Maternal behavior deficits in nulliparous oxytocin knockout mice

Neurobiological mechanisms underlying oxytocin-mediated parental behavior in rodents

Parental behavior is essential for mammalian offspring to survive. Because of this significance, elucidating the neurobiological mechanisms that facilitate parental behavior has received strong interest. Decades of studies utilizing pharmacology and molecular biology have revealed that in addition to its facilitatory effects on parturition and lactation, oxytocin (OT) promotes the expression of parental behavior in rodents. Recent studies have also described the modulation of sensory processing by OT and the interaction of the OT system with other brain regions associated with parental behavior. However, the precise neurobiological mechanisms underlying the facilitation of caregiving behaviors by OT remain unclear. In this Review, I summarize the findings from rats and mice with a view toward integrating past and recent progress. I then review recent advances in the understanding of the molecular, cellular, and circuit mechanisms of OT-mediated parental behavior. Based on these observations, I propose a hypothetical model that would explain the mechanisms underlying OT-mediated parental behavior. Finally, I conclude by discussing some major remaining questions and propose potential future research directions.

Estrogen-dependent oxytocin expression in the hypothalamus and estrogen-dependent vasopressin in the median eminence

The posterior pituitary (PP) hormones oxytocin (OXT) and arginine vasopressin (AVP) are synthesized within the hypothalamic nucleus and released from the PP into systemic circulation. Hypothalamic AVP projects its axons into the external layer of median eminence (eME) and regulates anterior pituitary hormone secretion during stress responses. Although similar as PP hormones, we demonstrate distinct regulatory roles of estrogen in hypothalamic OXT and AVP dynamics. OXT dynamics in the hypothalamus exhibit sex-dependent variations and that estrogen may influence dynamic OXT level changes, as observed in OXT-mRFP1 transgenic rats. Estrogen was also observed to modulate dynamic changes in AVP levels in the axon terminals of eME in female AVP-eGFP transgenic rats. Although OXT and AVP are produced within the similar hypothalamic region, both exhibit distinct dynamics within the hypothalamus. Estrogen acts on the hypothalamus, and further effects of estrogen replacement therapy can be expected.

Oxytocin receptors in the nucleus accumbens shell are necessary for the onset of maternal behavior

In rodents, oxytocin (Oxt) contributes to the onset of maternal care by shifting the perception of pups from aversive to attractive. Both Oxt receptor knockout (Oxtr -/-) and forebrain-specific Oxtr knockout (FB/FB) dams abandon their first litters, likely due to a failure of the brain to 'switch' to a more maternal state. Whether this behavioral shift is neurochemically similar in virgin females, who can display maternal behaviors when repeatedly exposed to pups, or what neuroanatomical substrate is critical for the onset of maternal care remains unknown. To understand similarities and differences in Oxtr signaling in virgin pup-sensitized Oxtr FB/FB as opposed to post-parturient Oxtr -/- and Oxtr FB/FB dams, maternal behavior (pup-sensitized females only) and immediate early gene activation were assessed. Pup-sensitized Oxtr FB/FB females retrieved pups faster on day one of testing and had reduced c-Fos expression in the dorsal lateral septum as compared to virgin pup-sensitized Oxtr +/+ females. This differs from what was observed in post-parturient Oxtr -/- and Oxtr FB/FB dams, where increased c-Fos expression was observed in the nucleus accumbens (NAcc) shell. Based on these data, we then disrupted Oxtr signaling in the NAcc shell or the posterior paraventricular thalamus (pPVT) (control region) of female Oxtr floxed mice using a Cre recombinase expressing adeno-associated virus. Knockout of the Oxtr only in the NAcc shell prevented the onset of maternal care post-parturient females. Our data suggest that a pup-sensitized brain may differ from a post-parturient brain and that Oxtr signaling in the NAcc shell is critical to the onset of maternal behavior.

Oxytocin Receptor-Expressing Neurons in the Medial Preoptic Area Are Essential for Lactation, whereas Those in the Lateral Septum Are Not Critical for Maternal Behavior

INTRODUCTION

In nurturing systems, the oxytocin (Oxt)-oxytocin receptor (Oxtr) system is important for parturition, and essential for lactation and parental behavior. Among the nerve nuclei that express Oxtr, the lateral septal nucleus (LS) and medial preoptic area (MPOA) are representative regions that control maternal behavior.

METHODS

We investigated the role of Oxtr- and Oxtr-expressing neurons, located in the LS and MPOA, in regulating maternal behavior by regulating Oxtr expression in a region-specific manner using recombinant mice and adeno-associated viruses. We quantified the prolactin (Prl) concentrations in the pituitary gland and plasma when Oxtr expression in the MPOA was reduced.

RESULTS

The endogenous Oxtr gene in the neurons of the LS did not seem to play an essential role in maternal behavior. Conversely, decreased Oxtr expression in the MPOA increased the frequency of pups being left outside the nest and reduced their survival rate. Deletion of Oxtr in MPOA neurons prevented elevation of Prl levels in plasma and pituitary at postpartum day 2.

DISCUSSION/CONCLUSION

Oxtr-expressing neurons in the MPOA are involved in the postpartum production of Prl. We confirmed the essential functions of Oxtr-expressing neurons and the Oxtr gene itself in the MPOA for the sustainability of maternal behavior, which involved Oxtr-dependent induction of Prl.

Genotypic sex shapes maternal care in the African pygmy mouse, Mus minutoides

Sexually dimorphic behaviours, such as parental care, have long been thought to be mainly driven by gonadal hormones. In the past two decades, a few studies have challenged this view, highlighting the direct influence of the sex chromosome complement (XX versus XY or ZZ versus ZW). The African pygmy mouse, Mus minutoides, is a wild mouse species with naturally occurring XY sex reversal induced by a third, feminizing X* chromosome, leading to three female genotypes: XX, XX* and X*Y. Here, we show that sex reversal in X*Y females shapes a divergent maternal care strategy (maternal aggression, pup retrieval and nesting behaviours) from both XX and XX* females. Although neuroanatomical investigations were inconclusive, we show that the dopaminergic system in the anteroventral periventricular nucleus of the hypothalamus is worth investigating further as it may support differences in pup retrieval behaviour between females. Combining behaviours and neurobiology in a rodent subject to natural selection, we evaluate potential candidates for the neural basis of maternal behaviours and strengthen the underestimated role of the sex chromosomes in shaping sex differences in brain and behaviours. All things considered, we further highlight the emergence of a third sexual phenotype, challenging the binary view of phenotypic sexes.

Oxytocin antagonist does not disrupt rabbit maternal behavior despite binding to brain oxytocin receptors

We explored a possible role of oxytocin (OXT) for the onset and maintenance of rabbit maternal behavior by: (a) confirming that a selective oxytocin receptor antagonist (OTA) widely used in rodents selectively binds to OXT receptors (OXTR) in the rabbit brain and (b) determining the effect of daily intracerebroventricular (icv) injections of OTA to primiparous and multiparous does from gestation day 29 to lactation day 3. OTA efficiently displaced the high affinity, selective oxytocin receptor (OXTR) radioligand, 125 I-labeled ornithine vasotocin analog (125 I-OVTA), but was much less effective at displacing the selective V1a vasopressin receptor radioligand, 125 I-labeled linear vasopressin, thus showing high affinity and selectivity of OTA for rabbit OXTR as in rodents. Further, ICV OTA injections did not modify nest-building, latency to enter the nest box, time spent nursing or the amount of milk produced, relative to vehicle-injected does. The percentage of mothers suckling the litter was also similar between both groups, regardless of parity. Together, our results do not support a role of OXT for the initiation or maintenance of rabbit maternal behavior. Future studies are warranted to determine if OXT participates in fine-tuning additional aspects of the maternal ethogram, for example, circadian periodicity of nursing and nest defense.

Hearing Vocalizations during First Social Experience with Pups Increase Bdnf Transcription in Mouse Auditory Cortex

While infant cues are often assumed to innately motivate maternal response, recent research highlights how the neural coding of infant cues is altered through maternal care. Infant vocalizations are important social signals for caregivers, and evidence from mice suggests that experience caring for mouse pups induces inhibitory plasticity in the auditory cortex (AC), though the molecular mediators for such AC plasticity during the initial pup experience are not well delineated. Here, we used the maternal mouse communication model to explore whether transcription in AC of a specific, inhibition-linked, memory-associated gene, brain-derived neurotrophic factor (Bdnf) changes due to the very first pup caring experience hearing vocalizations, while controlling for the systemic influence of the hormone estrogen. Ovariectomized and estradiol or blank-implanted virgin female mice hearing pup calls with pups present had significantly higher AC exon IV Bdnf mRNA compared to females without pups present, suggesting that the social context of vocalizations induces immediate molecular changes at the site of auditory cortical processing. E2 influenced the rate of maternal behavior but did not significantly affect Bdnf mRNA transcription in the AC. To our knowledge, this is the first time Bdnf has been associated with processing social vocalizations in the AC, and our results suggest that it is a potential molecular component responsible for enhancing future recognition of infant cues by contributing to AC plasticity.

Mother-Young Bonding: Neurobiological Aspects and Maternal Biochemical Signaling in Altricial Domesticated Mammals

Mother-young bonding is a type of early learning where the female and their newborn recognize each other through a series of neurobiological mechanisms and neurotransmitters that establish a behavioral preference for filial individuals. This process is essential to promote their welfare by providing maternal care, particularly in altricial species, animals that require extended parental care due to their limited neurodevelopment at birth. Olfactory, auditory, tactile, and visual stimuli trigger the neural integration of multimodal sensory and conditioned affective associations in mammals. This review aims to discuss the neurobiological aspects of bonding processes in altricial mammals, with a focus on the brain structures and neurotransmitters involved and how these influence the signaling during the first days of the life of newborns.

The importance of oxytocin neurons in the supraoptic nucleus for breastfeeding in mice

The hormone oxytocin, secreted from oxytocin neurons in the paraventricular (PVH) and supraoptic (SO) hypothalamic nuclei, promotes parturition, milk ejection, and maternal caregiving behaviors. Previous experiments with whole-body oxytocin knockout mice showed that milk ejection was the unequivocal function of oxytocin, whereas parturition and maternal behaviors were less dependent on oxytocin. Whole-body knockout, however, could induce the enhancement of expression of related gene(s), a phenomenon called genetic compensation, which may hide the actual functions of oxytocin. In addition, the relative contributions of oxytocin neurons in the PVH and SO have not been well documented. Here, we show that females with conditional knockout of oxytocin gene in both the PVH and SO undergo grossly normal parturition and maternal caregiving behaviors, while dams with a smaller number of remaining oxytocin-expressing neurons exhibit severe impairments in breastfeeding, leading to the death of their pups within 24 hours after birth. We also found that the growth of pups is normal even under oxytocin conditional knockout in PVH and SO as long as pups survive the next day of delivery, suggesting that the reduced oxytocin release affects the onset of lactation most severely. These phenotypes are largely recapitulated by SO-specific oxytocin conditional knockout, indicating the unequivocal role of oxytocin neurons in the SO in successful breastfeeding. Given that oxytocin neurons not only secrete oxytocin but also non-oxytocin neurotransmitters or neuropeptides, we further performed cell ablation of oxytocin neurons in the PVH and SO. We found that cell ablation of oxytocin neurons leads to no additional abnormalities over the oxytocin conditional knockout, suggesting that non-oxytocin ligands expressed by oxytocin neurons have negligible functions on the responses measured in this study. Collectively, our findings confirm the dispensability of oxytocin for parturition or maternal behaviors, as well as the importance of SO-derived oxytocin for breastfeeding.

The modulation of emotional and social behaviors by oxytocin signaling in limbic network

Neuropeptides can exert volume modulation in neuronal networks, which account for a well-calibrated and fine-tuned regulation that depends on the sensory and behavioral contexts. For example, oxytocin (OT) and oxytocin receptor (OTR) trigger a signaling pattern encompassing intracellular cascades, synaptic plasticity, gene expression, and network regulation, that together function to increase the signal-to-noise ratio for sensory-dependent stress/threat and social responses. Activation of OTRs in emotional circuits within the limbic forebrain is necessary to acquire stress/threat responses. When emotional memories are retrieved, OTR-expressing cells act as gatekeepers of the threat response choice/discrimination. OT signaling has also been implicated in modulating social-exposure elicited responses in the neural circuits within the limbic forebrain. In this review, we describe the cellular and molecular mechanisms that underlie the neuromodulation by OT, and how OT signaling in specific neural circuits and cell populations mediate stress/threat and social behaviors. OT and downstream signaling cascades are heavily implicated in neuropsychiatric disorders characterized by emotional and social dysregulation. Thus, a mechanistic understanding of downstream cellular effects of OT in relevant cell types and neural circuits can help design effective intervention techniques for a variety of neuropsychiatric disorders.

Linking oxytocin and arginine vasopressin signaling abnormalities to social behavior impairments in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a genetic neurodevelopmental disorder. Global hypothalamic dysfunction is a core feature of PWS and has been implicated as a driver of many of PWS's phenotypic characteristics (e.g., hyperphagia-induced obesity, hypogonadism, short stature). Although the two neuropeptides (i.e., oxytocin [OXT] and arginine vasopressin [AVP]) most implicated in mammalian prosocial functioning are of hypothalamic origin, and social functioning is markedly impaired in PWS, there has been little consideration of how dysregulation of these neuropeptide signaling pathways may contribute to PWS's social behavior impairments. The present article addresses this gap in knowledge by providing a comprehensive review of the preclinical and clinical PWS literature-spanning endogenous neuropeptide measurement to exogenous neuropeptide administration studies-to better understand the roles of OXT and AVP signaling in this population. The preponderance of evidence indicates that OXT and AVP signaling are indeed dysregulated in PWS, and that these neuropeptide pathways may provide promising targets for therapeutic intervention in a patient population that currently lacks a pharmacological strategy for its debilitating social behavior symptoms.

Oestrogen-dependent hypothalamic oxytocin expression with changes in feeding and body weight in female rats

Oxytocin (OXT) is produced in the hypothalamic nuclei and secreted into systemic circulation from the posterior pituitary gland. In the central nervous system, OXT regulates behaviours including maternal and feeding behaviours. Our aim is to evaluate whether oestrogen regulates hypothalamic OXT dynamics. Herein, we provide the first evidence that OXT dynamics in the hypothalamus vary with sex and that oestrogen may modulate dynamic changes in OXT levels, using OXT-mRFP1 transgenic rats. The fluorescence intensity of OXT-mRFP1 and expression of the OXT and mRFP1 genes in the hypothalamic nuclei is highest during the oestrus stage in female rats and decreased significantly in ovariectomised rats. Oestrogen replacement caused significant increases in fluorescence intensity and gene expression in a dose-related manner. This is also demonstrated in the rats' feeding behaviour and hypothalamic Fos neurons using cholecystokinin-8 and immunohistochemistry. Hypothalamic OXT expression is oestrogen-dependent and can be enhanced centrally by the administration of oestrogen.

The role of oxytocin in shaping complex social behaviours: possible interactions with other neuromodulators

This review explores the role of oxytocin in the mediation of select social behaviours, with particular emphasis on female rodents. These behaviours include social recognition, social learning, pathogen detection and avoidance, and maternal care. Specific brain regions where oxytocin has been shown to directly mediate various aspects of these social behaviours, as well as other proposed regions, are discussed. Possible interactions between oxytocin and other regulatory systems, in particular that of oestrogens and dopamine, in the modulation of social behaviour are considered. Similarities and differences between males and females are highlighted. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

Oxytocin interactions with central dopamine and serotonin systems regulate different components of motherhood

The role of oxytocin in maternal caregiving and other postpartum behaviours has been studied for more than five decades. How oxytocin interacts with other neurochemical systems to enact these behavioural changes, however, is only slowly being elucidated. The best-studied oxytocin-neurotransmitter interaction is with the mesolimbic dopamine system, and this interaction is essential for maternal motivation and active caregiving behaviours such as retrieval of pups. Considerably less attention has been dedicated to investigating how oxytocin interacts with central serotonin to influence postpartum behaviour. Recently, it has become clear that while oxytocin-dopamine interactions regulate the motivational and pup-approach aspects of maternal caregiving behaviours, oxytocin-serotonin interactions appear to regulate nearly all other aspects including postpartum nursing, aggression, anxiety-like behaviour and stress coping strategy. Collectively, oxytocin's interactions with central dopamine and serotonin systems are thus critical for the entire suite of behavioural adaptations exhibited in the postpartum period, and these sites of interaction are potential pharmacological targets for where oxytocin could help to ameliorate deficits in maternal caregiving and poor postpartum mental health. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

Dysfunctions of brain oxytocin signaling: Implications for poor mothering

Good mothering has profound impact on both the mother's and the young's well-being. Consequently, experiencing inadequate maternal care - or even neglect - in the first stages of life is a major risk factor for the development of psychiatric disorders, and even for poor parenting towards the future offspring. Thus, understanding the neurobiological basis of maternal neglect becomes crucial. Along with other neurotransmitters and neuropeptides, oxytocin (OXT) has long been known as one of the main modulators of maternal behavior. In rodents, disruptions of central OXT transmission have been associated with poor maternal responses, like impaired onset of nursing behaviors, and reduced care and defense of the pups. Importantly, such behavioral and molecular deficits can be transmitted through generations, creating a vicious circle of low-quality maternal behavior. Similarly, evidence from human studies shows that OXT signaling is defective in conditions of inadequate mothering and child neglect. On those premises, this review aims at providing a comprehensive overview of animal and human studies linking perturbed OXT transmission to poor maternal behavior. Considering the important fallouts of inadequate maternal responses, we believe that unraveling the alterations in OXT transmission might provide useful insights for a better understanding of maternal neglect and, ultimately, for future intervention approaches.

Species differences in the effect of oxytocin on maternal behavior: A model incorporating the potential for allomaternal contributions

Oxytocin has historically been linked to processes involved with maternal behavior. However, the relative importance of oxytocin for maternal behavior widely varies among mammalian species, from indispensable to apparently nonessential. This review proposes a new model in which the relative importance of oxytocin for mothering across species is explained by an evolutionary pressure which we term "allomaternal potential", or the degree to which other conspecifics are capable and likely to assist with caregiving. It is notable that in animals where allomaternal potential is high (i.e., many quality helpers are available), oxytocin is decoupled from mothering. However, in animals where allomaternal potential is low (i.e., conspecifics refuse to, or do not provide, quality help), oxytocin is crucial for mothering. We posit that this relationship is a form of kin selection, whereby oxytocin is a signal that leads mothers to preferentially dispense resources to their own young when quality helpers are unlikely.

Parental Behavior in Rodents

Members of the order Rodentia are among the best-studied mammals for understanding the patterns, outcomes, and biological determinants of maternal and paternal caregiving. This research has provided a wealth of information but has historically focused on just a few rodents, mostly members of the two Myomorpha families that easily breed and can be studied within a laboratory setting (including laboratory rats, mice, hamsters, voles, gerbils). It is unclear how well this small collection of animals represents the over 2000 species of extant rodents. This chapter provides an overview of the hormonal and neurobiological systems involved in parental care in rodents, with a purposeful eye on providing information known or could be gleaned about parenting in various less-traditional members of Rodentia. We conclude from this analysis that the few commonly studied rodents are not necessarily even representative of the highly diverse members of Myomorpha, let alone other rodent suborders, and that additional laboratory and field studies of members of this order more broadly would surely provide invaluable information toward revealing a more representative picture of the rich diversity in rodent parenting.

Effects of Prenatal Phthalate Exposure and Childhood Exercise on Maternal Behaviors in Female Rats at Postpartum: A Role of Oxtr Methylation in the Hypothalamus

Both the detrimental effect of prenatal exposure to di-(2-ethylhexyl)-phthalate (DEHP) and the beneficial effects of physical exercise on brain functions have been reported. The oxytocin pathway has been implicated in the onset of maternal behaviors. Epigenetic modification of the oxytocin receptor gene (OXTR) through DNA methylation has been associated with the pathogenesis of neuropsychiatric disorders. The purpose of this study was to investigate the effects of prenatal DEHP exposure on oxytocin-regulated maternal behaviors and to examine the protective effect of exercise. Pregnant rats (F0) were fed with vehicle or DEHP during gestation and the offspring females (F1) were assessed for their maternal behaviors by pup retrieval test at postpartum. The results showed that reduced pup retrieval activities without significant alteration of stress responses were observed in the prenatally DEHP-exposed females. Prenatal DEHP exposure decreased the expressions of oxytocin, Oxtr mRNA, and oxytocin receptor, and increased Oxtr methylation in the hypothalamus of postpartum female rats. There were no significant effects of exercise on behavioral, biochemical, and epigenetic measurements. These results suggest that prenatal DEHP exposure has a long-term adverse effect on maternal behaviors; Oxtr hyper-methylation may be a potential epigenetic mechanism for this alteration, which cannot be prevented by physical exercise during childhood.

Changes in maternal motivation across reproductive states in mice: A role for prolactin receptor activation on GABA neurons

The survival of newborn offspring in mammals is dependent on sustained maternal care. Mammalian mothers are highly motivated to interact with and care for offspring, however, it is unclear how hormonal signals act on neural circuitry to promote maternal motivation during the transition to motherhood. In this study we aimed to establish methods that enable us to evaluate change in maternal motivation across the reproductive life cycle in female mice. Using two behavioural testing paradigms; a novel T-maze retrieval test and a barrier climbing test, we found that pup retrieval behaviour was low in virgin and pregnant mice compared to lactating females, indicating that maternal motivation arises around the time of parturition. Furthermore, in reproductively experienced females, maternal motivation declined over time after weaning of pups. As we have previously shown that lactogenic action mediated through the prolactin receptor (Prlr) in the medial preoptic area (MPOA) is essential for the expression of maternal behaviour, we aimed to investigate the role of lactogenic hormones in promoting pup-related motivational behaviours. With GABAergic neurons expressing Prlr in multiple brain regions important for maternal behaviour, we conditionally deleted Prlr from GABA neurons. Compared to control females, lactating GABA neuron-specific Prlr knockout mice showed slower and incomplete pup retrieval behaviour in the T-maze test. Testing of anxiety behaviour on an elevated plus maze indicated that these mice did not have increased anxiety levels, suggesting that lactogenic action on GABA neurons is necessary for the full expression of motivational aspects of maternal behaviour during lactation.

Disturbance of the reciprocal-interaction between the OXTergic and DAergic systems in the CNS causes atypical social behavior in syntaxin 1A knockout mice

Several studies have shown that oxytocin (OXT) modulates social behavior. Similarly, monoamines such as dopamine (DA) play a role in regulating social behavior. Previous studies have demonstrated that the soluble N-ethylmaleimide-sensitive fusion attachment protein receptor (SNARE) protein syntaxin 1A (STX1A) regulates the secretion of OXT and monoamines, and that STX1A gene knockout (STX1A KO) mice exhibit atypical social behavior, such as deficient social recognition, due to reduced OXT release. In this study, we analyzed the neural mechanism regulating social behavior by OXT and/or DA using STX1A KO mice as a model animal. We found that OXT directly induced DA release from cultured DA neurons through OXT and V1a receptors. In STX1A KO mice, the atypical social behavior was partially improved by OXT administration, which was inhibited by D1 receptor blockade. In addition, the atypical social behavior in STX1A KO mice was partially improved by facilitation of DAergic signaling with the DA reuptake inhibitor GBR12909. Moreover, the amelioration by GBR12909 was inhibited by OXTR blockade. These results suggest that the reciprocal interaction between the DAergic and OXTergic neuronal systems in the CNS may be important in regulating social behavior.

An acute dose of intranasal oxytocin rapidly increases maternal communication and maintains maternal care in primiparous postpartum California mice

Maternal-offspring communication and care are essential for offspring survival. Oxytocin (OXT) is known for its role in initiation of maternal care, but whether OXT can rapidly influence maternal behavior or ultrasonic vocalizations (USVs; above 50 kHz) has not been examined. To test for rapid effects of OXT, California mouse mothers were administered an acute intranasal (IN) dose of OXT (0.8 IU/kg) or saline followed by a separation test with three phases: habituation with pups in a new testing chamber, separation via a wire mesh, and finally reunion with pups. We measured maternal care, maternal USVs, and pup USVs. In mothers, we primarily observed simple sweep USVs, a short downward sweeping call around 50 kHz, and in pups we only observed pup whines, a long call with multiple harmonics ranging from 20 kHz to 50 kHz. We found that IN OXT rapidly and selectively enhanced the normal increase in maternal simple sweep USVs when mothers had physical access to pups (habituation and reunion), but not when mothers were physically separated from pups. Frequency of mothers' and pups' USVs were correlated upon reunion, but IN OXT did not influence this correlation. Finally, mothers given IN OXT showed more efficient pup retrieval/carrying and greater total maternal care upon reunion. Behavioral changes were specific to maternal behaviors (e.g. retrievals) as mothers given IN OXT did not differ from controls in stress-related behaviors (e.g. freezing). Overall, these findings highlight the rapid effects and context-dependent effect a single treatment with IN OXT has on both maternal USV production and offspring care.

A Scientometric Approach to Review the Role of the Medial Preoptic Area (MPOA) in Parental Behavior

Research investigating the neural substrates underpinning parental behaviour has recently gained momentum. Particularly, the hypothalamic medial preoptic area (MPOA) has been identified as a crucial region for parenting. The current study conducted a scientometric analysis of publications from 1 January 1972 to 19 January 2021 using CiteSpace software to determine trends in the scientific literature exploring the relationship between MPOA and parental behaviour. In total, 677 scientific papers were analysed, producing a network of 1509 nodes and 5498 links. Four major clusters were identified: “C-Fos Expression”, “Lactating Rat”, “Medial Preoptic Area Interaction” and “Parental Behavior”. Their content suggests an initial trend in which the properties of the MPOA in response to parental behavior were studied, followed by a growing attention towards the presence of a brain network, including the reward circuits, regulating such behavior. Furthermore, while attention was initially directed uniquely to maternal behavior, it has recently been extended to the understanding of paternal behaviors as well. Finally, although the majority of the studies were conducted on rodents, recent publications broaden the implications of previous documents to human parental behavior, giving insight into the mechanisms underlying postpartum depression. Potential directions in future works were also discussed.

Dorsal raphe serotonin neurotransmission is required for the expression of nursing behavior and for pup survival

Proper maternal care is an essential factor of reproductive success in mammals, involving a repertoire of behaviors oriented toward the feeding and care of the offspring. Among the neurotransmitters involved in the initiation of these behaviors, serotonin (5-HT) seems to play an important role. Here we compared pup-oriented maternal behaviors in mice with constitutive 5-HT depletion, the tryptophan hydroxylase 2-knock-out (Tph2-KO) and the Pet1-KO mice. We report that the only common pup-oriented defect in these 2 hyposerotoninergic models is a defective nursing in parturient mice and altered nursing-like (crouching) behavior in virgin mice, while pup retrieval defects are only present in Tph2-KO. Despite a normal mammary gland development and milk production, the defect in appropriate nursing is responsible for severe growth retardation and early lethality of pups born to hyposerotonergic dams. This nursing defect is due to acute rather constitutive 5-HT depletion, as it is reproduced by adult knockdown of Tph2 in the dorsal raphe nucleus in mothers with a prior normal maternal experience. We conclude that 5-HT innervation from the dorsal raphe is required for both the initiation and maintenance of a normal nursing behavior. Our findings may be related to observations of reduced maternal/infant interactions in human depression.

The neurochemistry of social reward during development: What have we learned from rodent models?

Social rewards are fundamental to survival and overall health. Several studies suggest that adequate social stimuli during early life are critical for developing appropriate socioemotional and cognitive skills, whereas adverse social experiences negatively affect the proper development of brain and behavior, by increasing the susceptibility to develop neuropsychiatric conditions. Therefore, a better understanding of the neural mechanisms underlying social interactions, and their rewarding components in particular, is an important challenge of current neuroscience research. In this context, preclinical research has a crucial role: Animal models allow to investigate the neurobiological aspects of social reward in order to shed light on possible neurochemical alterations causing aberrant social reward processing in neuropsychiatric diseases, and they allow to test the validity and safety of innovative therapeutic strategies. Here, we discuss preclinical research that has investigated the rewarding properties of two forms of social interaction that occur in different phases of the lifespan of mammals, that is, mother-infant interaction and social interactions with peers, by focusing on the main neurotransmitter systems mediating their rewarding components. Together, the research performed so far helped to elucidate the mechanisms of social reward and its psychobiological components throughout development, thus increasing our understanding of the neurobiological substrates sustaining social functioning in health conditions and social dysfunction in major psychiatric disorders.

Oxytocin Signaling Pathway: From Cell Biology to Clinical Implications

BACKGROUND

In addition to the well-known role played in lactation and parturition, Oxytocin (OT) and OT receptor (OTR) are involved in many other aspects such as the control of maternal and social behavior, the regulation of the growth of the neocortex, the maintenance of blood supply to the cortex, the stimulation of limbic olfactory area to mother-infant recognition bond, and the modulation of the autonomic nervous system via the vagal pathway. Moreover, OT and OTR show antiinflammatory, anti-oxidant, anti-pain, anti-diabetic, anti-dyslipidemic and anti-atherogenic effects.

OBJECTIVE

The aim of this narrative review is to summarize the main data coming from the literature dealing with the role of OT and OTR in physiology and pathologic conditions focusing on the most relevant aspects.

METHODS

Appropriate keywords and MeSH terms were identified and searched in Pubmed. Finally, references of original articles and reviews were examined.

RESULTS

We report the most significant and updated data on the role played by OT and OTR in physiology and different clinical contexts.

CONCLUSION

Emerging evidence indicates the involvement of OT system in several pathophysiological mechanisms influencing brain anatomy, cognition, language, sense of safety and trust and maternal behavior, with the possible use of exogenous administered OT in the treatment of specific neuropsychiatric conditions. Furthermore, it modulates pancreatic β-cell responsiveness and lipid metabolism leading to possible therapeutic use in diabetic and dyslipidemic patients and for limiting and even reversing atherosclerotic lesions.

Neuropeptidergic and Neuroendocrine Systems Underlying Eusociality and the Concomitant Social Regulation of Reproduction in Naked Mole-Rats: A Comparative Approach

The African mole-rat family (Bathyergidae) includes the first mammalian species identified as eusocial: naked mole-rats. Comparative studies of eusocial and solitary mole-rat species have identified differences in neuropeptidergic systems that may underlie the phenomenon of eusociality. These differences are found in the oxytocin, vasopressin and corticotrophin-releasing factor (CRF) systems within the nucleus accumbens, amygdala, bed nucleus of the stria terminalis and lateral septal nucleus. As a corollary of their eusociality, most naked mole-rats remain pre-pubertal throughout life because of the presence of the colony's only reproductive female, the queen. To elucidate the neuroendocrine mechanisms that mediate this social regulation of reproduction, research on the hypothalamo-pituitary-gonadal axis in naked mole-rats has identified differences between the many individuals that are reproductively suppressed and the few that are reproductively mature: the queen and her male consorts. These differences involve gonadal steroids, gonadotrophin-releasing hormone-1 (GnRH-1), kisspeptin, gonadotrophin-inhibitory hormone/RFamide-related peptide-3 (GnIH/RFRP-3) and prolactin. The comparative findings in eusocial and solitary mole-rat species are assessed with reference to a broad range of studies on other mammals.

Mothering revisited: A role for cortisol?

This selective review first describes the involvement of the maternal hypothalamic-pituitary-adrenal (HPA) axis during pregnancy and the postpartum period, and the relation between peripartum HPA axis function and maternal behavior, stress reactivity and emotional dysregulation in human mothers. To provide experimental background to this correlational work, where helpful, animal studies are also described. It then explores the association between HPA axis function in mothers and their infants, under ongoing non-stressful conditions and during stressful challenges, the moderating role of mothers' sensitivity and behavior in the mother-child co-regulation and the effects of more traumatic risk factors on these relations. The overarching theme being explored is that the HPA axis - albeit a system designed to function during periods of high stress and challenge - also functions to promote adaptation to more normative processes, shown in the new mother who experiences both high cortisol and enhanced attraction and attention to and recognition of, their infants and their cues. Hence the same HPA system shows positive relations with behavior at some time points and inverse ones at others. However, the literature is not uniform and results vary widely depending on the number, timing, place, and type of samplings and assessments, and, of course, the population being studied and, in the present context, the state, the stage, and the stress levels of mother and infant.

Impaired experience-dependent maternal care in presynaptic active zone protein CAST-deficient dams

Although sociological studies affirm the importance of parental care in the survival of offspring, maltreatment—including child neglect—remains prevalent in many countries. While child neglect is well known to affect child development, the causes of maternal neglect are poorly understood. Here, we found that female mice with a deletion mutation of CAST (a presynaptic release-machinery protein) showed significantly reduced weaning rate when primiparous and a recovered rate when multiparous. Indeed, when nurturing, primiparous and nulliparous CAST knock out (KO) mice exhibited less crouching time than control mice and moved greater distances. Contrary to expectations, plasma oxytocin (OXT) was not significantly reduced in CAST KO mice even though terminals of magnocellular neurons in the posterior pituitary expressed CAST. We further found that compared with control mice, CAST KO mice drank significantly less water when nurturing and had a greater preference for sucrose during pregnancy. We suggest that deficiency in presynaptic release-machinery protein impairs the facilitation of some maternal behaviours, which can be compensated for by experience and learning.

Presynaptic glutamatergic transmission and feedback system of oxytocinergic neurons in the hypothalamus of a rat model of adjuvant arthritis

The neurohypophysial hormone oxytocin (OXT) is synthesized in the hypothalamic paraventricular and supraoptic nuclei. Recently, some studies have considered OXT to be important in sensory modulation and that the OXT protein is upregulated by acute and chronic nociception. However, the mechanism by which OXT is upregulated in neurons is unknown. In this study, we examined the resting membrane potentials and excitatory postsynaptic currents in OXT-ergic neurons in the paraventricular nucleus in adjuvant arthritis rat model, a model of chronic inflammation, using whole-cell patch-clamping. Transgenic rats expressing OXT and monomeric red fluorescent protein 1 (mRFP1) fusion protein to visualize the OXT-ergic neurons were used, and the OXT-mRFP1 transgenic rat model of adjuvant arthritis was developed by injection of heat-killed Mycobacterium butyricum. Furthermore, the feedback system of synthesized OXT was also examined using the OXT receptor antagonist L-368,899. We found that the resting membrane potentials and frequency of miniature excitatory postsynaptic currents and spontaneous excitatory postsynaptic currents in OXT-monomeric red fluorescent protein 1 neurons in the paraventricular nucleus were significantly increased in adjuvant arthritis rats. Furthermore, L-368,899 dose-dependently increased the frequency of miniature excitatory postsynaptic currents and spontaneous excitatory postsynaptic currents in OXT-ergic neurons. Following bath application of the GABAA receptor antagonist picrotoxin and the cannabinoid receptor 1 antagonist AM 251, L-368,899 still increased the frequency of miniature excitatory postsynaptic currents. However, following bath application of the nitric oxide synthase inhibitor Nω-Nitro-L-arginine methyl ester hydrochloride, L-368,899 did not alter the miniature excitatory postsynaptic current frequency. Thus, it is suggested that OXT-ergic neuron activity is upregulated via an increase in glutamate release, and that the upregulated OXT neurons have a feedback system with released endogenous OXT. It is possible that nitric oxide, but not GABA, may contribute to the feedback system of OXT neurons in chronic inflammation.

Do nonapeptides regulate parental care depending on experience in zebra finches?

Recent research suggests that the nonapeptide neurohormones regulate parental behaviors in a diverse array of vertebrates. However, it remains unclear how these neurohormones regulate parental care among birds, especially those which exhibit biparental care, or whether hormonal effects are contingent on a bird's previous experience as a parent. We measured the effects of nonapeptides on parental behaviors by peripherally injecting, over three treatment days, a short-acting nonapeptide receptor antagonist (OTA) or a saline control into breeding pairs of zebra finches (Taeniopygia guttata) that either did or did not have previous parental experience. We then compared how the duration of parental behaviors changed over the five days of observation (including one day before and two days after injections were administered). To compare treatment effects on parental outcomes, we also measured chick growth and mortality rates for each pair. There was a nearly significant interaction between treatment and experience for the amount of time birds spent in the nest, with time in the nest declining across the experiment inexperienced and experienced OTA birds. There was also a significant treatment by trial day interaction for nest guarding and a treatment by experience by trial day interaction for nest maintenance. Chicks reared by parents that received the OTA had significantly lower growth rates than chicks reared by control parents and, among experienced birds, higher mortality relative to control birds. Together, these results provide some support for the hypothesis that nonapeptides play a role in regulating parental outcomes and some parental behaviors in both experienced and inexperienced zebra finches.

Exploring associations between perinatal depression, anxiety, and urinary oxytocin levels in Latinas

Perinatal depression has been associated with lower oxytocin (OT) levels. However, few studies have explored this topic in relation to Latinas who are at high risk of perinatal depression. The objective of this study was to explore these associations in Latinas. A total of 108 Latinas in the third trimester of pregnancy participated in the study. Depression and urinary OT levels were assessed in pregnancy and 6 weeks postpartum. Nonparametric tests were implemented to test the proposed associations. Results revealed that 28% of the participants had probable depression in pregnancy, and 23% at 6 weeks postpartum. OT levels significantly decreased from prenatal to postpartum in the whole sample; however, participants with probable prenatal depression did not exhibit a significant change in OT levels. Participants who were depressed or anxious at 6 weeks postpartum exhibited persistently higher mean OT levels over time. A distinct pattern of higher levels of OT in depressed Latinas suggests that OT levels may be an important neuroendocrine factor contributing to depressive and anxious symptoms.

Centrally administered kisspeptin suppresses feeding via nesfatin-1 and oxytocin in male rats

Kisspeptin (KP), known as a hypothalamic neuropeptide, plays a critical role in the regulation of not only reproduction but also food intake. The anorectic neuropeptides, nesfatin-1 and oxytocin (OXT), are expressed in central nervous system, particulaly in various hypothalamic nuclei, and peripheral tissue. We examined the effects of the intracerebroventricular (icv) administration of KP-10 on feeding and nesfatin-1-immunoreactive (ir) or OXT-ir neurons in the rat hypothalamus, using Fos double immunohistochemistry in male rats. Cumulative food intake was remarkably decreased 0.5-3 h after icv administration of KP-10 (6.0 μg) compared to the vehicle treated and the KP-10 (3.8 μg) treated group. The icv administration of KP-10 significantly increased the number of nesfatin-1-ir neurons expressing Fos in the supraoptic nucleus (SON), paraventricular nucleus (PVN), arcuate nucleus (ARC), dorsal raphe nucleus, locus coeruleus, and nucleus tractus solitarius. The decreased food intake induced by KP-10 was significantly attenuated by pretreatment with the icv administration of antisense RNA against nucleobindin-2. After icv administration of KP-10, the percentages of OXT-ir neurons expressing FOS were remarkably higher in the SON and PVN than for vehicle treatment. The KP-10-induced anorexia was partially abolished by pretreatment with OXT receptor antagonist (OXTR-A). The percentage of nesfatin-1-ir neurons expressing Fos-ir in the ARC was also decreased by OXTR-A pretreatment. These results indicate that central administration of KP-10 activates nesfatin-1- and OXT neurons, and may play an important role in the suppression of feeding in male rats.

DNA Methylation and Hydroxymethylation and Behavior

Environmentally sensitive molecular mechanisms in the brain, such as DNA methylation, have become a significant focus of neuroscience research because of mounting evidence indicating that they are critical in response to social situations, stress, threats, and behavior. The recent identification of 5-hydroxymethylcytosine (5hmC), which is enriched in the brain (tenfold over peripheral tissues), raises new questions as to the role of this base in mediating epigenetic effects in the brain. The development of genome-wide methods capable of distinguishing 5-methylcytosine (5mC) from 5hmC has revealed that a growing number of behaviors are linked to independent disruptions of 5mC and 5hmC levels, further emphasizing the unique importance of both of these modifications in the brain. Here, we review the recent links that indicate DNA methylation (both 5mC and 5hmC) is highly dynamic and that perturbations in this modification may contribute to behaviors related to psychiatric disorders and hold clinical relevance.

Epigenetic dysregulation of Oxtr in Tet1-deficient mice has implications for neuropsychiatric disorders

OXTR modulates a variety of behaviors in mammals, including social memory and recognition. Genetic and epigenetic dysregulation of OXTR has been suggested to be implicated in neuropsychiatric disorders, including autism spectrum disorder (ASD). While the involvement of DNA methylation is suggested, the mechanism underlying epigenetic regulation of OXTR is largely unknown. This has hampered the experimental design and interpretation of the results of epigenetic studies of OXTR in neuropsychiatric disorders. From the generation and characterization of a new line of Tet1 mutant mice - by deleting the largest coding exon 4 (Tet1Δe4) - we discovered for the first time to our knowledge that Oxtr has an array of mRNA isoforms and a complex transcriptional regulation. Select isoforms of Oxtr are significantly reduced in the brain of Tet1Δe4-/- mice. Accordingly, CpG islands of Oxtr are hypermethylated during early development and persist into adulthood. Consistent with the reduced express of OXTR, Tet1Δe4-/- mice display impaired maternal care, social behavior, and synaptic responses to oxytocin stimulation. Our findings elucidate a mechanism mediated by TET1 protein in regulating Oxtr expression by preventing DNA hypermethylation of Oxtr. The discovery of epigenetic dysregulation of Oxtr in TET1-deficient mouse brain supports the necessity of a reassessment of existing findings and a value of future studies of OXTR in neuropsychiatric disorders.

The Role of Placental Hormones in Mediating Maternal Adaptations to Support Pregnancy and Lactation

During pregnancy, the mother must adapt her body systems to support nutrient and oxygen supply for growth of the baby in utero and during the subsequent lactation. These include changes in the cardiovascular, pulmonary, immune and metabolic systems of the mother. Failure to appropriately adjust maternal physiology to the pregnant state may result in pregnancy complications, including gestational diabetes and abnormal birth weight, which can further lead to a range of medically significant complications for the mother and baby. The placenta, which forms the functional interface separating the maternal and fetal circulations, is important for mediating adaptations in maternal physiology. It secretes a plethora of hormones into the maternal circulation which modulate her physiology and transfers the oxygen and nutrients available to the fetus for growth. Among these placental hormones, the prolactin-growth hormone family, steroids and neuropeptides play critical roles in driving maternal physiological adaptations during pregnancy. This review examines the changes that occur in maternal physiology in response to pregnancy and the significance of placental hormone production in mediating such changes.

Possible involvement of central oxytocin in cisplatin-induced anorexia in rats

During cancer chemotherapy, drugs such as 5-HT3 receptor antagonists have typically been used to control vomiting and anorexia. We examined the effects of oxytocin (OXT), which has been linked to appetite, on cisplatin-induced anorexia in rats. Fos-like immunoreactivity (Fos-LI) expressed in the supraoptic nucleus (SON), the paraventricular nucleus (PVN), the area postrema and the nucleus of the solitary tract (NTS) after intraperitoneal (ip) administration of cisplatin. We also examined the fluorescence intensity of OXT-mRFP1 after ip administration of cisplatin in OXT-mRFP1 transgenic rats. The mRFP1 fluorescence intensity was significantly increased in the SON, the PVN, and the NTS after administration of cisplatin. The cisplatin-induced anorexia was abolished by OXT receptor antagonist (OXTR-A) pretreatment. In the OXT-LI cells, cisplatin-induced Fos expression in the SON and the PVN was also suppressed by OXTR-A pretreatment. These results suggested that central OXT may be involved in cisplatin-induced anorexia in rats.

The Oxytocin Receptor: From Intracellular Signaling to Behavior

The many facets of the oxytocin (OXT) system of the brain and periphery elicited nearly 25,000 publications since 1930 (see FIGURE 1 , as listed in PubMed), which revealed central roles for OXT and its receptor (OXTR) in reproduction, and social and emotional behaviors in animal and human studies focusing on mental and physical health and disease. In this review, we discuss the mechanisms of OXT expression and release, expression and binding of the OXTR in brain and periphery, OXTR-coupled signaling cascades, and their involvement in behavioral outcomes to assemble a comprehensive picture of the central and peripheral OXT system. Traditionally known for its role in milk let-down and uterine contraction during labor, OXT also has implications in physiological, and also behavioral, aspects of reproduction, such as sexual and maternal behaviors and pair bonding, but also anxiety, trust, sociability, food intake, or even drug abuse. The many facets of OXT are, on a molecular basis, brought about by a single receptor. The OXTR, a 7-transmembrane G protein-coupled receptor capable of binding to either Gαior Gαqproteins, activates a set of signaling cascades, such as the MAPK, PKC, PLC, or CaMK pathways, which converge on transcription factors like CREB or MEF-2. The cellular response to OXT includes regulation of neurite outgrowth, cellular viability, and increased survival. OXTergic projections in the brain represent anxiety and stress-regulating circuits connecting the paraventricular nucleus of the hypothalamus, amygdala, bed nucleus of the stria terminalis, or the medial prefrontal cortex. Which OXT-induced patterns finally alter the behavior of an animal or a human being is still poorly understood, and studying those OXTR-coupled signaling cascades is one initial step toward a better understanding of the molecular background of those behavioral effects.

Role of oxytocin in parental behaviour

Both animal and human studies have provided conclusive evidence that oxytocin (OXT) acts in the brain (eg, medial preoptic area, ventral tegmental area, nucleus accumbens) to promote parental behaviour under different reproductive and physiological conditions. OXT appears to accelerate and strengthen the neural process that makes newborns attractive or rewarding. Furthermore, OXT reduces stress/anxiety and might improve mood and well being, resulting in indirect benefits for parents. However, OXT also plays a role in the development of species reproductive and social strategies, making some species or individuals more prone to display caring activities in nonreproductive contexts. There are important differences in the development of the OXT system and its regulation by gonadal hormones that can make individuals or species very different. Those intra- and interspecific differences in the OXT system have been associated with differences in parental behaviour. For example, differences in OXT levels in body fluids and genetic variants for the OXT and OXT receptor genes have been associated with variability in parental mood and behaviour in humans. Thus, OXT has received much attention as a potential therapeutic agent for affective, emotional and behavioural problems. Despite many preliminary studies indicating promising findings, several unknown aspects of the OXT system remain to be addressed before we can achieve a complete understanding of its function in the brain. The enormous interest that this area of study has attracted in the last decade will likely continually contribute to advancing our understanding of the role of OXT in parental behaviour and other behavioural and physiological functions.

Neuropeptide oxytocin enhances μ opioid receptor signaling as a positive allosteric modulator

Oxytocin (OT) is a 9-amine neuropeptide that plays an essential role in mammalian labor, lactation, maternal bonding, and social affiliation. OT has been reported to exert an analgesic effect in both humans and animals, and the results of certain animal experiments have shown that the analgesic effect of OT is partially blocked by opioid receptor antagonists. To investigate the relationship between OT and μ opioid receptor (MOR), we evaluated how OT affects MOR in vitro by performing an electrical impedance-based receptor biosensor assay (CellKey™ assay), an intracellular cAMP assay, and a competitive receptor-binding analysis by using cells stably expressing human MOR and OT receptor. In both the CellKey™ assay and the intracellular cAMP assay, OT alone exerted no direct agonistic effect on human MOR, but treatment with 10^-6 M OT markedly enhanced the MOR signaling induced by 10^-6 M endomorphin-1, β-endorphin, morphine, fentanyl, and DAMGO. Moreover, in the competitive receptor-binding assay, 10^-6 M OT did not alter the affinity of endomorphin-1 or morphine for MOR. These results suggest that OT could function as a positive allosteric modulator that regulates the efficacy of MOR signaling, and thus OT might represent a previously unrecognized candidate analgesic agent.

Increased aggression and lack of maternal behavior in Dio3-deficient mice are associated with abnormalities in oxytocin and vasopressin systems

Thyroid hormones regulate many aspects of brain development and function, and alterations in the levels of thyroid hormone action lead to abnormal anxiety- and depression-like behaviors. A complement of factors in the brain function independently of circulating levels of hormone to strictly controlled local thyroid hormone signaling. A critical factor is the type 3 deiodinase (DIO3), which is located in neurons and protects the brain from excessive thyroid hormone. Here, we examined whether a local increase in brain thyroid hormone action secondary to DIO3 deficiency is of consequence for social behaviors. Although we did not observe alterations in sociability, Dio3-/- mice of both sexes exhibited a significant increase in aggression-related behaviors and mild deficits in olfactory function. In addition, 85% of Dio3-/- dams manifested no pup-retrieval behavior and increased aggression toward the newborns. The abnormal social behaviors of Dio3-/- mice were associated with sexually dimorphic alterations in the physiology of oxytocin (OXT) and arginine vasopressin (AVP), 2 neuropeptides with important roles in determining social interactions. These alterations included low adult serum levels of OXT and AVP, and an abnormal expression of Oxt, Avp and their receptors in the neonatal and adult hypothalamus. Our results demonstrate that DIO3 is essential for normal aggression and maternal behaviors, and indicate that abnormal local regulation of thyroid hormone action in the brain may contribute to the social deficits associated with neurodevelopmental disorders.

HP1BP3 expression determines maternal behavior and offspring survival

Maternal care is an indispensable behavioral component necessary for survival and reproductive success in mammals, and postpartum maternal behavior is mediated by an incompletely understood complex interplay of signals including effects of epigenetic regulation. We approached this issue using our recently established mice with targeted deletion of heterochromatin protein 1 binding protein 3 (HP1BP3), which we found to be a novel epigenetic repressor with critical roles in postnatal growth. Here, we report a dramatic reduction in the survival of pups born to Hp1bp3(-/-) deficient mouse dams, which could be rescued by co-fostering with wild-type dams. Hp1bp3(-/-) females failed to retrieve both their own pups and foster pups in a pup retrieval test, and showed reduced anxiety-like behavior in the open-field and elevated-plus-maze tests. In contrast, Hp1bp3(-/-) females showed no deficits in behaviors often associated with impaired maternal care, including social behavior, depression, motor coordination and olfactory capability; and maintained unchanged anxiety-associated hallmarks such as cholinergic status and brain miRNA profiles. Collectively, our results suggest a novel role for HP1BP3 in regulating maternal and anxiety-related behavior in mice and call for exploring ways to manipulate this epigenetic process.

Effects of repeated pup exposure on behavioral, neural, and adrenocortical responses to pups in male California mice (Peromyscus californicus)

In biparental mammals, the factors facilitating the onset of male parental behavior are not well understood. While hormonal changes in fathers may play a role, prior experience with pups has also been implicated. We evaluated effects of prior exposure to pups on paternal responsiveness in the biparental California mouse (Peromyscus californicus). We analyzed behavioral, neural, and corticosterone responses to pups in adult virgin males that were interacting with a pup for the first time, adult virgin males that had been exposed to pups 3 times for 20min each in the previous week, and new fathers. Control groups of virgins were similarly tested with a novel object (marble). Previous exposure to pups decreased virgins' latency to approach pups and initiate paternal care, and increased time spent in paternal care. Responses to pups did not differ between virgins with repeated exposure to pups and new fathers. In contrast, repeated exposure to a marble had no effects. Neither basal corticosterone levels nor corticosterone levels following acute pup or marble exposure differed among groups. Finally, Fos expression in the medial preoptic area, ventral and dorsal bed nucleus of the stria terminalis was higher following exposure to a pup than to a marble. Fos expression was not, however, affected by previous exposure to these stimuli. These results suggest that previous experience with pups can facilitate the onset of parental behavior in male California mice, similar to findings in female rodents, and that this effect is not associated with a general reduction in neophobia.

Maternally involved galanin neurons in the preoptic area of the rat

Recent selective stimulation and ablation of galanin neurons in the preoptic area of the hypothalamus established their critical role in control of maternal behaviors. Here, we identified a group of galanin neurons in the anterior commissural nucleus (ACN), and a distinct group in the medial preoptic area (MPA). Galanin neurons in ACN but not the MPA co-expressed oxytocin. We used immunodetection of phosphorylated STAT5 (pSTAT5), involved in prolactin receptor signal transduction, to evaluate the effects of suckling-induced prolactin release and found that 76 % of galanin cells in ACN, but only 12 % in MPA were prolactin responsive. Nerve terminals containing tuberoinfundibular peptide 39 (TIP39), a neuropeptide that mediates effects of suckling on maternal motivation, were abundant around galanin neurons in both preoptic regions. In the ACN and MPA, 89 and 82 % of galanin neurons received close somatic appositions, with an average of 2.9 and 2.6 per cell, respectively. We observed perisomatic innervation of galanin neurons using correlated light and electron microscopy. The connection was excitatory based on the glutamate content of TIP39 terminals demonstrated by post-embedding immunogold electron microscopy. Injection of the anterograde tracer biotinylated dextran amine into the TIP39-expressing posterior intralaminar complex of the thalamus (PIL) demonstrated that preoptic TIP39 fibers originate in the PIL, which is activated by suckling. Thus, galanin neurons in the preoptic area of mother rats are innervated by an excitatory neuronal pathway that conveys suckling-related information. In turn, they can be topographically and neurochemically divided into two distinct cell groups, of which only one is affected by prolactin.

Oxytocin and Parental Behaviors

The oxytocin/vasopressin ancestor molecule has been regulating reproductive and social behaviors for more than 500 million years. In all mammals, oxytocin is the hormone indispensable for milk-ejection during nursing (maternal milk provision to offspring), a process that is crucial for successful mammalian parental care. In laboratory mice, a remarkable transcriptional activation occurs during parental behavior within the anterior commissural nucleus (AC), the largest magnocellular oxytocin cell population within the medial preoptic area (although the transcriptional activation was limited to non-oxytocinergic neurons in the AC). Furthermore, there are numerous recent reports on oxytocin's involvement in positive social behaviors in animals and humans. Given all those, the essential involvement of oxytocin in maternal/parental behaviors may seem obvious, but basic researchers are still struggling to pin down the exact role oxytocin plays in the regulation of parental behaviors. A major aim of this review is to more clearly define this role. The best conclusion at this moment is that OT can facilitate the onset of parental behavior, or parental behavior under stressful conditions.In this chapter, we will first review the basics of rodent parental behavior. Next, the neuroanatomy of oxytocin systems with respect to parental behavior in laboratory mice will be introduced. Then, the research history on the functional relationship between oxytocin and parental behavior, along with advancements in various techniques, will be reviewed. Finally, some technical considerations in conducting behavioral experiments on parental behavior in rodents will be addressed, with the aim of shedding light on certain pitfalls that should be avoided, so that the progress of research in this field will be facilitated. In this age of populism, researchers should strive to do even more scholarly works with further attention to methodological details.

Oxytocin and Animal Models for Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a group of complex neurodevelopmental conditions characterized by deficits in social communication and by repetitive and stereotypic patterns of behaviors, with no pharmacological treatments available to treat these core symptoms. Oxytocin is a neuropeptide that powerfully regulates mammalian social behavior and has been shown to exert pro-social effects when administered intranasally to healthy human subjects. In the last decade, there has been a significant interest in using oxytocin to treat social behavior deficits in ASD. However, little attention has been paid to whether the oxytocin system is perturbed in subgroups of individuals with ASD and whether these individuals are likely to benefit more from an oxytocin treatment. This oversight may in part be due to the enormous heterogeneity of ASD and the lack of methods to carefully probe the OXT system in human subjects. Animal models for ASD are valuable tools to clarify the implication of the oxytocin system in ASD and can help determine whether perturbation in this system should be considered in future clinical studies as stratifying biomarkers to inform targeted treatments in subgroups of individuals with ASD. In this chapter, we review the literature on genetic- and environmental-based animal models for ASD, in which perturbations in the oxytocin system and/or the effect of oxytocin administration on the ASD-associated phenotype have been investigated.

The neurobiology of parenting: A neural circuit perspective

Social interactions are essential for animals to reproduce, defend their territory, and raise their young. The conserved nature of social behaviors across animal species suggests that the neural pathways underlying the motivation for, and the execution of, specific social responses are also maintained. Modern tools of neuroscience have offered new opportunities for dissecting the molecular and neural mechanisms controlling specific social responses. We will review here recent insights into the neural circuits underlying a particularly fascinating and important form of social interaction, that of parental care. We will discuss how these findings open new avenues to deconstruct infant-directed behavioral control in males and females, and to help understand the neural basis of parenting in a variety of animal species, including humans. Please also see the video abstract here.

Effects of the Adult Attachment Projective Picture System on Oxytocin and Cortisol Blood Levels in Mothers

Oxytocin, a small neuropeptide of nine amino acids, has been characterized as the “hormone of affiliation” and is stimulated, for instance, in mothers when interacting with their offspring. Variations in maternal oxytocin levels were reported to predict differences in the quality of care provided by mothers. In this study, the Adult Attachment Projective Picture System (AAP) as a valid measure to assess attachment representations was used as an activating attachment-related stimulus. We investigated whether the AAP induces a release of oxytocin in mothers with a secure attachment representation and a stress-related cortisol response in mothers with an insecure attachment representation. Therefore, pre-post effects of AAP administration on plasma oxytocin and serum cortisol levels were investigated in n = 44 mothers 3 months after parturition. Oxytocin levels increased from pre to post in the significant majority of 73% participants (p = 0.004) and cortisol decreased in the significant majority of 73% participants (p = 0.004). Interestingly, no association between alterations in oxytocin and cortisol were found; this suggests taking a model of two independent processes into considerations. These results show that the AAP test procedure induces an oxytocin response. Concerning the results within the four AAP representation subgroups, our hypothesis of a particularly strong increase in oxytocin in secure mothers was not confirmed; however, in secure mothers we observed a particularly strong decrease in cortisol. Effect sizes are reported, allowing the replication of results in a larger study with sufficient sample size to draw final conclusions with respect to differences in OT and cortisol alterations depending on attachment representation. When interpreting the results, one should keep in mind that this study investigated lactating mothers. Thus, the generalizability of results is limited and future studies should investigate non-lactating healthy females as well as males and include a control stimulus condition.

Oxytocin and behavior: Lessons from knockout mice

It is well established that the nonapeptide oxytocin (Oxt) is important for the neural modulation of behaviors in many mammalian species. Since its discovery in 1906 and synthesis in the early 1950s, elegant pharmacological work has helped identify specific neural substrates on which Oxt exerts its effects. More recently, mice with targeted genetic disruptions of the Oxt system-i.e., both the peptide and its receptor (the Oxtr)-have further defined Oxt's actions and laid some important scientific groundwork for studies in other species. In this article, we highlight the scientific contributions that various mouse knockouts of the Oxt system have made to our understanding of Oxt's modulation of behavior. We specifically focus on how the use of these mice has shed light on our understanding of social recognition memory, maternal behavior, aggression, and several nonsocial behaviors. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 190-201, 2017.