Identification of quantitative trait Loci that affect aggressive behavior in mice

Roles of AMPA receptors in social behaviors

As a crucial player in excitatory synaptic transmission, AMPA receptors (AMPARs) contribute to the formation, regulation, and expression of social behaviors. AMPAR modifications have been associated with naturalistic social behaviors, such as aggression, sociability, and social memory, but are also noted in brain diseases featuring impaired social behavior. Understanding the role of AMPARs in social behaviors is timely to reveal therapeutic targets for treating social impairment in disorders, such as autism spectrum disorder and schizophrenia. In this review, we will discuss the contribution of the molecular composition, function, and plasticity of AMPARs to social behaviors. The impact of targeting AMPARs in treating brain disorders will also be discussed.

From Mouse to Man: N-Methyl-d-Aspartic Acid Receptor Activation as a Promising Pharmacotherapeutic Strategy for Autism Spectrum Disorders

The BALB/c mouse displays hypersensitivity to behavioral effects of MK-801 (dizocilpine), a noncompetitive N-methyl-d-aspartic acid (NMDA) receptor "open-channel" blocker, and shows both no preference for an enclosed stimulus mouse over an inanimate object and reduced social interaction with a freely behaving stimulus mouse. NMDA receptor agonist interventions improved measures of social preference and social interaction of the BALB/c mouse model of autism spectrum disorder (ASD). A "proof of principle/proof of concept" translational 10-week clinical trial with 8-week of active medication administration was conducted comparing 20 DSM-IV-TR-diagnosed older adolescent/young adult patients with ASD randomized to once-weekly pulsed administration (50 mg/d) versus daily administration of d-cycloserine (50 mg/d). The results showed that d-cycloserine, a partial glycine agonist, was well tolerated, the 2 dosing strategies did not differ, and improvement was noted on the "lethargy/social withdrawal" and "stereotypic behavior" subscales of the Aberrant Behavior Checklist. NMDA receptor activation contributes to the regulation of mTOR signaling, a pathologic point of convergence in several monogenic syndromic forms of ASD. Furthermore, both NMDA receptor hypofunction and imbalance between NMDA receptor activation mediated by GluN2B and GluN2A-containing NMDA receptors occur as "downstream" consequences of several genetically unrelated abnormalities associated with ASD. NMDA receptor-subtype selective "positive allosteric modulators (PAMs)" are particularly appealing medication candidates for future translational trials.

Dysfunction of AMPA receptor GluA3 is associated with aggressive behavior in human

Inappropriate aggression in humans hurts the society, families and individuals. The genetic basis for aggressive behavior, however, remains largely elusive. In this study, we identified two rare missense variants in X-linked GRIA3 from male patients who showed syndromes featuring aggressive outbursts. Both G630R and E787G mutations in AMPA receptor GluA3 completely lost their ion channel functions. Furthermore, a guanine-repeat single nucleotide polymorphism (SNP, rs3216834) located in the first intron of human GRIA3 gene was found to regulate GluA3 expression with longer guanine repeats (rs3216834-10G/-11G) suppressing transcription compared to the shorter ones (-7G/-8G/-9G). Importantly, the distribution of rs3216834-10G/-11G was elevated in a male violent criminal sample from Chinese Han population. Using GluA3 knockout mice, we showed that the excitatory neurotransmission and neuronal activity in the medial prefrontal cortex (mPFC) was impaired. Expressing GluA3 back into the mPFC alleviated the aggressive behavior of GluA3 knockout mice, suggesting that the defects in mPFC explained, at least partially, the neural mechanisms underlying the aggressive behavior. Therefore, our study provides compelling evidence that dysfunction of AMPA receptor GluA3 promotes aggressive behavior.

Early life social instability stress causes lasting cognitive decrement and elevated hippocampal stress-related gene expression

BACKGROUND

Early life stress may have profound effects on brain health, yielding both short- and long-term cognitive or psychiatric impairment. Early life Social Instability Stress (SIS) in rodents has been used to model the effects of early chronic human stress. While many studies have assessed acute and short-term responses to this stressor, less attention has been paid to the lasting effects of early life stress in rodents.

METHODS

The current study utilized SIS in young mice to assess the impact of early life adversity over the lifespan. Mice were assessed in adulthood between the ages of 18 to 66 weeks for changes in behaviors associated with anxiety, affect, sociability, aggression, motivation, and recognition memory. Additionally, mice were assessed for changes in glucocorticoid level and hippocampal mRNA expression in a subset of genes that display alterations in humans following exposure to stress (CRHR1, CRHR2, FKBP5, SLC6A4).

RESULTS

Mice exposed to early SIS showed disrupted memory and increased hippocampal expression of FKBP5, CRHR2 and SLC6A4 mRNA compared to non-stressed mice. Importantly, there was a significant association between increased FKBP5 and CRHR2 with reduced recognition memory. Additionally, mice exposed to SIS showed increased responding on a progressive ratio schedule of reinforcement, indicating that reduction in memory performance was not mediated by decreased effort.

CONCLUSIONS

Ecologically-relevant social stress in mice causes long-term decrements in recognition memory, possibly mediated by persistent changes in moderators of the stress cascade. Additionally, animals exposed to early life stress showed increased motivation for reward, which may contribute to a host of hedonic seeking behaviors throughout life. These data suggest that SIS can be used to evaluate therapeutic interventions to attenuate or reverse lasting effects of early life adversity.

GluA3-containing AMPA receptors: From physiology to synaptic dysfunction in brain disorders

In the mammalian brain, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) play a fundamental role in the activation of excitatory synaptic transmission and the induction of different forms of synaptic plasticity. The modulation of the AMPAR tetramer subunit composition at synapses defines the functional properties of the receptor. During the last twenty years, several studies have evaluated the roles played by each subunit, from GluA1 to GluA4, in both physiological and pathological conditions. Here, we have focused our attention on GluA3-containing AMPARs, addressing their functional role in synaptic transmission and synaptic plasticity and their involvement in a variety of brain disorders. Although several aspects remain to be fully understood, GluA3 is a widely expressed and functionally relevant subunit in AMPARs involved in several brain circuits, and its pharmacological modulation could represent a novel approach for the rescue of altered glutamatergic synapses associated with neurodegenerative and neurodevelopmental disorders.

An autism-linked missense mutation in SHANK3 reveals the modularity of Shank3 function

Genome sequencing has revealed an increasing number of genetic variations that are associated with neuropsychiatric disorders. Frequently, studies limit their focus to likely gene-disrupting mutations because they are relatively easy to interpret. Missense variants, instead, have often been undervalued. However, some missense variants can be informative for developing a more profound understanding of disease pathogenesis and ultimately targeted therapies. Here we present an example of this by studying a missense variant in a well-known autism spectrum disorder (ASD) causing gene SHANK3. We analyzed Shank3's in vivo phosphorylation profile and identified S685 as one phosphorylation site where one ASD-linked variant has been reported. Detailed analysis of this variant revealed a novel function of Shank3 in recruiting Abelson interactor 1 (ABI1) and the WAVE complex to the post-synaptic density (PSD), which is critical for synapse and dendritic spine development. This function was found to be independent of Shank3's other functions such as binding to GKAP and Homer. Introduction of this human ASD mutation into mice resulted in a small subset of phenotypes seen previously in constitutive Shank3 knockout mice, including increased allogrooming, increased social dominance, and reduced pup USV. Together, these findings demonstrate the modularity of Shank3 function in vivo. This modularity further indicates that there is more than one independent pathogenic pathway downstream of Shank3 and correcting a single downstream pathway is unlikely to be sufficient for clear clinical improvement. In addition, this study illustrates the value of deep biological analysis of select missense mutations in elucidating the pathogenesis of neuropsychiatric phenotypes.

Ecotype differences in aggression, neural activity and behaviorally relevant gene expression in cichlid fish

In Lake Malawi, two ecologically distinct lineages of cichlid fishes (rock- vs sand-dwelling ecotypes, each comprised of over 200 species) evolved within the last million years. The rock-dwelling species (Mbuna) are aggressively territorial year-round and males court and spawn with females over rocky substrate. In contrast, males of sand-dwelling species are not territorial and instead aggregate on seasonal breeding leks in which males construct courtship "bowers" in the sand. However, little is known about how phenotypic variation in aggression is produced by the genome. In this study, we first quantify and compare behavior in seven cichlid species, demonstrating substantial ecotype and species differences in unconditioned mirror-elicited aggression. Second, we compare neural activity in mirror-elicited aggression in two representative species, Mchenga conophoros (sand-dwelling) and Petrotilapia chitimba (rock-dwelling). Finally, we compare gene expression patterns between these two species, specifically within neurons activated during mirror aggression. We identified a large number of genes showing differential expression in mirror-elicited aggression, as well as many genes that differ between ecotypes. These genes, which may underly species differences in behavior, include several neuropeptides, genes involved in the synthesis of steroid hormones and neurotransmitter activity. This work lays the foundation for future experiments using this emerging genetic model system to investigate the genomic basis of evolved species differences in both brain and behavior.

Heritability of interpack aggression in a wild pedigreed population of North American grey wolves

Aggression is a quantitative trait deeply entwined with individual fitness. Mapping the genomic architecture underlying such traits is complicated by complex inheritance patterns, social structure, pedigree information and gene pleiotropy. Here, we leveraged the pedigree of a reintroduced population of grey wolves (Canis lupus) in Yellowstone National Park, Wyoming, USA, to examine the heritability of and the genetic variation associated with aggression. Since their reintroduction, many ecological and behavioural aspects have been documented, providing unmatched records of aggressive behaviour across multiple generations of a wild population of wolves. Using a linear mixed model, a robust genetic relationship matrix, 12,288 single nucleotide polymorphisms (SNPs) and 111 wolves, we estimated the SNP-based heritability of aggression to be 37% and an additional 14% of the phenotypic variation explained by shared environmental exposures. We identified 598 SNP genotypes from 425 grey wolves to resolve a consensus pedigree that was included in a heritability analysis of 141 individuals with SNP genotype, metadata and aggression data. The pedigree-based heritability estimate for aggression is 14%, and an additional 16% of the phenotypic variation was explained by shared environmental exposures. We find strong effects of breeding status and relative pack size on aggression. Through an integrative approach, these results provide a framework for understanding the genetic architecture of a complex trait that influences individual fitness, with linkages to reproduction, in a social carnivore. Along with a few other studies, we show here the incredible utility of a pedigreed natural population for dissecting a complex, fitness-related behavioural trait.

Nrg1 deficiency modulates the behavioural effects of prenatal stress in mice

Little is known about the exact genes that confer vulnerability or resilience to environmental stressors during early neurodevelopment. Partial genetic deletion of neuregulin 1 (Nrg1) moderates the neurobehavioural effects of stressors applied in adolescence and adulthood, however, no study has yet examined its impact on prenatal stress. Here we examined whether Nrg1 deficiency in mice modulated the impact of prenatal stress on various behaviours in adulthood. Male heterozygous Nrg1 mice were mated with wild-type female mice who then underwent daily restraint stress from days 13 to 19 of gestation. Surprisingly, prenatal stress had overall beneficial effects by facilitating sensorimotor gating, increasing sociability, decreasing depressive-like behaviour, and improving spatial memory in adulthood. Such benefits were not due to any increase in maternal care, as prenatal stress decreased nurturing of the offspring. Nrg1 deficiency negated the beneficial behavioural effects of prenatal stress on all measures except sociability. However, Nrg1 deficiency interacted with prenatal stress to trigger locomotor hyperactivity. Nrg1 deficiency, prenatal stress or their combination failed to alter acute stress-induced plasma corticosterone concentrations. Collectively these results demonstrate that Nrg1 deficiency moderates the effects of prenatal stress on adult behaviour, but it does so in a complex, domain-specific fashion.

Quantitative trait locus mapping and analysis of heritable variation in affiliative social behavior and co-occurring traits

Humans exhibit broad heterogeneity in affiliative social behavior. Twin and family studies show that individual differences in core dimensions of social behavior are heritable, yet there are knowledge gaps in understanding the underlying genetic and neurobiological mechanisms. Animal genetic reference panels (GRPs) provide a tractable strategy for examining the behavioral and genetic architecture of complex traits. Here, using males from 50 mouse strains from the BXD GRP, 4 domains of affiliative social behavior-social approach, social recognition, direct social interaction (DSI) (partner sniffing) and vocal communication-were examined in 2 widely used behavioral tasks-the 3-chamber and DSI tasks. There was continuous and broad variation in social and nonsocial traits, with moderate to high heritability of social approach sniff preference (0.31), ultrasonic vocalization (USV) count (0.39), partner sniffing (0.51), locomotor activity (0.54-0.66) and anxiety-like behavior (0.36). Principal component analysis shows that variation in social and nonsocial traits are attributable to 5 independent factors. Genome-wide mapping identified significant quantitative trait loci for USV count on chromosome (Chr) 18 and locomotor activity on Chr X, with suggestive loci and candidate quantitative trait genes identified for all traits with one notable exception-partner sniffing in the DSI task. The results show heritable variation in sociability, which is independent of variation in activity and anxiety-like traits. In addition, a highly heritable and ethological domain of affiliative sociability-partner sniffing-appears highly polygenic. These findings establish a basis for identifying functional natural variants, leading to a new understanding typical and atypical sociability.

Genetics and Genomics of Social Behavior in a Chicken Model

The identification of genes affecting sociality can give insights into the maintenance and development of sociality and personality. In this study, we used the combination of an advanced intercross between wild and domestic chickens with a combined QTL and eQTL genetical genomics approach to identify genes for social reinstatement, a social and anxiety-related behavior. A total of 24 social reinstatement QTL were identified and overlaid with over 600 eQTL obtained from the same birds using hypothalamic tissue. Correlations between overlapping QTL and eQTL indicated five strong candidate genes, with the gene TTRAP being strongly significantly correlated with multiple aspects of social reinstatement behavior, as well as possessing a highly significant eQTL.

A quantitative trait locus on chromosome 1 modulates intermale aggression in mice

Aggression between male conspecifics is a complex social behavior that is likely modulated by multiple gene variants. In this study, the BXD recombinant inbred mouse strains (RIS) were used to map quantitative trait loci (QTLs) underlying behaviors associated with intermale aggression. Four hundred and fifty-seven males from 55 strains (including the parentals) were observed at an age of 13 ± 1 week in a resident-intruder test following 10 days of isolation. Attack latency was measured directly within a 10-minute time period and the test was repeated 24 hours later. The variables we analyzed were the proportion of attacking males in a given strain as well as the attack latency (on days 1 and 2, and both days combined). On day 1, 29% of males attacked, and this increased to 37% on day 2. Large strain differences were obtained for all measures of aggression, indicating substantial heritability (intraclass correlations 0.10-0.18). We identified a significant QTL on chromosome (Chr) 1 and suggestive QTLs on mouse Chrs 1 and 12 for both attack and latency variables. The significant Chr 1 locus maps to a gene-sparse region between 82 and 88.5 Mb with the C57BL/6J allele increasing aggression and explaining about 18% of the variance. The most likely candidate gene modulating this trait is Htr2b which encodes the serotonin 2B receptor and has been implicated in aggressive and impulsive behavior in mice, humans and other species.

Strain differences in intermale aggression and possible factors regulating increased aggression in Japanese quail

The National Institute for Environmental Studies (NIES) of Japan established a strain of Japanese quail (Coturnix japonica) known as NIES-L by rotation breeding in a closed colony for over 35years; accordingly, the strain has highly inbred-like characteristics. Another strain called NIES-Brn has been maintained by randomized breeding in a closed colony to produce outbred-like characteristics. The current study aimed to characterize intermale aggressive behaviors in both strains and to identify possible factors regulating higher aggression in the hypothalamus, such as sex hormone and neuropeptide expression. Both strains displayed a common set of intermale aggressive behaviors that included pecking, grabbing, mounting, and cloacal contact behavior, although NIES-Brn quail showed significantly more grabbing, mounting, and cloacal contact behavior than did NIES-L quail. We examined sex hormone levels in the blood and diencephalon in both strains. Testosterone concentrations were significantly higher in the blood and diencephalon of NIES-Brn quail compared to NIES-L quail. We next examined gene expression in the hypothalamus of both strains using an Agilent gene expression microarray and real-time RT-PCR and found that gene expression of mesotocin (an oxytocin homologue) was significantly higher in the hypothalamus of NIES-Brn quail compared to NIES-L quail. Immunohistochemistry of the hypothalamus revealed that numbers of large cells (cell area>500μm²) expressing mesotocin were significantly higher in the NIES-Brn strain compared to the NIES-L strain. Taken together, our findings suggest that higher testosterone and mesotocin levels in the hypothalamus may be responsible for higher aggression in the NIES-Brn quail strain.

Histamine N-methyltransferase regulates aggression and the sleep-wake cycle

Histamine is a neurotransmitter that regulates diverse physiological functions including the sleep-wake cycle. Recent studies have reported that histaminergic dysfunction in the brain is associated with neuropsychiatric disorders. Histamine N-methyltransferase (HNMT) is an enzyme expressed in the central nervous system that specifically metabolises histamine; yet, the exact physiological roles of HNMT are unknown. Accordingly, we phenotyped Hnmt knockout mice (KO) to determine the relevance of HNMT to various brain functions. First, we showed that HNMT deficiency enhanced brain histamine concentrations, confirming a role for HNMT in histamine inactivation. Next, we performed comprehensive behavioural testing and determined that KO mice exhibited high aggressive behaviours in the resident-intruder and aggressive biting behaviour tests. High aggression in KO mice was suppressed by treatment with zolantidine, a histamine H2 receptor (H2R) antagonist, indicating that abnormal H2R activation promoted aggression in KO mice. A sleep analysis revealed that KO mice exhibited prolonged bouts of awakening during the light (inactive) period and compensatory sleep during the dark (active) period. Abnormal sleep behaviour was suppressed by treatment with pyrilamine, a H1R antagonist, prior to light period, suggesting that excessive H1R activation led to the dysregulation of sleep-wake cycles in KO mice. These observations inform the physiological roles of HNMT.

Genetics of Interactive Behavior in Silver Foxes (Vulpes vulpes)

Individuals involved in a social interaction exhibit different behavioral traits that, in combination, form the individual's behavioral responses. Selectively bred strains of silver foxes (Vulpes vulpes) demonstrate markedly different behaviors in their response to humans. To identify the genetic basis of these behavioral differences we constructed a large F₂ population including 537 individuals by cross-breeding tame and aggressive fox strains. 98 fox behavioral traits were recorded during social interaction with a human experimenter in a standard four-step test. Patterns of fox behaviors during the test were evaluated using principal component (PC) analysis. Genetic mapping identified eight unique significant and suggestive QTL. Mapping results for the PC phenotypes from different test steps showed little overlap suggesting that different QTL are involved in regulation of behaviors exhibited in different behavioral contexts. Many individual behavioral traits mapped to the same genomic regions as PC phenotypes. This provides additional information about specific behaviors regulated by these loci. Further, three pairs of epistatic loci were also identified for PC phenotypes suggesting more complex genetic architecture of the behavioral differences between the two strains than what has previously been observed.

Beyond main effects of gene-sets: harsh parenting moderates the association between a dopamine gene-set and child externalizing behavior

BACKGROUND

In a longitudinal cohort study, we investigated the interplay of harsh parenting and genetic variation across a set of functionally related dopamine genes, in association with children's externalizing behavior. This is one of the first studies to employ gene-based and gene-set approaches in tests of Gene by Environment (G × E) effects on complex behavior. This approach can offer an important alternative or complement to candidate gene and genome-wide environmental interaction (GWEI) studies in the search for genetic variation underlying individual differences in behavior.

METHODS

Genetic variants in 12 autosomal dopaminergic genes were available in an ethnically homogenous part of a population-based cohort. Harsh parenting was assessed with maternal (n = 1881) and paternal (n = 1710) reports at age 3. Externalizing behavior was assessed with the Child Behavior Checklist (CBCL) at age 5 (71 ± 3.7 months). We conducted gene-set analyses of the association between variation in dopaminergic genes and externalizing behavior, stratified for harsh parenting.

RESULTS

The association was statistically significant or approached significance for children without harsh parenting experiences, but was absent in the group with harsh parenting. Similarly, significant associations between single genes and externalizing behavior were only found in the group without harsh parenting. Effect sizes in the groups with and without harsh parenting did not differ significantly. Gene-environment interaction tests were conducted for individual genetic variants, resulting in two significant interaction effects (rs1497023 and rs4922132) after correction for multiple testing.

CONCLUSION

Our findings are suggestive of G × E interplay, with associations between dopamine genes and externalizing behavior present in children without harsh parenting, but not in children with harsh parenting experiences. Harsh parenting may overrule the role of genetic factors in externalizing behavior. Gene-based and gene-set analyses offer promising new alternatives to analyses focusing on single candidate polymorphisms when examining the interplay between genetic and environmental factors.

Aggression in non-human vertebrates: Genetic mechanisms and molecular pathways

Aggression is an adaptive behavioral trait that is important for the establishment of social hierarchies and competition for mating partners, food, and territories. While a certain level of aggression can be beneficial for the survival of an individual or species, abnormal aggression levels can be detrimental. Abnormal aggression is commonly found in human patients with psychiatric disorders. The predisposition to aggression is influenced by a combination of environmental and genetic factors and a large number of genes have been associated with aggression in both human and animal studies. In this review, we compare and contrast aggression studies in zebrafish and mouse. We present gene ontology and pathway analyses of genes linked to aggression and discuss the molecular pathways that underpin agonistic behavior in these species. © 2015 Wiley Periodicals, Inc.

Epilepsy, Antiepileptic Drugs, and Aggression: An Evidence-Based Review

Antiepileptic drugs (AEDs) have many benefits but also many side effects, including aggression, agitation, and irritability, in some patients with epilepsy. This article offers a comprehensive summary of current understanding of aggressive behaviors in patients with epilepsy, including an evidence-based review of aggression during AED treatment. Aggression is seen in a minority of people with epilepsy. It is rarely seizure related but is interictal, sometimes occurring as part of complex psychiatric and behavioral comorbidities, and it is sometimes associated with AED treatment. We review the common neurotransmitter systems and brain regions implicated in both epilepsy and aggression, including the GABA, glutamate, serotonin, dopamine, and noradrenaline systems and the hippocampus, amygdala, prefrontal cortex, anterior cingulate cortex, and temporal lobes. Few controlled clinical studies have used behavioral measures to specifically examine aggression with AEDs, and most evidence comes from adverse event reporting from clinical and observational studies. A systematic approach was used to identify relevant publications, and we present a comprehensive, evidence-based summary of available data surrounding aggression-related behaviors with each of the currently available AEDs in both adults and in children/adolescents with epilepsy. A psychiatric history and history of a propensity toward aggression/anger should routinely be sought from patients, family members, and carers; its presence does not preclude the use of any specific AEDs, but those most likely to be implicated in these behaviors should be used with caution in such cases.

Use of haloperidol and risperidone in highly aggressive Swiss Webster mice by applying the model of spontaneous aggression (MSA)

Aggression is defined as the act in which an individual intentionally harms or injures another of their own species. Antipsychotics are a form of treatment used in psychiatric routine. They have been used for decades in treatment of patients with aggressive behavior. Haloperidol and risperidone promote the control of psychiatric symptoms, through their respective mechanisms of action. Experimental models are obtained by behavioral, genetic, and pharmacological manipulations, and use a reduced number of animals. In this context, we applied the model of spontaneous aggression (MSA), originating the presence of highly aggressive mice (AgR) when reassembled in adulthood. We administered haloperidol and risperidone in escalating doses, for ten consecutive days. Using positive and negative control groups, we evaluated the effectiveness of these drugs and the reversal of the aggressive behavior, performing the tail suspension test (TST) and open field test (OFT) on 10th day of treatment and 10 days after its discontinuation. The results showed that both antipsychotic drugs were effective in AgR and reversed the aggressive phenotype, reducing the number of attacks by AgR and the extent of lesions in the subordinate mice (AgD) exposed to the pattern of aggressive behavior (PAB) of the aggressors. This conclusion is based on the reduction in the animals' motor and exploratory activity, and on the reversal of patterns of aggressive behavior. The association between the MSA and experiments with other therapeutic protocols and different antipsychotics can be an important methodology in the study of aggressive behavior in psychiatric patients.

Mapping of Genetic Factors That Elicit Intermale Aggressive Behavior on Mouse Chromosome 15: Intruder Effects and the Complex Genetic Basis

Despite high estimates of the heritability of aggressiveness, the genetic basis for individual differences in aggression remains unclear. Previously, we showed that the wild-derived mouse strain MSM/Ms (MSM) exhibits highly aggressive behaviors, and identified chromosome 15 (Chr 15) as the location of one of the genetic factors behind this escalated aggression by using a panel of consomic strains of MSM in a C57BL/6J (B6) background. To understand the genetic effect of Chr 15 derived from MSM in detail, this study examined the aggressive behavior of a Chr 15 consomic strain towards different types of opponent. Our results showed that both resident and intruder animals had to have the same MSM Chr 15 genotype in order for attack bites to increase and attack latency to be reduced, whereas there was an intruder effect of MSM Chr 15 on tail rattle behavior. To narrow down the region that contains the genetic loci involved in the aggression-eliciting effects on Chr 15, we established a panel of subconsomic strains of MSM Chr 15. Analysis of these strains suggested the existence of multiple genes that enhance and suppress aggressive behavior on Chr 15, and these loci interact in a complex way. Regression analysis successfully identified four genetic loci on Chr 15 that influence attack latency, and one genetic locus that partially elicits aggressive behaviors was narrowed down to a 4.1-Mbp region (from 68.40 Mb to 72.50 Mb) on Chr 15.

The relationship between DRD4 polymorphisms and phenotypic correlations of behaviors in the collared flycatcher

There is increasing evidence that the genetic architecture of exploration behavior includes the dopamine receptor D4 gene (DRD4). Such a link implies that the within-individual consistency in the same behavior has a genetic basis. Behavioral consistency is also prevalent in the form of between-individual correlation of functionally different behaviors; thus, the relationship between DRD4 polymorphism and exploration may also be manifested for other behaviors. Here, in a Hungarian population of the collared flycatcher, Ficedula albicollis, we investigate how males with distinct DRD4 genotypes differ in the consistent elements of their behavioral displays during the courtship period. In completely natural conditions, we assayed novelty avoidance, aggression and risk-taking, traits that were previously shown repeatable over time and correlate with each other, suggesting that they could have a common mechanistic basis. We identified two single-nucleotide polymorphisms (SNP554 and SNP764) in the exon 3 of the DRD4 gene by sequencing a subsample, then we screened 202 individuals of both sexes for these SNPs. Focusing on the genotypic variation in courting males, we found that “AC” heterozygote individuals at the SNP764 take lower risk than the most common “AA” homozygotes (the “CC” homozygotes were not represented in our subsample of males). We also found a considerable effect size for the relationship between SNP554 polymorphism and novelty avoidance. Therefore, in addition to exploration, DRD4 polymorphisms may also be associated with the regulation of behaviors that may incur fear or stress. Moreover, polymorphisms at the two SNPs were not independent indicating a potential role for genetic constraints or another functional link, which may partially explain behavioral correlations.

Cerebrospinal fluid glutamate concentration correlates with impulsive aggression in human subjects

Neurochemical studies have pointed to a modulatory role in human aggression for various central neurotransmitters. Some (e.g., serotonin) appear to play an inhibitory role, while others appear to play a facilitator role. While recent animal studies of glutaminergic activity suggest a facilitator role for central glutamate in the modulation of aggression, no human studies of central glutaminergic indices have yet been reported regarding aggression. Basal lumbar cerebrospinal fluid (CSF) was obtained from 38 physically healthy subjects with DSM-IV Personality Disorder (PD: n = 28) and from Healthy Volunteers (HV: n = 10) and assayed for glutamate, and other neurotransmitters, in CSF and correlated with measures of aggression and impulsivity. CSF Glutamate levels did not differ between the PD and HC subjects but did directly correlate with composite measures of both aggression and impulsivity and a composite measure of impulsive aggression in both groups. These data suggest a positive relationship between CSF Glutamate levels and measures of impulsive aggression in human subjects. Thus, glutamate function may contribute to the complex central neuromodulation of impulsive aggression in human subjects.

Analysis of male aggressive and sexual behavior in mice

Pheromone and odor signals play a pivotal role in male mouse reproductive behaviors, such as sexual and aggressive behavior. There are several methods used to assess male behaviors, each of which examines a unique aspect of the biological function of mice. There are two major ways of assessing male aggressive behavior in mice, one is using isolation-induced aggression, and the other is territorial aggression in pair-housed males. To analyze male sexual behavior, a female mouse that is hormone-primed with estradiol and progesterone is usually introduced into a male home range, and mounting, intromission, and ejaculation behaviors are observed for 1 h. Here, we summarize the detailed protocols for assessing male behaviors.

Neurogenetics of aggressive behavior: studies in rodents

Aggressive behavior is observed in many animal species, such as insects, fish, lizards, frogs, and most mammals including humans. This wide range of conservation underscores the importance of aggressive behavior in the animals' survival and fitness, and the likely heritability of this behavior. Although typical patterns of aggressive behavior differ between species, there are several concordances in the neurobiology of aggression among rodents, primates, and humans. Studies with rodent models may eventually help us to understand the neurogenetic architecture of aggression in humans. However, it is important to recognize the difference between the ecological and ethological significance of aggressive behavior (species-typical aggression) and maladaptive violence (escalated aggression) when applying the findings of aggression research using animal models to human or veterinary medicine. Well-studied rodent models for aggressive behavior in the laboratory setting include the mouse (Mus musculus), rat (Rattus norvegicus), hamster (Mesocricetus auratus), and prairie vole (Microtus ochrogaster). The neural circuits of rodent aggression have been gradually elucidated by several techniques, e.g., immunohistochemistry of immediate-early gene (c-Fos) expression, intracranial drug microinjection, in vivo microdialysis, and optogenetics techniques. Also, evidence accumulated from the analysis of gene-knockout mice shows the involvement of several genes in aggression. Here, we review the brain circuits that have been implicated in aggression, such as the hypothalamus, prefrontal cortex (PFC), dorsal raphe nucleus (DRN), nucleus accumbens (NAc), and olfactory system. We then discuss the roles of glutamate and γ-aminobutyric acid (GABA), excitatory and inhibitory amino acids in the brain, as well as their receptors, in controlling aggressive behavior, focusing mainly on recent findings. At the end of this chapter, we discuss how genes can be identified that underlie individual differences in aggression, using the so-called forward genetics approach.

Personality assessment and its association with genetic factors in captive Asian and African elephants

Elephants live in a complex society based on matrilineal groups. Management of captive elephants is difficult, partly because each elephant has a unique personality. For a better understanding of elephant well being in captivity, it would be helpful to systematically evaluate elephants' personalities and their underlying biological basis. We sent elephant' personality questionnaires to keepers of 75 elephants. We also used 196 elephant DNA samples to search for genetic polymorphisms in genes expressed in the brain that have been suggested to be related to personality traits. Three genes, androgen receptor (AR), fragile X related mental retardation protein interacting protein (NUFIP2), and acheate-scute homologs 1 (ASH1) contained polymorphic regions. We examined the association of personality with intraspecific genetic variation in 17 Asian and 28 African elephants. The results suggest that the ASH1 genotype was associated with neuroticism in Asian elephants. Subjects with short alleles had lower scores of neuroticism than those with long alleles. This is the first report of an association between a genetic polymorphism and personality in elephants.

The psychopharmacology of aggressive behavior: a translational approach: part 1: neurobiology

Patients with mental disorders are at an elevated risk for developing aggressive behavior. In the last 19 years, the psychopharmacological treatment of aggression has changed dramatically because of the introduction of atypical antipsychotics into the market and the increased use of anticonvulsants and lithium in the treatment of aggressive patients.Using a translational medicine approach, this review (part 1 of 2) examines the neurobiology of aggression, discussing the major neurotransmitter systems implicated in its pathogenesis, namely, serotonin, glutamate, norepinephrine, dopamine, and γ-aminobutyric acid, and also their respective receptors. The preclinical and clinical pharmacological studies concerning the role of these neurotransmitters have been reviewed, as well as research using transgenic animal models. The complex interaction among these neurotransmitters occurs at the level of brain areas and neural circuits such as the orbitoprefrontal cortex, anterior cortex, amygdala, hippocampus, periaqueductal gray, and septal nuclei, where the receptors of these neurotransmitters are expressed. The neurobiological mechanism of aggression is important to understand the rationale for using atypical antipsychotics, anticonvulsants, and lithium in treating aggressive behavior. Further research is necessary to establish how these neurotransmitter systems interact with brain circuits to control aggressive behavior at the intracellular level.

GluA3-deficiency in mice is associated with increased social and aggressive behavior and elevated dopamine in striatum

Glutamate signaling has been implicated in the regulation of social behavior. AMPA-glutamate receptors are assembled from four subunits (GluA1-4) of mainly GluA1/2 and GluA2/3 tetramers that form ion channels of distinct functional properties. Mice lacking GluA1 showed a reduced anxiety and male aggression. To understand the role of GluA3 in modulating social behavior, we investigated GluA3-deficient mice (Gria3-/Y) on C57BL/6J background. Compared to wild type (WT) littermates (n=14), Gria3-/Y mice (n=13) showed an increase in isolation-induced male aggression (p=0.011) in home cage resident-intruder test; an increase in sociability (p=0.01), and increase in male-male social interactions in neutral arena (p=0.005); an increase in peripheral activities in open field test (p=0.037) with normal anxiety levels in elevated plus maze and light-dark box; and minor deficits in motor and balance function in accelerating rotarod test (p=0.016) with normal grip strength. Gria3-/Y mice showed no significant deficit in spatial memory function in Morris-water maze and Y-maze tests, and normal levels of testosterone. Increased dopamine concentrations in stratum (p=0.034) and reduced serotonin turnover in olfactory bulb (p=0.002) were documented in Gria3-/Y mice. These results support a role of GluA3 in the modulation of social behavior through brain dopamine and/or serotonin signaling and different AMPA receptor subunits affect social behavior through distinct mechanisms.

Gene expression in aminergic and peptidergic cells during aggression and defeat: relevance to violence, depression and drug abuse

In this review, we examine how experiences in social confrontations alter gene expression in mesocorticolimbic cells. The focus is on the target of attack and threat due to the prominent role of social defeat stress in the study of coping mechanisms and victimization. The initial operational definition of the socially defeated mouse by Ginsburg and Allee (1942) enabled the characterization of key endocrine, cardiovascular, and metabolic events during the initial response to an aggressive opponent and during the ensuing adaptations. Brief episodes of social defeat stress induce an augmented response to stimulant challenge as reflected by increased locomotion and increased extracellular dopamine (DA) in the nucleus accumbens (NAC). Cells in the ventral tegmental area (VTA) that project to the NAC were more active as indicated by increased expression of c-fos and Fos-immunoreactivity and BDNF. Intermittent episodes of social defeat stress result in increased mRNA for MOR in brainstem and limbic structures. These behavioral and neurobiological indices of sensitization persist for several months after the stress experience. The episodically defeated rats also self-administered intravenous cocaine during continuous access for 24 h ("binge"). By contrast, continuous social stress, particularly in the form of social subordination stress, leads to reduced appetite, compromised endocrine activities, and cardiovascular and metabolic abnormalities, and prefer sweets less as index of anhedonia. Cocaine challenges in subordinate rats result in a blunted psychomotor stimulant response and a reduced DA release in NAC. Subordinate rats self-administer cocaine less during continuous access conditions. These contrasting patterns of social stress result from continuous vs. intermittent exposure to social stress, suggesting divergent neuroadaptations for increased vulnerability to cocaine self-administration vs. deteriorated reward mechanisms characteristic of depressive-like profiles.

Shared genetic background for regulation of mood and sleep: association of GRIA3 with sleep duration in healthy Finnish women

STUDY OBJECTIVES

Sleeping 7 to 8 hours per night appears to be optimal, since both shorter and longer sleep times are related to increased morbidity and mortality. Depressive disorder is almost invariably accompanied by disturbed sleep, leading to decreased sleep duration, and disturbed sleep may be a precipitating factor in the initiation of depressive illness. Here, we examined whether, in healthy individuals, sleep duration is associated with genes that we earlier found to be associated with depressive disorder.

DESIGN

Population-based molecular genetic study.

SETTING

Regression analysis of 23 risk variants for depressive disorder from 12 genes to sleep duration in healthy individuals.

PARTICIPANTS

Three thousand, one hundred, forty-seven individuals (25-75 y) from population-based Health 2000 and FINRISK 2007 samples.

MEASUREMENTS AND RESULTS

We found a significant association of rs687577 from GRIA3 on the X-chromosome with sleep duration in women (permutation-based corrected empirical P=0.00001, β=0.27; Bonferroni corrected P=0.0052; f=0.11). The frequency of C/C genotype previously found to increase risk for depression in women was highest among those who slept for 8 hours or less in all age groups younger than 70 years. Its frequency decreased with the lengthening of sleep duration, and those who slept for 9 to 10 hours showed a higher frequency of C/A or A/A genotypes, when compared with the midrange sleepers (7-8 hours) (permutation-based corrected empirical P=0.0003, OR=1.81).

CONCLUSIONS

The GRIA3 polymorphism that was previously found to be associated with depressive disorder in women showed an association with sleep duration in healthy women. Mood disorders and short sleep may share a common genetic background and biologic mechanisms that involve glutamatergic neurotransmission.

Genetic dissection of intermale aggressive behavior in BALB/cJ and A/J mice

Aggressive behaviors are disabling, treatment refractory, and sometimes lethal symptoms of several neuropsychiatric disorders. However, currently available treatments for patients are inadequate, and the underlying genetics and neurobiology of aggression is only beginning to be elucidated. Inbred mouse strains are useful for identifying genomic regions, and ultimately the relevant gene variants (alleles) in these regions, that affect mammalian aggressive behaviors, which, in turn, may help to identify neurobiological pathways that mediate aggression. The BALB/cJ inbred mouse strain exhibits relatively high levels of intermale aggressive behaviors and shows multiple brain and behavioral phenotypes relevant to neuropsychiatric syndromes associated with aggression. The A/J strain shows very low levels of aggression. We hypothesized that a cross between BALB/cJ and A/J inbred strains would reveal genomic loci that influence the tendency to initiate intermale aggressive behavior. To identify such loci, we conducted a genomewide scan in an F2 population of 660 male mice bred from BALB/cJ and A/J inbred mouse strains. Three significant loci on chromosomes 5, 10 and 15 that influence aggression were identified. The chromosome 5 and 15 loci are completely novel, and the chromosome 10 locus overlaps an aggression locus mapped in our previous study that used NZB/B1NJ and A/J as progenitor strains. Haplotype analysis of BALB/cJ, NZB/B1NJ and A/J strains showed three positional candidate genes in the chromosome 10 locus. Future studies involving fine genetic mapping of these loci as well as additional candidate gene analysis may lead to an improved biological understanding of mammalian aggressive behaviors.

No postnatal maternal effect on male aggressiveness in wild-derived strains of house mice

Male aggressiveness is a complex behavior influenced by a number of genetic and non-genetic factors. Traditionally, the contribution of each of these factors has been established from experiments using artificially selected strains for high/low aggressive phenotypes. However, little is known about the factors underlying aggressive behavior in natural populations. In this study, we assess the influence of genetic background vs. postnatal maternal environment using a set of cross-fostering experiments between two wild-derived inbred strains, displaying high (STRA, derived from Mus musculus domesticus) and low (BUSNA, derived from Mus musculus musculus) levels of aggressiveness. The role of maternal environment was tested in males with the same genetic background (i.e. strain origin) reared under three different conditions: unfostered (weaned by mother), infostered (weaned by an unfamiliar dam from the same strain), and cross-fostered (weaned by a dam from a different strain). All males were tested against non-aggressive opponents from the A/J inbred strain. Resource-holding potential was assessed through body weight gains and territory ownership. The STRA males were shown to be aggressive in both neutral cage and resident-intruder tests. On the contrary, the BUSNA males were less aggressive in all tests. We did not find a significant effect of postnatal maternal environment; however, we detected significant maternal effect on body weight with differences between the strains, fostering type and interactions between these factors. We conclude that the aggressiveness preserved in the two strains has significant genetic component whose genetic basis can be dissected by quantitative trait loci analysis.

Genomic mapping of social behavior traits in a F2 cross derived from mice selectively bred for high aggression

BACKGROUND

Rapid response to selection was previously observed in mice selected for high levels of inter-male aggression based on number of attacks displayed in a novel social interaction test after isolation housing. Attack levels in this high aggression line (NC900) increased significantly within just four generations of selective breeding, suggesting the presence of a locus with large effect. We conducted an experiment using a small (n ≈ 100) F2 cross between the ICR-derived, non-inbred NC900 strain and the low aggression inbred strain C57BL/6J, genotyped for 154 fully informative SNPs, to determine if a locus with large effect controls the high-aggression selection trait. A second goal was to use high density SNP genotyping (n = 549,000) in the parental strains to characterize residual patterns of heterozygosity within NC900, and evaluate regions that are identical by descent (IBD) between NC900 and C57BL/6J, to determine what impacts these may have on accuracy and resolution of quantitative trait locus (QTL) mapping in the F2 cross.

RESULTS

No evidence for a locus with major effect on aggressive behavior in mice was identified. However, several QTL with genomewide significance were mapped for aggression on chromosomes 7 and 19 and other social behavior traits on chromosomes 4, 7, 14, and 19. High density genotyping revealed that 28% of the genome is still segregating among the six NC900 females used to originate the F2 cross, and that segregating regions are present on every chromosome but are of widely different sizes. Regions of IBD between NC900 and C57BL/6J are found on every chromosome but are most prominent on chromosomes 10, 16 and X. No significant differences were found for amounts of heterozygosity or prevalence of IBD in QTL regions relative to global analysis.

CONCLUSIONS

While no major gene was identified to explain the rapid selection response in the NC900 line, transgressive variation (i.e. where the allele from the C57BL/6J increased attack levels) and a significant role for dominant gene action were hallmarks of the genetic architecture for aggressive behavior uncovered in this study. The high levels of heterozygosity and the distribution of minor allele frequency observed in the NC900 population suggest that maintenance of heterozygosity may have been under selection in this line.

Genetic mapping of social interaction behavior in B6/MSM consomic mouse strains

Genetic studies are indispensable for understanding the mechanisms by which individuals develop differences in social behavior. We report genetic mapping of social interaction behavior using inter-subspecific consomic strains established from MSM/Ms (MSM) and C57BL/6J (B6) mice. Two animals of the same strain and sex, aged 10 weeks, were introduced into a novel open-field for 10 min. Social contact was detected by an automated system when the distance between the centers of the two animals became less than ~12 cm. In addition, detailed behavioral observations were made of the males. The wild-derived mouse strain MSM showed significantly longer social contact as compared to B6. Analysis of the consomic panel identified two chromosomes (Chr 6 and Chr 17) with quantitative trait loci (QTL) responsible for lengthened social contact in MSM mice and two chromosomes (Chr 9 and Chr X) with QTL that inhibited social contact. Detailed behavioral analysis of males identified four additional chromosomes associated with social interaction behavior. B6 mice that contained Chr 13 from MSM showed more genital grooming and following than the parental B6 strain, whereas the presence of Chr 8 and Chr 12 from MSM resulted in a reduction of those behaviors. Longer social sniffing was observed in Chr 4 consomic strain than in B6 mice. Although the frequency was low, aggressive behavior was observed in a few pairs from consomic strains for Chrs 4, 13, 15 and 17, as well as from MSM. The social interaction test has been used as a model to measure anxiety, but genetic correlation analysis suggested that social interaction involves different aspects of anxiety than are measured by open-field test.

Indirect genetic effects and the evolution of aggression in a vertebrate system

Aggressive behaviours are necessarily expressed in a social context, such that individuals may be influenced by the phenotypes, and potentially the genotypes, of their social partners. Consequently, it has been hypothesized that indirect genetic effects (IGEs) arising from the social environment will provide a major source of heritable variation on which selection can act. However, there has been little empirical scrutiny of this to date. Here we test this hypothesis in an experimental population of deer mice (Peromyscus maniculatus). Using quantitative genetic models of five aggression traits, we find repeatable and heritable differences in agonistic behaviours of focal individuals when presented with an opponent mouse. For three of the traits, there is also support for the presence of IGEs, and estimated correlations between direct and indirect genetic (rAO,F) effects were high. As a consequence, any selection for aggression in the focal individuals should cause evolution of the social environment as a correlated response. In two traits, strong positive rAO,F will cause the rapid evolution of aggression, while in a third case changes in the phenotypic mean will be constrained by negative covariance between direct and IGEs. Our results illustrate how classical analyses may miss important components of heritable variation, and show that a full understanding of evolutionary dynamics requires explicit consideration of the genetic component of the social environment.

Quantitative trait locus analysis identifies rat genomic regions related to amphetamine-induced locomotion and Galpha(i3) levels in nucleus accumbens

Identification of the genetic factors that underlie stimulant responsiveness in animal models has significant implications for better understanding and treating stimulant addiction in humans. F(2) progeny derived from parental rat strains F344/NHsd and LEW/NHsd, which differ in responses to drugs of abuse, were used in quantitative trait locus (QTL) analyses to identify genomic regions associated with amphetamine-induced locomotion (AIL) and G-protein levels in the nucleus accumbens (NAc). The most robust QTLs were observed on chromosome 3 (maximal log ratio statistic score (LRS(max))=21.3) for AIL and on chromosome 2 (LRS(max)=22.0) for Galpha(i3). A 'suggestive' QTL (LRS(max)=12.5) was observed for AIL in a region of chromosome 2 that overlaps with the Galpha(i3) QTL. Novelty-induced locomotion (NIL) showed different QTL patterns from AIL, with the most robust QTL on chromosome 13 (LRS(max)=12.2). Specific unique and overlapping genomic regions influence AIL, NIL, and inhibitory G-protein levels in the NAc. These findings suggest that common genetic mechanisms influence certain biochemical and behavioral aspects of stimulant responsiveness.

Genetic tools for studying adaptation and the evolution of behavior

The rapid expansion of genomic and molecular genetic techniques in model organisms, and the application of these techniques to organisms that are less well studied genetically, make it possible to understand the genetic control of many behavioral phenotypes. However, many behavioral ecologists are uncertain about the value of including a genetic component in their studies. In this article, we review how genetic analyses of behavior are central to topics ranging from understanding past selection and predicting future evolution to explaining the neural and hormonal control of behavior. Furthermore, we review both new and old techniques for studying evolutionary behavior genetics and highlight how the choice of approach depends on both the question and the organism. Topics discussed include genetic architecture, detecting the past history of selection, and genotype-by-environment interactions. We show how these questions are being addressed with techniques including statistical genetics, QTL analyses, transgenic analyses, and microarrays. Many of the techniques were first applied to the behavior of genetic model organisms such as laboratory mice and flies. Two recent developments serve to expand the relevance of such studies to behavioral ecology. The first is to use model organisms for studies of the genetic basis of evolutionarily relevant behavior and the second is to apply methods developed in model genetic systems to species that have not previously been examined genetically. These conceptual advances, along with the rapid diversification of genetic tools and the recognition of widespread genetic homology, suggest a bright outlook for evolutionary genetic studies. This review provides access to tools through references to the recent literature and shows the great promise for evolutionary behavioral genetics.

Genetic influences on aggressive behaviors and arousability in animals

In a variety of species, strain differences in aggressive behaviors strongly indicate genetic influences. In people, as suggested, for example, by the work of Kagan, Rothbart, Cloninger, and their collaborators, long-lasting differences in temperament argue for genetic as well as environmental effects. After well-controlled experimentation in mice, we have learned five lessons about gene/behavior causal relations bearing on sociosexual and aggressive behaviors. The effect of a given gene on a given behavior depends upon: (1) exactly when and where that gene is expressed in the brain; (2) the gender of the animal in which it is expressed; (3) the age of the animal; (4) the nature of the opponent; and (5) the form of aggression (e.g., testosterone-facilitated aggression vs. maternal aggression). Moreover, in female mice, better social recognition is correlated with lower levels of aggression. We have gathered evidence for a four-gene micronet involving estrogen receptors alpha and beta, oxytocin, and the oxytocin receptor as expressed in the hypothalamus and amygdala. Normal performance of this micronet is required for social recognition and thus for control over aggression. Underlying certain genetic influences on sociosexual behaviors and aggression may be alterations in generalized brain arousal.

Chromosomal assignment of quantitative trait loci influencing modified hole board behavior in laboratory mice using consomic strains, with special reference to anxiety-related behavior and mouse chromosome 19

Male mice from a panel of chromosome substitution strains (CSS, also called consomic strains or lines)--in which a single full-length chromosome from the A/J inbred strain has been transferred onto the genetic background of the C57BL/6J inbred strain--and the parental strains were examined in the modified hole board test. This behavioral test allows to assess for a variety of different motivational systems in parallel (i.e. anxiety, risk assessment, exploration, memory, locomotion, and arousal). Such an approach is essential for behavioral characterization since the motivational system of interest is strongly influenced by other behavioral systems. Both univariate and bivariate analyses, as well as a factor analysis, were performed. The C57BL/6J and A/J mouse parental inbred strains differed in all motivational systems. The chromosome substitution strain survey indicated that nearly all mouse chromosomes (with the exception of chromosome 2) each contain at least one quantitative trait locus (QTL) that is involved in modified hole board behavior. The results agreed well with previous reports of QTLs for anxiety-related behavior using the A/J and C57BL/6J as parental strains. The present study confirmed that mouse chromosomes 5, 8, 10, 15, 18 and 19 likely contain at least one anxiety QTL. There was also evidence for a novel anxiety QTL on the Y chromosome. With respect to anxiety-related avoidance behavior towards an unprotected area, we have special interest for mouse chromosome 19. CSS-19 (C57BL/6J-Chr19(A)/NaJ) differed in avoidance behavior from the C57BL/6J, but not in locomotion. Thus pleiotropic contribution of locomotion could be excluded.

From genes to aggressive behavior: the role of serotonergic system

Recent investigations in neurogenomics have opened up new lines of research into a crucial genetic problem-the pathway from genes to behavior. This paper concentrates on the involvement of protein elements in the brain neurotransmitter serotonin (5-HT) system in the genetic control of aggressive behavior. Specifically, it describes: (1) the effect of the knockout of MAO A, the principal enzyme in 5-HT degradation, (2) the association of intermale aggression with the polymorphism in the Tph2 gene encoding the key enzyme in 5-HT synthesis in the brain, tryptophan hydroxylase (TPH), and (3) the effect of selective breeding for nonaggressive behavior on 5-HT metabolism, TPH activity and 5-HT(1A) receptors in the brain. The review provides converging lines of evidence that: (1) brain 5-HT contributes to a critical mechanism underlying genetically defined individual differences in aggressiveness, and (2) genes encoding pivotal enzymes in 5-HT metabolism (TPH and MAO A), 5-HT-transporter, 5-HT(1A) and 5-HT(1B) receptors belong to a group of genes that modulate aggressive behavior.

Methamphetamine causes alterations in the MAP kinase-related pathways in the brains of mice that display increased aggressiveness

Aggressive behaviors have been reported in patients who suffer from some psychiatric disorders, and are common in methamphetamine (METH) abusers. Herein, we report that multiple (but not single) injections of METH significantly increased aggressiveness in male CD-1 mice. This increase in aggressiveness was not secondary to METH-induced hyperactivity. Analysis of protein expression using antibody microarrays and Western blotting revealed differential changes in MAP kinase-related pathways after multiple and single METH injections. There were statistically significant (p<0.05) decreases in MEK1, Erk2p, GSK3alpha, 14-3-3e, and MEK7 in the striata of mice after multiple injections of METH. MEK1 was significantly decreased also after a single injection of METH, but to a much lesser degree than after multiple injections of METH. In the frontal cortex, there was a statistically significant decrease in GSK3alpha after multiple (but not single) injections of METH. These findings suggest that alterations in MAP kinase-related pathways in the prefronto-striatal circuitries might be involved in the manifestation of aggressive behaviors in mice.

A mouse model system for genetic analysis of sociability: C57BL/6J versus BALB/cJ inbred mouse strains

BACKGROUND

Impairments in social behaviors are highly disabling symptoms of autism, schizophrenia, and other psychiatric disorders. Mouse model systems are useful for identifying the many genes and environmental factors likely to affect complex behaviors, such as sociability (the tendency to seek social interaction). To progress toward developing such a model system, we tested the hypothesis that C57BL/6J inbred mice show higher levels of sociability than BALB/cJ inbred mice.

METHODS

Mice tested for sociability were 4- and 9-week-old, male and female C57BL/6J and BALB/cJ mice. On 2 consecutive days, the sociability of each test mouse toward an unfamiliar 4-week-old DBA/2J stimulus mouse was assessed with a social choice paradigm conducted in a three-chambered apparatus. Measures of sociability included the time that the test mouse spent near versus far from the stimulus mouse, the time spent directly sniffing the stimulus mouse, and the time spent in contact between test and stimulus mice in a free interaction.

RESULTS

C57BL/6J mice showed higher levels of sociability than BALB/cJ mice overall in each of these measures.

CONCLUSIONS

We propose that C57BL/6J and BALB/cJ mice will be a useful mouse model system for future genetic and neurobiological studies of sociability.