Neural mechanisms of aggression across species

Participation of kisspeptin, progesterone, and GnRH receptors on lordosis behavior induced by kisspeptin

The neuropeptide kisspeptin (Kiss) is crucial in regulating the hypothalamic-pituitary-gonadal axis. It is produced by two main groups of neurons in the hypothalamus: the rostral periventricular region around the third ventricle and the arcuate nucleus. Kiss is the peptide product of the KiSS-1 gene and serves as the endogenous agonist for the GPR54 receptor. The Kiss/GPR54 system functions as a critical regulator of the reproductive system. Thus, we examined the effect of intracerebroventricular administration of 3 μg of Kiss to the right lateral ventricle of ovariectomized rats primed with a dose of 5 μg subcutaneous (sc) of estradiol benzoate (EB). Kiss treatment increased the lordosis quotient at all times tested. However, the lordosis reflex score was comparatively lower yet still significant compared to the control group. To investigate receptor specificity and downstream mechanisms on lordosis, we infused 10 μg of GPR54 receptor antagonist, Kiss-234, 5 μg of the progestin receptor antagonist, RU486, or 3 μg of antide, a gonadotropin-releasing hormone-1 (GnRH-1) receptor antagonist, to the right lateral ventricle 30 min before an infusion of 3 μg of Kiss. Results demonstrated a significant reduction in the facilitation of lordosis behavior by Kiss at 60 and 120 min when Kiss-234, RU486, or antide were administered. These findings suggest that Kiss stimulates lordosis expression by activating GPR54 receptors on GnRH neurons and that Kiss/GPR54 system is an essential intermediary by which progesterone activates GnRH.

Sexually dimorphic oxytocin circuits drive intragroup social conflict and aggression in wild house mice

In nature, both males and females engage in competitive aggressive interactions to resolve social conflicts, yet the behavioral principles guiding such interactions and their underlying neural mechanisms remain poorly understood. Through circuit manipulations in wild mice, we unveil oxytocin-expressing (OT+) neurons in the hypothalamic paraventricular nucleus (PVN) as a neural hub governing behavior in dyadic and intragroup social conflicts, influencing the degree of behavioral sexual dimorphism. We demonstrate that OT+ PVN neurons are essential and sufficient in promoting aggression and dominance hierarchies, predominantly in females. Furthermore, pharmacogenetic activation of these neurons induces a change in the 'personality' traits of the mice within groups, in a sex-dependent manner. Finally, we identify an innervation from these OT neurons to the ventral tegmental area that drives dyadic aggression, in a sex-specific manner. Our data suggest that competitive aggression in naturalistic settings is mediated by a sexually dimorphic OT network connected with reward-related circuitry.

Social isolation and aggression training lead to escalated aggression and hypothalamus-pituitary-gonad axis hyperfunction in mice

Although the participation of sex hormones and sex hormone-responsive neurons in aggressive behavior has been extensively studied, the role of other systems within the hypothalamus-pituitary-gonadal (HPG) axis remains elusive. Here we assessed how the gonadotropin-releasing hormone (GnRH) and kisspeptin systems are impacted by escalated aggression in male mice. We used a combination of social isolation and aggression training (IST) to exacerbate mice's aggressive behavior. Next, low-aggressive (group-housed, GH) and highly aggressive (IST) mice were compared regarding neuronal activity in the target populations and hormonal levels, using immunohistochemistry and ELISA, respectively. Finally, we used pharmacological and viral approaches to manipulate neuropeptide signaling and expression, subsequently evaluating its effects on behavior. IST mice exhibited enhanced aggressive behavior compared to GH controls, which was accompanied by elevated neuronal activity in GnRH neurons and arcuate nucleus kisspeptin neurons. Remarkably, IST mice presented an increased number of kisspeptin neurons in the anteroventral periventricular nucleus (AVPV). In addition, IST mice exhibited elevated levels of luteinizing hormone (LH) in serum. Accordingly, activation and blockade of GnRH receptors (GnRHR) exacerbated and reduced aggression, respectively. Surprisingly, kisspeptin had intricate effects on aggression, i.e., viral ablation of AVPV-kisspeptin neurons impaired the training-induced rise in aggressive behavior whereas kisspeptin itself strongly reduced aggression in IST mice. Our results indicate that IST enhances aggressive behavior in male mice by exacerbating HPG-axis activity. Particularly, increased GnRH neuron activity and GnRHR signaling were found to underlie aggression whereas the relationship with kisspeptin remains puzzling.

Identifying behavioral links to neural dynamics of multifiber photometry recordings in a mouse social behavior network

Objective.Distributed hypothalamic-midbrain neural circuits help orchestrate complex behavioral responses during social interactions. Given rapid advances in optical imaging, it is a fundamental question how population-averaged neural activity measured by multi-fiber photometry (MFP) for calcium fluorescence signals correlates with social behaviors is a fundamental question. This paper aims to investigate the correspondence between MFP data and social behaviors.Approach:We propose a state-space analysis framework to characterize mouse MFP data based on dynamic latent variable models, which include a continuous-state linear dynamical system and a discrete-state hidden semi-Markov model. We validate these models on extensive MFP recordings during aggressive and mating behaviors in male-male and male-female interactions, respectively.Main results:Our results show that these models are capable of capturing both temporal behavioral structure and associated neural states, and produce interpretable latent states. Our approach is also validated in computer simulations in the presence of known ground truth.Significance:Overall, these analysis approaches provide a state-space framework to examine neural dynamics underlying social behaviors and reveals mechanistic insights into the relevant networks.

Sexually dimorphic control of aggression by androgen signaling in a cichlid

Innate social behaviors like aggression are modulated by sex steroid hormones such as androgens and estrogens. However, we know little about how the same hormone regulates similar behaviors in both sexes. We investigated the role of androgenic signaling in the regulation of aggression in Astatotilapia burtoni, a social fish in which males and females perform similar aggressive behaviors. We used androgen receptor (AR) α knockout (KO) animals for this study since this gene was recently shown to be required for male-typical aggression and mating. Surprisingly, ARα KO females did not show deficits in aggression. We also determined that females lacking the other AR, ARβ, showed normal levels of aggression. Blocking both ARs pharmacologically confirmed that neither AR is necessary for aggression in females. However, ARα KO males showed clear deficits in attacks. Thus, in A. burtoni there appears to be a sexual dimorphism in the role of ARα in the control of aggression.

Social threat alters the behavioral structure of social motivation and reshapes functional brain connectivity

Traumatic social experiences redefine socially motivated behaviors to enhance safety and survival. Although many brain regions have been implicated in signaling a social threat, the mechanisms by which global neural networks regulate such motivated behaviors remain unclear. To address this issue, we first combined traditional and modern behavioral tracking techniques in mice to assess both approach and avoidance, as well as sub-second behavioral changes, during a social threat learning task. We were able to identify previously undescribed body and tail movements during social threat learning and recognition that demonstrate unique alterations into the behavioral structure of social motivation. We then utilized inter-regional correlation analysis of brain activity after a mouse recognizes a social threat to explore functional communication amongst brain regions implicated in social motivation. Broad brain activity changes were observed within the nucleus accumbens, the paraventricular thalamus, the ventromedial hypothalamus, and the nucleus of reuniens. Inter-regional correlation analysis revealed a reshaping of the functional connectivity across the brain when mice recognize a social threat. Altogether, these findings suggest that reshaping of functional brain connectivity may be necessary to alter the behavioral structure of social motivation when a social threat is encountered.

Noncortical coding of biological motion in newborn chicks' brain

Biological motion, the typical movement of vertebrates, is perceptually salient for many animal species. Newly hatched domestic chicks and human newborns show a spontaneous preference for simple biological motion stimuli (point-light displays) at birth prior to any visual learning. Despite evidence of such preference at birth, neural studies performed so far have focused on a specialized neural network involving primarily cortical areas. Here, we presented newly hatched visually naïve domestic chicks to either biological or rigid motion stimuli and measured for the first time their brain activation. Immediate Early Gene (c-Fos) expression revealed selective activation in the preoptic area of the hypothalamus and the nucleus taeniae of the amygdala. These results suggest that subpallial/subcortical regions play a crucial role in biological motion perception at hatching, paving the way for future studies on adult animals, including humans.

Studying dominance and aggression requires ethologically relevant paradigms

Although aggression is associated with several psychiatric disorders, there is no effective treatment nor a rigorous definition for "pathological aggression". Mice make a valuable model for studying aggression. They have a dynamic social structure that depends on the habitat and includes reciprocal interactions between the mice's aggression levels, social dominance hierarchy (SDH), and resource allocation. Nevertheless, the classical behavioral tests for territorial aggression and SDH in mice are reductive and have limited ethological and translational relevance. Recent work has explored the use of semi-natural environments to simultaneously study dominance-related behaviors, resource allocation, and aggressive behavior. Semi-natural setups allow experimental control of the environment combined with manipulations of neural activity. We argue that these setups can help bridge the translational gap in aggression research toward discovering neuronal mechanisms underlying maladaptive aggression.

Role of neuroestrogens in the regulation of social behaviors - From social recognition to mating

In this mini-review, we summarize the brain distribution of aromatase, the enzyme catalyzing the synthesis of estrogens from androgens, and the mechanisms responsible for regulating estrogen production within the brain. Understanding this local synthesis of estrogens by neurons is pivotal as it profoundly influences various facets of social behavior. Neuroestrogen action spans from the initial processing of socially pertinent sensory cues to integrating this information with an individual's internal state, ultimately resulting in the manifestation of either pro-affiliative or - aggressive behaviors. We focus here in particular on aggressive and sexual behavior as the result of correct individual recognition of intruders and potential mates. The data summarized in this review clearly point out the crucial role of locally synthesized estrogens in facilitating rapid adaptation to the social environment in rodents and birds of both sexes. These observations not only shed light on the evolutionary significance but also indicate the potential implications of these findings in the realm of human health, suggesting a compelling avenue for further investigation.

Effects of Gabapentin on the Treatment of Behavioral Disorders in Dogs: A Retrospective Evaluation

The use of gabapentin in treating dogs with behavioral disorders is not well described. To characterize behavioral effects of gabapentin, this study surveyed 50 owners whose dogs were prescribed gabapentin at a veterinary behavior-focused practice over a five-year period. Most owners (72%) reported that gabapentin was moderately or very effective at improving their dog's behavior. The majority of owners reported at least one side effect (70%), with sedation being the most common. Sedation was more likely to be seen at doses higher than 30 mg/kg. Specific dose ranges (mg/kg) did not correlate with any other reports of side effects nor effectiveness. Dogs with a diagnosis of conflict-related aggression were more likely to have owners report that gabapentin was effective at improving behavior compared to dogs with other behavioral diagnoses (p = 0.04), while dogs diagnosed with aggression secondary to high arousal were less likely to have owners report that gabapentin was effective (p = 0.01). Overall, reports of effect varied widely and, with the exception of sedation, did not correlate with specific mg/kg dose ranges. Results suggest that some dogs may be more sensitive or resistant to adverse and/or therapeutic effects than others and multiple dosage trials may be needed before finding the best fit.

Modulation of aggression by social novelty recognition memory in the hippocampal CA2 region

The dorsal CA2 subregion (dCA2) of the hippocampus exerts a critical role in social novelty recognition (SNR) memory and in the promotion of social aggression. Whether the social aggression and SNR memory functions of dCA2 are related or represent independent processes is unknown. Here we investigated the hypotheses that an animal is more likely to attack a novel compared to familiar animal and that dCA2 promotes social aggression through its ability to discriminate between novel and familiar conspecifics. To test these ideas, we conducted a multi-day resident intruder (R-I) test of aggression towards novel and familiar conspecifics. We found that mice were more likely to attack a novel compared to familiarized intruder and that silencing of dCA2 caused a more profound inhibition of aggression towards a novel than familiarized intruder. To explore whether and how dCA2 pyramidal neurons encode aggression, we recorded their activity using microendoscopic calcium imaging throughout the days of the R-I test. We found that a fraction of dCA2 neurons were selectively activated or inhibited during exploration, dominance, and attack behaviors and that these signals were enhanced during interaction with a novel compared to familiarized conspecific. Based on dCA2 population activity, a set of binary linear classifiers accurately decoded whether an animal was engaged in each of these forms of social behavior. Of particular interest, the accuracy of decoding aggression was greater with novel compared to familiarized intruders, with significant cross-day decoding using the same familiar animal on each day but not for a familiar-novel pair. Together, these findings demonstrate that dCA2 integrates information about social novelty with signals of behavioral state to promote aggression towards novel conspecifics.

Central amygdala is related to the reduction of aggressive behavior by monosodium glutamate ingestion during the period of development in an ADHD model rat

Introduction

Monosodium glutamate (MSG), an umami substance, stimulates the gut-brain axis communication via gut umami receptors and the subsequent vagus nerves. However, the brain mechanism underlying the effect of MSG ingestion during the developmental period on aggression has not yet been clarified. We first tried to establish new experimental conditions to be more appropriate for detailed analysis of the brain, and then investigated the effects of MSG ingestion on aggressive behavior during the developmental stage of an ADHD rat model.

Methods

Long-Evans, WKY/Izm, SHR/Izm, and SHR-SP/Ezo were individually housed from postnatal day 25 for 5 weeks. Post-weaning social isolation (PWSI) was given to escalate aggressive behavior. The resident-intruder test, that is conducted during the subjective night, was used for a detailed analysis of aggression, including the frequency, duration, and latency of anogenital sniffing, aggressive grooming, and attack behavior. Immunohistochemistry of c-Fos expression was conducted in all strains to predict potential aggression-related brain areas. Finally, the most aggressive strain, SHR/Izm, a known model of attention-deficit hyperactivity disorder (ADHD), was used to investigate the effect of MSG ingestion (60 mM solution) on aggression, followed by c-Fos immunostaining in aggression-related areas. Bilateral subdiaphragmatic vagotomy was performed to verify the importance of gut-brain interactions in the effect of MSG.

Results

The resident intruder test revealed that SHR/Izm rats were the most aggressive among the four strains for all aggression parameters tested. SHR/Izm rats also showed the highest number of c-Fos + cells in aggression-related brain areas, including the central amygdala (CeA). MSG ingestion significantly decreased the frequency and duration of aggressive grooming and attack behavior and increased the latency of attack behavior. Furthermore, MSG administration successfully increased c-Fos positive cell number in the intermediate nucleus of the solitary tract (iNTS), a terminal of the gastrointestinal sensory afferent fiber of the vagus nerve, and modulated c-Fos positive cells in the CeA. Interestingly, vagotomy diminished the MSG effects on aggression and c-Fos expression in the iNTS and CeA.

Conclusion

MSG ingestion decreased PWSI-induced aggression in SHR/Izm, which was mediated by the vagus nerve related to the stimulation of iNTS and modulation of CeA activity.

A Principal Components Analysis and Functional Annotation of Differentially Expressed Genes in Brain Regions of Gray Rats Selected for Tame or Aggressive Behavior

The process of domestication, despite its short duration as it compared with the time scale of the natural evolutionary process, has caused rapid and substantial changes in the phenotype of domestic animal species. Nonetheless, the genetic mechanisms underlying these changes remain poorly understood. The present study deals with an analysis of the transcriptomes from four brain regions of gray rats (Rattus norvegicus), serving as an experimental model object of domestication. We compared gene expression profiles in the hypothalamus, hippocampus, periaqueductal gray matter, and the midbrain tegmental region between tame domesticated and aggressive gray rats and revealed subdivisions of differentially expressed genes by principal components analysis that explain the main part of differentially gene expression variance. Functional analysis (in the DAVID (Database for Annotation, Visualization and Integrated Discovery) Bioinformatics Resources database) of the differentially expressed genes allowed us to identify and describe the key biological processes that can participate in the formation of the different behavioral patterns seen in the two groups of gray rats. Using the STRING- DB (search tool for recurring instances of neighboring genes) web service, we built a gene association network. The genes engaged in broad network interactions have been identified. Our study offers data on the genes whose expression levels change in response to artificial selection for behavior during animal domestication.

Neural correlates of aggression outcome expectation and their association with aggression: A voxel-based morphometry study

BACKGROUND

Aggression outcome expectation is an important cognitive factor of aggression. Discovering the neural mechanism of aggression outcome expectation is conducive to developing aggression research. However, the neural correlates underlying aggression outcome expectation and its effect remain elusive.

METHODS

We utilized voxel-based morphometry (VBM) to unravel the neural architecture of aggression outcome expectation measured by the Social Emotional Information Processing Assessment for Adults and its relationship with aggression measured by the Buss Perry Aggression Questionnaire in a sample of 185 university students (114 female; mean age = 19.94 ± 1.62 years; age range: 17-32 years).

RESULTS

We found a significantly positive correlation between aggression outcome expectation and the regional gray matter volume (GMV) in the right middle temporal gyrus (MTG) (x = 55.5, y = -58.5, z = 1.5; t = 3.35; cluster sizes = 352, p < 0.05, GRF corrected). Moreover, aggression outcome expectation acted as a mediator underlying the association between the right MTG volume and aggression.

CONCLUSIONS

These results revealed the neural correlates of aggression outcome expectation and its effect on aggression for the first time, which may contribute to our understanding of the cognitive neural mechanism of aggression and potentially identifying neurobiological markers for aggression.

Addressing Combative Behaviour in Spanish Bulls by Measuring Hormonal Indicators

The fighting bull is characterised by its natural aggressiveness, but the physiological mechanisms that underlie its aggressive behaviour are poorly studied. This study determines the hormonal component of aggressiveness in fighting bulls by analysing their behaviour during a fight and correlating it to their serotonin, dopamine and testosterone levels. We also determine whether aggressive behaviour can be estimated in calves. Using 195 animals, samples were obtained when the animals were calves and after 5 years. Aggressiveness scores were obtained by an observational method during bullfights, and serotonin, dopamine and testosterone levels were determined in all animals using validated enzyme immunoassay kits. The results revealed a strong correlation of serotonin and dopamine levels with aggressiveness scores in bulls during fights, but no correlation was found with respect to testosterone. These correlations led to established cut-off point and linear regression curves to obtain expected aggressiveness scores for calves at shoeing. There were no significant differences between the expected scores obtained in calves and the observed scores in bulls. Therefore, this study demonstrates that hormone determination in calves may be a great indicator of combativeness in bulls and can reliably be used in the selection of fighting bulls.

Substance P in the medial amygdala regulates aggressive behaviors in male mice

Behavioral and clinical studies have revealed a critical role of substance P (SP) in aggression; however, the neural circuit mechanisms underlying SP and aggression remain elusive. Here, we show that tachykinin-expressing neurons in the medial amygdala (MeATac1 neurons) are activated during aggressive behaviors in male mice. We identified MeATac1 neurons as a key mediator of aggression and found that MeATac1→ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl) projections are critical to the regulation of aggression. Moreover, SP/neurokinin-1 receptor (NK-1R) signaling in the VMHvl modulates aggressive behaviors in male mice. SP/NK-1R signaling regulates aggression by influencing glutamate transmission in neurons in the VMHvl. In summary, these findings place SP as a key node in aggression circuits.

Sexually dimorphic control of aggression by androgen signaling in a cichlid

Innate social behaviors like aggression are modulated by sex steroid hormones such as androgens and estrogens. However, we know little about how the same hormone regulates similar behaviors in both sexes. We investigated the role of androgenic signaling in the regulation of aggression in Astatotilapia burtoni, a social fish in which males and females perform similar aggressive behaviors. We used ARa knockout (KO) animals for this study, which was recently shown to be required for male-typical aggression and mating. Surprisingly, ARα KO females did not show deficits in aggression. We also determined that females lacking the other AR, ARβ, showed normal levels of aggression. Blocking both ARs pharmacologically confirmed that neither AR is necessary for aggression in females. However, ARα KO males showed clear deficits in attacks. Thus, in A. burtoni there appears to be a sexual dimorphism in the role of ARα in the control of aggression.

Transforming aggression into creativity: Creative thinking training as a new strategy for aggression intervention

Although reducing students' aggressive behaviors and improving their creativity are both important commitments of educators, they are usually treated independently as unrelated tasks. However, cumulative evidence suggests potential links between aggression and creativity, not only from the perspectives of personality traits and psychological development, but also from their shared cognitive mechanisms. This implies that there may be an approach to achieving these two goals through a single intervention. Moreover, this new approach may overcome the limitation of the usually adopted aggression intervention, which is limited in its regulatory effectiveness and might bring about some disadvantageous impacts on creativity that are closely associated with aggression. To test this possibility, the present study implemented a four-session, 2-week creative thinking training (CTT) intervention for students with high aggression scores to examine whether it could simultaneously downregulate aggression and increase creativity. Our results demonstrate that, compared to the control group, the intervention group experienced significant improvements in creativity and a reduction in aggression following the CTT intervention. Furthermore, our findings suggest that this regulatory effect can persist for up to 6 months. The CTT-induced creativity change (increase) could significantly correlate with and predict the CTT-induced aggression decrease, thus suggesting that the CTT could transform aggression into creativity.

Effect of a Territorial Challenge on the Steroid Profile of a Juvenile Songbird

Aggression is a social behavior that is critical for survival and reproduction. In adults, circulating gonadal hormones, such as androgens, act on neural circuits to modulate aggressive interactions, especially in reproductive contexts. In many species, individuals also demonstrate aggression before reaching gonadal maturation. Adult male song sparrows, Melospiza melodia, breed seasonally but maintain territories year-round. Juvenile (hatch-year) males aggressively compete for territory ownership during their first winter when circulating testosterone is low. Here, we characterized the relationship between the steroid milieu and aggressive behavior in free-living juvenile male song sparrows in winter. We investigated the effect of a 10 min simulated territorial intrusion (STI) on behavior and steroid levels in blood, 10 microdissected brain regions, and four peripheral tissues (liver, pectoral muscle, adrenal glands, and testes). Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we quantified 12 steroids: pregnenolone, progesterone, corticosterone, 11-dehydrocorticosterone, dehydroepiandrosterone, androstenedione, testosterone, 5α-dihydrotestosterone, 17β-estradiol, 17α-estradiol, estrone, and estriol. We found that juvenile males are robustly aggressive, like adult males. An STI increases progesterone and corticosterone levels in blood and brain and increases 11-dehydrocorticosterone levels in blood only. Pregnenolone, androgens, and estrogens are generally non-detectable and are not affected by an STI. In peripheral tissues, steroid concentrations are very high in the adrenals. These data suggest that adrenal steroids, such as progesterone and corticosterone, might promote juvenile aggression and that juvenile and adult songbirds might rely on distinct neuroendocrine mechanisms to support similar aggressive behaviors.

Postweaning intermittent sleep deprivation enhances defensive attack in adult female mice via the microbiota-gut-brain axis

Sleep is one of the most important physiological activities in life and promotes the growth and development of an individual. In modern society, sleep deprivation (SD), especially among adolescents, has become a common phenomenon. However, long-term SD severely affected adolescents' neurodevelopment leading to abnormal behavioral phenotypes. Clinical studies indicated that sleep problems caused increased aggressive behavior in adolescents. Aggressive behavior was subordinate to social behaviors, in which defensive attack was often the last line for survival. Meanwhile, increasing studies shown that gut microbiota regulated social behaviors by affecting specific brain regions via the gut-brain axis. However, whether postweaning intermittent SD is related to defensive attack in adulthood, and if so, whether it is mediated by the microbiota-gut-brain axis are still elusive. Combined with microbial sequencing and hippocampal metabolomics, the present study mainly investigated the long-term effects of postweaning intermittent SD on defensive attack in adult mice. Our study demonstrated that postweaning intermittent SD enhanced defensive attack and impaired long-term memory formation in adult female mice. Moreover, microbial sequencing and LC-MS analysis showed that postweaning intermittent SD altered the gut microbial composition and the hippocampal metabolic profile in female mice, respectively. Our attention has been drawn to the neuroactive ligand-receptor interaction pathway and related metabolites. In conclusion, our findings provide a new perspective on the relationship of early-life SD and defensive attack in adulthood, and also highlight the importance of sleep in early-life, especially in females.

What does metaphoric language say about aggression? The relationships between metaphoric language, impulsivity, and aggression

Aggressive behavior among adolescents has been identified as a serious worldwide problem, especially when combined with trait impulsivity. This study investigates the impact of an overlooked aspect of language, namely, metaphor comprehension, on impulsivity and aggression in adolescents. A total of 204 adolescents completed self-reported questionnaires assessing impulsivity and aggression and underwent tests assessing familiar and less familiar metaphor comprehension. The findings reveal inverse relationships between metaphor comprehension and both impulsivity and aggression. Regarding aggression, notable distinctions were observed in the correlations between familiar and less familiar metaphors with specific aggression types. Additionally, impulsivity was found to mediate the relationship between the comprehension of familiar metaphors and aggression. These results are elucidated in the context of cognitive and executive functions, emphasizing the significance of considering metaphor comprehension as a cognitive process capable of modulating aggressive behavior.

Neurons underlying aggressive actions that are shared by both males and females in Drosophila

Aggression involves both sexually monomorphic and dimorphic actions. How the brain implements these two types of actions is poorly understood. We found that a set of neurons, which we call CL062, previously shown to mediate male aggression also mediate female aggression. These neurons elicit aggression acutely and without the presence of a target. Although the same set of actions is elicited in males and females, the overall behavior is sexually dimorphic. The CL062 neurons do not express fruitless , a gene required for sexual dimorphism in flies, and expressed by most other neurons important for controlling fly aggression. Connectomic analysis suggests that these neurons have limited connections with fruitless expressing neurons that have been shown to be important for aggression, and signal to different descending neurons. Thus, CL062 is part of a monomorphic circuit for aggression that functions parallel to the known dimorphic circuits.

Sex differences in aggression and its neural substrate in a cichlid fish

Aggression is ubiquitous among social species and functions to maintains social dominance hierarchies. The African cichlid fish Astatotilapia burtoni is an ideal study species for studying aggression due to their unique and flexible dominance hierarchy. However, female aggression in this species and the neural mechanisms of aggression in both sexes is not well understood. To further understand the potential sex differences in aggression in this species, we characterized aggression in male and female A. burtoni in a mirror assay. We then quantified neural activation patterns in brain regions of the social behavior network (SBN) to investigate if differences in behavior are reflected in the brain with immunohistochemistry by detecting the phosphorylated ribosome marker phospho-S6 ribosomal protein (pS6), a marker for neural activation. We found that A. burtoni perform both identical and sex-specific aggressive behaviors in response to a mirror assay. We observed sex differences in pS6 immunoreactivity in the Vv, a homolog of the lateral septum in mammals. Males but not females had higher ps6 immunoreactivity in the ATn after the aggression assay. The ATn is a homolog of the ventromedial hypothalamus in mammals, which is strongly implicated in the regulation of aggression in males. Several regions also have higher pS6 immunoreactivity in negative controls than fish exposed to a mirror, implicating a role for inhibitory neurons in suppressing aggression until a relevant stimulus is present. Male and female A. burtoni display both similar and sexually dimorphic behavioral patterns in aggression in response to a mirror assay. There are also sex differences in the corresponding neural activation patterns in the SBN. In mirror males but not females, the ATn clusters with the POA, revealing a functional connectivity of these regions that is triggered in an aggressive context in males. These findings suggest that distinct neural circuitry underlie aggressive behavior in male and female A. burtoni, serving as a foundation for future work investigating the molecular and neural underpinnings of sexually dimorphic behaviors in this species to reveal fundamental insights into understanding aggression.

Structural brain abnormalities and aggressive behaviour in schizophrenia: Mega-analysis of data from 2095 patients and 2861 healthy controls via the ENIGMA consortium

Background

Schizophrenia is associated with an increased risk of aggressive behaviour, which may partly be explained by illness-related changes in brain structure. However, previous studies have been limited by group-level analyses, small and selective samples of inpatients and long time lags between exposure and outcome.

Methods

This cross-sectional study pooled data from 20 sites participating in the international ENIGMA-Schizophrenia Working Group. Sites acquired T1-weighted and diffusion-weighted magnetic resonance imaging scans in a total of 2095 patients with schizophrenia and 2861 healthy controls. Measures of grey matter volume and white matter microstructural integrity were extracted from the scans using harmonised protocols. For each measure, normative modelling was used to calculate how much patients deviated (in z-scores) from healthy controls at the individual level. Ordinal regression models were used to estimate the associations of these deviations with concurrent aggressive behaviour (as odds ratios [ORs] with 99% confidence intervals [CIs]). Mediation analyses were performed for positive symptoms (i.e., delusions, hallucinations and disorganised thinking), impulse control and illness insight. Aggression and potential mediators were assessed with the Positive and Negative Syndrome Scale, Scale for the Assessment of Positive Symptoms or Brief Psychiatric Rating Scale.

Results

Aggressive behaviour was significantly associated with reductions in total cortical volume (OR [99% CI] = 0.88 [0.78, 0.98], p = .003) and global white matter integrity (OR [99% CI] = 0.72 [0.59, 0.88], p = 3.50 × 10-5) and additional reductions in dorsolateral prefrontal cortex volume (OR [99% CI] = 0.85 [0.74, 0.97], p =.002), inferior parietal lobule volume (OR [99% CI] = 0.76 [0.66, 0.87], p = 2.20 × 10-7) and internal capsule integrity (OR [99% CI] = 0.76 [0.63, 0.92], p = 2.90 × 10-4). Except for inferior parietal lobule volume, these associations were largely mediated by increased severity of positive symptoms and reduced impulse control.

Conclusions

This study provides evidence that the co-occurrence of positive symptoms, poor impulse control and aggressive behaviour in schizophrenia has a neurobiological basis, which may inform the development of therapeutic interventions.

Androgen receptor deficiency is associated with reduced aromatase expression in the ventromedial hypothalamus of male cichlids

Social behaviors are regulated by sex steroid hormones, such as androgens and estrogens. However, the specific molecular and neural processes modulated by steroid hormones to generate social behaviors remain to be elucidated. We investigated whether some actions of androgen signaling in the control of social behavior may occur through the regulation of estradiol synthesis in the highly social cichlid fish, Astatotilapia burtoni. Specifically, we examined the expression of cyp19a1, a brain-specific aromatase, in the brains of male A. burtoni lacking a functional ARα gene (ar1), which was recently found to be necessary for aggression in this species. We found that cyp19a1 expression is higher in wild-type males compared to ar1 mutant males in the anterior tuberal nucleus (ATn), the putative fish homolog of the mammalian ventromedial hypothalamus, a brain region that is critical for aggression across taxa. Using in situ hybridization chain reaction, we determined that cyp19a1+ cells coexpress ar1 throughout the brain, including in the ATn. We speculate that ARα may modulate cyp19a1 expression in the ATn to govern aggression in A. burtoni. These studies provide novel insights into the hormonal mechanisms of social behavior in teleosts and lay a foundation for future functional studies.

The serotonin blocker Ketanserin reduces coral reef fish Ctenochaetus striatus aggressive behaviour during between-species social interactions

A multitude of species engages in social interactions not only with their conspecifics but also with other species. Such interspecific interactions can be either positive, like helping, or negative, like aggressive behaviour. However, the physiological mechanisms of these behaviours remain unclear. Here, we manipulated the serotonin system, a well-known neurohormone for regulating intraspecific aggressive behaviour, to investigate its role in interspecific aggression. We tested whether serotonin blockade affects the aggressive behaviour of a coral reef fish species (Ctenochaetus striatus) that engages in mutualistic interactions with another species, the cleaner fish (Labroides dimidiatus). Although this mutualistic cleaning relationship may appear positive, cleaner fish do not always cooperate and remove ectoparasites from the other coral reef fish ("clients") but tend to cheat and bite the client's protective layer of mucus. Client fish thus often apply control mechanisms, like chasing, to deter their cleaner fish partners from cheating. Our findings show that blocking serotonin receptors 5-HT2A and 5-HT2C with ketanserin reduced the client fish's aggressive behaviour towards cleaner fish, but in the context where the latter did not cheat. These results are evidence of the involvement of serotonin in regulating aggressive behaviour at the between-species social interactions level. Yet, the direction of effect we found here is the opposite of previous findings using a similar experimental set-up and ecological context but with a different client fish species (Scolopsis bilineatus). Together, it suggests that serotonin's role in aggressive behaviour is complex, and at least in this mutualistic ecological context, its function is species-dependent. This warrants, to some extent, careful interpretations from single-species studies looking into the physiological mechanisms of social behaviour.

Male-specific vasotocin expression in the medaka tuberal hypothalamus: Androgen dependence and probable role in aggression

Terrestrial vertebrates have a population of androgen-dependent vasotocin (VT)-expressing neurons in the extended amygdala that are more abundant in males and mediate male-typical social behaviors, including aggression. Teleosts lack these neurons but instead have novel male-specific VT-expressing neurons in the tuberal hypothalamus. Here we found in medaka that vt expression in these neurons is dependent on post-pubertal gonadal androgens and that androgens can act on these neurons to directly stimulate vt transcription via the androgen receptor subtype Ara. Furthermore, administration of exogenous VT induced aggression in females and alterations in the androgen milieu led to correlated changes in the levels of tuberal hypothalamic vt expression and aggression in both sexes. However, genetic ablation of vt failed to prevent androgen-induced aggression in females. Collectively, our results demonstrate a marked androgen dependence of male-specific vt expression in the teleost tuberal hypothalamus, although its relevance to male-typical aggression needs to be further validated.

Identifying behavioral links to neural dynamics of multifiber photometry recordings in a mouse social behavior network

Distributed hypothalamic-midbrain neural circuits orchestrate complex behavioral responses during social interactions. How population-averaged neural activity measured by multi-fiber photometry (MFP) for calcium fluorescence signals correlates with social behaviors is a fundamental question. We propose a state-space analysis framework to characterize mouse MFP data based on dynamic latent variable models, which include continuous-state linear dynamical system (LDS) and discrete-state hidden semi-Markov model (HSMM). We validate these models on extensive MFP recordings during aggressive and mating behaviors in male-male and male-female interactions, respectively. Our results show that these models are capable of capturing both temporal behavioral structure and associated neural states. Overall, these analysis approaches provide an unbiased strategy to examine neural dynamics underlying social behaviors and reveals mechanistic insights into the relevant networks.

How it ends: A review of behavioral and psychological phenomena, physiological processes and neural circuits in the termination of aggression in other animals and anger in people

More is known about aggression initiation and persistence in other animals, and anger in people, than about their cessation. This review summarizes knowledge of relevant factors in aggression, mostly in vertebrates, and anger termination in people. The latency, probability and intensity of offensive aggression in mice is controlled by activity in a neuronal subpopulation in ventromedial hypothalamus [VMH]. This activity instantiates an aggressive state termed angriffsbereitschaft ["attack-readiness"]. Fighting in many species is broken into bouts with interbout breaks due to fatigue and/or signals from dorsal raphe to VMH. Eventually, losers decide durations and outcomes of fighting by transitioning to submission or flight. Factors reducing angriffsbereitschaft and triggering these defeat behaviors could include metabolic costs, e.g., lactate accumulation and glucose depletion detected by the hypothalamus, central fatigue perhaps sensed by the Salience Network [insula and anterior cingulate gyrus] and pain of injuries, the latter insufficiently blunted by opioid and non-opioid stress analgesia and transduced by anterior VMH neurons. Winners' angriffsbereitschaft continue for awhile, as indicated by post-victory attacks and, perhaps, triumph displays of some species, including humans. In longer term situations, sensory and/or response habituation of aggression may explain the "Dear enemy" tolerance of competitive neighbors. Prolonged satiation of predatory behavior could involve habenula-regulated reduction of dopaminergic reward in nucleus accumbens. Termination of human anger involves at least three processes, metaphorically termed decay, quenching and catharsis. Hypothesized neural mechanisms include anger diminution by negative feedback from accumbens to anterior cingulate and/or activity in the Salience Network that controls anger's "accumulation/offset" phase.

Disruption of Cdk5-GluN2B complex by a small interfering peptide attenuates social isolation-induced escalated intermale attack behavior and hippocampal oxidative stress in mice

Social isolation has emerged as a significant issue during the COVID-19 pandemic that can adversely impact human mental health and potentially lead to pathological aggression. Given the lack of effective therapeutic interventions for aggressive behavior, alternative approaches are necessary. In this study, we utilized a genetic method combined with a pharmacological approach to identify and demonstrate the crucial role of Cdk5 in escalated intermale attack behavior induced by 2-week social isolation. Moreover, we developed a small peptide that effectively disrupts the interaction between Cdk5 and GluN2B, given the known involvement of this complex in various neuropsychiatric disorders. Administration of the peptide, either systemically or via intrahippocampal injection, significantly reduced oxidative stress in the hippocampus and attenuated intermale attack behavior induced by 2-week social isolation. These findings highlight the previously unknown role of the hippocampal Cdk5-GluN2B complex in social isolation-induced aggressive behavior in mice and propose the peptide as a promising therapeutic strategy for regulating attack behavior and oxidative stress.

A New Behavioral Paradigm for Frustrative Nonreward in Juvenile Mice

Background

Irritability, defined as proneness to anger, can reach a pathological extent. It is a defining symptom of disruptive mood dysregulation disorder and one of the most common reasons youths present for psychiatric evaluation and care. Aberrant responses to frustrative nonreward (FNR), the response to omission of expected reward, are central to the pathophysiology of irritability. FNR is a translational construct to study irritability across species. The development of preclinical FNR models would advance mechanistic studies of the important and relatively understudied clinical phenomenon of irritability.

Methods

We used FNR as a conceptual framework to develop a novel mouse behavioral paradigm named alternate poking reward omission. Juvenile mice were exposed to alternate poking reward omission and then examined with a battery of behavioral tests to determine the behavioral effect of FNR.

Results

FNR increased locomotion and aggression regardless of sex. These behavioral changes elicited by FNR resemble the symptoms observed in youth with severe irritability. FNR had no effect on anxiety-like, depression-like, or nonaggressive social behaviors.

Conclusions

Our alternate poking reward omission paradigm effectively elevated aggression and locomotion in juvenile mice. These frustration effects are directly related to behavioral symptoms of youth with severe irritability. Our novel behavioral paradigm lays the groundwork for further mechanistic studies of frustration and irritability in rodents.

Transcriptionally defined amygdala subpopulations play distinct roles in innate social behaviors

Social behaviors are innate and supported by dedicated neural circuits, but the molecular identities of these circuits and how they are established developmentally and shaped by experience remain unclear. Here we show that medial amygdala (MeA) cells originating from two embryonically parcellated developmental lineages have distinct response patterns and functions in social behavior in male mice. MeA cells expressing the transcription factor Foxp2 (MeAFoxp2) are specialized for processing male conspecific cues and are essential for adult inter-male aggression. By contrast, MeA cells derived from the Dbx1 lineage (MeADbx1) respond broadly to social cues, respond strongly during ejaculation and are not essential for male aggression. Furthermore, MeAFoxp2 and MeADbx1 cells show differential anatomical and functional connectivity. Altogether, our results suggest a developmentally hardwired aggression circuit at the MeA level and a lineage-based circuit organization by which a cell's embryonic transcription factor profile determines its social information representation and behavioral relevance during adulthood.

Subcortical volumetric alterations in four major psychiatric disorders: a mega-analysis study of 5604 subjects and a volumetric data-driven approach for classification

Differential diagnosis is sometimes difficult in practical psychiatric settings, in terms of using the current diagnostic system based on presenting symptoms and signs. The creation of a novel diagnostic system using objective biomarkers is expected to take place. Neuroimaging studies and others reported that subcortical brain structures are the hubs for various psycho-behavioral functions, while there are so far no neuroimaging data-driven clinical criteria overcoming limitations of the current diagnostic system, which would reflect cognitive/social functioning. Prior to the main analysis, we conducted a large-scale multisite study of subcortical volumetric and lateralization alterations in schizophrenia, bipolar disorder, major depressive disorder, and autism spectrum disorder using T1-weighted images of 5604 subjects (3078 controls and 2526 patients). We demonstrated larger lateral ventricles volume in schizophrenia, bipolar disorder, and major depressive disorder, smaller hippocampus volume in schizophrenia and bipolar disorder, and schizophrenia-specific smaller amygdala, thalamus, and accumbens volumes and larger caudate, putamen, and pallidum volumes. In addition, we observed a leftward alteration of lateralization for pallidum volume specifically in schizophrenia. Moreover, as our main objective, we clustered the 5,604 subjects based on subcortical volumes, and explored whether data-driven clustering results can explain cognitive/social functioning in the subcohorts. We showed a four-biotype classification, namely extremely (Brain Biotype [BB] 1) and moderately smaller limbic regions (BB2), larger basal ganglia (BB3), and normal volumes (BB4), being associated with cognitive/social functioning. Specifically, BB1 and BB2-3 were associated with severe and mild cognitive/social impairment, respectively, while BB4 was characterized by normal cognitive/social functioning. Our results may lead to the future creation of novel biological data-driven psychiatric diagnostic criteria, which may be expected to be useful for prediction or therapeutic selection.

Neuropeptide Signaling is Required to Implement a Line Attractor Encoding a Persistent Internal Behavioral State

Internal states drive survival behaviors, but their neural implementation is not well understood. Recently we identified a line attractor in the ventromedial hypothalamus (VMH) that represents an internal state of aggressiveness. Line attractors can be implemented by recurrent connectivity and/or neuromodulatory signaling, but evidence for the latter is scant. Here we show that neuropeptidergic signaling is necessary for line attractor dynamics in this system, using a novel approach that integrates cell type-specific, anatomically restricted CRISPR/Cas9-based gene editing with microendoscopic calcium imaging. Co-disruption of receptors for oxytocin and vasopressin in adult VMH Esr1 + neurons that control aggression suppressed attack, reduced persistent neural activity and eliminated line attractor dynamics, while only modestly impacting neural activity and sex- or behavior-tuning. These data identify a requisite role for neuropeptidergic signaling in implementing a behaviorally relevant line attractor. Our approach should facilitate mechanistic studies in neuroscience that bridge different levels of biological function and abstraction.

Hypothalamic control of innate social behaviors

Sexual, parental, and aggressive behaviors are central to the reproductive success of individuals and species survival and thus are supported by hardwired neural circuits. The reproductive behavior control column (RBCC), which comprises the medial preoptic nucleus (MPN), the ventrolateral part of the ventromedial hypothalamus (VMHvl), and the ventral premammillary nucleus (PMv), is essential for all social behaviors. The RBCC integrates diverse hormonal and metabolic cues and adjusts an animal's physical activity, hence the chance of social encounters. The RBCC further engages the mesolimbic dopamine system to maintain social interest and reinforces cues and actions that are time-locked with social behaviors. We propose that the RBCC and brainstem form a dual-control system for generating moment-to-moment social actions. This Review summarizes recent progress regarding the identities of RBCC cells and their pathways that drive different aspects of social behaviors.

Neural dynamics in the limbic system during male social behaviors

Sexual and aggressive behaviors are vital for species survival and individual reproductive success. Although many limbic regions have been found relevant to these behaviors, how social cues are represented across regions and how the network activity generates each behavior remains elusive. To answer these questions, we utilize multi-fiber photometry (MFP) to simultaneously record Ca2+ signals of estrogen receptor alpha (Esr1)-expressing cells from 13 limbic regions in male mice during mating and fighting. We find that conspecific sensory information and social action signals are widely distributed in the limbic system and can be decoded from the network activity. Cross-region correlation analysis reveals striking increases in the network functional connectivity during the social action initiation phase, whereas late copulation is accompanied by a "dissociated" network state. Based on the response patterns, we propose a mating-biased network (MBN) and an aggression-biased network (ABN) for mediating male sexual and aggressive behaviors, respectively.

Endocannabinoid system and aggression across animal species

This narrative review article summarizes the current state of knowledge regarding the relationship between the endocannabinoid system (ECS) and aggression across multiple vertebrate species. Experimental evidence indicates that acute administration of phytocannabinoids, synthetic cannabinoids, and the pharmacological enhancement of endocannabinoid signaling decreases aggressive behavior in several animal models. However, research on the chronic effects of cannabinoids on animal aggression has yielded inconsistent findings, indicating a need for further investigation. Cannabinoid receptors, particularly cannabinoid receptor type 1, appear to be an important part of the endogenous mechanism involved in the dampening of aggressive behavior. Overall, this review underscores the importance of the ECS in regulating aggressive behavior and provides a foundation for future research in this area.

Effects of childhood trauma on aggressive behaviors and hippocampal function: the modulation of COMT haplotypes

Background

Aggression is a commonly hostile behavior linked to the hippocampal activity. Childhood trauma (CT) exposure has been associated with altered sensitization of the hypothalamic-pituitary-adrenal (HPA) axis and hippocampal volume，which could increase violent aggressive behaviors. Additionally, Catechol-O-methyltransferase (COMT), the major dopamine metabolism enzyme, is implicated in stress responsivity, including aggression. Hence, CT exposure may affect aggression through the effect on the hippocampal function, which might also be modulated by the COMT variations.

Objectives

This study examined whether both CT and haplotypes of COMT moderate hippocampal function and thus affect human aggressive behavior.

Methods

We obtained bilateral hippocampal functional connectivity maps using resting state functional magnetic resonance imaging (MRI) data. COMT haplotype estimation was performed using Haploview 4.2 and PHASE 2.1. Then we constructed a moderated mediation model to study the effect of the CTQ × COMT on aggressive behavior.

Results

Three major haplotypes were generated from thirteen single nucleotide polymorphisms (SNPs) within the COMT gene and formed three haplotypes corresponding to high, medium, and low enzymatic activity of COMT. The results showed interactive relationships between the Childhood Trauma Questionnaire (CTQ) and COMT with respect to the functional connectivity (FC) of the bilateral hippocampus (HIP)-orbital frontal cortex (OFC). Specifically, CT experience predicted lower negative HIP-OFC coupling in the APS and HPS haplotypes corresponding to the medium and high enzymatic activity of COMT, but greater FC in the LPS haplotypes corresponding to the low enzymatic activity. We also observed a conditional mediation effect of the right HIP-OFC coupling in the link between COMT and aggressive behavior that was moderated by CT experience.

Conclusions

These results suggest that CT and COMT have a combined effect on aggressive behavior through hippocampal function. This mediation analysis sheds light on the influence of childhood experience on aggressive behavior in different genetic backgrounds.

Fighting Flies: Quantifying and Analyzing Drosophila Aggression

Aggression is an innate behavior that likely evolved in the framework of defending or obtaining resources. This complex social behavior is influenced by genetic, environmental, and internal factors. Drosophila melanogaster remains an effective and exciting model organism with which to unravel the mechanistic basis of aggression due to its small but sophisticated brain, an impressive array of neurogenetic tools, and robust stereotypical behavioral patterns. The investigations of many laboratories have led to the identification of external and internal state factors that promote aggression, sex differences in the patterns and outcome of aggression, and neurotransmitters that regulate aggression.

A neural circuit for male sexual behavior and reward

Male sexual behavior is innate and rewarding. Despite its centrality to reproduction, a molecularly specified neural circuit governing innate male sexual behavior and reward remains to be characterized. We have discovered a developmentally wired neural circuit necessary and sufficient for male mating. This circuit connects chemosensory input to BNSTprTac1 neurons, which innervate POATacr1 neurons that project to centers regulating motor output and reward. Epistasis studies demonstrate that BNSTprTac1 neurons are upstream of POATacr1 neurons, and BNSTprTac1-released substance P following mate recognition potentiates activation of POATacr1 neurons through Tacr1 to initiate mating. Experimental activation of POATacr1 neurons triggers mating, even in sexually satiated males, and it is rewarding, eliciting dopamine release and self-stimulation of these cells. Together, we have uncovered a neural circuit that governs the key aspects of innate male sexual behavior: motor displays, drive, and reward.

The gradual coevolution of syntactic combinatorics and categorization under the effects of human self-domestication: a proposal

The gradual emergence of syntax has been claimed to be engaged in a feedback loop with Human Self-Domestication (HSD), both processes resulting from, and contributing to, enhanced connectivity in selected cortico-striatal networks, which is the mechanism for attenuating reactive aggression, the hallmark of HSD, but also the mechanism of cross-modality, relevant for syntax. Here, we aim to bridge the gap between these brain changes and further changes facilitated by the gradual complexification of grammars. We propose that increased cross-modality would have enabled and supported, more specifically, a feedback loop between categorization abilities relevant for vocabulary building and the gradual emergence of syntactic structure, including Merge. In brief, an enhanced categorization ability not only brings about more distinct categories, but also a critical number of tokens in each category necessary for Merge to take off in a systematic and productive fashion; in turn, the benefits of expressive capabilities brought about by productive Merge encourage more items to be categorized, and more categories to be formed, thus further potentiating categorization abilities, and with it, syntax again. We support our hypothesis with evidence from the domains of language development and animal communication, but also from biology, neuroscience, paleoanthropology, and clinical linguistics.

Sex and seasonal differences in neural steroid sensitivity predict territorial aggression in Siberian hamsters

Many animals display marked changes in physiology and behavior on a seasonal timescale, including non-reproductive social behaviors (e.g., aggression). Previous studies from our lab suggest that the pineal hormone melatonin acts via steroid hormones to regulate seasonal aggression in Siberian hamsters (Phodopus sungorus), a species in which both males and females display increased non-breeding aggression. The neural actions of melatonin on steroids and aggressive behavior, however, are relatively unexplored. Here, we housed male and female hamsters in long-day photoperiods (LDs, characteristic of breeding season) or short-day photoperiods (SDs, characteristic of non-breeding season) and administered timed melatonin (M) or control injections. Following 10 weeks of treatment, we quantified aggressive behavior and neural steroid sensitivity by measuring the relative mRNA expression of two steroidogenic enzymes (aromatase and 5α-reductase 3) and estrogen receptor 1 in brain regions associated with aggression or reproduction [medial preoptic area (MPOA), anterior hypothalamus (AH), arcuate nucleus (ARC), and periaqueductal gray (PAG)] via quantitative PCR. Although LD-M and SD males and females displayed increased aggression and similar changes in gene expression in the ARC, there were sex-specific effects of treatment with melatonin and SDs on gene expression in the MPOA, AH, and PAG. Furthermore, males and females exhibited different relationships between neural gene expression and aggression in response to melatonin and SDs. Collectively, these findings support a role for melatonin in regulating seasonal variation in neural steroid sensitivity and aggression and reveal how distinct neuroendocrine responses may modulate a similar behavioral phenotype in male and female hamsters.

Neural Control of Sexually Dimorphic Social Behavior: Connecting Development to Adulthood

Rapid advances in the neural control of social behavior highlight the role of interconnected nodes engaged in differential information processing to generate behavior. Many innate social behaviors are essential to reproductive fitness and therefore fundamentally different in males and females. Programming these differences occurs early in development in mammals, following gonadal differentiation and copious androgen production by the fetal testis during a critical period. Early-life programming of social behavior and its adult manifestation are separate but yoked processes, yet how they are linked is unknown. This review seeks to highlight that gap by identifying four core mechanisms (epigenetics, cell death, circuit formation, and adult hormonal modulation) that could connect developmental changes to the adult behaviors of mating and aggression. We further propose that a unique social behavior, adolescent play, bridges the preweaning to the postpubertal brain by engaging the same neural networks underpinning adult reproductive and aggressive behaviors.

A New Behavioral Paradigm for Frustrative Non-reward Reveals a Global Change in Brain Networks by Frustration

Background

Irritability, defined as proneness to anger, can reach a pathological extent. It is a defining symptom of Disruptive Mood Dysregulation Disorder (DMDD) and one of the most common reasons youth presents for psychiatric evaluation and care. Aberrant responses to frustrative non-reward (FNR, the response to omission of expected reward) are central to the pathophysiology of irritability. FNR is a translational construct to study irritability across species. The development of preclinical FNR models would advance mechanistic studies of the important and relatively understudied clinical phenomenon of irritability.

Methods

We used FNR as a conceptual framework to develop a novel mouse behavioral paradigm named Alternate Poking Reward Omission (APRO). After APRO, mice were examined with a battery of behavioral tests and processed for whole brain c-Fos imaging. FNR increases locomotion and aggression in mice regardless of sex. These behavioral changes resemble the symptoms observed in youth with severe irritability. There is no change in anxiety-like, depression-like, or non-aggressive social behaviors. FNR increases c-Fos+ neurons in 13 subregions of thalamus, iso-cortex and hippocampus including the prelimbic, ACC, hippocampus, dorsal thalamus, cuneiform nucleus, pons, and pallidum areas. FNR also shifts the brain network towards a more global processing mode.

Conclusion

Our novel FNR paradigm produces a frustration effect and alters brain processing in ways resembling the symptoms and brain network reconfiguration observed in youth with severe irritability. The novel behavioral paradigm and identified brain regions lay the groundwork for further mechanistic studies of frustration and irritability in rodents.

The (Co)Evolution of Language and Music Under Human Self-Domestication

Together with language, music is perhaps the most distinctive behavioral trait of the human species. Different hypotheses have been proposed to explain why only humans perform music and how this ability might have evolved in our species. In this paper, we advance a new model of music evolution that builds on the self-domestication view of human evolution, according to which the human phenotype is, at least in part, the outcome of a process similar to domestication in other mammals, triggered by the reduction in reactive aggression responses to environmental changes. We specifically argue that self-domestication can account for some of the cognitive changes, and particularly for the behaviors conducive to the complexification of music through a cultural mechanism. We hypothesize four stages in the evolution of music under self-domestication forces: (1) collective protomusic; (2) private, timbre-oriented music; (3) small-group, pitch-oriented music; and (4) collective, tonally organized music. This line of development encompasses the worldwide diversity of music types and genres and parallels what has been hypothesized for languages. Overall, music diversity might have emerged in a gradual fashion under the effects of the enhanced cultural niche construction as shaped by the progressive decrease in reactive (i.e., impulsive, triggered by fear or anger) aggression and the increase in proactive (i.e., premeditated, goal-directed) aggression.

A test of the social behavior network reveals differential patterns of neural responses to social novelty in bonded, but not non-bonded, male prairie voles

The social behavior network (SBN) has provided a framework for understanding the neural control of social behavior. The original SBN hypothesis proposed this network modulates social behavior and should exhibit distinct patterns of neural activity across nodes, which correspond to distinct social contexts. Despite its tremendous impact on the field of social neuroscience, no study has directly tested this hypothesis. Thus, we assessed Fos responses across the SBN of male prairie voles (Microtus ochrogaster). Virgin/non-bonded and pair bonded subjects were exposed to a sibling cagemate or pair bonded partner, novel female, novel male, novel meadow vole, novel object, or no stimulus. Inconsistent with the original SBN hypothesis, we did not find profoundly different patterns of neural responses across the SBN for different contexts, but instead found that the SBN generated significantly different patterns of activity in response to social novelty in pair bonded, but not non-bonded males. These findings suggest that non-bonded male prairie voles may perceive social novelty differently from pair bonded males or that SBN functionality undergoes substantial changes after pair bonding. This study reveals novel information about bond-dependent, context-specific neural responsivity in male prairie voles and suggests that the SBN may be particularly important for processing social salience. Further, our study suggests there is a need to reconceptualize the framework of how the SBN modulates social behavior.

Non-Invasive Brain Stimulation for the Modulation of Aggressive Behavior-A Systematic Review of Randomized Sham-Controlled Studies

INTRO

Aggressive behavior represents a significant public health issue, with relevant social, political, and security implications. Non-invasive brain stimulation (NIBS) techniques may modulate aggressive behavior through stimulation of the prefrontal cortex.

AIMS

To review research on the effectiveness of NIBS to alter aggression, discuss the main findings and potential limitations, consider the specifics of the techniques and protocols employed, and discuss clinical implications.

METHODS

A systematic review of the literature available in the PubMed database was carried out, and 17 randomized sham-controlled studies investigating the effectiveness of NIBS techniques on aggression were included. Exclusion criteria included reviews, meta-analyses, and articles not referring to the subject of interest or not addressing cognitive and emotional modulation aims.

CONCLUSIONS

The reviewed data provide promising evidence for the beneficial effects of tDCS, conventional rTMS, and cTBS on aggression in healthy adults, forensic, and clinical samples. The specific stimulation target is a key factor for the success of stimulation on aggression modulation. rTMS and cTBS showed opposite effects on aggression compared with tDCS. However, due to the heterogeneity of stimulation protocols, experimental designs, and samples, we cannot exclude other factors that may play a confounding role.

Pharmacological Inactivation of the Bed Nucleus of the Stria Terminalis Increases Affiliative Social Behavior in Rhesus Macaques

The bed nucleus of the stria terminalis (BNST) has been implicated in a variety of social behaviors, including aggression, maternal care, mating behavior, and social interaction. Limited evidence from rodent studies suggests that activation of the BNST results in a decrease in social interaction between unfamiliar animals. The role of the BNST in social interaction in primates remains wholly unexamined. Nonhuman primates provide a valuable model for studying social behavior because of both their rich social repertoire and neural substrates of behavior with high translational relevance to humans. To test the hypothesis that the primate BNST is a critical modulator of social behavior, we performed intracerebral microinfusions of the GABAA agonist muscimol to transiently inactivate the BNST in male macaque monkeys. We measured changes in social interaction with a familiar same-sex conspecific. Inactivation of the BNST resulted in significant increase in total social contact. This effect was associated with an increase in passive contact and a significant decrease in locomotion. Other nonsocial behaviors (sitting passively alone, self-directed behaviors, and manipulation) were not impacted by BNST inactivation. As part of the "extended amygdala," the BNST is highly interconnected with the basolateral (BLA) and central (CeA) nuclei of the amygdala, both of which also play critical roles in regulating social interaction. The precise pattern of behavioral changes we observed following inactivation of the BNST partially overlaps with our prior reports in the BLA and CeA. Together, these data demonstrate that the BNST is part of a network regulating social behavior in primates.SIGNIFICANCE STATEMENT The bed nucleus of the stria terminalis (BNST) has a well-established role in anxiety behaviors, but its role in social behavior is poorly understood. No prior studies have evaluated the impact of BNST manipulations on social behavior in primates. We found that transient pharmacological inactivation of the BNST increased social behavior in pairs of macaque monkeys. These data suggest the BNST contributes to the brain networks regulating sociability.

A hypothalamic pathway that suppresses aggression toward superior opponents

Aggression is costly and requires tight regulation. Here we identify the projection from estrogen receptor alpha-expressing cells in the caudal part of the medial preoptic area (cMPOAEsr1) to the ventrolateral part of the ventromedial hypothalamus (VMHvl) as an essential pathway for modulating aggression in male mice. cMPOAEsr1 cells increase activity mainly during male-male interaction, which differs from the female-biased response pattern of rostral MPOAEsr1 (rMPOAEsr1) cells. Notably, cMPOAEsr1 cell responses to male opponents correlated with the opponents' fighting capability, which mice could estimate based on physical traits or learn through physical combats. Inactivating the cMPOAEsr1-VMHvl pathway increased aggression, whereas activating the pathway suppressed natural intermale aggression. Thus, cMPOAEsr1 is a key population for encoding opponents' fighting capability-information that could be used to prevent animals from engaging in disadvantageous conflicts with superior opponents by suppressing the activity of VMHvl cells essential for attack behaviors.

Psychopharmacological treatment of disruptive behavior in youths: systematic review and network meta-analysis

To conduct a systematic review of the comparative efficacy of various psychotropic medications for the treatment of disruptive behavior (DBs) in youths. To this aim, we systematically reviewed randomized clinical trials (RCTs) of various psychotropic medications targeting symptoms of DBs and applied network meta-analysis to investigate their relative efficacy. Fifty-five RCTs meeting the inclusion criteria were selected. To predict and interpret relative treatment efficacy, we compared the efficacy of various psychotropic medications prescribed for DB symptoms based on their mechanism of action. Network meta-analysis revealed that for reducing DBs, second-generation antipsychotics, stimulants, and non-stimulant ADHD medications were more efficacious than placebo, and second-generation antipsychotics were the most efficacious. The dopaminergic modulation of top-down inhibitory process by these medications is discussed in this review. This study offers information on the relative efficacy of various psychotropic medications for the treatment of DB, and insight into a potential neurobiological underpinning for those symptoms. It also illustrates the potential utility of these neurobiological mechanisms as a target for future treatment studies.