Aberrant Early in Life Stimulation of the Stress-Response System Affects Emotional Contagion and Oxytocin Regulation in Adult Male Mice

Emotional contagion in rodents: A comprehensive exploration of mechanisms and multimodal perspectives

Emotional contagion, a fundamental aspect of empathy, is an automatic and unconscious process in which individuals mimic and synchronize with the emotions of others. Extensively studied in rodents, this phenomenon is mediated through a range of sensory pathways, each contributing distinct insights. The olfactory pathway, marked by two types of pheromones modulated by oxytocin, plays a crucial role in transmitting emotional states. The auditory pathway, involving both squeaks and specific ultrasonic vocalizations, correlates with various emotional states and is essential for expression and communication in rodents. The visual pathway, though less relied upon, encompasses observational motions and facial expressions. The tactile pathway, a more recent focus, underscores the significance of physical interactions such as allogrooming and socio-affective touch in modulating emotional states. This comprehensive review not only highlights plausible neural mechanisms but also poses key questions for future research. It underscores the complexity of multimodal integration in emotional contagion, offering valuable insights for human psychology, neuroscience, animal welfare, and the burgeoning field of animal-human-AI interactions, thereby contributing to the development of a more empathetic intelligent future.

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

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

Therapeutic uses of oxytocin in stress-related neuropsychiatric disorders

Oxytocin (OXT), produced and secreted in the paraventricular nucleus and supraoptic nucleus of magnocellular and parvocellular neurons. The diverse presence and activity of oxytocin suggests a potential for this neuropeptide in the pathogenesis and treatment of stress-related neuropsychiatric disorders (anxiety, depression and post-traumatic stress disorder (PTSD)). For a more comprehensive understanding of the mechanism of OXT's anti-stress action, the signaling cascade of OXT binding to targeting stress were summarized. Then the advance of OXT treatment in depression, anxiety, PTSD and the major projection region of OXT neuron were discussed. Further, the efficacy of endogenous and exogenous OXT in stress responses were highlighted in this review. To augment the level of OXT in stress-related neuropsychiatric disorders, current biological strategies were summarized to shed a light on the treatment of stress-induced psychiatric disorders. We also conclude some of the major puzzles in the therapeutic uses of OXT in stress-related neuropsychiatric disorders. Although some questions remain to be resolved, OXT has an enormous potential therapeutic use as a hormone that regulates stress responses.

Sex-dependent and long-lasting effects of adolescent sleep deprivation on social behaviors in adult mice

Increasing evidence indicates that sleep deprivation (SD) can exert multiple negative effects on neuronal circuits, resulting in memory impairment, depression, and anxiety, among other consequences. The long-term effects of SD during early life on behavioral phenotypes in adulthood are still poorly understood. In this study, we investigated the long-lasting effects of SD in adolescence on social behaviors, including empathic ability and social dominance, and the role of the gut microbiota in these processes, using a series of behavioral paradigms in mice combined with 16S rRNA gene pyrosequencing. Behavioral assay results showed that SD in adolescence significantly reduced the frequency of licking, the total time spent licking, and the time spent sniffing during the emotional contagion test in male mice, effects that were not observed in female mice. These findings indicated that SD in adolescence exerts long-term, negative effects on empathic ability in mice and that this effect is sex-dependent. In contrast, SD in adolescence had no significant effect on locomotor activities, social dominance but decreased social interaction in male mice in adulthood. Meanwhile, 16S rRNA gene pyrosequencing results showed that gut microbial richness and diversity were significantly altered in adult male mice subjected to SD in adolescence. Our data provide direct evidence that SD in youth can induce alterations in empathic ability in adult male mice, which may be associated with changes in the gut microbiota. These findings highlight the long-lasting effects of sleep loss in adolescence on social behaviors in adulthood and the role played by the brain-gut axis.

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

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

The Gasotransmitter Hydrogen Sulfide and the Neuropeptide Oxytocin as Potential Mediators of Beneficial Cardiovascular Effects through Meditation after Traumatic Events

Trauma and its related psychological and somatic consequences are associated with higher cardiovascular morbidity. The regulation of both the gasotransmitter hydrogen sulfide (H2S) and the neuropeptide oxytocin (OT) have been reported to be affected during physical and psychological trauma. Both mediators are likely molecular correlates of trauma-induced cardiovascular complications, because they share parallel roles and signaling pathways in the cardiovascular system, both locally as well as on the level of central regulation and the vagus nerve. Meditation can alter the structure of specific brain regions and can have beneficial effects on cardiovascular health. This perspective article summarizes the evidence pointing toward the significance of H2S and OT signaling in meditation-mediated cardio-protection.

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

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

Callous unemotional trait-like mice and their stressed dams

The co-occurrence of excess rates of aggression, general violation of societal norms and callous-unemotional trait confers specific risk for adult psychopathy. With the aim to address experimentally a model of conduct disorder, we investigated the male offspring of individual mouse dams characterized by high basal plasma corticosterone concentration (HC trait). Notably, classification indices correlated selectively in these females with quite poor maternal care devoted to their offspring. Contrary to their HC mothers, adult male offspring exhibited an integrated profile of dampened physiological reactivity to external stressors co-occurring poor sociability/emotional contagion, impaired punishment-induced memory, and exacerbated aggression. A significant reduction of glucocorticoid and opioid mu receptors' expression in frontal cortex of model HC offspring was also evidenced. Moreover, in the absence of changes in oxytocin receptor in behaviorally-relevant neural areas, we showed that intranasal oxytocin administration (0 or 20.0 µg/kg) selectively modulated specific components of the behavioral phenotype. Ultimately, current data support the notion that maternally-inoculated environmental stress early in development may represent a critical risk factor in disturbances characterised by abnormal aggression and excess callousness.

5-HT3 receptor within the amygdaloid complex modulates pain hypersensitivity induced by empathy model of cohabitation with a partner in chronic pain condition in mice

Cohabitation with a partner undergoing chronic pain induces pain hypersensitivity. Among a lot of other neurochemical pathways, the serotonin (5-HT) role, specifically the 5-HT₃ receptor (5-HT₃R), in the amygdala has never been evaluated in this model. Here we studied the effects of the amygdala's chemical inhibition, its neuronal activation pattern, and 5-HT, 5-HIAA, and 5-HT turnover within the amygdala. Furthermore, the systemic and intra-amygdala 5-HT₃R activation and blockade in mice that cohabited with a conspecific subjected to chronic constriction injury were investigated. Male Swiss mice were housed in partners for 28 days. The dyads were divided into two groups on the 14^th day: cagemate nerve constriction (CNC) and cagemate sham (CS). On the 24^th day, cagemates underwent a stereotaxic surgery (when necessary) and, on the 28^th day, they were evaluated on the writhing test. The amygdala inactivation promotes pain-hypersensitivity behaviors in groups and dyads; cohabitation with a partner with chronic pain did not change FosB-labeled cells in the amygdala's nucleus and increases 5-HT turnover in cagemates. Systemic and intra-amygdala 5-HT₃R activation attenuated and enhanced the number of writhes, respectively. In contrast, 5-HT₃R blockade reduced hypersensitivity pain response. Results suggest the involvement of amygdala serotonergic signaling via 5-HT₃R in empathy-like behavior.