Involvement of oxytocin and GABA in consolation behavior elicited by socially defeated individuals in mandarin voles

Distinct medial amygdala oxytocin receptor neurons projections respectively control consolation or aggression in male mandarin voles

The individuals often show consolation to distressed companions or show aggression to the intruders. The circuit mechanisms underlying switching between consolation and aggression remain unclear. In the present study, using male mandarin voles, we identified that two distinct subtypes of oxytocin receptor (OXTR) neurons in the medial amygdala (MeA) projecting to the anterior insula (AI) and ventrolateral aspect of ventromedial hypothalamus (VMHvl) response differently to stressed siblings or unfamiliar intruders using c-Fos or calcium recording. Oxytocin release and activities of PVN neurons projecting to MeA increased upon consoling and attacking. OXTR antagonist injection to the MeA reduced consoling and attacking. Apoptosis, optogenetic or pharmacogenetic manipulation of these two populations of neurons altered behavioral responses to these two social stimuli respectively. Here, we show that two subtypes of OXTR neurons in the MeA projecting to the AI or VMHvl causally control consolation or aggression that may underlie switch between consolation and aggression.

Modulation of empathic abilities by the interplay between estrogen receptors and arginine vasopressin

This review examines the complex interactions between estrogen receptors α and β (ERα and ERβ) and arginine vasopressin (AVP), delving into their significant roles in modulating empathy, a critical psychological component in human social dynamics. Empathy, integrating affective and cognitive elements, is anchored in neural regions like the amygdala and prefrontal cortex. ERα and ERβ, pivotal in estrogen regulation, influence neurotransmitter dynamics and neural network activities, crucial for empathic development. AVP, key in regulating water balance, blood pressure, and social behaviors, interplays with these receptors, profoundly impacting empathic responses. The study highlights that ERα predominantly enhances empathy, especially affective empathy, by stimulating AVP synthesis and release. In contrast, ERβ may diminish empathy in certain contexts by suppressing AVP expression and activity. The intricate interplay, homeostatic balance, and mutual conversion between ERα and ERβ in AVP regulation are identified as challenging yet crucial areas for future research. These findings provide essential insights into the neurobiological underpinnings of empathy, offering new avenues for therapeutic interventions in social cognitive disorders and emotional dysregulation.

Prosocial behaviors in rodents

Prosocial behaviors (i.e., actions that benefit others) are central for social interactions in humans and other animals, by fostering social bonding and cohesion. To study prosociality in rodents, scientists have developed behavioral paradigms where animals can display actions that benefit conspecifics in distress or need. These paradigms have provided insights into the role of social interactions and transfer of emotional states in the expression of prosociality, and increased knowledge of its neural bases. However, prosociality levels are variable: not all tested animals are prosocial. Such variation has been linked to differences in animals' ability to process another's state as well as to contextual factors. Moreover, evidence suggests that prosocial behaviors involve the orchestrated activity of multiple brain regions and neuromodulators. This review aims to synthesize findings across paradigms both at the level of behavior and neural mechanisms. Growing evidence confirms that these processes can be studied in rodents, and intense research in the past years is rapidly advancing our knowledge. We discuss a strong bias in the field towards the study of these processes in negative valence contexts (e.g., pain, fear, stress), which should be taken as an opportunity to open new venues for future research.

Paternal absence and increased caregiving independently and interactively shape the development of male prairie voles at subadult and adult life stages

The influence of maternal caregiving is a powerful force on offspring development. The absence of a father during early life in biparental species also has profound implications for offspring development, although it is far less studied than maternal influences. Moreover, we have limited understanding of the interactive forces that maternal and paternal caregiving impart on offspring. We investigated if behaviorally upregulating maternal care compensates for paternal absence on prairie vole (Microtus ochrogaster) pup development. We used an established handling manipulation to increase levels of caregiving in father-absent and biparental families, and later measured male offspring behavioral outcomes at sub-adulthood and adulthood. Male offspring raised without fathers were more prosocial (or possibly less socially anxious) than those raised biparentally. Defensive behavior and responses to contextual novelty were also influenced by the absence of fathers, but only in adulthood. Offensive aggression and movement in the open field test changed as a function of life-stage but not parental exposure. Notably, adult pair bonding was not impacted by our manipulations. Boosting parental care produced males that moved more in the open field test. Parental handling also increased oxytocin immunoreactive cells within the supraoptic nucleus of the hypothalamus (SON), and in the paraventricular nucleus (PVN) of biparentally-reared males. We found no differences in vasopressinergic cell groups. We conclude that male prairie voles are contextually sensitive to the absence of fathers and caregiving intensity. Our study highlights the importance of considering the ways early experiences synergistically shape offspring behavioral and neural phenotypes across the lifespan.

Out of touch? How trauma shapes the experience of social touch - Neural and endocrine pathways

Trauma can shape the way an individual experiences the world and interacts with other people. Touch is a key component of social interactions, but surprisingly little is known about how trauma exposure influences the processing of social touch. In this review, we examine possible neurobiological pathways through which trauma can influence touch processing and lead to touch aversion and avoidance in trauma-exposed individuals. Emerging evidence indicates that trauma may affect sensory touch thresholds by modulating activity in the primary sensory cortex and posterior insula. Disturbances in multisensory integration and oxytocin reactivity combined with diminished reward-related and anxiolytic responses may induce a bias towards negative appraisal of touch contexts. Furthermore, hippocampus deactivation during social touch may reflect a dissociative state. These changes depend not only on the type and severity of the trauma but also on the features of the touch. We hypothesise that disrupted touch processing may impair social interactions and confer elevated risk for future stress-related disorders.

Early life adversity reduces affiliative behavior with a stressed cagemate and leads to sex-specific alterations in corticosterone responses in adult mice

Experiencing early life adversity (ELA) alters stress physiology and increases the risk for developing psychiatric disorders. The social environment can influence dynamics of stress responding and buffer and/or transfer stress across individuals. Yet, the impact of ELA on sensitivity to the stress of others and social behavior following stress is unknown. Here, to test the impact of ELA on social and physiological responses to stress, circulating blood corticosterone (CORT) and social behaviors were assessed in adult male and female mice reared under limited bedding and nesting (LBN) or control conditions. To induce stress, one cagemate of a pair-housed cage underwent a footshock paradigm and was then returned to their unshocked partner. CORT was measured in both groups of mice 20 or 90 min after stress exposure, and social behaviors were recorded and analyzed. ELA rearing influenced the CORT response to stress in a sex-specific manner. In males, both control and ELA-reared mice exhibited similar stress transfer to unshocked cagemates and similar CORT dynamics. In contrast, ELA females showed a heightened stress transfer to unshocked cagemates, and sustained elevation of CORT relative to controls, indicating enhanced stress contagion and a failure to terminate the stress response. Behaviorally, ELA females displayed decreased allogrooming and increased investigative behaviors, while ELA males showed reduced huddling. Together, these findings demonstrate that ELA influenced HPA axis dynamics, social stress contagion and social behavior. Further research is needed to unravel the underlying mechanisms and long-term consequences of ELA on stress systems and their impact on behavioral outcomes.

Oxytocin, GABA, and dopamine interplay in autism

Oxytocin plays an important role in brain development and is associated with various neurotransmitter systems in the brain. Abnormalities in the production, secretion, and distribution of oxytocin in the brain, at least during some stages of the development, are critical for the pathogenesis of neuropsychiatric diseases, particularly in the autism spectrum disorder. The etiology of autism includes changes in local sensory and dopaminergic areas of the brain, which are also supplied by the hypothalamic sources of oxytocin. It is very important to understand their mutual relationship. In this review, the relationship of oxytocin with several components of the dopaminergic system, gamma-aminobutyric acid (GABA) inhibitory neurotransmission and their alterations in the autism spectrum disorder is discussed. Special attention has been paid to the results describing a reduced expression of inhibitory GABAergic markers in the brain in the context of dopaminergic areas in various models of autism. It is presumed that the altered GABAergic neurotransmission, due to the absence or dysfunction of oxytocin at certain developmental stages, disinhibits the dopaminergic signaling and contributes to the autism symptoms.

Vicarious Emotions of Fear and Pain in Rodents

Affective empathy, the ability to share the emotions of others, is an important contributor to the richness of our emotional experiences. Here, we review evidence that rodents show signs of fear and pain when they witness the fear and pain of others. This emotional contagion creates a vicarious emotion in the witness that mirrors some level of detail of the emotion of the demonstrator, including its valence and the vicinity of threats, and depends on brain regions such as the cingulate, amygdala, and insula that are also at the core of human empathy. Although it remains impossible to directly know how witnessing the distress of others feels for rodents, and whether this feeling is similar to the empathy humans experience, the similarity in neural structures suggests some analogies in emotional experience across rodents and humans. These neural homologies also reveal that feeling distress while others are distressed must serve an evolutionary purpose strong enough to warrant its stability across ~ 100 millions of years. We propose that it does so by allowing observers to set in motion the very emotions that have evolved to prepare them to deal with threats - with the benefit of triggering them socially, by harnessing conspecifics as sentinels, before the witness personally faces that threat. Finally, we discuss evidence that rodents can engage in prosocial behaviors that may be motivated by vicarious distress or reward.

Partner-seeking and limbic dopamine system are enhanced following social loss in male prairie voles (Microtus ochrogaster)

Death of a loved one is recognized as one of life's greatest stresses, and 10%-20% of bereaved individuals will experience a complicated or prolonged grieving period that is characterized by intense yearning for the deceased. The monogamous prairie vole (Microtus ochrogaster) is a rodent species that forms pair bonds between breeding partners and has been used to study the neurobiology of social behaviors and isolation. Male prairie voles do not display distress after isolation from a familiar, same-sex conspecific; however, separation from a bonded female partner increases emotional, stress-related, and proximity-seeking behaviors. Here, we tested the investigatory response of male voles to partner odor during a period of social loss. We found that males who lost their partner spent significantly more time investigating partner odor but not non-partner social odor or food odor. Bachelor males and males in intact pairings did not respond uniquely to any odor. Furthermore, we examined dopamine (DA) receptor mRNA expression in the anterior insula cortex (aIC), nucleus accumbens (NAc), and anterior cingulate (ACC), regions with higher activation in grieving humans. While we found some effects of relationship type on DRD1 and DRD2 expression in some of these regions, loss of a high-quality opposite-sex relationship had a significant effect on DA receptor expression, with pair-bonded/loss males having higher expression in the aIC and ACC compared with pair-bonded/intact and nonbonded/loss males. Together, these data suggest that both relationship type and relationship quality affect reunion-seeking behavior and motivational neurocircuits following social loss of a bonded partner.

Emotional Contagion and Social Support in Pigs with the Negative Stimulus

This study expects to confirm the existence of emotional transmission in pigs from multiple perspectives and to provide theoretical references for improving animal welfare in livestock farming. A group that could directly observe (DO) and a group that could not directly observe (NO) were created based on whether or not their peers observed the treatment process, as the treated pig (TP) was treated with electrical shock and the companion pig (CP) either witnessed the treatment inflicted upon TP or not, and a third group was a control group, in which neither pig was stimulated. The behavioral responses of both the TPs and CPs were recorded to evaluate the emotional reaction. The results found that in both the DO and NO groups, the frequency of TP freezing was significantly higher than that of CP, and CP was significantly higher than that of the control group. Interestingly, although the social interaction responses of the CPs were not similar in the DO and NO groups, there were no significant differences between the behaviors of TPs in the DO and NO groups, except for nose-nose contact and a single approach to the partition, which allowed us to conclude that, whether or not the pigs directly observed the negative treatment, they were able to respond accordingly to fear and provide similar social support to their companions who were treated negatively.

Early life adversity reduces affiliative behavior towards a distressed cagemate and leads to sex-specific alterations in corticosterone responses

Experiencing early life adversity (ELA) alters stress physiology and increases the risk for developing psychiatric disorders. The social environment can influence dynamics of stress responding and buffer and/or transfer stress across individuals. Yet, the impact of ELA on sensitivity to the stress of others and social behavior following stress is unknown. Here, to test the impact of ELA on social and physiological responses to stress, circulating blood corticosterone (CORT) and social behaviors were assessed in adult male and female mice reared under limited bedding and nesting (LBN) or control conditions. To induce stress, one cagemate of a pair-housed cage underwent a footshock paradigm and was then returned to their unshocked partner. CORT was measured in both mice 20 or 90 minutes after stress exposure, and social behaviors were recorded and analyzed. ELA rearing influenced the CORT response to stress in a sex-specific manner. In males, both control and ELA-reared mice exhibited similar stress transfer to unshocked cagemates and similar CORT dynamics. In contrast, ELA females showed a heightened stress transfer to unshocked cagemates, and sustained elevation of CORT relative to controls, indicating enhanced stress contagion and a failure to terminate the stress response. Behaviorally, ELA females displayed decreased allogrooming and increased investigative behaviors, while ELA males showed reduced huddling. Together, these findings demonstrate that ELA influenced HPA axis dynamics, social stress contagion and social behavior. Further research is needed to unravel the underlying mechanisms and long-term consequences of ELA on stress systems and their impact on behavioral outcomes.

Neural mechanisms of comforting: Prosocial touch and stress buffering

Comforting is a crucial form of prosocial behavior that is important for maintaining social unity and improving the physical and emotional well-being of social species. It is often expressed through affiliative social touch toward someone in distress, providing relief for their distressed state. In the face of increasing global distress, these actions are paramount to the continued improvement of individual welfare and the collective good. Understanding the neural mechanisms responsible for promoting actions focused on benefitting others is particularly important and timely. Here, we review prosocial comforting behavior, emphasizing synthesizing recent studies carried out using rodent models. We discuss its underlying behavioral expression and motivations, and then explore both the neurobiology of prosocial comforting in a helper animal and the neurobiology of stress relief following social touch in a recipient as part of a feedback loop interaction.

Evolutionarily conserved role of oxytocin in social fear contagion in zebrafish

Emotional contagion is the most ancestral form of empathy. We tested to what extent the proximate mechanisms of emotional contagion are evolutionarily conserved by assessing the role of oxytocin, known to regulate empathic behaviors in mammals, in social fear contagion in zebrafish. Using oxytocin and oxytocin receptor mutants, we show that oxytocin is both necessary and sufficient for observer zebrafish to imitate the distressed behavior of conspecific demonstrators. The brain regions associated with emotional contagion in zebrafish are homologous to those involved in the same process in rodents (e.g., striatum, lateral septum), receiving direct projections from oxytocinergic neurons located in the pre-optic area. Together, our results support an evolutionary conserved role for oxytocin as a key regulator of basic empathic behaviors across vertebrates.

Neural basis of prosocial behavior

The ability to behave in ways that benefit other individuals' well-being is among the most celebrated human characteristics crucial for social cohesiveness. Across mammalian species, animals display various forms of prosocial behaviors - comforting, helping, and resource sharing - to support others' emotions, goals, and/or material needs. In this review, we provide a cross-species view of the behavioral manifestations, proximate and ultimate drives, and neural mechanisms of prosocial behaviors. We summarize key findings from recent studies in humans and rodents that have shed light on the neural mechanisms underlying different processes essential for prosocial interactions, from perception and empathic sharing of others' states to prosocial decisions and actions.

Socially Transferred Stress Experience Modulates Social Affective Behaviors in Rats

Social communication of affective states between individuals, as well as actual experiences, influences their internal states and behaviors. Although prior stress experiences promote empathy-like behaviors, it remains unclear whether the social transmission of stress events modulates these behaviors. Here, we provide evidence that transferred stress experiences from cage mates modulate socioaffective approach-avoidance behaviors in rats. Male Wistar-Imamichi rats were assigned to one of five experimental groups (Control (n = 15); no shock with shocked cage mates (n = 15); low (0.1 mA, n = 15), middle (0.5 mA, n = 14), and high shock (1.0 mA, n = 14)). Except for the naïve and housed with stressed mate groups, rats received two foot-shocks (5 s for each). The next day, the subjects were allowed to explore two unfamiliar conspecifics; one was a naïve, while the other was a distressed conspecific that received two foot-shocks (1.0 mA, 5 s) immediately before the test. Rats that were housed with stressed mates, as well as those that experienced a higher intensity of foot-shocks, were more likely to approach, while naïve rats avoided, a distressed conspecific. These results suggest that socially transferred stress shifts socioaffective response styles from avoidance to approach toward a stressed conspecific in rats.

Emotional contagion and prosocial behavior in rodents

Empathy is critical to adjusting our behavior to the state of others. The past decade dramatically deepened our understanding of the biological origin of this capacity. We now understand that rodents robustly show emotional contagion for the distress of others via neural structures homologous to those involved in human empathy. Their propensity to approach others in distress strengthens this effect. Although rodents can also learn to favor behaviors that benefit others via structures overlapping with those of emotional contagion, they do so less reliably and more selectively. Together, this suggests evolution selected mechanisms for emotional contagion to prepare animals for dangers by using others as sentinels. Such shared emotions additionally can, under certain circumstances, promote prosocial behavior.

Mice Cohabiting With Familiar Conspecific in Chronic Stress Condition Exhibit Methamphetamine-Induced Locomotor Sensitization and Augmented Consolation Behavior

Recognizing and sharing emotions are essential for species survival, but in some cases, living with a conspecific in distress condition may induce negative emotional states through empathy-like processes. Studies have reported that stressors promote psychiatric disorders in both, those who suffer directly and who witness these aversive episodes, principally whether social proximity is involved. However, the mechanisms underlying the harmful outcomes of emotional contagion need more studies, mainly in the drug addiction-related behaviors. Here, we investigated the relevance of familiarity and the effects of cohabitation with a partner submitted to chronic stress in the anxiety-like, locomotor sensitization, and consolation behaviors. Male Swiss mice were housed in pairs during different periods to test the establishment of familiarity and the stress-induced anxiety behavior in the elevated plus maze. Another cohort was housed with a conspecific subjected to repeated restraint stress (1 h/day) for 14 days. During chronic restraint the allogrooming was measured and after the stress period mice were tested in the open field for evaluation of anxiety and locomotor cross-sensitization induced by methamphetamine. We found that familiarity was established after 14 days of cohabitation and the anxiogenic behavior appeared after 14 days of stress. Repeated restraint stress also increased anxiety in the open field test and induced locomotor cross-sensitization in the stressed mice and their cagemates. Cagemates also exhibited an increase in the consolation behavior after stress sessions when compared to control mice. These results indicate that changes in drug abuse-related, consolation, and affective behaviors may be precipitated through emotional contagion in familiar conspecifics.

Mean Girls: Social Stress Models for Female Rodents

Social stressors are known to have strong negative impacts on mental health. There is a long history of preclinical social defeat stress studies in rodents focusing on males that has produced important insights into the neural mechanisms that modulate depression- and anxiety-related behavior. Despite these impressive results, a historical weakness of rodent social stress models has been an under-representation of studies in females. This is problematic because rates of depression and anxiety are higher in women versus men. Recently there has been a surge of interest in adapting social stress methods for female rodents. Here we review new rodent models that have investigated numerous facets of social stress in females. The different models have different strengths and weaknesses, with some model systems having stronger ethological validity with other models having better access to molecular tools to manipulate neural circuits. Continued use and refinement of these complementary models will be critical for addressing gaps in understanding the function of neural circuits modulating depression- and anxiety-related behavior in females.

Roles of Oxytocin in Stress Responses, Allostasis and Resilience

Oxytocin has been revealed to work for anxiety suppression and anti-stress as well as for psychosocial behavior and reproductive functions. Oxytocin neurons are activated by various stressful stimuli. The oxytocin receptor is widely distributed within the brain, and oxytocin that is released or diffused affects behavioral and neuroendocrine stress responses. On the other hand, there has been an increasing number of reports on the role of oxytocin in allostasis and resilience. It has been shown that oxytocin maintains homeostasis, shifts the set point for adaptation to a changing environment (allostasis) and contributes to recovery from the shifted set point by inducing active coping responses to stressful stimuli (resilience). Recent studies have suggested that oxytocin is also involved in stress-related disorders, and it has been shown in clinical trials that oxytocin provides therapeutic benefits for patients diagnosed with stress-related disorders. This review includes the latest information on the role of oxytocin in stress responses and adaptation.

Prior stress experience modulates social preference for stressed conspecifics in male rats

Adult male rats tend to avoid adult conspecifics in distress. In this study, we asked whether prior stress experience would modulate social preference for a stressed conspecific using a social affective preference (SAP) test. Male Long-Evans adult rats were assigned to the shocked and non-shocked groups. In the shocked group, rats were acutely subjected to foot shocks (1.0 mA, 5 s duration × 2) 24 h before the SAP test. During the SAP test, the experimental rats were placed in an arena where two adult conspecific stimuli, one of which received the foot shocks immediately before the SAP test, were presented at both ends and allowed to explore freely for 5 min. We measured sniffing behavior toward each conspecific as an index of social preference. Non-shocked adult rats avoided, while shocked rats approached, the stressed conspecifics more than the non-stressed ones. These results suggest that prior stress promotes social preference for a stressed conspecific in adult male rats.

Systematic Input-Output Mapping Reveals Structural Plasticity of VTA Dopamine Neurons-Zona Incerta Loop Underlying the Social Buffering Effects in Learned Helplessness

A common phenomenon called social buffering (SB), communication within conspecific animals is a benefit for a stressed individual to better recover from aversive events, is crucial to all mammals. Although the dopamine reward system has been implicated in SB, it is not clear which neuronal populations are relevant and how they contribute. Here, we adopted a learned helplessness (LH) animal model of depression and found that LH subjects housed with a conspecific partner show better performance in the shuttle box test, showing that SB improves the stress-coping abilities to deal with stress. Bidirectional manipulation of ventral tegmental area (VTA) dopamine neurons by chemogenetic tools can mimic or block the SB effect in LH mice. To screen for SB-induced structure plasticity of VTA dopamine neurons, we employed viral genetic tools for mapping input and output architecture and found LH- and SB-triggered circuit-level changes in neuronal ensembles. Zona incerta (ZI), an overlapping brain region, was significantly changed in both anterograde and retrograde tracing during LH and SB. These results reveal a neural loop with structural plasticity between VTA dopamine neurons and ZI underlies the SB effects in LH and lays a foundation for studying how VTA dopamine neurons regulate SB-related neural circuits.

Neural control of affiliative touch in prosocial interaction

The ability to help and care for others fosters social cohesiveness and is vital to the physical and emotional well-being of social species, including humans^1-3. Affiliative social touch, such as allogrooming (grooming behaviour directed towards another individual), is a major type of prosocial behaviour that provides comfort to others^1-6. Affiliative touch serves to establish and strengthen social bonds between animals and can help to console distressed conspecifics. However, the neural circuits that promote prosocial affiliative touch have remained unclear. Here we show that mice exhibit affiliative allogrooming behaviour towards distressed partners, providing a consoling effect. The increase in allogrooming occurs in response to different types of stressors and can be elicited by olfactory cues from distressed individuals. Using microendoscopic calcium imaging, we find that neural activity in the medial amygdala (MeA) responds differentially to naive and distressed conspecifics and encodes allogrooming behaviour. Through intersectional functional manipulations, we establish a direct causal role of the MeA in controlling affiliative allogrooming and identify a select, tachykinin-expressing subpopulation of MeA GABAergic (γ-aminobutyric-acid-expressing) neurons that promote this behaviour through their projections to the medial preoptic area. Together, our study demonstrates that mice display prosocial comforting behaviour and reveals a neural circuit mechanism that underlies the encoding and control of affiliative touch during prosocial interactions.

CRF-CRFR1 system within the dorsal medial prefrontal cortex are involved in consolation deficits under acute restraint stress in mandarin voles

Consolation is a complex empathic behavior that has recently been observed in some socially living rodents. Despite the growing body of literature suggesting that stress affects some simple form of empathy, the relationship between stress and consolation remains largely understudied. Using monogamous mandarin voles, we found that an acute restraint stress exposure significantly reduced consolation-like behaviors and induced anxiety-like behaviors. Along with these behavioral changes, corticotropin-releasing factor (CRF) and CRF receptor 1 (CRFR1) neurons were activated within the anterior cingulate cortex (ACC) and prelimbic cortex (PrL) but not within the infralimbic cortex (IL). Chemogenetic activation of CRF neurons in the ACC and PrL, recaptured acute stress-induced behavioral dysfunctions. We further observed that intracellular PKA and PKC signaling pathways mediate CRF-induced behavioral dysfunctions, but they work in a regional-specific, sex-biased manner. Together, these results suggest that the local CRF-CRFR1 system within the ACC and PrL is involved in the consolation deficits and anxiety induced by acute stress.

Quality of early-life maternal care predicts empathy-like behavior in adult male rats: Linking empathy to BDNF gene expression in associated brain regions

Empathy is the ability to experience a shared affective state as others. It enhances group living and manifests itself as helping behavior towards a distressed person. It also can flourish by nurturing. Recent findings suggest that rodents exhibit empathy-like behavior towards their conspecifics. However, the role of early-life experiences (e.g., maternal care) is not clear on the development of empathy-like behavior. Moreover, brain-derived neutrophilic factor (BDNF) is a pivotal protein in modulating the brain's function and behaviors. Evidence suggests that the expression of the BDNF gene can be affected by the quality of maternal care. In this study, we questioned whether variation in maternal care modulates empathy-like behavior of male rats in adulthood. Additionally, gene expression of BDNF was measured in the amygdala, hippocampus, insula, anterior cingulate cortex, prefrontal cortex, and striatum in these adult male rats. Based on the pattern of maternal care, the offspring were divided into high maternal care (HMC) and low maternal care (LMC) groups. We confirmed that the early-life experience of HMC significantly promoted the empathy-like behavior of rats in adulthood compared to LMC. In terms of gene expression, the HMC group consistently had higher BDNF gene expression in all studied regions, except anterior cingulate cortex which groups were not different. Taken together, it suggests that maternal care in infancy predicts empathy-like behavior in adulthood and differences in BDNF gene expression in different brain regions may reflect the underlying mechanism.

Aggression: How the anterior cingulate cortex helps to ensure a fair fight

Violent behavior is the product of a diverse network of neural structures. A new study shows that the anterior cingulate cortex is important for helping to restrain overly aggressive acts, even within a fight, to ensure animals match their behavioral intensity with the challenge posed by their opponents.

Dorsal raphe nucleus to anterior cingulate cortex 5-HTergic neural circuit modulates consolation and sociability

Consolation is a common response to the distress of others in humans and some social animals, but the neural mechanisms underlying this behavior are not well characterized. By using socially monogamous mandarin voles, we found that optogenetic or chemogenetic inhibition of 5-HTergic neurons in the dorsal raphe nucleus (DR) or optogenetic inhibition of serotonin (5-HT) terminals in the anterior cingulate cortex (ACC) significantly decreased allogrooming time in the consolation test and reduced sociability in the three-chamber test. The release of 5-HT within the ACC and the activity of DR neurons were significantly increased during allogrooming, sniffing, and social approaching. Finally, we found that the activation of 5-HT1A receptors in the ACC was sufficient to reverse consolation and sociability deficits induced by the chemogenetic inhibition of 5-HTergic neurons in the DR. Our study provided the first direct evidence that DR-ACC 5-HTergic neural circuit is implicated in consolation-like behaviors and sociability.

Wild jackdaws respond to their partner's distress, but not with consolation

Individuals are expected to manage their social relationships to maximize fitness returns. For example, reports of some mammals and birds offering unsolicited affiliation to distressed social partners (commonly termed 'consolation') are argued to illustrate convergent evolution of prosocial traits across divergent taxa. However, most studies cannot discriminate between consolation and alternative explanations such as self-soothing. Crucially, no study that controls for key confounds has examined consolation in the wild, where individuals face more complex and dangerous environments than in captivity. Controlling for common confounds, we find that male jackdaws (Corvus monedula) respond to their mate's stress-states, but not with consolation. Instead, they tended to decrease affiliation and partner visit rate in both experimental and natural contexts. This is striking because jackdaws have long-term monogamous relationships with highly interdependent fitness outcomes, which is precisely where theory predicts consolation should occur. Our findings challenge common conceptions about where consolation should evolve, and chime with concerns that current theory may be influenced by anthropomorphic expectations of how social relationships should be managed. To further our understanding of the evolution of such traits, we highlight the need for our current predictive frameworks to incorporate the behavioural trade-offs inherent to life in the wild.

Sex-Dependent Effects of Chronic Social Defeat on Emotional and Social Behaviors, and Parameters of Oxytocin and Vasopressin Systems in Mandarin Voles (Microtus mandarinus)

In the regulation of emotional and social behaviors, both oxytocin (OT) and vasopressin (AVP) are sex specific. Although significant sex differences have been reported in the context of behavioral and hormonal responses to social stress, such differences in response to chronic social defeat stress (CSDS) and the underlying neural mechanisms remain largely unknown. By investigating monogamous mandarin voles (Microtus mandarinus), CSDS was found to decrease the percentages of time spent in the central area of the open field, in the open arms of the elevated plus maze, as well as in the light area of the light and dark boxes in both male and female voles. CSDS also increased the observed level of social withdrawal in both sex groups. However, CSDS exposure increased the percentages of immobile time in both the tail suspension test and the forced swim test and reduced the locomotor activity in the open field (in females only). Along with these behavioral changes, the oxytocin receptor (OTR) levels in the nucleus accumbens (NAc) were significantly lower in CSDS-exposed voles of both sexes; however, in males, the levels of OTR in the paraventricular nucleus (PVN) were reduced. CSDS-exposed males showed lower levels of V1aR in the NAc than CSDS-exposed females. Furthermore, induced by a single social defeat event, CSDS reduced c-Fos and OT double labeling in the PVN of females but increased c-Fos and AVP double-labeled neurons in the PVN of males exposed to a single social defeat event. Collectively, the present study indicates that OT and AVP systems may play important regulatory roles in the sex differences of behavioral performances in response to CSDS. These findings suggest mandarin voles as a useful animal model for studying sex-specific behavioral performance and the underlying neurobiological mechanisms of stress-related mental disorders in preclinical studies.

Neural mechanisms necessary for empathy-related phenomena across species

The neural basis of empathy and prosociality has received much interest over the past decades. Neuroimaging studies localized a network of brain regions with activity that correlates with empathy. Here, we review how the emergence of rodent and nonhuman primate models of empathy-related phenomena supplements human lesion and neuromodulation studies providing evidence that activity in several nodes is necessary for these phenomena to occur. We review proof that (i) affective states triggered by the emotions of others, (ii) motivations to act in ways that benefit others, and (iii) emotion recognition can be altered by perturbing brain activity in many nodes identified by human neuroimaging, with strongest evidence for the cingulate and the amygdala. We also include evidence that manipulations of the oxytocin system and analgesics can have such effects, the latter providing causal evidence for the recruitment of an individual's own nociceptive system to feel with the pain of others.

Convergent neuroendocrine mechanisms of social buffering and stress contagion

Social interactions play a key role in modulating the impact of stressful experiences. In some cases, social interactions can result in social buffering, the process in which the presence of one individual reduces the physiological and behavioral impact of stress in another individual. On the other hand, there is growing evidence that a key initiating factor of social buffering behaviors is the initiation of an anxiogenic state in the individual that was not directly exposed to the stress. This is referred to as stress contagion (a form of emotion contagion). Both processes involve the transmission of social information, suggesting that contagion and buffering could share similar neural mechanisms. In general, mechanistic studies of contagion and buffering are considered separately, even though behavioral studies show that a degree of contagion is usually necessary for social buffering behaviors to occur. Here we consider the extent to which the neuropeptides corticotropin releasing hormone and oxytocin are involved in contagion and stress buffering. We also assess the importance that frontal cortical areas such as the anterior cingulate cortex and infralimbic cortex play in these behavioral processes. We suggest that further work that directly compares neural mechanisms during stress contagion and stress buffering will be important for identifying what appear to be distinct but overlapping circuits mediating these processes.

Paraventricular thalamic nucleus plays a critical role in consolation and anxious behaviors of familiar observers exposed to surgery mice

Background: Consolation behaviors toward the sick are common in humans. Anxiety in the relatives of the sick is also common. Anxiety can cause detrimental effects on multiple systems. However, our understanding on the neural mechanisms of these behaviors is limited because of the lack of small animal models.

Methods: Five of 6- to 8-week-old CD-1 male mice were housed in a cage. Among them, 2 mice had right common artery exposure (surgery) and the rest were without surgery. Allo-grooming and performance in light and dark box and elevated plus maze tests of the mice were determined.

Results: Mice without surgery had increased allo-grooming toward mice with surgery but decreased allo-grooming toward non-surgery intruders. This increased allo-grooming toward surgery mice was higher in familiar observers of surgery mice than that of mice that were not cage-mates of surgery mice before the surgery. Familiar observers developed anxious behavior after being with surgery mice. Surgery mice with familiar observers had less anxious behavior than surgery mice without interacting with familiar observers. Multiple brain regions including paraventricular thalamic nucleus (PVT) were activated in familiar observers. The activated cells in PVT contained orexin receptors. Injuring the neurons with ibotenic acid, antagonizing orexin signaling with an anti-orexin antibody or inhibiting neurons by chemogenetic approach in PVT abolished the consolation and anxious behaviors of familiar observers.

Conclusions: Mice show consolation behavior toward the sick. This behavior attenuates the anxious behavior of surgery mice. The orexin signaling in the PVT neurons play a critical role in the consolation of familiar observers toward surgery mice and their anxious behavior. Considering that about 50 million patients have surgery annually in the United States, our study represents the initial attempt to understand neural mechanisms for consolation and anxiety of a large number of people.

Regulation of defeat-induced social avoidance by medial amygdala DRD1 in male and female prairie voles

Social interaction with unfamiliar individuals is necessary for species-preserving behaviors such as finding mates and establishing social groups. However, social conflict is a potential negative outcome to interaction with a stranger that can be distressing enough to cause an individual to later avoid interactions with other unfamiliar conspecifics. Unfortunately, stress research using a prominent model of social conflict, social defeat stress, has largely omitted female subjects. This has left a void in the literature regarding social strain on female stress biology and adequate comparison of the effect of sex in stress pathways. The prairie vole (Microtus ochrogaster) exhibits aggressive behavior in both sexes, making voles an attractive candidate to model social defeat in both sexes. This study sought to establish a model of social defeat stress in both male and female prairie voles, characterize behavioral changes in response to this stressor, and investigate the role of dopamine signaling in the response to social defeat stress. Defeated male and female prairie voles displayed social avoidance as well as an increase in the level of dopamine receptor D1 (DRD1) in the medial amygdala (MeA). Pharmacological manipulation of DRD1 signaling in the MeA revealed that increased DRD1 signaling is sufficient to induce a social avoidant state, and could be a necessary component in the defeat-induced social avoidance response. These findings provide the prairie vole as a model of social defeat in both sexes, and implicate the MeA in avoidance of unfamiliar conspecifics after a distressing social encounter.

Reduced Consolation Behaviors in Physically Stressed Mandarin Voles: Involvement of Oxytocin, Dopamine D2, and Serotonin 1A Receptors Within the Anterior Cingulate Cortex

BACKGROUND

Consolation is a type of empathy-like behavior that has recently been observed in some socially living rodents. Despite the growing body of literature suggesting that stress affects empathy, the relationship between stress and consolation remains understudied at the preclinical level. Here, we examined the effects of chronic emotional stress or physical stress exposure on consolation and emotional behaviors by using the socially monogamous mandarin vole (Microtus mandarinus) in both males and females.

METHOD/RESULTS

Physical stress voles were exposed to 14-day social defeat stress, whereas emotional stress voles vicariously experienced the defeat of their partners. We found that physical stress, but not emotional stress, voles showed reduced grooming toward their defeated partners and increased anxiety- and despair-like behaviors. Meanwhile, physical stress voles exhibited decreased neural activity in the anterior cingulate cortex, which is centrally involved in empathy. The densities of oxytocin receptors, dopamine D2 receptors, and serotonin 1A-receptors within the anterior cingulate cortex were significantly decreased in the physical stress group compared with controls. All the behavioral and physiological changes were similar between the sexes. Finally, we found that the reduced consolation behavior and some anxiety-like syndromes in physical stress voles could be alleviated by pretreatment with an oxytocin receptor, D2 receptors, or serotonin 1A-receptor agonist within the anterior cingulate cortex, whereas injections of corresponding receptor antagonists to the control voles decreased the consolation behavior and increased some anxiety-like behaviors.

CONCLUSIONS

Our results indicated that chronic physical stress exposure impaired consolation and induced anxiety-like behaviors in mandarin voles and oxytocin receptors, 5-HT1A receptors, and D2 receptors within the anterior cingulate cortex may play important roles in these processes.

Establishment of a rodent cooperation assay as a model of social cognition

INTRODUCTION

Impaired cooperative skills form a characteristic symptom in autism, which lacks adequate treatment. The objective of this study was to establish a rat cooperation assay which fits the feasibility and capacity requirements of drug development.

METHODS

Long-Evans and Lister Hooded rats were trained in pairs to simultaneously perform nose-pokes (within 1 s) for reward in a Skinner box equipped with two nose-poke modules. Conditioning took place first with naive-naive pairs, then with naive-experienced and finally with experienced-experienced pairs, when the task was familiar for both rats. In a control experiment, experienced Lister-hooded pairs were tested under the learnt schedule but without the possibility to communicate with each other.

RESULTS

Rats were able to learn the task in 8-15 sessions. Experienced-experienced Long-Evans pairs completed the training significantly faster than the other pairs Analysis of the nose-poke latency data, sample video-recordings and the significantly decreased performance of rats in the control experiment suggested that the animals solved the task via real cooperation.

DISCUSSION

The newly developed rat cooperation model is quick and has sufficiently high throughput, therefore it may be used in the drug development of putative social cognitive enhancer compounds.

Role of oxytocin in the control of stress and food intake

Oxytocin neurones in the hypothalamus are activated by stressful stimuli and food intake. The oxytocin receptor is located in various brain regions, including the sensory information-processing cerebral cortex; the cognitive information-processing prefrontal cortex; reward-related regions such as the ventral tegmental areas, nucleus accumbens and raphe nucleus; stress-related areas such as the amygdala, hippocampus, ventrolateral part of the ventromedial hypothalamus and ventrolateral periaqueductal gray; homeostasis-controlling hypothalamus; and the dorsal motor complex controlling intestinal functions. Oxytocin affects behavioural and neuroendocrine stress responses and terminates food intake by acting on the metabolic or nutritional homeostasis system, modulating emotional processing, reducing reward values of food intake, and facilitating sensory and cognitive processing via multiple brain regions. Oxytocin also plays a role in interactive actions between stress and food intake and contributes to adaptive active coping behaviours.