene Expression in the Course of Schizophrenia

Schizophrenia is a serious and chronic mental illness, the symptoms of which usually appear for the first time in late adolescence or early adulthood. To date, much research has been conducted on the etiology of schizophrenia; however, it is still not fully understood. Oxytocin and vasopressin as neuromodulators that regulate social and emotional behavior are promising candidates for determining the vulnerability to schizophrenia. The aim of this study was to evaluate the expression of OXT, OXTR, AVP, and AVPR1a genes at the mRNA and protein levels in patients with schizophrenia. Due to the neurodegenerative nature of schizophrenia, the study group was divided into two subgroups, namely, G1 with a diagnosis that was made between 10 and 15 years after the onset of the illness, and G2 with a diagnosis made up to two years after the onset of the illness. Moreover, the relationship between the examined genes and the severity of schizophrenia symptoms, assessed using PANSS (Positive and Negative Syndrome Scale) and CDSS scales (Clinical Depression Scale for Schizophrenia) was evaluated. The analysis of the expression of the studied genes at the mRNA and protein levels showed statistically significant differences in the expression of all the investigated genes. OXT and AVPR1a gene expression at both the mRNA and protein levels were significantly lower in the schizophrenia group, and OXTR and AVP gene expression at both the mRNA and protein levels was higher in the schizophrenia subjects than in the controls. Furthermore, a significant correlation of OXT gene expression at the mRNA and protein levels with the severity of depressive symptoms in schizophrenia as assessed by CDSS was found.

The Biology of Vasopressin

Vasopressins are evolutionarily conserved peptide hormones. Mammalian vasopressin functions systemically as an antidiuretic and regulator of blood and cardiac flow essential for adapting to terrestrial environments. Moreover, vasopressin acts centrally as a neurohormone involved in social and parental behavior and stress response. Vasopressin synthesis in several cell types, storage in intracellular vesicles, and release in response to physiological stimuli are highly regulated and mediated by three distinct G protein coupled receptors. Other receptors may bind or cross-bind vasopressin. Vasopressin is regulated spatially and temporally through transcriptional and post-transcriptional mechanisms, sex, tissue, and cell-specific receptor expression. Anomalies of vasopressin signaling have been observed in polycystic kidney disease, chronic heart failure, and neuropsychiatric conditions. Growing knowledge of the central biological roles of vasopressin has enabled pharmacological advances to treat these conditions by targeting defective systemic or central pathways utilizing specific agonists and antagonists.

Transcutaneous Electrical Acupoint Stimulation in Early Life Changes Synaptic Plasticity and Improves Symptoms in a Valproic Acid-Induced Rat Model of Autism

Autism spectrum disorder (ASD) is a developmental disorder characterized by social behavior deficit in childhood without satisfactory medical intervention. Transcutaneous electrical acupoint stimulation (TEAS) is a noninvasive technique derived from acupuncture and has been shown to have similar therapeutic effects in many diseases. Valproic acid- (VPA-) induced ASD is a known model of ASD in rats. The therapeutic efficacy of TEAS was evaluated in the VPA model of ASD in the present study. The offspring of a VPA-treated rat received TEAS in the early life stage followed by a series of examinations conducted in their adolescence. The results show that following TEAS treatment in early life, the social and cognitive ability in adolescence of the offspring of a VPA rat were significantly improved. In addition, the abnormal pain threshold was significantly corrected. Additional studies demonstrated that the dendritic spine density of the primary sensory cortex was decreased with Golgi staining. Results of the transcriptomic study showed that expression of some transcription factors such as the neurotrophic factor were downregulated in the hypothalamus of the VPA model of ASD. The reduced gene expression was reversed following TEAS. These results suggest that TEAS in the early life stage may mitigate disorders of social and recognition ability and normalize the pain threshold of the ASD rat model. The mechanism involved may be related to improvement of synaptic plasticity.

Linking Social Cognition to Learning and Memory

Many mammals have evolved to be social creatures. In humans, the ability to learn from others' experiences is essential to survival; and from an early age, individuals are surrounded by a social environment that helps them develop a variety of skills, such as walking, talking, and avoiding danger. Similarly, in rodents, behaviors, such as food preference, exploration of novel contexts, and social approach, can be learned through social interaction. Social encounters facilitate new learning and help modify preexisting memories throughout the lifespan of an organism. Moreover, social encounters can help buffer stress or the effects of negative memories, as well as extinguish maladaptive behaviors. Given the importance of such interactions, there has been increasing work studying social learning and applying its concepts in a wide range of fields, including psychotherapy and medical sociology. The process of social learning, including its neural and behavioral mechanisms, has also been a rapidly growing field of interest in neuroscience. However, the term "social learning" has been loosely applied to a variety of psychological phenomena, often without clear definition or delineations. Therefore, this review gives a definition for specific aspects of social learning, provides an overview of previous work at the circuit, systems, and behavioral levels, and finally, introduces new findings on the social modulation of learning. We contextualize such social processes in the brain both through the role of the hippocampus and its capacity to process "social engrams" as well as through the brainwide realization of social experiences. With the integration of new technologies, such as optogenetics, chemogenetics, and calcium imaging, manipulating social engrams will likely offer a novel therapeutic target to enhance the positive buffering effects of social experiences or to inhibit fear-inducing social stimuli in models of anxiety and post-traumatic stress disorder.

Morphofunctional Alterations of the Hypothalamus and Social Behavior in Autism Spectrum Disorders

An accumulating body of evidence indicates a tight relationship between the endocrine system and abnormal social behavior. Two evolutionarily conserved hypothalamic peptides, oxytocin and arginine-vasopressin, because of their extensively documented function in supporting and regulating affiliative and socio-emotional responses, have attracted great interest for their critical implications for autism spectrum disorders (ASD). A large number of controlled trials demonstrated that exogenous oxytocin or arginine-vasopressin administration can mitigate social behavior impairment in ASD. Furthermore, there exists long-standing evidence of severe socioemotional dysfunctions after hypothalamic lesions in animals and humans. However, despite the major role of the hypothalamus for the synthesis and release of oxytocin and vasopressin, and the evident hypothalamic implication in affiliative behavior in animals and humans, a rather small number of neuroimaging studies showed an association between this region and socioemotional responses in ASD. This review aims to provide a critical synthesis of evidences linking alterations of the hypothalamus with impaired social cognition and behavior in ASD by integrating results of both anatomical and functional studies in individuals with ASD as well as in healthy carriers of oxytocin receptor (OXTR) genetic risk variant for ASD. Current findings, although limited, indicate that morphofunctional anomalies are implicated in the pathophysiology of ASD and call for further investigations aiming to elucidate anatomical and functional properties of hypothalamic nuclei underlying atypical socioemotional behavior in ASD.

Vasopressin Differentially Affects Handgrip Force of Expectant Fathers in Reaction to Own and Unknown Infant Faces

The underlying mechanisms of paternal responses to infant signals are poorly understood. Vasopressin has previously been proposed to affect these responses. Using a double-blind, placebo-controlled, within-subject design (N = 25 expectant fathers), we examined the effect of vasopressin administration on the use of excessive handgrip force during exposure to infant crying versus matched control sounds, while participants saw morphed images representing their own infant versus an unknown infant. We found that, compared to placebo, AVP administration elicited more excessive force while viewing an unknown infant image compared to viewing the image representing one’s own infant, while the reverse was true under placebo. The results are discussed in light of vasopressin’s role in parenting and parental protection among human fathers.

Estradiol Drives the Anorexigenic Activity of Proopiomelanocortin Neurons in Female Mice

Energy balance is regulated by anorexigenic proopiomelanocortin (POMC) and orexigenic neuropeptide Y/agouti-related peptide (NPY/AgRP) neurons of the hypothalamic arcuate nucleus. POMC neurons make extensive projections and are thought to release both amino acid and peptide neurotransmitters. However, whether they communicate directly with NPY/AgRP neurons is debated. Initially, using single-cell RT-PCR, we determined that mouse POMC^eGFP neurons express Slc17a6 (Vglut2) and Slc18a2 (Vmat2), but not Slc31a1 (Vgat) mRNA, suggesting glutamate and non-canonical GABA release. Quantitative (q)RT-PCR of POMC^eGFP cells revealed that Vglut2 and Vmat2 expression was significantly increased in E2- versus oil-treated, ovariectomized (OVX) female mice. Since 17β-estradiol (E2) is anorexigenic, we hypothesized that an underlying mechanism is enhancement of POMC signaling. Therefore, we optogenetically stimulated POMC neurons in hypothalamic slices to examine evoked release of neurotransmitters onto NPY/AgRP neurons. Using brief light pulses, we primarily observed glutamatergic currents and, based on the paired pulse ratio (PPR), determined that release probability was higher in E2- versus oil-treated, OVX female, congruent with increased Vlgut2 expression. Moreover, bath perfusion of the Gq-coupled membrane estrogen receptor (ER) agonist STX recapitulated the effects of E2 treatment. In addition, high-frequency (20 Hz) stimulation generated a slow outward current that reversed near E_k+ and was antagonized by naloxone, indicative of β-endorphin release. Furthermore, individual NPY/AgRP neurons were found to express Oprm1, the transcript for μ-opioid receptor, and DAMGO, a selective agonist, elicited an outward current. Therefore, POMC excitability and neurotransmission are enhanced by E2, which would facilitate decreased food consumption through marked inhibition of NPY/AgRP neurons.

Balancing selection maintains polymorphisms at neurogenetic loci in field experiments

Most variation in behavior has a genetic basis, but the processes determining the level of diversity at behavioral loci are largely unknown for natural populations. Expression of arginine vasopressin receptor 1a (Avpr1a) and oxytocin receptor (Oxtr) in specific regions of the brain regulates diverse social and reproductive behaviors in mammals, including humans. That these genes have important fitness consequences and that natural populations contain extensive diversity at these loci implies the action of balancing selection. In Myodes glareolus, Avpr1a and Oxtr each contain a polymorphic microsatellite locus located in their 5' regulatory region (the regulatory region-associated microsatellite, RRAM) that likely regulates gene expression. To test the hypothesis that balancing selection maintains diversity at behavioral loci, we released artificially bred females and males with different RRAM allele lengths into field enclosures that differed in population density. The length of Avpr1a and Oxtr RRAMs was associated with reproductive success, but population density and the sex interacted to determine the optimal genotype. In general, longer Avpr1a RRAMs were more beneficial for males, and shorter RRAMs were more beneficial for females; the opposite was true for Oxtr RRAMs. Moreover, Avpr1a RRAM allele length is correlated with the reproductive success of the sexes during different phases of reproduction; for males, RRAM length correlated with the numbers of newborn offspring, but for females selection was evident on the number of weaned offspring. This report of density-dependence and sexual antagonism acting on loci within the arginine vasopressin-oxytocin pathway explains how genetic diversity at Avpr1a and Oxtr could be maintained in natural populations.

The Role of Hypothalamic Neuropeptides in Neurogenesis and Neuritogenesis

The hypothalamus is a source of neural progenitor cells which give rise to different populations of specialized and differentiated cells during brain development. Newly formed neurons in the hypothalamus can synthesize and release various neuropeptides. Although term neuropeptide recently undergoes redefinition, small-size hypothalamic neuropeptides remain major signaling molecules mediating short- and long-term effects on brain development. They represent important factors in neurite growth and formation of neural circuits. There is evidence suggesting that the newly generated hypothalamic neurons may be involved in regulation of metabolism, energy balance, body weight, and social behavior as well. Here we review recent data on the role of hypothalamic neuropeptides in adult neurogenesis and neuritogenesis with special emphasis on the development of food intake and social behavior related brain circuits.

Impact of Childhood Adversity and Vasopressin receptor 1a Variation on Social Interaction in Adulthood: A Cross-Sectional Study

Background

Arginine vasopressin (AVP) plays a role in social behavior, through receptor AVPR1A. The promoter polymorphism AVPR1A RS3 has been associated with human social behaviors, and with acute response to stress. Here, the relationships between AVPR1A RS3, early-life stressors, and social interaction in adulthood were explored.

Methods

Adult individuals from a Swedish population-based cohort (n = 1871) were assessed for self-reported availability of social integration and social attachment and for experience of childhood adversities. Their DNA samples were genotyped for the microsatellite AVPR1A RS3.

Results

Among males, particularly those homozygous for the long alleles of AVPR1A RS3 were vulnerable to childhood adversity for their social attachment in adulthood. A similar vulnerability to childhood adversity among long allele carriers was found on adulthood social integration, but here both males and females were influenced.

Limitation

Data were self-reported and childhood adversity data were retrospective.

Conclusions

Early-life stress influenced the relationship between AVPR1A genetic variants and social interaction. For social attachment, AVPR1A was of importance in males only. The findings add to previous reports on higher acute vulnerability to stress in persons with long AVPR1A RS3 alleles and increased AVP levels.

Prenatal stress produces social behavior deficits and alters the number of oxytocin and vasopressin neurons in adult rats

The present study investigated the long-lasting effects of prenatal repeated restraint stress on social behavior and anxiety, as well as its repercussions on oxytocin (OT) and vasopressin (VP)-positive neurons of the paraventricular (PVN) and supraoptic (SON) nuclei from stressed pups in adulthood. Female Wistar rats were exposed to restraint stress in the last 7 days of pregnancy. At birth, pups were cross-fostered and assigned to the following groups: prenatally non-stressed offspring raised by prenatally non-stressed mothers (NS:NS), prenatally non-stressed offspring raised by prenatally stressed mothers (S:NS), prenatally stressed offspring raised by prenatally non-stressed mothers (NS:S), prenatally stressed offspring raised by prenatally stressed mothers (S:S). As adults, male prenatally stressed offspring raised both by stressed mothers (S:S group) and non-stressed ones (NS:S group) showed impaired social memory and interaction. In addition, when both adverse conditions coexisted (S:S group), increased anxiety-like behavior and aggressiveness was observed in association with a decrease in the number of OT-positive magnocellular neurons, VP-positive magnocellular and parvocellular neurons of the PVN. The NS:S group exhibited a reduction in the amount of VP-positive magnocellular neurons compared to the S:NS. Thus, the social behavior deficits observed in the S:S and NS:S groups may be only partially associated with these alterations to the peptidergic systems. No changes were shown in the OT and VP cellular composition of the SON nucleus. Nevertheless, it is clear that a special attention should be given to the gestational period, since stressful events during this time may be related to the emergence of behavioral impairments in adulthood.

Neuromodulation by oxytocin and vasopressin

Oxytocin (OT) and vasopressin (VP) are two closely related neuropeptides, widely known for their peripheral hormonal effects. Specific receptors have also been found in the brain, where their neuromodulatory actions have meanwhile been described in a large number of regions. Recently, it has become possible to study their endogenous neuropeptide release with the help of OT/VP promoter-driven expression of fluorescent proteins and light-activated ion channels. In this review, I summarize the neuromodulatory effects of OT and VP in different brain regions by grouping these into different behavioral systems, highlighting their concerted, and at times opposite, effects on different aspects of behavior.

Autism-relevant social abnormalities and cognitive deficits in engrailed-2 knockout mice

ENGRAILED 2 (En2), a homeobox transcription factor, functions as a patterning gene in the early development and connectivity of rodent hindbrain and cerebellum, and regulates neurogenesis and development of monoaminergic pathways. To further understand the neurobiological functions of En2, we conducted neuroanatomical expression profiling of En2 wildtype mice. RTQPCR assays demonstrated that En2 is expressed in adult brain structures including the somatosensory cortex, hippocampus, striatum, thalamus, hypothalamus and brainstem. Human genetic studies indicate that EN2 is associated with autism. To determine the consequences of En2 mutations on mouse behaviors, including outcomes potentially relevant to autism, we conducted comprehensive phenotyping of social, communication, repetitive, and cognitive behaviors. En2 null mutants exhibited robust deficits in reciprocal social interactions as juveniles and adults, and absence of sociability in adults, replicated in two independent cohorts. Fear conditioning and water maze learning were impaired in En2 null mutants. High immobility in the forced swim test, reduced prepulse inhibition, mild motor coordination impairments and reduced grip strength were detected in En2 null mutants. No genotype differences were found on measures of ultrasonic vocalizations in social contexts, and no stereotyped or repetitive behaviors were observed. Developmental milestones, general health, olfactory abilities, exploratory locomotor activity, anxiety-like behaviors and pain responses did not differ across genotypes, indicating that the behavioral abnormalities detected in En2 null mutants were not attributable to physical or procedural confounds. Our findings provide new insight into the role of En2 in complex behaviors and suggest that disturbances in En2 signaling may contribute to neuropsychiatric disorders marked by social and cognitive deficits, including autism spectrum disorders.

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.

Nicotine-induced plasma corticosterone is attenuated by social interactions in male and female adolescent rats

Most smokers begin smoking during adolescence, a period during which social reward is highly influential. Initial exposure to nicotine can produce anxiogenic effects that may be influenced by social context. This study examined play behavior and plasma corticosterone following nicotine administration (0.6 mg/kg, s.c.) in both male and female adolescent (PND39) Sprague-Dawley rats in either isolate or social contexts. In blood samples collected immediately following the 15-min test session, nicotine increased plasma corticosterone relative to saline in both male and female isolate rats, but failed to do so in both males and females placed together in same-sex pairs. Nicotine also attenuated several indices of play behavior including nape attacks, pins and social contact. In isolate rats, nicotine selectively increased locomotor activity in females; however, when administered to social pairs, nicotine decreased locomotion in both sexes. These findings suggest that the presence of a social partner may decrease the initial negative, stress-activating effects of nicotine, perhaps leading to increased nicotine reward.

Adolescent social isolation changes social recognition in adult mice

Rearing in social isolation has profound effects on several aspects of behavior in adult rodents. However, little is known about effects of social stress on social behavior in these animals. In the present study, we examined social recognition in mice of both sexes that were individually housed from 30 days of age until testing at approximately 80 days of age, individually housed from day 30 until day 60, followed by group housing from day 60 until testing at around 80 days of age and in control mice that were group housed throughout experiment. A standard social recognition test was performed with ovariectomized female conspecifics introduced into the home cage of tested mice for 1 min, eight consecutive times with 9 min breaks between tests, and in the ninth test, new, unfamiliar females were introduced. The time spent investigating stimulus mice during each of the nine tests was recorded. Group housed male and female mice showed strong pattern of social learning, whereas mice reared in isolation from day 30 until testing did not show evidence of social recognition. Interestingly, mice reared in isolation from 30 until 60 days of age and then group housed again, also showed reduced ability for social learning in comparison to the controls housed in groups through the entire period. These results therefore show that social isolation has a profound effect on social behavior in mice, and that even isolation for a limited period can produce lasting behavioral deficits.

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

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

Asic3(-/-) female mice with hearing deficit affects social development of pups

Background

Infant crying is an important cue for mothers to respond adequately. Inappropriate response to infant crying can hinder social development in infants. In rodents, the pup-mother interaction largely depends on pup's calls. Mouse pups emit high frequency to ultrasonic vocalization (2–90 kHz) to communicate with their dam for maternal care. However, little is known about how the maternal response to infant crying or pup calls affects social development over the long term.

Methodology/Principal Findings

Here we used mice lacking acid-sensing ion channel 3 (Asic3^−/−) to create a hearing deficit to probe the effect of caregiver hearing on maternal care and adolescent social development. Female Asic3^−/− mice showed elevated hearing thresholds for low to ultrasonic frequency (4–32 kHz) on auditory brain stem response, which thus hindered their response to their pups' wriggling calls and ultrasonic vocalization, as well as their retrieval of pups. In adolescence, pups reared by Asic3^−/− mice showed a social deficit in juvenile social behaviors as compared with those reared by wild-type or heterozygous dams. The social-deficit phenotype in juvenile mice reared by Asic3^−/− mice was associated with the reduced serotonin transmission of the brain. However, Asic3^−/− pups cross-fostered to wild-type dams showed rescued social deficit.

Conclusions/Significance

Inadequate response to pups' calls as a result of ASIC3-dependent hearing loss confers maternal deficits in caregivers and social development deficits in their young.

The mechanism of life-threatening water imbalance in schizophrenia and its relationship to the underlying psychiatric illness

Impaired water excretion was noted to coincide with psychotic exacerbations in the first decades of the past century. In the ensuing decades, life-threatening water intoxication and elevated plasma levels of the antidiuretic hormone, arginine vasopressin (AVP) were reported in a subset of persons with schizophrenia. Subsequent studies demonstrated that the osmotic set point for AVP secretion was transiently reset in these patients by an unknown process and that this was further exacerbated by acute psychosis. More recent studies indicate that the AVP dysfunction is a manifestation of a hippocampal-mediated impairment in the regulation of both AVP and HPA axis responses to psychological, but not other types of, stimuli. Of potential significance, is that schizophrenic patients without water imbalance exhibit the opposite pattern of responses. Preliminary data indicate those with water imbalance also demonstrate a closely linked deficit in central oxytocin activity which may account for their diminished social function. These latter behavioral deficits are perhaps the most disabling and treatment resistant features of schizophrenia, which recent studies suggest, may respond to oxytocin agonists. Together these findings support the view that schizophrenia is a heterogeneous disorder, and provide novel biomarkers and approaches for exploring the pathophysiology and treatment of severe mental illness.

Association between arginine vasopressin 1a receptor (AVPR1a) promoter region polymorphisms and prepulse inhibition

Arginine vasopressin and the arginine vasopressin 1a (AVPR1a) gene contribute to a range of social behaviors both in lower vertebrates and in humans. Human promoter-region microsatellite repeat regions (RS1 and RS3) in the AVPR1a gene region have been associated with autism spectrum disorders, prosocial behavior and social cognition. Prepulse inhibition (PPI) of the startle response to auditory stimuli is a largely autonomic response that resonates with social cognition in both animal models and humans. Reduced PPI has been observed in disorders including schizophrenia that are distinguished by deficits in social skills. In the current investigation association was examined between PPI and the AVPR1a RS1 and RS repeat regions and PPI in a group of 113 nonclinical subjects. Using a robust family-based strategy, association was observed between AVPR1a promoter-region repeat length, especially RS3) and PPI (30 ms: global p=0.04; 60 ms p=0.006; 120 ms p=0.008). Notably, longer RS3 alleles were associated with greater levels of prepulse inhibition. Using a short/long classification scheme for the repeat regions, significant association was also observed between all three PPI intervals (30, 60 and 120 ms) and both RS1 and RS3 polymorphisms (PBAT: FBAT-PC(2) statistic p=0.047). Tests of within-subject effects (SPSS GLM) showed significant sexxRS3 interactions at 30 ms (p=0.045) and 60 ms (p=0.01). Longer alleles, especially in male subjects, are associated with significantly higher PPI response, consistent with a role for the promoter repeat region in partially molding social behavior in both animals and humans. This is the first report in humans demonstrating a role of the AVPR1a gene in contributing to the PPI response to auditory stimuli.

Psychobiology and molecular genetics of resilience

Every individual experiences stressful life events. In some cases acute or chronic stress leads to depression and other psychiatric disorders, but most people are resilient to such effects. Recent research has begun to identify the environmental, genetic, epigenetic and neural mechanisms that underlie resilience, and has shown that resilience is mediated by adaptive changes in several neural circuits involving numerous neurotransmitter and molecular pathways. These changes shape the functioning of the neural circuits that regulate reward, fear, emotion reactivity and social behaviour, which together are thought to mediate successful coping with stress.

The oxytocin receptor (OXTR) contributes to prosocial fund allocations in the dictator game and the social value orientations task

BACKGROUND

Economic games observe social decision making in the laboratory that involves real money payoffs. Previously we have shown that allocation of funds in the Dictator Game (DG), a paradigm that illustrates costly altruistic behavior, is partially determined by promoter-region repeat region variants in the arginine vasopressin 1a receptor gene (AVPR1a). In the current investigation, the gene encoding the related oxytocin receptor (OXTR) was tested for association with the DG and a related paradigm, the Social Values Orientation (SVO) task.

METHODOLOGY/PRINCIPAL FINDINGS

Association (101 male and 102 female students) using a robust-family based test between 15 single tagging SNPs (htSNPs) across the OXTR was demonstrated with both the DG and SVO. Three htSNPs across the gene region showed significant association with both of the two games. The most significant association was observed with rs1042778 (p = 0.001). Haplotype analysis also showed significant associations for both DG and SVO. Following permutation test adjustment, significance was observed for 2-5 locus haplotypes (p<0.05). A second sample of 98 female subjects was subsequently and independently recruited to play the dictator game and was genotyped for the three significant SNPs found in the first sample. The rs1042778 SNP was shown to be significant for the second sample as well (p = 0.004, Fisher's exact test).

CONCLUSIONS

The demonstration that genetic polymorphisms for the OXTR are associated with human prosocial decision making converges with a large body of animal research showing that oxytocin is an important social hormone across vertebrates including Homo sapiens. Individual differences in prosocial behavior have been shown by twin studies to have a substantial genetic basis and the current investigation demonstrates that common variants in the oxytocin receptor gene, an important element of mammalian social circuitry, underlie such individual differences.

Dopaminergic-neuropeptide interactions in the social brain

A well-mapped set of brain regions is dedicated to social cognition. It is responsive to social cues, engaged in moral decision-making and makes predictions about the likely behaviour of other people. Recent studies of affiliation, using animal models, have revealed that specific neurotransmitters and hormones influence the neural circuits of 'the social brain'. There is converging evidence that the interface between the neuropeptides oxytocin and vasopressin and dopaminergic reward circuits is of particular importance. In the context of recent research, we discuss emerging evidence for the impact of these neuropeptides on the regulation of the social brain. We also examine the putative role of allelic variation in candidate genes on individual differences in social cognitive processing and associated social behaviour.

Social memory in mice: disruption with an NMDA antagonist and attenuation with antipsychotic drugs

Social recognition reflects the ability of one animal to learn and remember the identity of another. Animal models of social learning and memory are pertinent to several different CNS diseases involving disruptions in cognition. Moreover, the increased understanding of the basic biology of memory increases the likelihood of discovery of memory-enhancing treatments in these human diseases. In the present study, we investigated the effects of the non-competitive NMDA antagonist ketamine on social recognition in mice across a broad dose range (5-30 mg/kg) and time-course (60 min-7 days). We also tested the ability of two antipsychotic drugs, haloperidol and olanzapine, to block the ketamine effect. Our results show that mice demonstrate social recognition over a several day period, with loss of recognition between 3-7 days. Ketamine disrupts social memory at doses which do not affect task performance. Chronic oral administration of haloperidol or olanzapine attenuates these ketamine-induced effects on social recognition, tending to normalize the memory behavior. The neural mechanisms of these actions are not known, although medial temporal lobe memory systems have been implicated.

Characterization of a novel vasopressin/oxytocin superfamily peptide and its receptor from an ascidian, Ciona intestinalis

The vasopressin (VP)/oxytocin (OT) superfamily peptides are one of the most widely distributed neuropeptides and/or neurohypophysial hormones, but have ever not been characterized from any deuterostome invertebrates including protochordates, ascidians. In the present study, we show the identification of a novel VP/OT superfamily peptide and its receptor in the ascidian, Ciona intestinalis. Intriguingly, the Ciona VP/OT-related peptide (Ci-VP), unlike other 9-amino acid and C-terminally amidated VP/OT superfamily peptides, consists of 13 amino acids and lacks a C-terminal amidation. Mass spectrometry confirmed the presence of the 13-residue Ci-VP in the neural complex. Furthermore, 10 of 14 cysteines are conserved in the neurophysin domain, compared with other VP/OT counterparts. These results revealed that the VP/OT superfamily is conserved in ascidians, but the Ci-VP gene encodes an unprecedented VP/OT-related peptide and neurophysin protein. Ci-VP was also shown to activate its endogenous receptor, Ci-VP-R, at physiological concentrations, confirming the functionality of Ci-VP as an endogenous ligand. The Ci-VP gene was expressed exclusively in neurons of the brain, whereas the Ci-TK-R mRNA was distributed in various tissues including the neural complex, alimentary tract, gonad, and heart. These expression profiles suggest that Ci-VP, like other VP/OT superfamily peptides, serves as a multifunctional neuropeptides. Altogether, our data revealed both evolutionary conservation and specific divergence of the VP/OT superfamily in protochordates. This is the first molecular characterization of a VP/OT superfamily peptide and its cognate receptor from not only ascidians but also deuterostome invertebrates.

From ultrasocial to antisocial: a role for oxytocin in the acute reinforcing effects and long-term adverse consequences of drug use?

Addictive drugs can profoundly affect social behaviour both acutely and in the long-term. Effects range from the artificial sociability imbued by various intoxicating agents to the depressed and socially withdrawn state frequently observed in chronic drug users. Understanding such effects is of great potential significance in addiction neurobiology. In this review we focus on the 'social neuropeptide' oxytocin and its possible role in acute and long-term effects of commonly used drugs. Oxytocin regulates social affiliation and social recognition in many species and modulates anxiety, mood and aggression. Recent evidence suggests that popular party drugs such as MDMA and gamma-hydroxybutyrate (GHB) may preferentially activate brain oxytocin systems to produce their characteristic prosocial and prosexual effects. Oxytocin interacts with the mesolimbic dopamine system to facilitate sexual and social behaviour, and this oxytocin-dopamine interaction may also influence the acquisition and expression of drug-seeking behaviour. An increasing body of evidence from animal models suggests that even brief exposure to drugs such as MDMA, cannabinoids, methamphetamine and phencyclidine can cause long lasting deficits in social behaviour. We discuss preliminary evidence that these adverse effects may reflect long-term neuroadaptations in brain oxytocin systems. Laboratory studies and preliminary clinical studies also indicate that raising brain oxytocin levels may ameliorate acute drug withdrawal symptoms. It is concluded that oxytocin may play an important, yet largely unexplored, role in drug addiction. Greater understanding of this role may ultimately lead to novel therapeutics for addiction that can improve mood and facilitate the recovery of persons with drug use disorders.

Diabetes insipidus and, partially, low anxiety-related behaviour are linked to a SNP-associated vasopressin deficit in LAB mice

Following secretion from the posterior pituitary, the neuropeptide vasopressin (AVP) stimulates the kidney to retain water, and when released centrally it can contribute to anxiety- and depression-like behaviours. We hypothesized that CD1 mice bred for low trait anxiety (LAB) suffer from a deficit in AVP. Both osmotically stimulated peripheral secretion and intra-paraventricular nucleus (PVN) release of AVP were found decreased in LAB animals compared with normal anxiety (NAB) or high anxiety (HAB) controls. Consequently, in addition to their extreme non-anxiety, LAB mice showed signs of central diabetes insipidus (cDI), including increased fluid intake and reduced urine osmolality, as well as a pathological increase in plasma osmolality upon water deprivation. These cDI symptoms were attenuated by administration of a selective AVP V2 receptor agonist. A single nucleotide polymorphism (SNP) in exon 1 (C(+40)T) of the Avp gene of LAB animals causes an amino acid substitution in the signal peptide of the AVP precursor, and is likely to impair processing and trafficking of the precursor, as suggested by reduced axonal transport of AVP from the hypothalamic PVN, finally contributing to cDI symptoms and low trait anxiety. In an F2 panel, this SNP co-segregated with fluid intake and showed a partial contribution to low anxiety-related behaviour, indicated by its co-segregation with time spent on the open arms of the elevated plus-maze in a subset of F2 mice. Thus, the SNP-associated deficit in plasma and central AVP contributes to signs of cDI and, at least partially, to low trait anxiety, both features being typical of LAB animals.

Overview of cellular electrophysiological actions of vasopressin

The nonapeptide vasopressin acts both as a hormone and as a neurotransmitter/neuromodulator. As a hormone, its target organs include kidney, blood vessels, liver, platelets and anterior pituitary. As a neurotransmitter/neuromodulator, vasopressin plays a role in autonomic functions, such as cardiovascular regulation and temperature regulation and is involved in complex behavioral and cognitive functions, such as sexual behavior, pair-bond formation and social recognition. At the neuronal level, vasopressin acts by enhancing membrane excitability and by modulating synaptic transmission. The present review will focus on the electrophysiological effects of vasopressin at the cellular level. A large proportion of the experiments summarized here have been performed in in vitro systems, especially in brain and spinal cord slices of the rat. Vasopressin exerts a powerful excitatory action on motoneurons of young rats and mice. It acts by generating a cationic inward current and/or by reducing a potassium conductance. In addition, vasopressin enhances the inhibitory synaptic input to motoneurons. By virtue of these actions, vasopressin may regulate the functioning of neuronal networks involved in motor control. In the amygdala, vasopressin can directly excite a subpopulation of neurons, whereas oxytocin, a related neuropeptide, can indirectly inhibit these same neurons. In the lateral septum, vasopressin exerts a similar dual action: it excites directly a neuronal subpopulation, but causes indirect inhibition of virtually all lateral septal neurons. The actions of vasopressin in the amygdala and lateral septum may represent at least part of the neuronal substrate by which vasopressin influences fear and anxiety-related behavior and social recognition, respectively. Central vasopressin can modulate cardiovascular parameters by causing excitation of spinal sympathetic preganglionic neurons, by increasing the inhibitory input to cardiac parasympathetic neurons in the nucleus ambiguus, by depressing the excitatory input to parabrachial neurons, or by inhibiting glutamate release at solitary tract axon terminals. By acting in or near the hypothalamic supraoptic nucleus, vasopressin can influence magnocellular neuron activity, suggesting that the peptide may exert some control on its own release at neurohypophyseal axon terminals. The central actions of vasopressin are mainly mediated by receptors of the V(1A) type, although recent studies have also reported the presence of vasopressin V(1B) receptors in the brain. Major unsolved problems are: (i) what is the transduction pathway activated following stimulation of central vasopressin V(1A) receptors? (ii) What is the precise nature of the cation channels and/or potassium channels operated by vasopressin? (iii) Does vasopressin, by virtue of its second messenger(s), interfere with other neurotransmitter/neuromodulator systems? In recent years, information concerning the mechanism of action of vasopressin at the neuronal level and its possible role and function at the whole-animal level has been accumulating. Translation of peptide actions at the cellular level into autonomic, behavioral and cognitive effects requires an intermediate level of integration, i.e. the level of neuronal circuitry. Here, detailed information is lacking. Further progress will probably require the introduction of new techniques, such as targeted in vivo whole-cell recording, large-scale recordings from neuronal ensembles or in vivo imaging in small animals.

The vasopressin system--from antidiuresis to psychopathology

Vasopressin is a neuropeptide with multiple functions. In addition to its predominantly antidiuretic action after peripheral secretion from the posterior pituitary, it seems to fulfill--together with its receptor subtype--all requirements for a neuropeptide system critically involved in higher brain functions, including cognitive abilities and emotionality. Following somatodendritic and axonal release in distinct brain areas, vasopressin acts as a neuromodulator and neurotransmitter in multiple and varying modes of interneuronal communication. Accordingly, changes in vasopressin expression and release patterns may have wide-spread consequences. As shown in mice, rats, voles, and humans, central vasopressin release along a continuum may be beneficial to the individual, serving to adjust physiology and behavior in stressful scenarios, possibly at the potential expense of increasing susceptibility to disease. Indeed, if over-expressed and over-released, it may contribute to hyper-anxiety and depression-like behaviors. A vasopressin deficit, in turn, may cause signs of both diabetes insipidus and total hypo-anxiety. The identification of genetic polymorphisms underlying these phenomena does not only explain individual variation in social memory and emotionality, but also help to characterize potential targets for therapeutic interventions. The capability of both responding to stressful stimuli and mediating genetic polymorphisms makes the vasopressin system a key mediator for converging (i.e., environmentally and genetically driven) behavioral regulation.

How mice cope with stressful social situations

Individuals differ greatly in their psychological responses to chronic stress. As a step toward understanding the neural basis for these individual differences, Krishnan et al. (2007) reveal molecular changes in the brain's reward circuits that make some mice resistant to the effects of social defeat.

Diminished plasma oxytocin in schizophrenic patients with neuroendocrine dysfunction and emotional deficits

Polydipsic hyponatremic schizophrenic patients (PHS) exhibit enhanced plasma arginine vasopressin (pAVP) and hypothalamic pituitary adrenal (HPA) axis responses to stress that appear attributable to anterior hippocampal dysfunction. Neuroanatomic and electrophysiologic studies indicate oxytocin activity in PHS patients should also be affected. Furthermore, oxytocin normally diminishes HPA responses to stress and facilitates cognitive and behavioral functions impaired in schizophrenia, suggesting that diminished oxytocin activity could contribute to this subsets' neuropsychiatric disorder. In the present study, we measured plasma oxytocin levels at intervals before and after stress induction in six polydipsic hyponatremic (PHS), four polydipsic normonatremic (PNS), five nonpolydipsic normonatremic schizophrenic (NNS) patients and seven healthy controls. Most of these subjects also completed studies measuring their medial temporal lobe volumes, their hippocampal-mediated HPA feedback and their ability to discriminate different facial emotions (an oxytocin-sensitive measure which is markedly impaired in schizophrenia). Results demonstrated that 1) plasma oxytocin levels were lower (p=.006) in hyponatremic patients relative to the other three groups, whose levels were similar and did not change. Oxytocin levels across all subjects were 2) inversely correlated with anterior hippocampal (p=.004) (but not posterior hippocampal or amygdala volumes), and 3) directly correlated with the integrity of hippocampal-mediated HPA feedback (p=.039). Finally, 4) oxytocin levels predicted schizophrenic patients' ability to correctly identify facial emotions (p=.004). These preliminary data provide further evidence that neuroendocrine dysfunction in PHS reflects anterior hippocampal pathology and contributes to a characteristic neuropsychiatric syndrome.

FMRFamide-like neuropeptides and mechanosensory touch receptor neurons regulate male sexual turning behavior in Caenorhabditis elegans

Caenorhabditis elegans male mating provides a powerful model to study the relationship between the nervous system, genes, and innate sexual behaviors. Male mating is the most complex behavior exhibited by the nematode C. elegans and involves the steps of response, backing, turning, vulva location, spicule insertion, and sperm transfer. Because neuropeptides are important neural regulators of many complex animal behaviors, we explored the function of the FMRFamide-like neuropeptide (flp) gene family in regulating male copulation. We found that peptidergic signaling mediated by FMRF-amide like neuropeptides (FLPs) FLP-8, FLP-10, FLP-12, and FLP-20 is required for the sensory transduction involved in male turning behavior. flp-8, flp-10, flp-12, and flp-20 mutant males significantly increase repetition of substep(s) of turning behavior compared with wild-type males. Genes controlling neuropeptide processing and secretion in general, including egl-3, egl-21, ida-1, and unc-31, are also required for inhibiting repetitive turning behavior. Neuropeptidergic signaling adjusts the repetitiveness of turning independently of serotonergic modulation of the timing of turning. Surprisingly, the mechanosensitive touch receptor neurons are found to be part of the neural circuitry regulating male turning behavior, indicating the existence of functional dimorphisms in the nervous system with regard to sex-specific behaviors.

Opposite effects of maternal separation on intermale and maternal aggression in C57BL/6 mice: link to hypothalamic vasopressin and oxytocin immunoreactivity

Early life stress, in particular child abuse and neglect, is an acknowledged risk factor for the development of pathological anxiety and aggression. In rodents, 3-h daily maternal separation (MS) during the first 2 weeks of life is an established animal model of early life stress and has repeatedly been shown to increase anxiety and stress responsiveness in adulthood. However, preclinical studies on the effects of postnatal stress on adult aggression are limited. The present study investigated whether MS affects intermale aggression and/or maternal aggression in C57BL/6 mice. In both adult male and virgin female mice, MS elevated anxiety-related behavior as tested on the elevated plus-maze, in the open field and during novel object exploration. The latency to attack an unknown male intruder, as assessed with the resident-intruder test, was significantly longer in MS male mice compared with control male mice. In contrast, the latency to attack a novel male intruder was significantly shorter in MS females compared with control females on days 3 and 5 of lactation. These opposite effects of MS can be explained by the fact that intermale and maternal aggression are two different forms of aggression, and hence, might be modulated by different neurobiological pathways. Indeed, in the paraventricular nucleus of the hypothalamus, MS was found to selectively increase vasopressin immunoreactivity in males, whereas MS selectively decreased oxytocin immunoreactivity in lactating females. In conclusion, MS has long-lasting and differential effects on adult intermale and maternal aggression in C57BL/6 mice. Alterations in hypothalamic vasopressin and oxytocin immunoreactivity may, in part, underlie the opposite effects of MS on intermale and maternal aggression. The MS paradigm represents a promising animal model to reveal underlying mechanisms of aggressive behavioral dysfunctions associated with early life stress.

High ambient temperature increases 3,4-methylenedioxymethamphetamine (MDMA, “ecstasy”)-induced Fos expression in a region-specific manner

3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy") is a popular drug that is often taken under hot conditions at dance clubs. High ambient temperature increases MDMA-induced hyperthermia and recent studies suggest that high temperatures may also enhance the rewarding and prosocial effects of MDMA in rats. The present study investigated whether ambient temperature influences MDMA-induced expression of Fos, a marker of neural activation. Male Wistar rats received either MDMA (10 mg/kg i.p.) or saline, and were placed in test chambers for 2 h at either 19 or 30 degrees C. MDMA caused significant hyperthermia at 30 degrees C and a modest hypothermia at 19 degrees C. The 30 degrees C ambient temperature had little effect on Fos expression in vehicle-treated rats. However MDMA-induced Fos expression was augmented in 15 of 30 brain regions at the high temperature. These regions included (1) sites associated with thermoregulation such as the median preoptic nucleus, dorsomedial hypothalamus and raphe pallidus, (2) the supraoptic nucleus, a region important for osmoregulation and a key mediator of oxytocin and vasopressin release, (3) the medial and central nuclei of the amygdala, important in the regulation of social and emotional behaviors, and (4) the shell of the nucleus accumbens and (anterior) ventral tegmental area, regions associated with the reinforcing effects of MDMA. MDMA-induced Fos expression was unaffected by ambient temperature at many other sites, and was diminished at high temperature at one site (the islands of Calleja), suggesting that the effect of temperature on MDMA-induced Fos expression was not a general pharmacokinetic effect. Overall, these results indicate that high temperatures accentuate key neural effects of MDMA and this may help explain the widespread use of the drug under hot conditions at dance parties as well as the more hazardous nature of MDMA taken under such conditions.

The hypothalamic-pituitary-adrenal axis response to stress in mice lacking functional vasopressin V1b receptors

The role of arginine vasopressin (Avp) as an ACTH secretagogue is mediated by the Avp 1b receptor (Avpr1b) found on anterior pituitary corticotropes. Avp also potentiates the actions of CRH (Crh) and appears to be an important mediator of the hypothalamic-pituitary-adrenal axis response to chronic stress. To investigate the role of Avp in the hypothalamic-pituitary-adrenal axis response to stress, we measured plasma ACTH and corticosterone (CORT) levels in Avpr1b knockout (KO) mice and wild-type controls in response to two acute (restraint and insulin administration) and one form of chronic (daily restraint for 14 d) stress. No significant difference was found in the basal plasma levels of ACTH and CORT between the two genotypes. Acute restraint (30 min) increased plasma ACTH and CORT to a similar level in both the Avpr1b mutant and wild-type mice. In contrast, plasma ACTH and CORT levels induced by hypoglycemia were significantly decreased in the Avpr1b KO mice when compared with wild-type littermates. There was no difference in the ACTH response to acute and chronic restraint in wild-type mice. In the Avpr1b KO group subjected to 14 sessions of daily restraint, plasma ACTH was decreased when compared with wild-type mice. On the other hand, the CORT elevations induced by restraint did not adapt in the Avpr1b KO or wild-type mice. The data suggest that the Avpr1b is required for the normal pituitary and adrenal response to some acute stressful stimuli and is necessary only for a normal ACTH response during chronic stress.

Effects of intracerebroventricular infusions of arginine vasopressin in sheep

In sheep, neither the in vivo effect of vasopressin administered by a method other than systemic infusion nor the central effects on behavior from the perspective of stress regulation has been fully elucidated in an intact animal. We examined changes in behavioral, adrenocorticotropic, and autonomic nervous functions after intracerebroventricular infusions of arginine vasopressin (AVP) to elucidate its central role. Intracerebroventricular infusions of AVP (0, 0.12, 1.2 and 12 microg/500 microl/30 min) evoked a dose-related increase in plasma cortisol concentration. There were significant treatment-related effects on the total duration of sham-chewing (Friedman's test, X2=12.75, p=.0052), on the total duration of bar-biting (Friedman's test, X2=15.0, p=.0018), and on the total duration of rubbing (Friedman's test, X2=12.0, p=.0074). AVP 12 microg treatment induced a greater degree of sham-chewing and bar-biting than the other three treatments did (Nemenyi multiple comparisons: p<0.1). These findings indicate, together with our previous findings, that AVP has the same corticotropic potential as corticotropin-releasing hormone infused intracerebroventricularly in equal molar concentrations. Although the degree to which central stress signaling pathways are involved in these responses remains speculative, the relationships between stereotypies and central AVP are of particular interest.

Candidate genes of anxiety-related behavior in HAB/LAB rats and mice: Focus on vasopressin and glyoxalase-I

Two animal models of trait anxiety, HAB/LAB rats and mice, are described, representing inborn extremes in anxiety-related behavior. The comprehensive phenotypical characterization included basal behavioral features, stress-coping strategies and neuroendocrine responses upon stressor exposure with HAB animals being hyper-anxious, preferring passive coping, emitting more stressor-induced ultrasonic vocalization calls and showing typical peculiarities of the hypothalamic-pituitary-adrenocortical axis and line-specific patterns of Fos expression in the brain indicative of differential neuronal activation. In most cases, unselected Wistar rats and CD1 mice, respectively, displayed intermediate behaviors. In both HAB/LAB rats and mice, the behavioral phenotype has been found to be significantly correlated with the expression of the neuropeptide arginine vasopressin (AVP) at the level of the hypothalamic paraventricular nucleus (PVN). Additional receptor antagonist approaches in HABs confirmed that intra-PVN release of AVP is likely to contribute to hyper-anxiety and depression-like behavior. As shown exemplarily in HAB rats and LAB mice, single nucleotide polymorphisms (SNPs) in regulatory structures of the AVP gene underlie AVP-mediated phenotypic phenomena; in HAB rats, a SNP in the promoter of the AVP gene leads to reduced binding of the transcriptional repressor CBF-A, thus causing AVP overexpression and overrelease. Conversely, in LAB mice, a SNP in the AVP gene seems to cause an amino acid exchange in the signal peptide, presumably leading to a deficit in bioavailable AVP likely to underlie the total hypo-anxiety of LAB mice in combination with signs of central diabetes insipidus. Another feature of LAB mice is overexpression of glyoxalase-I. The functional characterization of this enzyme will determine its involvement in anxiety-related behavior beyond that of a reliable biomarker. The further identification of quantitative trait loci, candidate genes (and their products) and SNPs will not only help to explain inter-individual variation in emotional behavior, but will also reveal novel targets for anxiolytic and antidepressive interventions.

Visually guided whole cell patch clamp of mouse supraoptic nucleus neurons in cultured and acute conditions

Recent advances in neuronal culturing techniques have supplied a new set of tools for studying neural tissue, providing effective means to study molecular aspects of regulatory elements in the supraoptic nucleus of the hypothalamus (SON). To combine molecular biology techniques with electrophysiological recording, we modified an organotypic culture protocol to permit transfection and whole cell patch-clamp recordings from SON cells. Neonatal mouse brain coronal sections containing the SON were dissected out, placed on a filter insert in culture medium, and incubated for at least 4 days to allow attachment to the insert. The SON was identifiable using gross anatomical landmarks, which remained intact throughout the culturing period. Immunohistochemical staining identified both vasopressinergic and oxytocinergic cells present in the cultures, typically appearing in well-defined clusters. Whole cell recordings from these cultures demonstrated that certain properties of the neonatal mouse SON were comparable to adult mouse magnocellular neurons. SON neurons in both neonatal cultures and acute adult slices showed similar sustained outward rectification above -60 mV and action potential broadening during evoked activity. Membrane potential, input resistance, and rapidly inactivating potassium current density (IA) were reduced in the cultures, whereas whole cell capacitance and spontaneous synaptic excitation were increased, perhaps reflecting developmental changes in cell physiology that warrant further study. The use of the outlined organotypic culturing procedures will allow the study of such electrophysiological properties of mouse SON using whole cell patch-clamp, in addition to various molecular, techniques that require longer incubation times.