Social factors and the neurobiology of pathogen avoidance

Where's my mom? Resilient maternal preference in post-weaning male and female mice within a multi-chamber social behavior task

One of the earliest and most critical social bonds for many mammals is formed with their mother, who provides essential benefits for offspring development and survival. Growing evidence suggests that this social bond is retained even when animals gain independence, such as during the juvenile period immediately post-weaning. Here, we investigated whether juvenile (postnatal day (P)26) mice retain the ability to recognize and prefer their mothers post-weaning. We further investigated the strength of this bond using an acute immune activator. On P26, male and female C57BL/6J mice were intraperitoneally injected with the endotoxin lipopolysaccharide (LPS) or saline control (0.5 mg/kg). Four hours later, mice were subject to a five-chamber social preference task (the AGORA) containing their biological mother, a sex-matched novel mouse, a sex-matched sibling, a novel object, and an empty chamber. Our findings reveal that juvenile mice exhibit a strong maternal preference, significantly greater than chance and higher compared to any other social or non-social stimuli. While LPS exposure reduced the time spent investigating all stimuli, juvenile maternal preference was not significantly altered by LPS exposure. These effects were especially pronounced in females, while subtle shifts towards novel exploration began to emerge in males by P26. These results suggest that juvenile mice have a robust social preference for their mother that is resilient to early-life immune activation. Moreover, the novel multi-chamber task employed in the present study offered a more nuanced understanding of how social bonds evolve and vary across sex.

Sex and Region-Specific Differences in Microglial Morphology and Function Across Development

Microglia are exceptionally dynamic resident innate immune cells within the central nervous system, existing on a continuum of morphologies and functions throughout their lifespan. They play vital roles in response to injuries and infections, clearing cellular debris, and maintaining neural homeostasis throughout development. Emerging research suggests that microglia are strongly influenced by biological factors, including sex, developmental stage, and their local environment. This review synthesizes findings on sex differences in microglial morphology and function in key brain regions, including the frontal cortex, hippocampus, amygdala, hypothalamus, basal ganglia, and cerebellum, across the lifespan. Where available, we examine how gonadal hormones influence these microglial characteristics. Additionally, we highlight the limitations of relying solely on morphology to infer function and underscore the need for comprehensive, multimodal approaches to guide future research. Ultimately, this review aims to advance the dialogue on these spatiotemporally heterogeneous cells and their implications for sex differences in brain function and vulnerability to neurological and psychiatric disorders.

The costs and benefits of a dynamic host microbiome

All species host a rich community of microbes. This microbiome is dynamic, and displays seasonal, daily, and even hourly changes, but also needs to be resilient to fulfill important roles for the host. In evolutionary ecology, the focus of microbiome dynamism has been on how it can facilitate host adaptation to novel environments. However, an hitherto largely overlooked issue is that the host needs to keep its microbiome in check, which is costly and leads to trade-offs with investing in other fitness-related traits. Investigating these trade-offs in natural vertebrate systems by collecting longitudinal data will lead to deeper insight into the evolutionary mechanisms that shape host-microbiome interactions.

Shaping behaviors through social experience and their proposed sensitivity to stress

Mammals have evolved with a range of innate drives, such as thirst and hunger, that promote motivated behaviors to ensure survival. A drive for social engagement promotes social interaction and bond formation. While a stable social environment maintains the opportunity for resource sharing and protection, an additional benefit is provided by the social transmission of information. Social experiences, and information obtained from conspecifics, can be used to learn about threats and opportunities in the environment. This review examines the primary forms of social learning and how they can shape behavior. Additionally, while there is much known about the effects of stress on learning and memory, there is much less known about its effects on social learning and memory. This review will therefore dissect the major factors that contribute to social learning and propose how stress may impact these factors. This may serve as a way to formulate new hypotheses about how stress might impact social learning and the effects of social experiences on behavior.

Loss of cilia in chemosensory neurons inhibits pathogen avoidance in Caenorhabditis elegans

Pathogen avoidance is a crucial and evolutionarily conserved behavior that enhances survival by preventing infection in diverse species, including Caenorhabditis elegans (C. elegans). This behavior relies on multiple chemosensory neurons equipped with cilia that are exposed to the external environment. However, the specific role of neuronal cilia in pathogen avoidance has not been completely elucidated. Herein, we discovered that osm-3(p802) mutants, which lack chemosensory neuronal cilia, exhibit slower avoidance of the pathogen Pseudomonas aeruginosa PA14, but not Escherichia coli OP50. This observation was consistent when osm-3(p802) mutants were exposed to P. aeruginosa PAO1. Following an encounter with PA14, the pumping, thrashing, and defecation behaviors of osm-3 mutants were comparable to those of the wild-type. However, the osm-3 mutants demonstrated reduced intestinal colonization of PA14, suggesting that they have stronger intestinal clearance ability. We conducted RNA-seq to identify genes responding to external stimuli that were differentially expressed owing to the loss of osm-3 and PA14 infection. Using RNAi, we demonstrated that three of these genes were essential for normal pathogen avoidance. In conclusion, our findings demonstrate that the loss of chemosensory neuronal cilia reduces pathogen avoidance in C. elegans while delaying intestinal colonization.

Social transmission of inflammation in mice

The ability to detect and respond to sickness in others promotes survival. Here we show that mouse dams respond to immune challenged pups by mirroring their inflammatory response. Dams with pups subjected to immune challenge displayed a marked induction of inflammatory mediators in both the brain and the periphery, accompanied by an increase in maternal behaviors and corticosterone levels. This social transmission of inflammation did not require physical contact, and it contributed to the stress hormone response in the dams. In adult dyads, interaction with an immune challenged cagemate did not elicit robust inflammatory signaling but induced an increased responsiveness to a subsequent immune challenge. The identification of social transmission of inflammation, or inflammatory responsiveness, may open new avenues for research on social behavior, just like the description of similar phenomena such as observational fear and transmitted pain has done.

Neural cell-types and circuits linking thermoregulation and social behavior

Understanding how social and affective behavioral states are controlled by neural circuits is a fundamental challenge in neurobiology. Despite increasing understanding of central circuits governing prosocial and agonistic interactions, how bodily autonomic processes regulate these behaviors is less resolved. Thermoregulation is vital for maintaining homeostasis, but also associated with cognitive, physical, affective, and behavioral states. Here, we posit that adjusting body temperature may be integral to the appropriate expression of social behavior and argue that understanding neural links between behavior and thermoregulation is timely. First, changes in behavioral states-including social interaction-often accompany changes in body temperature. Second, recent work has uncovered neural populations controlling both thermoregulatory and social behavioral pathways. We identify additional neural populations that, in separate studies, control social behavior and thermoregulation, and highlight their relevance to human and animal studies. Third, dysregulation of body temperature is linked to human neuropsychiatric disorders. Although body temperature is a "hidden state" in many neurobiological studies, it likely plays an underappreciated role in regulating social and affective states.

Is disgust more resistant to extinction than fear? A meta-analytic review of laboratory paradigms

Disgust can be acquired via evaluative conditioning; a process by which a neutral stimulus (conditioned stimulus; CS) comes to be evaluated as disgusting due to its pairing with an inherently disgusting stimulus (unconditioned stimulus; US). Research has shown that conditioned disgust responses are resistant to extinction which may have implications for disorders (i.e., contamination-based obsessive-compulsive disorder, specific phobias, and post-traumatic stress disorder) in which heightened disgust has been implicated. Importantly, extinction is the primary mechanism by which exposure therapies are thought to achieve symptom reduction for these disorders. Exposure therapies were originally modeled on fear extinction, whereas disgust extinction was largely overlooked until recently. Accordingly, differences in the degree to which learned disgust and fear can be attenuated via extinction learning remains unclear. The present investigation was a meta-analysis directly comparing the degree of extinction of conditioned disgust (n = 14) and conditioned fear (n = 14) in laboratory paradigms. Extinction was operationalized as the standardized mean difference (SMD) in evaluative ratings between the CS+ (the CS paired with the US) and CS- (the unpaired CS) after extinction training. Results of a subgroup analysis indicated that disgust (SMD = 0.52) was significantly more resistant to extinction than fear (SMD = 0.37). Additionally, a series of meta-regression analyses indicated that extinction was not influenced by important study characteristics (e.g., sex, age, number of conditioning and extinction trials). The findings suggest that extinction-based approaches may be less effective at attenuating learned disgust and research is needed to better optimize treatments for disgust-related disorders.

Lipopolysaccharide (LPS) attenuates the primary conditioning of lithium chloride (LiCl)-induced context aversion but not the secondary conditioning of context aversion or taste avoidance

A first-order association can be formed between toxin-induced nausea and a context, as well as nausea and a taste cue. However, comparatively little is understood about second-order associations. The present study examined if the bacterial endotoxin, LPS, could impair the first- and second-order conditioning of context aversion (anticipatory nausea paradigm) and subsequent conditioned taste avoidance (two-bottle task). Adult male Long Evans rats were treated with LiCl (127 mg/kg, intraperitoneal [i.p.]) or vehicle control (NaCl) and then exposed to a distinct context for 4 first-order conditioning trials. LPS (200 μg/kg, i.p.) or NaCl were administered 24 h after each trial. Seventy-two h after the final first-order conditioning trial, rats underwent 2 second-order conditioning trials where they were treated with 2% saccharin (i.p.) and then exposed to the same context. Twenty-four h after the final second-order conditioning trial, rats were tested in a two-bottle task (2 trials), where they were given a choice between water and a palatable 0.2% saccharin solution. LiCl-treated rats demonstrated a context aversion by the 3rd conditioning trial in the anticipatory nausea paradigm. Rats previously exposed to LiCl also displayed a conditioned taste avoidance of saccharin within the two-bottle task. LPS attenuated first-order context aversion but did not alter either second-order context aversion or conditioned taste avoidance in the two-bottle task. This study demonstrated that a secondary association formed within an aversive context could result in a conditioned taste avoidance. Further, LPS may be able to attenuate primary conditioning, but not secondary conditioning.

Disgust sensitivity and psychopathic behavior: A narrative review

Humans live under constant threat from pathogenic microorganisms and minimizing such threat has been a major evolutionary selective force in shaping human behavior and health. A particular adaptive mechanism against the harm caused by parasites and their infectiousness is disgust sensitivity, which has evolved to detect and avoid poisonous foods as well as bodily secretions harboring virulent microorganisms. This ubiquitous and reflexive behavior requires the integration of several internal and external sensory signals between the brain, the autonomic nervous system (ANS), and the gastrointestinal tract. Although the emotional expression of disgust is experienced by almost all individuals, the neural mechanisms of sensory signals underlying disgust sensitivity may differ in certain psychiatric conditions. Psychopathy, for instance, is a personality disorder in which disgust sensitivity to contagious bodily secretions is apparently absent or downregulated from its atypical personality temperament. In this review, we provide convergent behavioral, anatomical, and cellular evidence to suggest that a fractured experience of disgust sensitivity might be an additional feature of psychopathic behavior. First, we discuss the neural networks of certain brain regions mediating the emotional states of disgust and then discuss the intersection of the ANS and gastrointestinal tract in the processing of disgust and its relevance to aberrant antisocial behavior. Together, this work highlights the interconnections between the brain and the bilateral body plan as an integrated cell network that is relevant for understanding common principles underlying function and dysfunction of disgust levels in psychiatric domains.

Polygonum Cuspidatum Alcohol Extract Exerts Analgesic Effects via the MAPK/ERK Signaling Pathway

OBJECTIVE

Traditional Chinese medicine Polygonum cuspidatum (PC) has significant effects on reducing pain. In this study, we investigated the analgesic effects of the alcohol extract of PC on three types of inflammatory pain and explored its mechanism.

METHODS

Potential targets for the analgesic effects of the main active components of PC alcohol extract were screened by network pharmacology and molecular docking. Three different inflammatory pain mouse models (acetic acid twisting, formalin foot swelling, and xylene ear swelling) were used to study the analgesic effects of PC. The expression of latent signaling pathways in L4-6 spinal cord tissues in formalin foot swelling mice was evaluated using real-time qPCR (RT-qPCR), Western blot (WB), and immunohistochemistry (IHC) analyses.

RESULTS

Network pharmacology analysis shows that PC analgesic mechanism is related to the MAPK/ERK signaling pathway. The five main active components of PC have good docking ability with JNK and p38. PC alcohol extract significantly reduced the pain behavior and alleviated inflammatory reactions in three mouse models, inhibited the mRNA and protein phosphorylation levels of JNK, ERK, p38, and CREB in spinal cord tissues.

CONCLUSION

PC alcohol extract can inhibit inflammation and alleviate pain, which is related to its inhibition of the MAPK/ERK signaling pathway in spinal cord. Thus, PC alcohol extract is a promising candidate for pain treatment.

Of Germs and Culture; Parasite Stress as the Origin of Individualism-Collectivism

Among four proposed origins of individualism-collectivism, modernization theory, rice versus wheat theory, climato-economic theory, and pathogen stress theory, the latter has gained more attention in cross-cultural and evolutionary psychology. Since the parasite stress theory of values and sociality makes a connection between infectious diseases and cultural orientations, it gained even more popularity during the COVID pandemic. But despite extensive research on parasite stress theory, it is not still clear what kind of infectious disease contributes more to the emergence of cultures, what are the possible mechanisms through which pathogenic threat gives rise to cultural systems, and how parasite stress might affect vertical vs. horizontal dimensions of individualism-collectivism. This review summarizes and integrates major findings of parasite stress theory related to individualism-collectivism and its closely related variables and discusses future directions that researchers can take to answer the remaining questions.

Hearing, touching, and multisensory integration during mate choice

Mate choice is a potent generator of diversity and a fundamental pillar for sexual selection and evolution. Mate choice is a multistage affair, where complex sensory information and elaborate actions are used to identify, scrutinize, and evaluate potential mating partners. While widely accepted that communication during mate assessment relies on multimodal cues, most studies investigating the mechanisms controlling this fundamental behavior have restricted their focus to the dominant sensory modality used by the species under examination, such as vision in humans and smell in rodents. However, despite their undeniable importance for the initial recognition, attraction, and approach towards a potential mate, other modalities gain relevance as the interaction progresses, amongst which are touch and audition. In this review, we will: (1) focus on recent findings of how touch and audition can contribute to the evaluation and choice of mating partners, and (2) outline our current knowledge regarding the neuronal circuits processing touch and audition (amongst others) in the context of mate choice and ask (3) how these neural circuits are connected to areas that have been studied in the light of multisensory integration.

Infectious disease and cognition in wild populations

Infectious disease is linked to impaired cognition across a breadth of host taxa and cognitive abilities, potentially contributing to variation in cognitive performance within and among populations. Impaired cognitive performance can stem from direct damage by the parasite, the host immune response, or lost opportunities for learning. Moreover, cognitive impairment could be compounded by factors that simultaneously increase infection risk and impair cognition directly, such as stress and malnutrition. As highlighted in this review, however, answers to fundamental questions remain unresolved, including the frequency, duration, and fitness consequences of infection-linked cognitive impairment in wild animal populations, the cognitive abilities most likely to be affected, and the potential for adaptive evolution of cognition in response to accelerating emergence of infectious disease.