Early deprivation induces competitive subordinance in C57BL/6 male mice

Induction of territorial dominance and subordination behaviors in laboratory mice

Territorial behaviors comprise a set of coordinated actions and response patterns found across animal species that promote the exclusive access to resources. House mice are highly territorial with a subset of males consistently attacking and chasing competing males to expel them from their territories and performing urine marking behaviors to signal the extent of their territories. Natural variation in territorial behaviors within a mouse colony leads to the formation of dominance hierarchies in which subordinate males can reside within the territory of a dominant male. While the full repertoire of such territorial behaviors and hierarchies has been extensively studied in wild-derived mice in semi-natural enclosures, so far they have not been established in the smaller enclosures and with the genetically-defined laboratory strains required for the application of neural recording and manipulation methods. Here, we present a protocol to rapidly induce an extensive repertoire of territorial behaviors in pairs of laboratory mice in an enclosure compatible with tethered neurocircuit techniques, including a method for the simultaneous tracking of urine marking behavior in mouse pairs. Using this protocol we describe the emergence of robust dominant-subordinate hierarchies between pairs of CD1 outbred or CD1xB6 F1 hybrid mice, but unexpectedly not in C57BL/6 inbred animals. Our behavioral paradigm opens the door for neurocircuit studies of territorial behaviors and social hierarchy in the laboratory.

Characterization of Mice Carrying a Neurodevelopmental Disease-Associated GluN2B(L825V) Variant

N-Methyl-d-aspartate receptors (NMDARs), encoded by GRIN genes, are ionotropic glutamate receptors playing a critical role in synaptic transmission, plasticity, and synapse development. Genome sequence analyses have identified variants in GRIN genes in patients with neurodevelopmental disorders, but the underlying disease mechanisms are not well understood. Here, we have created and evaluated a transgenic mouse line carrying a missense variant Grin2bL825V , corresponding to a de novo GRIN2B variant encoding GluN2B(L825V) found in a patient with intellectual disability (ID) and autism spectrum disorder (ASD). We used HEK293T cells expressing recombinant receptors and primary hippocampal neurons prepared from heterozygous Grin2bL825V/+ (L825V/+) and wild-type (WT) Grin2b+/+ (+/+) male and female mice to assess the functional impact of the variant. Whole-cell NMDAR currents were reduced in neurons from L825V/+ compared with +/+ mice. The peak amplitude of NMDAR-mediated evoked excitatory postsynaptic currents (NMDAR-eEPSCs) was unchanged, but NMDAR-eEPSCs in L825V/+ neurons had faster deactivation compared with +/+ neurons and were less sensitive to a GluN2B-selective antagonist ifenprodil. Together, these results suggest a decreased functional contribution of GluN2B subunits to synaptic NMDAR currents in hippocampal neurons from L825V/+ mice. The analysis of the GluN2B(L825V) subunit surface expression and synaptic localization revealed no differences compared with WT GluN2B. Behavioral testing of mice of both sexes demonstrated hypoactivity, anxiety, and impaired sensorimotor gating in the L825V/+ strain, particularly affecting males, as well as cognitive symptoms. The heterozygous L825V/+ mouse offers a clinically relevant model of GRIN2B-related ID/ASD, and our results suggest synaptic-level functional changes that may contribute to neurodevelopmental pathology.

Adverse effects of early-life stress: focus on the rodent neuroendocrine system

Early-life stress is associated with a high prevalence of mental illnesses such as post-traumatic stress disorders, attention-deficit/hyperactivity disorder, schizophrenia, and anxiety or depressive behavior, which constitute major public health problems. In the early stages of brain development after birth, events such as synaptogenesis, neuron maturation, and glial differentiation occur in a highly orchestrated manner, and external stress can cause adverse long-term effects throughout life. Our body utilizes multifaceted mechanisms, including neuroendocrine and neurotransmitter signaling pathways, to appropriately process external stress. Newborn individuals first exposed to early-life stress deploy neurogenesis as a stress-defense mechanism; however, in adulthood, early-life stress induces apoptosis of mature neurons, activation of immune responses, and reduction of neurotrophic factors, leading to anxiety, depression, and cognitive and memory dysfunction. This process involves the hypothalamus-pituitary-adrenal axis and neurotransmitters secreted by the central nervous system, including norepinephrine, dopamine, and serotonin. The rodent early-life stress model is generally used to experimentally assess the effects of stress during neurodevelopment. This paper reviews the use of the early-life stress model and stress response mechanisms of the body and discusses the experimental results regarding how early-life stress mediates stress-related pathways at a high vulnerability of psychiatric disorder in adulthood.

IntelliCage: the development and perspectives of a mouse- and user-friendly automated behavioral test system

IntelliCage for mice is a rodent home-cage equipped with four corner structures harboring symmetrical double panels for operant conditioning at each of the two sides, either by reward (access to water) or by aversion (non-painful stimuli: air-puffs, LED lights). Corner visits, nose-pokes and actual licks at bottle-nipples are recorded individually using subcutaneously implanted transponders for RFID identification of up to 16 adult mice housed in the same home-cage. This allows for recording individual in-cage activity of mice and applying reward/punishment operant conditioning schemes in corners using workflows designed on a versatile graphic user interface. IntelliCage development had four roots: (i) dissatisfaction with standard approaches for analyzing mouse behavior, including standardization and reproducibility issues, (ii) response to handling and housing animal welfare issues, (iii) the increasing number of mouse models had produced a high work burden on classic manual behavioral phenotyping of single mice. and (iv), studies of transponder-chipped mice in outdoor settings revealed clear genetic behavioral differences in mouse models corresponding to those observed by classic testing in the laboratory. The latter observations were important for the development of home-cage testing in social groups, because they contradicted the traditional belief that animals must be tested under social isolation to prevent disturbance by other group members. The use of IntelliCages reduced indeed the amount of classic testing remarkably, while its flexibility was proved in a wide range of applications worldwide including transcontinental parallel testing. Essentially, two lines of testing emerged: sophisticated analysis of spontaneous behavior in the IntelliCage for screening of new genetic models, and hypothesis testing in many fields of behavioral neuroscience. Upcoming developments of the IntelliCage aim at improved stimulus presentation in the learning corners and videotracking of social interactions within the IntelliCage. Its main advantages are (i) that mice live in social context and are not stressfully handled for experiments, (ii) that studies are not restricted in time and can run in absence of humans, (iii) that it increases reproducibility of behavioral phenotyping worldwide, and (iv) that the industrial standardization of the cage permits retrospective data analysis with new statistical tools even after many years.

Increased paternal corticosterone exposure influences offspring behaviour and expression of urinary pheromones

BACKGROUND

Studies have shown that paternal stress prior to conception can influence the innate behaviours of their offspring. The evolutionary impacts of such intergenerational effects are therefore of considerable interest. Our group previously showed in a model of daily stress that glucocorticoid treatment of adult male mouse breeders prior to conception leads to increased anxiety-related behaviours in male offspring. Here, we aimed to understand the transgenerational effects of paternal stress exposure on the social behaviour of progeny and its potential influence on reproductive success.

RESULTS

We assessed social parameters including social reward, male attractiveness and social dominance, in the offspring (F1) and grand-offspring (F2). We report that paternal corticosterone treatment was associated with increased display of subordination towards other male mice. Those mice were unexpectedly more attractive to female mice while expressing reduced levels of the key rodent pheromone Darcin, contrary to its conventional role in driving female attraction. We investigated the epigenetic regulation of major urinary protein (Mup) expression by performing the first Oxford Nanopore direct methylation of sperm DNA in a mouse model of stress, but found no differences in Mup genes that could be attributed to corticosterone-treatment. Furthermore, no overt differences of the prefrontal cortex transcriptome were found in F1 offspring, implying that peripheral mechanisms are likely contributing to the phenotypic differences. Interestingly, no phenotypic differences were observed in the F2 grand-offspring.

CONCLUSIONS

Overall, our findings highlight the potential of moderate paternal stress to affect intergenerational (mal)adaptive responses, informing future studies of adaptiveness in rodents, humans and other species.

Maternal neglect alters reward-anticipatory behavior, social status stability, and reward circuit activation in adult male rats

Introduction

Adverse early life experiences affect neuronal growth and maturation of reward circuits that modify behavior under reward predicting conditions. Previous studies demonstrate that rats undergoing denial of expected reward in the form of maternal contact (DER-animal model of maternal neglect) during early post-natal life developed anhedonia, aggressive play-fight behaviors and aberrant prefrontal cortex structure and neurochemistry. Although many studies revealed social deficiency following early-life stress most reports focus on individual animal tasks. Thus, attention needs to be given on the social effects during group tasks in animals afflicted by early life adversity.

Methods

To investigate the potential impact of the DER experience on the manifestation of behavioral responses induced by natural rewards, we evaluated: 1) naïve adult male sexual preference and performance, and 2) anticipatory behavior during a group 2-phase food anticipation learning task composed of a context-dependent and a cue-dependent learning period.

Results

DER rats efficiently spent time in the vicinity of and initiated sexual intercourse with receptive females suggesting an intact sexual reward motivation and consummation. Interestingly, during the context-dependent phase of food anticipation training DER rats displayed a modified exploratory activity and lower overall reward-context association. Moreover, during the cue-dependent phase DER rats displayed a mild deficit in context-reward association while increased cue-dependent locomotion. Additionally, DER rats displayed unstable food access priority following food presentation. These abnormal behaviours were accompanied by overactivation of the ventral prefrontal cortex and nucleus accumbens, as assessed by pCREB levels.

Conclusions/discussion

Collectively, these data show that the neonatal DER experience resulted in adulthood in altered activation of the reward circuitry, interfered with the normal formation of context-reward associations, and disrupted normal reward access hierarchy formation. These findings provide additional evidence to the deleterious effects of early life adversity on reward system, social hierarchy formation, and brain function.

Long-term behavioral effects of social separation during early life in a social mammal, Octodon degus

Social separation is thought to induce a strong stress response in social juvenile mammals, but little is known about how this response might vary throughout the development. The present study examines the long-term effects of early-life stress (ELS) induced by social separation on individual behaviors later in life using the social and precocious species Octodon degus. Four experimental groups were established a positive control group of mothers and siblings from six litters comprised the socially housed (SH) group, while pups from seven litters were randomly assigned to three treatments: pups experiencing no separation (NS) treatment while their siblings did; repeated bouts of consecutive separation (CS); intermittent separation (IS). We analyzed the effects of separation treatment on the frequency and duration of freezing, rearing and grooming behaviors. ELS was correlated with higher hyperactivity, and hyperactivity increased with more frequent separation. However, the behavioral trend of the NS group changed to hyperactive in long-term observation. The findings suggest that the NS group was indirectly affected by ELS. In addition, suggesting ELS acts to converge an individual's behavioral tendencies in a certain direction.

Advancing social behavioral neuroscience by integrating ethology and comparative psychology methods through machine learning

Social behavior is naturally occurring in vertebrate species, which holds a strong evolutionary component and is crucial for the normal development and survival of individuals throughout life. Behavioral neuroscience has seen different influential methods for social behavioral phenotyping. The ethological research approach has extensively investigated social behavior in natural habitats, while the comparative psychology approach was developed utilizing standardized and univariate social behavioral tests. The development of advanced and precise tracking tools, together with post-tracking analysis packages, has recently enabled a novel behavioral phenotyping method, that includes the strengths of both approaches. The implementation of such methods will be beneficial for fundamental social behavioral research but will also enable an increased understanding of the influences of many different factors that can influence social behavior, such as stress exposure. Furthermore, future research will increase the number of data modalities, such as sensory, physiological, and neuronal activity data, and will thereby significantly enhance our understanding of the biological basis of social behavior and guide intervention strategies for behavioral abnormalities in psychiatric disorders.

Long-lasting and sex-dependent effects of late lactational maternal deprivation on socioemotional behaviors in adult mice

The lactation period is an important period for individual development and a sensitive period for the behavioral phenotypes and plasticity of individual offspring. Early life experiences (e.g., maternal deprivation (MD) and neglect) have significant long-lasting and dual effects on individual stress reactivities during adulthood. Theoretically, stress inoculation can improve the adaptive capacity of the body, but overstress can lead to dysfunction when adaptive mechanisms fail.To date, the potential effects of late lactational MD on the socioemotional behaviors of mouse offspring during adulthood are still not fully understood. In the present study, mice were subjected to early deprivation by individually separating pups from their dam for 0 min, 15 min, and 3 h per day from PND 13-25. The social dominance test (SDT), social interaction test (SI), open field test (OFT), and forced swim test (FST) were carried out during adulthood. The results showed that the social dominance of male mice in the 15 min/d MD group significantly increased, especially in low-rank mice. In the 3 h/d MD group, the social dominance of female mice was decreased, especially in the lower-rank mice. The anxiolytic and antidepressant-like effects of the 15 min/d MD group were significantly increased in male mice. Our study provides direct evidence that MD during late lactation period results in long-lasting effects on social dominance as well as on anxiety and depression phenotypes in a sex-dependent manner.

Enduring effects of early-life adversity on reward processes: A systematic review and meta-analysis of animal studies

Two-thirds of individuals experience adversity during childhood such as neglect, abuse or highly-stressful events. Early-life adversity (ELA) increases the life-long risk of developing mood and substance use disorders. Reward-related deficits has emerged as a key endophenotype of such psychiatric disorders. Animal models are invaluable for studying how ELA leads to reward deficits. However, the existing literature is heterogenous with difficult to reconcile findings. To create an overview, we conducted a systematic review containing multiple meta-analyses regarding the effects of ELA on reward processes overall and on specific aspects of reward processing in animal models. A comprehensive search identified 120 studies. Most studies omitted key details resulting in unclear risk of bias. Overall meta-analysis showed that ELA significantly reduced reward behaviors (SMD: -0.42 [-0.60; -0.24]). The magnitude of ELA effects significantly increased with longer exposure. When reward domains were analyzed separately, ELA only significantly dampened reward responsiveness (SMD: -0.525[-0.786; -0.264]) and social reward processing (SMD: -0.374 [-0.663; -0.084]), suggesting that ELA might lead to deficits in specific reward domains.

Generation and Characterization of a Novel Angelman Syndrome Mouse Model with a Full Deletion of the Ube3a Gene

Angelman syndrome (AS) is a neurodevelopmental disorder caused by deficits in maternally inherited UBE3A. The disease is characterized by intellectual disability, impaired motor skills, and behavioral deficits, including increased anxiety and autism spectrum disorder features. The mouse models used so far in AS research recapitulate most of the cardinal AS characteristics. However, they do not mimic the situation found in the majority of AS patients who have a large deletion spanning 4–6 Mb. There is also a large variability in phenotypes reported in the available models, which altogether limits development of therapeutics. Therefore, we have generated a mouse model in which the Ube3a gene is deleted entirely from the 5′ UTR to the 3′ UTR of mouse Ube3a isoform 2, resulting in a deletion of 76 kb. To investigate its phenotypic suitability as a model for AS, we employed a battery of behavioral tests directed to reveal AS pathology and to find out whether this model better mirrors AS development compared to other available models. We found that the maternally inherited Ube3a-deficient line exhibits robust motor dysfunction, as seen in the rotarod and DigiGait tests, and displays abnormalities in additional behavioral paradigms, including reduced nest building and hypoactivity, although no apparent cognitive phenotype was observed in the Barnes maze and novel object recognition tests. The AS mice did, however, underperform in more complex cognition tasks, such as place reversal in the IntelliCage system, and exhibited a different circadian rhythm activity pattern. We show that the novel UBE3A-deficient model, based on a whole-gene deletion, is suitable for AS research, as it recapitulates important phenotypes characteristic of AS. This new mouse model provides complementary possibilities to study the Ube3a gene and its function in health and disease as well as possible therapeutic interventions to restore function.

A meta-analytic study of the effects of early maternal separation on cognitive flexibility in rodent offspring

Adverse early life experiences, such as maternal separation, are associated with an increased risk for several mental health problems. Symptoms induced by maternal separation that mirror clinically relevant aspects of mental problems, such as cognitive inflexibility, open the possibility of testing putative therapeutics prior to clinical development. Although several animal (e.g., rodent) studies have evaluated the effects of early maternal separation on cognitive flexibility, no consistent conclusions have been drawn. To clarify this issue, in this study, a meta-analysis method was used to systematically explore the relationship between early maternal separation and cognitive flexibility in rodent offspring. Results indicate that early maternal separation could significantly impair cognitive flexibility in rodent offspring. Moderator analyses further showed that the relationship between early maternal separation and cognitive flexibility was not consistent in any case, but was moderated by variations in the experimental procedures, such as the deprivation levels, task characteristics, and rodent strains. These clarify the inconsistent effects of maternal separation on cognitive flexibility in rodents and help us better understand the association between early life adversity and cognitive development.

•

Meta-analysis method was used to discuss the inconsistent effects of maternal separation on cognitive flexibility in rodent.

•

Maternal separation was found to necessarily impair the cognitive flexibility in rodent.

•

Variations in the experimental procedures moderated the relationship between maternal separation and cognitive flexibility.

•

Further studies on environment-cognition associations in rodents should take experimental procedural factors into account.

Mouse Model of Weak Depression Exhibiting Suppressed cAMP Signaling in the Amygdala, Lower Lipid Catabolism in Liver, and Correlated Gut Microbiota

To establish a mouse model of weak depression, we raised 6-week-old C57BL/6N mice in single (SH) or group housing (GH) conditions for 2 weeks. The SH group showed less social interaction with stranger mice, learning disability in behavioral tests, and lower plasma corticosterone levels. The cecal microbiota of the SH group showed significant segregation from the GH group in the principal coordinate analysis (PCoA). Transcriptome analysis of the amygdala and liver detected multiple differentially expressed genes (DEGs). In the amygdala of SH mice, suppression of the cyclic adenine monophosphate (cAMP) signal was predicted and confirmed by the reduced immunoreactivity of phosphorylated cAMP-responsive element-binding protein. In the liver of SH mice, downregulation of beta-oxidation was predicted. Interestingly, the expression levels of over 100 DEGs showed a significant correlation with the occupancy of two bacterial genera, Lactobacillus (Lactobacillaceae) and Anaerostipes (Lachnospiraceae). These bacteria-correlated DEGs included JunB, the downstream component of cAMP signaling in the amygdala, and carnitine palmitoyltransferase 1A (Cpt1a), a key enzyme of beta-oxidation in the liver. This trans-omical analysis also suggested that nicotinamide adenine dinucleotide (NAD) synthesis in the liver may be linked to the occupancy of Lactobacillus through the regulation of nicotinamide phosphoribosyltransferase (NAMPT) and kynureninase (KYNU) genes. Our results suggested that SH condition along with the presence of correlated bacteria species causes weak depression phenotype in young mice and provides a suitable model to study food ingredient that is able to cure weak depression.

Effects of early life adversities upon memory processes and cognition in rodent models

Exposure to stressors in early postnatal life induces long-lasting modifications in brainfunction.Thisplasticity,an essential characteristic of the brain that enables adaptation to the environment, may also induce impairments in some psychophysiological functions, including learning and memory. Early life stress (ELS) has long-term effects on thehypothalamic-pituitary-adrenal axisresponse to stressors, and has been reported to lead toneuroinflammation,altered levelsof neurotrophic factors, modifications inneurogenesis andsynaptic plasticity,with changes in neurotransmitter systems and network functioning. In this review, we focus on early postnatal stress in animal models and their effects on learning and memory.Many studies have reported ELS-induced impairments in different types of memories, including spatial memory, fear memory, recognition (both for objects and social) memory, working memory and reversal learning. Studies are not always in agreement, however, no effects, or sometimes facilitation, being reported, depending on the nature and intensity of the early intervention, as well as the age when the outcome was evaluated and the sex of the animals. When considering processes occurring after consolidation, related with memory maintenance or modification, there are a very reduced number of reports. Future studies addressing the mechanisms underlying memory changes for ELS should shed some light on the understanding of the different effects induced by stressors of different types and intensities on cognitive functions.

Effects of early life adversity on immediate early gene expression: Systematic review and 3-level meta-analysis of rodent studies

Early-life adversity (ELA) causes long-lasting structural and functional changes to the brain, rendering affected individuals vulnerable to the development of psychopathologies later in life. Immediate-early genes (IEGs) provide a potential marker for the observed alterations, bridging the gap between activity-regulated transcription and long-lasting effects on brain structure and function. Several heterogeneous studies have used IEGs to identify differences in cellular activity after ELA; systematically investigating the literature is therefore crucial for comprehensive conclusions. Here, we performed a systematic review on 39 pre-clinical studies in rodents to study the effects of ELA (alteration of maternal care) on IEG expression. Females and IEGs other than cFos were investigated in only a handful of publications. We meta-analyzed publications investigating specifically cFos expression. ELA increased cFos expression after an acute stressor only if the animals (control and ELA) had experienced additional hits. At rest, ELA increased cFos expression irrespective of other life events, suggesting that ELA creates a phenotype similar to naïve, acutely stressed animals. We present a conceptual theoretical framework to interpret the unexpected results. Overall, ELA likely alters IEG expression across the brain, especially in interaction with other negative life events. The present review highlights current knowledge gaps and provides guidance to aid the design of future studies.

Microglial synaptic pruning on axon initial segment spines of dentate granule cells: Sexually dimorphic effects of early-life stress and consequences for adult fear response

Axon initial segments (AIS) of dentate granule cells in the hippocampus exhibit prominent spines (AISS) during early development that are associated with microglial contacts. In the present study, we investigated whether developmental changes in AISS could be modified by early-life stress (ELS), specifically neonatal maternal separation (MS), through stress hormones and microglial activation and examined the potential behavioural consequences. We examined AISS at postnatal day (PND)5, 15 and 50, using Golgi-Cox staining and anatomical analysis. Neurone-microglial interaction was assessed using antibodies against ankyrin-G, PSD-95 and Iba1, for AIS, AISS and microglia visualisation, respectively, in normally reared and neonatal maternally separated male and female rats. We observed a higher density of AISS in ELS rats at both PND15 and PND50 compared to controls. Effects were more pronounced in females than males. AIS-associated microglia in ELS rats showed a hyper-ramified morphology and less co-localisation with PSD-95 compared to controls at PND15. ELS-associated alteration in microglial morphology and synaptic pruning was mimicked by treatment of acute hippocampal slices of normally reared rats with vasopressin. ELS rats exhibited increased freezing behaviour during auditory fear memory testing, which was more pronounced in female subjects and corresponded with increased Fos expression in dorsal and ventral dentate granule cells. Thus, microglial synaptic pruning in dentate AIS of hippocampus is influenced by ELS, with demonstrable sex bias regarding its anatomical characteristics and subsequent fear-induced defensive behaviours.

Exogenous microbiota-derived metabolite trimethylamine N-oxide treatment alters social behaviors: Involvement of hippocampal metabolic adaptation

Increasing evidence indicates that gut microbiota and its metabolites can influence the brain function and the related behaviors. Trimethylamine N-oxide (TMAO), an indirect metabolite of gut microbiota, has been linked to aging, cognitive impairment, and many brain disorders. However, the potential effects of TMAO on social behaviors remain elusive. The present study investigated the effects of early life systemic TMAO exposure and intra-hippocampal TMAO infusion during adulthood on social behaviors in mice. We also analyzed the effects of intra-hippocampus infusion of TMAO during adulthood on levels of metabolites. The results showed that both systemic TMAO exposure in the post-weaning period and intra-hippocampal TMAO infusion during adulthood decreased social rank and reduced sexual preference in adult mice. Data from LC-MS metabolomics analysis showed that intra-hippocampal TMAO infusion induced a total 207 differential metabolites, which belongs to several metabolic or signaling pathways, especially FoxO signaling pathway and retrograde endocannabinoid signaling pathway. These data suggest that TMAO may affect social behaviors by regulating metabolites in the hippocampus, which may provide a new insight into the role of gut microbiota in regulating social behaviors.

Expression of human-specific ARHGAP11B in mice leads to neocortex expansion and increased memory flexibility

Neocortex expansion during human evolution provides a basis for our enhanced cognitive abilities. Yet, which genes implicated in neocortex expansion are actually responsible for higher cognitive abilities is unknown. The expression of human-specific ARHGAP11B in embryonic/foetal mouse, ferret and marmoset neocortex was previously found to promote basal progenitor proliferation, upper-layer neuron generation and neocortex expansion during development, features commonly thought to contribute to increased cognitive abilities. However, a key question is whether this phenotype persists into adulthood and if so, whether cognitive abilities are indeed increased. Here, we generated a transgenic mouse line with physiological ARHGAP11B expression that exhibits increased neocortical size and upper-layer neuron numbers persisting into adulthood. Adult ARHGAP11B-transgenic mice showed altered neurobehaviour, notably increased memory flexibility and a reduced anxiety level. Our data are consistent with the notion that neocortex expansion by ARHGAP11B, a gene implicated in human evolution, underlies some of the altered neurobehavioural features observed in the transgenic mice, such as the increased memory flexibility, a neocortex-associated trait, with implications for the increase in cognitive abilities during human evolution.

The effects of maternal separation on behaviours under social-housing environments in adult male C57BL/6 mice

Adverse experience in early life can affect the formation of neuronal circuits during postnatal development and exert long-lasting influences on neural functions that can lead to the development of a variety of psychiatric disorders including depression, anxiety disorders, and post-traumatic stress disorder. Many studies have demonstrated that daily repeated maternal separation, an animal model of early-life stress, can induce impairments in emotional behaviours and cognitive function during adolescence and adulthood. However, the behavioural phenotypes of maternally separated mice under long-term group-housing conditions are largely unknown. In this study, we applied our newly developed assay system to investigate the effects of maternal separation on behaviours under group-housing conditions during four days of continuous observations. Using our system, we found that repeated maternal separation resulted in inappropriate social distance from cagemates, altered approach preferences to others, and induced a lower rank in the time spent on the running wheel under group-housing conditions in adult male mice. Focussing on these behavioural abnormalities that appear in an environment with a social context will be important insights to understand the pathogenesis of psychiatric disorders.

The Promise of Automated Home-Cage Monitoring in Improving Translational Utility of Psychiatric Research in Rodents

Large number of promising preclinical psychiatric studies in rodents later fail in clinical trials, raising concerns about the efficacy of this approach to generate novel pharmacological interventions. In this mini-review we argue that over-reliance on behavioral tests that are brief and highly sensitive to external factors play a critical role in this failure and propose that automated home-cage monitoring offers several advantages that will increase the translational utility of preclinical psychiatric research in rodents. We describe three of the most commonly used approaches for automated home cage monitoring in rodents [e.g., operant wall systems (OWS), computerized visual systems (CVS), and automatic motion sensors (AMS)] and review several commercially available systems that integrate the different approaches. Specific examples that demonstrate the advantages of automated home-cage monitoring over traditional tests of anxiety, depression, cognition, and addiction-like behaviors are highlighted. We conclude with recommendations on how to further expand this promising line of preclinical research.

Collective Housing of Mice of Different Age Groups before Maturity Affects Mouse Behavior

Background

Although population housing is recommended by many animal management and ethical guidelines, the effect of collective housing of mice of different age groups on mouse behavior has not been clarified. Since the development of the central nervous system continues to occur before sexual maturation, the stress of social ranking formation among male individuals in mixed housing conditions can affect postmaturation behavior. To assess these effects, sexually immature mice of different ages were housed in the same cage and a series of behavioral tests were performed after maturation.

Results

The findings for three groups of mice—junior mice housed with older mice, senior mice housed with younger mice, and mice housed with other mice of the same age—were compared. Junior mice showed higher body weight and activity as well as lower grip strength and anxiety-like behaviors than other mice. In contrast, senior mice showed lower body temperature and increased aggression, antinociceptive effect, and home-cage activity in the dark period in comparison with other mice.

Conclusions

Thus, combined housing of immature mice of different age groups affects mouse behavior after maturation. Appropriate prematuration housing conditions are crucial to eliminate the uncontrollable bias caused by age-related social stratification.

Effects of Early-Life Stress on the Brain and Behaviors: Implications of Early Maternal Separation in Rodents

Early-life stress during the prenatal and postnatal periods affects the formation of neural networks that influence brain function throughout life. Previous studies have indicated that maternal separation (MS), a typical rodent model equivalent to early-life stress and, more specifically, to child abuse and/or neglect in humans, can modulate the hypothalamic-pituitary-adrenal (HPA) axis, affecting subsequent neuronal function and emotional behavior. However, the neural basis of the long-lasting effects of early-life stress on brain function has not been clarified. In the present review, we describe the alterations in the HPA-axis activity-focusing on serum corticosterone (CORT)-and in the end products of the HPA axis as well as on the CORT receptor in rodents. We then introduce the brain regions activated during various patterns of MS, including repeated MS and single exposure to MS at various stages before weaning, via an investigation of c-Fos expression, which is a biological marker of neuronal activity. Furthermore, we discuss the alterations in behavior and gene expression in the brains of adult mice exposed to MS. Finally, we ask whether MS repeats itself and whether intergenerational transmission of child abuse and neglect is possible.

A mouse model of Timothy syndrome exhibits altered social competitive dominance and inhibitory neuron development

Multiple genetic factors related to autism spectrum disorder (ASD) have been identified, but the biological mechanisms remain obscure. Timothy syndrome (TS), associated with syndromic ASD, is caused by a gain-of-function mutation, G406R, in the pore-forming subunit of L-type Ca2+ channels, Cav 1.2. In this study, a mouse model of TS, TS2-neo, was used to enhance behavioral phenotyping and to identify developmental anomalies in inhibitory neurons. Using the IntelliCage, which enables sequential behavioral tasks without human handling and mouse isolation stress, high social competitive dominance was observed in TS2-neo mice. Furthermore, histological analysis demonstrated inhibitory neuronal abnormalities in the neocortex, including an excess of smaller-sized inhibitory presynaptic terminals in the somatosensory cortex of young adolescent mice and higher numbers of migrating inhibitory neurons from the medial ganglionic eminence during embryonic development. In contrast, no obvious changes in excitatory synaptic terminals were found. These novel neural abnormalities in inhibitory neurons of TS2-neo mice may result in a disturbed excitatory/inhibitory (E/I) balance, a key feature underlying ASD.

Social subordination induced by early life adversity rewires inhibitory control of the prefrontal cortex via enhanced Npy1r signaling

Social hierarchies are present in most mammalian species. In nature, hierarchies offer a tradeoff between reduction of in-group fighting between males, at the expense of an asymmetric sharing of resources. Early life experiences and stress are known to influence the rank an individual attains in adulthood, but the associated cellular and synaptic alterations are poorly understood. Using a maternal separation protocol, we show that care-deprived mice display a long-lasting submissive phenotype, increased social recognition, and enhanced explorative behavior. These alterations are consistent with an adaptation that favors exploration rather than confrontation within a group setting. At the neuronal level, these animals display dendritic atrophy and enhanced inhibitory synaptic inputs in medial prefrontal cortex (mPFC) neurons. To determine what could underlie this synaptic modification, we first assessed global gene expression changes via RNAseq, and next focused on a smaller subset of putatively altered synaptic receptors that could explain the changes in synaptic inhibition. Using different cohorts of maternally deprived mice, we validated a significant increase in the expression of Npy1r, a receptor known to play a role in maternal care, anxiety, foraging, and regulation of group behavior. Using electrophysiological recordings in adult mice while blocking NPY1R signaling, we determined that this receptor plays a key role in enhancing GABAergic currents in mice that experience maternal deprivation. Taken together, our work highlights the potential of regulating NPY1R in social anxiety disorders and the alterations induced in brain circuitry as a consequence of early life stress and adversity.

Hippocampal transcriptome analysis following maternal separation implicates altered RNA processing in a mouse model of fetal alcohol spectrum disorder

Background

Fetal alcohol spectrum disorders (FASD) are common, seen in 1–5% of the population in the USA and Canada. Children diagnosed with FASD are not likely to remain with their biological parents, facing early maternal separation and foster placements throughout childhood.

Methods

We model FASD in mice via prenatal alcohol exposure and further induce early life stress through maternal separation. We use RNA-seq followed by clustering of expression profiles through weighted gene co-expression network analysis (WGCNA) to analyze transcriptomic changes that result from the treatments. We use reverse transcription qPCR to validate these changes in the mouse hippocampus.

Results

We report an association between adult hippocampal gene expression and prenatal ethanol exposure followed by postnatal separation stress that is related to behavioral changes. Expression profile clustering using WGCNA identifies a set of transcripts, module 19, associated with anxiety-like behavior (r = 0.79, p = 0.002) as well as treatment group (r = 0.68, p = 0.015). Genes in this module are overrepresented by genes involved in transcriptional regulation and other pathways related to neurodevelopment. Interestingly, one member of this module, Polr2a, polymerase (RNA) II (DNA directed) polypeptide A, is downregulated by the combination of prenatal ethanol and postnatal stress in an RNA-Seq experiment and qPCR validation (q = 2e−12, p = 0.004, respectively).

Conclusions

Together, transcriptional control in the hippocampus is implicated as a potential underlying mechanism leading to anxiety-like behavior via environmental insults. Further research is required to elucidate the mechanism involved and use this insight towards early diagnosis and amelioration strategies involving children born with FASD.

IntelliCage as a tool for measuring mouse behavior - 20 years perspective

Since the 1980s, we have witnessed the rapid development of genetically modified mouse models of human diseases. A large number of transgenic and knockout mice have been utilized in basic and applied research, including models of neurodegenerative and neuropsychiatric disorders. To assess the biological function of mutated genes, modern techniques are critical to detect changes in behavioral phenotypes. We review the IntelliCage, a high-throughput system that is used for behavioral screening and detailed analyses of complex behaviors in mice. The IntelliCage was introduced almost two decades ago and has been used in over 150 studies to assess both spontaneous and cognitive behaviors. We present a critical analysis of experimental data that have been generated using this device.

Hippocampal DNA Methylation in a Mouse Model of Fetal Alcohol Spectrum Disorder That Includes Maternal Separation Stress Only Partially Explains Changes in Gene Expression

Fetal alcohol spectrum disorder (FASD) is characterized by developmental and behavioral deficits caused by maternal drinking during pregnancy. Children born with FASD often face additional stresses, including maternal separation, that add yet additional deficits. The mechanism associated with this interaction is not known. We have used a mouse model for prenatal ethanol exposure and maternal separation to demonstrate that the combination of the two treatments results in more than additive deficits. Furthermore, the behavioral deficits are associated with changes in hippocampal gene expression that persist into adulthood. What initiates and maintains these changes remains to be established and forms the focus of this report. Specifically, MeDIP-Seq was used to assess if changes in promoter DNA methylation are affected by exposure to prenatal ethanol and maternal separation including its relationship to gene expression. The novel results show that different sets of genes implicated by promoter DNA methylation are affected by both treatments independently, and a relatively unique set of genes are affected by the combination of the two treatments. Prenatal ethanol exposure leads to altered promoter DNA methylation at genes important for transcriptional regulation. Maternal separation leads to changes at genes important for histone methylation and immune response, and the combination of two treatments results in DNA methylation changes at genes important for neuronal migration and immune response. Our dual results from the same hippocampal samples suggest there is minimal complementarity between changes in promoter DNA methylation and gene expression, although genes involved tend to be critical for brain development and function. While remaining to be validated, such results argue that mechanisms beyond promoter DNA methylation must be involved in lasting gene expression alterations leading to behavioral deficits implicated in FASD. They may facilitate early and reliable diagnosis, as well as novel strategies for the amelioration of FASD-related deficits.

Animal models of major depression: drawbacks and challenges

Major depression is a leading contributor to the global burden of disease. This situation is mainly related to the chronicity and/or recurrence of the disorder, and to poor response to antidepressant therapy. Progress in this area requires valid animal models. Current models are based either on manipulating the environment to which rodents are exposed (during the developmental period or adulthood) or biological underpinnings (i.e. gene deletion or overexpression of candidate genes, targeted lesions of brain areas, optogenetic control of specific neuronal populations, etc.). These manipulations can alter specific behavioural and biological outcomes that can be related to different symptomatic and pathophysiological dimensions of major depression. However, animal models of major depression display substantial shortcomings that contribute to the lack of innovative pharmacological approaches in recent decades and which hamper our capabilities to investigate treatment-resistant depression. Here, we discuss the validity of these models, review putative models of treatment-resistant depression, major depression subtypes and recurrent depression. Furthermore, we identify future challenges regarding new paradigms such as those proposing dimensional rather than categorical approaches to depression.

Progress in Research on Brain Development and Function of Mice During Weaning

Lactation is a critical phase for brain function development. New dietary experiences of mouse caused by weaning can regulate brain development and function, increase their response to food and environment, and eventually give rise to corresponding behavioral changes. Changes in weaning time induce the alteration of brain tissues morphology and molecular characteristics, glial cell activity and behaviors in the offspring. In addition, it is also sensitive to the intervention of environment and drugs during this period. That is to say, the study focused on brain development and function based on mouse weaning is critical to demonstrate the underlying pathogenesis of neuropsychiatric diseases and find new drug targets. This article mainly focuses on the developmental differentiation of the brain during lactation, especially during weaning in mice.

Multiple animal positioning system shows that socially-reared mice influence the social proximity of isolation-reared cagemates

Social relationships are a key determinant of social behaviour, and disruption of social behaviour is a major symptom of several psychiatric disorders. However, few studies have analysed social relationships among multiple individuals in a group or how social relationships within a group influence the behaviour of members with impaired socialisation. Here, we developed a video-analysis-based system, the Multiple-Animal Positioning System (MAPS), to automatically and separately analyse the social behaviour of multiple individuals in group housing. Using MAPS, we show that social isolation of male mice during adolescence leads to impaired social proximity in adulthood. The phenotype of these socially isolated mice was partially rescued by cohabitation with group-housed (socially-reared) mice, indicating that both individual behavioural traits and those of cagemates influence social proximity. Furthermore, we demonstrate that low reactive behaviour of other cagemates also influence individual social proximity in male mice.

[Genetic and Environmental Factors in Childhood Affecting High Brain Function]

The brain and mind are not only determined genetically but are also nurtured by environmental stimuli in early life. However, the relationship between early life environment and phenotypes in adulthood remains elusive. Using the IntelliCage-based competition task for group-housed mice, we previously found that maternal exposure to a low dose of an environmental pollutant, dioxin, resulted in abnormal social behavior, that is, low competitive dominance, which is defined by decreased occupancy of limited resource sites under highly competitive circumstances. Although we were unable to identify which behavioral phenotype applies to abnormalities such as "human social nature", we found signs of hypoactivation of the medial prefrontal cortex, as seen in patients with autism spectrum disorder. In addition, another model of environmental factors, repeated isolation during development, and that of genetic factors including mice with neuronal heterotopia, which refers to brain malformations resulting from deficits of neuronal migration, showed low competitive dominance. These results indicate that a constitutive approach to capture the neural network of the whole brain is necessary especially in cases where the temporal gap of causal relationships is large such as DOHaD.

(R)-fluoxetine enhances cognitive flexibility and hippocampal cell proliferation in mice

Fluoxetine is a clinically successful antidepressant. It is a racemic mixture of (R) and (S) stereoisomers. In preclinical studies, chronic treatment with fluoxetine (10 mg/kg) had antidepressant effects correlated with increased hippocampal cell proliferation in adult rodents. However, the contribution of the enantiomers of fluoxetine is largely unknown. We investigated the effects of treatment with (R)- and (S)-fluoxetine on cognitive behavioral paradigms and examined cell proliferation in the hippocampus of C57BL/6J female mice. In a behavioral sequencing task using the IntelliCage system in which discriminated spatial patterns of rewarded and never-rewarded corners were reversed serially, (R)-fluoxetine-treated mice showed rapid acquisition of behavioral sequencing (compared with S-fluoxetine) and cognitive flexibility in subsequent reversal stages in intra- and inter-session analysis. (R)-fluoxetine also increased cell proliferation in the hippocampus, in particular in the suprapyramidal blade of the dentate gyrus. (R)-fluoxetine had superior effects to (S)-fluoxetine in elevated plus maze, forced-swim and tail-suspension tests. These results suggest that (R)-fluoxetine, which has been reported to have a shorter half-life than (S)-fluoxetine, has superior antidepressant effects and more consistently improves spatial learning and memory. This profile offers advantages in depression treatment and may also aid management of the neurocognitive impairments associated with depression.

Behavioural characterization of C57BL/6N and BALB/c female mice in social home cage - Effect of mixed housing in complex environment

Developing reliable mouse models for social behaviour is challenging. Different tests have been proposed, but most of them consist of rather artificial confrontations of unfamiliar mice in novel arenas or are relying on social stress induced by aggressive conspecifics. Natural social interaction in home cage in laboratory has not been investigated well. IntelliCage is a fully automated home-cage system, where activity of the group-housed mice can be monitored along with various cognitive tasks. Here we report the behavioural profile of C57BL/6N (B6) and BALB/c (BALB) female mice in IntelliCage when separated by strain, followed by monitoring of activity and formation of 'home-base' after mixing two strains. For that purpose, 3 cages were connected. Significant differences between the strains were established in baseline behaviour in conventional tests and in IntelliCage. The B6 mice showed reduced anxiety-like behaviour in open field and light-dark box, slightly enhanced exploratory activity in IntelliCage during initial adaptation and clearly distinct circadian activity. Mixing of two strains resulted in reduction of body weight and anhedonia in B6 mice. In addition, the B6 mice showed clear preference to previous home-cage, and formed a new home-base faster than BALB mice. In contrast, BALB mice showed enhanced activity and moving between the cages without showing any preference to previous home-cage. It could be argued that social challenge caused changes in both strains and different coping styles are responsible for behavioural manifestations. Altogether, this approach could be useful in modelling and validating mouse models for disorders with disturbed social behaviour.

Maternal separation affects expression of stress response genes and increases vulnerability to ethanol consumption

INTRODUCTION

Maternal separation is an early life stress event associated with behavioral alterations and ethanol consumption. We aimed to expand the current understanding on the molecular mechanisms mediating the impact of postnatal stress on ethanol consumption.

METHODS

In the first experiment (T1), some of the pups were separated from their mothers for 6 hr daily (Maternal Separation group - MS), whereas the other pups remained in the cage with their respective mothers (Control group - C). In the second experiment (T2), mice from both groups were subjected to the model of free-choice between water and sucrose solution or between water and ethanol solution. Maternal behavior was assessed at the end of T1. At the end of both T1 and T2, pups were subjected to the light/dark box behavioral test and blood corticosterone concentrations were analyzed.

RESULTS

Our maternal separation protocol led to intense maternal care and affected weight gain of the animals. The expression of stress response genes was altered with higher levels of Crh and Pomc being observed in the hypothalamus, and higher levels of Crhr1, Crhr2, Htr2a and lower levels of Nr3c1 and Htr1a being observed in the hippocampus after T1. At the end of T2, we observed higher levels of Avp and Pomc in the hypothalamus, and higher levels of Crhr1, Crhr2, Nr3c1, Slc6a4, Bdnf and lower levels of Htr1a in the hippocampus. Additionally, maternal separation increased vulnerability to ethanol consumption during adolescence and induced changes in anxiety/stress-related behavior after T2. Furthermore, voluntary ethanol consumption attenuated stress response and modified expression of reward system genes: enhancing Drd1 and Drd2, and reducing Gabbr2 in the striatum.

CONCLUSION

Maternal separation induced behavioral changes and alterations in the expression of key genes involved in HPA axis and in the serotonergic and reward systems that are likely to increase vulnerability to ethanol consumption in adolescence. We demonstrated, for the first time, that ethanol consumption masked stress response by reducing the activity of the HPA axis and the serotonergic system, therefore, suggesting that adolescent mice from the MS group probably consumed ethanol for stress relieving purposes.

Competition for oestrous ewes between rams reared by their mothers or artificially reared: Effects on sexual behaviour and testosterone and cortisol serum concentrations

The objective of this study was to determine how the social competition for an oestrous ewe affects the sexual behaviour and the endocrine response in two groups of rams, one reared by their mothers and another artificially reared. Thus, we compared the sexual behaviour and testosterone and cortisol changes in each group of rams in competitive and non-competitive tests, both during the first and second breeding seasons. Two groups of rams were: 1) artificially reared lambs, separated from their dams 24-36 h after birth (Week 0) and artificially fed with sheep milk until 10 weeks of age (group AR, n = 14); and 2) lambs reared by their dams until 10 weeks of age (group DR, n = 13). Rams were subjected to non-competitive and competitive tests for an oestrous ewe during their first and second breeding seasons, when they were 8 and 20 months old, respectively. Sexual behaviours toward an oestrous ewe were recorded during 20 min and the testosterone and cortisol concentrations were determined in serum samples collected immediately before the test, and 20, 40 and 60 min after it. During the first breeding season, the number of flehmen decreased in DR rams, and the number of flehmen and ano-genital sniffings also decreased in DR rams, but the frequency of some copulatory behaviours increased (matings and ejaculation/total mounts in DR rams, and total mounts in AR rams) in competitive tests. During the second breeding season, competition caused a decrease in the number of all the recorded behaviours (courtship and copulation) with the exception of flehmen in AR rams; however, in DR rams only the number of the copulatory behaviours decreased under competition. Competition did not affect the endocrine response during the first breeding season. During the second breeding season, while testosterone concentrations were greater in non-competitive than in competitive tests at 60 min (P = 0.0008) in AR rams, in DR rams it tended to be greater (P = 0.09). Competition did not affect cortisol concentrations in any group or season, but in all tests the concentrations increased at the end of the test (P < 0.05). In conclusion, the lack of the mother during rearing negatively affected the sexual motivation and the testosterone response of rams to oestrous ewes in competitive tests, effects that were more evident when adults. Neither the absence of the mother during rearing nor competition for oestrous ewes affected the stress response (evidenced by increase in cortisol concentration) in rams during both seasons.

Maternal Deprivation Influences Pup Ultrasonic Vocalizations of C57BL/6J Mice

Maternal deprivation (MD) is frequently used as an early life stress model in rodents to investigate behavioral and neurological responses under stressful conditions. However, the effect of MD on the early postnatal development of rodents, which is when multiple neural systems become established, is rarely investigated due to methodological limitations. Ultrasonic vocalizations (USVs) are one of the few responses produced by neonatal rodents that can be quantitatively analyzed, and the quantification of USVs is regarded as a novel approach to investigate possible alterations in the neurobehavioral and emotional development of infant rodents under stress. To investigate the effect of MD on pup mice, we subjected C57BL/6J mice to MD and recorded the USVs of pups on postnatal days 1, 3, 7, 8, and 14. To determine whether the effect of MD on USVs was acute or cumulative, pre- and post-separation USV groups were included; sex differences in pup USV emission were also investigated. Our results suggest that (i) USV activity was high on postnatal days 3-8; (ii) the MD effect on USVs was acute, and a cumulative effect was not found; (iii) the MD mice vocalized more and longer than the controls at a lower frequency, and the effect was closely related to age; and (iv) female pups were more susceptible than males to the effect of MD on USV number and duration between postnatal days 3-8.

[Development of Higher Brain Function Tests in Rodents and Its Application to Neurotoxicity Assessment of Environmental Chemicals]

The brain during developmental period is thought to be highly sensitive to environmental insults including exposure to chemicals. However, it has been extremely difficult to detect and assess the features and degree of adversity particularly at low exposure levels. I describe here the effects of maternal exposure to dioxin on higher brain functions later in life, which we detected using our originally developed behavioral tests for quantifying higher brain functions in rodents. We first found changes in the mRNA expression levels of glutamate NMDA receptor subunits that have critical roles in learning and memory function in the neocortex and hippocampus. To assess the neocortical and hippocampal functions in rats, we established novel behavioral tests for assessing paired-associate learning, which is the hippocampal and medial prefrontal NMDA-dependent function. Maternal exposure to dioxin, at a low level of which does not affect simple memory formation, resulted in the disturbance of the paired-associate learning. On the basis of the above learning paradigm, we next developed a behavioral flexibility task and a social competitive task for mice using the automated behavioral assessment system ‘IntelliCage’: this system can accommodate 16 mice at the same time to monitor and record their behavior. Using this system, we found that male mice born to dams exposed to very low doses of dioxin showed inflexibility in a serial reversal learning task and socially low-dominance behavior under a competitive situation. Immunohistochemical analysis of putative neuronal activity markers revealed hypoactivity in the medial prefrontal cortex (mPFC) of dioxin-exposed mice. We speculate that mPFC hypoactivity reflects the dioxin-induced higher brain dysfunction and may be associated with some psychiatric illnesses and related problems. These behavioral tests were found to be useful for studying the higher brain functions of rats and mice.

Neuronal Heterotopias Affect the Activities of Distant Brain Areas and Lead to Behavioral Deficits

Neuronal heterotopia refers to brain malformations resulting from deficits of neuronal migration. Individuals with heterotopias show a high incidence of neurological deficits, such as epilepsy. More recently, it has come to be recognized that focal heterotopias may also show a range of psychiatric problems, including cognitive and behavioral impairments. However, because focal heterotopias are not always located in the brain areas responsible for the symptoms, the causal relationship between the symptoms and heterotopias remains elusive. In this study, we showed that mice with focal heterotopias in the somatosensory cortex generated by in utero electroporation exhibited spatial working memory deficit and low competitive dominance behavior, which have been shown to be closely associated with the activity of the medial prefrontal cortex (mPFC) in rodents. Analysis of the mPFC activity revealed that the immediate-early gene expression was decreased and the local field potentials of the mPFC were altered in the mice with heterotopias compared with the control mice. Moreover, activation of these ectopic and overlying sister neurons using the DREADD (designer receptor exclusively activated by designer drug) system improved the working memory deficits. These findings suggest that cortical regions containing focal heterotopias can affect distant brain regions and give rise to behavioral abnormalities. Significance statement: Recent studies reported that patients with heterotopias have a variety of clinical symptoms, such as cognitive disturbance, psychiatric symptoms, and autistic behavior. However, the causal relationship between the symptoms and heterotopias remains elusive. Here we showed that mice with focal heterotopias in the somatosensory cortex generated by in utero electroporation exhibited behavioral deficits that have been shown to be associated with the mPFC activity in rodents. The existence of heterotopias indeed altered the neural activities of the mPFC, and direct manipulation of the neural activity of the ectopic neurons and their sister neurons in the overlying cortex improved the behavioral deficit. Thus, our results indicate that focal heterotopias could affect the activities of distant brain areas and cause behavioral abnormalities.

Gene expression patterns and environmental enrichment-induced effects in the hippocampi of mice suggest importance of Lsamp in plasticity

Limbic system associated membrane protein (Lsamp) gene is involved in behavioral adaptation in social and anxiogenic environments and has been associated with a broad spectrum of psychiatric diseases. Here we studied the activity of alternative promoters of Lsamp gene in mice in three rearing conditions (standard housing, environmental enrichment and social isolation) and in two different genetic backgrounds (129S6/SvEv and C57BL/6). Isolation had no effect on the expression levels of Lsamp. Environmental enrichment elevated the expression levels of Lsamp 1b transcript specifically in the hippocampus in B6 mice, and the same tendency existed across both mouse lines and both transcripts. Furthermore, we showed that the density of cells exhibiting 1b promoter activity is remarkably higher in the subgranular zone of the dentate gyrus in the hippocampal formation which is a specific area of enrichment-induced neurogenesis in adult rodents. On the contrary to 1b, 1a promoter is selectively active in the pyramidal and granule cell layers. We provide evidence that Lsamp modulates enrichment-induced activation of Bdnf as the enrichment-induced elevation of Bdnf in the hippocampus is significantly diminished in Lsamp-deficient mice; furthermore, a significant correlation was found between the expression levels of Lsamp and Bdnf transcripts in the hippocampus and frontal cortex. Significant strain differences in Lsamp expression were detected in the hippocampus, frontal cortex and thalamus that could be related to the different behavioral phenotype of B6 and 129Sv mice. Our data provides further evidence that LSAMP is implicated in the hippocampal connectivity and plasticity thereby modulating adaptability in changing environments.

Environmental insults in early life and submissiveness later in life in mouse models

Dominant and subordinate dispositions are not only determined genetically but also nurtured by environmental stimuli during neuroendocrine development. However, the relationship between early life environment and dominance behavior remains elusive. Using the IntelliCage-based competition task for group-housed mice, we have previously described two cases in which environmental insults during the developmental period altered the outcome of dominance behavior later in life. First, mice that were repeatedly isolated from their mother and their littermates (early deprivation; ED), and second, mice perinatally exposed to an environmental pollutant, dioxin, both exhibited subordinate phenotypes, defined by decreased occupancy of limited resource sites under highly competitive circumstances. Similar alterations found in the cortex and limbic area of these two models are suggestive of the presence of neural systems shared across generalized dominance behavior.