Oxytocin in the medial prefrontal cortex regulates maternal care, maternal aggression and anxiety during the postpartum period

Postweaning sodium citrate exposure induces long-lasting and sex-dependent effects on social behaviours in mice

BACKGROUND

Postweaning is a pivotal period for brain development and individual growth. As an important chemical used in medicines, foods and beverages, sodium citrate (SC) is commonly available. Although some effects of SC exposure on individual physiology have been demonstrated, the potential long-lasting effects of postweaning dietary SC exposure on social behaviours are still elusive.

METHODS

Both postweaning male and female C57BL/6 mice were exposed to SC through drinking water for a total of 3 weeks. A series of behavioural tests, including social dominance test (SDT), social interaction test (SIT), bedding preference test (BPT) and sexual preference test (SPT), were performed in adolescence and adulthood. After these tests, serum oxytocin (OT) levels and gut microbiota were detected.

RESULTS

The behavioural results revealed that postweaning SC exposure decreased the social dominance of male mice in adulthood and female mice in both adolescence and adulthood. SC exposure also reduced the sexual preference rates of both males and females, while it had no effect on social interaction behaviour. ELISA results indicated that SC exposure decreased the serum OT levels of females but not males. 16S rRNA sequencing analysis revealed a significant difference in β-diversity after SC exposure in both males and females. The correlation coefficient indicated the correlation between social behaviours, OT levels and dominant genera of gut microbiota.

CONCLUSION

Our findings suggest that postweaning SC exposure may have enduring and sex-dependent effects on social behaviours, which may be correlated with altered serum OT levels and gut microbiota composition.

Roadmap for maternal behavior research in domestic dogs: lessons from decades of laboratory rodent work

Maternal behavior research in laboratory rats has revealed important behavioral and neurobiological mechanisms governing the onset, maintenance and decline of maternal behavior. However, the extent to which these mechanisms are evolutionarily conserved across species is less clear. This manuscript proposes that examining these mechanisms in dogs may be a viable approach to test their generality and help bridge the gap between rodent and human research, as domestic dogs show greater individual differences and exhibit more human-like maternal characteristics than rodents. These aspects represent advantages over rodent models, which in turn allow systems biological approaches not available in rodents. Additionally, domestic dogs share similar social environments with humans, suffer from the same mental disorders as humans, and can be treated with the same medications. This paper begins with a summary of key findings and theoretical developments from decades of rat maternal behavior research, followed by a literature review of the extant maternal behavior research on dogs and related methodology, highlighting the unique behavioral characteristics of dog maternal behavior and similarities and differences from rat maternal behavior. Finally, several knowledge gaps in dog maternal behavior research, as well as the future research in this area is discussed. It concludes that research on dog maternal behavior will not only advance our understanding of the universality of the neurobiological and behavioral mechanisms in maternal behavior, but also improve our understanding of risk factors associated with postpartum mental disorders.

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.

Stimulating oxytocin receptors in the basolateral amygdala enhances stimulus processing: Differential and consistent effects for stimuli paired with fear versus sucrose in extinction and reversal learning

Oxytocin (OT) influences a range of social behaviors by enhancing the salience of social cues and regulating the expression of specific social behaviors (e.g., maternal care versus defensive aggression). We previously showed that stimulating OT receptors in the basolateral amygdala of rats also enhanced the salience of fear conditioned stimuli: relative to rats given vehicle infusions, rats infused with [Thr4,Gly7]-oxytocin (TGOT), a selective OT receptor agonist, showed greater discrimination between a cue predictive of danger, and one that signaled safety. In the present series of experiments using male rats, the effects of OT receptor activation in the basolateral amygdala on stimulus processing were examined further using conditioning protocols that consist of changes in stimulus-outcome contingencies (i.e., extinction and reversal), and with stimuli paired with aversive (i.e., foot shock) and appetitive (i.e., sucrose) outcomes. It was revealed that the effects of OTR stimulation diverge for aversive and appetitive learning - enhancing the former but not the latter. However, across both types of learning, OTR stimulation enhanced the detection of conditioned stimuli. Overall, these results are consistent with an emerging view of OT's effects on stimulus salience; facilitating the detection of meaningful stimuli while reducing responding to those that are irrelevant.

The Multifaceted Role of Oxytocinergic System and OXTR Gene

The article explores the multifaceted role of the neuropeptide oxytocin in human behavior and its connection to the oxytocin receptor ( OXTR ) gene. Oxytocin, produced in specific brain nuclei, is implicated in emotional, social, and maternal behaviors, stress reduction, uterine contraction during childbirth, and lactation. The OXTR gene, located on chromosome 3, encodes oxytocin receptors found in various body parts, including critical brain regions associated with social behaviors. The article delves into studies on rodents, revealing correlations between OXTR gene expression and pair bonding in the prefrontal cortex and social behavior regulation in the amygdala. The discussion extends to the impact of oxytocin on social support-seeking behavior, focusing on a specific genetic variation, rs53576. The article explores how this genetic variation influences empathy, stress reactivity, and susceptibility to disorders such as autism and social anxiety. Furthermore, the article examines structural and functional changes in the brain associated with OXTR gene variations. It discusses the role of DNA methylation in influencing oxytocin receptor availability, affecting social perception and responsiveness to negative stimuli. The article also highlights the oxytocinergic system's involvement in disorders such as autism and social anxiety, emphasizing the interplay between genetics and environmental factors. The article also touches on the potential therapeutic use of exogenous oxytocin in mitigating symptoms associated with these disorders. In summary, the article underscores the intricate relationship between oxytocin, the OXTR gene, and diverse aspects of human behavior, providing insights into social bonding, perception, and the development of behavioral disorders.

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.

Parental factors that impact the ecology of human mammary development, milk secretion, and milk composition-a report from "Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN)" Working Group 1

The goal of Working Group 1 in the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project was to outline factors influencing biological processes governing human milk secretion and to evaluate our current knowledge of these processes. Many factors regulate mammary gland development in utero, during puberty, in pregnancy, through secretory activation, and at weaning. These factors include breast anatomy, breast vasculature, diet, and the lactating parent's hormonal milieu including estrogen, progesterone, placental lactogen, cortisol, prolactin, and growth hormone. We examine the effects of time of day and postpartum interval on milk secretion, along with the role and mechanisms of lactating parent-infant interactions on milk secretion and bonding, with particular attention to the actions of oxytocin on the mammary gland and the pleasure systems in the brain. We then consider the potential effects of clinical conditions including infection, pre-eclampsia, preterm birth, cardiovascular health, inflammatory states, mastitis, and particularly, gestational diabetes and obesity. Although we know a great deal about the transporter systems by which zinc and calcium pass from the blood stream into milk, the interactions and cellular localization of transporters that carry substrates such as glucose, amino acids, copper, and the many other trace metals present in human milk across plasma and intracellular membranes require more research. We pose the question of how cultured mammary alveolar cells and animal models can help answer lingering questions about the mechanisms and regulation of human milk secretion. We raise questions about the role of the lactating parent and the infant microbiome and the immune system during breast development, secretion of immune molecules into milk, and protection of the breast from pathogens. Finally, we consider the effect of medications, recreational and illicit drugs, pesticides, and endocrine-disrupting chemicals on milk secretion and composition, emphasizing that this area needs much more research attention.

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.

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'.

Whole-Brain Wiring Diagram of Oxytocin System in Adult Mice

Oxytocin (Oxt) neurons regulate diverse physiological responses via direct connections with different neural circuits. However, the lack of comprehensive input-output wiring diagrams of Oxt neurons and their quantitative relationship with Oxt receptor (Oxtr) expression presents challenges to understanding circuit-specific Oxt functions. Here, we establish a whole-brain distribution and anatomic connectivity map of Oxt neurons, and their relationship with Oxtr expression using high-resolution 3D mapping methods in adult male and female mice. We use a flatmap to describe Oxt neuronal expression in four hypothalamic domains including under-characterized Oxt neurons in the tuberal nucleus (TU). Oxt neurons in the paraventricular hypothalamus (PVH) broadly project to nine functional circuits that control cognition, brain state, and somatic visceral response. In contrast, Oxt neurons in the supraoptic (SO) and accessory (AN) nuclei have limited central projection to a small subset of the nine circuits. Surprisingly, quantitative comparison between Oxt output and Oxtr expression showed no significant correlation across the whole brain, suggesting abundant indirect Oxt signaling in Oxtr-expressing areas. Unlike output, Oxt neurons in both the PVH and SO receive similar monosynaptic inputs from a subset of the nine circuits mainly in the thalamic, hypothalamic, and cerebral nuclei areas. Our results suggest that PVH-Oxt neurons serve as a central modulator to integrate external and internal information via largely reciprocal connection with the nine circuits while the SO-Oxt neurons act mainly as unidirectional Oxt hormonal output. In summary, our Oxt wiring diagram provides anatomic insights about distinct behavioral functions of Oxt signaling in the brain.SIGNIFICANCE STATEMENT Oxytocin (Oxt) neurons regulate diverse physiological functions from prosocial behavior to pain sensation via central projection in the brain. Thus, understanding detailed anatomic connectivity of Oxt neurons can provide insight on circuit-specific roles of Oxt signaling in regulating different physiological functions. Here, we use high-resolution mapping methods to describe the 3D distribution, monosynaptic input and long-range output of Oxt neurons, and their relationship with Oxt receptor (Oxtr) expression across the entire mouse brain. We found Oxt connections with nine functional circuits controlling cognition, brain state, and somatic visceral response. Furthermore, we identified a quantitatively unmatched Oxt-Oxtr relationship, suggesting broad indirect Oxt signaling. Together, our comprehensive Oxt wiring diagram advances our understanding of circuit-specific roles of Oxt neurons.

GABA System Modifications During Periods of Hormonal Flux Across the Female Lifespan

The female lifespan is marked by periods of dramatic hormonal fluctuation. Changes in the ovarian hormones estradiol and progesterone, in addition to the progesterone metabolite allopregnanolone, are among the most significant and have been shown to have widespread effects on the brain. This review summarizes current understanding of alterations that occur within the GABA system during the major hormonal transition periods of puberty, the ovarian cycle, pregnancy and the postpartum period, as well as reproductive aging. The functional impacts of altered inhibitory activity during these times are also discussed. Lastly, avenues for future research are identified, which, if pursued, can broaden understanding of the GABA system in the female brain and potentially lead to better treatments for women experiencing changes in brain function at each of these hormonal transition periods.

Plasticity of neural connections underlying oxytocin-mediated parental behaviors of male mice

The adult brain can flexibly adapt behaviors to specific life-stage demands. For example, while sexually naive male mice are aggressive to the conspecific young, they start to provide caregiving to infants around the time when their own young are expected. How such behavioral plasticity is implemented at the level of neural connections remains poorly understood. Here, using viral-genetic approaches, we establish hypothalamic oxytocin neurons as the key regulators of the parental caregiving behaviors of male mice. We then use rabies-virus-mediated unbiased screening to identify excitatory neural connections originating from the lateral hypothalamus to the oxytocin neurons to be drastically strengthened when male mice become fathers. These connections are functionally relevant, as their activation suppresses pup-directed aggression in virgin males. These results demonstrate the life-stage associated, long-distance, and cell-type-specific plasticity of neural connections in the hypothalamus, the brain region that is classically assumed to be hard-wired.

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.

Induction of Relaxation by Autonomous Sensory Meridian Response

Background: Autonomous sensory meridian response (ASMR) is used by young people to induce relaxation and sleep and to reduce stress and anxiety; it comprises somatosensation caused by audiovisual stimuli (triggers) that lead to positive emotions. Auditory stimuli play the most important role among the triggers involved in ASMR and have been reported to be more triggering than visual stimuli. On the other hand, classical music is also known to have a relaxing effect. This is the first study to clarify the difference in brain activation associated with relaxation effects between ASMR and classical music by limiting ASMR to auditory stimulation alone.

Methods: Thirty healthy subjects, all over 20 years of age, underwent fMRI while listening to ASMR and classical music. We compared the differences in brain activation associated with classical music and ASMR stimulation. After the experiment, the subjects were administered a questionnaire on somatosensation and moods. After the experiment, the participants were asked whether they experienced ASMR somatosensation or frisson. They were also asked to rate the intensity of two moods during stimulation: “comfortable mood,” and “tingling mood”.

Result: The results of the questionnaire showed that none of the participants experienced any ASMR somatosensation or frisson. Further, there was no significant difference in the ratings given to comfort mood, but there was a significant difference in those given to tingling mood. In terms of brain function, classical music and ASMR showed significant activation in common areas, while ASMR showed activation in more areas, with the medial prefrontal cortex being the main area of activation during ASMR.

Conclusion: Both classical music and the ASMR auditory stimulus produced a pleasant and relaxed state, and ASMR involved more complex brain functions than classical music, especially the activation of the medial prefrontal cortex. Although ASMR was limited to auditory stimulation, the effects were similar to those of listening to classical music, suggesting that ASMR stimulation can produce a pleasant state of relaxation even if it is limited to the auditory component, without the somatic sensation of tingling. ASMR stimulation is easy to use, and appropriate for wellness purposes and a wide range of people.

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.

Oxytocin receptors in the midbrain dorsal raphe are essential for postpartum maternal social and affective behaviors

Oxytocin receptors (OTRs) in the midbrain dorsal raphe (DR; the source of most forebrain serotonin) have recently been identified as a potential pharmacological target for treating numerous psychiatric disorders. However, almost all research on this topic has been conducted on males and the role of DR OTRs in female social and affective behaviors is mostly unknown. This may be particularly relevant during early motherhood, which is a time of high endogenous oxytocin signaling, but also a time of elevated risk for psychiatric dysfunction. To investigate whether OTRs in the DR are necessary for postpartum female social and affective behaviors, we constructed and then injected into the DR an adeno-associated virus permanently expressing an shRNA targeting OTR mRNA. We then observed a suite of social and affective behaviors postpartum. OTR knockdown in the maternal DR led to pup loss after parturition, decreased nursing, increased aggression, and increased behavioral despair. These effects of OTR knockdown in the DR may be due to disrupted neuroplasticity in the primary somatosensory cortex (S1), which mediates maternal sensitivity to the tactile cues from young, as we found significantly more plasticity-restricting perineuronal nets (PNNs) in the S1 rostral barrel field and fewer PNNs in the caudal barrel field of OTR-knockdown mothers. These results demonstrate that OTRs in the midbrain DR are essential for postpartum maternal social and affective behaviors, are involved in postpartum cortical plasticity, and suggest that pharmacotherapies targeting OTRs in the DR could be effective treatments for some peripartum affective disorders.

Oxytocin receptor expression in the midbrain dorsal raphe is dynamic across female reproduction in rats

Central oxytocin receptor (OTR) expression is extremely sensitive to circulating steroid hormones and OTRs influence many of the neurobehavioural adaptations associated with female reproduction (e.g., postpartum caregiving, aggression, cognition, affective responses). Changes in central OTR expression across female reproduction have often been studied, but almost all of such research has focused on the forebrain, ignoring hormone-sensitive midbrain sites such as the serotonergic dorsal raphe (DR) that are also critical for postpartum behaviours. To investigate the effects of female reproductive state on OTRs in the DR, we first used autoradiography to examine OTR binding across four female reproductive states in laboratory rats: dioestrous virgin, pregnancy day 10, the day of parturition and postpartum day 7. OTR binding in the rostral DR (but not other DR subregions) was approximately 250% higher in parturient rats compared to dioestrous virgins and dropped back down to virgin levels by postpartum day 7. Given the chemical heterogeneity of the DR, we then examined OTR expression in the three most abundant neuronal phenotypes of the DR (i.e., serotonin, GABA and dopamine) in dioestrous virgins and recently parturient females. Using dual-label immunohistochemistry and in situ hybridisation, we found that twice as many dopaminergic cells in the parturient rostral DR contained OTR immunoreactivity compared to that found in virgins. On the other hand, mothers had fewer rostral DR GABAergic cells expressing OTRs than did virgins. OTR expression in serotonin cells did not differ between the two groups. Overall, these results suggest that the rostral subregion of the midbrain DR is uniquely sensitive to oxytocin around the time of parturition, with subpopulations of cells that become more sensitive (i.e., dopamine), less sensitive (i.e., GABA) and show no change (i.e., serotonin) to this neuropeptide. This dynamic OTR signalling in the female DR may help drive the numerous behavioural changes across female reproduction that are necessary for successful motherhood.

Neurotensin 1 receptor in the prelimbic cortex regulates anxiety-like behavior in rats

The central neurotensin system has been implicated in reward, memory processes, also in the regulation of anxiety. However, the neural substrates where neurotensin acts to regulate anxiety have not been fully identified. The prelimbic region of medial prefrontal cortex (PrL) holds a key position in the modulation of anxiety-related behaviors and expresses neurotensin 1 receptor (NTS1). This study investigated the effects of activation or blockade of NTS1 in the PrL on anxiety-like behaviors of rats. Our results demonstrated that infusion of a selective NTS1 agonist or neurotensin into the PrL produced anxiogenic-like effects. Administration of a NTS1 antagonist into the PrL did not affect anxiety-like behaviors of normal rats, but attenuated anxiogenic effects induced by restraint stress. Moreover, we employed molecular approaches to downregulate the expression of NTS1 in the PrL, and found that downregulation of NTS1 in the PrL induced anxiolytic effects in restraint stress rats, also confirming the pharmacological results. Together, these findings suggest that NTS1 in the PrL is actively involved in the regulation of anxiety.

How stress can influence brain adaptations to motherhood

Research shows that a woman's brain and body undergo drastic changes to support her transition to parenthood during the perinatal period. The presence of this plasticity suggests that mothers' brains may be changed by their experiences. Exposure to severe stress may disrupt adaptive changes in the maternal brain and further impact the neural circuits of stress regulation and maternal motivation. Emerging literature of human mothers provides evidence that stressful experience, whether from the past or present environment, is associated with altered responses to infant cues in brain circuits that support maternal motivation, emotion regulation, and empathy. Interventions that reduce stress levels in mothers may reverse the negative impact of stress exposure on the maternal brain. Finally, outstanding questions regarding the timing, chronicity, types, and severity of stress exposure, as well as study design to identify the causal impact of stress, and the role of race/ethnicity are discussed.

Commensal microbe-derived propionic acid mediates juvenile social isolation-induced social deficits and anxiety-like behaviors

Social experiences during early life are thought to be critical for proper social and emotional development. Conversely, social insults during development causes long-lasting behavioral abnormalities later in life. However, how juvenile social deprivation influences social and emotional behaviors remains poorly understood. Here, we show that juvenile social isolation induces a shift in microbial ecology that negatively impacts social and emotional behaviors in adulthood. These behavioral changes, which occur during this critical period are transferable to antibiotic pre-treated mice by fecal microbiota transplant. In addition, juvenile social isolation decreases the expression of oxytocin receptor (OXTR) in the medial prefrontal cortex (mPFC), and increases the amounts of fecal propionic acid (PA), a short-chain fatty acid derived from gut micobiota. Accordingly, infusion with an OXTR antagonist (OXTR-A, l-368,899) specifically in the mPFC or supplementation of PA both can cause social deficits and anxiety-like behaviors in group housed mice. Collectively, our findings reveal that juvenile social experience regulates prefrontal cortical OXTR expression through gut microbiota-produced PA and that is essential for normal social and emotional behaviors, thus providing a cellular and molecular context to understand the consequences of juvenile social deprivation.

Associations between stress exposure and new mothers' brain responses to infant cry sounds

Exposure to severe stress has been linked to negative postpartum outcomes among new mothers including mood disorders and harsh parenting. Non-human animal studies show that stress exposure disrupts the normative adaptation of the maternal brain, thus identifying a neurobiological mechanism by which stress can lead to negative maternal outcomes. However, little is known about the impact of stress exposure on the maternal brain response to infant cues in human mothers. We examined the association of stress exposure with brain response to infant cries and maternal behaviors, in a socioeconomically diverse (low- and middle-income) sample of first-time mothers (N=53). Exposure to stress across socioeconomic, environmental, and psychosocial domains was associated with reduced brain response to infant cry sounds in several regions, including the right insula/inferior frontal gyrus and superior temporal gyrus. Reduced activation in these regions was further associated with lower maternal sensitivity observed during a mother-infant interaction. The findings demonstrate that higher levels of stress exposure may be associated with reduced brain response to an infant’s cry in regions that are important for emotional and social information processing, and that reduced brain responses may further be associated with increased difficulties in developing positive mother-infant relationships.

Oxytocin in the dorsal raphe nucleus antagonizes the inhibition of maternal care induced by food deprivation

Lactation is indispensable for the pup's survival, but is considered a survival burden in dams under negative energy conditions. In the present study, we tested our hypothesis that oxytocin may facilitate energy investment to pups through behavioral control as well as milk ejection. Maternal care was observed in dams at 3 h but not 8 h after food deprivation. We investigated whether oxytocin in the dorsal raphe nucleus (DRN), which is involved in energy state-dependent regulation of maternal care, regulates maternal care. For this purpose, 2-pmol L368899, an oxytocin receptor antagonist, was injected into the DRN; after treatment, maternal care was inhibited in the dams with 3-h fasting, but not in the fed dams. In contrast, recovery of maternal care was observed in the dams with 8-h fasting who underwent 100-pmol oxytocin injection at the DRN. These results indicate that oxytocin in the DRN is required for displaying maternal behavior under fasting conditions, but not under fed conditions. Next, we investigated the site of oxytocin release. Presentation of pups decreased the oxytocin immunoreactivity at the paraventricular nucleus (PVN) of the hypothalamus in the 3-h-fasted dams, but not in the fed or 8-h-fasted dams. No change of the serum oxytocin level was observed. Few oxytocin-positive neurons projecting from the PVN to the DRN were detected through labeling with the retrograde tracer fluorogold. Oxytocin secreted at the PVN, which reaches the DRN, but not released as a hormone or neurotransmitter may mediate maternal care under food-restricted conditions.

The oxytocinergic system in PTSD following traumatic childbirth: endogenous and exogenous oxytocin in the peripartum period

Birth experiences can be traumatic and may give rise to PTSD following childbirth (PTSD-FC). Peripartum neurobiological alterations in the oxytocinergic system are highly relevant for postpartum maternal behavioral and affective adaptions like bonding and lactation but are also implicated in the response to traumatic events. Animal models demonstrated that peripartum stress impairs beneficial maternal postpartum behavior. Early postpartum activation of the oxytocinergic system may, however, reverse these effects and thereby prevent adverse long-term consequences for both mother and infant. In this narrative review, we discuss the impact of trauma and PTSD-FC on normal endogenous oxytocinergic system fluctuations in the peripartum period. We also specifically focus on the potential of exogenous oxytocin (OT) to prevent and treat PTSD-FC. No trials of exogenous OT after traumatic childbirth and PTSD-FC were available. Evidence from non-obstetric PTSD samples and from postpartum healthy or depressed samples implies restorative functional neuroanatomic and psychological effects of exogenous OT such as improved PTSD symptoms and better mother-to-infant bonding, decreased limbic activation, and restored responsiveness in dopaminergic reward regions. Adverse effects of intranasal OT on mood and the increased fear processing and reduced top-down control over amygdala activation in women with acute trauma exposure or postpartum depression, however, warrant cautionary use of intranasal OT. Observational and experimental studies into the role of the endogenous and exogenous oxytocinergic system in PTSD-FC are needed and should explore individual and situational circumstances, including level of acute distress, intrapartum exogenous OT exposure, or history of childhood trauma.

Nonapeptides mediate trade-offs in parental care strategy

Parental care represents a suite of distinct behaviors performed by parents to maximize fitness. Dynamic shifts in parental care behaviors, such as between nest defense and direct provisioning of the offspring, are required in response to environmental variation. However, the neural mechanisms which mediate such behavioral shifts remain a mystery. The anemonefish, Amphiprion ocellaris, represents an experimentally valuable model in social neuroscience which is conducive to manipulating the environment while simultaneously measuring parental care. The goal of this study was to determine the extent to which arginine vasotocin (AVT) and isotocin (IT) signaling are necessary for males to shift between direct egg care and aggressive nest defense in the presence of intruders, Domino damselfish (Dascyllus trimaculatus). The IT receptor antagonist desGly-NH₂-d(CH₂)₅[D-Tyr²,Thr⁴]OVT, significantly reduced direct egg care, while at the same time increased levels of aggressive nest defense relative to vehicle. Conversely, blockade of AVT using the antagonist d(CH₂)₅[Tyr(Me)²]AVP, reduced aggression and tended to increase egg care. Results demonstrate that male anemonefish alter their parental strategy in response to allospecific intruders, and that IT and AVT signaling oppositely regulate parental care displays of aggression versus egg care.

Preweaning Paternal Deprivation Impacts Parental Responses to Pups and Alters the Serum Oxytocin and Corticosterone Levels and Oxytocin Receptor, Vasopressin 1A Receptor, Oestrogen Receptor, Dopamine Type I Receptor, Dopamine Type II Receptor Levels in Relevant Brain Regions in Adult Mandarin Voles

Although maternal separation and neonatal paternal deprivation (PD) have been found to exert a profound and persistent effects on the physiological and behavioural development of offspring, whether preweaning PD (PPD; from PND 10 to 21) affects maternal and parental responses to pups and the underlying neuroendocrine mechanism are under-investigated. Using monogamous mandarin voles (Microtus mandarinus), the present study found that PPD increased the latency to approach a pup-containing ball, decreased the total durations of sniffing and contacting a pup-containing ball and walking and increased the total duration of inactivity in both sexes. Moreover, PPD decreased serum oxytocin levels and increased corticosterone levels, but only in females. Furthermore, in both males and females, PPD decreased the expression of oxytocin receptor mRNA and protein in the medial preoptic area (MPOA), nucleus accumbens (NAcc) and medial prefrontal cortex (mPFC), but increased it in the medial amygdala (MeA) and decreased the expression of oestrogen receptor mRNA and protein in the MPOA. PPD increased the expression of dopamine type I receptor in the NAcc, but decreased it in the mPFC. PPD decreased dopamine type II receptor (D2R) in the NAcc both in males and females, but increased D2R in the mPFC in females and decreased D2R protein expression in males. Moreover, PPD decreased vasopressin 1A receptor (V1AR) in the MPOA, MeA and mPFC, but only in males. Our results suggest that the reduction of parental responses to pups induced by PPD may be associated with the sex-specific alteration of several neuroendocrine parameters in relevant brain regions.

Neurobiology of maternal mental illness

This chapter provides an overview of current research discoveries beginning to uncover the neurobiology of maternal mental illness. Results are described according to standard diagnostic categories (specifically, perinatal depression, perinatal anxiety and OCD, postpartum psychosis and bipolar disorder, and trauma and posttraumatic stress disorder), yet we aim to put this approach in context with the introduction of a classification model for psychiatric research, the research domain criteria, gaining traction in basic and clinical translational fields. We first review a new area of study, the neuroplasticity of the pregnant and postpartum brain, as work here has relevance for understanding the pathophysiology of mental disorders and may provide clues to changes in brain functioning that are related to compromised parenting in the context of postpartum depression. We next provide background information on neuroendocrine and immune changes during pregnancy and, to a lesser extent, the postpartum period, as alterations in these systems are significantly implicated in underlying neurobiology of mental illness for peripartum women. Our discussion of the major mental illnesses for pregnant and postpartum women includes neuroendocrine changes, neuroinflammation, and neurotransmitter alterations, as well as circuit dysfunction. Overall, remarkable progress has been made in identifying variations in neurobiology (and related systems) involved in maternal mental illness; yet, it is clear that, as classified with standard diagnostic systems, these are heterogeneous disorders and there is individual variability in the alterations in neurobiology for the same illness.

Effects of oxytocin receptor antagonism on social function and corticosterone release after adolescent social instability in male rats

Oxytocin influences social behaviour and hypothalamic-pituitary-adrenal (HPA) function. We previously found that social instability stress (SS) from postnatal day 30 to 45 increased oxytocin receptor (OTR) densities in the lateral septum and nucleus accumbens of adolescent male rats. Here, we investigated social behaviour and HPA function in adolescent male SS rats compared with age- and sex-matched controls after intraperitoneal treatment with an OTR antagonist L-368,899 (OTR-A). Regardless of OTR antagonism, adolescent SS rats spent more time in social approach (investigation through wire mesh) but less time in social interaction (physical interaction) with unfamiliar same-sex and same-age peers than did controls. However, OTR-A-treatment caused SS rats to be more socially avoidant than OTR-A-treated controls and saline-treated rats of the same condition. Additionally, the predicted rise in plasma corticosterone in response to OTR-A treatment was blunted in SS rats. Fos immunoreactivity (IR) was used as a marker of neural activation in social brain regions and oxytocin-IR was examined in the paraventricular nucleus of the hypothalamus (PVN) in response to interacting with unfamiliar peers in SS and control rats after OTR-A treatment. OTR-A treatment had little effect on Fos-IR and oxytocin-IR in the analyzed brain regions, but SS rats had lower Fos-IR and oxytocin-IR in the PVN and greater Fos-IR in subregions of the prefrontal cortex, and hippocampus, and lateral septum than did controls. Finally, binding density of OTR was measured in the PVN and hippocampus, and greater OTR binding density was found in the PVN of SS rats. Together, these data demonstrate a greater influence of OTR antagonism on social behaviour and a reduced influence of OTR antagonism on HPA responses after adolescent SS in male rats. The results also suggest that differences in neural functioning in the prefrontal cortex, hippocampus and lateral septum of adolescent SS rats may be involved in their altered social behaviour relative to that of controls.

Intergenerational transmission of depression: clinical observations and molecular mechanisms

Maternal mental illness can have a devastating effect during the perinatal period, and has a profound impact on the care that the baby receives and on the relationships that the baby forms. This review summarises clinical evidence showing the effects of perinatal depression on offspring physical and behavioural development, and on the transmission of psychopathology between generations. We then evaluate a number of factors which influence this relationship, such as genetic factors, the use of psychotropic medications during pregnancy, the timing within the perinatal period, the sex of the foetus, and exposure to maltreatment in childhood. Finally, we examine recent findings regarding the molecular mechanisms underpinning these clinical observations, and identify relevant epigenetic and biomarker changes in the glucocorticoid, oxytocin, oestrogen and immune systems, as key biological mediators of these clinical findings. By understanding these molecular mechanisms in more detail, we will be able to improve outcomes for both mothers and their offspring for generations.

Early Life Adversity and Adult Social Behavior: Focus on Arginine Vasopressin and Oxytocin as Potential Mediators

Exposure to stress during the early postnatal period (i.e., early life stress, ES) can impact brain physiology and modify individual variability in adult social behavior. Arginine vasopressin (AVP) and oxytocin (OXT) are two centrally released neuropeptides that are involved in shaping essential social behaviors, like aggression, social recognition, and social motivation. AVP and OXT modulate activity in brain regions important for the establishment of social behavior, and may be particularly sensitive to ES. In this review, we discuss whether ES alters the characteristics of the AVP- and OXT- systems in rodents, and whether these changes are associated with later alterations in aggression, social recognition, and social motivation. We have integrated causal studies indicating that (1) ES affects AVP/OXT, and (2) that changing AVP/OXT in affected regions alters social behavior. Although there is encouraging evidence that ES causes AVP- and OXT-system changes, and that these may mediate social behavior, a comprehensive understanding of the exact nature of AVP- and OXT changes and whether they are causal in establishing these behavioral disturbances needs further investigation. As there are indications that ES alters AVP- and OXT characteristics in humans as well, and that these may interact with adult predisposition to psychopathology with social dysfunction, future rodent studies may lay ground for a better understanding of such changes in humans. Ultimately, this may assist in developing therapeutic strategies to target ES effects on social behavior.

Pharmacological manipulation of DNA methylation normalizes maternal behavior, DNA methylation, and gene expression in dams with a history of maltreatment

The quality of parental care received during development profoundly influences an individual's phenotype, including that of maternal behavior. We previously found that female rats with a history of maltreatment during infancy mistreat their own offspring. One proposed mechanism through which early-life experiences influence behavior is via epigenetic modifications. Indeed, our lab has identified a number of brain epigenetic alterations in female rats with a history of maltreatment. Here we sought to investigate the role of DNA methylation in aberrant maternal behavior. We administered zebularine, a drug known to alter DNA methylation, to dams exposed during infancy to the scarcity-adversity model of low nesting resources, and then characterized the quality of their care towards their offspring. First, we replicate that dams with a history of maltreatment mistreat their own offspring. Second, we show that maltreated-dams treated with zebularine exhibit lower levels of adverse care toward their offspring. Third, we show that administration of zebularine in control dams (history of nurturing care) enhances levels of adverse care. Lastly, we show altered methylation and gene expression in maltreated dams normalized by zebularine. These findings lend support to the hypothesis that epigenetic alterations resulting from maltreatment causally relate to behavioral outcomes.

The parental brain and behavior: A target for endocrine disruption

During pregnancy, the sequential release of progesterone, 17β-estradiol, prolactin, oxytocin and placental lactogens reorganize the female brain. Brain structures such as the medial preoptic area, the bed nucleus of the stria terminalis and the motivation network including the ventral tegmental area and the nucleus accumbens are reorganized by this specific hormonal schedule such that the future mother will be ready to provide appropriate care for her offspring right at parturition. Any disruption to this hormone pattern, notably by exposures to endocrine disrupting chemicals (EDC), is therefore likely to affect the maternal brain and result in maladaptive maternal behavior. Development effects of EDCs have been the focus of intense study, but relatively little is known about how the maternal brain and behavior are affected by EDCs. We encourage further research to better understand how the physiological hormone sequence prepares the mother's brain and how EDC exposure could disturb this reorganization.

Effects of exogenous oxytocin and atosiban antagonist on GABA in different region of brain

Gamma amino butyric acid (GABA) is the primary inhibitory neurotransmitter in the vertebral central nervous system. It functions by altering the membrane conductance of Cl- ions, maintaining the membrane potential close to the resting potential. The hormone oxytocin (OT) has a central action where it acts as a neuromodulatory peptide and exerts its action depending upon the distribution of OT receptors (OTR) in the target site. OTRs are G-protein-coupled receptors (GPCRs) comprising different subunits (Gq, Gi, and Gs). The G- protein isoforms have the ability to activate different pathways, but specific agonists and antagonists may show different affinities to OTRs, depending on the specific G-protein isoform to which they are coupled. It is well documented that OTR distribution varies with age and species and in regions of the brain. In this study, we attempted to observe the impact of OT and atosiban (OTA), an OT antagonist, on GABA levels in different regions of the brain. Study animals were exposed intraperitoneally (i.p.) to normal saline (0.89%), OT 0.0116 mg/kg, and OTA 1 mg/kg in different combinations, for 30days. It was observed that OT and OTA administration modulated GABA levels in different regions of brain, while normal saline had no effect. It may be due to OTR receptor expression in different regions of the brain. This is significant because region-specific expression of different receptors could be important in the development of new drugs targeting specific neuropsychiatric disorders.

Neural correlates of emotion processing comparing antidepressants and exogenous oxytocin in postpartum depressed women: An exploratory study

Despite common use of antidepressants to treat postpartum depression, little is known about the impact of antidepressant use on postpartum brain activity. Additionally, although oxytocin has been investigated as a potential treatment for postpartum depression, the interaction between antidepressants and exogenous oxytocin on brain activity is unknown. We explored postpartum depressed women's neural activation in areas identified as important to emotion and reward processing and potentially, antidepressant response: the amygdala, nucleus accumbens and ventral tegmental area. We conducted a secondary analysis of a functional imaging study of response to sexual, crying infant and smiling infant images in 23 postpartum depressed women with infants under six months (11 women taking antidepressants, 12 unmedicated). Participants were randomized to receive a single dose of oxytocin or placebo nasal spray. There was significantly higher amygdala activation to sexual stimuli than either neutral or infant-related stimuli among women taking antidepressants or receiving oxytocin nasal spray. Among unmedicated women receiving placebo, amygdala activation was similar across stimuli types. There were no significant effects of antidepressants nor oxytocin nasal spray on reward area processing (i.e., in the nucleus accumbens or ventral tegmental area). Among postpartum women who remain depressed, there may be significant interactions between the effects of antidepressant use and exogenous oxytocin on neural activity associated with processing emotional information. Observed effect sizes were moderate to large, strongly suggesting the need for further replication with a larger sample.

Clinical potential of oxytocin in autism spectrum disorder: current issues and future perspectives

The effects of oxytocin on social cognition and behavior have recently attracted considerable attention. In particular, oxytocin has been proposed as a novel therapeutic for psychiatric disorders with social deficits such as autism spectrum disorders. This review provides a brief overview of behavioral and neural responses to oxytocin manipulations in humans and animal models. Although the differences in findings between human and animal studies should be interpreted carefully, shared behavioral phenotypes have been recognized, such as social bonding, social responses, and recognition and usage of social cues. Previous literature suggests that the neural effects of oxytocin in humans and animals overlap in the prefrontal, limbic, and paralimbic cortices. Oxytocin-induced alterations in these regions may indicate a fundamental basis for how oxytocin modulates social behaviors and facilitate the discovery of new pharmaceutical targets for treating social deficits.

Increased anxiety and decreased sociability induced by paternal deprivation involve the PVN-PrL OTergic pathway

Early adverse experiences often have devastating consequences. However, whether preweaning paternal deprivation (PD) affects emotional and social behaviors and their underlying neural mechanisms remain unexplored. Using monogamous mandarin voles, we found that PD increased anxiety-like behavior and attenuated social preference in adulthood. PD also decreased the number of oxytocin (OT)-positive neurons projecting from the paraventricular nucleus (PVN) and reduced the levels of the medial prefrontal cortex OT receptor protein in females and of the OT receptor and V1a receptor proteins in males. Intra-prelimbic cortical OT injections reversed the PD-induced changes in anxiety-like behavior and social preferences. Optogenetic activation of the prelimbic cortex OT terminals from PVN OT neurons reversed the PD-induced changes in emotion and social preference behaviors, whereas optogenetic inhibition was anxiogenic and impaired social preference in naive voles. These findings demonstrate that PD increases anxiety-like behavior and attenuates social preferences through the involvement of PVN OT neuron projections to the prelimbic cortex.

Parental care early in life is essential for normal development of the brain in humans and some other animals. It also lays the ground work for healthy behaviors later in life. Many studies have looked at the importance of a mother’s care, but less attention has been paid to the role played by fathers. Research shows that children who grow up without a father are at risk of emotional and behavioral problems later in life. But it is not clear how missing a father’s care affects brain development.

Oxytocin, a chemical produced by a part of the brain called the paraventricular nucleus, plays a key role in parental bonding. Another part of the brain called the prelimbic cortex regulates many emotions and many complex behaviors. Studying animals, like the mandarin vole, that form strong bonds with both parents is one way to learn more about how the loss of paternal care affects oxytocin or emotional and behavioral health.

Now, He et al. show that mandarin voles raised without a father are more anxious and socialize less with other voles than those raised with a father. The voles deprived of paternal care also have fewer oxytocin-producing cells in the paraventricular nucleus and fewer receptors for oxytocin in the prelimbic cortex. Injecting oxytocin into the prelimbic cortex eliminated the anxious and antisocial behavior seen in the voles lacking paternal care. Using a technique called optogenetics to restore the release of oxytocin in the prelimbic cortex reduced anxious behavior and restored normal social interactions. Using the same approach to interfere with communication between the paraventricular nucleus and prelimbic cortex in voles raised with a father also triggered anxious and antisocial behavior.

The experiments reveal that fathers play an important role in brain and behavioral development in mandarin voles. He et al. show that a lack of paternal care leads to deficits in oxytocin and a poor communication between the paraventricular nucleus and prelimbic cortex that contribute to emotional and social abnormalities in the voles. More studies are needed to determine father’s care has similar effects in humans. But if this relationship is confirmed, it might lead scientists to develop new strategies for treating psychiatric disorders in people deprived of paternal care.

Acute and long-lasting effects of oxytocin in cortico-limbic circuits: consequences for fear recall and extinction

The extinction of conditioned fear responses entrains the formation of safe new memories to decrease those behavioral responses. The knowledge in neuronal mechanisms of extinction is fundamental in the treatment of anxiety and fear disorders. Interestingly, the use of pharmacological compounds that reduce anxiety and fear has been shown as a potent co-adjuvant in extinction therapy. However, the efficiency and mechanisms by which pharmacological compounds promote extinction of fear memories remains still largely unknown and would benefit from a validation based on functional neuronal circuits, and the neurotransmitters that modulate them. From this perspective, oxytocin receptor signaling, which has been shown in cortical and limbic areas to modulate numerous functions (Eliava et al. Neuron 89(6):1291-1304, 2016), among them fear and anxiety circuits, and to enhance the salience of social stimuli (Stoop Neuron 76(1):142-59, 2012), may offer an interesting perspective. Experiments in animals and humans suggest that oxytocin could be a promising pharmacological agent at adjusting memory consolidation to boost fear extinction. Additionally, it is possible that long-term changes in endogenous oxytocin signaling can also play a role in reducing expression of fear at different brain targets. In this review, we summarize the effects reported for oxytocin in cortico-limbic circuits and on fear behavior that are of relevance for the modulation and potential extinction of fear memories.

Neuromodulation of maternal circuits by oxytocin

Motherhood in mammals involves tremendous changes throughout the body and central nervous system, which support attention and nurturing of infants. Maternal care consists of complex behaviors, such as nursing and protection of the offspring, requiring new mothers to become highly sensitive to infant needs. Long-lasting neural plasticity in various regions of the cerebral cortex may enable the perception and recognition of infant cues, important for appropriate caregiving responses. Recent findings have demonstrated that the neuropeptide oxytocin is involved in a number of physiological processes, including parturition and lactation and dynamically shaping neuronal responses to infant stimuli as well. Here, we review experience-dependent changes within the cortex occurring throughout motherhood, focusing on plasticity of the somatosensory and auditory cortex. We outline the role of oxytocin in gating cortical plasticity and discuss potential mechanisms regulating oxytocin release in response to different sensory stimuli.

Glutamatergic Signals in the Dorsal Raphe Nucleus Regulate Maternal Aggression and Care in an Opposing Manner in Mice

Lactating female mice nurture their pups and attack intruders in their territory. When an intruder invades a dam's territory, she needs to switch her behavior from care to aggression to protect her pups and territory. Although the neuronal mechanisms underlying each distinct behavior have been studied, it is unclear how these behaviors are displayed alternatively. The dorsal raphe nucleus (DRN) regulates both nurturing and aggressive behaviors. In the present study, we examined whether the DRN is involved in regulating alternative display of maternal care and aggression. We first examined neuronal activity in the medial prefrontal cortex (mPFC) and lateral habenula (LHb), which send glutamatergic input to the DRN, in dams by injecting Fluorogold, a retrograde tracer, into the DRN. The number of c-Fos- and Fluorogold-positive neurons in the mPFC and LHb increased in the dams that displayed biting behavior in response to an intruder, but remained unchanged in the dams that displayed nurturing behavior. Injections of N-methyl-d-aspartic acid (NMDA) receptor antagonists or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonists into the DRN inhibited biting behavior but not nurturing behavior. In contrast, injections of NMDA or AMPA into the DRN inhibited nurturing behavior. These results suggest that glutamatergic signals in the DRN, which may originate from the mPFC and/or LHb, regulate the preferential display of biting behavior over nurturing behavior in dams.

Oxytocin receptor activation in the basolateral complex of the amygdala enhances discrimination between discrete cues and promotes configural processing of cues

Oxytocin (OT) is a neuropeptide which influences the expression of social behavior and regulates its distribution according to the social context - OT is associated with increased pro-social effects in the absence of social threat and defensive aggression when threats are present. The present experiments investigated the effects of OT beyond that of social behavior by using a discriminative Pavlovian fear conditioning protocol with rats. In Experiment 1, an OT receptor agonist (TGOT) microinjected into the basolateral amygdala facilitated the discrimination between an auditory cue that signaled shock and another auditory cue that signaled the absence of shock. This TGOT-facilitated discrimination was replicated in a second experiment where the shocked and non-shocked auditory cues were accompanied by a common visual cue. Conditioned responding on probe trials of the auditory and visual elements indicated that TGOT administration produced a qualitative shift in the learning mechanisms underlying the discrimination between the two compounds. This was confirmed by comparisons between the present results and simulated predictions of elemental and configural associative learning models. Overall, the present findings demonstrate that the neuromodulatory effects of OT influence behavior outside of the social domain.

An fMRI investigation of the neural correlates underlying the autonomous sensory meridian response (ASMR)

Introduction : The "autonomous sensory meridian response" (ASMR) is a neologism used to describe an internal sensation of deep relaxation and pleasant head tingling which is often stimulated by gentle sounds, light touch, and personal attention. Methods : An fMRI-based methodology was employed to examine the brain activation of subjects prescreened for ASMR-receptivity (n=10) as they watched ASMR videos and identified specific moments of relaxation and tingling. Results : Subjects who experienced ASMR showed significant activation in regions associated with both reward (NAcc) and emotional arousal (dACC and Insula/IFG). Brain activation during ASMR showed similarities to patterns previously observed in musical frisson as well as affiliative behaviors. Conclusion : This is the first study to measure the activation of various brain regions during ASMR and these results may help to reveal the mechanistic underpinnings of this sensation.

Where is the love? A double-blind, randomized study of the effects of intranasal oxytocin on stress regulation and aggression

Previous studies reveal that oxytocin (OT) encourages prosocial behavior in humans; however, animal studies and recent work in humans suggest that OT may also play a role in aggressive behavior and feelings. The present study investigated these competing predictions in the context of a competitive task among 85 healthy human participants (males and females). Using a randomized double-blind design, participants were assigned to an experimental (intranasal OT) or control (intranasal placebo) group. Hostility (Aggression Questionnaire) was measured at home (T1) and in the lab after intranasal administration (T2). Behavioral aggression was assessed post-intranasal administration. There was a significant difference between the OT and the placebo group on hostility scores (p = 0.03) and a significant time by group interaction for behavioral aggression (p < 0.05). Self-reported hostility was significantly higher at T2 compared to T1 (p < 0.001) among participants in the oxytocin group while no significant change was found in hostility among the placebo group. Behavioral aggression was slightly higher in the OT group (compared to the placebo group) directly after OT administration, however, the opposite relationship was found as the study period progressed. Both hostility and behavioral aggression findings were consistent across gender.

Oxytocin facilitates adaptive fear and attenuates anxiety responses in animal models and human studies-potential interaction with the corticotropin-releasing factor (CRF) system in the bed nucleus of the stria terminalis (BNST)

Despite its relatively well-understood role as a reproductive and pro-social peptide, oxytocin (OT) tells a more convoluted story in terms of its modulation of fear and anxiety. This nuanced story has been obscured by a great deal of research into the therapeutic applications of exogenous OT, driving more than 400 ongoing clinical trials. Drawing from animal models and human studies, we review the complex evidence concerning OT's role in fear learning and anxiety, clarifying the existing confusion about modulation of fear versus anxiety. We discuss animal models and human studies demonstrating the prevailing role of OT in strengthening fear memory to a discrete signal or cue, which allows accurate and rapid threat detection that facilitates survival. We also review ostensibly contrasting behavioral studies that nonetheless provide compelling evidence of OT attenuating sustained contextual fear and anxiety-like behavior, arguing that these OT effects on the modulation of fear vs. anxiety are not mutually exclusive. To disambiguate how endogenous OT modulates fear and anxiety, an understudied area compared to exogenous OT, we survey behavioral studies utilizing OT receptor (OTR) antagonists. Based on emerging evidence about the role of OTR in rat dorsolateral bed nucleus of stria terminalis (BNST) and elsewhere, we postulate that OT plays a critical role in facilitating accurate discrimination between stimuli representing threat and safety. Supported by human studies, we demonstrate that OT uniquely facilitates adaptive fear but reduces maladaptive anxiety. Last, we explore the limited literature on endogenous OT and its interaction with corticotropin-releasing factor (CRF) with a special emphasis on the dorsolateral BNST, which may hold the key to the neurobiology of phasic fear and sustained anxiety.

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.

Sex differences in the regulation of social and anxiety-related behaviors: insights from vasopressin and oxytocin brain systems

To understand how the brain regulates behavior, many variables must be taken into account, with sex as a prominent variable. In this review, we will discuss recent human and rodent studies showing the sex-specific involvement of the neuropeptides vasopressin and oxytocin in social and anxiety-related behaviors. We discuss that sex differences can be evident at pre-pubertal ages as seen in the sex-specific regulation of social recognition, social play, and anxiety by the vasopressin system in juvenile rats. We further discuss that the oxytocin system in humans and rodents alters brain activation, anxiety, and sociosexual motivation in sex-specific ways. Finally, we propose that knowledge of vasopressin and oxytocin mediated sex-specific brain mechanisms can provide essential insights into how these neuropeptide systems contribute to sex-specific vulnerability as well as resilience to perturbations, with subsequent relevance to social and emotional disorders.

Oxytocin and Aggression

The neuropeptide oxytocin (OT) has a solid reputation as a facilitator of social interactions such as parental and pair bonding, trust, and empathy. The many results supporting a pro-social role of OT have generated the hypothesis that impairments in the endogenous OT system may lead to antisocial behavior, most notably social withdrawal or pathological aggression. If this is indeed the case, administration of exogenous OT could be the "serenic" treatment that psychiatrists have for decades been searching for.In the present review, we list and discuss the evidence for an endogenous "hypo-oxytocinergic state" underlying aggressive and antisocial behavior, derived from both animal and human studies. We furthermore examine the reported effects of synthetic OT administration on aggression in rodents and humans.Although the scientific findings listed in this review support, in broad lines, the link between a down-regulated or impaired OT system activity and increased aggression, the anti-aggressive effects of synthetic OT are less straightforward and require further research. The rather complex picture that emerges adds to the ongoing debate questioning the unidirectional pro-social role of OT, as well as the strength of the effects of intranasal OT administration in humans.

Postpartum Lactation-Mediated Behavioral Outcomes and Drug Responses in a Spontaneous Mouse Model of Obsessive-Compulsive Disorder

Using a spontaneous mouse model of obsessive-compulsive disorder (OCD), the current study evaluated the influence of postpartum lactation on the expression of compulsive-like behaviors, SSRI effectiveness, and the putative role of oxytocin and dopamine in mediating these lactation specific behavioral outcomes. Compulsive-like lactating mice were less compulsive-like in nest building and marble burying and showed enhanced responsiveness to fluoxetine (50 mg/kg) in comparison to compulsive-like nonlactating and nulliparous females. Lactating mice exhibited more anxiety-like behavior in the open field test compared to the nulliparous females, while chronic fluoxetine reduced anxiety-like behaviors. Blocking the oxytocin receptor with L368-899 (5 mg/kg) in the lactating mice exacerbated the compulsive-like and depression-like behaviors. The dopamine D2 receptor (D2R) agonist bromocriptine (10 mg/kg) suppressed marble burying, nest building, and central entries in the open field, but because it also suppressed overall locomotion in the open field, activation of the D2R receptor may have inhibited overall activity nonspecifically. Lactation- and fluoxetine-mediated behavioral outcomes in compulsive-like mice, therefore, appear to be partly regulated by oxytocinergic mechanisms. Serotonin immunoreactivity and serum levels were higher in lactating compulsive-like mice compared to nonlactating and nulliparous compulsive-like females. Together, these results suggest behavioral modulation, serotonergic alterations, and changes in SSRI effectiveness during lactation in compulsive-like mice. This warrants further investigation of postpartum events in OCD patients.

Mothers with substance addictions show reduced reward responses when viewing their own infant's face

Maternal addiction constitutes a major public health problem affecting children, with high rates of abuse, neglect, and foster care placement. However, little is known about the ways in which substance addiction alters brain function related to maternal behavior. Prior studies have shown that infant face cues activate similar dopamine-associated brain reward regions to substances of abuse. Here, we report on a functional MRI study documenting that mothers with addictions demonstrate reduced activation of reward regions when shown reward-related cues of their own infants. Thirty-six mothers receiving inpatient treatment for substance addiction were scanned at 6 months postpartum, while viewing happy and sad face images of their own infant compared to those of a matched unknown infant. When viewing happy face images of their own infant, mothers with addictions showed a striking pattern of decreased activation in dopamine- and oxytocin-innervated brain regions, including the hypothalamus, ventral striatum, and ventromedial prefrontal cortex-regions in which increased activation has previously been observed in mothers without addictions. Our results are the first to demonstrate that mothers with addictions show reduced activation in key reward regions of the brain in response to their own infant's face cues. Hum Brain Mapp 38:5421-5439, 2017. © 2017 Wiley Periodicals, Inc.