Social modulation of pain as evidence for empathy in mice

Insular Cortex Projections to Nucleus Accumbens Core Mediate Social Approach to Stressed Juvenile Rats

Social interactions are shaped by features of the interactants, including age, emotion, sex, and familiarity. Age-specific responses to social affect are evident when an adult male rat is presented with a pair of unfamiliar male conspecifics, one of which is stressed via two foot shocks and the other naive to treatment. Adult test rats prefer to interact with stressed juvenile (postnatal day 30, PN30) conspecifics but avoid stressed adult (PN50) conspecifics. This pattern depends upon the insular cortex (IC), which is anatomically connected to the nucleus accumbens core (NAc). The goal of this work was to test the necessity of IC projections to NAc during social affective behavior. Here, bilateral pharmacological inhibition of the NAc with tetrodotoxin (1 μm; 0.5 μl/side) abolished the preference for stressed PN30, but did not alter interactions with PN50 conspecifics. Using a combination of retrograding tracing and c-Fos immunohistochemistry, we report that social interactions with stressed PN30 conspecifics elicit greater Fos immunoreactivity in IC → NAc neurons than interactions with naive PN30 conspecifics. Chemogenetic stimulation of IC terminals in the NAc increased social exploration with juvenile, but not adult, conspecifics, whereas chemogenetic inhibition of this tract blocked the preference to investigate stressed PN30 conspecifics, which expands upon our previous finding that optogenetic inhibition of IC projection neurons mediated approach and avoidance. These new findings suggest that outputs of IC to the NAc modulate social approach, which provides new insight to the neural circuitry underlying social decision-making.SIGNIFICANCE STATEMENT Social decision-making underlies an animal's behavioral response to others in a range of social contexts. Previous findings indicate the insular cortex (IC) and the nucleus accumbens (NAc) play important roles in social behaviors, and human neuroimaging implicates both IC and NAc in autism and other psychiatric disorders characterized by aberrant social cognition. To test whether IC projections to the NAc are involved in social decision-making, circuit-specific chemogenetic manipulations demonstrated that the IC → NAc pathway mediates social approach toward distressed juvenile, but not adult, conspecifics. This finding is the first to implicate this circuit in rodent socioemotional behaviors and may be a neuroanatomical substrate for integration of emotion with social reward.

The translatability of pain across species

The poor translational record of pain research has suggested to some observers that species differences in pain biology might be to blame. In this review, I consider the evidence for species similarity and differences in the pain research literature. Impressive feats of translation have been demonstrated in relation to certain genetic effects, social modulation of pain and pain memory. The degree to which pain biology in rodents predicts pain biology in humans has important implications both for evolutionary accounts of pain, but also the success of analgesic drug development going forward. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Methylphenidate administration promotes sociability and reduces aggression in a mouse model of callousness

RATIONALE

Deficits in empathy constitute a distinctive feature of several psychopathologies, including conduct disorder (CD). The co-occurrence of callous-unemotional (CU) traits, excess rates of aggression and violation of societal norms confers specific risk for adult psychopathy. To date, the off-label use of methylphenidate (MPH) constitutes the drug treatment of choice.

OBJECTIVES

Herein, we tested the therapeutic potential of MPH in a recently devised mouse model recapitulating the core phenotypic abnormalities of CD.

METHODS

Two subgroups of BALB/cJ male mice exhibiting opposite profiles of emotional contagion (i.e. socially transmitted adoption of another's emotional states) were investigated for reactive aggression, sociability, attention control, anxiety-related behaviours and locomotor activity, in response to MPH administration (0.0, 3.0 or 6.0 mg/kg).

RESULTS

Our data indicate that mice selected for excess callousness exhibit phenotypic abnormalities isomorphic to the symptoms of CD: stability of the low emotional contagion trait, increased aggression and reduced sociability. In accordance with our predictions, MPH reduced aggression and increased sociability in callous mice; yet, it failed to restore the low responsiveness to the emotions of a conspecific in pain, isomorphic to CU traits.

CONCLUSIONS

Although our data support the notion that MPH may contribute to the management of excess aggression in CD patients, additional studies shall identify specific treatments to target the callousness domain. The latter, unaffected by MPH in our experimental model, demands focused consideration whereby it constitutes a specifier associated with a worse prognosis.

Rescue-like Behaviour in Mice is Mediated by Their Interest in the Restraint Tool

Acting without the expectation of compensation is called prosocial behaviour. Since prosocial behaviour requires high cognitive and social abilities, it has been thought to be only shown by primates. Although prosocial behaviour has been recently reported in rats, there are still questions regarding this finding. We demonstrated rescue-like behaviour in mice in a previous report. In this study, we investigated the motives underlying rescue-like behaviour for constrained cage-mates among mice. We prepared either a tube containing a ball of yarn or an opaque tube and assessed whether mice displayed the same rescue-like behaviour shown in the case of tube-restrained cage-mates. Mice did not open the lid of the tube containing the ball of yarn but opened the opaque tube lid. Mice showed a high interest in the tube in which the cage-mate had been restrained and prioritized staying in this tube rather than rescuing additional cage-mates. Oxytocin, which increases empathy, had no effect on the lid-opening behaviour. Thus, the rescue-like behaviour of mice is not based on empathy but is related to social interest in the cage-mate and the tube itself. These results suggest that rodent lid-opening behaviour may not conclusively prove the presence of prosocial behaviour.

An insular view of the social decision-making network

Social animals must detect, evaluate and respond to the emotional states of other individuals in their group. A constellation of gestures, vocalizations, and chemosignals enable animals to convey affect and arousal to others in nuanced, multisensory ways. Observers integrate social information with environmental and internal factors to select behavioral responses to others via a process call social decision-making. The Social Decision Making Network (SDMN) is a system of brain structures and neurochemicals that are conserved across species (mammals, reptiles, amphibians, birds) that are the proximal mediators of most social behaviors. However, how sensory information reaches the SDMN to shape behavioral responses during a social encounter is not well known. Here we review the empirical data that demonstrate the necessity of sensory systems in detecting social stimuli, as well as the anatomical connectivity of sensory systems with each node of the SDMN. We conclude that the insular cortex is positioned to link integrated social sensory cues to this network to produce flexible and appropriate behavioral responses to socioemotional cues.

Behavioural alterations in piglets after surgical castration: Effects of analgesia and anaesthesia

The present study aimed to use behavioural measures to assess pain induced by surgical castration of piglets, and evaluate the efficacy of pain-relief medications. In total, 143 male piglets from 29 sows were used. The treatments included: 1) non-castration (NC; n = 28), 2) castration without medication (SC; n = 29), 3) castration with meloxicam injection 0.4 mg/kg i.m. (ME; n = 28), 4) castration with 0.5 ml of 2% lidocaine in each testicle (LA; n = 29), and 5) castration with general inhalation anaesthesia using isoflurane (1.5%) and meloxicam injection (GA; n = 29). Behaviour was monitored continuously for a ten minute period one hour prior to castration (-1 h), as well as immediately (0 h), one hour (1 h), and two hours (2 h) after castration. Behaviour was also monitored twice (08:00 and 20:00) during the following day. Compared to -1 h, castration induced changes in several behavioural measures in SC piglets at 0 h, suggesting that castration was painful. Furthermore, inactive standing or sitting, tail wagging and aggressive behaviour differed between SC and NC piglets at 0 h. ME and LA piglets spent less time standing or sitting inactively, and LA and GA piglets showed more tail wagging than SC piglets at 0 h (P < 0.05 for all). No other behavioural measures differed among the various groups of castrated piglets. In conclusion, the results indicate that surgical castration is indeed painful. However, the efficacy of various pain-relief protocols in piglets shortly after castration was not verified.

Emotional Contagion From Humans to Dogs Is Facilitated by Duration of Ownership

Emotional contagion is a primitive form of empathy that does not need higher psychological functions. Recent studies reported that emotional contagion exists not only between humans but also among various animal species. The dog (Canis familiaris) is a unique animal and the oldest domesticated species. Dogs have coexisted with humans for more than 30,000 years and are woven into human society as partners bonding with humans. Dogs have acquired human-like communication skills and, likely as a result of the domestication process, the ability to read human emotions; therefore, it is feasible that there may be emotional contagion between human and dogs. However, the higher time-resolution of measurement of emotional contagion between them is yet to be conducted. We assessed the emotional reactions of dogs and humans by heart rate variability (HRV), which reflects emotion, under a psychological stress condition on the owners. The correlation coefficients of heart beat (R-R) intervals (RRI), the standard deviations of all RR intervals (SDNN), and the square root of the mean of the sum of the square of differences between adjacent RR intervals (RMSSD) between dogs and owners were positively correlated with the duration of dog ownership. Dogs’ sex also influenced the correlation coefficients of the RRI, SDNN, and RMSSD in the control condition; female showed stronger values. These results suggest that emotional contagion from owner to dog can occur especially in females and the time sharing the same environment is the key factor in inducing the efficacy of emotional contagion.

The Role of Emotional Contagion in the Distress Exhibited by Grouped Mice Exposed to CO₂

The 2013 AVMA Guidelines for the Euthanasia of Animals recommends a chamber volume displacement rate of 10% to 30% per minute (v/min) when euthanizing small laboratory rodents with CO₂. Group euthanasia of mice is a common practice, and grouping strangers is often avoided to minimize distress; however, emotional contagion, which occurs between familiar animals but not strangers, has not been studied in the context of group CO₂ euthanasia. This study examined cagemate- and stranger-grouped mice exposed to 10%, 30%, or 50% v/min CO₂ to determine whether emotional contagion plays a role in this context and whether that role is influenced by CO₂ flow rate. Videos of adult male C57BL/6J mice exposed to different CO₂ flow rates were scored for durations of dyspnea, ataxia, and consciousness as well as the numbers of face pawing and jump behaviors. Blood was collected at time of unconsciousness and assayed for ACTH. Cagemates experienced significantly longer durations of conscious dyspnea and ataxia with 10% v/min CO₂ compared with 30% and 50% v/min. Similarly, strangers experienced significantly longer duration of conscious dyspnea with 10% v/min CO₂ compared with 30% and 50% v/min and significantly longer duration of ataxia with 10% compared with 50% v/min. Cagemates showed significantly more jumps with 10% v/min CO₂ compared with 30% and 50% v/min, whereas jumping was unaffected by CO₂ flow rate in strangers. We conclude that more potential for distress exists when cagemate and stranger mice are exposed to a 10% v/min CO₂ flow rate and that emotional contagion may contribute to distress in cagemates at this flow rate. Therefore, we propose that 30% v/min CO₂ should be used for euthanasia of mice, and that 50% v/min should also be considered humane.

Increased pain sensitivity and decreased opioid analgesia in T-cell-deficient mice and implications for sex differences

The processing of pain in the central nervous system is now known to have an important immune component, including T cells of the adaptive immune system. T cells have been shown to release endogenous opioids, and although it is well known that opioids have effects on T-cell populations, very little attention has been given to the converse: how T cells may affect opioid regulation. We find here that, in addition to displaying significantly increased baseline pain sensitivity across various pain modalities, T-cell-deficient mice (CD-1 nude, Rag1 null mutant, and Cd4 null mutant) exhibit pronounced deficiencies in morphine inhibition of thermal or inflammatory pain. Nude mice are also deficient in endogenous opioid-mediated analgesia, exhibiting no stress-induced analgesia from restraint. The relevant T-cell subpopulation seems to be CD4 T cells because adoptive transfer of them but not CD8 cells into nude mice rescues both the pain and morphine analgesia phenotypes. As previously reported, we also observe a sex difference in CD-1 mice, with females requiring 2- to 3-fold more morphine than males to produce equal analgesia. Nude mice display no sex differences in morphine analgesia, and the sex difference is restored in nude mice of either sex receiving CD4 T cells from CD-1 donor male or female mice. These results suggest that CD4 T cells play an as yet unappreciated role in opioid analgesia and may be a driver of sex differences therein.

Rat Model of Empathy for Pain

Empathy for pain is referred to as an evolutionary behavior of social animals and humans associated with the ability to feel, recognize, understand and share the other's distressing (pain, social rejection and catastrophe) states. Impairment of empathy can definitely lead to deficits in social communication and sociability (attachment, bond, reciprocity, altruism and morality) that may be fundamental to some psychiatric disorders such as autism spectrum disorder (ASD), psychopathy, misconduct, antisocial personality disorder and schizophrenia. So far, the underlying mechanisms of empathy are poorly known due to lack of animal models and scarce understanding of its biological basis. Recently, we have successfully identified and validated the behavioral identities of empathy for pain in rats that can be widely used as a rodent model for studying the underlying biological mechanisms of empathy. Priming dyadic social interaction between a naive cagemate observer (CO) and a cagemate demonstrator (CD), rather than a non-cagemate, in pain for 30 min in a testing box can repeatedly and constantly result in empathic responses of the CO toward the familiar CD's distressing condition, displaying as allo-licking at the injury site, allo-grooming at the body and social transfer of pain. The familiarity-based, distress-specific social consolation and subsequent social transfer of pain can be qualitatively and quantitatively rated as experimental biomarkers for empathy for pain. The rodent model of empathy for pain is state-of-the-art and has more advantages than the existing ones used for social neuroscience since it can reflect sensory, emotional and cognitive processes of the brain in running the prosocial and altruistic behaviors in animals who could not report verbally. Here we would like to provide and share the protocol of the model for wide use.

Enhanced histamine-induced itch in diacylglycerol kinase iota knockout mice

Subsets of small-diameter dorsal root ganglia (DRG) neurons detect pruritogenic (itch-causing) and algogenic (pain-causing) stimuli and can be activated or sensitized by chemical mediators. Many of these chemical mediators activate receptors that are coupled to lipid hydrolysis and diacylglycerol (DAG) production. Diacylglycerol kinase iota (DGKI) can phosphorylate DAG and is expressed at high levels in small-diameter mouse DRG neurons. Given the importance of these neurons in sensing pruritogenic and algogenic chemicals, we sought to determine if loss of DGKI impaired responses to itch- or pain-producing stimuli. Using male and female Dgki-knockout mice, we found that in vivo sensitivity to histamine—but not other pruritogens—was enhanced. In contrast, baseline pain sensitivity and pain sensitization following inflammatory or neuropathic injury were equivalent between wild type and Dgki^-/- mice. In vitro calcium responses in DRG neurons to histamine was enhanced, while responses to algogenic ligands were unaffected by Dgki deletion. These data suggest Dgki regulates sensory neuron and behavioral responses to histamine, without affecting responses to other pruritogenic or algogenic agents.

Contagious itch can be induced in humans but not in rodents

Itch contagion has been reported in human when people watch someone scratching in a video. The basic mechanism of contagious itch induced by scratching video is still being investigated. A recent study has reported that adult mice showed itch like responses after watching itch-like video or mice showing itching responses. However, such contagious itch behaviors failed to be reproduced by another study by repeating the same experiments of viewing itching mice. It is unclear if contagious itch induced by seeing itching video may be reproducible. In the present study, we used a four-iPad paradigm to repeat these experiments, and found that mice showed no significant itch-like responses after watching itching video of mice. To test if mice actually can see the video, we placed mirrors at the same location. Interestingly, mice showed altered activities in the open field with the mirrors. Finally, in healthy subjects, we found that viewing human itch video did cause itch sensation or responses. Our results indicate that the mouse model may not appropriate for studying contagious itch in humans.

Fear Conditioning by Proxy: Social Transmission of Fear Between Interacting Conspecifics

We describe a method of social fear transmission to a discrete auditory cue in freely behaving rats. Extending beyond traditional observer/demonstrator paradigms, rats are allowed to physically interact and integrate cues from all sensory modalities. In the protocol described in this article, "observer" rats experience social fear conditioning through a proxy cage mate that serves as a "demonstrator" during retrieval of a cued fear memory. We find that a specific auditory cue can come to elicit fear expression in an animal with no foot shock experience simply by interacting with a conspecific expressing a conditioned response in the presence of an otherwise benign stimulus. In this "fear conditioning by proxy" paradigm, we have demonstrated that some, but not all, rats display conditioned responding (e.g., freezing) to a cue after interacting with a cage mate during fear memory retrieval. The amount of freezing exhibited by this fear conditioned "by proxy" rat 24 hr after learning critically depends on social influences, including social relationships and social interactions during learning. © 2018 by John Wiley & Sons, Inc.

Helping-Like Behaviour in Mice Towards Conspecifics Constrained Inside Tubes

Prosocial behaviour, including helping behaviour, benefits others. Recently, helping-like behaviour has been observed in rats, but whether it is oriented towards rescue, social contact with others, or other goals remains unclear. Therefore, we investigated whether helping-like behaviour could be observed in mice similar to that in rats. Because mice are social animals widely used in neuroscience, the discovery of helping-like behaviour in mice would be valuable in clarifying the psychological and biological mechanisms underlying pro-sociability. We constrained mice inside tubes. Subject mice were allowed to move freely in cages with tubes containing constrained conspecifics. The subject mice released both cagemates and stranger mice but did not engage in opening empty tubes. Furthermore, the same behaviour was observed under aversive conditions and with anesthetised conspecifics. Interestingly, hungry mice opened the tubes containing food before engaging in tube-opening behaviour to free constrained conspecifics. Mice showed equal preferences for constrained and freely moving conspecifics. We demonstrated for the first time that mice show tube-opening behaviour. Furthermore, we partly clarified the purpose and motivation of this behaviour. An effective mouse model for helping-like behaviour would facilitate research on the mechanisms underlying prosocial behaviour.

Oxytocin administration modulates rats' helping behavior depending on social context

The affiliative effect of oxytocin on behavior toward other individuals can be modulated by positive and negative aspects of those individuals. However, the context-dependent effect of oxytocin on helping behavior is still unclear. In this study, we examined the effect of oxytocin administration on helping behavior in rats. The rats learned to open a door to help a cagemate soaked with water. The rats were divided into Pair and Solo groups. The rats in the Pair group were housed with their cagemates and those in the Solo group were housed individually. The rats in both groups received oxytocin (1.0 mg/kg) or saline injections intraperitoneally for 5 consecutive days before starting the experimental sessions. In the rats injected with oxytocin, the Solo group showed helping behavior faster than those in the Pair group. The results suggest that the effects of oxytocin administration on helping behavior are dependent on the social context.

Social modulation of drug use and drug addiction

This review aims to demonstrate how social science and behavioral neurosciences have highlighted the influence of social interactions on drug use in animal models. In neurosciences, the effect of global social context that are distal from drug use has been widely studied. For human and other social animals such as monkeys and rodents, positive social interactions are rewarding, can overcome drug reward and, in all, protect from drug use. In contrast, as other types of stress, negative social experiences facilitate the development and maintenance of drug abuse. However, interest recently emerged in the effect of so-called "proximal" social factors, that is, social interactions during drug-taking. These recent studies have characterized the role of the drug considered, the sharing of drug experience and the familiarity of the peer which interaction are made with. We also examine the few studies regarding the sensorial mediator of social behaviors and critically review the neural mediation of social factors on drug use. However, despite considerable characterization of the factors modulating distal influences, the mechanisms for proximal influences on drug use remain largely unknown. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Conducta de ayuda en ratas: ¿acción o hábito?

En los últimos años, se han reportado varios estudios sobre la empatía en roedores. En particular, las tareas que evalúan los comportamientos de ayuda en ratas han propuesto que el mecanismo que subyace a dichas conductas es la empatía. Aunque varios autores apoyan dicha propuesta, existe evidencia inconsistente con el mecanismo empático. Por ejemplo, si se asume que la conducta de ayuda es motivada por la empatía, dicha conducta únicamente debería ejecutarse cuando sea necesaria (eliminar el distrés en otra rata). Sin embargo, recientemente se ha reportado que las ratas continúan realizando la conducta de ayuda incluso en situaciones en que dicho comportamiento no funciona. Se diseñó un experimento con ratas para evaluar si la cantidad de entrenamiento afecta la sensibilidad de la conducta de ayuda a la consecuencia (reducción del distrés). Se utilizó una tarea que implicó que una rata liberase a otra de un contenedor tubular. El Grupo Corto realizó dicha conducta durante pocas sesiones, mientras que el grupo Extenso ejecutó la conducta de ayuda por un periodo más largo. Finalmente, ambos grupos recibieron una prueba de generalización en la que el contenedor estuvo vacío. Los resultados mostraron que en las sesiones de prueba las ratas del Grupo Corto no abrieron el contenedor, mientras que el grupo Extenso sí lo abrió. Se discute el papel de los hábitos en la ejecución de conductas pro-sociales.

The link between social context-dependent anxious behavior and habenular mast cells in fear-conditioned rats

Affiliative social behavior relieves the physiological reactivity to stressors, while social inequity, represented by unfairness in the social environment, causes emotional distress in animals. Mast cells are immune cells found in the brain that affect both the nervous system and emotional behavior. To determine the role of neuro-immunity in the programming of emotional behaviors, we observed brain mast cells and anxiety-like behaviors in female rats exposed to electrical foot shocks in different social environments. The following groups of rats were used in this study: control (unshocked) rats, solitarily shock-exposed rats, and shock-exposed rats in the presence of unshocked (unequal) or shocked (equal) conspecifics. An absence of significant difference in body weight or sucrose preference was seen among the different groups. Additionally, fear memory was augmented in rats shocked in the presence of either unshocked or shocked conspecifics than rats in the solitarily shocked group. Furthermore, rats shocked in the presence of unshocked conspecifics showed intensified anxiety-like behaviors after fear conditioning. Finally, we found an increase in the number of habenular mast cells in the intensified anxiogenic group, which had a significant correlation with the decreasing rate of anxiety-like behaviors. This provides evidence that habenular mast cells might be of importance in relieving the amplified biopsychological responses caused by social stress.

Genetic factors associated with empathy in humans and mice

The neurocognitive ability to recognize and share the mental states of others is crucial for our emotional experience and social interaction. Extensive human studies have informed our understanding of the psychobehavioral and neurochemical bases of empathy. Recent evidence shows that simple forms of empathy are conserved from rodents to humans, and rodent models have become particularly useful for understanding the neurobiological correlates of empathy. In this review, we first summarize aspects of empathy at the behavioral and neural circuit levels, and describe recent developments in rodent model behavioral paradigms. We then highlight different neurobiological pathways involved in empathic abilities, with special emphasis on genetic polymorphisms associated with individual differences in empathy. By directly assessing various neurochemical correlates at molecular and neural circuit levels using relevant animal models, we conclude with the suggestion that rodent research can significantly advance our understanding of the neural basis of empathy. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Effects of Maternal Deprivation on Anxiety, Depression, and Empathy in Male and Female Offspring of Wistar Rats in the Face of Novel Objects

Background:

Early life stress (ELS) models such as maternal deprivation (MD) are used to investigate behavioral changes in rodents under stressful situations. MD is a situation in which rat pups are separated from the dam; MD has different paradigms. The purpose of this research is to evaluate the effects of maternal deprivation on anxiety, depression, and empathy in adult Wistar rats.

Materials and Methods:

MD was applied to pups as per specifically designed protocol to compare rats of the control group with maternal deprivation rats and also the group, which faced novel objects. Each group consisted of eight rats. In this study, separation started from postnatal day (PND) 14 for various periods up to PND 60. EPM test was undertaken to measure anxiety; moreover, FST was used to indicate levels of depression. Also, changes in the empathy ratio were also demonstrated. One-way analysis of variance (ANOVA), Tukey’s post hoc analysis, and t-test were applied to analyze the results.

Results:

MD-treated rats showed a significant decrease in anxiety and empathy indexes compared with those in the control group (P<0.05). However, MD significantly increased depression in both male and female rats (P<0.05). Finally, exposure to novel objects decreased depression but did not have any effect on anxiety and empathy levels in MD rats (P<0.05).

Conclusion:

ELS may lead to various states of mood and behavior in adulthood. According to the findings of this study, depression increases due to MD, though both anxiety and empathy decrease in both male and female Wistar rats. Moreover, exposure to novel objects decreases depression, while anxiety and empathy do not change significantly with exposure to novel objects.

Doubled-Edged Swords in the Biology of Conflict

Considerable advances have been made in understanding the biological roots of conflict, and such understanding requires a multidisciplinary approach, recognizing the relevance of neurobiological, endocrine, genetic, developmental, and evolutionary perspectives. With these insights comes the first hints of biological interventions that may mitigate violence. However, such interventions are typically double-edged swords, with the potential to foster conflict rather than lessen it. This review constitutes a cautionary note of being careful of what one wishes for.

Social transfer of alcohol withdrawal-induced hyperalgesia in female prairie voles

The expression of pain serves as a way for animals to communicate potential dangers to nearby conspecifics. Recent research demonstrated that mice undergoing alcohol or morphine withdrawal, or inflammation, could socially communicate their hyperalgesia to nearby mice. However, it is unknown whether such social transfer of hyperalgesia can be observed in other species of rodents. Therefore, the present study investigated if the social transfer of hyperalgesia occurs in the highly social prairie vole (Microtus ochrogaster). We observe that adult female prairie voles undergoing withdrawal from voluntary two-bottle choice alcohol drinking display an increase in nociception. This alcohol withdrawal-induced hypersensitiity is socially transferred to female siblings within the same cage and female strangers housed in separate cages within the same room. These experiments reveal that the social transfer of pain phenomenon is not specific to inbred mouse strains and that prairie voles display alcohol withdrawal and social transfer-induced hyperalgesia.

Rat behavior and dopamine release are modulated by conspecific distress

Rats exhibit 'empathy' making them a model to understand the neural underpinnings of such behavior. We show data consistent with these findings, but also that behavior and dopamine (DA) release reflects subjective rather than objective evaluation of appetitive and aversive events that occur to another. We recorded DA release in two paradigms: one that involved cues predictive of unavoidable shock to the conspecific and another that allowed the rat to refrain from reward when there were harmful consequences to the conspecific. Behavior and DA reflected pro-social interactions in that DA suppression was reduced during cues that predicted shock in the presence of the conspecific and that DA release observed on self-avoidance trials was present when the conspecific was spared. However, DA also increased when the conspecific was shocked instead of the recording rat and DA release during conspecific avoidance trials was lower than when the rat avoided shock for itself.

Empathy for Pain: Insula Inactivation and Systemic Treatment With Midazolam Reverses the Hyperalgesia Induced by Cohabitation With a Pair in Chronic Pain Condition

Empathy for pain is the ability to perceive and understand the pain in the other individual. Recent studies suggested that rodents have this social ability. GABAergic system has receptors in the brain structures involved in emotional processes as well as in the insular cortex. This area has been described as an important key in modulation of pain and empathy. The present study has investigated the role of insula and its Benzodiazepine-GABAA system on social modulation of pain induced by cohabiting with a mouse submitted to sciatic nerve constriction, a neuropathic pain model. The insular cortex function was assessed by the structure inactivation (Experiments 1 and 2); the role of GABA system was evaluated by systemic treatment of midazolam (MDZ 0.5, 1, and 2 mg/kg) (Experiment 3); and the role of GABAA receptors of insula were studied by bilateral MDZ (3 and 30 nmol/0.1 μl) microinjections in the structure (Experiment 4). Male Swiss mice were housed in groups or dyads. On dyads, after 14 days of cohabitation they were divided into two groups: cagemate nerve constriction and cagemate sham (CS). After 14 days of familiarity, cagemates were evaluated on the writhing test. For group-housed, insula inactivation did not change nociception. For dyad-housed, cohabiting with a mouse in chronic pain increased the nociceptive response and the insula inactivation has reverted this response. Systemic MDZ attenuated nociception and intra-insula MDZ did not alter it. Our results suggest that cohabitation with a pair in chronic pain induces hypernociception, insula possibly modulates this response and the GABA system is also possibly involved, but not its insular mechanisms.

From bedside to bench and back: Translating ASD models

Autism spectrum disorders (ASD) represent a heterogeneous group of disorders defined by deficits in social interaction/communication and restricted interests, behaviors, or activities. Models of ASD, developed based on clinical data and observations, are used in basic science, the "bench," to better understand the pathophysiology of ASD and provide therapeutic options for patients in the clinic, the "bedside." Translational medicine creates a bridge between the bench and bedside that allows for clinical and basic science discoveries to challenge one another to improve the opportunities to bring novel therapies to patients. From the clinical side, biomarker work is expanding our understanding of possible mechanisms of ASD through measures of behavior, genetics, imaging modalities, and serum markers. These biomarkers could help to subclassify patients with ASD in order to better target treatments to a more homogeneous groups of patients most likely to respond to a candidate therapy. In turn, basic science has been responding to developments in clinical evaluation by improving bench models to mechanistically and phenotypically recapitulate the ASD phenotypes observed in clinic. While genetic models are identifying novel therapeutics targets at the bench, the clinical efforts are making progress by defining better outcome measures that are most representative of meaningful patient responses. In this review, we discuss some of these challenges in translational research in ASD and strategies for the bench and bedside to bridge the gap to achieve better benefits to patients.

Spontaneous Discriminative Response to the Biological Motion Displays Involving a Walking Conspecific in Mice

Recent translational studies using mice have contributed toward elucidating the neural, genetic, and molecular basis of social communication deficits. Nevertheless, many components of visual processes underlying mice sociality remain unresolved, including perception of bodily-movement. Here, we aimed to reveal the visual sensitivity of mice to information on bodily motion using biological motion displays depicted by simple geometric dots. We introduced biological motions extracted from walking mice vs. corresponding meaningless scrambled motions, in which the spatial configurations of each path of dots were shuffled. The apparatus was a three-chambered box with an opening between the chambers, and each side chamber had a monitor. We measured the exploration time of mice within the apparatus during the test, with two types of displays being presented. Mice spent more time in the chamber with the scrambled motion displays, indicating that animals spontaneously discriminated stimuli, with the scrambled motion being relatively novel. Furthermore, mice might have detected socially familiar cues from the biological motion displays. Subsequent testing revealed that additional mice showed no bias to the static versions of the stimuli used in the Movie test. Thus, we confirmed that mice modulated their behavior by focusing on the motion information of the stimuli, rather than the spatial configurations of each dot. Our findings provide a new perspective on how visual processing contributes to underlying social behavior in mice, potentially facilitating future translational studies of social deficits with respect to genetic and neural bases.

Validating Rat Model of Empathy for Pain: Effects of Pain Expressions in Social Partners

Pain can be socially transferred between familiar rats due to empathic responses. To validate rat model of empathy for pain, effects of pain expressions in a cagemate demonstrator (CD) in pain on empathic pain responses in a naïve cagemate observer (CO) after 30 min priming dyadic social interactions (PDSI) were evaluated. The CD rats were prepared with four pain models: bee venom (BV), formalin, complete Freund's adjuvant (CFA), and spared nerve injury (SNI). Both BV and formalin tests are characterized by displayable and eye-identifiable spontaneous pain-related behaviors (SPRB) immediately after treatment, while CFA and SNI models are characterized by delayed occurrence of evoked pain hypersensitivity but with less eye-identifiable SPRB. After 30 min PDSI with a CD immediately after BV and formalin, respectively, the empathic mechanical pain hypersensitivity (EMPH) could be identified at both hind paws in CO rats. The BV—or formalin-induced EMPH in CO rats lasted for 4–5 h until full recovery. However, EMPH failed to develop in CO after socially interacting with a CD immediately after CFA, or 2 h after BV when SPRB completely disappeared. The CO's EMPH was partially relieved when socially interacting with an analgecized CD whose SPRB had been significantly suppressed. Moreover, repeated exposures to a CD in pain could enhance EMPH in CO. Finally, social transfer of pain hypersensitivity was also identified in CO who was being co-housed in pairs with a conspecific treated with CFA or SNI. The results suggest that development of EMPH in CO rats would be determined not only by extent of familiarity but also by visually identifiable pain expressions in the social partners during short period of PDSI. However, the visually unidentifiable pain can also be transferred to naïve cagemate when being co-housed in pairs with a distressed conspecific. In summary, the vicariously social contagion of pain between familiar rats is dependent upon not only expressions of pain in social partners but also the time that dyads spent in social communications. The rat model of empathy for pain is a highly stable, reproducible and valid model for studying the neural mechanisms of empathy in lower animals.

Familiarity modulates social approach toward stressed conspecifics in female rats

Familiarity between conspecifics may influence how social affective cues shape social behaviors. In a social affective preference test, experimental rats, when given the choice to explore an unfamiliar stressed or a naive adult, will avoid interaction with a stressed conspecific. To determine if familiarity would influence social interactions with stressed conspecifics, male and female test rats underwent 2 social affective preference tests in isosexual triads where an experimental rat was presented with a naïve and a stressed target conspecific who were either familiar (cagemate) or unfamiliar. Male and female experimental rats avoided stressed unfamiliar conspecifics. However, experimental female rats demonstrated a preference to interact with their stressed, familiar cagemates. Male and female rats exhibited more self-grooming and immobility behavior in the presence of stressed conspecifics, which may indicate emotion contagion. These findings suggest a sex-specific role of familiarity in social approach and avoidance, and warrant further mechanistic exploration.

Animal Morality: What It Means and Why It Matters

It has been argued that some animals are moral subjects, that is, beings who are capable of behaving on the basis of moral motivations (Rowlands 2011, 2012, 2017). In this paper, we do not challenge this claim. Instead, we presuppose its plausibility in order to explore what ethical consequences follow from it. Using the capabilities approach (Nussbaum 2004, 2007), we argue that beings who are moral subjects are entitled to enjoy positive opportunities for the flourishing of their moral capabilities, and that the thwarting of these capabilities entails a harm that cannot be fully explained in terms of hedonistic welfare. We explore the implications of this idea for the assessment of current practices involving animals.

Susceptibility to others' emotions moderates immediate self-reported and biological stress responses to witnessing trauma

BACKGROUND

The peri-traumatic stress response is a strong predictor of symptom development after trauma exposure. Regarding witnessing trauma, the stress response might depend on the susceptibility to others' emotions (emotional contagion, EC). This study investigated whether EC moderates the immediate stress response using a trauma film paradigm.

METHODS

Ninety-five healthy participants were randomly exposed to a trauma or a neutral film. Perceived stressfulness of the film and pre-to post-film changes in self-reported anxiety, heart rate and saliva cortisol levels were assessed. EC towards negative and positive emotions was measured using the emotional contagion scale and its emotion-specific subscales.

RESULTS

Overall, the trauma film was perceived as distressing and elicited an increase in self-reported anxiety, heart rate and saliva cortisol levels relative to the neutral film. EC towards negative emotions was positively related to the perceived stressfulness of the film, increased anxiety and increased heart rate. The association with saliva cortisol levels was also in the expected direction, but not statistically significant. These associations were not found for EC towards positive emotions.

DISCUSSION

EC towards negative emotions may be an important predictor of trauma exposure outcomes. Further research should clarify its specific contribution in witnessing and undergoing trauma.

Impaired social contacts with familiar anesthetized conspecific in CA3-restricted brain-derived neurotrophic factor knockout mice

Familiarity is conveyed by social cues and determines behaviors toward conspecifics. Here, we characterize a novel assay for social behaviors in mice-contacts with anesthetized conspecific-which eliminates reciprocal interactions, including intermale aggression and shows behaviors that are independent of the demonstrator's activity. During the initial 10 minutes (phase-1), the wild-type (WT) subjects contacted the anesthetized conspecifics vigorously regardless of familiarity. During the subsequent 80 minutes (phase-2), however, they contacted more with familiar than unfamiliar conspecifics. We then applied this test to highly aggressive mice with a hippocampal CA3-restricted knockout (KO) of brain-derived neurotrophic factor (BDNF), in which aggression may mask other social behaviors. The KO mice showed less preference for contacting familiar conspecifics than did WT mice during phase-2 but no differences during phase-1. Among nonsocial behaviors, WT mice also spent less time eating in the presence of familiar than with unfamiliar conspecifics, which was not seen in KO mice. In addition, KO mice exhibited reduced pain sensitization. Altogether, these findings suggest that CA3-specific deletion of BDNF results in deficits in circuits that process social cues from familiar conspecifics as well as pain and may underlie empathy-like behaviors.

Ethanol facilitates socially evoked memory recall in mice by recruiting pain-sensitive anterior cingulate cortical neurons

Alcohol is a traditional social-bonding reinforcer; however, the neural mechanism underlying ethanol-driven social behaviors remains elusive. Here, we report that ethanol facilitates observational fear response. Observer mice exhibited stronger defensive immobility while observing cagemates that received repetitive foot shocks if the observer mice had experienced a brief priming foot shock. This enhancement was associated with an observation-induced recruitment of subsets of anterior cingulate cortex (ACC) neurons in the observer mouse that were responsive to its own pain. The vicariously activated ACC neurons projected their axons preferentially to the basolateral amygdala. Ethanol shifted the ACC neuronal balance toward inhibition, facilitated the preferential ACC neuronal recruitment during observation, and enhanced observational fear response, independent of an oxytocin signaling pathway. Furthermore, ethanol enhanced socially evoked fear response in autism model mice.

Does a rat free a trapped rat due to empathy or for sociality?

This report evaluates whether a rat releasing a trapped rat from a restraint tube is better explained as due to its empathic motivation or to the pursuit of social contact. In the first condition, each of six rats chose in an E maze between entering an empty goal box versus entering a goal box where its entrance caused a rat trapped in a restraint tube to be released. Rats preferred the goal box with the trapped rat over the empty goal box. In the second condition, these rats chose between releasing a restraint-tube-trapped rat in one goal box and another rat in the second goal box that was not locked into its restraint tube. Rats showed no preference between alternatives. In the third condition, rats chose between a goal box containing a rat with an open restraint tube and an empty goal box. Rats preferred the rat with the open restraint tube over the empty goal box. These results support attributing the response of releasing a rat from a restraint tube to the reinforcing power of social contact rather than interpreting this response as empathically motivated.

Socially-mediated arousal and contagion within domestic chick broods

Emotional contagion - an underpinning valenced feature of empathy - is made up of simpler, potentially dissociable social processes which can include socially-mediated arousal and behavioural/physiological contagion. Previous studies of emotional contagion have often conflated these processes rather than examining their independent contribution to empathic response. We measured socially-mediated arousal and contagion in 9-week old domestic chicks (n = 19 broods), who were unrelated but raised together from hatching. Pairs of observer chicks were exposed to two conditions in a counterbalanced order: air puff to conspecifics (AP) (during which an air puff was applied to three conspecifics at 30 s intervals) and control with noise of air puff (C) (during which the air puff was directed away from the apparatus at 30 s intervals). Behaviour and surface eye temperature of subjects and observers were measured throughout a 10-min pre-treatment and 10-min treatment period. Subjects and observers responded to AP with increased freezing, and reduced preening and ground pecking. Subjects and observers also showed reduced surface eye temperature - indicative of stress-induced hyperthermia. Subject-Observer behaviour was highly correlated within broods during both C and AP conditions, but with higher overall synchrony during AP. We demonstrate the co-occurrence of socially-mediated behavioural and physiological arousal and contagion; component features of emotional contagion.