Distinct prefrontal projection activity and transcriptional state conversely orchestrate social competition and hierarchy

The Tailtag: A multi-mouse tracking system to measure social dynamics in complex environments

Despite recent advances, tracking individual movements safely and reliably over extended periods, particularly within complex social groups, remains a challenge. Traditional methods like color coding, tagging, and RFID tracking, while effective, have notable practical limitations. State-of-the-art neural network-based trackers often struggle to maintain individual identities in large groups for more than a few seconds. Fiducial tags such as ArUco codes present a potential solution to enable accurate tracking and identity management. However, their application to large groups of socially interacting mice in complex, enriched environments remain an open challenge. Here, we present the Tailtag system, a novel approach designed to address this challenge. The Tailtag is a non-invasive, safe, and ergonomic tail ring embedded with an ArUco marker allowing to track individual mice in colonies of up to 20 individuals in complex environments for at least seven days without performance degradation or behavioral alteration. We provide a comprehensive parameter optimization guide and practical recommendations for marker selection, for reproducibility across diverse experimental setups. Using data collected from Tailtag-equipped mice, we revealed the formation and evolution of social groups within the colony. Our analysis identified social hub regions within the vivarium where social contacts occur at different frequencies throughout one week of recordings. We quantified interactions and avoidance patterns between specific pairs of mice within the most active social hubs. Overall, our findings indicate that while the zone preferences and peer associations among the mice change over time, certain groups and pairwise interactions consistently form within the social colony.

Reevaluating the role of Pou3f1 in striatal development: Evidence from transgenic mouse models

The striatum, a critical component of the basal ganglia, is essential for motor control, cognitive processing, and emotional regulation. Medium spiny neurons (MSNs) are the primary neuronal population in the striatum, classified into D1 and D2 subtypes. The transcription factor Pou3f1 has been hypothesized to play a crucial role in the development of pyramidal neurons. Recently, a comprehensive analysis of the human embryonic scRNA-seq dataset predicted and emphasized the bridging function of POU3F1 between striatal progenitor cells and immature neurons, though this finding lacked genetic validation. In this study, we found that Pou3f1 expression was significantly reduced after Six3 deletion. However, Pou3f1 deletion does not significantly affect the number or subtype composition of MSNs, nor the proliferation and differentiation of progenitor cells, in our Pou3f1 conditional knockout (cko) mice, challenging the in silico predictions based on human data. These results suggest that Pou3f1 is not required for the specification, generation, or differentiation of MSNs, though its potential involvement in other aspects of striatal development cannot be entirely ruled out.

Brain circuits that regulate social behavior

Social interactions are essential for the survival of individuals and the reproduction of populations. Social stressors, such as social defeat and isolation, can lead to emotional disorders and cognitive impairments. Furthermore, dysfunctional social behaviors are hallmark symptoms of various neuropsychiatric disorders, including autism spectrum disorder (ASD) and post-traumatic stress disorder (PTSD). Consequently, understanding the neural circuit mechanisms underlying social behaviors has become a major focus in neuroscience. Social behaviors, which encompass a wide range of expressions and phases, are regulated by complex neural networks. In this review, we summarize recent progress in identifying the circuits involved in different types of social behaviors, including general social investigation, social preference, mating, aggression, parenting, prosocial behaviors, and dominance behaviors. We also outline the circuit mechanisms associated with social deficits in neuropsychiatric disorders, such as ASD, schizophrenia, and PTSD. Given the pivotal role of rodents in social behavior research, our review primarily focuses on neural circuits in these animals. Finally, we propose future research directions, including the development of specific behavioral paradigms, the identification of circuits involved in motor output, the integration of activity, transcriptome, and connectome data, the multifunctional roles of neurons with multiple targets, and the interactions among multiple brain regions.

Social hierarchy modulates drug reinforcement and protein phosphorylation in the nucleus accumbens

Introduction

Drug reinforcement, a form of behavioral plasticity in which behavioral changes happen in response to a reinforcing drug, would finally lead to drug addiction after chronical drug exposure. Drug reinforcement is affected by genetic and environmental factors. Social hierarchy has been reported to regulate drug reinforcement and drug-seeking behaviors, but the underlying molecular mechanism is almost unknown.

Methods

We take advantage of the tube test to assess the social hierarchy between two co-housed rats. And then, we investigated the drug reinforcement between dominant and subordinate rats via conditioned place preference (CPP). Then we adopted 4-D label-free mass spectrometry to explore the complex phosphoproteome in the nucleus accumbens (NAc) between dominant and subordinate rats. Functional enrichment, protein-protein, motif analysis and kinase prediction interaction analysis were used to investigate the mechanism between substance use disorder and social hierarchy. Specifically, we identified histone deacetylase 4 (HDAC4) which has been previously shown to play critical roles in drug addiction as a key node protein by phosbind-SDS. Finally, we forcibly altered the social hierarchy of rats through behavioral training, follow by which we accessed the HDAC4 phosphorylation levels and drug reinforcement.

Results

In this study, we found that methamphetamine exhibited stronger reinforcement in the subordinate rats. We identified 660 sites differing between dominant and subordinate rats via 4-D label-free mass spectrometry. Functional enrichment and protein-protein interaction analysis revealed that synaptic remodeling related pathways and substance use disorder related pathway are significantly characterized by social hierarchy. Motif analysis and kinase prediction showed that CaMKIIδ and its downstream proteins maybe the central hub. Phosbind-SDS revealed that higher HDAC4 phosphorylation levels in dominants. After the social hierarchy of rats were forcibly altered by behavioral training, the differences in HDAC4 phosphorylation levels induced by social hierarchy were eliminated, correspondingly the drug reinforcement is also reversed between the two group rats.

Discussion

In conclusion, our research proves that protein phosphorylation in the NAc may be a vital link between social hierarchy and drug reinforcement.

Essential Role of the Anterior Piriform Cortex in Mediating Social Novelty Output via a Top-Down Circuit

Social novelty is indispensable for a wide range of social behaviors. The medial prefrontal cortex (mPFC), along with other social information hubs, composes the foundational circuitry of social novelty. However, the precise circuit mechanisms that govern social novelty processing remain elusive. The piriform cortex, as the largest olfactory cortex, receives extensive innervation from top-down centers that dictate social behavior. Here, it is shown that the anterior piriform cortex (APC) exhibited an increase in gamma event incidence during social engagement in male mice. In vivo electrophysiology and fiber photometry reveal that APC pyramidal neurons respond more intensely to novel mice than familiar ones. Intriguingly, silencing APC neurons selectively impairs social novelty processing, yet leaves the basic olfactory discrimination capabilities intact. Moreover, the APC inherits social cues from the mPFC and sends feedback projections to the olfactory bulb (OB) to modulate social novelty. These findings unveil the APC's role as extending well beyond olfaction, encompassing a specialized function in social novelty recognition in male mice.

Perturbations in the microbiota-gut-brain axis shaped by social status loss

Social status is closely linked to physiological and psychological states. Loss of social dominance can lead to brain disorders such as depression, but the underlying mechanisms remain unclear. The gut microbiota can sense stress and contribute to brain disorders via the microbiota-gut-brain axis (MGBA). Here, using a forced loss paradigm to demote dominant mice to subordinate ranks, we find that stress alters the composition and function of the gut microbiota, increasing Muribaculaceae abundance and enhancing butanoate metabolism, and gut microbial depletion resists forced loss-induced hierarchical demotion and behavioral alteration. Single-nucleus transcriptomic analysis of the prefrontal cortex (PFC) indicates that social status loss primarily affected interneurons, altering GABAergic synaptic transmission. Weighted gene co-expression network analysis (WGCNA) reveals modules linked to forced loss in the gut microbiota, colon, PFC, and PFC interneurons, suggesting changes in the PI3K-Akt signaling pathway and the glutamatergic synapse. Our findings provide evidence for MGBA perturbations induced by social status loss, offering potential intervention targets for related brain disorders.

Opposing and segregated cortical circuits control winning and losing behaviors

In this issue of Neuron, Xin et al.1 reveal how the dorsomedial prefrontal cortex (dmPFC) orchestrates social dominance through subcortical pathways to the amygdala and brainstem. Using optogenetics and functional mapping, they identify opposing win- and lose-related circuits, uncovering a laminar organization driving competitive behavior in mice.

Deconstructing the neural circuit underlying social hierarchy in mice

Social competition determines hierarchical social status, which profoundly influences animals' behavior and health. The dorsomedial prefrontal cortex (dmPFC) plays a fundamental role in regulating social competitions, but it was unclear how the dmPFC orchestrates win- and lose-related behaviors through its downstream neural circuits. Here, through whole-brain c-Fos mapping, fiber photometry, and optogenetics- or chemogenetics-based manipulations, we identified anatomically segregated win- and lose-related neural pathways downstream of the dmPFC in mice. Specifically, layer 5 neurons projecting to the dorsal raphe nucleus (DRN) and periaqueductal gray (PAG) promote social competition, whereas layer 2/3 neurons projecting to the anterior basolateral amygdala (aBLA) suppress competition. These two neuronal populations show opposite changes in activity during effortful pushes in competition. In vivo and in vitro electrophysiology recordings revealed inhibition from the lose-related pathway to the win-related pathway. Such antagonistic interplay may represent a central principle in how the mPFC orchestrates complex behaviors through top-down control.

The role of the prefrontal cortex in modulating aggression in humans and rodents

Accumulating evidence suggests that the prefrontal cortex (PFC) plays an important role in aggression. However, the findings regarding the key neural mechanisms and molecular pathways underlying the modulation of aggression by the PFC are relatively scattered, with many inconsistencies and areas that would benefit from exploration. Here, we highlight the relationship between the PFC and aggression in humans and rodents and describe the anatomy and function of the human PFC, along with homologous regions in rodents. At the molecular level, we detail how the major neuromodulators of the PFC impact aggression. At the circuit level, this review provides an overview of known and potential subcortical projections that regulate aggression in rodents. Finally, at the disease level, we review the correlation between PFC alterations and heightened aggression in specific human psychiatric disorders. Our review provides a framework for PFC modulation of aggression, resolves several intriguing paradoxes from previous studies, and illuminates new avenues for further study.

Oxytocin receptor controls distinct components of pair bonding and development in prairie voles

Oxytocin receptor (Oxtr) signaling influences complex social behaviors in diverse species, including social monogamy in prairie voles. How Oxtr regulates specific components of social attachment behaviors and the neural mechanisms mediating them remains unknown. Here, we examine prairie voles lacking Oxtr and demonstrate that pair bonding comprises distinct behavioral modules: the preference for a bonded partner, and the rejection of novel potential mates. Our longitudinal study of social attachment shows that Oxtr sex-specifically influences early interactions between novel partners facilitating the formation of partner preference. Additionally, Oxtr suppresses promiscuity towards novel potential mates following pair bonding, contributing to rejection. Oxtr function regulates coordinated patterns of gene expression in regions implicated in attachment behaviors and regulates the expression of oxytocin in the paraventricular nucleus of the hypothalamus, a principal source of oxytocin. Thus, Oxtr controls genetically separable components of pair bonding behaviors and coordinates development of the neural substrates of attachment.

Dissociable Roles of the mPFC-to-VTA Pathway in the Control of Impulsive Action and Risk-Related Decision-Making in Roman High- and Low-Avoidance Rats

BACKGROUND

Impulsive action and risk-related decision-making (RDM) are associated with various psychiatric disorders, including drug abuse. Both behavioral traits have also been linked to reduced frontocortical activity and alterations in dopamine function in the ventral tegmental area (VTA). However, despite direct projections from the medial prefrontal cortex (mPFC) to the VTA, the specific role of the mPFC-to-VTA pathway in controlling impulsive action and RDM remains unexplored.

METHODS

We used positron emission tomography with [18F]-fluorodeoxyglucose to evaluate brain metabolic activity in Roman high- (RHA) and low-avoidance (RLA) rats, which exhibit innate differences in impulsive action and RDM. Notably, we used a viral-based double dissociation chemogenetic strategy to isolate, for the first time to our knowledge, the role of the mPFC-to-VTA pathway in controlling these behaviors. We selectively activated the mPFC-to-VTA pathway in RHA rats and inhibited it in RLA rats, assessing the effects on impulsive action and RDM in the rat gambling task.

RESULTS

Our results showed that RHA rats displayed higher impulsive action, less optimal decision-making, and lower cortical activity than RLA rats at baseline. Chemogenetic activation of the mPFC-to-VTA pathway reduced impulsive action in RHA rats, whereas chemogenetic inhibition had the opposite effect in RLA rats. However, these manipulations did not affect RDM. Thus, by specifically targeting the mPFC-to-VTA pathway in a phenotype-dependent way, we reverted innate patterns of impulsive action but not RDM.

CONCLUSION

Our findings suggest a dissociable role of the mPFC-to-VTA pathway in impulsive action and RDM, highlighting its potential as a target for investigating impulsivity-related disorders.

Mesocorticolimbic circuit mechanisms of social dominance behavior

Social animals, including rodents, primates, and humans, partake in competition for finite resources, thereby establishing social hierarchies wherein an individual's social standing influences diverse behaviors. Understanding the neurobiological underpinnings of social dominance is imperative, given its ramifications for health, survival, and reproduction. Social dominance behavior comprises several facets, including social recognition, social decision-making, and actions, indicating the concerted involvement of multiple brain regions in orchestrating this behavior. While extensive research has been dedicated to elucidating the neurobiology of social interaction, recent studies have increasingly delved into adverse social behaviors such as social competition and hierarchy. This review focuses on the latest advancements in comprehending the mechanisms of the mesocorticolimbic circuit governing social dominance, with a specific focus on rodent studies, elucidating the intricate dynamics of social hierarchies and their implications for individual well-being and adaptation.

Transcriptional programming of social hierarchy

In this issue of Neuron, Choi and colleagues1 uncover the direct role of the transcription factor Pou3f1 in regulating dominance hierarchy in mice. Pou3f1 accomplishes this role via its action in specific prefrontal projection neurons that regulate behaviors associated with low social status.