Social modulation of pain as evidence for empathy in mice

Prenatal bystander stress alters brain, behavior, and the epigenome of developing rat offspring

The prenatal environment, including prenatal stress, has been extensively studied in laboratory animals and humans. However, studies of the prenatal environment usually directly stress pregnant females, but stress may come 'indirectly', through stress to a cage-mate. The current study used indirect prenatal bystander stress and investigated the effects on the gross morphology, pre-weaning behavior, and epigenome of rat offspring. Pregnant Long-Evans rats were housed with another female rat that underwent elevated platform stress from gestational days 12 to 16. We found that ultrasonic vocalizations of female cage-mates were disrupted following the stress procedure. After birth, offspring were tested on two behavioral tasks and sacrificed at postnatal day 21 (p21). Frontal cortex and hippocampal tissue was used to measure global DNA methylation and gene expression changes. At p21, bystander-stressed female offspring exhibited increased body weight. Offspring behavior on the negative geotaxis task was altered by prenatal bystander stress, and locomotor behavior was reduced in female offspring. Global DNA methylation increased in the frontal cortex and hippocampus of bystander-stressed offspring. Microarray analysis revealed significant gene expression level changes in 558 different genes, of which only 10 exhibited overlap between males and females or brain areas. These alterations in gene expression were associated with overrepresentation of 36 biological processes and 34 canonical pathways. Prenatal stress thus does not have to be experienced by the mother herself to influence offspring brain development. Furthermore, this type of 'indirect' prenatal stress alters offspring DNA methylation patterns, gene expression profiles, and behavior.

Pain and emotion: a biopsychosocial review of recent research

OBJECTIVE AND METHOD

Research on emotion and pain has burgeoned. We review the last decade's literature, focusing on links between emotional processes and persistent pain.

RESULTS

Neurobiological research documents the neural processes that distinguish affective from sensory pain dimensions, link emotion and pain, and generate central nervous system pain sensitization. Psychological research demonstrates that greater pain is related to emotional stress and limited emotional awareness, expression, and processing. Social research shows the potential importance of emotional communication, empathy, attachment, and rejection.

CONCLUSIONS

Emotions are integral to the conceptualization, assessment, and treatment of persistent pain. Research should clarify when to eliminate or attenuate negative emotions, and when to access, experience, and express them. Theory and practice should integrate emotion into cognitive-behavioral models of persistent pain.

Empathy and reversed empathy of stress in mice

Empathy is an emotional response to display of distress in others and reversed-empathy is an emotional response to non-distressed others in distressed subjects. Stress has memory enhancing effect on aversive experience. Here, I examine empathy and reversed empathy using the memory enhancing effects of stress in mice. Restrain stress enhanced aversive memory of a floor with electric shock, but restrain stress, with cage mates also restrained, reduced the enhancing effect. On the other hand, restrain stress with free-moving cage mates increased the memory enhancing effect, suggesting the stronger stress. This is the reversed-empathy. Level of corticosterone is the highest after the restrain with free-moving mates and lowest after the restrain with restrained mates.

Prenatal bystander stress induces neuroanatomical changes in the prefrontal cortex and hippocampus of developing rat offspring

The rapid period of growth and development that occurs prenatally renders the brain vulnerable to experiences that may disrupt cortical plasticity. Although there is extensive literature examining anatomical changes in fully matured brain, there has been very little investigation of younger offspring. The current study used an indirect prenatal bystander stress and analyzed neuroanatomical changes in postnatal day 21 (P21) Long Evans rats. Dendritic architecture (dendritic length, branch order, and spine density) along with cell quantification (neuron and glia) was generated for layer 3 pyramidal cells of the medial prefrontal cortex (mPFC/Cg3), orbital prefrontal cortex (OFC/AID), and CA1 of the hippocampus. We found that prenatal bystander stress significantly altered the complexity and length of dendritic arbor, the density of excitatory spines and the actual volume of neuronal and glial cell numbers in the mPFC, OFC, and CA1 of developing rat offspring. Neuroanatomical changes of this extent occurring at such a critical time period will likely impact healthy maturation of the brain and long-term development.

Experience modulates vicarious freezing in rats: a model for empathy

The study of the neural basis of emotional empathy has received a surge of interest in recent years but mostly employing human neuroimaging. A simpler animal model would pave the way for systematic single cell recordings and invasive manipulations of the brain regions implicated in empathy. Recent evidence has been put forward for the existence of empathy in rodents. In this study, we describe a potential model of empathy in female rats, in which we studied interactions between two rats: a witness observes a demonstrator experiencing a series of footshocks. By comparing the reaction of witnesses with or without previous footshock experience, we examine the role of prior experience as a modulator of empathy. We show that witnesses having previously experienced footshocks, but not naïve ones, display vicarious freezing behavior upon witnessing a cage-mate experiencing footshocks. Strikingly, the demonstrator's behavior was in turn modulated by the behavior of the witness: demonstrators froze more following footshocks if their witness froze more. Previous experiments have shown that rats emit ultrasonic vocalizations (USVs) when receiving footshocks. Thus, the role of USV in triggering vicarious freezing in our paradigm is examined. We found that experienced witness-demonstrator pairs emitted more USVs than naïve witness-demonstrator pairs, but the number of USVs was correlated with freezing in demonstrators, not in witnesses. Furthermore, playing back the USVs, recorded from witness-demonstrator pairs during the empathy test, did not induce vicarious freezing behavior in experienced witnesses. Thus, our findings confirm that vicarious freezing can be triggered in rats, and moreover it can be modulated by prior experience. Additionally, our result suggests that vicarious freezing is not triggered by USVs per se and it influences back onto the behavior of the demonstrator that had elicited the vicarious freezing in witnesses, introducing a paradigm to study empathy as a social loop.

Coexisting mechanical hypersensitivity and anxiety in a rat model of spinal cord injury and the effect of pregabalin, morphine, and midazolam treatment

Background and purpose

Spinal cord injury (SCI) has detrimental consequences that include chronic neuropathic pain, which is seen in 40-50% of patients, and symptoms of anxiety and depression, which affect 13-45% of SCI patients. The coexistence of pain, anxiety, and depression is known from other neuropathic pain conditions, but the relationship between these symptoms is not clear and has not been investigated in a preclinical model of SCI so far.

The aim of this study was to investigate anxiety-like behavior and at-level mechanical hypersensitivity following experimental spinal cord contusion (SCC) in female Sprague-Dawley rats, and the effects of analgesic and anxiolytic drugs.

Methods

Mechanical sensitivity and elevated plus maze (EPM) behavior were measured pre- and postinjury in SCC and sham animals. Pregabalin 30 mg/kg, morphine 3 mg/kg, midazolam 0.5 mg/kg, and 0.9% NaCl were evaluated in a randomly allocated, blinded balanced design.

Results

SCC animals developed persistent at-level mechanical hypersensitivity and decreased open arm activity in the EPM, which indicates an anxiety-like state. Pregabalin, a dual-acting analgesic and anxiolytic drug reduced both hypersensitivity and anxiety-like behavior, while the analgesic drug morphine only reduced hypersensitivity. The anxiolytic drug midazolam in the dose used had no effect on either parameter.

Conclusions

SCC animals developed long lasting coexisting at-level mechanical hypersensitivity and anxiety-like behavior, but there was no evidence to support a causal relationship between pain and anxiety following SCI.

Implications

The findings that at-level mechanical hypersensitivity and anxiety-like behavior develops concomitantly in the spinal cord contusion models and that both symptoms is persistent provide basis for further investigation of the mechanisms and connection behind these two clinically relevant symptoms after injury to the central nervous system.

Conserved subcortical and divergent cortical expression of proteins encoded by orthologs of the autism risk gene MET

Met receptor tyrosine kinase signaling regulates the growth and development of axons and may contribute to the wiring of cortical and limbic circuits in the rodent forebrain. Whether the orthologous MET receptor functions similarly in the developing primate forebrain is not known but is of considerable interest considering the association of variant MET alleles with social and communication phenotypes in autism. To begin addressing this question, we compared Met/MET protein expression in the developing mouse and rhesus macaque forebrain. There was a strong temporal conservation of expression during the time of rapid axon development and the onset of robust synapse formation. Expression patterns of Met/MET in limbic-related structures were almost identical between species. In marked contrast, there was highly divergent expression in the neocortex. In mouse, Met was broadly distributed throughout neocortex. In the macaque, robust MET expression was largely restricted to the posterior cingulate, inferior temporal, posterior parietal, and visual cortices, including face processing regions. The pattern is consistent with the importance of vision in the social repertoire of the primate. Collectively, these data suggest a conserved developmental function of the MET receptor in wiring together limbic and neocortical circuits that facilitate species-appropriate responses, including social behavior.

The neuroevolution of empathy

There is strong evidence that empathy has deep evolutionary, biochemical, and neurological underpinnings. Even the most advanced forms of empathy in humans are built on more basic forms and remain connected to core mechanisms associated with affective communication, social attachment, and parental care. Social neuroscience has begun to examine the neurobiological mechanisms that instantiate empathy, especially in response to signals of distress and pain, and how certain dispositional and contextual moderators modulate its experience. Functional neuroimaging studies document a circuit that responds to the perception of others' distress. Activation of this circuit reflects an aversive response in the observer, and this information may act as a trigger to inhibit aggression or prompt motivation to help. Moreover, empathy in humans is assisted by other domain-general high-level cognitive abilities, such as executive functions, mentalizing, and language, which expand the range of behaviors that can be driven by empathy.

Prolonged depression-like behavior caused by immune challenge: influence of mouse strain and social environment

Immune challenge by bacterial lipopolysaccharide (LPS) causes short-term behavioral changes indicative of depression. The present study sought to explore whether LPS is able to induce long-term changes in depression-related behavior and whether such an effect depends on mouse strain and social context. LPS (0.83 mg/kg) or vehicle was administered intraperitoneally to female CD1 and C57BL/6 mice that were housed singly or in groups of 4. Depression-like behavior was assessed with the forced swim test (FST) 1 and 28 days post-treatment. Group-housed CD1 mice exhibited depression-like behavior 1 day post-LPS, an effect that leveled off during the subsequent 28 days, while the behavior of singly housed CD1 mice was little affected. In contrast, singly housed C57BL/6 mice responded to LPS with an increase in depression-like behavior that was maintained for 4 weeks post-treatment and confirmed by the sucrose preference test. Group-housed C57BL/6 mice likewise displayed an increased depression-like behavior 4 weeks post-treatment. The behavioral changes induced by LPS in C57BL/6 mice were associated with a particularly pronounced rise of interleukin-6 in blood plasma within 1 day post-treatment and with changes in the dynamics of the corticosterone response to the FST. The current data demonstrate that immune challenge with LPS is able to induce prolonged depression-like behavior, an effect that depends on genetic background (strain). The discovery of an experimental model of long-term depression-like behavior after acute immune challenge is of relevance to the analysis of the epigenetic and pathophysiologic mechanisms of immune system-related affective disorders.

Antinociceptive effect of cyclic phosphatidic acid and its derivative on animal models of acute and chronic pain

1. Abstract

Ingroup-outgroup bias in contagious yawning by chimpanzees supports link to empathy

Humans favor others seen as similar to themselves (ingroup) over people seen as different (outgroup), even without explicitly stated bias. Ingroup-outgroup bias extends to involuntary responses, such as empathy for pain. However, empathy biases have not been tested in our close primate relatives. Contagious yawning has been theoretically and empirically linked to empathy. If empathy underlies contagious yawning, we predict that subjects should show an ingroup-outgroup bias by yawning more in response to watching ingroup members yawn than outgroup. Twenty-three chimpanzees (Pan troglodytes) from two separate groups watched videos of familiar and unfamiliar individuals yawning or at rest (control). The chimpanzees yawned more when watching the familiar yawns than the familiar control or the unfamiliar yawns, demonstrating an ingroup-outgroup bias in contagious yawning. These results provide further empirical support that contagious yawning is a measure of empathy, which may be useful for evolutionary biology and mental health.

Social neuroscience: challenges and opportunities in the study of complex behavior

Social species are so characterized because they form organizations that extend beyond the individual. The goal of social neuroscience is to investigate the biological mechanisms that underlie these social structures, processes, and behavior and the influences between social and neural structures and processes. Such an endeavor is challenging because it necessitates the integration of multiple levels. Mapping across systems and levels (from genome to social groups and cultures) requires interdisciplinary expertise, comparative studies, innovative methods, and integrative conceptual analysis. Examples of how social neuroscience is contributing to our understanding of the functions of the brain and nervous system are described, and societal implications of social neuroscience are considered.

Communicative genes in the evolution of empathy and altruism

This paper discusses spontaneous communication and its implications for understanding empathy and altruism. The question of the possibility of "true" altruism-giving up one's genetic potential in favor of the genetic potential of another-is a fundamental issue common to the biological, behavioral, and social sciences. Darwin regarded "social instincts and sympathies" to be critical to the social order, but the possibility of biologically-based prosocial motives and emotions was questioned when selection was interpreted as operating at the level of the gene. In the selfish gene hypothesis, Dawkins argued that the unit of evolutionary selection must be an active, germ-line replicator: a unit whose activities determine whether copies of it are made across evolutionary timescales. He argued that the only active replicator existing across evolutionary timescales is the gene, so that the "selfish gene" is a replicator motivated only to make copies of itself. The communicative gene hypothesis notes that genes function by communicating, and the phenotype communication involves not only the individual sending and receiving abilities of the individual genes involved, but also the relationship between them relative to other genes. Therefore the selection of communication as phenotype involves the selection of individual genes and also their relationship. Relationships become replicators, and are selected across evolutionary timescales including social relationships (e.g., sex, nurturance, dominance-submission). An interesting implication of this view: apparent altruism has been interpreted by selfish gene theorists as due to kin selection and reciprocity, in which the survival of kin and comrade indirectly favor the genetic potential of the altruist. From the viewpoint of the communicative gene hypothesis, rather than underlying altruism, kin selection and reciprocity are ways of restricting altruism to kin and comrade: they are mechanisms not of altruism but of xenophobia.

'Canis empathicus'? A proposal on dogs' capacity to empathize with humans

Empathy has long attracted the attention of philosophers and psychologists, and more recently, of evolutionary biologists. Interestingly, studies suggest that empathy is a phylogenetically continuous phenomenon, ranging across animals from automatic emotional activation in response to the emotions of others, to perspective-taking that becomes increasingly complex with increasing brain size. Although suggestions have been made that the domestic dog may have the capacity to empathize with humans, no discussion has yet addressed the topic, nor have experimental routes been proposed to further explore the level of emotional and cognitive processing underlying dogs' seemingly empathic behaviour towards humans. In this opinion piece, we begin by contextualizing our topic of interest within the larger body of literature on empathy. Thereafter we: (i) outline the reasons for why we believe dogs may be capable of empathizing with humans, perhaps even at some level beyond emotional contagion; (ii) review available evidence both pro and against our opinion; and (iii) propose routes for future studies to accurately address the topic. Also, we consider the use of dogs to further explore open questions regarding empathy in humans.

Prosocial primates: selfish and unselfish motivations

Non-human primates are marked by well-developed prosocial and cooperative tendencies as reflected in the way they support each other in fights, hunt together, share food and console victims of aggression. The proximate motivation behind such behaviour is not to be confused with the ultimate reasons for its evolution. Even if a behaviour is ultimately self-serving, the motivation behind it may be genuinely unselfish. A sharp distinction needs to be drawn, therefore, between (i) altruistic and cooperative behaviour with knowable benefits to the actor, which may lead actors aware of these benefits to seek them by acting cooperatively or altruistically and (ii) altruistic behaviour that offers the actor no knowable rewards. The latter is the case if return benefits occur too unpredictably, too distantly in time or are of an indirect nature, such as increased inclusive fitness. The second category of behaviour can be explained only by assuming an altruistic impulse, which-as in humans-may be born from empathy with the recipient's need, pain or distress. Empathy, a proximate mechanism for prosocial behaviour that makes one individual share another's emotional state, is biased the way one would predict from evolutionary theories of cooperation (i.e. by kinship, social closeness and reciprocation). There is increasing evidence in non-human primates (and other mammals) for this proximate mechanism as well as for the unselfish, spontaneous nature of the resulting prosocial tendencies. This paper further reviews observational and experimental evidence for the reciprocity mechanisms that underlie cooperation among non-relatives, for inequity aversion as a constraint on cooperation and on the way defection is dealt with.

Commentary: Intersubjectivity, interobjectivity, and the embryonic fallacy in developmental science

Traditional research adopts the embryonic fallacy: the assumption that as soon as life begins, the individual becomes the source of psychological experiences. The embryonic fallacy has resulted in intersubjectivity being treated as ‘a problem’: how can each individual, the source of private experiences, understand the private experiences of ‘self-contained’ others? This ‘problem’ disappears when we recognize that intersubjectivity is regulated through interobjectivity: how individuals understand others arises out of the cultural collective in which they are socialized. The source of our understandings of others is ‘out there’ in the social world.

The neural bases for empathy

Human empathy relies on the ability to share emotions as well as the ability to understand the other's thoughts, desires, and feelings. Recent evidence points to 2 separate systems for empathy: an emotional system that supports our ability to empathize emotionally and a cognitive system that involves cognitive understanding of the other's perspective. Converging evidence from neuroimaging and lesion studies shows that a neural network that includes the inferior frontal gyrus and the inferior parietal lobule is necessary for emotion recognition and emotional contagion. On the other hand, the involvement of the ventromedial prefrontal cortex, temporoparietal junction, and the medial temporal lobe in self-reflection and autobiographical memory places these key regions as necessary for cognitive empathy. The proposed dissociation between these systems is supported by recent neurochemical experiments involving administration of oxytocin as well as by ethological, psychiatric, and developmental studies. Finally, although the emotional and cognitive systems appear to work independently, every empathic response may still evoke both components to some extent, depending on the social context.

Is there a core neural network in empathy? An fMRI based quantitative meta-analysis

Whilst recent neuroimaging studies have identified a series of different brain regions as being involved in empathy, it remains unclear concerning the activation consistence of these brain regions and their specific functional roles. Using MKDA, a whole-brain based quantitative meta-analysis of recent fMRI studies of empathy was performed. This analysis identified the dACC-aMCC-SMA and bilateral anterior insula as being consistently activated in empathy. Hypothesizing that what are here termed affective-perceptual and cognitive-evaluative forms of empathy might be characterized by different activity patterns, the neural activations in these forms of empathy were compared. The dorsal aMCC was demonstrated to be recruited more frequently in the cognitive-evaluative form of empathy, whilst the right anterior insula was found to be involved in the affective-perceptual form of empathy only. The left anterior insula was active in both forms of empathy. It was concluded that the dACC-aMCC-SMA and bilateral insula can be considered as forming a core network in empathy, and that cognitive-evaluative and affective-perceptual empathy can be distinguished at the level of regional activation.

Validity of acute and chronic tactile sensory testing after spinal cord injury in rats

Spinal cord injury (SCI) impairs sensory systems causing allodynia. Measuring the development of allodynia in rodent models of SCI is challenging due to spinal shock and marked motor impairments. Assessment of SCI-induced allodynia is not standardized across labs, making interpretation of results difficult. Therefore, we validated sensory threshold assessment after SCI and developed a novel assessment of allodynia prior to motor recovery in a rat SCI model. One hundred fifty-six Sprague-Dawley rats received T8 laminectomy or mild to moderate SCI using the OSU SCI device (0.3 mm to 1.3 mm cord displacement). To determine tactile thresholds, von Frey hairs (VFH) were applied in Up-Down or ascending order to the dorsal or plantar hindpaw. The most efficient and valid procedures that maintain high sensitivity and specificity were identified. Ten Up-Down VFH applications yielded stable thresholds; reducing the risk of threshold decay and unnecessary exposure to painful stimuli. Importantly, distraction of SCI-rats with food revealed differential decay of thresholds than when distraction is not provided. The new test uses dorsal VFH stimulation and is independent of trunk or hindlimb control. Acute dorsal VFH thresholds collected before recovery of hindlimb weight support accurately predicted plantar VFH thresholds measured at late timepoints (chi(2)=8.479; p<0.05). Thus, standardized testing early after SCI using the dorsal VFH test or later using 10 stimuli in the Up-Down test produces valid measures of tactile sensation across many SCI severities. Early detection of allodynia in experimental SCI will allow identification of mechanisms responsible for pain development and determine targets for therapeutic interventions.

Spinal-, brainstem- and cerebrally mediated responses at- and below-level of a spinal cord contusion in rats: evaluation of pain-like behavior

Pain is a frequent consequence of spinal cord injury (SCI) which may profoundly impair the patients' quality of life. Valid experimental models and methods are therefore desirable in the search for better treatments. Usually, experimental pain assays depend on stimulus-evoked withdrawal responses; however, this spinal-mediated reflex response may be particularly problematic when evaluating below-level SCI pain due to the development of hyperactive reflex circuitries. In this study, we applied and compared assays measuring cold (acetone), static (von Frey filaments), and dynamic mechanical (soft brush) hypersensitivity at different levels of the neuroaxis at and below the level of injury in a rat model of SCI. We induced an experimental SCI (MASCIS 25 mm weight-drop) and evaluated the development of spinal reflexes (withdrawal), spinal-brainstem-spinal reflexes (licking, guarding, struggling, vocalizing, jumping, and biting) and cerebral-dependent behavior (place escape/avoidance paradigm (PEAP)). We demonstrated increased brainstem reflexes and cerebrally mediated aversive reactions to stimuli applied at the level of SCI, suggesting development of at-level evoked pain behavior. Furthermore, stimulation below-level increased innate reflex responses without increasing brainstem reflexes or aversive behavior in the PEAP, suggesting development of the spasticity syndrome rather than pain-like behavior. While spinal reflex measures are acceptable for studying changes in the spinal reflex pathways and spinal cord, they are not suited as nociceptive behavioral measures. Measuring brainstem organized responses eliminates the bias associated with the spastic syndrome, but pain requires cortical involvement. Methods depending on cortical structures, as the PEAP, are therefore optimal endpoints in animal models of central pain.

Social influences on morphine sensitization in adolescent females

We recently observed that social interactions influence morphine responsiveness in adolescent males. Given sex-related differences in both social interactions and responses to morphine, the present study examines social influences on morphine sensitization in adolescent female mice. Four experimental groups were examined: (1) morphine-treated mice (twice daily, 10-40 mg/kg, s.c.) housed physically and visually separated from saline-treated mice ('morphine only'), (2) morphine-treated mice housed together with saline-treated mice ('morphine cage-mates (of saline)'), (3) saline-treated mice housed together with morphine-treated mice ('saline cage-mates (of morphine)'), and (4) saline-treated mice housed physically and visually separated from morphine-treated mice ('saline only'). Following the treatment period, mice were tested individually for their locomotor response to 20 mg/kg morphine (s.c.). There were no significant differences in morphine-induced hyper-locomotion between saline only and saline cage-mates (of morphine) female adolescent mice. Notably, morphine only mice exhibited significantly greater morphine sensitization as compared to morphine cage-mates (of saline). Thus, this study demonstrates social influences on morphine sensitization in adolescent females. Drug use during early adolescence is a key predictor of later drug abuse and dependence during adulthood. Thus, understanding the specific vulnerabilities to drug use in this age group may represent a first step in helping develop more effective treatment programs.

Behavioural phenotyping assays for mouse models of autism

Autism is a heterogeneous neurodevelopmental disorder of unknown aetiology that affects 1 in 100-150 individuals. Diagnosis is based on three categories of behavioural criteria: abnormal social interactions, communication deficits and repetitive behaviours. Strong evidence for a genetic basis has prompted the development of mouse models with targeted mutations in candidate genes for autism. As the diagnostic criteria for autism are behavioural, phenotyping these mouse models requires behavioural assays with high relevance to each category of the diagnostic symptoms. Behavioural neuroscientists are generating a comprehensive set of assays for social interaction, communication and repetitive behaviours to test hypotheses about the causes of autism. Robust phenotypes in mouse models hold great promise as translational tools for discovering effective treatments for components of autism spectrum disorders.

Repeated psychological stress-induced alterations of visceral sensitivity and colonic motor functions in mice: influence of surgery and postoperative single housing on visceromotor responses

Visceral pain modulation by chronic stress in mice has been little studied. Electromyography (EMG) recording of abdominal muscle contractions, as a proxy to the visceromotor response (VMR), requires electrode implantation and post-surgical single housing (SH) which could affect the VMR to stress. To test this hypothesis, male mice had electrode implantation surgery (S) plus SH, or no surgery and were group housed (NS-GH) or single housed (NS-SH) and exposed to either water avoidance stress (WAS, 1 h/day) or left undisturbed in their home cages for 10 days. The VMR to phasic ascending colorectal distension (CRD) was assessed before (basal) and 24 h after 10 days of WAS or no stress using a surgery-free method of intraluminal colonic pressure (ICP) recording (solid-state manometry). WAS heightened significantly the VMR to CRD at 30, 45, and 60 mmHg in S-SH vs. NS-GH, but not compared to NS-SH conscious mice. Compared to basal CRD, WAS increased VMR at 60 mmHg in the S-SH group and decreased it at 30-60 mmHg in NS-GH mice, while having no effect in NS-SH mice. The average defecation during the hour of repeated WAS over 10 days was 1.9 and 2.4 fold greater in S-SH vs. NS-GH and NS-SH mice, respectively. These data indicate that the combination of S-SH required for VMR monitoring with EMG is an important component of repeated WAS-induced post-stress visceral hypersensitivity and defecation in mice.

Oxytocin-induced analgesia and scratching are mediated by the vasopressin-1A receptor in the mouse

The neuropeptides oxytocin (OXT) and arginine vasopressin (AVP) contribute to the regulation of diverse cognitive and physiological functions including nociception. Indeed, OXT has been reported to be analgesic when administered directly into the brain, the spinal cord, or systemically. Here, we characterized the phenotype of oxytocin receptor (OTR) and vasopressin-1A receptor (V1AR) null mutant mice in a battery of pain assays. Surprisingly, OTR knock-out mice displayed a pain phenotype identical to their wild-type littermates. Moreover, systemic administration of OXT dose-dependently produced analgesia in both wild-type and OTR knock-out mice in three different assays, the radiant-heat paw withdrawal test, the von Frey test of mechanical sensitivity, and the formalin test of inflammatory nociception. In contrast, OXT-induced analgesia was completely absent in V1AR knock-out mice. In wild-type mice, OXT-induced analgesia could be fully prevented by pretreatment with a V1AR but not an OTR antagonist. Receptor binding studies demonstrated that the distribution of OXT and AVP binding sites in mouse lumbar spinal cord resembles the pattern observed in rat. AVP binding sites diffusely label the lumbar spinal cord, whereas OXT binding sites cluster in the substantia gelatinosa of the dorsal horn. In contrast, quantitative real-time reverse transcription (RT)-PCR revealed that V1AR but not OTR mRNA is abundantly expressed in mouse dorsal root ganglia, where it localizes to small- and medium-diameter cells as shown by single-cell RT-PCR. Hence, V1ARs expressed in dorsal root ganglia might represent a previously unrecognized target for the analgesic action of OXT and AVP.

Consolation as possible expression of sympathetic concern among chimpanzees

Chimpanzees are known to spontaneously provide contact comfort to recent victims of aggression, a behavior known as consolation. Similar behavior in human children is attributed to empathic or sympathetic concern. In line with this empathy hypothesis, chimpanzee consolation has been shown to reduce the recipient's state of arousal, hence to likely alleviate distress. Other predictions from the empathy hypothesis have rarely been tested, however, owing to small sample sizes in previous studies. An exceptionally large database of spontaneous consolation in two outdoor-housed groups of chimpanzees lends further support to the empathy hypothesis in that consolation occurred disproportionally between individuals that are socially close (i.e., kin and affiliation partners) and was more typical of females than males, which differences are also known of human empathy. These effects were demonstrated using generalized linear mixed models, which control multiple variables at once. An exception to the above pattern was formed by the highest-ranking males, which frequently offered consolation to victims of aggression, probably as part of their general policing function in chimpanzee society. Consolation occurred more frequently in the absence of reconciliation between former opponents, suggesting that actors are sensitive to the contact need of victims of aggression, which may be greater if the aggressor ignores them. That consolation is an integrated part of close mutual relationships is supported by the tendency for it being reciprocated.

Hypolocomotion, asymmetrically directed behaviors (licking, lifting, flinching, and shaking) and dynamic weight bearing (gait) changes are not measures of neuropathic pain in mice

BACKGROUND

Spontaneous (non-evoked) pain is a major clinical symptom of neuropathic syndromes, one that is understudied in basic pain research for practical reasons and because of a lack of consensus over precisely which behaviors reflect spontaneous pain in laboratory animals. It is commonly asserted that rodents experiencing pain in a hind limb exhibit hypolocomotion and decreased rearing, engage in both reflexive and organized limb directed behaviors, and avoid supporting their body weight on the affected side. Furthermore, it is assumed that the extent of these positive or negative behaviors can be used as a dependent measure of spontaneous chronic pain severity in such animals. In the present study, we tested these assumptions via blinded, systematic observation of digital video of mice with nerve injuries (chronic constriction or spared nerve injury), and automated assessment of locomotor behavior using photocell detection and dynamic weight bearing (i.e., gait) using the CatWalk system.

RESULTS

We found no deficits in locomotor activity or rearing associated with neuropathic injury. The frequency of asymmetric (ipsilaterally directed) behaviors were too rare to be seriously considered as representing spontaneous pain, and in any case did not statistically exceed what was blindly observed on the contralateral hind paw and in control (sham operated and unoperated) mice. Changes in dynamic weight bearing, on the other hand, were robust and ipsilateral after spared nerve injury (but not chronic constriction injury). However, we observed timing, pharmacological, and genetic dissociation of mechanical allodynia and gait alterations.

CONCLUSIONS

We conclude that spontaneous neuropathic pain in mice cannot be assessed using any of these measures, and thus caution is warranted in making such assertions.

Do ravens show consolation? Responses to distressed others

BACKGROUND

Bystander affiliation (post-conflict affiliation from an uninvolved bystander to the conflict victim) may represent an expression of empathy in which the bystander consoles the victim to alleviate the victim's distress ("consolation"). However, alternative hypotheses for the function of bystander affiliation also exist. Determining whether ravens spontaneously offer consolation to distressed partners may not only help us to understand how animals deal with the costs of aggressive conflict, but may also play an important role in the empathy debate.

METHODOLOGY/PRINCIPAL FINDINGS

This study investigates the post-conflict behavior of ravens, applying the predictive framework for the function of bystander affiliation for the first time in a non-ape species. We found weak evidence for reconciliation (post-conflict affiliation between former opponents), but strong evidence for both bystander affiliation and solicited bystander affiliation (post-conflict affiliation from the victim to a bystander). Bystanders involved in both interactions were likely to share a valuable relationship with the victim. Bystander affiliation offered to the victim was more likely to occur after intense conflicts. Renewed aggression was less likely to occur after the victim solicited affiliation from a bystander.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that in ravens, bystanders may console victims with whom they share a valuable relationship, thus alleviating the victims' post-conflict distress. Conversely victims may affiliate with bystanders after a conflict in order to reduce the likelihood of renewed aggression. These results stress the importance of relationship quality in determining the occurrence and function of post-conflict interactions, and show that ravens may be sensitive to the emotions of others.

Sensory stimulation prior to spinal cord injury induces post-injury dysesthesia in mice

Chronic pain and dysesthesias are debilitating conditions that can arise following spinal cord injury (SCI). Research studies frequently employ rodent models of SCI to better understand the underlying mechanisms and develop better treatments for these phenomena. While evoked withdrawal tests can assess hypersensitivity in these SCI models, there is little consensus over how to evaluate spontaneous sensory abnormalities that are seen in clinical SCI subjects. Overgrooming (OG) and biting after peripheral nerve injury or spinal cord excitotoxic lesions are thought to be one behavioral demonstration of spontaneous neuropathic pain or dysesthesia. However, reports of OG after contusion SCI are largely anecdotal and conditions causing this response are poorly understood. The present study investigated whether repeated application of sensory stimuli to the trunk prior to mid-thoracic contusion SCI would induce OG after SCI in mice. One week prior to SCI or laminectomy, mice were subjected either to nociceptive and mechanical stimulation, mechanical stimulation only, the testing situation without stimulation, or no treatment. They were then examined for 14 days after surgery and the sizes and locations of OG sites were recorded on anatomical maps. Mice subjected to either stimulus paradigm showed increased OG compared with unstimulated or uninjured mice. Histological analysis showed no difference in spinal cord lesion size due to sensory stimulation, or between mice that overgroomed or did not overgroom. The relationship between prior stimulation and contusion injury in mice that display OG indicates a critical interaction that may underlie one facet of spontaneous neuropathic symptoms after SCI.

Cognition and animal welfare

Animals exhibit species-typical adaptations of behavior and may suffer stress in captivity if they are prevented from performing these patterns of behavior. This article considers whether these particular 'needs' rely on cognitive processes or are performed without complex cognition despite their appearance of behavioral complexity. Emotion and cognition in animals are also discussed, particularly whether animals can feel emotions and, if so, what ranges of emotions they might feel. Cognitive capacities that would contribute to suffering include empathy with the suffering of others, memories of negative events and suffering in anticipation of future events. Cognitive bias of individual animals toward positive or negative feelings is related to dominance of the left or right hemisphere, respectively. These biases might be reflected in the animal's preferred limb to pick up food. Hence, limb preference could be a useful measure of cognitive bias. Post-traumatic stress disorder is a cognitive condition that, it is suggested, might involve dominance of the right hemisphere. This debilitating condition is experience-dependent and not infrequently seen in animals in captivity. In conclusion, it is argued that there is an obvious need for more research on cognition as it relates to animal welfare and as a basis for changing legislature to protect animals from suffering. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.

Observational fear learning involves affective pain system and Cav1.2 Ca2+ channels in ACC

Fear can be acquired vicariously through social observation of others suffering from aversive stimuli. We found that mice (observers) developed freezing behavior by observing other mice (demonstrators) receive repetitive foot shocks. Observers had higher fear responses when demonstrators were socially related to themselves, such as siblings or mating partners. Inactivation of anterior cingulate cortex (ACC) and parafascicular or mediodorsal thalamic nuclei, which comprise the medial pain system representing pain affection, substantially impaired this observational fear learning, whereas inactivation of sensory thalamic nuclei had no effect. The ACC neuronal activities were increased and synchronized with those of the lateral amygdala at theta rhythm frequency during this learning. Furthermore, an ACC-limited deletion of Ca(v)1.2 Ca(2+) channels in mice impaired observational fear learning and reduced behavioral pain responses. These results demonstrate the functional involvement of the affective pain system and Ca(v)1.2 channels of the ACC in observational social fear.

Socially induced morphine pseudosensitization in adolescent mice

Given that social influences are among the strongest predictors of adolescents' drug use, this study examined the effect of social interaction on morphine-induced hyperlocomotion in both adolescent and adult mice. Three experimental groups of adolescent and adult male mice were examined (i) morphine-treated mice (twice daily, 10-40 mg/kg, subcutaneous), (ii) saline-injected mice housed together with the morphine-treated mice ('saline cage-mates'), and (iii) saline-injected mice housed physically and visually separated from the morphine-treated mice ('saline alone'). After the treatment period, mice were tested individually for their locomotor response to 10 mg/kg morphine (subcutaneous). Adolescent saline cage-mates, though administered morphine for the very first time, exhibited an enhanced hyperlocomotion response similar to the locomotor sensitization response exhibited by the morphine-treated mice. This was not observed in adults. In adults, there were no significant differences in morphine-induced hyperlocomotion between saline alone and saline cage-mates. As expected, morphine-treated adults and adolescents both exhibited locomotor sensitization. These results show a vulnerability to social influences in adolescent mice, which does not exist in adult mice.

Spouses' cardiovascular reactivity to their partners' suffering

A laboratory study of older adults with osteoarthritis and their spouses was conducted to examine the unique influence of exposure to suffering on caregivers' risk for impaired psychological and physical health. Spouses' blood pressure (BP) and heart rate (HR) were monitored during 2 tasks designed to capture their partners' suffering. First, spouses watched their partners (and a stranger) carry heavy logs across an 8-ft space for 3 min, a task that elicited pain expression. Second, spouses spoke about their partners' suffering (and also about a typical meal with their partners). Results showed that spouses' BP and HR increased when watching and talking about their partners' suffering, and exposure to a partner's suffering was more physiologically stressful than to a stranger's suffering. These findings suggest that heightened physiological stress caused by exposure to a loved one's suffering may be one pathway to caregivers' increased risk for cardiovascular disease.

A partial L5 spinal nerve ligation induces a limited prolongation of mechanical allodynia in rats: an efficient model for studying mechanisms of neuropathic pain

The relationship between pain severity and the extent of injury to a peripheral nerve remains elusive. In this study, we compared the pain behavior resulting from partial (1/3-1/2 thickness) and full L5 spinal nerve ligation (SNL) in rats. The decrease in paw withdrawal threshold (PWT) to mechanical stimuli in the hindpaw ipsilateral to the injury was comparable in the two groups on days 3-21 post-injury. However, the decreased PWT recovered earlier in the partial SNL group than in the full SNL group. These observations suggest that the duration of neuropathic pain behavior, but not the early development of mechanical allodynia, is dependent on the extent of nerve injury. On days 6 and 15 post-injury, when the mechanical allodynia was similar in the two groups, systemic morphine induced a greater reduction of mechanical allodynia in the partial SNL group than in the full SNL group. Furthermore, in partial SNL rats, at post-injury time points when they had largely recovered from the neuropathic pain state, systemic administration of naloxone hydrochloride (day 53) or naloxone methiodide (a non-selective peripherally acting opioid receptor antagonist; day 64) or intra-plantar injection of naloxone methiodide rekindled mechanical pain hypersensitivity in the ipsilateral hindpaw, suggesting a prolonged activation of endogenous opioidergic pain-inhibition. Therefore, partial SNL in rats may represent an efficient model for studying the mechanisms of neuropathic pain, testing effects of analgesic/antihyperalgesic drugs, and understanding endogenous pain-inhibitory mechanisms that lead to reversal of the pain behavior with time.

Species differences in pharmacokinetics and pharmacodynamics

Veterinary medicine faces the unique challenge of having to treat many types of domestic animal species, including mammals, birds, and fishes. Moreover, these species have evolved into genetically unique breeds having certain distinguishable characteristics developed by artificial selection. The main challenge for veterinarians is not to select a drug but to determine, for the selected agent, a rational dosing regimen because the dosage regimen for a drug in a given species may depend on its anatomy, biochemistry, physiology, and behaviour as well as on the nature and causes of the condition requiring treatment. Both between- and within-species differences in drug response can be explained either by variations in drug pharmacokinetics (PK) or drug pharmacodynamics (PD), the magnitude of which varies from drug to drug. This chapter highlights selected aspects of species differences in PK and PD and considers underlying physiological and patho-physiological mechanisms in the main domestic species. Particular attention was paid to aspects of animal behaviour (food behaviour, social behavior, etc.) as a determinant of interspecies differences in PK or/and PD. Modalities of drug administration are many and result not only from anatomical, physiological and/or behavioural differences across species but also from management options. The latter is the case for collective/group treatment of food-producing animals, frequently dosed by the oral route at a herd or flock level. After drug administration, the main causes of observed inter-species differences arise from species differences in the handling of drugs (absorption, distribution, metabolism, and elimination). Such differences are most common and of greatest magnitude when functions which are phylogenetically divergent between species, such as digestive functions (ruminant vs. non-ruminant, carnivore vs. herbivore, etc.), are involved in drug absorption. Interspecies differences also exist in drug action but these are generally more limited, except when a particular targeted function has evolved, as is the case for reproductive physiology (mammals vs. birds vs. fishes; annual vs. seasonal reproductive cycle in mammals; etc.). In contrast, for antimicrobial and antiparasitic drugs, interspecies differences are more limited and rather reflect those of the pathogens than of the host. Interspecies difference in drug metabolism is a major factor accounting for species differences in PK and also in PD (production or not of active metabolites). Recent and future advances in molecular biology and pharmacogenetics will enable a more comprehensive view of interspecies differences and also between breeds with existing polymorphism. Finally, the main message of this review is that differences between species are not only numerous but also often unpredictable so that no generalisations are possible, even though for several drugs allometric approaches do allow some valuable interspecies extrapolations. Instead, each drug must be investigated on a species-by-species basis to guarantee its effective and safe use, thus ensuring the well-being of animals and safeguarding of the environment and human consumption of animal products.