Genetic relationship between anxiety-related and fear-related behaviors in BXD recombinant inbred mice

Investigating Motor Coordination Using BXD Recombinant Inbred Mice to Model the Genetic Underpinnings of Developmental Coordination Disorder

The fundamental skills for motor coordination and motor control emerge through development. Neurodevelopmental disorders such as developmental coordination disorder (DCD) lead to impaired acquisition of motor skills. This study investigated motor behaviors that reflect the core symptoms of human DCD through the use of BXD recombinant inbred strains of mice that are known to have divergent phenotypes in many behavioral traits, including motor activity. We sought to correlate behavior in basic motor control tasks with the known genotypes of these reference populations of mice using quantitative trait locus (QTL) mapping. We used 12 BXD strains with an average of 16 mice per group to assess the onset of reflexes during the early neonatal stage of life and differences in motor coordination using the tests for open field, rotarod, and gait behaviors during the adolescent/young adulthood period. Results indicated significant variability between strains in when neonatal reflexes appeared and significant strain differences for all measures of motor coordination. Five strains (BXD15, BXD27, BXD28, BXD75, BXD86) struggled with sensorimotor coordination as seen in gait analysis, rotarod, and open field, similar to human presentation of DCD. We identified three significant quantitative trait loci for gait on proximal Chr 3, Chr 4, and distal Chr 6. Based on expression, function, and polymorphism within the mapped QTL intervals, seven candidate genes (Gpr63, Spata5, Trpc3, Cntn6, Chl1, Grm7, Ogg1) emerged. This study offers new insights into mouse motor behavior, which promises to be a first murine model to explore the genetics and neural correlates of DCD.

Male and female behavioral variability and morphine response in C57BL/6J, DBA/2J, and their BXD progeny following chronic stress exposure

Drug addiction is a multifactorial syndrome in which genetic predispositions and exposure to environmental stressors constitute major risk factors for the early onset, escalation, and relapse of addictive behaviors. While it is well known that stress plays a key role in drug addiction, the genetic factors that make certain individuals particularly sensitive to stress and, thereby, more vulnerable to becoming addicted are unknown. In an effort to test a complex set of gene x environment interactions-specifically gene x chronic stress-here we leveraged a systems genetics resource: BXD recombinant inbred mice (BXD5, BXD8, BXD14, BXD22, BXD29, and BXD32) and their parental mouse lines, C57BL/6J and DBA/2J. Utilizing the chronic social defeat stress (CSDS) and chronic variable stress (CVS) paradigms, we first showed sexual dimorphism in social and exploratory behaviors between the mouse strains. Further, we observed an interaction between genetic background and vulnerability to prolonged exposure to non-social stressors. Finally, we found that DBA/2J and C57BL/6J mice pre-exposed to stress displayed differences in morphine sensitivity. Our results support the hypothesis that genetic variation influences chronic stress-induced behavioral outcomes such as social and approach-avoidance behaviors, reward responses, as well as morphine sensitivity, and is likely to modulate the development of drug addiction.

Maternal alcohol drinking patterns predict offspring neurobehavioral outcomes

The timing, rate, and quantity of gestational alcohol consumption, collectively referred to here as Maternal Drinking Patterns (MDPs), are of known importance to fetal developmental outcomes. However, few studies have directly evaluated the impact of MDPs on offspring behavior. To do so, we used specialized equipment to record the precise amount and timing of alcohol consumption in pregnant dams, and then characterized MDPs using Principle Component Analysis (PCA). We next tested offspring on behaviors we have previously identified as impacted by prenatal alcohol exposure, and evaluated them where possible in the context of MDPs. Male alcohol exposed mice exhibited longer latencies to fall on the rotarod compared to their controls, which we attribute to a delayed decrease in body weight-gain. This effect was mediated by MDPs within the first 15 min of alcohol access (i.e. alcohol frontloading), where the highest performing male offspring came from dams exhibiting the highest rate of alcohol frontloading. Female alcohol exposed mice displayed reduced locomotor activity in the open field compared to controls, which was mediated by MDPs encompassing the entire drinking session. Surprisingly, total gestational alcohol exposure alone was not associated with any behavioral outcomes. Finally, we observed allodynia in alcohol exposed mice that developed more quickly in males compared to females, and which was not observed in controls. To our knowledge, this report represents the highest resolution assessment of alcohol drinking throughout gestation in mice, and one of few to have identified relationships between specific alcohol MDPs and neurobehavioral outcomes in offspring.

Complementation testing identifies genes mediating effects at quantitative trait loci underlying fear-related behavior

Knowing the genes involved in quantitative traits provides an entry point to understanding the biological bases of behavior, but there are very few examples where the pathway from genetic locus to behavioral change is known. To explore the role of specific genes in fear behavior, we mapped three fear-related traits, tested fourteen genes at six quantitative trait loci (QTLs) by quantitative complementation, and identified six genes. Four genes, Lamp, Ptprd, Nptx2, and Sh3gl, have known roles in synapse function; the fifth, Psip1, was not previously implicated in behavior; and the sixth is a long non-coding RNA, 4933413L06Rik, of unknown function. Variation in transcriptome and epigenetic modalities occurred preferentially in excitatory neurons, suggesting that genetic variation is more permissible in excitatory than inhibitory neuronal circuits. Our results relieve a bottleneck in using genetic mapping of QTLs to uncover biology underlying behavior and prompt a reconsideration of expected relationships between genetic and functional variation.

Complementation testing identifies causal genes at quantitative trait loci underlying fear related behavior

Knowing the genes involved in quantitative traits provides a critical entry point to understanding the biological bases of behavior, but there are very few examples where the pathway from genetic locus to behavioral change is known. Here we address a key step towards that goal by deploying a test that directly queries whether a gene mediates the effect of a quantitative trait locus (QTL). To explore the role of specific genes in fear behavior, we mapped three fear-related traits, tested fourteen genes at six QTLs, and identified six genes. Four genes, Lsamp, Ptprd, Nptx2 and Sh3gl, have known roles in synapse function; the fifth gene, Psip1, is a transcriptional co-activator not previously implicated in behavior; the sixth is a long non-coding RNA 4933413L06Rik with no known function. Single nucleus transcriptomic and epigenetic analyses implicated excitatory neurons as likely mediating the genetic effects. Surprisingly, variation in transcriptome and epigenetic modalities between inbred strains occurred preferentially in excitatory neurons, suggesting that genetic variation is more permissible in excitatory than inhibitory neuronal circuits. Our results open a bottleneck in using genetic mapping of QTLs to find novel biology underlying behavior and prompt a reconsideration of expected relationships between genetic and functional variation.

Single-cell methylation analysis of brain tissue prioritizes mutations that alter transcription

Relating genetic variants to behavior remains a fundamental challenge. To assess the utility of DNA methylation marks in discovering causative variants, we examined their relationship to genetic variation by generating single-nucleus methylomes from the hippocampus of eight inbred mouse strains. At CpG sequence densities under 40 CpG/Kb, cells compensate for loss of methylated sites by methylating additional sites to maintain methylation levels. At higher CpG sequence densities, the exact location of a methylated site becomes more important, suggesting that variants affecting methylation will have a greater effect when occurring in higher CpG densities than in lower. We found this to be true for a variant's effect on transcript abundance, indicating that candidate variants can be prioritized based on CpG sequence density. Our findings imply that DNA methylation influences the likelihood that mutations occur at specific sites in the genome, supporting the view that the distribution of mutations is not random.

Developmental coordination disorder: What can we learn from RI mice using motor learning tasks and QTL analysis

Developmental Coordination Disorder (DCD) is a neurodevelopmental disorder of unknown etiology that affects one in 20 children. There is an indication that DCD has an underlying genetic component due to its high heritability. Therefore, we explored the use of a recombinant inbred family of mice known as the BXD panel to understand the genetic basis of complex traits (i.e., motor learning) through identification of quantitative trait loci (QTLs). The overall aim of this study was to utilize the QTL approach to evaluate the genome-to-phenome correlation in BXD strains of mice in order to better understand the human presentation of DCD. Results of this current study confirm differences in motor learning in selected BXD strains and strains with altered cerebellar volume. Five strains - BXD15, BXD27, BXD28, BXD75, and BXD86 - exhibited the most DCD-like phenotype when compared with other BXD strains of interest. Results indicate that BXD15 and BXD75 struggled primarily with gross motor skills, BXD28 primarily had difficulties with fine motor skills, and BXD27 and BXD86 strains struggled with both fine and gross motor skills. The functional roles of genes within significant QTLs were assessed in relation to DCD-like behavior. Only Rab3a (Ras-related protein Rab-3A) emerged as a high likelihood candidate gene for the horizontal ladder rung task. This gene is associated with brain and skeletal muscle development, but lacked nonsynonymous polymorphisms. This study along with Gill et al. (same issue) is the first studies to specifically examine the genetic linkage of DCD using BXD strains of mice.

Systems genetic analysis of nicotine withdrawal deficits in hippocampus-dependent learning

Cognitive deficits, such as disrupted learning, are a major symptom of nicotine withdrawal. These deficits are heritable, yet their genetic basis is largely unknown. Our lab has developed a mouse model of nicotine withdrawal deficits in learning, using chronic nicotine exposure via osmotic minipumps and fear conditioning. Here, we utilized the BXD genetic reference panel to identify genetic variants underlying nicotine withdrawal deficits in learning. Male and female mice (n = 6-11 per sex per strain, 31 strains) received either chronic saline or nicotine (6.3 mg/kg per day for 12 days), and were then tested for hippocampus-dependent learning deficits using contextual fear conditioning. Quantitative trait locus (QTL) mapping analyses using GeneNetwork identified a significant QTL on Chromosome 4 (82.13 Mb, LRS = 20.03, p < 0.05). Publicly available hippocampal gene expression data were used to identify eight positional candidates (Snacpc3, Mysm1, Rps6, Plaa, Lurap1l, Slc24a2, Hacd4, Ptprd) that overlapped with our behavioral QTL and correlated with our behavioral data. Overall, this study demonstrates that genetic factors impact cognitive deficits during nicotine withdrawal in the BXD recombinant inbred panel and identifies candidate genes for future research.

Comparison of memory, affective behavior, and neuropathology in APPNLGF knock-in mice to 5xFAD and APP/PS1 mice

Transgenic mouse models of Aβ amyloidosis generated by knock-in of a humanized Aβ sequence can offer some advantages over the transgenic models that overexpress amyloid precursor protein (APP). However, systematic comparison of memory, behavioral, and neuropathological phenotypes between these models has not been well documented. In this study, we compared memory and affective behavior in APP^NLGF mice, an APP knock-in model, to two widely used mouse models of Alzheimer's disease, 5xFAD and APP/PS1 mice, at 10 months of age. We found that, despite similar deficits in working memory, object recognition, and social recognition memory, APP^NLGF and 5xFAD mice but not APP/PS1 mice show compelling anxiety- and depressive-like behavior, and exhibited a marked impairment of social interaction. We quantified corticolimbic Aβ plaques, which were lowest in APP^NLGF, intermediate in APP/PS1, and highest in 5xFAD mice. Interestingly, analysis of plaque size revealed that plaques were largest in APP/PS1 mice, intermediate in 5xFAD mice, and smallest in APP^NLGF mice. Finally, we observed a significantly higher percentage of the area occupied by plaques in both 5xFAD and APP/PS1 relative to APP^NLGF mice. Overall, our findings suggest that the severity of Aβ neuropathology is not directly correlated with memory and affective behavior impairments between these three transgenic mouse models. Additionally, APP^NLGF may represent a valid mouse model for studying AD comorbid with anxiety and depression.

Evolution of brain-wide activity in the awake behaving mouse after acute fear by longitudinal manganese-enhanced MRI

Life threatening fear after a single exposure evolves in a subset of vulnerable individuals to anxiety, which may persist for their lifetime. Yet neither the whole brain's response to innate acute fear nor how brain activity evolves over time is known. Sustained neuronal activity may be a factor in the development of a persistent fear response. We couple two experimental protocols to provoke acute fear leading to prolonged fear: Predator stress (PS), a naturalistic approach to induce fear in rodents; and Serotonin transporter knockout mouse (SERT-KO) that responds to PS with sustained defensive behavior. Behavior was monitored before, during and at short and long times after PS in wild type (WT) and SERT-KO mice. Both genotypes responded to PS with defensive behavior. SERT-KO retained defensive behavior for 23 days, while WT mice returned to baseline exploratory behavior by 9 days. Thus, differences in neural activity between WT and SERT-KO 9 days after PS identifies neural correlates of persistent defensive behavior, in mice. We used longitudinal manganese-enhanced magnetic resonance imaging (MEMRI) to identify brain-wide neural activity associated with different behaviors. Mn2+ accumulation in active neurons occurs in awake, behaving mice and is retrospectively imaged. Following the same two cohorts of mice, WT and SERT-KO, longitudinally allowed unbiased quantitative comparisons of brain-wide activity by statistical parametric mapping (SPM). During natural behavior in WT, only low levels of activity-induced Mn2+-accumulation were detected, while much more accumulation appeared immediately after PS in both WT and SERT-KO, and evolved at 9 days to a new activity pattern (p < 0.0001, uncorr., T = 5.4). Patterns of accumulation differed between genotypes, with more regions of the brain and larger volumes within regions involved in SERT-KO than WT. A new computational segmentation analysis, using our InVivo Atlas based on a manganese-enhanced MR image of a living mouse, revealed dynamic changes in the volume of significantly enhanced voxels within each segment that differed between genotypes across 45 of 87 segmented regions. At Day 9 after PS, the striatum and ventral pallidum were active in both genotypes but more so in the SERT-KO. SERT-KO also displayed sustained or increased volume of Mn2+ accumulations between Post-Fear and Day 9 in eight segments where activity was decreased or silenced in WT. C-fos staining, an alternative neural activity marker, of brains from the same mice fixed at conclusion of imaging sessions confirmed that MEMRI detected active neurons. Intensity measurements in 12 regions of interest (ROIs) supported the SPM results. Between group comparisons by SPM and of ROI measurements identified specific regions differing between time points and genotypes. We report brain-wide activity in response to a single exposure of acute fear, and, for the first time, its evolution to new activity patterns over time in individuals vulnerable to persistent fear. Our results show multiple regions with dynamic changes in neural activity and that the balance of activity between segments is disordered in the SERT-KO. Thus, longitudinal MEMRI represents a powerful approach to discover how brain-wide activity evolves from the natural state either after an experience or during a disease process.

Sex and Strain Variation in Initial Sensitivity and Rapid Tolerance to Δ9-Tetrahydrocannabinol

Background and Objectives: For cannabis and other drugs of abuse, initial response and/or tolerance to drug effects can predict later dependence and problematic use. Our objective is to identify sex and genetic (strain) differences in initial response and rapid tolerance to Δ9–tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, between highly genetically divergent inbred mouse strains—C57BL/6J (B6) and DBA/2J (D2).

Experimental Approach: Sex and strain responses relative to baseline were quantified following daily exposure (i.p.) to 10 mg/kg THC or vehicle (VEH) over the course of 5 days. Dependent measures included hypothermia (decreased body temperature) and ataxia (decreased spontaneous activity in the open field), and antinociception (increase in tail withdrawal latency to a thermal stimulus). Initial sensitivity to THC was defined as the difference in response between baseline and day 1. Rapid tolerance to THC was defined as the difference in response between days 1 and 2.

Results: B6 exhibited greater THC-induced motor activity suppression and initial sensitivity to ataxia relative to the D2 strain. Females demonstrated greater levels of THC-induced hypothermia and initial sensitivity relative to males. Higher levels of THC-induced antinociception and initial sensitivity were observed for D2 relative to B6. Rapid tolerance to THC was observed for hypothermia and antinociception. Much less tolerance was observed for THC-induced ataxia. D2 exhibited rapid tolerance to THC-induced hypothermia and antinociception at time points associated with peak THC initial response. Likewise, at the peak initial THC response time point, females demonstrated greater levels of rapid tolerance to hypothermic effects relative to males.

Conclusions: Both sex and genetic factors drive variation in initial response and rapid tolerance to the ataxic, antinociceptive, and hypothermic effects of THC. As these traits directly result from THC activation of the cannabinoid receptor 1, gene variants between B6 and D2 in cannabinoid signaling pathways are likely to mediate strain differences in response to THC.

Exploring the involvement of Tac2 in the mouse hippocampal stress response through gene networking

Tachykinin 2 (Tac2) is expressed in a number of areas throughout the brain, including the hippocampus. However, knowledge about its function has been only well explored in the hypothalamus in the context of reproductive health. In this study, we identified and validated increased hippocampal Tac2 mRNA expression in response to chronic mild stress in mice. Expression quantitative trait locus (eQTL) analysis showed Tac2 is cis-regulated in the hippocampus. Using a systems genetics approach, we constructed a Tac2 co-expression network to better understand the relationship between Tac2 and the hippocampal stress response. Our network identified 69 total genes associated with Tac2, several of which encode major neuropeptides involved in hippocampal stress signaling as well as critical genes for producing neural plasticity, indicating that Tac2 is involved in these processes. Pathway analysis for the member of Tac2 gene network revealed a strong connection between Tac2 and neuroactive ligand-receptor interaction, calcium signaling pathway, as well as cardiac muscle contraction. In addition, we also identified 46 stress-related phenotypes, specifically fear conditioning response, that were significantly correlated with Tac2 expression. Our results provide evidence for Tac2 as a strong candidate gene who likely plays a role in hippocampal stress processing and neural plasticity.

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

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

Brain region-specific expression of genes mapped within quantitative trait loci for behavioral responsiveness to acute stress in Fisher 344 and Wistar Kyoto male rats

Acute stress responsiveness is a quantitative trait that varies in severity from one individual to another; however, the genetic component underlying the individual variation is largely unknown. Fischer 344 (F344) and Wistar Kyoto (WKY) rat strains show large differences in behavioral responsiveness to acute stress, such as freezing behavior in response to footshock during the conditioning phase of contextual fear conditioning (CFC). Quantitative trait loci (QTL) have been identified for behavioral responsiveness to acute stress in the defensive burying (DB) and open field test (OFT) from a reciprocal F2 cross of F344 and WKY rat strains. These included a significant QTL on chromosome 6 (Stresp10). Here, we hypothesized that the Stresp10 region harbors genes with sequence variation(s) that contribute to differences in multiple behavioral response phenotypes between the F344 and WKY rat strains. To test this hypothesis, first we identified differentially expressed genes within the Stresp10 QTL in the hippocampus, amygdala, and frontal cortex of F344 and WKY male rats using genome-wide microarray analyses. Genes with both expression differences and non-synonymous sequence variations in their coding regions were considered candidate quantitative trait genes (QTGs). As a proof-of-concept, the F344.WKY-Stresp10 congenic strain was generated with the Stresp10 WKY donor region into the F344 recipient strain. This congenic strain showed behavioral phenotypes similar to those of WKYs. Expression patterns of Gpatch11 (G-patch domain containing 11), Cdkl4 (Cyclin dependent kinase like 4), and Drc1 (Dynein regulatory complex subunit 1) paralleled that of WKY in the F344.WKY-Stresp10 strain matching the behavioral profiles of WKY as opposed to F344 parental strains. We propose that these genes are candidate QTGs for behavioral responsiveness to acute stress.

Differential Expression of Munc13-2 Produces Unique Synaptic Phenotypes in the Basolateral Amygdala of C57BL/6J and DBA/2J Mice

C57BL/6J (B6) and DBA/2J (D2) mice are well known to differentially express a number of behavioral phenotypes, including anxiety-like behavior, fear conditioning, and drug self-administration. However, the cellular mechanisms contributing to these differences remain unclear. Given the basolateral amygdala (BLA) contributes to these behaviors, we characterized strain-dependent differences in presynaptic and postsynaptic function in BLA neurons by integrating electrophysiological, biochemical, and genetic approaches to identify specific molecular mechanisms. We found that D2 glutamatergic synapses expressed enhanced release probability and lower sensitivity to both the inhibitory effects of low extracellular calcium and facilitation by phorbol esters. Furthermore, repetitive stimulation of BLA afferents at low (2 Hz) or high (40 Hz) frequencies revealed that B6 terminals, relative to D2 terminals, were more sensitive to synaptic fatigue principally because of reduced vesicle recycling rates. Additionally, B6 synapses exhibited more robust augmentation of spontaneous release after repetitive stimulation relative to the D2 strain. In silico analysis of the inheritance of synaptic physiology from an array of BXD recombinant inbred strains (Jansen et al., 2011) identified a segment on chromosome 4 containing the gene encoding Munc13-2, which has calcium-/phorbol ester-binding domains and controls presynaptic function. We subsequently found that B6 mice express substantially higher levels of Munc13-2 compared with the D2 strain whereas expression of several release-related proteins, including Munc13-1, was equivalent. We then knocked down the expression of Munc13-2 in B6 mice using a short hairpin RNA and found this recapitulated the presynaptic phenotype of D2 BLA synapses.

SIGNIFICANCE STATEMENT

DBA/2J and C57BL/6J mice have been used to understand the genetic mechanisms controlling behaviors related to a number of psychiatric illnesses. However, the fundamental neurobiological mechanisms producing these behavioral characteristics remain unresolved. Here we identify a critical family of presynaptic proteins differentially expressed by these strains that control strain-dependent synaptic physiology. This family of proteins regulates excitation/secretion coupling, vesicle recycling, and short-term plasticity throughout the CNS. Thus, differential inheritance of proteins like Munc13-2 has broad implications for genetic control over a wide variety of pathological behaviors. Importantly, these proteins also contain a large number of modulatory sites, making them attractive potential targets for the development of novel neuropharmaceutical treatments.

Alterations in the expression of a neurodevelopmental gene exert long-lasting effects on cognitive-emotional phenotypes and functional brain networks: translational evidence from the stress-resilient Ahi1 knockout mouse

Many psychiatric disorders are highly heritable and may represent the clinical outcome of early aberrations in the formation of neural networks. The placement of brain connectivity as an 'intermediate phenotype' renders it an attractive target for exploring its interaction with genomics and behavior. Given the complexity of genetic make up and phenotypic heterogeneity in humans, translational studies are indicated. Recently, we demonstrated that a mouse model with heterozygous knockout of the key neurodevelopmental gene Ahi1 displays a consistent stress-resilient phenotype. Extending these data, the current research describes our multi-faceted effort to link early variations in Ahi1 expression with long-term consequences for functional brain networks and cognitive-emotional phenotypes. By combining behavioral paradigms with graph-based analysis of whole-brain functional networks, and then cross-validating the data with robust neuroinformatic data sets, our research suggests that physiological variation in gene expression during neurodevelopment is eventually translated into a continuum of global network metrics that serve as intermediate phenotypes. Within this framework, we suggest that organization of functional brain networks may result, in part, from an adaptive trade-off between efficiency and resilience, ultimately culminating in a phenotypic diversity that encompasses dimensions such as emotional regulation and cognitive function.

Analyses of differentially expressed genes after exposure to acute stress, acute ethanol, or a combination of both in mice

Alcohol abuse is a complex disorder, which is confounded by other factors, including stress. In the present study, we examined gene expression in the hippocampus of BXD recombinant inbred mice after exposure to ethanol (NOE), stress (RSS), and the combination of both (RSE). Mice were given an intraperitoneal (i.p.) injection of 1.8 g/kg ethanol or saline, and subsets of both groups were exposed to acute restraint stress for 15 min or controls. Gene expression in the hippocampus was examined using microarray analysis. Genes that were significantly (p < 0.05, q < 0.1) differentially expressed were further evaluated. Bioinformatic analyses were predominantly performed using tools available at GeneNetwork.org, and included gene ontology, presence of cis-regulation or polymorphisms, phenotype correlations, and principal component analyses. Comparisons of differential gene expression between groups showed little overlap. Gene Ontology demonstrated distinct biological processes in each group with the combined exposure (RSE) being unique from either the ethanol (NOE) or stress (RSS) group, suggesting that the interaction between these variables is mediated through diverse molecular pathways. This supports the hypothesis that exposure to stress alters ethanol-induced gene expression changes and that exposure to alcohol alters stress-induced gene expression changes. Behavior was profiled in all groups following treatment, and many of the differentially expressed genes are correlated with behavioral variation within experimental groups. Interestingly, in each group several genes were correlated with the same phenotype, suggesting that these genes are the potential origins of significant genetic networks. The distinct sets of differentially expressed genes within each group provide the basis for identifying molecular networks that may aid in understanding the complex interactions between stress and ethanol, and potentially provide relevant therapeutic targets. Using Ptp4a1, a candidate gene underlying the quantitative trait locus for several of these phenotypes, and network analyses, we show that a large group of differentially expressed genes in the NOE group are highly interrelated, some of which have previously been linked to alcohol addiction or alcohol-related phenotypes.

Initial genetic dissection of serum neuroactive steroids following chronic intermittent ethanol across BXD mouse strains

Neuroactive steroids modulate alcohol's impact on brain function and behavior. Ethanol exposure alters neuroactive steroid levels in rats, humans, and some mouse strains. We conducted an exploratory analysis of the neuroactive steroids (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP), (3α,5α)-3,21-dihydroxypregnan-20-one (3α,5α-THDOC), and pregnenolone across 126-158 individuals and 19 fully inbred strains belonging to the BXD family, which were subjected to air exposure, or chronic intermittent ethanol (CIE) exposure. Neuroactive steroids were measured by gas chromatography-mass spectrometry in serum following five cycles of CIE or air exposure (CTL). Pregnenolone levels in CTLs range from 272 to 578 pg/mL (strain variation of 2.1 fold with p = 0.049 for strain main effect), with heritability of 0.20 ± 0.006 (SEM), whereas in CIE cases values range from 304 to 919 pg/mL (3.0-fold variation, p = 0.007), with heritability of 0.23 ± 0.005. 3α,5α-THP levels in CTLs range from 375 to 1055 pg/mL (2.8-fold variation, p = 0.0007), with heritability of 0.28 ± 0.01; in CIE cases they range from 460 to 1022 pg/mL (2.2-fold variation, p = 0.004), with heritability of 0.23 ± 0.005. 3α,5α-THDOC levels in CTLs range from 94 to 448 pg/mL (4.8-fold variation, p = 0.002), with heritability of 0.30 ± 0.01, whereas levels in CIE cases do not differ significantly. However, global averages across all BXD strains do not differ between CTL and CIE for any of the steroids. 3α,5α-THDOC levels were lower in females than males in both groups (CTL -53%, CIE -55%, p < 0.001). Suggestive quantitative trait loci are identified for pregnenolone and 3α,5α-THP levels. Genetic variation in 3α,5α-THP was not correlated with two-bottle choice ethanol consumption in CTL or CIE-exposed animals. However, individual variation in 3α,5α-THP correlated negatively with ethanol consumption in both groups. Moreover, strain variation in neuroactive steroid levels correlated with numerous behavioral phenotypes of anxiety sensitivity accessed in GeneNetwork, consistent with evidence that neuroactive steroids modulate anxiety-like behavior.

Identification of quantitative trait loci and candidate genes for an anxiolytic-like response to ethanol in BXD recombinant inbred strains

Genetic differences in acute behavioral responses to ethanol contribute to the susceptibility to alcohol use disorder and the reduction of anxiety is a commonly reported motive underlying ethanol consumption among alcoholics. Therefore, we studied the genetic variance in anxiolytic-like responses to ethanol across the BXD recombinant inbred (RI) mouse panel using the light-dark transition model of anxiety. Strain-mean genetic mapping and a mixed-model quantitative trait loci (QTL) analysis replicated several previously published QTL for locomotor activity and identified several novel anxiety-related loci. Significant loci included a chromosome 11 saline anxiety-like QTL (Salanq1) and a chromosome 12 locus (Etanq1) influencing the anxiolytic-like response to ethanol. Etanq1 was successfully validated by studies with BXD advanced intercross strains and fine-mapped to a region comprising less than 3.5 Mb. Through integration of genome-wide mRNA expression profiles of the mesocorticolimbic reward circuit (prefrontal cortex, nucleus accumbens and ventral midbrain) across the BXD RI panel, we identified high priority candidate genes within Etanq1, the strongest of which was Ninein (Nin), a Gsk3β-interacting protein that is highly expressed in the brain.

Quantitative Trait Loci and a Novel Genetic Candidate for Fear Learning

Trauma- and stress-related disorders are clinically heterogeneous and associated with substantial genetic risk. Understanding the biological origins of heterogeneity of key intermediate phenotypes such as cognition and emotion can provide novel mechanistic insights into disorder pathogenesis. Performing quantitative genetics in animal models is a tractable strategy for examining both the genetic basis of intermediate phenotypes and functional testing of candidate quantitative traits genes (QTGs). Here, existing and newly collected data were used for collaborative genome-wide mapping of cued fear acquisition and expression in 65 mouse strains from the BXD genetic reference panel. For fear acquisition, we identified a significant locus on chromosome (Chr) 10 and eight suggestive loci on Chr 2, 4, 5, 11, 13, and 15. For fear expression, we identified one significant and another highly suggestive locus on Chr 13, as well as four suggestive loci on Chr 10, 11, and X. Across these loci, 60 putative QTGs were identified. The quantitative trait locus on distal Chr 13 contained a single, highly promising gene at the location of the peak likelihood ratio statistic score. The gene, hyperpolarization-activated cyclic nucleotide-gated channel 1 (Hcn1), regulates neuronal excitability. Validation experiments using behavioral pharmacology revealed that functional Hcn channels in the basolateral amygdala are necessary for conditioned fear acquisition and expression. Hcn1, together with the other candidate QTGs, thus provide new targets for neurobiological and treatment studies of fear learning and trauma- and stress-related disorders.

SIGNIFICANCE STATEMENT

There is a knowledge gap in understanding the genetic contributions to behavioral heterogeneity in typical and atypical populations. Mouse genetic reference panels (GRPs) provide one approach for identifying genetic sources of variation. Here, we identified three loci for conditioned fear acquisition and expression in a mouse GRP. Each locus contained candidate quantitative trait genes (QTGs). One locus had a single QTG, Hcn1 (hyperpolarization-activated cyclic nucleotide-gated channel 1), which has been implicated in neuronal excitability and learning. This discovery was validated using behavioral pharmacology, revealing that Hcn channels in the basolateral amygdala are required for fear acquisition and expression. The study thus identifies novel candidate QTGs that may contribute to variation in emotional learning and highlight the utility of mouse GRPs for the identification of genes underlying complex traits.

Mixed Linear Model Approaches of Association Mapping for Complex Traits Based on Omics Variants

Precise prediction for genetic architecture of complex traits is impeded by the limited understanding on genetic effects of complex traits, especially on gene-by-gene (GxG) and gene-by-environment (GxE) interaction. In the past decades, an explosion of high throughput technologies enables omics studies at multiple levels (such as genomics, transcriptomics, proteomics, and metabolomics). The analyses of large omics data, especially two-loci interaction analysis, are very time intensive. Integrating the diverse omics data and environmental effects in the analyses also remain challenges. We proposed mixed linear model approaches using GPU (Graphic Processing Unit) computation to simultaneously dissect various genetic effects. Analyses can be performed for estimating genetic main effects, GxG epistasis effects, and GxE environment interaction effects on large-scale omics data for complex traits, and for estimating heritability of specific genetic effects. Both mouse data analyses and Monte Carlo simulations demonstrated that genetic effects and environment interaction effects could be unbiasedly estimated with high statistical power by using the proposed approaches.

Perinatal vs genetic programming of serotonin states associated with anxiety

Large numbers of women undergo antidepressant treatment during pregnancy; however, long-term consequences for their offspring remain largely unknown. Rodents exposed to serotonin transporter (SERT)-inhibiting antidepressants during development show changes in adult emotion-like behavior. These changes have been equated with behavioral alterations arising from genetic reductions in SERT. Both models are highly relevant to humans yet they vary in their time frames of SERT disruption. We find that anxiety-related behavior and, importantly, underlying serotonin neurotransmission diverge between the two models. In mice, constitutive loss of SERT causes life-long increases in anxiety-related behavior and hyperserotonemia. Conversely, early exposure to the antidepressant escitalopram (ESC; Lexapro) results in decreased anxiety-related behavior beginning in adolescence, which is associated with adult serotonin system hypofunction in the ventral hippocampus. Adult behavioral changes resulting from early fluoxetine (Prozac) exposure were different from those of ESC and, although somewhat similar to SERT deficiency, were not associated with changes in hippocampal serotonin transmission in late adulthood. These findings reveal dissimilarities in adult behavior and neurotransmission arising from developmental exposure to different widely prescribed antidepressants that are not recapitulated by genetic SERT insufficiency. Moreover, they support a pivotal role for serotonergic modulation of anxiety-related behavior.

TRPC3 channels critically regulate hippocampal excitability and contextual fear memory

Memory formation requires de novo protein synthesis, and memory disorders may result from misregulated synthesis of critical proteins that remain largely unidentified. Plasma membrane ion channels and receptors are likely candidates given their role in regulating neuron excitability, a candidate memory mechanism. Here we conduct targeted molecular monitoring and quantitation of hippocampal plasma membrane proteins from mice with intact or impaired contextual fear memory to identify putative candidates. Here we report contextual fear memory deficits correspond to increased Trpc3 gene and protein expression, and demonstrate TRPC3 regulates hippocampal neuron excitability associated with memory function. These data provide a mechanistic explanation for enhanced contextual fear memory reported herein following knockdown of TRPC3 in hippocampus. Collectively, TRPC3 modulates memory and may be a feasible target to enhance memory and treat memory disorders.

Unique genetic loci identified for emotional behavior in control and chronic stress conditions

An individual's genetic background affects their emotional behavior and response to stress. Although studies have been conducted to identify genetic predictors for emotional behavior or stress response, it remains unknown how prior stress history alters the interaction between an individual's genome and their emotional behavior. Therefore, the purpose of this study is to identify chromosomal regions that affect emotional behavior and are sensitive to stress exposure. We utilized the BXD behavioral genetics mouse model to identify chromosomal regions that predict fear learning and emotional behavior following exposure to a control or chronic stress environment. 62 BXD recombinant inbred strains and C57BL/6 and DBA/2 parental strains underwent behavioral testing including a classical fear conditioning paradigm and the elevated plus maze. Distinct quantitative trait loci (QTLs) were identified for emotional learning, anxiety and locomotion in control and chronic stress populations. Candidate genes, including those with already known functions in learning and stress were found to reside within the identified QTLs. Our data suggest that chronic stress history reveals novel genetic predictors of emotional behavior.

Delay and trace fear conditioning in C57BL/6 and DBA/2 mice: issues of measurement and performance

Strain comparison studies have been critical to the identification of novel genetic and molecular mechanisms in learning and memory. However, even within a single learning paradigm, the behavioral data for the same strain can vary greatly, making it difficult to form meaningful conclusions at both the behavioral and cellular level. In fear conditioning, there is a high level of variability across reports, especially regarding responses to the conditioned stimulus (CS). Here, we compare C57BL/6 and DBA/2 mice using delay fear conditioning, trace fear conditioning, and a nonassociative condition. Our data highlight both the significant strain differences apparent in these fear conditioning paradigms and the significant differences in conditioning type within each strain. We then compare our data to an extensive literature review of delay and trace fear conditioning in these two strains. Finally, we apply a number of commonly used baseline normalization approaches to compare how they alter the reported differences. Our findings highlight three major sources of variability in the fear conditioning literature: CS duration, number of CS presentations, and data normalization to baseline measures.

Abnormal vibrissa-related behavior and loss of barrel field inhibitory neurons in 5xFAD transgenics

A recent study reported lower anxiety in the 5xFAD transgenic mouse model of Alzheimer's disease, as measured by reduced time on the open arms of an elevated plus maze. This is important because all behaviors in experimental animals must be interpreted in light of basal anxiety and response to novel environments. We conducted a comprehensive anxiety battery in the 5xFAD transgenics and replicated the plus-maze phenotype. However, we found that it did not reflect reduced anxiety, but rather abnormal avoidance of the closed arms on the part of transgenics and within-session habituation to the closed arms on the part of wild-type controls. We noticed that the 5xFAD transgenics did not engage in the whisker-barbering behavior typical of mice of this background strain. This is suggestive of abnormal social behavior, and we suspected it might be related to their avoidance of the closed arms on the plus maze. Indeed, transgenic mice exhibited excessive home-cage social behavior and impaired social recognition, and did not permit barbering by wild-type mice when pair-housed. When their whiskers were snipped the 5xFAD transgenics no longer avoided the closed arms on the plus maze. Examination of parvalbumin (PV) staining showed a 28.9% reduction in PV+ inhibitory interneurons in the barrel fields of 5xFAD mice, and loss of PV+ fibers in layers IV and V. This loss of vibrissal inhibition suggests a putatively aversive overstimulation that may be responsible for the transgenics' avoidance of the closed arms in the plus maze.

Strains and stressors: an analysis of touchscreen learning in genetically diverse mouse strains

Touchscreen-based systems are growing in popularity as a tractable, translational approach for studying learning and cognition in rodents. However, while mouse strains are well known to differ in learning across various settings, performance variation between strains in touchscreen learning has not been well described. The selection of appropriate genetic strains and backgrounds is critical to the design of touchscreen-based studies and provides a basis for elucidating genetic factors moderating behavior. Here we provide a quantitative foundation for visual discrimination and reversal learning using touchscreen assays across a total of 35 genotypes. We found significant differences in operant performance and learning, including faster reversal learning in DBA/2J compared to C57BL/6J mice. We then assessed DBA/2J and C57BL/6J for differential sensitivity to an environmental insult by testing for alterations in reversal learning following exposure to repeated swim stress. Stress facilitated reversal learning (selectively during the late stage of reversal) in C57BL/6J, but did not affect learning in DBA/2J. To dissect genetic factors underlying these differences, we phenotyped a family of 27 BXD strains generated by crossing C57BL/6J and DBA/2J. There was marked variation in discrimination, reversal and extinction learning across the BXD strains, suggesting this task may be useful for identifying underlying genetic differences. Moreover, different measures of touchscreen learning were only modestly correlated in the BXD strains, indicating that these processes are comparatively independent at both genetic and phenotypic levels. Finally, we examined the behavioral structure of learning via principal component analysis of the current data, plus an archival dataset, totaling 765 mice. This revealed 5 independent factors suggestive of "reversal learning," "motivation-related late reversal learning," "discrimination learning," "speed to respond," and "motivation during discrimination." Together, these findings provide a valuable reference to inform the choice of strains and genetic backgrounds in future studies using touchscreen-based tasks.

A large QTL for fear and anxiety mapped using an F2 cross can be dissected into multiple smaller QTLs

Using chromosome substitution strains (CSS), we previously identified a large quantitative trait locus (QTL) for conditioned fear (CF) on mouse chromosome 10. Here, we used an F2 cross between CSS-10 and C57BL/6J (B6) to localize that QTL to distal chromosome 10. That QTL accounted for all the difference between CSS-10 and B6. We then produced congenic strains to fine-map that interval. We identified two congenic strains that captured some or all the QTL. The larger congenic strain (Line 1: 122.387121-129.068 Mb; build 37) appeared to account for all the difference between CSS-10 and B6. The smaller congenic strain (Line 2: 127.277-129.068 Mb) was intermediate between CSS-10 and B6. We used haplotype mapping followed by quantitative polymerase chain reaction to identify one gene that was differentially expressed in both lines relative to B6 (Rnf41) and one that was differentially expressed between only Line 1 and B6 (Shmt2). These cis-eQTLs may cause the behavioral QTLs; however, further studies are required to validate these candidate genes. More generally, our observation that a large QTL mapped using CSS and F2 crosses can be dissected into multiple smaller QTLs shows a weaknesses of two-stage approaches that seek to use coarse mapping to identify large regions followed by fine-mapping. Indeed, additional dissection of these congenic strains might result in further subdivision of these QTL regions. Despite these limitations, we have successfully fine-mapped two QTLs to small regions and identified putative candidate genes, showing that the congenic approach can be effective for fine-mapping QTLs.

What are we measuring when we test strain differences in anxiety in mice?

We examined measures of locomotor and anxiety-like behavior in male and female mice of 15 inbred strains on the elevated-plus maze, light/dark transition box and open field. Strain differences were found on all measures of locomotor activity and anxiety. Strain means for measures of locomotor activity on the three apparatus were significantly correlated, but strain means for commonly used measures of anxiety were not correlated. Principal component analysis revealed a common locomotor activity factor, which accounted for 28.6 % of the variance, but no common anxiety factor. Species-typical behaviors (defecations, stretch-attend postures, grooming) accounted for smaller proportions (<11 %) of the variance. These results plus comparisons with previously published data suggest that the elevated-plus maze, light/dark box and open field measure different facets of anxiety, and that the reliability of genetic differences on anxiety is highly dependent on apparatus, procedural variables and laboratory factors. Locomotor activity, however, is a stable trait that differs across strains and is reliably measured in different apparatus and laboratories. We conclude that anxiety traits of inbred mouse strains are best reflected by species-typical behaviors in each apparatus. These results suggest that new ways of measuring trait anxiety are required in order to determine the neural and genetic correlates of anxiety-like behaviour in mice.

High-anxious individuals show increased chronic stress burden, decreased protective immunity, and increased cancer progression in a mouse model of squamous cell carcinoma

In spite of widespread anecdotal and scientific evidence much remains to be understood about the long-suspected connection between psychological factors and susceptibility to cancer. The skin is the most common site of cancer, accounting for nearly half of all cancers in the US, with approximately 2-3 million cases of non-melanoma cancers occurring each year worldwide. We hypothesized that a high-anxious, stress-prone behavioral phenotype would result in a higher chronic stress burden, lower protective-immunity, and increased progression of the immuno-responsive skin cancer, squamous cell carcinoma. SKH1 mice were phenotyped as high- or low-anxious at baseline, and subsequently exposed to ultraviolet-B light (1 minimal erythemal dose (MED), 3 times/week, 10-weeks). The significant strengths of this cancer model are that it uses a normal, immunocompetent, outbred strain, without surgery/injection of exogenous tumor cells/cell lines, and produces lesions that resemble human tumors. Tumors were counted weekly (primary outcome), and tissues collected during early and late phases of tumor development. Chemokine/cytokine gene-expression was quantified by PCR, tumor-infiltrating helper (Th), cytolytic (CTL), and regulatory (Treg) T cells by immunohistochemistry, lymph node T and B cells by flow cytometry, adrenal and plasma corticosterone and tissue vascular-endothelial-growth-factor (VEGF) by ELISA. High-anxious mice showed a higher tumor burden during all phases of tumor development. They also showed: higher corticosterone levels (indicating greater chronic stress burden), increased CCL22 expression and Treg infiltration (increased tumor-recruited immuno-suppression), lower CTACK/CCL27, IL-12, and IFN-γ gene-expression and lower numbers of tumor infiltrating Th and CTLs (suppressed protective immunity), and higher VEGF concentrations (increased tumor angiogenesis/invasion/metastasis). These results suggest that the deleterious effects of high trait anxiety could be: exacerbated by life-stressors, accentuated by the stress of cancer diagnosis/treatment, and mediate increased tumor progression and/or metastasis. Therefore, it may be beneficial to investigate the use of chemotherapy-compatible anxiolytic treatments immediately following cancer diagnosis, and during cancer treatment/survivorship.

Genome-wide association for fear conditioning in an advanced intercross mouse line

Fear conditioning (FC) may provide a useful model for some components of post-traumatic stress disorder (PTSD). We used a C57BL/6J × DBA/2J F(2) intercross (n = 620) and a C57BL/6J × DBA/2J F(8) advanced intercross line (n = 567) to fine-map quantitative trait loci (QTL) associated with FC. We conducted an integrated genome-wide association analysis in QTLRel and identified five highly significant QTL affecting freezing to context as well as four highly significant QTL associated with freezing to cue. The average percent decrease in QTL width between the F(2) and the integrated analysis was 59.2%. Next, we exploited bioinformatic sequence and expression data to identify candidate genes based on the existence of non-synonymous coding polymorphisms and/or expression QTLs. We identified numerous candidate genes that have been previously implicated in either fear learning in animal models (Bcl2, Btg2, Dbi, Gabr1b, Lypd1, Pam and Rgs14) or PTSD in humans (Gabra2, Oprm1 and Trkb); other identified genes may represent novel findings. The integration of F(2) and AIL data maintains the advantages of studying FC in model organisms while significantly improving resolution over previous approaches.

The neuropeptide galanin and variants in the GalR1 gene are associated with nicotine dependence

The neuropeptide galanin and its receptors are expressed in brain regions implicated in drug dependence. Indeed, several lines of evidence support a role for galanin in modulating the effects of drugs of abuse, including morphine, cocaine, amphetamine, and alcohol. Despite these findings, the role of galanin and its receptors in the effects of nicotine is largely underexplored. Here, using mouse models of nicotine reward and withdrawal, we show that there is a significant correlation between mecamylamine-precipitated nicotine withdrawal somatic signs and basal galanin or galanin receptor 1 (GALR1) expression in mesolimbocortical dopamine regions across the BXD battery of recombinant inbred mouse lines. The non-peptide galanin receptor agonist, galnon, also blocks nicotine rewarding effects and reverses mecamylamine-precipitated nicotine withdrawal signs in ICR mice. Additionally, we conducted a meta-analysis using smoking information from six European-American and African-American data sets. In support of our animal data, results from the association study show that variants in the GALR1 gene are associated with a protective effect in nicotine dependence (ND). Taken together, our data suggest that galanin has a protective role against progression to ND, and these effects may be mediated through GALR1.

Pavlovian fear memory circuits and phenotype models of PTSD

Pavlovian fear conditioning, also known as classical fear conditioning is an important model in the study of the neurobiology of normal and pathological fear. Progress in the neurobiology of Pavlovian fear also enhances our understanding of disorders such as posttraumatic stress disorder (PTSD) and with developing effective treatment strategies. Here we describe how Pavlovian fear conditioning is a key tool for understanding both the neurobiology of fear and the mechanisms underlying variations in fear memory strength observed across different phenotypes. First we discuss how Pavlovian fear models aspects of PTSD. Second, we describe the neural circuits of Pavlovian fear and the molecular mechanisms within these circuits that regulate fear memory. Finally, we show how fear memory strength is heritable; and describe genes which are specifically linked to both changes in Pavlovian fear behavior and to its underlying neural circuitry. These emerging data begin to define the essential genes, cells and circuits that contribute to normal and pathological fear. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Anxiety and fear in a cross of C57BL/6J and DBA/2J mice: mapping overlapping and independent QTL for related traits

Anxiety, like other psychiatric disorders, is a complex neurobehavioral trait, making identification of causal genes difficult. In this study, we examined anxiety-like behavior and fear conditioning (FC) in an F(2) intercross of C57BL/6J and DBA/2J mice. We identified numerous quantitative trait loci (QTL) influencing anxiety-like behavior in both open field (OF) and FC tests. Many of these QTL were mapped back to the same chromosomal regions, regardless of behavior or test. For example, highly significant overlapping QTL on chromosome 1 were found in all FC measures as well as in center time measures in the OF. Other QTL exhibited strong temporal profiles over testing, highlighting dynamic relationship between genotype, test and changes in behavior. Next, we implemented a factor analysis design to account for the correlated nature of the behaviors measured. OF and FC behaviors loaded onto four main factors representing both anxiety and fear behaviors. Using multiple QTL modeling, we calculated the percentage variance in anxiety and fear explained by multiple QTL using both additive and interactive terms. Quantitative trait loci modeling resulted in a broad description of the genetic architecture underlying anxiety and fear accounting for 14-37% of trait variance. Factor analysis and multiple QTL modeling showed both unique and shared QTL for anxiety and fear; suggesting a partially overlapping genetic architecture for these two different models of anxiety.

Neocortical molecular layer heterotopia in substrains of C57BL/6 and C57BL/10 mice

Abnormal development of the neocortex is often associated with cognitive deficits and epilepsy. Rodent models are widely used to study normal and abnormal cortical development and have revealed the roles of many important genetic and environmental factors. Interestingly, several inbred mouse strains commonly used in behavioral, anatomical, and/or physiological studies display neocortical malformations including C57BL/6J mice, which are among the most widely utilized mice. In the present report we describe the prevalence and cytoarchitecture of molecular-layer heterotopia in C57BL/6J mice and related strains obtained from three commercial vendors as well as mice bred in academic vivaria from founders obtained commercially. In particular, we found that the prevalence of molecular-layer heterotopia vaired according to the sex as well as the vendor-of-origin of the mouse. These data are relevant to the use of this strain as a mouse-model in the study of brain-behavior relationships.

Enhanced fear expression in a psychopathological mouse model of trait anxiety: pharmacological interventions

The propensity to develop an anxiety disorder is thought to be determined by genetic and environmental factors. Here we investigated the relationship between a genetic predisposition to trait anxiety and experience-based learned fear in a psychopathological mouse model. Male CD-1 mice selectively bred for either high (HAB), or normal (NAB) anxiety-related behaviour on the elevated plus maze were subjected to classical fear conditioning. During conditioning both mouse lines showed increased fear responses as assessed by freezing behaviour. However, 24 h later, HAB mice displayed more pronounced conditioned responses to both a contextual or cued stimulus when compared with NAB mice. Interestingly, 6 h and already 1 h after fear conditioning, freezing levels were high in HAB mice but not in NAB mice. These results suggest that trait anxiety determines stronger fear memory and/or a weaker ability to inhibit fear responses in the HAB line. The enhanced fear response of HAB mice was attenuated by treatment with either the α(2,3,5)-subunit selective benzodiazepine partial agonist L-838,417, corticosterone or the selective neurokinin-1 receptor antagonist L-822,429. Overall, the HAB mouse line may represent an interesting model (i) for identifying biological factors underlying misguided conditioned fear responses and (ii) for studying novel anxiolytic pharmacotherapies for patients with fear-associated disorders, including post-traumatic stress disorder and phobias.

Behavioral characterization of A/J and C57BL/6J mice using a multidimensional test: association between blood plasma and brain magnesium-ion concentration with anxiety

Up to 29% of all adults will experience an anxiety-related disorder during their lives. Treatment of these disorders is still difficult and the exact mechanisms and pathways behind anxiety disorders remain to be elucidated. Although evidence exists for genetically based susceptibility of human psychiatric diseases, risk genes have rarely been identified up to now. Inbred mouse strains are, together with the crosses and genetic reference populations derived from them, important tools for the genetic dissection of complex behavioral traits in the mouse. Thus, inbred mouse models of human anxiety may be a potent starting tool to search for candidate genes in mice, which could then via comparative genomics be translated to the human situation. In this paper we investigate whether the A/J and C57BL/6J mouse inbred strains differ in a limited number of motivational systems (anxiety, exploration, memory, locomotion, and social affinity), but especially in anxiety-related behavior from each other. Young adult individuals from both genders of A/J and C57BL/6J strains were behaviorally phenotyped using a multidimensional test: the modified hole board. This paradigm basically is a combination of the traditional hole board and the open field test allowing to test for anxiety-related avoidance behavior, risk assessment, arousal, exploration, memory, locomotor activity, and social affinity, using just one single test. An acute, aversive stimulus (intra-peritoneal injection with saline) was applied to the animals to test for the robustness of their behavioral phenotype. In addition, presumed physiological indicators for anxiety (circulating glucose, cholesterol, and corticosterone, adrenal tyrosine hydroxylase, and blood plasma and brain magnesium) were investigated. It could be concluded that C57BL/6J and A/J mice differ with respect to almost all tested motivational systems. For some measures, including anxiety-related behavioral parameters, there were clear gender effects. The high-anxiety phenotype of A/J mice could be shown to represent a primary and robust characteristic. Further, blood plasma and brain magnesium levels were significantly correlated with several anxiety-related behavioral parameters. These results emphasize the hypothesized, and possibly causal, association between magnesium status and emotionality.

Does gene deletion of AMPA GluA1 phenocopy features of schizoaffective disorder?

Glutamatergic dysfunction is strongly implicated in schizophrenia and mood disorders. GluA1 knockout (KO) mice display schizophrenia- and depression-related abnormalities. Here, we asked whether GluA1 KO show mania-related abnormalities. KO were tested for behavior in approach/avoid conflict tests, responses to repeated forced swim exposure, and locomotor responses under stress and after psychostimulant treatment. The effects of rapid dopamine depletion and treatment with lithium or GSK-3β inhibitor on KO locomotor hyperactivity were tested. Results showed that KO exhibited novelty- and stress-induced locomotor hyperactivity, reduced forced swim immobility and alterations in approach/avoid conflict tests. Psychostimulant treatment and dopamine depletion exacerbated KO locomotor hyperactivity. Lithium, but not GSK-3β inhibitor, treatment normalized KO anxiety-related behavior and partially reversed hyperlocomotor behavior, and also reversed elevated prefrontal cortex levels of phospho-MARCKS and phospho-neuromodulin. Collectively, these findings demonstrate mania-related abnormalities in GluA1 KO and, combined with previous findings, suggest this mutant may provide a novel model of features of schizoaffective disorder.

Measuring anxiety- and locomotion-related behaviours in mice: a new way of using old tests

RATIONALE

Batteries of tests that are thought to measure different aspects of anxiety-related behaviour are used to characterise mice after genetic or pharmacological manipulation. However, because of the potentially confounding effects of repeated testing and natural intra-individual variations in behaviour over time, subjecting mice to a succession of tests is not ideal.

OBJECTIVES

The aim of this study was to investigate, in mice, the utility of an integrated apparatus that combines three classical tests of anxiety, the open field, elevated plus maze (EPM) and light/dark box.

METHODS

Mice from four different strains (CD-1, BALB/cJ, DBA/2J, C57BL/6J) were used in a series of five experiments where their behaviour was observed for 15 min in the integrated apparatus. Responses to anxiety-modulating drugs and 2-day repeated testing were evaluated.

RESULTS

CD-1 mice explored the apparatus thoroughly, providing measures from all areas throughout the entire testing session. Factor analysis showed that measures of locomotion and anxiety-related behaviour were dissociable. BALB/cJ, DBA/2J and C57BL/6J showed markedly different behavioural profiles, largely consistent with previous studies examining individual tests. Avoidance of aversive environments did not increase with repeated testing. In CD-1 mice, the anxiolytics diazepam and alprazolam (4 and 2 mg/kg, respectively) increased the approach towards the EPM open arms. Alprazolam also had sedative effects, whereas the anxiogenic pentylenetetrazole had no effects.

CONCLUSIONS

These findings suggest that the triple test is sensitive to genetic/pharmacological influences on anxiety and locomotion and that, by providing quasi-simultaneous measures from three different apparatuses, it may represent an alternative to the use of test batteries.

Strain differences in stress responsivity are associated with divergent amygdala gene expression and glutamate-mediated neuronal excitability

Stress is a major risk factor for numerous neuropsychiatric diseases. However, susceptibility to stress and the qualitative nature of stress effects on behavior differ markedly among individuals. This is partly because of the moderating influence of genetic factors. Inbred mouse strains provide a relatively stable and restricted range of genetic and environmental variability that is valuable for disentangling gene-stress interactions. Here, we screened a panel of inbred strains for anxiety- and depression-related phenotypes at baseline (trait) and after exposure to repeated restraint. Two strains, DBA/2J and C57BL/6J, differed in trait and restraint-induced anxiety-related behavior (dark/light exploration, elevated plus maze). Gene expression analysis of amygdala, medial prefrontal cortex, and hippocampus revealed divergent expression in DBA/2J and C57BL/6J both at baseline and after repeated restraint. Restraint produced strain-dependent expression alterations in various genes including glutamate receptors (e.g., Grin1, Grik1). To elucidate neuronal correlates of these strain differences, we performed ex vivo analysis of glutamate excitatory neurotransmission in amygdala principal neurons. Repeated restraint augmented amygdala excitatory postsynaptic signaling and altered metaplasticity (temporal summation of NMDA receptor currents) in DBA/2J but not C57BL/6J. Furthermore, we found that the C57BL/6J-like changes in anxiety-related behavior after restraint were absent in null mutants lacking the modulatory NMDA receptor subunit Grin2a, but not the AMPA receptor subunit Gria1. Grin2a null mutants exhibited significant ( approximately 30%) loss of dendritic spines on amygdala principal neurons under nonrestraint conditions. Collectively, our data support a model in which genetic variation in glutamatergic neuroplasticity in corticolimbic circuitry underlies phenotypic variation in responsivity to stress.

High-throughput behavioral phenotyping in the expanded panel of BXD recombinant inbred strains

Genetic reference populations, particularly the BXD recombinant inbred (BXD RI) strains derived from C57BL/6J and DBA/2J mice, are a valuable resource for the discovery of the bio-molecular substrates and genetic drivers responsible for trait variation and covariation. This approach can be profitably applied in the analysis of susceptibility and mechanisms of drug and alcohol use disorders for which many predisposing behaviors may predict the occurrence and manifestation of increased preference for these substances. Many of these traits are modeled by common mouse behavioral assays, facilitating the detection of patterns and sources of genetic coregulation of predisposing phenotypes and substance consumption. Members of the Tennessee Mouse Genome Consortium (TMGC) have obtained phenotype data from over 250 measures related to multiple behavioral assays across several batteries: response to, and withdrawal from cocaine, 3,4-methylenedioxymethamphetamine; "ecstasy" (MDMA), morphine and alcohol; novelty seeking; behavioral despair and related neurological phenomena; pain sensitivity; stress sensitivity; anxiety; hyperactivity and sleep/wake cycles. All traits have been measured in both sexes in approximately 70 strains of the recently expanded panel of BXD RI strains. Sex differences and heritability estimates were obtained for each trait, and a comparison of early (N = 32) and recent (N = 37) BXD RI lines was performed. Primary data are publicly available for heritability, sex difference and genetic analyses using the MouseTrack database, and are also available in GeneNetwork.org for quantitative trait locus (QTL) detection and genetic analysis of gene expression. Together with the results of related studies, these data form a public resource for integrative systems genetic analysis of neurobehavioral traits.