Oxytocin receptor disruption in Avil-expressing cells results in blunted sociability and increased inter-male aggression.

Social behaviors are foundational to society and quality of life while social behavior extremes are core symptoms in a variety of psychopathologies and developmental disabilities. Oxytocin (OXT) is a neuroactive hormone that regulates social behaviors through its receptor (OXTR), with all previously identified social behavior effects attributed to the central nervous system, which has developmental origins in the neural tube. However, OXTR are also present in neural crest-derived tissue including sensory ganglia of the peripheral nervous system. Avil encodes for the actin-binding protein ADVILLIN, is expressed in neural crest-derived cells, and was therefore used as a target in this study to knock out OXTR expression in neural-crest derived cells. Here, we tested if OXTRs specifically expressed in Avil positive neural crest-derived cells are necessary for species-typical adult social behaviors using a Cre-LoxP strategy. Genetically modified male and female mice lacking OXTR in Avil expressing cells (OXTRAvil KO) were tested for sociability and preference for social novelty. Males were also tested for resident intruder aggression. OXTRAvil KO males and females had reduced sociability compared to OXTRAvil WT controls. Additionally, OXTRAvil KO males had increased aggressive behaviors compared to controls. These data indicate that OXTRs in cells of neural crest origin are important regulators of typical social behaviors in C57BL/6J adult male and female mice and point to needed directions of future research.

Oxytocin-MCH circuit regulates monosynaptic inputs to MCH neurons and modulates social recognition memory.

Oxytocin regulates social behaviors and has been linked to the etiology of autism and schizophrenia. Oxytocin and another hypothalamic neuropeptide, melanin concentrating hormone (MCH), share several physiological actions such as emotion, social behavior and recognition, maternal care, sexual behavior and stress, which suggests that these two systems may interact, however, how they would do it is not known. Here, we study the interactions between the oxytocin and MCH systems in behaviors related to autism and schizophrenia. Specifically, we examined the synaptic inputs of the oxytocin-to the MCH neurons. We selectively deleted oxytocin receptors (OXTR) from MCH neurons (OXTR-cKO mice) using a Cre/loxP recombinase-technology, and used rabies-mediated circuit mapping technique to reveal the changes in the direct monosynaptic inputs to MCH neurons. We examined the behavioral responses of OXTR-cKO mice. Deletion of OXTR from MCH neurons induced a significant decrease in the primary inputs received by MCH neurons from the paraventricular nucleus and the lateral hypothalamus, and from the nucleus accumbens and ventral tegmental area. While OXTR-cKO mice exhibited similar social interactions as control mice, they displayed significantly impaired social recognition memory and increased stereotypic behavior. Our study identifies a selective role for the oxytocin-MCH pathway in social recognition memory and stereotyped behavior that are relevant to psychiatric disorders such as schizophrenia and autism, and warrant further investigation of this circuit to uncover potential benefit of targeting the oxytocin-MCH circuit as a novel therapeutic target for treatment of social recognition deficits in these two disorders.

Oxytocin Protects against Stress-Induced Cell Death in Murine Pancreatic ß-Cells.

Oxytocin (Oxt) is a key neuropeptide that regulates maternal behaviors as well as social behaviors in mammals. Interestingly, recent studies have shown that the impairment of Oxt signaling is associated with the disturbance of metabolic homeostasis, resulting in obesity and diabetes. However, the molecular mechanism by which Oxt signaling controls metabolic responses is largely unknown. Here, we report that Oxt signaling attenuates the death of pancreatic beta cells in islets exposed to cytotoxic stresses. The protective effect of Oxt was diminished in islets isolated from oxytocin receptor knockout (Oxtr(-/-)) mice. Oxtr(-/-) mice developed normally, but exhibited impaired insulin secretion and showed glucose intolerance under a high-fat diet. Mechanistically, the deficiency of Oxtr impaired MAPK/ERK-CREB signaling, which exaggerated the endoplasmic reticulum stress response and ultimately increased the death of beta cells in pancreatic islets under stressed conditions. These results reveal that Oxt protects pancreatic beta cells against death caused by metabolic stress, and Oxt signaling may be a potential therapeutic target.

[Oxytocin in the treatment of the social deficits associated to autism spectrum disorders]. / La oxitocina en el tratamiento de los déficits sociales asociados a los trastornos del espectro autista.

INTRODUCTION: The recent involvement of oxytocin in social behavior of animals and humans has motivated the study of its effects on the social behavior of individuals with autism spectrum disorders (ASD). AIMS: To review the current state of oxytocin studies concerning its therapeutic potential in treating social deficits of the ASD population, and to establish likely future directions to be taken by the studies in this field. DEVELOPMENT: Some studies have linked oxytocin to the pathophysiology of autistic disorders. Most studies that have administered oxytocin (mainly with intranasal administration of 24 IU) to ASD subjects have shown significant improvements in their social performance with acceptable safety parameters. However, there is controversial data as the outcome measures are widely dispersed, the samples are reduced and heterogeneous, and the treatment durations are different. The limitations related to the lack of understanding of the oxytocin's action mechanisms and the symptomatic heterogeneity of ASD are hampering progress towards the establishment of oxytocin as a treatment of ASD patients. Recent studies suggest the investigation of the combination of the oxytocin treatment with social skills training, and the enhancement of endogenous secretion of oxytocin. CONCLUSION: The effects of oxytocin are promising regarding the treatment of social deficits in ASD individuals. Future studies should aim to facilitate understanding of the oxytocin's ways of action and to establish the optimal treatment regime.

TITLE: La oxitocina en el tratamiento de los deficits sociales asociados a los trastornos del espectro autista.Introduccion. La implicacion de la oxitocina en la conducta social de animales y humanos ha llevado a estudiar los efectos de su administracion en el comportamiento y cognicion social de pacientes con trastornos del espectro autista (TEA). Objetivos. Revisar la investigacion sobre el potencial terapeutico de la oxitocina en el tratamiento de los deficits sociales de la poblacion con TEA y discutir las probables direcciones futuras de los estudios en este campo. Desarrollo. Diversos trabajos han relacionado la oxitocina con la fisiopatologia de los TEA. La mayoria de los estudios que han administrado oxitocina, generalmente por via intranasal (24 UI), ha observado mejoras significativas en el rendimiento social, sin detectar efectos secundarios destacables. No obstante, existen datos contradictorios debido a la heterogeneidad de las variables analizadas por los diferentes estudios, al uso de muestras heterogeneas y pequeñas o a la diferente duracion de los tratamientos. Las limitaciones relacionadas con la falta de comprension de los mecanismos de accion de la oxitocina y la diversidad sintomatologica de los TEA dificultan el establecimiento de este peptido como tratamiento de los pacientes autistas. Estudios recientes destacan la conveniencia de explorar el efecto de la combinacion del tratamiento de oxitocina con programas conductuales de intervencion en habilidades sociales, asi como la potenciacion de la secrecion endogena de oxitocina. Conclusiones. Los efectos de la administracion de oxitocina resultan prometedores en relacion con el tratamiento de los deficits sociales en individuos con TEA. Estudios futuros deberian facilitar la comprension de las vias de accion de la oxitocina y el establecimiento de pautas optimas de tratamiento.

RNAi knockdown of oxytocin receptor in the nucleus accumbens inhibits social attachment and parental care in monogamous female prairie voles.

Oxytocin modulates many aspects of social cognition and behaviors, including maternal nurturing, social recognition and bonding. Natural variation in oxytocin receptor (OXTR) density in the nucleus accumbens (NAcc) is associated with variation in alloparental behavior, and artificially enhancing OXTR expression in the NAcc enhances alloparental behavior and pair bonding in socially monogamous prairie voles. Furthermore, infusion of an OXTR antagonist into the NAcc inhibits alloparental behavior and partner preference formation. However, antagonists can promiscuously interact with other neuropeptide receptors. To directly examine the role of OXTR signaling in social bonding, we used RNA interference to selectively knockdown, but not eliminate, OXTR in the NAcc of female prairie voles and examined the impact on social behaviors. Using an adeno-associated viral vector expressing a short hairpin RNA (shRNA) targeting Oxtr mRNA, we reduced accumbal OXTR density in female prairie voles from juvenile age through adulthood. Females receiving the shRNA vector displayed a significant reduction in alloparental behavior and disrupted partner preference formation. These are the first direct demonstrations that OXTR plays a critical role in alloparental behavior and adult social attachment, and suggest that natural variation in OXTR expression in this region alone can create variation in social behavior.

Raphe serotonin neuron-specific oxytocin receptor knockout reduces aggression without affecting anxiety-like behavior in male mice only.

Serotonin and oxytocin influence aggressive and anxiety-like behaviors, though it is unclear how the two may interact. That the oxytocin receptor is expressed in the serotonergic raphe nuclei suggests a mechanism by which the two neurotransmitters may cooperatively influence behavior. We hypothesized that oxytocin acts on raphe neurons to influence serotonergically mediated anxiety-like, aggressive and parental care behaviors. We eliminated expression of the oxytocin receptor in raphe neurons by crossing mice expressing Cre recombinase under control of the serotonin transporter promoter (Slc6a4) with our conditional oxytocin receptor knockout line. The knockout mice generated by this cross are normal across a range of behavioral measures: there are no effects for either sex on locomotion in an open-field, olfactory habituation/dishabituation or, surprisingly, anxiety-like behaviors in the elevated O and plus mazes. There was a profound deficit in male aggression: only one of 11 raphe oxytocin receptor knockouts showed any aggressive behavior, compared to 8 of 11 wildtypes. In contrast, female knockouts displayed no deficits in maternal behavior or aggression. Our results show that oxytocin, via its effects on raphe neurons, is a key regulator of resident-intruder aggression in males but not maternal aggression. Furthermore, this reduction in male aggression is quite different from the effects reported previously after forebrain or total elimination of oxytocin receptors. Finally, we conclude that when constitutively eliminated, oxytocin receptors expressed by serotonin cells do not contribute to baseline anxiety-like behaviors or maternal care.

Osteoblast regulation via ligand-activated nuclear trafficking of the oxytocin receptor.

We report that oxytocin (Oxt) receptors (Oxtrs), on stimulation by the ligand Oxt, translocate into the nucleus of osteoblasts, implicating this process in the action of Oxt on osteoblast maturation. Sequential immunocytochemistry of intact cells or isolated nucleoplasts stripped of the outer nuclear membrane showed progressive nuclear localization of the Oxtr; this nuclear translocation was confirmed by monitoring the movement of Oxtr-EGFP as well as by immunogold labeling. Nuclear Oxtr localization was conclusively shown by Western immunoblotting and MS of nuclear lysate proteins. We found that the passage of Oxtrs into the nucleus was facilitated by successive interactions with ß-arrestins (Arrbs), the small GTPase Rab5, importin-ß (Kpnb1), and transportin-1 (Tnpo1). siRNA-mediated knockdown of Arrb1, Arrb2, or Tnpo1 abrogated Oxt-induced expression of the osteoblast differentiation genes osterix (Sp7), Atf4, bone sialoprotein (Ibsp), and osteocalcin (Bglap) without affecting Erk phosphorylation. Likewise and again, without affecting pErk, inhibiting Arrb recruitment by mutating Ser rich clusters of the nuclear localization signal to Ala abolished nuclear import and Oxtr-induced gene expression. These studies define a previously unidentified mechanism for Oxtr action on bone and open possibilities for direct transcriptional modulation by nuclear G protein-coupled receptors.

Impairments in the initiation of maternal behavior in oxytocin receptor knockout mice.

Oxytocin (Oxt) acting through its single receptor subtype, the Oxtr, is important for the coordination of physiology and behavior associated with parturition and maternal care. Knockout mouse models have been helpful in exploring the contributions of Oxt to maternal behavior, including total body Oxt knockout (Oxt -/-) mice, forebrain conditional Oxtr knockout (Oxtr FB/FB) mice, and total body Oxtr knockout (Oxtr -/-) mice. Since Oxtr -/- mice are unable to lactate, maternal behavior has only been examined in virgin females, or in dams within a few hours of parturition, and there have been no studies that have examined their anxiety-like and depression-like behavior following parturition. To improve our understanding of how the absence of Oxt signaling affects maternal behavior, mood and anxiety, we designed a study using Oxtr -/- mice that separated nursing behavior from other aspects of maternal care, such as licking and grooming by thelectomizing (i.e. removing the nipples) of Oxtr +/+ mice and sham-thelectomizing Oxtr -/- mice, and pairing both genotypes with a wet nurse. We then measured pup abandonment, maternal behavior, and postpartum anxiety-like and depression-like behaviors. We hypothesized that genetic disruption of the Oxtr would impact maternal care, mood and anxiety. Specifically, we predicted that Oxtr -/- dams would have impaired maternal care and increased anxiety-like and depression-like behaviors in the postpartum period. We found that Oxtr -/- dams had significantly higher levels of pup abandonment compared to controls, which is consistent with previous work in Oxtr FB/FB mice. Interestingly, Oxtr -/- dams that initiated maternal care did not differ from wildtype controls in measures of maternal behavior. We also did not find any evidence of altered anxiety-like or depressive-like behavior in the postpartum period of Oxtr -/- dams. Thus, our data suggest that Oxt lowers the threshold for the initiation of maternal behavior.

Social reward requires coordinated activity of nucleus accumbens oxytocin and serotonin.

Social behaviours in species as diverse as honey bees and humans promote group survival but often come at some cost to the individual. Although reinforcement of adaptive social interactions is ostensibly required for the evolutionary persistence of these behaviours, the neural mechanisms by which social reward is encoded by the brain are largely unknown. Here we demonstrate that in mice oxytocin acts as a social reinforcement signal within the nucleus accumbens core, where it elicits a presynaptically expressed long-term depression of excitatory synaptic transmission in medium spiny neurons. Although the nucleus accumbens receives oxytocin-receptor-containing inputs from several brain regions, genetic deletion of these receptors specifically from dorsal raphe nucleus, which provides serotonergic (5-hydroxytryptamine; 5-HT) innervation to the nucleus accumbens, abolishes the reinforcing properties of social interaction. Furthermore, oxytocin-induced synaptic plasticity requires activation of nucleus accumbens 5-HT1B receptors, the blockade of which prevents social reward. These results demonstrate that the rewarding properties of social interaction in mice require the coordinated activity of oxytocin and 5-HT in the nucleus accumbens, a mechanistic insight with implications for understanding the pathogenesis of social dysfunction in neuropsychiatric disorders such as autism.

Antidepressant-like effect of sildenafil through oxytocin-dependent cyclic AMP response element-binding protein phosphorylation.

Oxytocin (OT) levels in plasma increase during sexual response and are significantly lower in patients with depression. A drug for the treatment of sexual dysfunction, sildenafil, enhances the electrically evoked release of OT from the posterior pituitary. In this study, we showed that sildenafil had an antidepressant-like effect through activation of an OT signaling pathway. Application of sildenafil reduced depression-related behavior in male mice. The antidepressant-like effect was blocked by an OT receptor (OTR) antagonist and was absent in OTR knockout (KO) mice. Sildenafil increased the phosphorylation of cAMP response element-binding protein (CREB) in the hippocampus. The OTR antagonist inhibited sildenafil-induced CREB phosphorylation and sildenafil had no effect on CREB phosphorylation in OTR KO mice. These results suggest sildenafil to have an antidepressant-like effect through the activation of OT signaling and to be a promising drug for the treatment of depression.

Oxytocin signaling in mouse taste buds.

BACKGROUND: The neuropeptide, oxytocin (OXT), acts on brain circuits to inhibit food intake. Mutant mice lacking OXT (OXT knockout) overconsume salty and sweet (i.e. sucrose, saccharin) solutions. We asked if OXT might also act on taste buds via its receptor, OXTR. METHODOLOGY/PRINCIPAL FINDINGS: Using RT-PCR, we detected the expression of OXTR in taste buds throughout the oral cavity, but not in adjacent non-taste lingual epithelium. By immunostaining tissues from OXTR-YFP knock-in mice, we found that OXTR is expressed in a subset of Glial-like (Type I) taste cells, and also in cells on the periphery of taste buds. Single-cell RT-PCR confirmed this cell-type assignment. Using Ca2+ imaging, we observed that physiologically appropriate concentrations of OXT evoked [Ca2+]i mobilization in a subset of taste cells (EC50 approximately 33 nM). OXT-evoked responses were significantly inhibited by the OXTR antagonist, L-371,257. Isolated OXT-responsive taste cells were neither Receptor (Type II) nor Presynaptic (Type III) cells, consistent with our immunofluorescence observations. We also investigated the source of OXT peptide that may act on taste cells. Both RT-PCR and immunostaining suggest that the OXT peptide is not produced in taste buds or in their associated nerves. Finally, we also examined the morphology of taste buds from mice that lack OXTR. Taste buds and their constituent cell types appeared very similar in mice with two, one or no copies of the OXTR gene. CONCLUSIONS/SIGNIFICANCE: We conclude that OXT elicits Ca2+ signals via OXTR in murine taste buds. OXT-responsive cells are most likely a subset of Glial-like (Type I) taste cells. OXT itself is not produced locally in taste tissue and is likely delivered through the circulation. Loss of OXTR does not grossly alter the morphology of any of the cell types contained in taste buds. Instead, we speculate that OXT-responsive Glial-like (Type I) taste bud cells modulate taste signaling and afferent sensory output. Such modulation would complement central pathways of appetite regulation that employ circulating homeostatic and satiety signals.

Oxytocin mediates the antidepressant effects of mating behavior in male mice.

A significant association between plasma oxytocin (OT) levels and depression has been demonstrated. A recent study found that sexual activity and mating with a female induced the release of OT in the central nervous system of male rats. Here we examined the effect of mating behavior on depression-related behavior in wild-type (WT) and OT receptor-deficient (OTR KO) male mice. The WT males showed a reduction in depression-related behavior after mating behavior, but the OTR KO mice did not. Application of an OTR antagonist inhibited mating behavior-induced antidepressant effect in WT males. OT may mediate the antidepressant effects of mating behavior.

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.

Social approach to pain in laboratory mice.

It has been recently demonstrated that pain behavior in the mouse can be modulated by the presence of a conspecific, but what remains unclear is whether such pain behavior can serve the function of soliciting social approach. Using a novel social approach paradigm, we tested mice in various dyadic or triadic conditions, including "jailed" mice-some in pain via intraperitoneal injection of 0.9% acetic acid-and test mice free to approach or avoid the jailed mice. We observed a sex-specific effect whereby female, but not male, test mice approached a familiar same-sex conspecific in pain more frequently than an unaffected familiar or unfamiliar, but affected, conspecific. Despite a substantial literature emphasizing oxytocin's role in affiliative and pair-bonding behavior, this effect was also observed in female mice lacking the oxytocin receptor, suggesting that pain-related social approach may not be mediated by oxytocin. Furthermore, we found that the frequency of contact by the test mouse was negatively correlated with the pain behavior of the jailed mouse, suggesting that proximity of a familiar unaffected conspecific may have analgesic properties.

Genomic and epigenetic evidence for oxytocin receptor deficiency in autism.

BACKGROUND: Autism comprises a spectrum of behavioral and cognitive disturbances of childhood development and is known to be highly heritable. Although numerous approaches have been used to identify genes implicated in the development of autism, less than 10% of autism cases have been attributed to single gene disorders. METHODS: We describe the use of high-resolution genome-wide tilepath microarrays and comparative genomic hybridization to identify copy number variants within 119 probands from multiplex autism families. We next carried out DNA methylation analysis by bisulfite sequencing in a proband and his family, expanding this analysis to methylation analysis of peripheral blood and temporal cortex DNA of autism cases and matched controls from independent datasets. We also assessed oxytocin receptor (OXTR) gene expression within the temporal cortex tissue by quantitative real-time polymerase chain reaction (PCR). RESULTS: Our analysis revealed a genomic deletion containing the oxytocin receptor gene, OXTR (MIM accession no.: 167055), previously implicated in autism, was present in an autism proband and his mother who exhibits symptoms of obsessive-compulsive disorder. The proband's affected sibling did not harbor this deletion but instead may exhibit epigenetic misregulation of this gene through aberrant gene silencing by DNA methylation. Further DNA methylation analysis of the CpG island known to regulate OXTR expression identified several CpG dinucleotides that show independent statistically significant increases in the DNA methylation status in the peripheral blood cells and temporal cortex in independent datasets of individuals with autism as compared to control samples. Associated with the increase in methylation of these CpG dinucleotides is our finding that OXTR mRNA showed decreased expression in the temporal cortex tissue of autism cases matched for age and sex compared to controls. CONCLUSION: Together, these data provide further evidence for the role of OXTR and the oxytocin signaling pathway in the etiology of autism and, for the first time, implicate the epigenetic regulation of OXTR in the development of the disorder.See the related commentary by Gurrieri and Neri: http://www.biomedcentral.com/1741-7015/7/63.

Oxytocin receptors: ligand binding, signalling and cholesterol dependence.

The G protein coupled oxytocin receptor (OTR) reveals some specific molecular and physiological characteristics. Ligand-receptor interaction has been analysed by photoaffinity labelling, site-directed mutagenesis, the construction of receptor chimeras and molecular modelling. Major results of these studies will be summarized. The N-terminus of the OTR is mainly involved in agonist binding. Notably, antagonists that are derived from the ground structure of oxytocin, bind the receptor at distinct sites partly non-overlapping with the agonist binding site. OTRs are able to couple to different G proteins, with a subsequent stimulation of phospholipase C-beta isoforms. In dependence on G protein coupling, OTRs can transduce growth-inhibitory or proliferatory signals. Some evidence is provided that OTRs are also present in form of dimeric or oligomeric complexes at the cell surface. The affinity of the receptor for ligands is strongly dependent on the presence of divalent cations (Mg(2+)) and cholesterol that both act like positive allosteric modulators. While the high-affinity state of the receptor for agonists requires divalent cations and cholesterol, the high-affinity state for antagonists is only dependent on a sufficient amount of cholesterol. Cholesterol affects ligand-binding affinity, receptor signalling and stability. Since the purification of the OTR has never been achieved, alternative methods to study the receptor in its native environment are necessary. Promising strategies for the site-specific labelling of the OTR will be presented. The employment of diverse reporter molecules introduced at different positions within the OTR might allow us in the near future to measure conformational changes of the receptor in its native lipid environment.

Behavioural studies using temporal and spatial inactivation of the oxytocin receptor.

Oxytocin (Oxt), synthesized in magnocellular neurons of the paraventricular (PVN) and supraoptic (SON) hypothalamic nuclei for transport to and release from the posterior pituitary, is released during parturition and is essential for lactation. Lesser amounts of Oxt are made by smaller cells of the PVN and a few other forebrain nuclei and released into the central nervous system (CNS) to influence various other behaviours. In both the periphery and CNS, Oxt actions are transduced by the oxytocin receptor (Oxtr). Previously, it has been reported that Oxt(-/-) (knockout, KO) mice show a failure of milk ejection and thus are incapable of rearing their offspring. Unexpectedly, these mice have largely normal reproductive and maternal behaviours, perhaps due to compensatory mechanisms through activation of the Oxtr by vasopressin or through development. To examine the specific roles of the Oxtr during development and in particular brain areas, we created conditional Oxtr(-/-) mice in which we could control the spatial and temporal inactivation of the Oxtr. We flanked the neomycin-resistance selectable marker in an Oxtr intron with FRT sites to enable its removal using FLP recombinase. Coding sequence within exons 2 and 3 was flanked by two loxP sites enabling subsequent inactivation of the gene by targeted expression of Cre recombinase. The first Oxtr KO lines we created have either total or relatively specific forebrain elimination. The latter was achieved by crossing the conditional Oxtr line with a transgenic line in which the Camk2a promoter drives expression of Cre recombinase to significant levels beginning 21-28 days after birth, thus eliminating potential compensation for a deleted Oxtr gene during early development. This Cre-expressing line also significantly spares the main olfactory bulb reducing the potential confound of an olfactory deficit. We have investigated various behaviours, most notably social recognition, in both Oxtr KO strains (Oxtr(-/-) and Oxtr(FB/FB)).

New aspects of oxytocin receptor function revealed by knockout mice: sociosexual behaviour and control of energy balance.

To further define the function of the oxytocin receptor (OXTR) in vivo, we generated mice deficient in the Oxtr gene (Oxtr-/-). Oxtr-/- mice had no obvious deficits in fertility or sexual behaviour, but displayed several aberrations in social behaviours, including male aggression, and mother-offspring interaction. In addition, they showed novel physiological defects including obesity, and dysfunction in body temperature control when exposed to cold. We review here our new findings with Oxtr-/- mice, and introduce newly generated Oxtr-Venus knockin mice as a potential tool for examining molecular physiology of Oxtr-neurons.

Oxytocin receptor-deficient mice developed late-onset obesity.

The oxytocin receptor has been suggested to be involved in energy metabolism, such as food intake and energy consumption. Here, we demonstrate that oxytocin receptor-deficient (Oxtr-/-) male mice exhibited late-onset obesity with increases in abdominal fat pads and fasting plasma triglycerides. Daily food intake and spontaneous motor activity of Oxtr-/- mice were not significantly different as compared with wild-type mice. In contrast, brown adipose tissue in Oxtr-/- mice contained large lipid droplets and cold-induced thermogenesis was impaired. This study demonstrates that oxytocin receptor plays essential roles in the regulation of energy homeostasis.

Pervasive social deficits, but normal parturition, in oxytocin receptor-deficient mice.

The oxytocin receptor (OXTR) and its ligand, oxytocin (OXT), regulate reproductive physiology (i.e., parturition and lactation) and sociosexual behaviors. To define the essential functions of OXTR, we generated mice with a null mutation in the Oxtr gene (Oxtr(-/-)) and compared them with OXT-deficient (Oxt(-/-)) mice. Oxtr(-/-) mice were viable and had no obvious deficits in fertility or reproductive behavior. Oxtr(-/-) dams exhibited normal parturition but demonstrated defects in lactation and maternal nurturing. Infant Oxtr(-/-) males emitted fewer ultrasonic vocalizations than wild-type littermates in response to social isolation. Adult Oxtr(-/-) males also showed deficits in social discrimination and elevated aggressive behavior. Ligand Oxt(-/-) males from Oxt(-/-) dams, but not from Oxt(+/-) dams, showed similar high levels of aggression. These data suggest a developmental role for the OXT/OXTR system in shaping adult aggressive behavior. Our studies demonstrate that OXTR plays a critical role in regulating several aspects of social behavior and may have important implications for developmental psychiatric disorders characterized by deficits in social behavior.