Reunion of separated sibling mice: neurobiological and behavioral aspects

CFA-treated mice induce hyperalgesia in healthy mice via an olfactory mechanism

BACKGROUND

Social interactions with subjects experiencing pain can increase nociceptive sensitivity in observers, even without direct physical contact. In previous experiments, extended indirect exposure to soiled bedding from mice with alcohol withdrawal-related hyperalgesia enhanced nociception in their conspecifics. This finding suggested that olfactory cues could be sufficient for nociceptive hypersensitivity in otherwise untreated animals (also known as "bystanders").

AIM

The current study addressed this possibility using an inflammation-based hyperalgesia model and long- and short-term exposure paradigms in C57BL/6J mice.

MATERIALS & METHOD

Adult male and female mice received intraplantar injection of complete Freund's adjuvant (CFA) and were used as stimulus animals to otherwise naïve same-sex bystander mice (BS). Another group of untreated mice (OLF) was simultaneously exposed to the bedding of the stimulus mice.

RESULTS

In the long-term, 15-day exposure paradigm, the presence of CFA mice or their bedding resulted in reduced von Frey threshold but not Hargreaves paw withdrawal latency in BS or OLF mice. In the short-term paradigm, 1-hr interaction with CFA conspecifics or 1-hr exposure to their bedding induced mechanical hypersensitivity in BS and OLF mice lasting for 3 hrs. Chemical ablation of the main olfactory epithelium prevented bedding-induced and stimulus mice-induced mechanical hypersensitivity. Gas chromatography-mass spectrometry (GC-MS) analysis of the volatile compounds in the bedding of experimental mice revealed that CFA-treated mice released an increased number of compounds indicative of disease states.

DISCUSSION AND CONCLUSION

These results demonstrate that CFA-induced inflammatory pain can modulate nociception in bystander mice via an olfactory mechanism involving dynamic changes in volatile compounds detectable in the rodent bedding.

SIGNIFICANCE

Social context can influence nociceptive sensitivity. Recent studies suggested involvement of olfaction in this influence. In agreement with this idea, the present study shows that the presence of mice with inflammatory pain produces nociceptive hypersensitivity in nearby conspecifics. This enhanced nociception occurs via olfactory cues present in the mouse bedding. Analysis of the bedding from mice with inflammatory pain identifies a number of compounds indicative of disease states. These findings demonstrate the importance of olfactory system in influencing pain states.

IUPHAR review: Navigating the role of preclinical models in pain research

Chronic pain is a complex and challenging medical condition that affects millions of people worldwide. Understanding the underlying mechanisms of chronic pain is a key goal of preclinical pain research so that more effective treatment strategies can be developed. In this review, we explore nociception, pain, and the multifaceted factors that lead to chronic pain by focusing on preclinical models. We provide a detailed look into inflammatory and neuropathic pain models and discuss the most used animal models for studying the mechanisms behind these conditions. Additionally, we emphasize the vital role of these preclinical models in developing new pain-relief drugs, focusing on biologics and the therapeutic potential of NMDA and cannabinoid receptor antagonists. We also discuss the challenges of TRPV1 modulation for pain treatment, the clinical failures of neurokinin (NK)- 1 receptor antagonists, and the partial success story of Ziconotide to provide valuable lessons for preclinical pain models. Finally, we highlight the overall success and limitations of current treatments for chronic pain while providing critical insights into the development of more effective therapies to alleviate the burden of chronic pain.

Behavioral, neurochemical, and neuroimmune changes associated with social buffering and stress contagion

Social buffering can provide protective effects on stress responses and their subsequent negative health outcomes. Although social buffering is beneficial for the recipient, it can also have anxiogenic effects on the provider of the social buffering - a phenomena referred to as stress contagion. Social buffering and stress contagion usually occur together, but they have traditionally been studied independently, thus limiting our understanding of this dyadic social interaction. In the present study, we examined the effects of preventative social buffering and stress contagion in socially monogamous prairie voles (Microtus ochrogaster). We tested the hypothesis that this dynamic social interaction is associated with coordinated alterations in behaviors, neurochemical activation, and neuroimmune responses. To do so, adult male prairie voles were stressed via an acute immobilization restraint tube (IMO) either alone (Alone) or with their previously pair-bonded female partner (Partner) in the cage for 1 h. In contrast, females were placed in a cage containing either an empty IMO tube (Empty) or one that contained their pair-bonded male (Partner). Anxiety-like behavior was tested on the elevated plus maze (EPM) following the 60-mins test and brain sections were processed for neurochemical/neuroimmune marker labeling for all subjects. Our data indicate that females in the Partner group were in contact with and sniffed the IMO tube more, showed fewer anxiety-like behaviors, and had a higher level of oxytocin expression in the paraventricular nucleus of the hypothalamus (PVN) compared to the Empty group females. Males in the Partner group had lower levels of anxiety-like behavior during the EPM test, greater activation of corticotropin-releasing hormone expressing neurons in the PVN, lower activation of serotonin neurons in the dorsal raphe, and lower levels of microgliosis in the nucleus accumbens. Taken together, these data suggest brain region- and neurochemical-specific alterations as well as neuroinflammatory changes that may be involved in the regulation of social buffering and stress contagion behaviors.

Maternal presence or absence alters nociceptive responding and cortical anandamide levels in juvenile female rats

The influence of parental support on child pain experiences is well recognised. Accordingly, animal studies have revealed both short- and long-term effects of early life stress on nociceptive responding and neural substrates such as endocannabinoids. The endocannabinoid system plays an important role in mediating and modulating stress, social interaction, and nociception. This study examined the effects of maternal support or acute isolation on nociceptive responding of female rats to a range of stimuli during the juvenile pre-adolescent period and accompanying changes in the endocannabinoid system. The data revealed that juvenile female Sprague Dawley rats (PND21-24) isolated from the dam for 1 h prior to nociceptive testing exhibited increased latency to withdraw in the hot plate test and increased mechanical withdrawal threshold in the Von Frey test, compared to rats tested in the presence of the dam. Furthermore, isolated rats exhibited reduced latency to respond in the acetone drop test and enhanced nociceptive responding in the formalin test when compared to dam-paired counterparts. Anandamide, but not 2-AG, levels were reduced in the prefrontal cortex of dam-paired, but not isolated, juvenile rats following nociceptive testing. There was no change in the expression of CB₁, FAAH or MAGL; however, CB₂ receptor expression was reduced in both dam-paired and isolated rats following nociceptive testing. Taken together the data demonstrate that brief social isolation or the presence of the dam modulates nociceptive responding of juvenile rat pups in a modality specific manner, and suggest a possible role for the endocannabinoid system in the prefrontal cortex in sociobehavioural pain responses during early life.

Effects of opioid receptor stimulation and blockade on touch pleasantness: a double-blind randomised trial

The μ-opioid receptor (MOR) system has long been thought to underpin the rewarding properties of pleasant touch. Numerous non-human animal studies implicate MORs in social behaviours involving touch, but little is currently known about MOR involvement in human touch reward. Here, we employed a bi-directional pharmacological double-blind crossover design to assess the role of the human MOR system for touch pleasantness and motivation. Forty-nine male volunteers received 10 mg per-oral morphine, 50 mg per-oral naltrexone and placebo before being brushed on their forearm at three different velocities (0.3, 3 and 30 cm/s). In a touch liking task, pleasantness ratings were recorded after each 15 s brushing trial. In a touch wanting task, participants actively manipulated trial duration through key presses. As expected, 3 cm/s was the preferred velocity, producing significantly higher pleasantness ratings and wanting scores than the other stimuli. Contrary to our hypothesis, MOR drug manipulations did not significantly affect either touch pleasantness or wanting. The null effects were supported by post hoc Bayesian analyses indicating that the models with no drug effect were more than 25 times more likely than the alternative models given the data. We conclude that μ-opioid signalling is unlikely to underpin non-affiliative touch reward in humans.

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.

Nucleus accumbens mu opioid receptors regulate context-specific social preferences in the juvenile rat

The μ opioid receptor (MOR) in the nucleus accumbens (NAc) is involved in assigning pleasurable, or hedonic value to rewarding stimuli. Importantly, the hedonic value of a given rewarding stimulus likely depends on an individual's current motivational state. Here, we examined the involvement of MORs in the motivation to interact with a novel or a familiar (cage mate) conspecific in juvenile rats. First, we demonstrated that the selective MOR antagonist CTAP administered into the NAc reduces social novelty preference of juvenile males, by decreasing the interaction time with the novel conspecific and increasing the interaction time with the cage mate. Next, we found that a 3-h separation period from the cage mate reduces social novelty preference in both juvenile males and females, which was primarily driven by an increase in interaction time with the cage mate. Last, we showed that MOR agonism (intracerebroventricularly or in the NAc) restored social novelty preference in juvenile males that did not show social novelty preference following social isolation. Taken together, these data support a model in which endogenous MOR activation in the NAc facilitates the relative hedonic value of novel over familiar social stimuli. Our results may implicate the MOR in neuropsychiatric disorders characterized by altered social motivation, such as major depression and autism spectrum disorder.

To Group or Not to Group? Good Practice for Housing Male Laboratory Mice

Simple Summary

Wild mice live in territories inhabited by one adult male, several females, and their offspring. This cannot be replicated in the laboratory, so male mice are usually housed in single-sex groups or individually. However, there can be serious animal welfare problems associated with both these approaches, such as lack of social contact when housed individually or aggression between males when kept in groups. Group housing is widely recommended to give male laboratory mice the opportunity to behave as ‘social animals’, but social stress can be detrimental to the welfare of these animals, even without injurious fighting. All of this can also affect the quality of the science, giving rise to ethical concerns. This review discusses whether it is in the best welfare interests of male mice to be housed in groups, or alone. We conclude that it is not possible to give general recommendations for good practice for housing male laboratory mice, as responses to single- and group-housing can be highly context-dependent. The welfare implications of housing protocols should be researched and considered in each case.

Abstract

It is widely recommended to group-house male laboratory mice because they are ‘social animals’, but male mice do not naturally share territories and aggression can be a serious welfare problem. Even without aggression, not all animals within a group will be in a state of positive welfare. Rather, many male mice may be negatively affected by the stress of repeated social defeat and subordination, raising concerns about welfare and also research validity. However, individual housing may not be an appropriate solution, given the welfare implications associated with no social contact. An essential question is whether it is in the best welfare interests of male mice to be group- or singly housed. This review explores the likely impacts—positive and negative—of both housing conditions, presents results of a survey of current practice and awareness of mouse behavior, and includes recommendations for good practice and future research. We conclude that whether group- or single-housing is better (or less worse) in any situation is highly context-dependent according to several factors including strain, age, social position, life experiences, and housing and husbandry protocols. It is important to recognise this and evaluate what is preferable from animal welfare and ethical perspectives in each case.

Laboratory environmental factors and pain behavior: the relevance of unknown unknowns to reproducibility and translation

The poor record of basic-to-clinical translation in recent decades has led to speculation that preclinical research is "irreproducible", and this irreproducibility in turn has largely been attributed to deficiencies in reporting and statistical practices. There are, however, a number of other reasonable explanations of both poor translation and difficulties in one laboratory replicating the results of another. This article examines these explanations as they pertain to preclinical pain research. I submit that many instances of apparent irreproducibility are actually attributable to interactions between the phenomena and interventions under study and "latent" environmental factors affecting the rodent subjects. These environmental variables-often causing stress, and related to both animal husbandry and the specific testing context-differ greatly between labs, and continue to be identified, suggesting that our knowledge of their existence is far from complete. In pain research in particular, laboratory stressors can produce great variability of unpredictable direction, as stress is known to produce increases (stress-induced hyperalgesia) or decreases (stress-induced analgesia) in pain depending on its parameters. Much greater attention needs to be paid to the study of the laboratory environment if replication and translation are to be improved.

Genetic deletion of the Histone Deacetylase 6 exacerbates selected behavioral deficits in the R6/1 mouse model for Huntington's disease

INTRODUCTION

The inhibition of the Histone Deacetylase 6 (HDAC6) increases tubulin acetylation, thus stimulating intracellular vesicle trafficking and brain-derived neurotrophic factor (BDNF) release, that is, cellular processes markedly reduced in Huntington's disease (HD).

METHODS

We therefore tested that reducing HDAC6 levels by genetic manipulation would attenuate early cognitive and behavioral deficits in R6/1 mice, a mouse model which develops progressive HD-related phenotypes.

RESULTS

In contrast to our initial hypothesis, the genetic deletion of HDAC6 did not reduce the weight loss or the deficits in cognitive abilities and nest-building behavior shown by R6/1 mice, and even worsened their social impairments, hypolocomotion in the Y-maze, and reduced ultrasonic vocalizations.

CONCLUSIONS

These results weaken the validity of HDAC6 reduction as a possible therapeutic strategy for HD. The data are discussed in terms of additional cellular consequences and anatomical specificity of HDAC6 that could explain these unexpected effects.

Effects of acute chemotherapy-induced mucositis on spontaneous behaviour and the grimace scale in laboratory rats

Intestinal mucositis is a frequent side-effect of chemotherapy treatment. Many oncological research programs aim to identify novel treatments for this distressing condition, and these programs frequently use rat models. Little is known about the presence and progression of pain in these models and how this can best be treated by analgesic therapy. We used a number of behaviour-based methods of pain assessment to determine which tools were best suited for pain identification. Baseline measures for behavioural assessment, rat grimace score and sociability were determined through analysis of continuously recorded video data and an applied social interaction test ( n = 16). Mucositis was then induced by intraperitoneal injection of 5-fluorouracil (150 mg/kg) and further behavioural analyses undertaken. An assessment of enrichment interaction was also made by determining the mass of a plastic chew toy gnawed both pre- and post-chemotherapy injection. Behavioural scoring was performed 1, 6, 12, 24 and 48 h after injection, with facial expression being scored at the 12, 24 and 48 h time-points. Sociability testing was performed once during the post-injection period. No significant differences were found in grimace scores between baseline and later daily measures. Behaviours similar to those previously reported post-laparotomy were observed. Writhing, twitching and back-arching behaviours were most evident in rats affected by mucositis and were increased in frequency (respective P values: 0.002, 0.004 and 0.008) 48 h after chemotherapy injection compared with baseline, implying that pain onset occurred around this time-point. Social investigatory behaviour was also increased ( P = 0.002) following disease onset. Each day, rats post-5FU injection gnawed a greater percentage of their nylabone enrichment by weight than the saline-injected control rats ( P = 0.046). These data suggest that, of the tools tested, behavioural assessment scoring may find greatest utility in rodent models of intestinal mucositis and should be investigated further.

State-dependent μ-opioid modulation of social motivation

Social mammals engage in affiliative interactions both when seeking relief from negative affect and when searching for pleasure and joy. These two motivational states are both modulated by μ-opioid transmission. The μ-opioid receptor (MOR) system in the brain mediates pain relief and reward behaviors, and is implicated in social reward processing and affiliative bonding across mammalian species. However, pharmacological manipulation of the μ-opioid system has yielded opposite effects on rodents and primates: in rodents, social motivation is generally increased by MOR agonists and reduced by antagonists, whereas the opposite pattern has been shown in primates. Here, we address this paradox by taking into account differences in motivational state. We first review evidence for μ-opioid mediation of reward processing, emotion regulation, and affiliation in humans, non-human primates, rodents and other species. Based on the consistent cross-species similarities in opioid functioning, we propose a unified, state-dependent model for μ-opioid modulation of affiliation across the mammalian species. Finally, we show that this state-dependent model is supported by evidence from both rodent and primate studies, when species and age differences in social separation response are taken into account.

The interaction between pain and social behavior in humans and rodents

Pain elicits behaviors in humans and nonhuman animals that serve as social cues. Pain behaviors serve a communicative function in humans, and this may be true as well in other animals. This review considers the current evidence for modulation of acute pain in different social contexts in humans and rodents, with a focus on dyadic social interactions. Increasing data supports the ability of social buffering, emotional contagion (a form of empathy), vicarious learning, and social stress to modulate pain sensitivity and pain behavior in mice and rats. As in humans, many of these social factors operate, and affect pain, in a sex-dependent manner. The development of a true social neuroscience of pain, with detailed explication of the underlying neurochemistry and genetics, now seems achievable.

The social brain: neurobiological basis of affiliative behaviours and psychological well-being

The social brain hypothesis proposes that the demands of the social environment provided the evolutionary pressure that led to the expansion of the primate brain. Consistent with this notion, that functioning in the social world is crucial to our survival, while close supportive relationships are known to enhance well-being, a range of social stressors such as abuse, discrimination and dysfunctional relationships can increase the risk of psychiatric disorders. The centrality of the social world to our everyday lives is further exemplified by the fact that abnormality in social behaviour is a salient feature of a range of neurodevelopmental and psychiatric disorders. This paper aims to provide a selective overview of current knowledge of the neurobiological basis of our ability to form and maintain close personal relationships, and of the benefits these relationships confer on our health. Focusing on neurochemical and neuroendocrine interactions within affective and motivational neural circuits, it highlights the specific importance of cutaneous somatosensation in affiliative behaviours and psychological well-being and reviews evidence, in support of the hypothesis, that a class of cutaneous unmyelinated, low threshold mechanosensitive nerves, named c-tactile afferents, have a direct and specific role in processing affiliative tactile stimuli.

Modulation of nociception by social factors in rodents: contribution of the opioid system

RATIONALE

The opioid system is involved in the regulation of several behavioral and physiological responses, controlling pain, reward, and addictive behaviors. Opioid administration, depending on drugs and doses, usually affects sociability reducing interactions between conspecifics, whereas some affiliative behaviors such as sexual activity, social grooming, and play behavior increase the endogenous opioid activity.

OBJECTIVES

The possible interaction between endogenous opioids released during socio/sexual behavior and their analgesic effect on pain response is reviewed in the rodent literature.

RESULTS

Direct evidence for socially mediated opioid changes resulting in increase in nociceptive threshold derives from studies exploring the effects of defeat experiences, social isolation, maternal, sexual behavior, and social reunion among kin or familiar animals in laboratory rodents. Indirect evidence for endogenous activation of the opioid system, possibly affecting pain sensitivity, derives from studies investigating the relevance of natural social reward using the conditioned place preference protocols or analyzing ultrasonic vocalizations associated to positive affective contexts. Finally, genetic and epigenetic factors that affect the opioid system during development are reported to be involved in modulating the response to social stimuli as well as nociception.

CONCLUSIONS

All studies highlight the relevance of affiliative contact behavior between conspecifics that is responsible for the activation of the endogenous mu-opioid system, inducing nociceptive threshold increase.

Sex-dependent changes in social behaviors in motor pre-symptomatic R6/1 mice

BACKGROUND

The R6/1 mouse line is one of the most widely employed models of Huntington Disease (HD), a complex syndrome characterized by motor and non-motor deficits. Surprisingly, its behavioral phenotype during the early phases of the pathology when the motor impairments are not manifest yet has been poorly investigated. It is also not clear whether the expression of HD-like symptoms at the pre-motor stage in this mouse model differs between the two sexes.

METHODS

Male and female 12 weeks-old R6/1 mice and their wild-type littermates were tested on a battery of tests modeling some of the major neuropsychiatric non-motor symptoms of HD: alterations in social interest, social interaction and communication, as well as disturbances in prepulse inhibition of the acoustic startle response (PPI) and circadian patterns of activity. The lack of motor symptoms was confirmed during the entire experimental period by means of the tail test for clasping.

RESULTS

R6/1 mice displayed marked alterations in all social behaviors which were mainly observed in males. Male R6/1 animals were also the only ones showing reduced body weight. Both male and female transgenic mice displayed mild alterations in the circadian activity patterns, but no deficits in PPI.

CONCLUSIONS

These results demonstrate the validity of the R6/1 mouse in mimicking selected neuropsychiatric symptoms of HD, the social deficits being the clearest markers of the pre-motor phase of the pathology. Furthermore, our data suggest that male R6/1 mice are more suitable for future studies on the early stages of HD.

Genetic-background modulation of core and variable autistic-like symptoms in Fmr1 knock-out mice

BACKGROUND

No animal models of autism spectrum disorders (ASD) with good construct validity are currently available; using genetic models of pathologies characterized by ASD-like deficits, but with known causes, may be therefore a promising strategy. The Fmr1-KO mouse is an example of this approach, modeling Fragile X syndrome, a well-known genetic disorder presenting ASD symptoms. The Fmr1-KO is available on different genetic backgrounds (FVB versus C57BL/6), which may explain some of the conflicting results that have been obtained with these mutants up till now.

METHODS

Fmr1 KO and their wild-type littermates on both the FVB and C57BL/6 genetic backgrounds were examined on a battery of tests modeling the clinical symptoms of ASD, including the triad of core symptoms (alterations in social interaction and communication, presence of repetitive behaviors), as well as the secondary symptoms (disturbances in sensori-motor reactivity and in circadian patterns of activity, epileptic events).

RESULTS

Fmr1-KO mice displayed autistic-like core symptoms of altered social interaction and occurrence of repetitive behaviors with additional hyperactivity. The genetic background modulated the effects of the Fmr1 deletion and it appears that the C57BL/6 background may be more suitable for further research on core autistic-like symptoms.

CONCLUSIONS

The Fmr1-mouse line does not recapitulate all of the main core and secondary ASD symptoms, but still can be useful to elucidate the neurobiological mechanisms underlying specific ASD-like endophenotypes.

Social buffering: relief from stress and anxiety

Communication is essential to members of a society not only for the expression of personal information, but also for the protection from environmental threats. Highly social mammals have a distinct characteristic: when conspecific animals are together, they show a better recovery from experiences of distress. This phenomenon, termed 'social buffering', has been found in rodents, birds, non-human primates and also in humans. This paper reviews classical findings on social buffering and focuses, in particular, on social buffering effects in relation to neuroendocrine stress responses. The social cues that transmit social buffering signals, the neural mechanisms of social buffering and a partner's efficacy with respect to social buffering are also detailed. Social contact appears to have a very positive influence on the psychological and the physiological aspects of social animals, including human beings. Research leading towards further understanding of the mechanisms of social buffering could provide alternative medical treatments based on the natural, individual characteristics of social animals, which could improve the quality of life.

Neurobiological and behavioral aspects of recognition in female mice

Female mice were tested for their capability to recognize female littermates in adulthood. Sibling females did not show any of the behavioral indices of recognition reported in the literature for sibling males during a 2-h social interaction. Conversely, adult females that experienced 7 days of separation from unrelated cagemates were able to recognize each other: during reunion, they showed reduced olfactory exploration, higher levels of affiliative behavior, and changes in nociception that were opioid dependent. Familiar females treated with naloxone (5.0 mg/kg, i.p.) did not show the increase in tail-flick latency that characterized saline-treated familiar pairs. Unfamiliar females did not show any behavioral modifications during social interaction. These data stress the role of familiarity in female-female social interaction and suggest that more recent experiences conceal earlier information gained before weaning. The importance of familiarity in females was found to be in contrast with the relevance of genetic recognition in male mice, but was well adapted to male and female roles within the social structure of mouse populations.

Physiological evidence for genetically mediated sibling recognition in mice

The kin selection theory predicts that individuals would behave differently toward one another, depending on their genetic relatedness. Kin discrimination has been demonstrated in mice from social behavior, and previous familiarity, as well as familiarity with the partner's phenotype, has been postulated to represent proximate mechanisms. It has already been demonstrated that siblings' reunion resulted in a decrease in pain sensitivity that is mediated by endogenous opioids. In this study, using a cross-transferring design, it is shown that genetic relatedness with the male partner, independently of postnatal association, is responsible for changes in nociceptive threshold. Conversely, previous association till weaning has no effect on pain sensitivity. These data suggest that endogenous opioids activity and social behavior represent indices of different processes: the recognition of related animals and the discrimination of familiar (and also usually related) subjects, respectively.