Altered anxiety-related and social behaviors in the Fmr1 knockout mouse model of fragile X syndrome

The loss of fragile X mental retardation (FMR1) gene function causes fragile X syndrome (FXS), a common mental retardation syndrome. Anxiety and abnormal social behaviors are prominent features of FXS in humans. To better understand the role of FMR1 in these behaviors, we analyzed anxiety-related and social behaviors in Fmr1 knockout (KO) mice. In the mirrored chamber test, Fmr1 KO mice showed greater aversion to the central mirrored chamber than wild-type (WT) littermates, suggesting increased anxiety-like responses to reflected images of mice. Fmr1 KO mice exhibited abnormal social interactions in a tube test of social dominance, winning fewer matches than WT littermates. In a partition test, Fmr1 KO mice had normal levels of social interest and social recognition. However, during direct interaction tests, Fmr1 KO mice showed significant increases in sniffing behaviors. We further tested the influence of environmental familiarity on the social responses of Fmr1 KO mice to unfamiliar partners. In unfamiliar partitioned cages, Fmr1 KO mice did not differ from WT mice in investigation of unfamiliar partners. However, in familiar partitioned cages, Fmr1 KO mice showed less investigation of a newly introduced partner during the first 5 min and more investigation during the last 5 min of a 20-min partition test, behaviors consistent with initial social anxiety followed by enhanced social investigation. Our findings indicate that the loss of Fmr1 gene function results in altered anxiety and social behavior in mice and demonstrate that the Fmr1 KO mouse is a relevant animal model for the abnormal social responses seen in FXS.     

Complex, multimodal behavioral profile of the Homer1 knockout mouse

Proteins of the Homer1 immediate early gene family have been associated with synaptogenesis and synaptic plasticity suggesting broad behavioral consequences of loss of function. This study examined the behavior of male Homer1 knockout (KO) mice compared with wild-type (WT) and heterozygous mice using a battery of 10 behavioral tests probing sensory, motor, social, emotional and learning/memory functions. KO mice showed mild somatic growth retardation, poor motor coordination, enhanced sensory reactivity and learning deficits. Heterozygous mice showed increased aggression in social interactions with conspecifics. The distribution of mGluR5 and N-methyl-D-aspartate receptors (NMDA) receptors appeared to be unaltered in the hippocampus (HIP) of Homer1 KO mice. The results indicate an extensive range of disrupted behaviors that should contribute to the understanding of the Homer1 gene in brain development and behavior.     

Oxytocin receptor knockout mice display deficits in the expression of autism-related behaviors

A wealth of studies has implicated oxytocin (Oxt) and its receptors (Oxtr) in the mediation of social behaviors and social memory in rodents. It has been suggested that failures in this system contribute to deficits in social interaction that characterize autism spectrum disorders (ASD). In the current analyses, we investigated the expression of autism-related behaviors in mice that lack the ability to synthesize the oxytocin receptor itself, Oxtr knockout (KO) mice, as compared to their wild-type (WT) littermates. In the visible burrow system, Oxtr KO mice showed robust reductions in frontal approach, huddling, allo-grooming, and flight, with more time spent alone, and in self-grooming, as compared to WT. These results were corroborated in the three-chambered test: unlike WT, Oxtr KO mice failed to spend more time in the side of the test box containing an unfamiliar CD-1 mouse. In the social proximity test, Oxtr KO mice showed clear reductions in nose to nose and anogenital sniff behaviors oriented to an unfamiliar C57BL/6J (B6) mouse. In addition, our study revealed no differences between Oxtr WT and KO genotypes in the occurrence of motor and cognitive stereotyped behaviors. A significant genotype effect was found in the scent marking analysis, with Oxtr KO mice showing a decreased number of scent marks, as compared to WT. Overall, the present data indicate that the profile for Oxtr KO mice, including consistent social deficits, and reduced levels of communication, models multiple components of the ASD phenotype. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.     

The Influence of Relatedness, Neighbourhood and Overall Distance on Colony Mate Recognition in a Polydomous Ant

The ‘dear enemy phenomenon’ predicts that territorial animals respond less aggressively towards more familiar neighbours than towards unfamiliar conspecifics if potential losses to strangers are more costly than potential losses to neighbours. Conversely, territorial animals should respond more aggressively to neighbours, if potential losses to them are more costly than potential losses to strangers. In social insects the question of how colony members distinguish neighbours from strangers, however, is intertwined with the more general question of how colony members discriminate themselves from non‐colony members; both genetic and spatial distance can correlate with levels of inter‐colonial aggression. In this paper I disentangle the role of experience, genetic and spatial distance on inter‐colonial aggression in a polydomous population of Iridomyrmex purpureus. In I. purpureus, aggression is related to the spatial distance between colonies irrespective of genetic similarity. Spatial distance affected aggression in two different ways. First, workers were more likely to exhibit aggression towards alien conspecifics of adjoining rather than non‐adjoining territories, suggesting the opposite of the dear enemy phenomenon. Second, workers were more often aggressive towards conspecifics of more distant colonies, implying that environmental cues play a role in the recognition system of I. purpureus.     

Deficiency of sterol regulatory element‐binding protein‐1c induces schizophrenia‐like behavior in mice

Schizophrenia is a hereditary disease that approximately 1% of the worldwide population develops. Many studies have investigated possible underlying genes related to schizophrenia. Recently, clinical studies suggested sterol regulatory element‐binding protein (SREBP) as a susceptibility gene in patients with schizophrenia. SREBP controls cellular lipid homeostasis by three isoforms: SREBP‐1a, SREBP‐1c and SREBP‐2. This study used SREBP‐1c knockout (KO) mice to examine whether a deficiency in SREBP‐1c would affect their emotional and psychiatric behaviors. Altered mRNA expression in genes downstream from SREBP‐1c was confirmed in the brains of SREBP‐1c KO mice. Schizophrenia‐like behavior, including hyperactivity during the dark phase, depressive‐like behavior, aggressive behavior and deficits in social interaction and prepulse inhibition, was observed in SREBP‐1c KO mice. Furthermore, increased volume of the lateral ventricle was detected in SREBP‐1c KO mice. The mRNA levels of several γ‐aminobutyric acid (GABA)‐receptor subtypes and/or glutamic acid decarboxylase 65/67 decreased in the hippocampus and medial prefrontal cortex of SREBP‐1c KO mice. Thus, SREBP‐1c deficiency may contribute to enlargement of the lateral ventricle and development of schizophrenia‐like behaviors and be associated with altered GABAergic transmission.     

Rival recognition in the territorial tawny dragon (Ctenophorus decresii)

The ability to discriminate between familiar and unfamiliar conspecifics is important in territorial animals as it allows animals to distinguish neighbours from non-neighbours. This prevents wasting time and energy in unnecessary aggressive interactions. I investigated the ability of adult males of a territorial lizard, the tawny dragon (Ctenophorus decresii), to distinguish familiar from unfamiliar rivals in a laboratory setting. Males significantly reduced their aggression levels in repeat interactions with familiar rivals and increased their aggression levels towards unfamiliar males. The time taken for interactions to be settled was also significantly lower towards familiar than unfamiliar males. The results of this study suggest that adult male tawny dragons can discriminate familiar from unfamiliar conspecifics. Furthermore, animals were presented with three new rivals in succession and showed a robust ability to discriminate between familiar and unfamiliar males.     

Activity‐regulated cytoskeleton‐associated protein (Arc/Arg3.1) regulates anxiety‐ and novelty‐related behaviors

The activity‐regulated cytoskeleton‐associated protein (Arc, also known as Arg3.1) regulates glutamatergic synapse plasticity and has been linked to neuropsychiatric illness; however, its role in behaviors associated with mood and anxiety disorders remains unclear. We find that stress upregulates Arc expression in the adult mouse nucleus accumbens (NAc)—a brain region implicated in mood and anxiety behaviors. Global Arc knockout mice have altered AMPAR‐subunit surface levels in the adult NAc, and the Arc‐deficient mice show reductions in anxiety‐like behavior, deficits in social novelty preference, and antidepressive‐like behavior. Viral‐mediated expression of Arc in the adult NAc of male, global Arc KO mice restores normal levels of anxiety‐like behavior in the elevated plus maze (EPM). Consistent with this finding, viral‐mediated reduction of Arc in the adult NAc reduces anxiety‐like behavior in male, but not female, mice in the EPM. NAc‐specific reduction of Arc also produced significant deficits in both object and social novelty preference tasks. Together our findings indicate that Arc is essential for regulating normal mood‐ and anxiety‐related behaviors and novelty discrimination, and that Arc's function within the adult NAc contributes to these behavioral effects.     

Delayed cutaneous wound closure in HO‐2 deficient mice despite normal HO‐1 expression

Impaired wound healing can lead to scarring, and aesthetical and functional problems. The cytoprotective haem oxygenase (HO) enzymes degrade haem into iron, biliverdin and carbon monoxide. HO‐1 deficient mice suffer from chronic inflammatory stress and delayed cutaneous wound healing, while corneal wound healing in HO‐2 deficient mice is impaired with exorbitant inflammation and absence of HO‐1 expression. This study addresses the role of HO‐2 in cutaneous excisional wound healing using HO‐2 knockout (KO) mice. Here, we show that HO‐2 deficiency also delays cutaneous wound closure compared to WT controls. In addition, we detected reduced collagen deposition and vessel density in the wounds of HO‐2 KO mice compared to WT controls. Surprisingly, wound closure in HO‐2 KO mice was accompanied by an inflammatory response comparable to WT mice. HO‐1 induction in HO‐2 deficient skin was also similar to WT controls and may explain this protection against exaggerated cutaneous inflammation but not the delayed wound closure. Proliferation and myofibroblast differentiation were similar in both two genotypes. Next, we screened for candidate genes to explain the observed delayed wound closure, and detected delayed gene and protein expression profiles of the chemokine (C‐X‐C) ligand‐11 (CXCL‐11) in wounds of HO‐2 KO mice. Abnormal regulation of CXCL‐11 has been linked to delayed wound healing and disturbed angiogenesis. However, whether aberrant CXCL‐11 expression in HO‐2 KO mice is caused by or is causing delayed wound healing needs to be further investigated.     

Brain‐derived neurotrophic factor,corticotropin‐releasing factor,and hypothalamic neuronal histamine interact to regulate feeding behavior

Brain‐derived neurotrophic factor (BDNF), corticotropin‐releasing factor (CRF), and hypothalamic neuronal histamine are anorexigenic substances within the hypothalamus. This study examined the interactions among BDNF, CRF, and histamine during the regulation of feeding behavior in rodents. Food intake was measured after treatment with BDNF, α‐fluoromethyl histidine (FMH; a specific suicide inhibitor of histidine decarboxylase that depletes hypothalamic neuronal histamine), or CRF antagonist. We measured food intake in wild‐type mice and mice with targeted disruption of the histamine H1 receptor (H1KO mice) after central BDNF infusion. Furthermore, we investigated CRF content and histamine turnover in the hypothalamus after BDNF treatment, and conversely, BDNF content in the hypothalamus after histamine treatment. We used immunohistochemical staining for histamine H1 receptors (H1‐R) in BDNF neurons. BDNF‐induced feeding suppression was partially attenuated in rats pre‐treated with FMH or a CRF antagonist, and in H1KO mice. BDNF treatment increased CRF content and histamine turnover in the hypothalamus. Histamine increased BDNF content in the hypothalamus. Immunohistochemical analysis revealed that H1‐Rs were expressed on BDNF neurons in the ventromedial nucleus of the hypothalamus. These results indicate that CRF and hypothalamic neuronal histamine mediate the suppressive effects of BDNF on feeding behavior and body weight.     

Social Reversal of Sex‐Biased Aggression and Dominance in a Biparental Cichlid Fish (Julidochromis marlieri)

In biparental species, aggression, dominance, and parental care are typically sexually dimorphic. While behavioral dimorphism is often strongly linked to gonadal sex, the environment—either social or ecological—may also influence sex‐biased behavior. In the biparental cichlid fish Julidochromis marlieri, the typical social environment for breeding pairs consists of large females paired with smaller males. While both sexes are capable of providing territory defense and parental care, the larger female provides the majority of defense for the pair, while the smaller male remains in the nest guarding their offspring. We examine the contributions of sex and relative mate size to these sex‐biased behaviors in monogamous J. marlieri pairs. Both female‐larger and male‐larger pairs were formed in the laboratory and were observed for territorial aggression (against conspecifics and heterospecifics), dominance, and parental care. In female‐larger pairs, territorial aggression and intra‐pair dominance were female‐biased, while in male‐larger pairs this bias was reversed. For both pairing types, the presence of an intruder amplified sex differences in territorial aggression, with the larger fish always attacking with greater frequency than its mate. Though less robust, there was evidence for plasticity of sex‐bias for some egg care related behaviors in the inverse direction. Our study suggests that relative mate size strongly influences the sex bias of aggression and dominance in J. marlieri and that this aspect of the social environment can override the influence of gonadal sex on an individual's behavior. The remarkable plasticity of this species makes Julidochromis an exciting model that could be used to address the relationship between proximate and ultimate mechanisms of behavioral plasticity.     

Size-Dependent Chemosensory Responses to Familiar and Unfamiliar Conspecific Faecal Pellets by the Iberian Rock-Lizard, Lacerta monticola

We conducted a field study to analyse the social relationships between males of the Iberian rock lizard (Lacerta monticola). The degree of familiarity was determined based on the degree of overlap between their home ranges. We then designed a laboratory experiment to test whether the same males were able to discriminate between familiar and unfamiliar conspecifics using faecal pellet odours. Differential tongue‐flick rates suggest that large males (snout‐to‐vent length, SVL > 75 mm), at least, may discriminate between odours of familiar and unfamiliar males. The behavioural responses were dependent on relative differences in body size between the responding male and the male that donated the faecal pellet. Thus, as responding small males increased in size relative to their corresponding familiar male, their rate of tongue‐flicking significantly decreased; this was not the case in response to unfamiliar males. In contrast, there were no significant correlations between the response of large males to familiar or unfamiliar male stimuli, regardless of size differences. These results suggest that chemical cues contained in faecal pellets allow individual recognition in male L. monticola, and that the response depends on body size. We suggest that faecal pellets might be used to scent‐mark home ranges, which would contribute to lowering the costs of aggressive interactions.     

Chemosensory Recognition of Familiar and Unfamiliar Conspecifics by Juveniles of the Iberian Wall Lizard Podarcis hispanica

Chemosensory recognition of familiar conspecifics has been reported in studies with members of several lizard families and may be advantageous to distinguish between intruders and neighbors or group members. However, few species have been studied and information on the ability to discriminate between familiar and unfamiliar conspecifics by chemosensory means is lacking for most lizard families. In this paper we ask whether juveniles of the Iberian wall lizard Podarcis hispanica (Lacertidae), can discriminate between chemical signals from familiar conspecifics with whom they have shared a terrarium for several months and those from unfamiliar conspecifics housed in a different terrarium. Experimental trials were conducted by transferring juveniles to a test terrarium with a filter paper substrate. We tested the responses of lizards to paper substrates labeled by familiar cage-mates, unfamiliar conspecifics, or unlabeled. Tongue-flicks and other behaviors in response to pheromonal stimuli were recorded for 10 min Juveniles directed more chemosensory behavior towards paper substrates bearing chemicals from familiar conspecifics than towards similar paper substrates labeled by unfamiliar conspecifics. These results indicate that juveniles in this lizard species can recognize familiar conspecifics and discriminate between familiar and unfamiliar individuals using only chemical stimuli. We discuss the role of habituation in familiar conspecific recognition and review possible explanations of the functional significance of this type of discrimination in lizards.     

Robust Memories of Individual Identity in Ant Queens

Individual recognition (IR) has been demonstrated in some Pachycondyla ants. The maintenance of such memories is challenged when queens are separated for the few hours of forage (attenuation) or when they are simultaneously interacting with conspecifics in a reduced space, that is, the nest (interference). By quantifying the level of aggression among familiar and unfamiliar queens of P. inversa, we showed that memories of social partner’s identity are robust to attenuation over the course of 2 days and to interference from subsequent interaction with five other individuals. Because wasps and crabs also remember familiar partners after separation and interaction with other conspecifics, we propose that robustness of social memories is widespread in invertebrates with IR abilities.     

Experience with adults shapes multisensory representation of social familiarity in the brain of a songbird

Social animals learn to perceive their social environment, and their social skills and preferences are thought to emerge from greater exposure to and hence familiarity with some social signals rather than others. Familiarity appears to be tightly linked to multisensory integration. The ability to differentiate and categorize familiar and unfamiliar individuals and to build a multisensory representation of known individuals emerges from successive social interactions, in particular with adult, experienced models. In different species, adults have been shown to shape the social behavior of young by promoting selective attention to multisensory cues. The question of what representation of known conspecifics adult-deprived animals may build therefore arises. Here we show that starlings raised with no experience with adults fail to develop a multisensory representation of familiar and unfamiliar starlings. Electrophysiological recordings of neuronal activity throughout the primary auditory area of these birds, while they were exposed to audio-only or audiovisual familiar and unfamiliar cues, showed that visual stimuli did, as in wild-caught starlings, modulate auditory responses but that, unlike what was observed in wild-caught birds, this modulation was not influenced by familiarity. Thus, adult-deprived starlings seem to fail to discriminate between familiar and unfamiliar individuals. This suggests that adults may shape multisensory representation of known individuals in the brain, possibly by focusing the young's attention on relevant, multisensory cues. Multisensory stimulation by experienced, adult models may thus be ubiquitously important for the development of social skills (and of the neural properties underlying such skills) in a variety of species.     

Regulation of lipopolysaccharide‐induced inflammatory response and endotoxemia by β‐arrestins

β‐Arrestins are scaffolding proteins implicated as negative regulators of TLR4 signaling in macrophages and fibroblasts. Unexpectedly, we found that β‐arrestin‐1 (β‐arr‐1) and ‐2 knockout (KO) mice are protected from TLR4‐mediated endotoxic shock and lethality. To identify the potential mechanisms involved, we examined the plasma levels of inflammatory cytokines/chemokines in the wild‐type (WT) and β‐arr‐1 and ‐2 KO mice after lipopolysaccharide (LPS, a TLR4 ligand) injection. Consistent with lethality, LPS‐induced inflammatory cytokine levels in the plasma were markedly decreased in both β‐arr‐1 and ‐2 KO, compared to WT mice. To further explore the cellular mechanisms, we obtained splenocytes (separated into CD11^b+ and CD11^b? populations) from WT, β‐arr‐1, and ‐2 KO mice and examined the effect of LPS on cytokine production. Similar to the in vivo observations, LPS‐induced inflammatory cytokines were significantly blocked in both splenocyte populations from the β‐arr‐2 KO compared to the WT mice. This effect in the β‐arr‐1 KO mice, however, was restricted to the CD11^b? splenocytes. Our studies further indicate that regulation of cytokine production by β‐arrestins is likely independent of MAPK and IκBα‐NFκB pathways. Our results, however, suggest that LPS‐induced chromatin modification is dependent on β‐arrestin levels and may be the underlying mechanistic basis for regulation of cytokine levels by β‐arrestins in vivo. Taken together, these results indicate that β‐arr‐1 and ‐2 mediate LPS‐induced cytokine secretion in a cell‐type specific manner and that both β‐arrestins have overlapping but non‐redundant roles in regulating inflammatory cytokine production and endotoxic shock in mice. J. Cell. Physiol. 225: 406–416, 2010. © 2010 Wiley‐Liss, Inc.     

Conditioned odor aversion induces social anxiety towards females in wild‐type and TrpC2 knockout male mice

Female‐emitted pheromonal inputs possess an intrinsic rewarding value for conspecific males, promoting approach and investigation of the potential mating partner. In mice these inputs are detected mainly by the vomeronasal organ (VNO) and the main olfactory epithelium (MOE). We investigated the role of VNO‐mediated inputs in experience‐dependent plasticity of reproductive responses. We applied a sex‐specific conditioned odor aversion (COA) paradigm on adult, wild‐type (WT) male mice and on male mice impaired in VNO‐mediated signal transduction (TrpC2^?/?). We found that WT males, which underwent COA to female‐soiled bedding, lost their innate preference to female odors and presented lower motivation to approach a sexually receptive female. COA also abolished the testosterone surge normally seen following exposure to female odors. Moreover, the conditioned males displayed impairments in copulatory behaviors, which lasted for several weeks. Surprisingly, these males also exhibited phobic behaviors towards receptive females, including freezing and fleeing responses. In contrast, WT males which underwent COA specifically to male pheromones showed no change in olfactory preference and only a marginally significant elevation in intermale aggression. Finally, we show that TrpC2^?/? males were able to acquire aversion to female‐soiled bedding and presented similar behavioral alterations following COA in their responses to female cues. Our results demonstrate that the intrinsic rewarding value of female pheromones can be overridden through associative olfactory learning, which occurs independently of VNO inputs, probably through MOE signaling.     

Domestication‐related variation in social preferences in chickens is affected by genotype on a growth QTL

A growth‐related QTL on chicken chromosome 1 has previously been shown to influence domestication behaviour in chickens. In this study, we used Red Junglefowl (RJF) and White Leghorn (WL) as well as the intercross between them to investigate whether stress affects the way birds allocate their time between familiar and unfamiliar conspecifics in a social preference test (‘social support seeking’), and how this is related to genotype at specific loci within the growth QTL. Red Junglefowl males spent more time with unfamiliar chickens before the stressful event compared to the other birds, whereas all birds except WL males tended to spend less time with unfamiliar ones after stress. A significant QTL locus was found to influence both social preference under undisturbed circumstances and social support seeking. The WL allele at this QTL was associated not only with a preference for unfamiliar individuals but also with a shift towards familiar ones in response to stress (social support seeking). A second, suggestive QTL also affected social support seeking, but in the opposite direction; the WL allele was associated with increased time spent with unfamiliar individuals. The region contains several possible candidate genes, and gene expression analysis of a number of them showed differential expression between RJF and WL of AVPR2 (receptor for vasotocin), and possibly AVPR1a (another vasotocin receptor) and NRCAM (involved in neural development) in the lower frontal lobes of the brains of RJF and WL animals. These three genes continue to be interesting candidates for the observed behavioural effects .     

Social modulation of fear: Facilitation vs buffering

Social behaviors largely constitute mutual exchanges of social cues and the responses to them. The adaptive response also requires proper interpretation of the current context. In fear behaviors, social signals have bidirectional effects—some cues elicit or enhance fear whereas other suppress or buffer it. Studies on the social facilitation and social buffering of fear provide evidence of competition between social cues of opposing meanings. Co‐expression of opposing cues by the same animal may explain the contradicting outcomes from the interaction between naive and frightened conspecifics, which reflect the fine balance between fear facilitation and buffering. The neuronal mechanisms that determine that balance provide an exciting target for future studies to probe the brain circuits underlying social modulation of emotional behaviors.     

Transient receptor potential ankyrin 1 (TRPA1) positively regulates imiquimod‐induced,psoriasiform dermal inflammation in mice

Transient receptor potential ankyrin 1 (TRPA1), a membrane protein ion channel, is known to mediate itch and pain in skin. The function of TRPA1, however, in psoriasiform dermatitis (PsD) is uncertain. Herein, we found that expression of TRPA1 is highly up‐regulated in human psoriatic lesional skin. To study the role of TRPA1 in PsD, we assessed Psoriasis Severity Index (PSI) scores, transepidermal water loss (TEWL), skin thickness and pathology, and examined dermal inflammatory infiltrates, Th17‐related genes and itch‐related genes in c57BL/6 as wild‐type (WT) and TRPA1 gene knockout (KO) mice following daily application of topical IMQ cream for 5 days. Compared with WT mice, clinical scores, skin thickness change and TEWL scores were similar on day 3, but were significantly decreased on day 5 in IMQ‐treated TRPA1 KO mice (vs WT mice), suggesting reduced inflammation and skin barrier defects. Additionally, the relative area of epidermal Munro's microabscesses and mRNA levels of neutrophil inducible chemokines (S100A8, S100A9 and CXCL1) were decreased in the treated skin of TRPA1 KO mice, suggesting that neutrophil recruitment was impaired in the KO mice. Furthermore, mast cells, CD31⁺ blood vascular cells, CD45⁺ leukocytes and CD3⁺ T cells were all reduced in the treated skin of TRPA1 KO mice. Lastly, mRNA expression levels of IL‐1β, IL‐6, IL‐23, IL‐17A, IL‐17F and IL‐22 were decreased in TRPA1 KO mice. In summary, these results suggest a key role for TRPA1 in psoriasiform inflammation and raising its potential as a target for therapeutic intervention.