Oxytocin is required for nursing but is not essential for parturition or reproductive behavior

Successful production of offspring using cryopreserved sperm via nonsurgical artificial insemination in rats

In rats, artificial insemination (AI) is surgically performed as a general tool to obtain offspring using cryopreserved spermatozoa. Nonsurgical AI is a more desirable technology because it does not require any surgical procedures. However, there has never been a successful nonsurgical AI since frozen-thawed rat spermatozoa show low motility. We show here for the first time successful nonsurgical AI in rats using oxytocin treatment. Intraperitoneal injection of oxytocin (1/800 IU) immediately before nonsurgical AI significantly increased the number of sperm collected from the oviducts compared with that without oxytocin treatment. Therefore, to obtain pups, oxytocin was intraperitoneally injected into females mated with vasectomized males, and the rats were then used for nonsurgical AI. Seven of the 12 oxytocin-treated rats became pregnant after nonsurgical AI, and 37 pups were obtained. Only one rat (1/13) without oxytocin treatment was pregnant after nonsurgical AI, and only 1 pup was delivered. These results show success for the first time in obtaining offspring using frozen-thawed rat spermatozoa via nonsurgical AI. Our results also suggest the possibility that oxytocin treatment is effective for improvement of nonsurgical AI even in other species.

Modular genetic control of sexually dimorphic behaviors

Sex hormones such as estrogen and testosterone are essential for sexually dimorphic behaviors in vertebrates. However, the hormone-activated molecular mechanisms that control the development and function of the underlying neural circuits remain poorly defined. We have identified numerous sexually dimorphic gene expression patterns in the adult mouse hypothalamus and amygdala. We find that adult sex hormones regulate these expression patterns in a sex-specific, regionally restricted manner, suggesting that these genes regulate sex typical behaviors. Indeed, we find that mice with targeted disruptions of each of four of these genes (Brs3, Cckar, Irs4, Sytl4) exhibit extremely specific deficits in sex specific behaviors, with single genes controlling the pattern or extent of male sexual behavior, male aggression, maternal behavior, or female sexual behavior. Taken together, our findings demonstrate that various components of sexually dimorphic behaviors are governed by separable genetic programs.

The role of oxytocin in mating and pregnancy

The hormone oxytocin (OT) is released both centrally and peripherally during and after mating. Although research in humans suggests a central role in sexuality, the most reliable findings to date involve peripheral activation. This review will discuss these results and will particularly focus on understanding the most recent findings from fMRI data and the effects of exogenous peripheral OT administration. We will then consider hypotheses of the roles played by central and systemic OT release as well as their control and modulation in the female, summarizing recent findings from animal research. Finally, we will discuss the contribution of OT to the initiation of pregnancy in rodents. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Variation in maternal and anxiety-like behavior associated with discrete patterns of oxytocin and vasopressin 1a receptor density in the lateral septum

The relationship between anxiety and maternal behavior has been explored across species using a variety of approaches, yet there is no clear consensus on the nature or direction of this relationship. In the current study, we have assessed stable individual differences in anxiety-like behavior in a large cohort (n=57) of female F2 hybrid mice. Using open-field behavior as a continuous and categorical (high vs. low) measure we examined the relationship between the anxiety-like behavior of virgin F2 females and the subsequent maternal behavior of these females. In addition, we quantified oxytocin (OTR) and vasopressin (V1a) receptor density within the lateral septum to determine the possible correlation with anxiety-like and maternal behavior. We find that, though activity levels within the open-field do predict latency to engage in pup retrieval, anxiety-like measures on this test are otherwise not associated with subsequent maternal behavior. OTR density in the dorsal lateral septum was found to be negatively correlated with activity levels in the open-field and positively correlated with frequency of nursing behavior. V1a receptor density was significantly correlated with postpartum licking/grooming of pups. Though we do not find support for the hypothesis that individual differences in trait anxiety predict variation in maternal behavior, we do find evidence for the role of OTR and V1a receptors in predicting maternal behavior in mice and suggest possible methodological issues (such as distinguishing between trait and state anxiety) that will be a critical consideration for subsequent studies of the anxiety-maternal behavior relationship. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Developmental experiences and the oxytocin receptor system

The long-term effects of developmental experiences on social behavior, and the neuropeptide systems such as oxytocin which subserve the behavior, are still little understood. In this article, we review various types of early experience, including normal development, knockout models, pharmacological exposures, and early social experiences. We consider the processes by which experience can affect oxytocin receptor binding, and what is known about the directionality of experience effects on oxytocin receptors. Finally, we attempt to synthesize the literature into a predictive model as to the direction of early experience effects on oxytocin receptor binding potential, and whether these changes have functional significance. These predictions are relevant to current human health practice, given proposals to use chronic intranasal oxytocin to treat developmental disorders including autism and schizophrenia. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Both oxytocin and vasopressin are mediators of maternal care and aggression in rodents: from central release to sites of action

In the mammalian peripartum period, the activity of both the brain oxytocin and vasopressin system is elevated as part of the physiological adaptations occurring in the mother. This is reflected by increased expression and intracerebral release of oxytocin and vasopressin, as well as increased neuropeptide receptor expression and binding. In this review we discuss the functional role of the brain oxytocin and vasopressin system in the context of maternal behavior, specifically maternal care and maternal aggression in rodents. In order to enable the identification of significant and peptide-specific contributions to the display of maternal behavior, various complementary animal models of maternal care and/or maternal aggression were studied, including rats selectively bred for differences in anxiety-related behavior (HAB and LAB dams), monitoring of local neuropeptide release during ongoing maternal behavior, and local pharmacological or genetic manipulations of the neuropeptide systems. The medial preoptic area was identified as a major site for oxytocin- and vasopressin-mediated maternal care. Furthermore, both oxytocin and vasopressin release and receptor activation in the central amygdala and the bed nucleus of the stria terminalis play an important role for maternal aggression. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

CD38 and its role in oxytocin secretion and social behavior

Here, we review the functional roles of cyclic ADP-ribose and CD38, a transmembrane protein with ADP-ribosyl cyclase activity, in mouse social behavior via the regulation of oxytocin (OXT) release, an essential component of social cognition. Herein we describe data detailing the molecular mechanism of CD38-dependent OXT secretion in CD38 knockout mice. We also review studies that used OXT, OXT receptor (OXTR), or CD38 knockout mice. Additionally, we compare the behavioral impairments that occur in these knockout mice in relation to the OXT system and CD38. This review also examines autism spectrum disorder (ASD), which is characterized by social and communication impairments, in relation to defects in the OXT system. Two single nucleotide polymorphisms (SNPs) in the human CD38 gene are possible risk factors for ASD via inhibition of OXT function. Further analysis of CD38 in relation to the OXT system may provide a better understanding of the neuroendocrinological roles of OXT and CD38 in the hypothalamus and of the pathophysiology of ASD. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Social memory, amnesia, and autism: brain oxytocin secretion is regulated by NAD+ metabolites and single nucleotide polymorphisms of CD38

Previously, we demonstrated that CD38, a transmembrane protein with ADP-ribosyl cyclase activity, plays a critical role in mouse social behavior by regulating the release of oxytocin (OXT), which is essential for mutual recognition. When CD38 was disrupted, social amnesia was observed in Cd38 knockout mice. The autism spectrum disorders (ASDs), characterized by defects in reciprocal social interaction and communication, occur either sporadically or in a familial pattern. However, the etiology of ASDs remains largely unknown. Therefore, the theoretical basis for pharmacological treatments has not been established. Hence, there is a rationale for investigating single nucleotide polymorphisms (SNPs) in the human CD38 gene in ASD subjects. We found several SNPs in this gene. The SNP rs3796863 (C>A) was associated with high-functioning autism (HFA) in American samples from the Autism Gene Resource Exchange. Although this finding was partially confirmed in low-functioning autism subjects in Israel, it has not been replicated in Japanese HFA subjects. The second SNP of interest, rs1800561 (4693C>T), leads to the substitution of an arginine (R) at codon 140 by tryptophan (W; R140W) in CD38. This mutation was found in four probands of ASD and in family members of three pedigrees with variable levels of ASD or ASD traits. The plasma levels of OXT in ASD subjects with the R140W allele were lower than those in ASD subjects lacking this allele. The OXT levels were unchanged in healthy subjects with or without this mutation. One proband with the R140W allele receiving intranasal OXT for approximately 3years showed improvement in areas of social approach, eye contact and communication behaviors, emotion, irritability, and aggression. Five other ASD subjects with mental deficits received nasal OXT for various periods; three subjects showed improved symptoms, while two showed little or no effect. These results suggest that SNPs in CD38 may be possible risk factors for ASD by abrogating OXT function and that some ASD subjects can be treated with OXT in preliminary clinical trials.

Circadian aspects of mammalian parturition: a review

The identification of circadian clocks in endocrine tissues has added considerable depth and complexity to our understanding of their physiology. A growing body of research reveals circadian clock gene expression in the uterus of non-pregnant and pregnant rodents. This review will focus on the mammalian uterus and its rhythmicity, particularly as it pertains to the circadian timing of parturition. This key event in the reproductive axis shows dramatic species-specific differences in its circadian phase. It is proposed here that these differences in the phasing of mammalian parturition are likely a function of opposite uterine cell responses to humoral cues. The argument will be made that melatonin fulfills many of the criteria to serve as a circadian signal in the initiation of human parturition, including specific actions on uterine smooth muscle cells that are consistent with a role for this hormone in the circadian timing of parturition.

A novel deletion partly removing the AVP gene causes autosomal recessive inheritance of early-onset neurohypophyseal diabetes insipidus

Familial neurohypophyseal diabetes insipidus (FNDI) typically presents with age-dependent penetrance and autosomal dominant inheritance caused by missense variations in one allele of the AVP gene encoding the arginine vasopressin (AVP) prohormone. We present the molecular genetic characteristics underlying an unusual form of FNDI occurring with very early onset and seemingly autosomal recessive inheritance. By DNA amplification and sequencing, we identified a novel variant allele of the AVP gene carrying a 10,396 base pair deletion involving the majority of the AVP gene as well as its regulatory sequences in the intergenic region between the AVP and the OXT gene, encoding the oxytocin prohormone. We found two chromosomes carrying the deletion in affected family members and one in unaffected family members suspected to transmit the deleted allele. Whole-genome array analysis confirmed the results and excluded the presence of any additional major pathogenic abnormalities. The deletion is predicted to abolish the transcription of the AVP gene, thus the fact that family members heterozygous for the deletion remain healthy argues, in general, against haploinsufficiency as the pathogenic mechanism FNDI. Accordingly, our data is strong support to the prevailing idea that dominant inheritance of FNDI is due to a dominant-negative effect exerted by variant AVP prohormone.

Oxytocin in the treatment of dystocia in mice

Physicians and veterinarians often prescribe oxytocin to treat dystocia. However, oxytocin administration to pregnant women or animals is not without risk. In the venue of laboratory animal medicine, the use of oxytocin may present confounding variables to research. Although oxytocin has been studied extensively, many of its physiologic effects and interactions with other hormones remain unclear. Investigator concerns about adverse and confounding effects of oxytocin in their research mice prompted the current review of oxytocin and its use to treat murine dystocia. Well-controlled studies of oxytocin in dystocic mice have not been conducted. However, in humans and other animals, inconsistent and adverse effects are well-documented. Limited knowledge of the complex physiologic and molecular mechanisms of action of oxytocin and scant support for the efficacy of oxytocin in dystocic mice fail to meet the standards of evidence-based veterinary medical practice. The administration of oxytocin is contraindicated in many cases of dystocia in research mice, and its use in dystocic mice may be unfounded. A brief review of oxytocin and the physiologic mechanisms of parturition are provided to support this conclusion. Alternative treatments for murine dystocia are discussed, and a holistic approach is advocated to better serve animal welfare and to safeguard the integrity of valuable research. Laboratory animal veterinarians overseeing the development of guidelines or standard operating procedures for technician or investigator treatment of dystocic mice should understand the effects of oxytocin administration in light of relevant research.

Chronic overexpression of corticotropin-releasing factor from the central amygdala produces HPA axis hyperactivity and behavioral anxiety associated with gene-expression changes in the hippocampus and paraventricular nucleus of the hypothalamus

Environmental stress has been demonstrated to increase susceptibility for mood and anxiety disorders, and hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, the primary endocrine response to stress, is often observed in these patients. HPA axis activation is initiated by corticotropin-releasing factor (CRF) from the hypothalamus, leading to the hypothesis that hypothalamic CRF overexpression contributes to HPA axis hyperactivity in psychiatric patients. In addition, elevated CRF in cerebrospinal fluid is observed in mood and anxiety disorder patients, suggesting that CRF is also being overproduced from extrahypothalamic sources such as the central amygdala (CeA) and overactivity of the amygdala in neuroimaging studies is a consistent finding in anxiety and depression patients. Due to the importance of CRF and the amygdala in the etiology of stress-sensitive psychiatric disorders, the present study sought to further dissect the impact of CRF overexpression (OE) in the amygdala on downstream behavioral, endocrine, and gene-expression changes typically associated with chronic stress. To test the hypothesis that elevated CRF output from the amygdala would reproduce HPA axis hyperactivity and behavioral symptoms of chronic stress, we developed a lentiviral vector in which 3.0kb of the CRF promoter drives overexpression of CRF (LVCRFp3.0CRF). In adult male rats, Experiment-1 examined behavioral consequences of chronic CRF overexpression from the amygdala; the dexamethasone (Dex)/CRF test was used to measure HPA axis reactivity. Experiment-2 focused on HPA axis disruptions; the dexamethasone-suppression and CRF-stimulation tests as well as the Dex/CRF test were used. In both experiments, expression of HPA-axis related transcripts were assessed.

CD38 gene knockout juvenile mice: a model of oxytocin signal defects in autism

Oxytocin (OXT) in the hypothalamus is the biological basis of social recognition, trust, and bonding. We showed that CD38, a leukaemia cell marker, plays an important role in the hypothalamus in the process of OXT release in adult mice. Disruption of Cd38 (Cd38(-/-)) produced impairment of maternal behavior and male social recognition in mice, similar to the behavior observed in Oxt and OXT receptor (Oxtr) gene knockout (Oxt(-/-) and Oxtr(-/-), respectively) mice. Locomotor activity induced by separation from the dam was higher and the number of ultrasonic vocalization (USV) calls was lower in Cd38(-/-) than Cd38(+/+) pups. These phenotypes seemed to be caused by the high plasma OXT levels during development from neonates to 3-week-old juvenile mice. ADP-ribosyl cyclase activity was markedly lower in the knockout mice from birth, suggesting that weaning for mice is a critical time window of differentiating plasma OXT. Contribution by breastfeeding was an important exogenous source for regulating plasma OXT before weaning by the presence of OXT in milk and the dam's mammary glands. The dissimilarity of Cd38(-/-) infant behaviour to Oxt(-/-) or Oxtr(-/-) mice can be explained partly by this exogenous source of OXT. These results suggest that secretion of OXT into the brain in a CD38-dependent manner may play an important role in the development of social behavior, and mice with OXT signalling deficiency, including Cd38(-/-), Oxt(-/-) and Oxtr(-/-) mice are good animal models for developmental disorders, such as autism.

The hormone of love attracts a partner for life

Neurovascular integration during embryonic development is essential for adult physiology. In this issue of Developmental Cell, Gutnick et al. (2011) report that hypothalamic neurons secrete oxytocin as a guidance cue for endothelial cells to establish their vascular supply-a prerequisite for neuroendocrine secretion from the neurohyophysis in adult life.

Differential expression of arrestins is a predictor of breast cancer progression and survival

Emerging evidence has implicated G protein-coupled receptors, such as CXCR4 and PAR2, in breast cancer progression and the development of metastatic breast cancer. However, the role of proteins that regulate the function of these receptors, such as arrestins, in breast cancer has yet to be determined. Examination of the expression of the two nonvisual arrestins, arrestin2 and 3, in various breast cancer cell lines revealed comparable expression of arrestin3 in basal and luminal lines while arrestin2 expression was much higher in the luminal lines compared to the more aggressive basal lines. Analysis of normal human breast tissue revealed that arrestin2 and 3 were expressed in both luminal and myoepithelial cells of mammary epithelia with arrestin2 highest in myoepithelial cells and arrestin3 comparable in both cell types. Quantitative immunofluorescence-based examination of primary breast tumors revealed that arrestin2 expression significantly decreased with cancer progression from ductal carcinoma in situ to invasive carcinoma and further to lymph node metastasis (P < 0.001). Moreover, decreased arrestin2 expression was associated with decreased survival (P = 0.0007) as well as positive lymph node status and increased tumor size and nuclear grade. In contrast, arrestin3 expression significantly increased during breast cancer progression (P < 0.001) and increased expression was associated with decreased survival (P = 0.014). Arrestin3 was also an independent prognostic marker of breast cancer with a hazard ratio of 1.65. Overall, these studies demonstrate that arrestin2 levels decrease while arrestin3 levels increase during breast cancer progression and these changes correlate with a poor clinical outcome.

Smooth muscle α actin is specifically required for the maintenance of lactation

Smooth muscle α-actin (Acta2) is one of six highly conserved mammalian actin isoforms that appear to exhibit functional redundancy. Nonetheless, we have postulated a specific functional role for the smooth muscle specific isoform. Here, we show that Acta2 deficient mice have a remarkable mammary phenotype such that dams lacking Acta2 are unable to nurse their offspring effectively. The phenotype was rescued in cross fostering experiments with wild type mice, excluding a developmental defect in Acta2 null pups. The mechanism for the underlying phenotype is due to myoepithelial dysfunction postpartum resulting in precocious involution. Further, we demonstrate a specific defect in myoepithelial cell contractility in Acta2 null mammary glands, despite normal expression of cytoplasmic actins. We conclude that Acta2 specifically mediates myoepithelial cell contraction during lactation and that this actin isoform therefore exhibits functional specificity.

A bold view of the lactating brain: functional magnetic resonance imaging studies of suckling in awake dams

Functional magnetic resonance imaging (fMRI) has been used to investigate the responsiveness of the maternal rat brain to pup-suckling under various experimental paradigms. Our research employing the lactating rat model has explored the cortical sensory processing of pup stimuli and the effect of suckling on the brain's reward system. Suckling was observed to increase blood-oxygen-level-dependent (BOLD) signal intensity in the midbrain, striatum and prefrontal cortex, which are areas that receive prominent dopaminergic inputs. The BOLD activation of the reward system occurs in parallel with the activation of extensive cortical sensory areas. The observed regions include the olfactory cortex, auditory cortex and gustatory cortex, and could correspond to cortical representations of pup odours, vocalisations and taste that are active during lactation. Activation patterns within reward regions are consistent with past research on maternal motivation and we explore the possibility that exposure to drugs of abuse might be disruptive of maternal neural responses to pups, particularly in the prefrontal cortex. Our ongoing fMRI studies support and extend past research on the maternal rat brain and its functional neurocircuitry.

Kisspeptin activation of supraoptic nucleus neurons in vivo

Oxytocin and vasopressin are synthesized by magnocellular neurosecretory cells in the hypothalamic supraoptic and paraventricular nuclei and are released from the posterior pituitary gland into the circulation. Intravenous administration of the ligand for the G protein-coupled receptor 54 receptor, kisspeptin-10, increases plasma oxytocin levels and intracerebroventricular kisspeptin-10 increases vasopressin levels, indicating that kisspeptin might play a role in various physiological functions via stimulation of oxytocin and vasopressin secretion. Because posterior pituitary hormone secretion is dependent on action potential (spike) discharge, we used in vivo extracellular single unit recording to determine the effects of kisspeptin-10 on supraoptic nucleus neurons in urethane-anaesthetized female rats. Intravenous kisspeptin-10 (100 μg) increased the firing rate of oxytocin neurons from 3.7 ± 0.8 to 4.7 ± 0.8 spikes/sec (P = 0.0004), but only a quarter of vasopressin neurons responded to iv kisspeptin-10, showing a short (<3 sec) high-frequency (>15 spikes/sec) burst of firing. By contrast, intracerebroventricular kisspeptin-10 (2 and 40 μg) did not alter oxytocin or vasopressin neuron firing rate. To investigate the pathway involved in the peripheral action of kisspeptin-10, we used i.p. capsaicin to desensitize vagal afferents, which prevented the i.v. kisspeptin-10-induced increase of oxytocin neuron firing rate. This is the first report to show that peripheral, but not central, kisspeptin-10 increases the activity of oxytocin neurons and a proportion of vasopressin neurons and that endogenous kisspeptin regulation of supraoptic nucleus neurons is likely via vagal afferent input, with kisspeptin acting as a hormone rather than as a neuropeptide in this system.

Oxytocin and social motivation

Humans are fundamentally social creatures who are ‘motivated’ to be with others. In this review we examine the role of oxytocin (OT) as it relates to social motivation. OT is synthesized in the brain and throughout the body, including in the heart, thymus, gastrointestinal tract, as well as reproductive organs. The distribution of the OT receptor (OTR) system in both the brain and periphery is even more far-reaching and its expression is subject to changes over the course of development. OTR expression is also sensitive to changes in the external environment and the internal somatic world. The OT system functions as an important element within a complex, developmentally sensitive biobehavioral system. Other elements include sensory inputs, the salience, reward, and threat detection pathways, the hypothalamic-pituitary-gonadal axis, and the hypothalamic-pituitary-adrenal stress response axis. Despite an ever expanding scientific literature, key unresolved questions remain concerning the interplay of the central and peripheral components of this complex biobehavioral system that dynamically engages the brain and the body as humans interact with social partners over the course of development.

Data supporting a new physiological role for brain apelin in the regulation of hypothalamic oxytocin neurons in lactating rats

Apelin is a bioactive peptide identified as the endogenous ligand of the human orphan G protein-coupled receptor APJ in 1998. The present data show that apelin modulates the activity of magnocellular and parvocellular oxytocin (OXY) neurons in the lactating rat. A combination of in situ hybridization and immunohistochemistry demonstrated the presence of apelin receptor mRNA in hypothalamic OXY neurons. Double immunofluorescence labeling then revealed the colocalization of apelin with OXY in about 20% of the hypothalamic OXY-positive neurons. Intracerebroventricular apelin administration inhibited the activity of magnocellular and parvocellular OXY neurons, as shown by measuring the c-fos expression in OXY neurons or by direct electrophysiological measurements of the electrical activity of these neurons. This effect was correlated with a decrease in the amount of milk ejected. Thus, apelin inhibits the activity of OXY neurons through a direct action on apelin receptors expressed by these neurons in an autocrine and paracrine manner. In conclusion, these findings highlight the inhibitory role of apelin as an autocrine/paracrine peptide acting on OXY neurons during breastfeeding.

Misexpression of wingless-related MMTV integration site 5A in mouse mammary gland inhibits the milk ejection response and regulates connexin43 phosphorylation

Wingless-related MMTV integration site 5A (Wnt5a) is a noncanonical signaling WNT that is expressed in every stage of mouse mammary gland development except lactation. Using slow release pellets containing WNT5A as well as Wnt5a-null tissue, we previously showed that WNT5A acts to limit mammary development. Here, we generated transgenic mice that overexpress WNT5A in the mammary epithelium using the mouse mammary tumor virus promoter (M5a mice). Lactation was impaired in two high WNT5A-expressing lines. Lactation defects could not be explained by differences in apoptosis, lineage differentiation, milk synthesis, or secretion. Instead, misexpression of WNT5A led to a failure in oxytocin response and milk ejection. Noting the similarity between the M5a phenotype and that of mice with a mutation in connexin43 (Cx43; official gene symbol Gja1), we examined Cx43 phosphorylation and localization in M5a mice. In wild-type mice, Cx43 switched from a phosphorylated to a more hypophosphorylated form after parturition. In contrast, the phosphorylated form of Cx43 was maintained after parturition in M5a mice. Using a nontumorigenic breast cell line, MCF10A, we showed that, in addition to increasing the levels of phosphorylation of Cx43 on serine-368, ectopic expression of WNT5A reduced or blocked the amount of dye transferred between cells. In summary, we propose that WNT5A inhibits the response to oxytocin and prevents milk ejection through regulation of Cx43 function.

Neuromolecular basis of parental behavior in laboratory mice and rats: with special emphasis on technical issues of using mouse genetics

To support the well-being of the parent-infant relationship, the neuromolecular mechanisms of parental behaviors should be clarified. From neuroanatomical analyses in laboratory rats, the medial preoptic area (MPOA) has been shown to be of critical importance in parental retrieving behavior. More recently, various gene-targeted mouse strains have been found to be defective in different aspects of parental behaviors, contributing to the identification of molecules and signaling pathways required for the behavior. Therefore, the neuromolecular basis of "mother love" is now a fully approachable research field in modern molecular neuroscience. In this review, we will provide a summary of the required brain areas and gene for parental behavior in laboratory mice (Mus musculus) and rats (Rattus norvegicus). Basic protocols and technical considerations on studying the mechanism of parental behavior using genetically-engineered mouse strains will also be presented.

Oestrogen-independent, experience-induced maternal behaviour in female mice

Nulliparous female mice that have not experienced mating, pregnancy or parturition show near immediate spontaneous maternal behaviour when presented with foster pups. The fact that virgin mice display spontaneous maternal behaviour indicates that the hormonal events of pregnancy and parturition are not necessary to produce a rapid onset of maternal behaviour in mice. However, it is not known how similar maternal behaviour is between virgin and lactating mice. In the present study, we show that naturally postpartum females are faster to retrieve pups and spend more time crouching over pups than spontaneously maternal virgin females, and that these differences diminish with increased maternal experience. Moreover, 4 days of experience with pups induced pup retrieval on a novel T-maze. Furthermore, the effects of experience on subsequent maternal responsiveness are not dependent on gonadal hormones because ovariectomised females with 4 days of pup experience show pup retrieval on a novel T-maze similar to that of postpartum mice. Four days of maternal experience also induced T-maze pup retrieval in ovariectomised aromatase knockout female mice that was not significantly different from the maternal responsiveness of ovariectomised wild-type littermates. These data suggest that maternal experience can induce maternal behaviour in females that have never been exposed to oestradiol at any time in development or adulthood. Finally, ovariectomised pup-experienced females continue to retrieve pups on a novel T-maze 1 month after the initial experience, suggesting that, even in the absence of oestradiol, maternal experience produces long-lasting modifications in maternal responsiveness.

Annual Research Review: Transgenic mouse models of childhood-onset psychiatric disorders

Childhood-onset psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), mood disorders, obsessive compulsive spectrum disorders (OCSD), and schizophrenia (SZ), affect many school-age children, leading to a lower quality of life, including difficulties in school and personal relationships that persist into adulthood. Currently, the causes of these psychiatric disorders are poorly understood, resulting in difficulty diagnosing affected children, and insufficient treatment options. Family and twin studies implicate a genetic contribution for ADHD, ASD, mood disorders, OCSD, and SZ. Identification of candidate genes and chromosomal regions associated with a particular disorder provide targets for directed research, and understanding how these genes influence the disease state will provide valuable insights for improving the diagnosis and treatment of children with psychiatric disorders. Transgenic mouse models are one important approach in the study of human diseases, allowing for the use of a variety of experimental approaches to dissect the contribution of a specific chromosomal or genetic abnormality in human disorders. While it is impossible to model an entire psychiatric disorder in a single mouse model, these models can be extremely valuable in dissecting out the specific role of a gene, pathway, neuron subtype, or brain region in a particular abnormal behavior. In this review we discuss existing transgenic mouse models for childhood-onset psychiatric disorders. We compare the strength and weakness of various transgenic mouse models proposed for each of the common childhood-onset psychiatric disorders, and discuss future directions for the study of these disorders using cutting-edge genetic tools.

Endocrine immune interactions in human parturition

Human parturition is an inflammatory event, modulated and influenced by a host of other environmental and physiological processes, including the endocrine hormones. Complex bidirectional communication occurs between the two systems to bring about some of the changes that are seen in labour, an event that is not yet fully understood. Preterm birth is a major problem in obstetrics and neonatology, with dysfunctional labour or prolonged pregnancy also making increasingly significant contributions to maternal morbidity. With better understanding of normal and abnormal parturition we may be able to develop novel ways of treating these complications of pregnancy and reduce maternal and neonatal morbidity and mortality. This review discusses the crucial role that endocrine-immune interaction plays in the process of labour and in the processes of abnormal and preterm labour. We propose that amongst these complex interactions it is the immune system that is the driving force behind human parturition.

Myoepithelial cell contraction and milk ejection are impaired in mammary glands of mice lacking smooth muscle alpha-actin

Mammary myoepithelial cells are specialized smooth musclelike epithelial cells that express the smooth muscle actin isoform: smooth muscle alpha-actin (ACTA2). These cells contract in response to oxytocin to generate the contractile force required for milk ejection during lactation. It is believed that ACTA2 contributes to myoepithelial contractile force generation; however, this hypothesis has not been directly tested. To evaluate the contribution of ACTA2 to mammary myoepithelial cell contraction, Acta2 null mice were utilized and milk ejection and myoepithelial cell contractile force generation were evaluated. Pups suckling on Acta2 null dams had a significant reduction in weight gain starting immediately postbirth. Cross-fostering demonstrated the lactation defect is with the Acta2 null dams. Carmine alum whole mounts and conventional histology revealed no underlying structural defects in Acta2 null mammary glands that could account for the lactation defect. In addition, myoepithelial cell formation and organization appeared normal in Acta2 null lactating mammary glands as evaluated using an Acta2 promoter-GFP transgene or phalloidin staining to visualize myoepithelial cells. However, mammary myoepithelial cell contraction in response to oxytocin was significantly reduced in isolated Acta2 null lactating mammary glands and in in vivo studies using Acta2 null lactating dams. These results demonstrate that lack of ACTA2 expression impairs mammary myoepithelial cell contraction and milk ejection and suggests that ACTA2 expression in mammary myoepithelial cells has the functional consequence of enhancing contractile force generation required for milk ejection.

Social behavior of offspring following prenatal cocaine exposure in rodents: a comparison with prenatal alcohol

Clinical and experimental reports suggest that prenatal cocaine exposure (PCE) alters the offsprings' social interactions with caregivers and conspecifics. Children exposed to prenatal cocaine show deficits in caregiver attachment and play behavior. In animal models, a developmental pattern of effects that range from deficits in play and social interaction during adolescence, to aggressive reactions during competition in adulthood is seen. This review will focus primarily on the effects of PCE on social behaviors involving conspecifics in animal models. Social relationships are critical to the developing organism; maternally directed interactions are necessary for initial survival. Juvenile rats deprived of play behavior, one of the earliest forms of non-mother directed social behaviors in rodents, show deficits in learning tasks and sexual competence. Social behavior is inherently complex. Because the emergence of appropriate social skills involves the interplay between various conceptual and biological facets of behavior and social information, it may be a particularly sensitive measure of prenatal insult. The social behavior surveyed include social interactions, play behavior/fighting, scent marking, and aggressive behavior in the offspring, as well as aspects of maternal behavior. The goal is to determine if there is a consensus of results in the literature with respect to PCE and social behaviors, and to discuss discrepant findings in terms of exposure models, the paradigms, and dependent variables, as well as housing conditions, and the sex and age of the offspring at testing. As there is increasing evidence that deficits in social behavior may be sequelae of developmental exposure alcohol, we compare changes in social behaviors reported for prenatal alcohol with those reported for prenatal cocaine. Shortcomings in the both literatures are identified and addressed in an effort to improve the translational value of future experimentation.

Using transgenic mouse models to study oxytocin's role in the facilitation of species propagation

Oxytocin and its receptor are important for a wide range of effects, from social memory to uterine contractions. It is an evolutionarily well-conserved hormone that is particularly important in social and gregarious animals. Research on small mammals has yielded a rich literature on oxytocin's many functions. Recently a new tool has been created that has furthered our understanding of oxytocin's role in behavior: transgenic mice that lack either the ability to synthesize oxytocin or the oxytocin receptor itself. The study of these lines, while still in its infancy, is already bearing fruit and offers the promise of insight into some human disorders characterized by aberrant social behavior.

Placental leucine aminopeptidase- and aminopeptidase A- deficient mice offer insight concerning the mechanisms underlying preterm labor and preeclampsia

Preeclampsia and preterm delivery are important potential complications in pregnancy and represent the leading causes for maternal and perinatal morbidity and mortality. The mechanisms underlying both diseases remain unknown, thus available treatments (beta2-stimulants and magnesium sulfate) are essentially symptomatic. Both molecules have molecular weights less than 5–8 kDa, cross the placental barrier, and thus exert their effects on the fetus. The fetus produces peptides that are highly vasoactive and uterotonic and increase in response to maternal stress and with continued development. Fetal peptides are also small molecules that inevitably leak across into the maternal circulation. Aminopeptidases such as placental leucine aminopeptidase (P-LAP) and aminopeptidase A (APA) are large molecules that do not cross the placental barrier. We have shown that APA acts as an antihypertensive agent in the pregnant spontaneously hypertensive rat by degrading vasoactive peptides and as a result returns the animal to a normotensive state. P-LAP also acts as an antiuterotonic agent by degrading uterotonic peptides and thus prolongs gestation in the pregnant mouse. Given the ever increasing worldwide incidences of preeclampsia and preterm labor, it is imperative that new agents be developed to safely prolong gestation. We believe that the use of aminopeptidases hold promise in this regard.

Neuroendocrine mechanisms in pregnancy and parturition

The complex mechanisms controlling human parturition involves mother, fetus, and placenta, and stress is a key element activating a series of physiological adaptive responses. Preterm birth is a clinical syndrome that shares several characteristics with term birth. A major role for the neuroendocrine mechanisms has been proposed, and placenta/membranes are sources for neurohormones and peptides. Oxytocin (OT) is the neurohormone whose major target is uterine contractility and placenta represents a novel source that contributes to the mechanisms of parturition. The CRH/urocortin (Ucn) family is another important neuroendocrine pathway involved in term and preterm birth. The CRH/Ucn family consists of four ligands: CRH, Ucn, Ucn2, and Ucn3. These peptides have a pleyotropic function and are expressed by human placenta and fetal membranes. Uterine contractility, blood vessel tone, and immune function are influenced by CRH/Ucns during pregnancy and undergo major changes at parturition. Among the others, neurohormones, relaxin, parathyroid hormone-related protein, opioids, neurosteroids, and monoamines are expressed and secreted from placental tissues at parturition. Preterm birth is the consequence of a premature and sustained activation of endocrine and immune responses. A preterm birth evidence for a premature activation of OT secretion as well as increased maternal plasma CRH levels suggests a pathogenic role of these neurohormones. A decrease of maternal serum CRH-binding protein is a concurrent event. At midgestation, placental hypersecretion of CRH or Ucn has been proposed as a predictive marker of subsequent preterm delivery. While placenta represents the major source for CRH, fetus abundantly secretes Ucn and adrenal dehydroepiandrosterone in women with preterm birth. The relevant role of neuroendocrine mechanisms in preterm birth is sustained by basic and clinic implications.

miR-200 family and targets, ZEB1 and ZEB2, modulate uterine quiescence and contractility during pregnancy and labor

Throughout most of pregnancy, uterine quiescence is maintained by increased progesterone receptor (PR) transcriptional activity, whereas spontaneous labor is initiated/facilitated by a concerted series of biochemical events that activate inflammatory pathways and have a negative impact on PR function. In this study, we uncovered a previously undescribed regulatory pathway whereby micro-RNAs (miRNAs) serve as hormonally modulated and conserved mediators of contraction-associated genes in the pregnant uterus in the mouse and human. Using miRNA and gene expression microarray analyses of uterine tissues, we identified a conserved family of miRNAs, the miR-200 family, that is highly induced at term in both mice and humans as well as two coordinately down-regulated targets, zinc finger E-box binding homeobox proteins ZEB1 and ZEB2, which act as transcriptional repressors. We also observed up-regulation of the miR-200 family and down-regulation of ZEB1 and ZEB2 in two different mouse models of preterm labor. We further demonstrated that ZEB1 is directly up-regulated by the action of progesterone (P(4))/PR at the ZEB1 promoter. Excitingly, we observed that ZEB1 and ZEB2 inhibit expression of the contraction-associated genes, oxytocin receptor and connexin-43, and block oxytocin-induced contractility in human myometrial cells. Together, these findings implicate the miR-200 family and their targets, ZEB1 and ZEB2, as unique P(4)/PR-mediated regulators of uterine quiescence and contractility during pregnancy and labor and shed light on the molecular mechanisms involved in preterm birth.

A new approach regarding the treatment of preeclampsia and preterm labor

Both preeclampsia and preterm delivery are important complications in pregnancy and are leading causes for maternal and perinatal morbidity and mortality. The underlying molecular mechanisms of both diseases remain unknown, thus treatments (beta2-stimulants and magnesium sulfate) are essentially symptomatic. Both molecules have molecular weights less than 5-8 kDa and cross the placental barrier thus exerting their effects on the fetus. In addition, the fetus produces peptide hormones that are highly vasoactive and uterotonic and increase in response to maternal stress and with continued development. Fetal peptides are also small molecules that inevitably leak across into the maternal circulation. Aminopeptidases such as placental leucine aminopeptidase (P-LAP) and aminopeptidase A (APA) are large molecules that do not cross the placental barrier. We have shown that APA acts as an antihypertensive agent in the pregnant spontaneously hypertensive rat by degrading vasoactive peptides and as a result returns the animal to a normotensive state. We have also noted that P-LAP acts as an anti-uterotonic agent by degrading uterotonic peptides, and as a result prolongs gestation in the pregnant mouse. Thus, P-LAP and APA represent promising agents for the treatment of preeclampsia and preterm labor by degrading bioactive hormones derived from the feto-placental circulation.

Normal maternal behavior, but increased pup mortality, in conditional oxytocin receptor knockout females

Oxytocin (Oxt) and the Oxt receptor (Oxtr) are implicated in the onset of maternal behavior in a variety of species. Recently, we developed two Oxtr knockout lines: a total body knockout (Oxtr-/-) and a conditional Oxtr knockout (OxtrFB/FB) in which the Oxtr is lacking only in regions of the forebrain, allowing knockout females to potentially nurse and care for their biological offspring. In the current study, we assessed maternal behavior of postpartum OxtrFB/FB females toward their own pups and maternal behavior of virgin Oxtr-/- females toward foster pups and compared knockouts of both lines to wildtype (Oxtr+/+) littermates. We found that both Oxtr-/- and OxtrFB/FB females appear to have largely normal maternal behaviors. However, with first litters, approximately 40% of the OxtrFB/FB knockout dams experienced high pup mortality, compared to fewer than 10% of the Oxtr+/+ dams. We then went on to test whether or not this phenotype occurred in subsequent litters or when the dams were exposed to an environmental disturbance. We found that regardless of the degree of external disturbance, OxtrFB/FB females lost more pups on their first and second litters compared to wildtype females. Possible reasons for higher pup mortality in OxtrFB/FB females are discussed.

Abnormal hypothalamic oxytocin system in fibroblast growth factor 8-deficient mice

Oxytocin (OT) is a nonapeptide essential for maternal care. The development of the OT neuroendocrine system is a multi-step process dependent on the action of many transcription factors, but upstream signaling molecules regulating this process are still poorly understood. In this study, we examined if fibroblast growth factor 8 (FGF8), a signaling molecule critical for forebrain development, is essential for the proper formation of the OT system. Using immunohistochemistry, we showed a significant reduction in the number of neurons immunoreactive for the mature OT peptide in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) in the hypothalamus of homozygous (HOMO) FGF8 hypomorphic mice compared to wild-type mice. The number of neurons positive for oxyphysin prohormone in the SON but not the PVN was also significantly reduced in FGF8 HOMO hypomorphs. However, steady-state mRNA levels of the oxyphysin prohormone were not significantly different between FGF8 hypomorphs and WT mice. These data suggest that a global reduction in FGF8 signaling leads to an overall reduction of mature OT and oxyphysin prohormone levels that may have resulted from defects in multiple stages of the hormone-synthesis pathway. Since proper hormone synthesis is a hallmark of mature OT neurons, this study suggests that FGF8 signaling may contribute to the phenotypic maturation of a neuroendocrine system that originates within the diencephalon.

Dopamine and oxytocin interactions underlying behaviors: potential contributions to behavioral disorders

Dopamine is an important neuromodulator that exerts widespread effects on the central nervous system (CNS) function. Disruption in dopaminergic neurotransmission can have profound effects on mood and behavior and as such is known to be implicated in various neuropsychiatric behavioral disorders including autism and depression. The subsequent effects on other neurocircuitries due to dysregulated dopamine function have yet to be fully explored. Due to the marked social deficits observed in psychiatric patients, the neuropeptide, oxytocin is emerging as one particular neural substrate that may be influenced by the altered dopamine levels subserving neuropathologic-related behavioral diseases. Oxytocin has a substantial role in social attachment, affiliation and sexual behavior. More recently, it has emerged that disturbances in peripheral and central oxytocin levels have been detected in some patients with dopamine-dependent disorders. Thus, oxytocin is proposed to be a key neural substrate that interacts with central dopamine systems. In addition to psychosocial improvement, oxytocin has recently been implicated in mediating mesolimbic dopamine pathways during drug addiction and withdrawal. This bi-directional role of dopamine has also been implicated during some components of sexual behavior. This review will discuss evidence for the existence dopamine/oxytocin positive interaction in social behavioral paradigms and associated disorders such as sexual dysfunction, autism, addiction, anorexia/bulimia, and depression. Preliminary findings suggest that whilst further rigorous testing has to be conducted to establish a dopamine/oxytocin link in human disorders, animal models seem to indicate the existence of broad and integrated brain circuits where dopamine and oxytocin interactions at least in part mediate socio-affiliative behaviors. A profound disruption to these pathways is likely to underpin associated behavioral disorders. Central oxytocin pathways may serve as a potential therapeutic target to improve mood and socio-affiliative behaviors in patients with profound social deficits and/or drug addiction.

p-Nitrobenzyl protection for cysteine and selenocysteine: a more stable alternative to the acetamidomethyl group

This study evaluated the acidic lability of the acetamidomethyl (Acm), trimethylacetamidomethyl (Tacm), and the p-nitrobenzyl (pNB) as protecting groups for cysteine and selenocysteine (Sec) during the tert-butyloxycarbonyl (Boc)-chemistry solid-phase peptide synthesis of oxytocin (OT). Two novel Sec building blocks (Nalpha-tert-butyloxycarbonyl-Se(acetamidomethyl)-L-selenocysteine (Boc-L-Sec(Acm)-OH) and Nalpha-tert-butyloxycarbonyl-S(4-nitrobenzyl)-L-selenocysteine (Boc-L-Sec(pNB)-OH)) were developed for this study. Six partially protected thio- and seleno-OT analogues were synthesized, purified, and exposed to neat trifluoroacetic acid (TFA) at temperatures of 25, 40, 50, and 60 degrees C for 1 h, and HF treatment at 0 degrees C for 1 h. Significant losses were observed for the Acm and Tacm group in TFA at temperatures greater than 25 degrees C and during HF treatment at 0 degrees C, whereas the pNB group remained intact. Removal of the pNB was achieved via reduction to the p-aminobenzyl group either with zinc in acetic acid in solution or via tin chloride in hydrochloric acid on solid support, followed by oxidative cleavage with iodine yielding the corresponding disulfide or diselenide bond. No major side reactions were observed. This study confirms the occasionally described Acm instability and underpins the development of the pNB group as an alternative for cysteine and Sec protection.

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.

Preventing preterm birth: the past limitations and new potential of animal models

The high rate of preterm birth in the USA and many other countries is a potential target for improving children’s immediate health and reducing the medical problems they face as adults. The acute complications for infants born prematurely often require intensive care management and are followed by long-lasting cognitive, sensory, motor, and cardiovascular deficits that substantially limit adult capabilities and survival. The inability to effectively reduce preterm birth stems from the failure to understand normal mechanisms of parturition in humans. Although studies from several model organisms help define the physiology of maintenance and termination of pregnancy, there are fundamental differences between species. For example, species regulate their production of progesterone, the crucial hormone in sustaining pregnancy, differently. This limits the extent to which models can provide meaningful information about the physiological mechanisms of human gestation. The growing wealth of sequenced mammalian genomes, computational comparative genomic tools and systems biology approaches provides new potential to utilize the divergence of DNA sequences and physiology between species to understand the genetic underpinnings of preterm birth.

Baby on board: do responses to stress in the maternal brain mediate adverse pregnancy outcome?

Stress and adverse environmental surroundings result in suboptimal conditions in a pregnant mother such that she may experience poor pregnancy outcome including complete pregnancy failure and preterm labor. Furthermore her developing baby is at risk of adverse programming, which confers susceptibility to long term ill health. While some mechanisms at the feto-maternal interface underlying these conditions are understood, the underlying cause for their adverse adaptation is often not clear. Progesterone plays a key role at many levels, including control of neuroendocrine responses to stress, procuring the required immune balance and controlling placental and decidual function, and lack of progesterone can explain many of the unwanted consequences of stress. How stress that is perceived by the mother inhibits progesterone secretion and action is beginning to be investigated. This overview of maternal neuroendocrine responses to stress throughout pregnancy analyses how they interact to compromise progesterone secretion and precipitate undesirable effects in mother and offspring.

Reproductive hormones and bone

Hypothalamic gonadotropin-releasing hormone (GnRH) stimulates secretion of pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which directly regulate ovarian function. Pituitary FSH can modulate osteoclast development, and thereby influence bone turnover. Pituitary oxytocin and prolactin effects on the skeleton are not merely limited to pregnancy and lactation; oxytocin stimulates osteoblastogenesis and bone formation, whereas prolactin exerts skeletal effects in an age-dependent manner. Cyclic levels of inhibins and estrogen suppress FSH and LH, respectively, and also suppress bone turnover via their suppressive effects on osteoblast and osteoclast differentiation. However, continuous exposure to inhibins or estrogen/androgens is anabolic for the skeleton in intact animals and protects against gonadectomy-induced bone loss. Alterations of one hormone in the hypothalamic-pituitary-gonadal (HPG) axis influence other bone-active hormones in the entire feedback loop in the axis. Thus, we propose that the action of the HPG axis should be extended to include its combined effects on the skeleton, thus creating the HPG skeletal (HPGS) axis.

Oxytocin signal and social behaviour: comparison among adult and infant oxytocin, oxytocin receptor and CD38 gene knockout mice

Oxytocin in the hypothalamus is the biological basis of social recognition, trust, love and bonding. Previously, we showed that CD38, a proliferation marker in leukaemia cells, plays an important role in the hypothalamus in the process of oxytocin release in adult mice. Disruption of Cd38 (Cd38 (-/-)) elicited impairment of maternal behaviour and male social recognition in adult mice, similar to the behaviour observed in Oxt and oxytocin receptor (Oxtr) gene knockout (Oxt (-/-) and Oxtr (-/-), respectively) mice. Locomotor activity induced by separation from the dam was higher and the number of ultrasonic vocalisation calls was lower in Cd38 (-/-) than Cd38( +/+) pups. However, these behavioural changes were much milder than those observed in Oxt (-/-) and Oxtr (-/-) mice, indicating less impairment of social behaviour in Cd38 (-/-) pups. These phenotypes appeared to be caused by the high plasma oxytocin levels during development from the neonatal period to 3-week-old juvenile mice. ADP-ribosyl cyclase activity was markedly lower in the knockout mice from birth, suggesting that weaning for mice is a critical time window of plasma oxytocin differentiation. Breastfeeding was an important exogenous source of plasma oxytocin regulation before weaning as a result of the presence of oxytocin in milk and the dam's mammary glands. The dissimilarity between Cd38 (-/-) infant behaviour and those of Oxt (-/-) or Oxtr (-/-) mice can be explained partly by this exogenous source of oxytocin. These results suggest that secretion of oxytocin into the brain in a CD38-dependent manner may play an important role in the development of social behaviour.

Uterine-specific p53 deficiency confers premature uterine senescence and promotes preterm birth in mice

Many signaling pathways that contribute to tumorigenesis are also functional in pregnancy, although they are dysregulated in the former and tightly regulated in the latter. Transformation-related protein 53 (Trp53), which encodes p53, is a tumor suppressor gene whose mutation is strongly associated with cancer. However, its role in normal physiological processes, including female reproduction, is poorly understood. Mice that have a constitutive deletion of Trp53 exhibit widespread development of carcinogenesis at early reproductive ages, compromised spermatogenesis, and fetal exencephaly, rendering them less amenable to studying the role of p53 in reproduction. To overcome this obstacle, we generated mice that harbor a conditional deletion of uterine Trp53 and examined pregnancy outcome in females with this genotype. These mice had normal ovulation, fertilization, and implantation; however, postimplantation uterine decidual cells showed terminal differentiation and senescence-associated growth restriction with increased levels of phosphorylated Akt and p21, factors that are both known to participate in these processes in other systems. Strikingly, uterine deletion of Trp53 increased the incidence of preterm birth, a condition that was corrected by oral administration of the selective COX2 inhibitor celecoxib. We further generated evidence to suggest that deletion of uterine Trp53 induces preterm birth through a COX2/PGF synthase/PGF(2alpha) pathway. Taken together, our observations underscore what we believe to be a new critical role of uterine p53 in parturition.

The challenge of translation in social neuroscience: a review of oxytocin, vasopressin, and affiliative behavior

Social neuroscience is rapidly exploring the complex territory between perception and action where recognition, value, and meaning are instantiated. This review follows the trail of research on oxytocin and vasopressin as an exemplar of one path for exploring the "dark matter" of social neuroscience. Studies across vertebrate species suggest that these neuropeptides are important for social cognition, with gender- and steroid-dependent effects. Comparative research in voles yields a model based on interspecies and intraspecies variation of the geography of oxytocin receptors and vasopressin V1a receptors in the forebrain. Highly affiliative species have receptors in brain circuits related to reward or reinforcement. The neuroanatomical distribution of these receptors may be guided by variations in the regulatory regions of their respective genes. This review describes the promises and problems of extrapolating these findings to human social cognition, with specific reference to the social deficits of autism.

Ligand-based peptide design and combinatorial peptide libraries to target G protein-coupled receptors

G protein-coupled receptors (GPCRs) are considered to represent the most promising drug targets; it has been repeatedly said that a large fraction of the currently marketed drugs elicit their actions by binding to GPCRs (with cited numbers varying from 30-50%). Closer scrutiny, however, shows that only a modest fraction of (≈60) GPCRs are, in fact, exploited as drug targets, only ≈20 of which are peptide-binding receptors. The vast majority of receptors in the humane genome have not yet been explored as sites of action for drugs. Given the drugability of this receptor class, it appears that opportunities for drug discovery abound. In addition, GPCRs provide for binding sites other than the ligand binding sites (referred to as the "orthosteric site"). These additional sites include (i) binding sites for ligands (referred to as "allosteric ligands") that modulate the affinity and efficacy of orthosteric ligands, (ii) the interaction surface that recruits G proteins and arrestins, (iii) the interaction sites of additional proteins (GIPs, GPCR interacting proteins that regulate G protein signaling or give rise to G protein-independent signals). These sites can also be targeted by peptides. Combinatorial and natural peptide libraries are therefore likely to play a major role in identifying new GPCR ligands at each of these sites. In particular the diverse natural peptide libraries such as the venom peptides from marine cone-snails and plant cyclotides have been established as a rich source of drug leads. High-throughput screening and combinatorial chemistry approaches allow for progressing from these starting points to potential drug candidates. This will be illustrated by focusing on the ligand-based drug design of oxytocin (OT) and vasopressin (AVP) receptor ligands using natural peptide leads as starting points.

The power of mouse genetics to study spermatogenesis

Approximately 80 million people worldwide are infertile, and nearly half of all infertility cases are attributed to a male factor. Therefore, progress in reproductive genetics becomes crucial for future diagnosis and treatment of infertility. In recent years, enormous progress has been made in this field. More than 400 mutant mouse models with specific reproductive abnormalities have been produced, and numerous human association studies have been discovered. However, the translation of basic science findings to clinical practice remains protracted, with only modest progress in the application of novel findings to clinical genetic testing and cures. To date, the most significant findings in male infertility remain numeric and structural chromosomal abnormalities and Y-chromosome microdeletions in infertile men. Thus, we anticipate that future genetic investigations will focus on infertile men with a normal somatic karyotype but with various spermatozoal defects, like insufficient production of spermatozoa (oligozoospermia), inadequate motility (asthenozoospermia), abnormal morphology (teratozoospermia), or combinations of these defects. Ultimately, basic advances in mammalian nonhuman reproduction will translate to clinical advances in human reproduction and testing for infertile humans, thereby helping to improve diagnostics and health care for infertile patients.