Hierarchy in the home cage affects behaviour and gene expression in group-housed C57BL/6 male mice

Social hierarchy differentially influences the anxiety-like behaviors and dendritic spine density in prefrontal cortex and limbic areas in male rats

Social hierarchy is a fundamental feature of social organization that can influence brain and emotional processing regarding social ranks. Several areas, including the medial prefrontal cortex (mPFC), the hippocampus, and the basolateral nucleus of the amygdala (BLA), are recognized to be involved in the regulation of emotional processing. However, its delicate structural correlates in brain regions are poorly understood. To address this issue, social hierarchy in home-caged sibling Wistar rats (three male rats/cage) was determined by employing a social confrontation tube test (postnatal weeks 9-12). Then, locomotor activity and anxiety-like behaviors were evaluated using an open-field test (OFT) and elevated plus-maze (EPM) at 13 weeks of age. The rapid Golgi impregnation method was conducted to quantify the spine density of the first secondary branch of the primary dendrite in 20 µm length. The results indicated that dominant rats had significantly higher anxiety-like behaviors compared to subordinates, as was evident by lower open-arm entries and time spent in the EPM and lower entries and time spent in the center of OFT. The spine density analysis revealed a significantly higher number of spines in subordinates compared to the dominant rats in dmPFC pyramidal neurons and the apical and basal dendrites of hippocampal CA1 pyramidal neurons. However, the spine density of pyramidal-like neurons in the BLA was higher in dominant rats. Our findings suggest that dominant social rank is associated with higher anxiety and differential density of the dendritic spine in the prefrontal cortex and limbic regions of the brain in male rats.

Association between social dominance hierarchy and PACAP expression in the extended amygdala, corticosterone, and behavior in C57BL/6 male mice

The natural alignment of animals into social dominance hierarchies produces adaptive, and potentially maladaptive, changes in the brain that influence health and behavior. Aggressive and submissive behaviors assumed by animals through dominance interactions engage stress-dependent neural and hormonal systems that have been shown to correspond with social rank. Here, we examined the association between social dominance hierarchy status established within cages of group-housed mice and the expression of the stress peptide PACAP in the bed nucleus of the stria terminalis (BNST) and central nucleus of the amygdala (CeA). We also examined the relationship between social dominance rank and blood corticosterone (CORT) levels, body weight, motor coordination (rotorod) and acoustic startle. Male C57BL/6 mice were ranked as either Dominant, Submissive, or Intermediate based on counts of aggressive/submissive encounters assessed at 12 weeks-old following a change in homecage conditions. PACAP expression was significantly higher in the BNST, but not the CeA, of Submissive mice compared to the other groups. CORT levels were lowest in Submissive mice and appeared to reflect a blunted response following events where dominance status is recapitulated. Together, these data reveal changes in specific neural/neuroendocrine systems that are predominant in animals of lowest social dominance rank, and implicate PACAP in brain adaptations that occur through the development of social dominance hierarchies.

The impact of cage dividers on mouse aggression, dominance and hormone levels

Home cage aggression in group-housed male mice is a major welfare concern and may compromise animal research. Conventional cages prevent flight or retreat from sight, increasing the risk that agonistic encounters will result in injury. Moreover, depending on social rank, mice vary in their phenotype, and these effects seem highly variable and dependent on the social context. Interventions that reduce aggression, therefore, may reduce not only injuries and stress, but also variability between cage mates. Here we housed male mice (Balb/c and SWISS, group sizes of three and five) with or without partial cage dividers for two months. Mice were inspected for wounding weekly and home cages were recorded during housing and after 6h isolation housing, to assess aggression and assign individual social ranks. Fecal boli and fur were collected to quantify steroid levels. We found no evidence that the provision of cage dividers improves the welfare of group housed male mice; The prevalence of injuries and steroid levels was similar between the two housing conditions and aggression was reduced only in Balb/c strain. However, mice housed with cage dividers developed less despotic hierarchies and had more stable social ranks. We also found a relationship between hormone levels and social rank depending on housing type. Therefore, addition of cage dividers may play a role in stabilizing social ranks and modulating the activation of hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes, thus reducing phenotypic variability between mice of different ranks.

Sex- and region-specific cortical and hippocampal whole genome transcriptome profiles from control and APP/PS1 Alzheimer's disease mice

A variety of Alzheimer's disease (AD) mouse models has been established and characterized within the last decades. To get an integrative view of the sophisticated etiopathogenesis of AD, whole genome transcriptome studies turned out to be indispensable. Here we carried out microarray data collection based on RNA extracted from the retrosplenial cortex and hippocampus of age-matched, eight months old male and female APP/PS1 AD mice and control animals to perform sex- and brain region specific analysis of transcriptome profiles. The results of our studies reveal novel, detailed insight into differentially expressed signature genes and related fold changes in the individual APP/PS1 subgroups. Gene ontology and Venn analysis unmasked that intersectional, upregulated genes were predominantly involved in, e.g., activation of microglial, astrocytic and neutrophilic cells, innate immune response/immune effector response, neuroinflammation, phagosome/proteasome activation, and synaptic transmission. The number of (intersectional) downregulated genes was substantially less in the different subgroups and related GO categories included, e.g., the synaptic vesicle docking/fusion machinery, synaptic transmission, rRNA processing, ubiquitination, proteasome degradation, histone modification and cellular senescence. Importantly, this is the first study to systematically unravel sex- and brain region-specific transcriptome fingerprints/signature genes in APP/PS1 mice. The latter will be of central relevance in future preclinical and clinical AD related studies, biomarker characterization and personalized medicinal approaches.

Differential expression of Hdac2 in male and female mice of differing social status

Mice naturally form social hierarchies, and their experiences as subordinate or dominant mice inform future behavioural strategies. To better understand the neural bases of social dominance, we investigated hippocampal gene and protein expression of histone deacetylase 2 (HDAC2), an epigenetic regulator that decreases expression of synaptic plasticity genes and reduces excitatory synaptic function. Hdac2 in hippocampus was associated with social status. The gene for a closely related histone deacetylase (Hdac1), and HDAC2 protein expression, were not associated with social rank in hippocampus. These findings suggest that Hdac2 expression in hippocampus is distinctly linked with social status.

Dopamine D2 receptor within the intermediate region of the lateral septum modulate social hierarchy in male mice

The dopamine (DA) system has long been involved in social hierarchies; however, the specific mechanisms have not been elucidated. The lateral septum (LS) is a limbic brain structure that regulates various emotional, motivational, and social behaviors. DA receptors are abundantly expressed in the LS, modulating its functions. In this study, we evaluated the functions of DA receptors within different subregions of the LS in social dominance using a confrontation tube test in male mice. The results showed that mice living in social groups formed linear dominance hierarchies after a few days of cohousing, and the subordinates showed increased anxiety. Fos expressions was elevated in the entire LS after a confrontation tube test in the subordinates. However, DA neurons were more activated in the dominates within the ventral tegmental area and the dorsal raphe nucleus. Quantitative real-time polymerase chain reaction results showed that D2 receptor (D2R) within the intermediate region of the LS (LSi) were elevated in the subordinate. In the following pharmacological studies, we found simultaneous D2R activation in the dominants and D2R inhibition in the subordinates switched the original dominant-subordinate relationship. The aforementioned results suggested that D2R within the LSi plays an important role in social dominance in male mice. These findings improve our understanding of the neural mechanisms underlying the social hierarchy, which is closely related to our social life and happiness.

Dopamine D2 receptors in the dorsomedial prefrontal cortex modulate social hierarchy in male mice

Social hierarchy greatly influences behavior and health. Both human and animal studies have signaled the medial prefrontal cortex (mPFC) as specifically related to social hierarchy. Dopamine D1 receptors (D1Rs) and D2 receptors (D2Rs) are abundantly expressed in the mPFC, modulating its functions. However, it is unclear how DR-expressing neurons in the mPFC regulate social hierarchy. Here, using a confrontation tube test, we found that most adult C57BL/6J male mice could establish a linear social rank after 1 week of cohabitation. Lower rank individuals showed social anxiety together with decreased serum testosterone levels. D2R expression was significantly downregulated in the dorsal part of mPFC (dmPFC) in lower rank individuals, whereas D1R expression showed no significant difference among the rank groups in the whole mPFC. Virus knockdown of D2Rs in the dmPFC led to mice being particularly prone to lose the contests in the confrontation tube test. Finally, simultaneous D2R activation in the subordinates and D2R inhibition in the dominants in a pair switched their dominant-subordinate relationship. The above results indicate that D2Rs in the dmPFC play an important role in social dominance. Our findings provide novel insights into the divergent functions of prefrontal D1Rs and D2Rs in social dominance, which may contribute to ameliorating social dysfunctions along with abnormal social hierarchy.

Function of gastrin-releasing peptide receptors in ocular itch transmission in the mouse trigeminal sensory system

The prevalence of allergic conjunctivitis in itchy eyes has increased constantly worldwide owing to environmental pollution. Currently, anti-allergic and antihistaminic eye drops are used; however, there are many unknown aspects about the neural circuits that transmit itchy eyes. We focused on the gastrin-releasing peptide (GRP) and GRP receptor (GRPR), which are reportedly involved in itch transmission in the spinal somatosensory system, to determine whether the GRP system is involved in itch neurotransmission of the eyes in the trigeminal sensory system. First, the instillation of itch mediators, such as histamine (His) and non-histaminergic itch mediator chloroquine (CQ), exhibited concentration-dependent high levels of eye scratching behavior, with a significant sex differences observed in the case of His. Histological analysis revealed that His and CQ significantly increased the neural activity of GRPR-expressing neurons in the caudal part of the spinal trigeminal nucleus of the medulla oblongata in GRPR transgenic mice. We administered a GRPR antagonist or bombesin-saporin to ablate GRPR-expressing neurons, followed by His or CQ instillation, and observed a decrease in CQ-induced eye-scratching behavior in the toxin experiments. Intracisternal administration of neuromedin C (NMC), a GRPR agonist, resulted in dose-dependent excessive facial scratching behavior, despite the absence of an itch stimulus on the face. To our knowledge, this is the first study to demonstrate that non-histaminergic itchy eyes were transmitted centrally via GRPR-expressing neurons in the trigeminal sensory system, and that NMC in the medulla oblongata evoked facial itching.

5-HT1A receptor in the central amygdala and 5-HT2A receptor in the basolateral amygdala are involved in social hierarchy in male mice

Most social animals self-organize into dominance hierarchies that strongly influence their behavior and health. The serotonin (5-HT) system is believed to play an important role in the formation of social hierarchy. 5-HT receptors are abundantly expressed in the amygdala, which is considered as the central node for the perception and learning of social hierarchy. In this study, we assessed the functions of various 5-HT receptor subtypes related to social rank determination in different subregions of the amygdala using the confrontation tube test in mice. We revealed that most adult C57BL/6 J male mice exhibited a linear social rank after a few days of cohousing. The tube test ranks were slightly related to anxiety-like behavioral performance. After the tube test, the amygdala and 5-HT neurons in the dorsal raphe nucleus were activated in lower-rank individuals. Quantitative real-time polymerase chain reaction analysis revealed that despite the high expression of 5-HT1A receptor mRNA in the central amygdala (CeA), 5-HT2A receptor mRNA expression was downregulated in the basolateral amygdala (BLA) in higher-rank individuals. The dominant-subordinate relationship between mouse pairs could be switched via pharmacological modulation of these receptors in CeA and BLA, suggesting that these expression changes are essential for establishing social ranks. Our findings provide novel insights into the divergent functions of 5-HT receptors in the amygdala related to social hierarchy, which is closely related to our health and welfare.

Endocannabinoid basis of personality-Insights from animal model of social behavior

Rationale: The endocannabinoid system is known to be involved in learning, memory, emotional processing and regulation of personality patterns. Here we assessed the endocannabinoid profile in the brains of mice with strong characteristics of social dominance and submissiveness. Methods: A lipidomics approach was employed to assess the endocannabinoidome in the brains of Dominant (Dom) and Submissive (Sub) mice. The endocannabinoid showing the greatest difference in concentration in the brain between the groups, docosatetraenoyl ethanolamine (DEA), was synthesized, and its effects on the physiological and behavioral responses of Dom and Sub mice were evaluated. mRNA expression of the endocannabinoid receptors and enzymes involved in PUFA biosynthesis was assessed using qRT-PCR. Results: Targeted LC/MS analysis revealed that long-chain polyunsaturated ethanolamides including arachidonoyl ethanolamide (AEA), DEA, docosatrienoyl ethanolamide (DTEA), eicosatrienoyl ethanolamide (ETEA), eicosapentaenoyl ethanolamide (EPEA) and docosahexaenoyl ethanolamide (DHEA) were higher in the Sub compared with the Dom mice. Untargeted LC/MS analysis showed that the parent fatty acids, docosatetraenoic (DA) and eicosapentaenoic (EPA), were higher in Sub vs. Dom. Gene expression analysis revealed increased mRNA expression of genes encoding the desaturase FADS2 and the elongase ELOVL5 in Sub mice compared with Dom mice. Acute DEA administration at the dose of 15 mg/kg produced antinociceptive and locomotion-inducing effects in Sub mice, but not in Dom mice. Subchronic treatment with DEA at the dose of 5 mg/kg augmented dominant behavior in wild-type ICR and Dom mice but not in Sub mice. Conclusion: This study suggests that the endocannabinoid system may play a role in the regulation of dominance and submissiveness, functional elements of social behavior and personality. While currently we have only scratched the surface, understanding the role of the endocannabinoid system in personality may help in revealing the mechanisms underlying the etiopathology of psychiatric disorders.

Minimal influence of estrous cycle on studies of female mouse behaviors

Introduction

Sex bias has been an issue in many biomedical fields, especially in neuroscience. In rodent research, many scientists only focused on male animals due to the belief that female estrous cycle gives rise to unacceptable, high levels of variance in the experiments. However, even though female sexual behaviors are well known to be regulated by estrous cycle, which effects on other non-sexual behaviors were not always consistent in previous reports. Recent reviews analyzing published literature even suggested that there is no evidence for larger variation in female than male in several phenotypes.

Methods

To further investigate the impact of estrous cycle on the variability of female behaviors, we conducted multiple behavioral assays, including the open field test, forced swimming test, and resident-intruder assay to assess anxiety-, depression-like behaviors, as well as social interaction respectively. We compared females in the estrus and diestrus stages across four different mouse strains: C57BL/6, BALB/c, C3H, and DBA/2.

Results

Our results found no significant difference in most behavioral parameters between females in these two stages. On the other hand, the differences in behaviors among certain strains are relatively consistent in both stages, suggesting a very minimal effect of estrous cycle for detecting the behavioral difference. Last, we compared the behavioral variation between male and female and found very similar variations in most behaviors between the two sexes.

Discussion

While our study successfully identified behavioral differences among strains and between the sexes, we did not find solid evidence to support the notion that female behaviors are influenced by the estrous cycle. Additionally, we observed similar levels of behavioral variability between males and females. Female mice, therefore, have no reason to be excluded in future behavioral research.

Social confrontation stress decreases hepatic fibroblast growth factor-21 expression in aged mice

We previously showed that social stress exposure in mature adult mice increased blood corticosterone concentrations at 2 days, disrupted hepatic lipid metabolism-related pathway at 30 days, and increased the risk of overweight with hepatic hypertrophy at 90 days. To further investigate the effects of aging on the physiological responses to social stress, we conducted a study using male BALB/c mice at the ages of 2 months (mature age), 14 months (middle age) and 26 months (old age), and exposed them to confrontation stress for 2 or 7 days. Blood corticosterone concentrations were increased at 2 days of stress, and then returned to baseline concentrations. This change was observed only at 2 months of age. We further examined the effect of aging on hepatic gene expression of fibroblast growth factor-21 (Fgf21) and found that its expression was significantly decreased after 7 days of stress at 14 months of age and after 2 days of stress at 26 months of age, indicating these decreasing effects became more pronounced with age. In conclusion, our study suggests that hepatic Fgf21 expression decrease under exposure to confrontation stress at middle or more age, indicating that stress response on Fgf21 related pathway might be more pronounced with age when exposed to stress.

Exogenous oxytocin microinjection into the nucleus accumbens shell attenuates social dominance in group-housed male mice

The nucleus accumbens (NAc), a part of the brain's limbic system, is involved in a variety of brain functions, including reward motivation and social hierarchy. Here, the study investigated the effect of intra-NAc different subregions microinjections of oxytocin on social hierarchy regulation. The hierarchical ranking of group-housed male mice in laboratory settings was determined through the tube test, and a new reliable and robust behavior assay-the mate competition test-was proposed. The mice were randomly divided into two groups, and the bilateral guide cannula was implanted into the shell and core of the NAc, respectively. After social dominance stabilized, changes in social hierarchy were determined through the tube test, warm spot, and mate competition tests. Intra-NAc shell microinjections of oxytocin (0.5 μg/site), but not the core (0.5 μg/site), significantly reduced the social dominance of mice. In addition, oxytocin microinjection into both the shell and core of the NAc significantly increased locomotor ability without affecting anxious behaviors. These findings are tremendously important in understanding the functions of the NAc subregions for social dominance and are more likely to indicate the potential of an oxytocin therapeutic strategy for psychiatric disorders and social impairments.

Impact of social dominance hierarchy on PACAP expression in the extended amygdala, corticosterone, and behavior in C57BL/6 male mice

The natural alignment of animals into social dominance hierarchies produces adaptive, and potentially maladaptive, changes in the brain that influence health and behavior. Aggressive and submissive behaviors assumed by animals through dominance interactions engage stress-dependent neural and hormonal systems that have been shown to correspond with social rank. Here, we examined the impact of social dominance hierarchies established within cages of group-housed laboratory mice on expression of the stress peptide pituitary adenylate cyclase-activating polypeptide (PACAP) in areas of the extended amygdala comprising the bed nucleus of the stria terminalis (BNST) and central nucleus of the amygdala (CeA). We also quantified the impact of dominance rank on corticosterone (CORT), body weight, and behavior including rotorod and acoustic startle response. Weight-matched male C57BL/6 mice, group-housed (4/cage) starting at 3 weeks of age, were ranked as either most-dominant (Dominant), least-dominant (Submissive) or in-between rank (Intermediate) based on counts of aggressive and submissive encounters assessed at 12 weeks-old following a change in homecage conditions. We found that PACAP expression was significantly higher in the BNST, but not the CeA, of Submissive mice compared to the other two groups. CORT levels were lowest in Submissive mice and appeared to reflect a blunted response following social dominance interactions. Body weight, motor coordination, and acoustic startle were not significantly different between the groups. Together, these data reveal changes in specific neural/neuroendocrine systems that are predominant in animals of lowest social dominance rank, and implicate PACAP in brain adaptations that occur through the development of social dominance hierarchies.

The interaction between social hierarchy and depression/anxiety: Involvement of glutamatergic pyramidal neurons in the medial prefrontal cortex (mPFC)

Social hierarchy greatly impacts physical and mental health, but the relationship between social hierarchy and depression/anxiety and the underlying neural mechanism remain unclear. The present study used the tube test to determine the social hierarchy status of mice and then performed several behavioral tests to evaluate depression-like and anxiety-like behaviors. Electrophysiological techniques were used to record the firing activities of glutamatergic pyramidal neurons and local field potentials in the medial prefrontal cortex (mPFC). The results suggested that the mice in each cage (4 per cage) established a stable social hierarchy after 2 weeks. Subordinate mice displayed significantly fewer pushing and advancing behaviors, and more retreat behaviors compared with dominant mice. Furthermore, subordinate mice had significantly more immobility durations in the TST, but significantly fewer distances, entries, and time into the center in the OFT, as well as significantly less percent of distances, entries, and time into the open arms in the EPMT, compared with dominant mice, which indicated that subordinate mice displayed depression- and anxiety-like behaviors. In addition, chronic restraint stress (CRS) significantly induced depression- and anxiety-like behaviors in mice and altered social dominance behaviors in the tube test. CRS mice displayed significantly fewer pushing and advancing behaviors, and more retreat behaviors compared with control mice. Furthermore, low social rank and CRS significantly decreased the firing of pyramidal neurons and γ-oscillation activity in the mPFC. Taken together, the present study revealed an inverse relationship between social hierarchy and depression/anxiety, and the neural basis underlying this association might be the excitability of pyramidal neurons and γ oscillation in the mPFC. These findings established an important foundation for a depression/anxiety model based on social hierarchy and provided a new avenue for the development of therapies for stress-related mood disorders.

Chronic exposure to dim light at night disrupts cell-mediated immune response and decreases longevity in aged female mice

Circadian rhythms are endogenous biological cycles that regulate physiology and behavior for optimal adaptive function and survival; they are synchronized to precisely 24 hours by daily light exposure. Disruption of the daily light-dark (LD) cycle by exposure to artificial light at night (ALAN) dysregulates core clock genes and biological function. Exposure to ALAN has been associated with increased health risks in humans, and elderly individuals are at elevated risk for poor outcome from disease and often experience elevated exposure to ALAN due to increased care requirements. The role of disrupted circadian rhythms in healthy, aged animals remains unspecified; thus, we hypothesized that disrupted circadian rhythms via chronic exposure to dim ALAN (dLAN) impair immune response and survival in aged mice. Twenty-month-old C57BL/6 male and female mice were exposed to 24 weeks of LD conditions or dLAN (5 lux); then, cell-mediated immune response was assessed using a delayed-type hypersensitivity test. Aged female mice exposed to dLAN displayed dysregulated hypersensitivity and inflammation as a measure of cell-mediated immune response and decreased lifespan compared to females housed in dark nights. Nighttime lighting did not affect cell-mediated immune response or lifespan in males but dysregulated body mass and increased adrenal mass after immune challenge after chronic exposure to dLAN. Together, these data indicate that chronic exposure to dLAN affects lifespan in aged females and suggest that females are more susceptible to the detrimental consequences of disrupted circadian rhythms.

Beneficial effects of prolonged 2-phenylethyl alcohol inhalation on chronic distress-induced anxio-depressive-like phenotype in female mice

Chronic distress-induced hypothalamic-pituitary-adrenal axis deregulations have been associated with the development of neuropsychiatric disorders such as anxiety and depression. Currently available drugs treating such pathological conditions have limited efficacy and diverse side effects, revealing the need of new safer strategies. Aromatic plant-based compounds are largely used in herbal medicine due to their therapeutic properties on mood, physiology, and general well-being. The purpose of this study was to investigate the effects of 2-phenylethyl alcohol (PEA), one of the pharmacologically active constituents of rose essential oil, on chronic corticosterone (CORT)-induced behavioral and neurobiological changes in female mice. Animals followed a prolonged PEA inhalation exposure (30 min per day) for 15 consecutive days prior to behavioral evaluation with open-field, forced swim and novelty-suppressed feeding tests. CORT treatment induced an anxio-depressive-like phenotype, evidenced by a reduced locomotor activity in the open-field, and an increased latency to feed in the novelty-suppressed feeding paradigms. To elucidate the neural correlates of our behavioral results, immunohistochemistry was further performed to provide a global map of neural activity based on cerebral cFos expression. The altered feeding behavior was accompanied by a significant decrease in the number of cFos-positive cells in the olfactory bulb, and altered functional brain connectivity as shown by cross-correlation-based network analysis. CORT-induced behavioral and neurobiological alterations were reversed by prolonged PEA inhalation, suggesting a therapeutic action that allows regulating the activity of neural circuits involved in sensory, emotional and feeding behaviors. These findings might contribute to better understand the therapeutic potential of PEA on anxio-depressive symptoms.

Social Relationship as a Factor for the Development of Stress Incubation in Adult Mice

While stress reactions can emerge long after the triggering event, it remains elusive how they emerge after a protracted, seemingly stress-free period during which stress incubates. Here, we study the behavioral development in mice isolated after observing an aggressive encounter inflicted upon their pair-housed partners. We developed a spatially resolved fine-scale behavioral analysis and applied it to standard behavioral tests. It reveals that the seemingly sudden behavioral changes developed gradually. These behavioral changes were not observed if the aggressive encounter happened to a stranger mouse, suggesting that social bonding is a prerequisite for stress incubation in this paradigm. This finding was corroborated by hemisphere-specific morphological changes in cortex regions centering at the anterior cingulate cortex, a cognitive and emotional center. Our non-invasive analytical methods to capture informative behavioral details may have applications beyond laboratory animals.

Potential cross-species correlations in social hierarchy and memory between mice and young children

Social hierarchy is associated with various phenotypes. Although memory is known to be important for hierarchy formation, the difference in memory abilities between dominant and subordinate individuals remains unclear. In this study, we examined memory performance in mice with different social ranks and found better memory abilities in dominant mice, along with greater long-term potentiation and higher memory-related gene expression in the hippocampus. Daily injection of memory-improving drugs could also enhance dominance. To validate this correlation across species, through inventory, behavioral and event-related potential studies, we identified better memory abilities in preschool children with higher social dominance. Better memory potentially helped children process dominance facial cues and learn social strategies to acquire higher positions. Our study shows a remarkable similarity between humans and mice in the association between memory and social hierarchy and provides valuable insight into social interactions in young animals, with potential implications for preschool education.

Memory performance and hippocampal memory-related gene expression are shown to both be increased in more dominant mice, with memory-improving drugs enhancing dominant behaviour. The data also suggests that children with better memory can recognise dominance more easily, demonstrating a potential cross-species correlation in the association between memory and social hierarchy.

Characterizing the behavioral and neuroendocrine features of susceptibility and resilience to social stress

Evaluating and coping with stressful social events as they unfold is a critical strategy in overcoming them without long-lasting detrimental effects. Individuals display a wide range of responses to stress, which can manifest in a variety of outcomes for the brain as well as subsequent behavior. Chronic Social Defeat Stress (CSDS) in mice has been widely used to model individual variation following a social stressor. Following a course of repeated intermittent psychological and physical stress, mice diverge into separate populations of social reactivity: resilient (socially interactive) and susceptible (socially avoidant) animals. A rich body of work reveals distinct neurobiological and behavioral consequences of this experience that map onto the resilient and susceptible groups. However, the range of factors that emerge over the course of defeat have not been fully described. Therefore, in the current study, we focused on characterizing behavioral, physiological, and neuroendocrine profiles of mice in three separate phases: before, during, and following CSDS. We found that following CSDS, traditional read-outs of anxiety-like and depression-like behaviors do not map on to the resilient and susceptible groups. By contrast, behavioral coping strategies used during the initial social stress encounter better predict which mice will eventually become resilient or susceptible. In particular, mice that will emerge as susceptible display greater escape behavior on Day 1 of social defeat than those that will emerge as resilient, indicating early differences in coping mechanisms used between the two groups. We further show that the social avoidance phenotype in susceptible mice is specific to the aggressor strain and does not generalize to conspecifics or other strains, indicating that there may be features of threat discrimination that are specific to the susceptible mice. Our findings suggest that there are costs and benefits to both the resilient and susceptible outcomes, reflected in their ability to cope and adapt to the social stressor.

Spatial working memory is disparately interrelated with social status through different developmental stages in rats

Social life necessitates cognitive competence to meet the dynamic demands of social development. The formation of dominance hierarchy is a general phenomenon in social groups. As an essential element of executive and cognitive function, working memory could influence and be influenced by social status in a dominance hierarchy. However, the direction and degree of the association between them through different developmental stages remain unclear. To address this issue and clarify the "cause or consequence" problem, we investigated the spatial working memory performance in a Y-maze and Morris water maze in home-caged sibling Wistar rats (N = 26 cages, three rats/cage) through three stages of their life: before (week 7), during (week 10), and after (week 20) assumed timings of the social dominance hierarchy formation (SDHF). We used the social dominance tube test during the assumed time of hierarchy formation (weeks 9-11) to measure the relative dominance status in each cage. Here, we found that higher working memory index before SDHF could be predictive of later acquisition of higher social status. Working memory performance declined for all animals during SDHF, in which agonistic conflicts are increased. However, living within an established hierarchical social network for several weeks deteriorated the working memory performance of dominant and middle-ranked animals, while the performance of subordinates improved and got significantly better than higher-ranked animals. In conclusion, while working memory and social status were correlated positively before dominance hierarchy formation, there was a trade-off between them after the formation of it. In contrast to the common view, these results highlight the adverse effect of higher social status on cognitive behavior.

Sleep restriction prior to antigen exposure does not alter the T cell receptor repertoire but impairs germinal center formation during a T cell-dependent B cell response in murine spleen

It is well known that sleep promotes immune functions. In line with this, a variety of studies in animal models and humans have shown that sleep restriction following an antigen challenge dampens the immune response on several levels which leads to e.g. worsening of disease outcome and reduction of vaccination efficiency, respectively. However, the inverse scenario with sleep restriction preceding an antigen challenge is only investigated in a few animal models where it has been shown to reduce antigen uptake and presentation as well as pathogen clearance and survival rates. Here, we use injection of sheep red blood cells to investigate the yet unknown effect on a T cell-dependent B cell response in a well-established mouse model. We found that 6 ​h of sleep restriction prior to the antigen challenge does not impact the T cell reaction including the T cell receptor repertoire but dampens the development of germinal centers which correlates with reduced antigen-specific antibody titer indicating an impaired B cell response. These changes concerned a functionally more relevant level than those found in the same experimental model with the inverse scenario when sleep restriction followed the antigen challenge. Taken together, our findings showed that the outcome of the T cell-dependent B cell response is indeed impacted by sleep restriction prior to the antigen challenge which highlights the clinical significance of this scenario and the need for further investigations in humans, for example concerning the effect of sleep restriction preceding a vaccination.

Individual history of winning and hierarchy landscape influence stress susceptibility in mice

Social hierarchy formation is strongly evolutionarily conserved. Across species, rank within social hierarchy has large effects on health and behavior. To investigate the relationship between social rank and stress susceptibility, we exposed ranked male and female mice to social and non-social stressors and manipulated social hierarchy position. We found that rank predicts same sex social stress outcomes: dominance in males and females confers resilience while subordination confers susceptibility. Pre-existing rank does not predict non-social stress outcomes in females and weakly does so in males, but rank emerging under stress conditions reveals social interaction deficits in male and female subordinates. Both history of winning and rank of cage mates affect stress susceptibility in males: rising to the top rank through high mobility confers resilience and mice that lose dominance lose stress resilience, although gaining dominance over a subordinate animal does not confer resilience. Overall, we have demonstrated a relationship between social status and stress susceptibility, particularly when taking into account individual history of winning and the overall hierarchy landscape in male and female mice.

N6 -Methyladenosine Modification in Chronic Stress Response Due to Social Hierarchy Positioning of Mice

Appropriately responding to stressful events is essential for maintaining health and well-being of any organism. Concerning social stress, the response is not always as straightforward as reacting to physical stressors, e.g., extreme heat, and thus has to be balanced subtly. Particularly, regulatory mechanisms contributing to gaining resilience in the face of mild social stress are not fully deciphered yet. We employed an intrinsic social hierarchy stress paradigm in mice of both sexes to identify critical factors for potential coping strategies. While global transcriptomic changes could not be observed in male mice, several genes previously reported to be involved in synaptic plasticity, learning, and anxiety-like behavior were differentially regulated in female mice. Moreover, changes in N⁶-methyladenosine (m⁶A)-modification of mRNA occurred associated with corticosterone level in both sexes with, e.g., increased global amount in submissive female mice. In accordance with this, METTL14 and WTAP, subunits of the methyltransferase complex, showed elevated levels in submissive female mice. N⁶-adenosyl-methylation is the most prominent type of mRNA methylation and plays a crucial role in processes such as metabolism, but also response to physical stress. Our findings underpin its essential role by also providing a link to social stress evoked by hierarchy building within same-sex groups. As recently, search for small molecule modifiers for the respective class of RNA modifying enzymes has started, this might even lead to new therapeutic approaches against stress disorders.

Behavior Testing in Rodents: Highlighting Potential Confounds Affecting Variability and Reproducibility

Rodent models of brain disorders including neurodevelopmental, neuropsychiatric, and neurodegenerative diseases are essential for increasing our understanding of underlying pathology and for preclinical testing of potential treatments. Some of the most important outcome measures in such studies are behavioral. Unfortunately, reports from different labs are often conflicting, and preclinical studies in rodent models are not often corroborated in human trials. There are many well-established tests for assessing various behavioral readouts, but subtle aspects can influence measurements. Features such as housing conditions, conditions of testing, and the sex and strain of the animals can all have effects on tests of behavior. In the conduct of behavior testing, it is important to keep these features in mind to ensure the reliability and reproducibility of results. In this review, we highlight factors that we and others have encountered that can influence behavioral measures. Our goal is to increase awareness of factors that can affect behavior in rodents and to emphasize the need for detailed reporting of methods.

Evolution of Boldness and Exploratory Behavior in Giant Mice from Gough Island

Island populations are hallmarks of extreme phenotypic evolution. Radical changes in resource availability and predation risk accompanying island colonization drive changes in behavior, which Darwin likened to tameness in domesticated animals. Although many examples of animal boldness are found on islands, the heritability of observed behaviors, a requirement for evolution, remains largely unknown. To fill this gap, we profiled anxiety and exploration in island and mainland inbred strains of house mice raised in a common laboratory environment. The island strain was descended from mice on Gough Island, the largest wild house mice on record. Experiments utilizing open environments across two ages showed that Gough Island mice are bolder and more exploratory, even when a shelter is provided. Concurrently, Gough Island mice retain an avoidance response to predator urine. F1 offspring from crosses between these two strains behave more similarly to the mainland strain for most traits, suggesting recessive mutations contributed to behavioral evolution on the island. Our results provide a rare example of novel, inherited behaviors in an island population and demonstrate that behavioral evolution can be specific to different forms of perceived danger. Our discoveries pave the way for a genetic understanding of how island populations evolve unusual behaviors.

Major oscillations in spontaneous home-cage activity in C57BL/6 mice housed under constant conditions

The mouse is the most important mammalian model in life science research and the behavior of the mouse is a key read-out of experimental interventions and genetic manipulations. To serve this purpose a solid understanding of the mouse normal behavior is a prerequisite. Using 14-19 months of cumulative 24/7 home-cage activity recorded with a non-intrusive technique, evidence is here provided for a highly significant circannual oscillation in spontaneous activity (1-2 SD of the mean, on average 65% higher during peak of highs than lows; P = 7E-50) of male and female C57BL/6 mice held under constant conditions. The periodicity of this hitherto not recognized oscillation is in the range of 2-4 months (average estimate was 97 days across cohorts of cages). It off-sets responses to environmental stimuli and co-varies with the feeding behavior but does not significantly alter the preference for being active during the dark hours. The absence of coordination of this rhythmicity between cages with mice or seasons of the year suggest that the oscillation of physical activity is generated by a free-running intrinsic oscillator devoid of external timer. Due to the magnitude of this rhythmic variation it may be a serious confounder in experiments on mice if left unrecognized.

A Systematic Review and Meta-Analysis of the Relationship Between Social Dominance Status and Common Behavioral Phenotypes in Male Laboratory Mice

Background: Social dominance status (e.g., dominant or subordinate) is often associated with individual differences in behavior and physiology but is largely neglected in experimental designs and statistical analysis plans in biomedical animal research. In fact, the extent to which social dominance status affects common experimental outcomes is virtually unknown. Given the pervasive use of laboratory mice and culminating evidence of issues with reproducibility, understanding the role of social dominance status on common behavioral measures used in research may be of paramount importance.

Methods: To determine whether social dominance status—one facet of the social environment—contributes in a systematic way to standard measures of behavior in biomedical science, we conducted a systematic review of the existing literature searching the databases of PubMed, Embase, and Web of Science. Experiments were divided into several domains of behavior: exploration, anxiety, learned helplessness, cognition, social, and sensory behavior. Meta-analyses between experiments were conducted for the open field, elevated plus-maze, and Porsolt forced swim test.

Results: Of the 696 publications identified, a total of 55 experiments from 20 published studies met our pre-specified criteria. Study characteristics and reported results were highly heterogeneous across studies. A systematic review and meta-analyses, where possible, with these studies revealed little evidence for systematic phenotypic differences between dominant and subordinate male mice.

Conclusion: This finding contradicts the notion that social dominance status impacts behavior in significant ways, although the lack of an observed relationship may be attributable to study heterogeneity concerning strain, group-size, age, housing and husbandry conditions, and dominance assessment method. Therefore, further research considering these secondary sources of variation may be necessary to determine if social dominance generally impacts treatment effects in substantive ways.

Biological sex, not reproductive cycle, influences peripheral blood immune cell prevalence in mice

KEY POINTS

Traditionally the female sex, compared with the male sex, has been perceived as having greater variability in many physiological traits, including within the immune system. We investigated effects of biological sex and the female reproductive cycle on numbers of circulating leukocytes in C57BL/6J mice. We show that biological sex, but not female reproductive cyclicity, has a significant effect on peripheral blood immune cell prevalence and variability, and that sex differences were not consistent amongst common inbred laboratory mouse strains. We found that male C57BL/6J mice, compared with female mice, have greater variability in peripheral blood immunophenotype, and that this was influenced by body weight. We created summary tables for researchers to facilitate experiment planning and sample size calculations for peripheral immune cells that consider the effects of biological sex.

ABSTRACT

Immunophenotyping (i.e. quantifying the number and types of circulating leukocytes) is used to characterize immune changes during health and disease, and in response to pharmacological and other interventions. Despite the importance of biological sex in immune function, there is considerable uncertainty amongst researchers as to the extent to which biological sex or the female reproductive cycle influence blood immunophenotype. We quantified circulating leukocytes by multicolour flow cytometry in young C57BL/6J mice and assessed the effects of the reproductive cycle, biological sex, and other experimental and biological factors on data variability. We found that there are no significant effects of the female reproductive cycle on the prevalence of peripheral blood B cells, NK cells, CD4⁺ T cells, CD8⁺ T cells, monocytes, or neutrophils. Immunophenotype composition and variability do not significantly change between stages of the female reproductive cycle. There are, however, sex-specific differences in immune cell prevalence, with fewer monocytes, neutrophils, and NK cells in female mice. Surprisingly, immunophenotype is more variable in male mice, and weight is a significant contributing factor. We provide tools for researchers to perform a priori sample size calculations for two-group and factorial analyses. We show that immunophenotype varies between inbred mouse strains, and that using equal sample sizes of male and female mice is not always appropriate for within-sex evaluations of immune cell populations in peripheral blood.

Collective Housing of Mice of Different Age Groups before Maturity Affects Mouse Behavior

Background

Although population housing is recommended by many animal management and ethical guidelines, the effect of collective housing of mice of different age groups on mouse behavior has not been clarified. Since the development of the central nervous system continues to occur before sexual maturation, the stress of social ranking formation among male individuals in mixed housing conditions can affect postmaturation behavior. To assess these effects, sexually immature mice of different ages were housed in the same cage and a series of behavioral tests were performed after maturation.

Results

The findings for three groups of mice—junior mice housed with older mice, senior mice housed with younger mice, and mice housed with other mice of the same age—were compared. Junior mice showed higher body weight and activity as well as lower grip strength and anxiety-like behaviors than other mice. In contrast, senior mice showed lower body temperature and increased aggression, antinociceptive effect, and home-cage activity in the dark period in comparison with other mice.

Conclusions

Thus, combined housing of immature mice of different age groups affects mouse behavior after maturation. Appropriate prematuration housing conditions are crucial to eliminate the uncontrollable bias caused by age-related social stratification.

What it takes to be at the top: The interrelationship between chronic social stress and social dominance

INTRODUCTION

Dominance hierarchies of social animal groups are very sensitive to stress. Stress experienced prior to social interactions between conspecifics may be a determinant of their future social dynamics. Additionally, long-term occupancy of a specific hierarchical rank can have psychophysiological effects which increase vulnerability to future stressors.

METHODS

We aimed to delineate differential effects of stress acting before or after hierarchy formation. We studied whether exposure to the chronic social defeat stress (CSDS) paradigm before a two-week-long hierarchy formation affected the attainment of a dominant status using the social confrontation tube test (TT). These animals were singly housed for at least one week before CSDS to decrease confounding effects of prior hierarchy experience. Additionally, we investigated whether social rank predicted vulnerability to CSDS, measured by a social interaction test.

RESULTS

In TT, mice termed as dominant (high rank) win the majority of social confrontations, while the subordinates (low rank) lose more often. Within newly established hierarchies of stress-naïve mice, the subordinate, but not dominant, mice exhibited significantly greater avoidance of novel social targets. However, following exposure to CSDS, both lowest- and highest-ranked mice exhibited susceptibility to stress as measured by decreased interactions with a novel social target. In contrast, after CSDS, both stress-susceptible (socially avoidant) and stress-resilient (social) mice were able to attain dominant ranks in newly established hierarchies.

CONCLUSION

These results suggest that the response to CSDS did not determine social rank in new cohorts, but low-status mice in newly established groups exhibited lower sociability to novel social targets. Interestingly, exposure of a hierarchical social group to chronic social stress led to stress susceptibility in both high- and low-status mice as measured by social interaction.

Social dominance mediates behavioral adaptation to chronic stress in a sex-specific manner

Sex differences and social context independently contribute to the development of stress-related disorders. However, less is known about how their interplay might influence behavior and physiology. Here we focused on social hierarchy status, a major component of the social environment in mice, and whether it influences behavioral adaptation to chronic stress in a sex-specific manner. We used a high-throughput automated behavioral monitoring system to assess social dominance in same-sex, group-living mice. We found that position in the social hierarchy at baseline was a significant predictor of multiple behavioral outcomes following exposure to chronic stress. Crucially, this association carried opposite consequences for the two sexes. This work demonstrates the importance of recognizing the interplay between sex and social factors and enhances our understating of how individual differences shape the stress response.

Most people experience chronic stress at some point in their life, which may increase their chances of developing depression or anxiety. There is evidence that chronic stress may more negatively impact the well-being of women, placing them as higher risk of developing these mental health conditions. The biological factors that underlie these differences are not well understood, which leaves clinicians and scientists struggling to develop and provide effective treatments.

The social environment has a powerful influence on how people experience and cope with stress. For example, a person’s social and socioeconomic status can change their perception of and reaction to everyday stress. Researchers have found differences in how men and women relate to their social standing. One way for scientists to learn more about the biological processes involved is to study the effect of social standing and chronic stress in male and female mice.

Now, Karamihalev, Brivio et al. show that social status influences the behavior of stressed mice in a sex-specific way. In the experiments, an automated observation system documented the behavior of mice living in all female or male groups. Karamihalev, Brivio et al. determined where each animal fit into the social structure of their group. Then, they exposed some groups of mice to mild chronic stress and compared their behaviors to groups of mice housed in normal conditions. They found that both the sex and social status of each played a role in how they responded to stress. For example, subordinate males displayed more anxious behavior under stressful circumstances, while dominant females acted bolder and less anxious.

More studies in mice are needed to understand the biological basis of these social- and sex-based differences in stress response. Learning more may help scientists understand why some individuals are more susceptible to the effects of stress and lead to the development of personalized prevention or treatment strategies for anxiety and depression.

Stearidonic-Enriched Soybean Oil Modulates Obesity, Glucose Metabolism, and Fatty Acid Profiles Independently of Akkermansia muciniphila

SCOPE

Previous studies have suggested that diets rich in omega-3 and low in omega-6 long-chain polyunsaturated fatty acids (PUFAs) can limit the development of metabolic syndrome (MetS). Transgenic soybeans yielding oils enriched for omega-3 PUFAs represent a new and readily-available option for incorporating omega-3 PUFAs into diets to provide health benefits.

METHODS AND RESULTS

Transgenic soybean oils, enriched for either stearidonic acid (SDA) or eicosapentaenoic acid (EPA), are incorporated into diets to test their effects on limiting the development of MetS in a mouse model of diet-induced obesity. Supplementation with SDA- but not EPA-enriched oils improved features of MetS compared to feeding a control wild-type oil. Because previous studies have linked the gut microorganism Akkermansia muciniphila to the metabolic effects of feeding omega-3 PUFAs, the causal contribution of A. muciniphila to mediating the metabolic benefits provided by SDA-enriched diets is investigated. Although A. muciniphila is not required for SDA-induced metabolic improvements, this microorganism does modulate levels of saturated and mono-unsaturated fatty acids in host adipose tissues.

CONCLUSION

Together, these findings support the utilization of SDA-enriched diets to modulate weight gain, glucose metabolism, and fatty acid profiles of liver and adipose tissue.

What it takes to be at the top: The interrelationship between chronic social stress and social dominance.. [DOI: 10.1101/2020.06.29.177410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Dominance hierarchies of social animal groups are influenced by complex factors such as stress. Stress experienced by an animal prior to social interactions with a conspecific may be a determinant of their future social dynamics. Additionally, long-term occupancy of a specific hierarchical rank can have psychophysiological effects, leading to vulnerability to future stress.

The current study aimed to delineate differential effects of stress acting before or after hierarchy formation. Using the chronic social defeat stress (CSDS) paradigm we performed behavioural investigations to determine whether exposure to CSDS before hierarchy formation predicted the new dominance status. Moreover, in another study we investigated whether social rank predicted stress vulnerability.

We found that CSDS did not impede the establishment of dominance in new hierarchies as both stress-susceptible (socially avoidant) and –resilient (social) mice were able to attain dominant ranks. In contrast, within newly established hierarchies of stress-naïve mice, the subordinate, but not dominant, mice exhibit significantly greater avoidance of novel social targets. However, following exposure to CSDS, both lowest- and highest-ranked mice exhibit strong susceptibility to stress as measured by decreased interactions with a novel social target.

These results suggest that the response to chronic social stress did not determine social rank in new cohorts, but low-status mice in newly established groups exhibited lower sociability to novel social targets. Interestingly, exposure of a hierarchical social group to chronic social stress led to stress-susceptibility in both high- and low-status mice as measured by social interaction.

Highlights

Stress susceptibility to chronic social defeat did not impede the establishment of dominance in new hierarchies.

Subordinate mice exhibit reduced social preference after hierarchy formation.

Following chronic social defeat stress, both subordinate and dominant mice exhibit susceptible-like reduction in social interaction, but dominant mice exhibit the greater decrease in social preference as compared to baseline.

A High-Fat Diet Exacerbates the Course of Experimental Trypanosoma cruzi Infection That Can Be Mitigated by Treatment with Simvastatin

The protozoan Trypanosoma cruzi is responsible for triggering a damage immune response in the host cardiovascular system. This parasite has a high affinity for host lipoproteins and uses the low-density lipoprotein (LDL) receptor for its invasion. Assuming that the presence of LDL cholesterol in tissues could facilitate T. cruzi proliferation, dietary composition may affect the parasite-host relationship. Therefore, the aim of this study was to evaluate myocarditis in T. cruzi-infected C57BL/6 mice-acute phase-fed a high-fat diet and treated with simvastatin, a lipid-lowering medication. Animals (n = 10) were infected with 5 × 10³ cells of the VL-10 strain of T. cruzi and treated or untreated daily with 20 mg/kg simvastatin, starting 24 h after infection and fed with a normolipidic or high-fat diet. Also, uninfected mice, treated or not with simvastatin and fed with normolipidic or high-fat diet, were evaluated as control groups. Analyses to measure the production of chemokine (C-C motif) ligand 2 (CCL2), interferon- (IFN-) γ, interleukin- (IL-) 10, and tumor necrosis factor (TNF); total hepatic lipid dosage; cholesterol; and fractions, as well as histopathological analysis, were performed on day 30 using cardiac and fat tissues. Our results showed that the high-fat diet increased (i) parasite replication, (ii) fat accumulation in the liver, (iii) total cholesterol and LDL levels, and (iv) the host inflammatory state through the production of the cytokine TNF. However, simvastatin only reduced the production of CCL2 but not that of other inflammatory mediators or biochemical parameters. Together, our data suggest that the high-fat diet may have worsened the biochemical parameters of the uninfected and T. cruzi-infected animals, as well as favored the survival of circulating parasites.

Effects of repetitive gentle handling of male C57BL/6NCrl mice on comparative behavioural test results

Mice are the most commonly used laboratory animals for studying diseases, behaviour, and pharmacology. Behavioural experiment battery aids in evaluating abnormal behaviour in mice. During behavioural experiments, mice frequently experience human contact. However, the effects of repeated handling on mice behaviour remains unclear. To minimise mice stress, methods of moving mice using transparent tunnels or cups have been recommended but are impractical in behavioural tests. To investigate these effects, we used a behavioural test battery to assess differences between mice accustomed to the experimenter’s handling versus control mice. Repeatedly handled mice gained slightly more weight than control mice. In behavioural tests, repeatedly handled mice showed improved spatial cognition in the Y-maze test and reduced anxiety-like behaviour in the elevated plus-maze test. However, there was no change in anxiety-like behaviour in the light/dark transition test or open-field test. Grip strength, rotarod, sociability, tail suspension, Porsolt forced swim, and passive avoidance tests revealed no significant differences between repeatedly handled and control mice. Our findings demonstrated that mice repeatedly handled by the experimenter before behavioural tests showed reduced anxiety about high altitudes and improved spatial cognition, suggesting that repeated contact can affect the results of some behavioural tests.

MouseBytes, an open-access high-throughput pipeline and database for rodent touchscreen-based cognitive assessment

Open Science has changed research by making data accessible and shareable, contributing to replicability to accelerate and disseminate knowledge. However, for rodent cognitive studies the availability of tools to share and disseminate data is scarce. Automated touchscreen-based tests enable systematic cognitive assessment with easily standardised outputs that can facilitate data dissemination. Here we present an integration of touchscreen cognitive testing with an open-access database public repository (mousebytes.ca), as well as a Web platform for knowledge dissemination (https://touchscreencognition.org). We complement these resources with the largest dataset of age-dependent high-level cognitive assessment of mouse models of Alzheimer’s disease, expanding knowledge of affected cognitive domains from male and female mice of three strains. We envision that these new platforms will enhance sharing of protocols, data availability and transparency, allowing meta-analysis and reuse of mouse cognitive data to increase the replicability/reproducibility of datasets.

Male C57BL6/N and C57BL6/J Mice Respond Differently to Constant Light and Running-Wheel Access

Previous studies have shown that exposure to circadian disruption produces negative effects on overall health and behavior. More recent studies illustrate that strain differences in the behavioral and physiological responses to circadian disruption exist, even if the strains have similar genetic backgrounds. As such, we investigated the effects of constant room-level light (LL) with running-wheel access on the behavior and physiology of male C57BL6/J from Jackson Laboratories and C57BL6/N from Charles River Laboratories mice. Mice were exposed to either a 12:12 light-dark (LD) cycle or LL and given either a standard home cage or a cage with a running-wheel. Following 6 weeks of LD or LL, their response to behavioral assays (open-field, light-dark box, novel object) and measures of metabolism were observed. Under standard LD, C57BL6/J mice exhibited increased locomotor activity and reduced exploratory behavior compared to C57BL6/N mice. In LL, C57BL6/J mice had greater period lengthening and increased anxiety, while C57BL6/N mice exhibited increased weight gain and no change in exploratory behavior. C57BL6/J mice also decreased exploration with running-wheel access while C57BL6/N mice did not. These results further demonstrate that C57BL/6 substrains exhibit different behavioral and physiological responses to circadian disruption and wheel-running access.

Feeding Behavior of Mice under Different Food Allocation Regimens

Social interaction, a basic survival strategy for many animal species, helps maintain a social environment that has limited conflict. Social dominance has a dramatic effect on motivation. Recent evidence suggests that some primate and nonprimate species display aversive behavior toward food allocation regimens that differ from their peers. Thus, we examined the behaviors displayed by mice under different food allocation regimens. We analyzed changes in food intake using several parameters. In the same food condition, the mice received the same food; in the quality different condition, the mice received different foods; in the quantity different condition, one mouse did not receive food; and in the no food condition, none of the mice received food. To test differences based on food quality, one mouse received normal solid food as a less preferred reward, and the other received chocolate chips as a high-level reward. No behavioral change was observed in comparison to the same food condition. To test differences based on food quantity, one mouse received chocolate chips while the other received nothing. Mice who received nothing spent more time on the other side of the reward throughout the experiment. Interestingly, highly rewarded mice required more time to consume the chocolate chips. Thus, under different food allocation regimens, mice changed their behavior by being more hesitant. Moreover, mice alter food intake behavior according to the social environment. The findings help elucidate potential evolutionary aspects that help maintain social cohesion while providing insights into potential mechanisms underlying socially anxious behavior.

Social status and modern-type depression: A review

BACKGROUNDS

Social hierarchy is one of the most influential social structures employed by social species. While dominants in such hierarchies can preferentially access rich resources, subordinates are forced into lower social statuses and lifestyles with inferior resources. Previous studies have indicated that the social rank regulates social behaviors and emotion in a variety of species, whereby individual organisms live within the framework of their ranks. However, in human societies, people, particularly young men, who cannot accept their own social status may show social withdrawal behaviors such as hikikomori to avoid confronting their circumstances.

METHODS

This article reviews the neural mechanisms underlying social status identified in animal studies with rodents and primates, and assesses how social rank affects animal's social behaviors and emotion which may be relevant to modern type depression.

RESULTS

Several brain regions such as medial prefrontal cortex are implicated in the formation of animal's social status, which leads to the differences in vulnerability and resilience to social stress.

CONCLUSION

On the basis of these findings, we propose that physical interventions such as voluntary exercise, diet, transcranial direct current stimulation, and psychotherapy, rather than psychotropic drugs, may be useful therapeutic approaches for modern type depression, which is a typical example of social status conflict and a phenotype of adjustment disorder to the traditional hierarchical social order.

Sex-Dependent Changes in miRNA Expression in the Bed Nucleus of the Stria Terminalis Following Stress

Anxiety disorders disproportionately affect women compared to men, which may arise from sex differences in stress responses. MiRNAs are small non-coding RNAs known to regulate gene expression through actions on mRNAs. MiRNAs are regulated, in part, by factors such as stress and gonadal sex, and they have been implicated in the pathophysiology of multiple psychiatric disorders. Here, we assessed putative sex differences in miRNA expression in the bed nucleus of the stria terminalis (BNST) - a sexually dimorphic brain region implicated in anxiety - of adult male and female rats that had been exposed to social isolation (SI) stress throughout adolescence. To assess the translational utility of our results, we assessed if childhood trauma in humans resulted in changes in blood miRNA expression that are similar to those observed in rats. Male and female Sprague-Dawley rats underwent SI during adolescence or remained group housed (GH) and were tested for anxiety-like behavior in the elevated plus maze as adults. Small RNA sequencing was performed on tissue extracted from the BNST. Furthermore, we re-analyzed an already available small RNA sequencing data set from the Grady Trauma Project (GTP) from men and women to identify circulating miRNAs that are associated with childhood trauma exposure. Our results indicated that there were greater anxiogenic-like effects and changes in BNST miRNA expression in SI versus GH females compared to SI versus GH males. In addition, we found nine miRNAs that were regulated in both the BNST from SI compared to GH rats and in blood samples from humans exposed to childhood trauma. These studies emphasize the utility of rodent models in studying neurobiological mechanisms underlying psychiatric disorders and suggest that rodent models could be used to identify novel sex-specific pharmacotherapies for anxiety disorders.

Social dominance hierarchy type and rank contribute to phenotypic variation within cages of laboratory mice

A tacit assumption in laboratory animal research is that animals housed within the same cage or pen are phenotypically more similar than animals from different cages or pens, due to their shared housing environment. This assumption drives experimental design, randomization schemes, and statistical analysis plans, while neglecting social context. Here, we examined whether a domain of social context-social dominance-accounted for more phenotypic variation in mice than cage-identity. First, we determined that cages of mice could be categorized into one of three dominance hierarchies with varying degrees of dominance behavior between cage-mates, and low levels of agonistic behavior in the home-cage. Most groups formed dynamic hierarchies with unclear ranks, contrasting with recent accounts of stable transitive hierarchies in groups of mice. Next, we measured some phenotypic traits, and found that social dominance (i.e. dominance hierarchy type and degree of dominance behavior) consistently accounted for some phenotypic variation in all outcome measures, while cage-identity accounted for phenotypic variation in some measures but virtually no variation in others. These findings highlight the importance of considering biologically relevant factors, such as social dominance, in experimental designs and statistical plans.

Sex differences in fear extinction

Despite the exponential increase in fear research during the last years, few studies have included female subjects in their design. The need to include females arises from the knowledge gap of mechanistic processes underlying the behavioral and neural differences observed in fear extinction. Moreover, the exact contribution of sex and hormones in relation to learning and behavior is still largely unknown. Insights from this field could be beneficial as fear-related disorders are twice as prevalent in women compared to men. Here, we review an up-to-date summary of animal and human studies in adulthood that report sex differences in fear extinction from a structural and functional approach. Furthermore, we describe how these factors could contribute to the observed sex differences in fear extinction during normal and pathological conditions.

Social Interaction Test in Home Cage as a Novel and Ethological Measure of Social Behavior in Mice

Sociability is the disposition to interact with one another. Rodents have a rich repertoire of social behaviors and demonstrate strong sociability. Various methods have been established to measure the sociability of rodents in simple and direct ways, which includes reciprocal social interaction, juvenile social play, and three-chamber social tests. There are possible confounding factors while performing some of these tasks, such as aggression, avoidance of interaction by the stimulus mouse, exposure to a new environment, and lengthy procedures. The present study devised a method to complement these shortcomings and measure sociability as a group in the home cage setting, which prevents group-housed mice from isolation or exposure to a new environment. The home cage social test can allow high-throughput screening of social behaviors in a short amount of time. We developed two types of home cage setup: a home cage social target interaction test that measures sociability by putting the wire cage in the center area of the cage and a home cage two-choice sociability and social preference test that measures both sociability or social preference by putting cage racks at opposite sides of the cage. Interestingly, our results showed that the two types of home cage setup that we used in this study can extract abnormal social behaviors in various animal models, similar to the three-chamber assay. Thus, this study establishes a new and effective method to measure sociability or social preference that could be a complementary assay to evaluate the social behavior of mice in various setup conditions.

Navigating Social Space

Cognitive maps are encoded in the hippocampal formation and related regions and range from the spatial to the purely conceptual. Neural mechanisms that encode information into relational structures, up to an arbitrary level of abstraction, may explain such a broad range of representation. Research now indicates that social life can also be mapped by these mechanisms: others' spatial locations, social memory, and even a two-dimensional social space framed by social power and affiliation. The systematic mapping of social life onto a relational social space facilitates adaptive social decision making, akin to social navigation. This emerging line of research has implications for cognitive mapping research, clinical disorders that feature hippocampal dysfunction, and the field of social cognitive neuroscience.

Phenotypic variability between Social Dominance Ranks in laboratory mice

The laboratory mouse is the most prevalent animal used in experimental procedures in the biomedical and behavioural sciences. Yet, many scientists fail to consider the animals’ social context. Within a cage, mice may differ in their behaviour and physiology depending on their dominance relationships. Therefore, dominance relationships may be a confounding factor in animal experiments. The current study housed male and female C57BL/6ByJ mice in same-sex groups of 5 in standard laboratory conditions and investigated whether dominance hierarchies were present and stable across three weeks, and whether mice of different dominance ranks varied consistently in behaviour and physiology. We found that dominance ranks of most mice changed with time, but were most stable between the 2^nd and 3^rd week of testing. Phenotypic measures were also highly variable, and we found no relation between dominance rank and phenotype. Further, we found limited evidence that variation in measures of phenotype was associated with cage assignment for either males or females. Taken together, these findings do not lend support to the general assumption that individual variation among mice is larger between cages than within cages.