Contrasting phenotypes of C57BL/6JOlaHsd, 129S2/SvHsd and 129/SvEv mice in two exploration-based tests of anxiety-related behaviour

Nature and nurture: comparing mouse behavior in classic versus revised anxiety-like and social behavioral assays in genetically or environmentally defined groups

Widely used rodent anxiety assays like the elevated plus maze (EPM) and the open field test (OFT) are often conflated with rodents' natural preference for dark over light environments or protected over open spaces. The EPM and OFT have been used for many decades, yet have also been criticized by generations of behavioral scientists. Several years ago, two revised anxiety assays were designed to improve upon the "classic" tests by excluding the possibility to avoid or escape aversive areas of each maze. The 3-D radial arm maze (3DR) and the 3-D open field test (3Doft) each consist of an open space connected to ambiguous paths toward uncertain escape. This introduces continual motivational conflict, thereby increasing external validity as an anxiety model. But despite this improvement, the revised assays have not caught on. One issue may be that studies to date have not directly compared classic and revised assays in the same animals. To remedy this, we contrasted behavior in a battery of assays (EPM, OFT, 3DR, 3Doft, and a sociability test) in mice defined either genetically by isogenic strain, or environmentally by postnatal experience. Findings indicate that the optimal assay to assess anxiety-like behavior may depend upon grouping variable (e.g. genetic versus environment). We argue that the 3DR may be the most ecologically valid of the anxiety assays tested, while the OFT and 3Doft provided the least useful information. Finally, exposure to multiple assays significantly affected sociability measures, raising concerns for designing and interpreting batteries of behavioral tests in mice.

Linking mPFC circuit maturation to the developmental regulation of emotional memory and cognitive flexibility

The medial prefrontal cortex (mPFC) and its abundant connections with other brain regions play key roles in memory, cognition, decision making, social behaviors, and mood. Dysfunction in mPFC is implicated in psychiatric disorders in which these behaviors go awry. The prolonged maturation of mPFC likely enables complex behaviors to emerge, but also increases their vulnerability to disruption. Many foundational studies have characterized either mPFC synaptic or behavioral development without establishing connections between them. Here, we review this rich body of literature, aligning major events in mPFC development with the maturation of complex behaviors. We focus on emotional memory and cognitive flexibility, and highlight new work linking mPFC circuit disruption to alterations of these behaviors in disease models. We advance new hypotheses about the causal connections between mPFC synaptic development and behavioral maturation and propose research strategies to establish an integrated understanding of neural architecture and behavioral repertoires.

Positive allosteric modulation of the mu-opioid receptor produces analgesia with reduced side effects

Positive allosteric modulators (PAMs) of the mu-opioid receptor (MOR) have been hypothesized as potentially safer analgesics than traditional opioid drugs. This is based on the idea that PAMs will promote the action of endogenous opioid peptides while preserving their temporal and spatial release patterns and so have an improved therapeutic index. However, this hypothesis has never been tested. Here, we show that a mu-PAM, BMS-986122, enhances the ability of the endogenous opioid Methionine-enkephalin (Met-Enk) to stimulate G protein activity in mouse brain homogenates without activity on its own and to enhance G protein activation to a greater extent than β-arrestin recruitment in Chinese hamster ovary (CHO) cells expressing human mu-opioid receptors. Moreover, BMS-986122 increases the potency of Met-Enk to inhibit GABA release in the periaqueductal gray, an important site for antinociception. We describe in vivo experiments demonstrating that the mu-PAM produces antinociception in mouse models of acute noxious heat pain as well as inflammatory pain. These effects are blocked by MOR antagonists and are consistent with the hypothesis that in vivo mu-PAMs enhance the activity of endogenous opioid peptides. Because BMS-986122 does not bind to the orthosteric site and has no inherent agonist action at endogenously expressed levels of MOR, it produces a reduced level of morphine-like side effects of constipation, reward as measured by conditioned place preference, and respiratory depression. These data provide a rationale for the further exploration of the action and safety of mu-PAMs as an innovative approach to pain management.

Altered baseline and amphetamine-mediated behavioral profiles in dopamine transporter Cre (DAT-Ires-Cre) mice compared to tyrosine hydroxylase Cre (TH-Cre) mice

RATIONALE

Transgenic mouse lines expressing Cre-recombinase under the regulation of either dopamine transporter (DAT) or tyrosine hydroxylase (TH) promoters are commonly used to study the dopamine (DA) system. While use of the TH promoter appears to have less liability to changes in native gene expression, transgene insertion in the DAT locus results in reduced DAT expression and function. This confound is sometimes overlooked in genetically targeted behavioral experiments.

OBJECTIVES

We sought to evaluate the suitability of DAT-Ires-Cre and TH-Cre transgenic lines for behavioral pharmacology experiments with DA agonists. We hypothesized that DAT-Ires-Cre expression would impact DAT-mediated behaviors, but no impact of TH-Cre expression would be observed.

METHODS

DAT-Ires-Cre and TH-Cre mice bred on mixed 129S6/C57BL/6 and pure C57BL/6 backgrounds were evaluated for novelty-induced, baseline, and amphetamine (AMPH)-induced locomotion, and for AMPH and D1 agonist (SKF-38393)-induced preservative behaviors.

RESULTS

DAT-Ires-Cre mice on both mixed 129S6/C57BL/6 and pure C57BL/6 backgrounds displayed increased novelty-induced activity and decreased AMPH-induced locomotion, with mixed results for AMPH-induced stereotypy. TH-Cre mice on both backgrounds showed typical baseline activity and AMPH-induced stereotypy, with a difference in AMPH-induced locomotion observed only on the mixed background. Both transgenic lines displayed unaltered SKF-38393-induced grooming behavior.

CONCLUSIONS

Our findings indicate that the DAT-Ires-Cre transgenic line may lead to confounds for experiments that are dependent on DAT expression. The TH-Cre transgenic line studied here may be a more useful option, depending on background strain, because of its lack of baseline and drug-induced phenotypes. These data highlight the importance of appropriate controls in studies employing transgenic mice.

Salient safety conditioning improves novel discrimination learning

Generalized fear is one purported mechanism of anxiety that is a target of clinical and basic research. Impaired fear discrimination has been primarily examined from the perspective of increased fear learning, rather than how learning about non-threatening stimuli affects fear discrimination. To address this question, we tested how three Safety Conditioning protocols with varied levels of salience allocated to the safety cue compared to classic Fear Conditioning in their impact on subsequent innate anxiety, and differential fear learning of new aversive and neutral cues. Using a high anxiety strain of mice (129SvEv, Taconic), we show that Fear Conditioned animals show little exploration of the anxiogenic center of an open field 24 h later, and poor discrimination during new differential conditioning 7 days later. Three groups of mice underwent Safety Conditioning, (i) the safety tone was unpaired with a shock, (ii) the safety tone was unpaired with the shock and co-terminated with a house light signaling the end of the safety period, and (iii) the safety tone was unpaired with the shock and its beginning co-occurred with a house light, signaling the start of a safety period. Mice from all Safety Conditioning groups showed higher levels of open field exploration than the Fear Conditioned mice 24 h after training. Furthermore, Safety Conditioned animals showed improved discrimination learning of a novel non-threat, with the Salient Beginning safety conditioned group performing best. These findings indicate that high anxiety animals benefit from salient safety training to improve exploration and discrimination of new non-threating stimuli.

Anxiety and Startle Phenotypes in Glrb Spastic and Glra1 Spasmodic Mouse Mutants

A GWAS study recently demonstrated single nucleotide polymorphisms (SNPs) in the human GLRB gene of individuals with a prevalence for agoraphobia. GLRB encodes the glycine receptor (GlyRs) β subunit. The identified SNPs are localized within the gene flanking regions (3' and 5' UTRs) and intronic regions. It was suggested that these nucleotide polymorphisms modify GlyRs expression and phenotypic behavior in humans contributing to an anxiety phenotype as a mild form of hyperekplexia. Hyperekplexia is a human neuromotor disorder with massive startle phenotypes due to mutations in genes encoding GlyRs subunits. GLRA1 mutations have been more commonly observed than GLRB mutations. If an anxiety phenotype contributes to the hyperekplexia disease pattern has not been investigated yet. Here, we compared two mouse models harboring either a mutation in the murine Glra1 or Glrb gene with regard to anxiety and startle phenotypes. Homozygous spasmodic animals carrying a Glra1 point mutation (alanine 52 to serine) displayed abnormally enhanced startle responses. Moreover, spasmodic mice exhibited significant changes in fear-related behaviors (freezing, rearing and time spent on back) analyzed during the startle paradigm, even in a neutral context. Spastic mice exhibit reduced expression levels of the full-length GlyRs β subunit due to aberrant splicing of the Glrb gene. Heterozygous animals appear normal without an obvious behavioral phenotype and thus might reflect the human situation analyzed in the GWAS study on agoraphobia and startle. In contrast to spasmodic mice, heterozygous spastic animals revealed no startle phenotype in a neutral as well as a conditioning context. Other mechanisms such as a modulatory function of the GlyRs β subunit within glycinergic circuits in neuronal networks important for fear and fear-related behavior may exist. Possibly, in human additional changes in fear and fear-related circuits either due to gene-gene interactions e.g., with GLRA1 genes or epigenetic factors are necessary to create the agoraphobia and in particular the startle phenotype.

The Effects of 1-Hz rTMS on Emotional Behavior and Dendritic Complexity of Mature and Newly Generated Dentate Gyrus Neurons in Male Mice

Low-frequency repetitive transcranial magnetic stimulation (1-Hz rTMS) is a promising noninvasive tool for the treatment of depression. Hippocampal neuronal plasticity is thought to play a pivotal role in the pathophysiology of depressive disorders and the mechanism of action of antidepressant treatments. We investigated the effect of 1-Hz rTMS treatment on hippocampal dentate gyrus structural plasticity and related emotional behaviors modifications. Experimentally, adult male mice received either five days of 1-Hz rTMS or Sham stimulation. After stimulation, the mice underwent a battery of tests for anxiety-like and depression-like behaviors. We also tested the effect of treatment on mature and newly generated granule cell dendritic complexity. Our data showed that 1-Hz rTMS induced structural plasticity in mature granule cells, as evidenced by increased dendritic length and number of intersections. However, the stimulation did not increase the proliferation of the dentate gyrus progenitor cells. On the contrary, the stimulated mice showed increased dendritic complexity of newly generated neurons. Moreover, 1-Hz rTMS resulted in antidepressant-like effects in the tail suspension test, but it did not affect anxiety-like behaviors. Therefore, our results indicate that 1-Hz rTMS modulates dentate gyrus morphological plasticity in mature and newly generated neurons. Furthermore, our data provide some evidence of an association between the antidepressant-like activity of 1-Hz rTMS and structural plasticity in the hippocampus.

Gpr158 Deficiency Impacts Hippocampal CA1 Neuronal Excitability, Dendritic Architecture, and Affects Spatial Learning

G-protein-coupled receptor 158 (Gpr158) is highly expressed in striatum, hippocampus and prefrontal cortex. It gained attention as it was implicated in physiological responses to stress and depression. Recently, Gpr158 has been shown to act as a pathway-specific synaptic organizer in the hippocampus, required for proper mossy fiber-CA3 neurocircuitry establishment, structure, and function. Although rodent Gpr158 expression is highest in CA3, considerable expression occurs in CA1 especially after the first postnatal month. Here, we combined hippocampal-dependent behavioral paradigms with subsequent electrophysiological and morphological analyses from the same group of mice to assess the effects of Gpr158 deficiency on CA1 physiology and function. We demonstrate deficits in spatial memory acquisition and retrieval in the Morris water maze paradigm, along with deficits in the acquisition of extinction memory in the passive avoidance test in Gpr158 KO mice. Electrophysiological recordings from CA1 pyramidal neurons revealed normal basal excitatory and inhibitory synaptic transmission, however, Schaffer collateral stimulation yielded dramatically reduced post-synaptic currents. Interestingly, intrinsic excitability of CA1 pyramidals was found increased, potentially acting as a compensatory mechanism to the reductions in Schaffer collateral-mediated drive. Both ex vivo and in vitro, neurons deficient for or with lowered levels of Gpr158 exhibited robust reductions in dendritic architecture and complexity, i.e., reduced length, surface, bifurcations, and branching. This effect was localized in the apical but not basal dendrites of adult CA1 pyramidals, indicative of compartment-specific alterations. A significant positive correlation between spatial memory acquisition and extent of complexity of CA1 pyramidals was found. Taken together, we provide first evidence of significant disruptions in hippocampal CA1 neuronal dendritic architecture and physiology, driven by Gpr158 deficiency. Importantly, the hippocampal neuronal morphology deficits appear to support the impairments in spatial memory acquisition observed in Gpr158 KO mice.

Contrasting characteristic behaviours among common laboratory mouse strains

Mice are widely used to model wide-ranging human neurological disorders, from development to degenerative pathophysiology. Behavioural and molecular characteristics of these mouse models are influenced by the genetic background of each strain. Among the most commonly used strains, the inbred C57BL/6J, BALB/c, CBA and 129SvEv lines and the CD1 outbred line are particularly predominant. Despite their prevalence, comparative performance of these strains on many standard behavioural tests commonly used to assess neurological conditions remains diffusely and indirectly accessible in the literature. Given that independent studies may be conducted with mice of differing genetic backgrounds, any variation in characteristic behavioural responses of specific strains should be delineated in order to properly interpret results among studies. Thus, in the present study, we aimed to characterize these commonly used mice strains through several standard behavioural tests. Here, we found that animals from different genetic background strains exhibited varying behavioural patterns when assessed for sociability/novelty, memory function, and negative behaviours like despair and stress calls. These results suggest that genetic variation among strains may be responsible-in part-for strain-specific behavioural phenotypes and potential predisposition to some neurological disorders.

Behavioral tests that reveal long-term deficits after permanent focal cerebral ischemia in mouse

Efforts are still needed regarding the research of therapeutics for ischemic stroke. While in experimental studies the protective effect of pharmacological agents is often highlighted by a reduction of the lesion size evaluated in the short term (days), in clinical studies a functional recovery of patients suffering from stroke is expected on the long-term (months and years). Long-term functional preclinical studies are highly recommended to evaluate potential neuroprotective agents for stroke, rather than an assessment of the infarction size at a short time point. The present study thus aimed to select among various behavioral tests those able to highlight long-term deficits (3 months) after cerebral ischemia in mice. Permanent focal cerebral ischemia was carried out in male Swiss mice by intraluminal occlusion of the left middle cerebral artery (MCA). Fourteen behavioral tests were assessed from 7 days to 90 days after ischemia (locomotor activity, neurological score, exit circle test, grip and string tests, chimney test, adhesive removal test, pole test, beam-walking tests, elevated plus maze, marble burying test, forced swimming test, novel object recognition test). The present study clearly identified a battery of behavioral tests able to highlight deficits up to 3 months in our mouse model of permanent MCA occlusion (locomotor activity, neurological score, adhesive removal test, pole test, beam-walking tests, elevated plus maze, marble burying test, forced swimming test and novel object recognition test). This battery of behavioral tests highlighting long-term deficits is useful to study future neuroprotective strategies for stroke treatment.

Serotonin inputs to the dorsal BNST modulate anxiety in a 5-HT1A receptor-dependent manner

Serotonin (5-HT) neurons project from the raphe nuclei throughout the brain where they act to maintain homeostasis. Here, we study 5-HT inputs into the bed nucleus of the stria terminalis (BNST), a major subdivision of the extended amygdala that has been proposed to regulate responses to anxiogenic environments in humans and rodents. While the dorsal part of the BNST (dBNST) receives dense 5-HT innervation, whether and how 5-HT in the dBNST normally modulates anxiety remains unclear. Using optogenetics, we demonstrate that activation of 5-HT terminals in the dBNST reduces anxiety in a highly anxiogenic environment. Further analysis revealed that optogenetic inhibition of 5-HT inputs into the dBNST increases anxiety in a less anxiogenic environment. We found that 5-HT predominantly hyperpolarizes dBNST neurons, reducing their activity in a manner that can be blocked by a 5-HT_1A antagonist. Finally, we demonstrate that activation of 5-HT_1A receptors in the dBNST is necessary for the anxiolytic effect observed following optogenetic stimulation of 5-HT inputs into the dBNST. These data reveal that 5-HT release in the dBNST modulates anxiety-like behavior via 5-HT_1A receptors under naturalistic conditions.

A Novel Integrative Mechanism in Anxiolytic Behavior Induced by Galanin 2/Neuropeptide Y Y1 Receptor Interactions on Medial Paracapsular Intercalated Amygdala in Rats

Anxiety is evoked by a threatening situation and display adaptive or defensive behaviors, found similarly in animals and humans. Neuropeptide Y (NPY) Y1 receptor (NPYY1R) and Galanin (GAL) receptor 2 (GALR2) interact in several regions of the limbic system, including the amygdala. In a previous study, GALR2 enhanced NPYY1R mediated anxiolytic actions on spatiotemporal parameters in the open field and elevated plus maze, involving the formation of GALR2/NPYY1R heteroreceptor complexes in the amygdala. Moreover, the inclusion of complementary ethological parameters provides a more comprehensive profile on the anxiolytic effects of a treatment. The purpose of the current study is to evaluate the anxiolytic effects and circuit activity modifications caused by coactivation of GALR2 and NPYY1R. Ethological measurements were performed in the open field, the elevated plus-maze and the light-dark box, together with immediate early gene expression analysis within the amygdala-hypothalamus-periaqueductal gray (PAG) axis, as well as in situ proximity ligation assay (PLA) to demonstrate the formation of GALR2/NPYY1R heteroreceptor complexes. GALR2 and NPYY1R coactivation resulted in anxiolytic behaviors such as increased rearing and head-dipping, reduced stretch attend postures and freezing compared to single agonist or aCSF injection. Neuronal activity indicated by cFos expression was decreased in the dorsolateral paracapsular intercalated (ITCp-dl) subregion of the amygdala, ventromedial hypothalamic (VMH) nucleus and ventrolateral part of the periaqueductal gray (vlPAG), while increased in the perifornical nucleus of the hypothalamus (PFX) following coactivation of GALR2 and NPYY1R. Moreover, an increased density of GALR2/NPYY1R heteroreceptor complexes was explicitly observed in ITCp-dl, following GALR2 and NPYY1R coactivation. Besides, knockdown of GALR2 was found to reduce the density of complexes in ITCp-dl. Taken together, these results open up the possibility that the increased anxiolytic activity demonstrated upon coactivation of NPYY1R and GALR2 receptor was related to actions on the ITCp-dl. GALR2-NPYY1R heteroreceptor complexes may inhibit neuronal activity, by also modifying the neuronal networks of the hypothalamus and the PAG. These results indicate that GALR2/NPYY1R interactions in medial paracapsular intercalated amygdala can provide a novel integrative mechanism in anxiolytic behavior and the basis for the development of heterobivalent agonist drugs targeting GALR2/NPYY1R heteromers, especially in the ITCp-dl of the amygdala for the treatment of anxiety.

Neuropeptide S precursor knockout mice display memory and arousal deficits

Activation of neuropeptide S (NPS) signaling has been found to produce arousal, wakefulness, anxiolytic-like behaviors, and enhanced memory formation. In order to further study physiological functions of the NPS system, we generated NPS precursor knockout mice by homologous recombination in embryonic stem cells. NPS^-/- mice were viable, fertile, and anatomically normal, when compared to their wild-type and heterozygous littermates. The total number of NPS neurons-although no longer synthesizing the peptide - was not affected by the knockout, as analyzed in NPS^-/- /NPS^EGFP double transgenic mice. Analysis of behavioral phenotypes revealed significant deficits in exploratory activity in NPS^-/- mice. NPS precursor knockout mice displayed attenuated arousal in the hole board test, visible as reduced total nose pokes and number of holes inspected, that was not confounded by increased repetitive or stereotypic behavior. Importantly, long-term memory was significantly impaired in NPS^-/- mice in the inhibitory avoidance paradigm. NPS precursor knockout mice displayed mildly increased anxiety-like behaviors in three different tests measuring responses to stress and novelty. Interestingly, heterozygous littermates often presented behavioral deficits similar to NPS^-/- mice or displayed intermediate phenotype. These observations may suggest limited ligand availability in critical neural circuits. Overall, phenotypical changes in NPS^-/- mice are similar to those observed in NPS receptor knockout mice and support earlier findings that suggest major functions of the NPS system in arousal, regulation of anxiety and stress, and memory formation.

CNS Target Identification and Validation: Avoiding the Valley of Death or Naive Optimism?

There are many challenges along the path to the approval of new drugs to treat CNS disorders, one of the greatest areas of unmet medical need with a large societal burden and health-care impact. Unfortunately, over the past two decades, few CNS drug approvals have succeeded, leading many pharmaceutical companies to deprioritize this therapeutic area. The reasons for the failures in CNS drug discovery are likely to be multifactorial. However, selecting the most biologically plausible molecular targets that are relevant to the disorder is a critical first step to improve the probability of success. In this review, we outline previous methods for identifying and validating novel targets for CNS drug discovery, and, cognizant of previous failures, we discuss potential new strategies that may improve the probability of success of developing novel treatments for CNS disorders.

Postnatal training of 129/Sv mice confirms the long-term influence of early exercising on the motor properties of mice

A previous study showed that motor experiences during critical periods of development durably affect the motor properties of adult C57BL/6J mice. However, dependence on early environmental features may vary with the genetic profile. To evaluate the contribution of the genetic background on external influences to motricity, we performed the same experiment in a 129/Sv mouse strain that show a strongly different motor profile. Mice were subjected to endurance training (enriched environment or forced treadmill), hypergravity (chronic centrifugation), or simulated microgravity (hindlimb unloading) between postnatal days 10 and 30. They were then returned to standard housing until testing at the age of nine months. The endurance-trained mice showed a fast-slow shift in the deep zone of the tibialis. In addition, mice reared in the enriched environment showed a modified gait and body posture, and improved performance on the rotarod, whereas forced treadmill training did not affect motor output. Hypergravity induced a fast-slow shift in the superficial zone of the tibialis, with no consequence on motor output. Hindlimb unloading provoked an increased percentage of immature hybrid fibres in the tibialis and a shift in the soleus muscle. When compared with similarly reared C57BL/6J mice, 129/Sv mice showed qualitative differences attributable to the lower efficiency of early training due to their lower basal motor activity level. Nevertheless, the results are essentially consistent in both strains, and support the hypothesis that early motor experience influences the muscle phenotype and motor output.

Preclinical animal anxiety research - flaws and prejudices

The current tests of anxiety in mice and rats used in preclinical research include the elevated plus-maze (EPM) or zero-maze (EZM), the light/dark box (LDB), and the open-field (OF). They are currently very popular, and despite their poor achievements, they continue to exert considerable constraints on the development of novel approaches. Hence, a novel anxiety test needs to be compared with these traditional tests, and assessed against various factors that were identified as a source of their inconsistent and contradictory results. These constraints are very costly, and they are in most cases useless as they originate from flawed methodologies. In the present report, we argue that the EPM or EZM, LDB, and OF do not provide unequivocal measures of anxiety; that there is no evidence of motivation conflict involved in these tests. They can be considered at best, tests of natural preference for unlit and/or enclosed spaces. We also argued that pharmacological validation of a behavioral test is an inappropriate approach; it stems from the confusion of animal models of human behavior with animal models of pathophysiology. A behavioral test is developed to detect not to produce symptoms, and a drug is used to validate an identified physiological target. In order to overcome the major methodological flaws in animal anxiety studies, we proposed an open space anxiety test, a 3D maze, which is described here with highlights of its various advantages over to the traditional tests.

No man is an island. A personal tribute to Bob Blanchard and ethoexperimental approaches to the study of behaviour

I first met Bob Blanchard at an international conference in Paris some 40 years ago. We collaborated intensively during the late 1980s/early 1990s on the ethopharmacology of antipredator defence in wild and laboratory rats, and remained good friends until his untimely passing in November 2013. Bob will undoubtedly be remembered as one of the most influential behavioural neuroscientists of the 20th century and, with Caroline, the most eloquent advocate of ethoexperimental approaches to the study of behaviour. In this brief trip down memory lane, I describe when and where Bob and I first met and how, over a lengthy period, he directly and indirectly helped shape my own research career. His profound influence in this regard is illustrated by reference to not only our collaborative research on antipredator behaviour but also my other work on the ethopharmacology of agonistic behaviour, social conflict analgesia, anxiety, and appetite. The element common to all of this work has been ethoexperimental analysis and, for teaching me the true value of this approach, I shall always remain indebted to the big man. Literally and figuratively, Bob was most certainly larger than life.

d-amino acid oxidase knockout (Dao(-/-) ) mice show enhanced short-term memory performance and heightened anxiety, but no sleep or circadian rhythm disruption

d-amino acid oxidase (DAO, DAAO) is an enzyme that degrades d-serine, the primary endogenous co-agonist of the synaptic N-methyl-d-aspartate receptor. Convergent evidence implicates DAO in the pathophysiology and potential treatment of schizophrenia. To better understand the functional role of DAO, we characterized the behaviour of the first genetically engineered Dao knockout (Dao(-/-) ) mouse. Our primary objective was to assess both spatial and non-spatial short-term memory performance. Relative to wildtype (Dao(+/+) ) littermate controls, Dao(-/-) mice demonstrated enhanced spatial recognition memory performance, improved odour recognition memory performance, and enhanced spontaneous alternation in the T-maze. In addition, Dao(-/-) mice displayed increased anxiety-like behaviour in five tests of approach/avoidance conflict: the open field test, elevated plus maze, successive alleys, light/dark box and novelty-suppressed feeding. Despite evidence of a reciprocal relationship between anxiety and sleep and circadian function in rodents, we found no evidence of sleep or circadian rhythm disruption in Dao(-/-) mice. Overall, our observations are consistent with, and extend, findings in the natural mutant ddY/Dao(-) line. These data add to a growing body of preclinical evidence linking the inhibition, inactivation or deletion of DAO with enhanced cognitive performance. Our results have implications for the development of DAO inhibitors as therapeutic agents.

Prototypical anxiolytics do not reduce anxiety-like behavior in the open field in C57BL/6J mice

Understanding and effectively treating anxiety disorders are a challenge for both scientists and clinicians. Despite a variety of available therapies, the efficacy of current treatments is still not optimal and adverse side effects can result in non-compliance. Animal models have been useful for studying the underlying biology of anxiety and assessing the anxiolytic properties of potential therapeutics. The open field (OF) is a commonly used assay of anxiety-like behavior. The OF was developed and validated in rats and then transferred to use in the mouse with only limited validation. The present study tests the efficacy of prototypical benzodiazepine anxiolytics, chlordiazepoxide (CDP) and diazepam (DZ), for increasing center time in the OF in C57BL/6J (B6) mice. Multiple doses of CDP and DZ did not change time spent in the center of the OF. Increasing illumination in the OF did not alter these results. The non-benzodiazepine anxiolytic, buspirone (BUSP) also failed to increase center time in the OF while the anxiogenic meta-chlorophenylpiperazine (mCPP) increased center time. Additional inbred mouse strains, BALB/cJ (BALB) and DBA/2J (D2) did not show any change in center time in response to CDP. Moreover, evaluation of CDP in B6 mice in the elevated plus maze (EPM), elevated zero maze (EZM) and light dark assay (LD) did not reveal changes in anxiety-like behavior while stress-induced hyperthermia (SIH) was decreased by DZ. Pharmacokinetic (PK) studies suggest that adequate CDP is present to induce anxiolysis. We conclude that the measure of center time in the OF does not show predictive validity for anxiolysis in these inbred mouse strains.

Postnatal day 2 to 11 constitutes a 5-HT-sensitive period impacting adult mPFC function

Early-life serotonin [5-hydroxytryptamine (5-HT)] signaling modulates brain development, which impacts adult behavior, but 5-HT-sensitive periods, neural substrates, and behavioral consequences remain poorly understood. Here we identify the period ranging from postnatal day 2 (P2) to P11 as 5-HT sensitive, with 5-HT transporter (5-HTT) blockade increasing anxiety- and depression-like behavior, and impairing fear extinction learning and memory in adult mice. Concomitantly, P2-P11 5-HTT blockade causes dendritic hypotrophy and reduced excitability of infralimbic (IL) cortex pyramidal neurons that normally promote fear extinction. By contrast, the neighboring prelimbic (PL) pyramidal neurons, which normally inhibit fear extinction, become more excitable. Excitotoxic IL but not PL lesions in adult control mice reproduce the anxiety-related phenotypes. These findings suggest that increased 5-HT signaling during P2-P11 alters adult mPFC function to increase anxiety and impair fear extinction, and imply a differential role for IL and PL neurons in regulating affective behaviors. Together, our results support a developmental mechanism for the etiology and pathophysiology of affective disorders and fear-related behaviors.

Tests of unconditioned anxiety - pitfalls and disappointments

The plus-maze, the light-dark box and the open-field are the main current tests of unconditioned anxiety for mice and rats. Despite their disappointing achievements, they remain as popular as ever and seem to play an important role in an ever-growing demand for behavioral phenotyping and drug screening. Numerous reviews have repeatedly reported their lack of consistency and reliability but they failed to address the core question of whether these tests do provide unequivocal measures of fear-induced anxiety, that these measurements are not confused with measures of fear-induced avoidance or natural preference responses - i.e. discriminant validity. In the present report, I examined numerous issues that undermine the validity of the current tests, and I highlighted various flaws in the aspects of these tests and the methodologies pursued. This report concludes that the evidence in support of the validity of the plus-maze, the light/dark box and the open-field as anxiety tests is poor and methodologically questionable.

Assessment of mouse anxiety-like behavior in the light-dark box and open-field arena: role of equipment and procedure

Light-dark box and open field are conventional tests for assessment of anxiety-like behavior in the laboratory mice, based on approach-avoidance conflict. However, except the basic principles, variations in the equipment and procedures are very common. Therefore, contribution of certain methodological issues in different settings was investigated. Three inbred strains (C57BL/6, 129/Sv, DBA/2) and one outbred stock (ICR) of mice were used in the experiments. An effect of initial placement of mice either in the light or dark compartment was studied in the light-dark test. Moreover, two tracking systems were applied - position of the animals was detected either by infrared sensors in square box (1/2 dark) or by videotracking in rectangular box (1/3 dark). Both approaches revealed robust and consistent strain differences in the exploratory behavior. In general, C57BL/6 and ICR mice showed reduced anxiety-like behavior as compared to 129/Sv and DBA/2 strains. However, the latter two strains differed markedly in their behavior. DBA/2 mice displayed high avoidance of the light compartment accompanied by thigmotaxis, whereas the hypoactive 129 mice spent a significant proportion of time in risk-assessment behavior at the opening between two compartments. Starting from the light side increased the time spent in the light compartment and reduced the latency to the first transition. In the open field arena, black floor promoted exploratory behavior - increased time and distance in the center and increased rearing compared to white floor. In conclusion, modifications of the apparatus and procedure had significant effects on approach-avoidance behavior in general whereas the strain rankings remained unaffected.

Microglia are polarized to M1 type in high-anxiety inbred mice in response to lipopolysaccharide challenge

Immune activation in the brain has been shown to contribute to neurodevelopmental and pathological progression of mental disorders, and microglia play a central role in these processes. But how genetic predisposition and environmental risk factors may act in combination to affect microglial activation and the underlying molecular mechanisms are largely unclear. In this work, we studied the inflammatory profile of microglia across four inbred strains of mice with different anxiety traits: C57BL/6J, FVB/N, DBA/2J, and 129S2/Sv. Importantly, we found that a high-anxiety strain, naïve DBA/2J mice, had significantly more M1 (MHCII(+)CD206(-))-polarized microglia, whereas another high-anxiety strain, naïve 129S2/Sv mice, expressed significantly more activated (MHCII(+)) perivascular macrophages than the other strains. After a systemic LPS challenge, polarization to M1 microglia in DBA/2J and 129S2/Sv mice was even more prominent than in C57BL/6J and FVB/N mice, and was correlated with their anxiety-like behaviors. Macrophage M1/M2 polarization in the spleen showed a similar pattern in DBA/2J and 129S2/Sv mice in response to LPS stimulation. Furthermore, DBA/2J mice expressed higher mRNA levels of Il1b, Il6, and Tnf, and higher Nos2/Arg1 ratio but lower Chi3l3 level in the hypothalamus before and after LPS stimulation, respectively. In comparison, 129S1/Sv, a sibling line of 129S2/Sv, expressed significantly higher levels of other immune-related genes in the brain. We further discovered a group of myeloid transcription factors that may underpin the strain-specific differences in microglial activation. We conclude that proinflammatory microglial activation reflects anxiety traits in mice, especially after a peripheral innate immune challenge. Our work sheds new light in understanding the potential molecular mechanisms of stress-induced microglial activation and polarization.

Anxiolytic-like effects of antisauvagine-30 in mice are not mediated by CRF2 receptors

The role of brain corticotropin-releasing factor type 2 (CRF₂) receptors in behavioral stress responses remains controversial. Conflicting findings suggest pro-stress, anti-stress or no effects of impeding CRF₂ signaling. Previous studies have used antisauvagine-30 as a selective CRF₂ antagonist. The present study tested the hypotheses that 1) potential anxiolytic-like actions of intracerebroventricular (i.c.v.) administration of antisauvagine-30 also are present in mice lacking CRF₂ receptors and 2) potential anxiolytic-like effects of antisauvagine-30 are not shared by the more selective CRF₂ antagonist astressin₂-B. Cannulated, male CRF₂ receptor knockout (n = 22) and wildtype littermate mice (n = 21) backcrossed onto a C57BL/6J genetic background were tested in the marble burying, elevated plus-maze, and shock-induced freezing tests following pretreatment (i.c.v.) with vehicle, antisauvagine-30 or astressin₂-B. Antisauvagine-30 reduced shock-induced freezing equally in wildtype and CRF₂ knockout mice. In contrast, neither astressin₂-B nor CRF₂ genotype influenced shock-induced freezing. Neither CRF antagonist nor CRF₂ genotype influenced anxiety-like behavior in the plus-maze or marble burying tests. A literature review showed that the typical antisauvagine-30 concentration infused in previous intracranial studies (∼1 mM) was 3 orders greater than its IC₅₀ to block CRF₁-mediated cAMP responses and 4 orders greater than its binding constants (K_d, K_i) for CRF₁ receptors. Thus, increasing, previously used doses of antisauvagine-30 also exert non-CRF₂-mediated effects, perhaps via CRF₁. The results do not support the hypothesis that brain CRF₂ receptors tonically promote anxiogenic-like behavior. Utilization of CRF₂ antagonists, such as astressin₂-B, at doses that are more subtype-selective, can better clarify the significance of brain CRF₂ systems in stress-related behavior.

Effects of Chronic D-Serine Elevation on Animal Models of Depression and Anxiety-Related Behavior

NMDA receptors are activated after binding of the agonist glutamate to the NR2 subunit along with a co-agonist, either L-glycine or D-serine, to the NR1 subunit. There is substantial evidence to suggest that D-serine is the most relevant co-agonist in forebrain regions and that alterations in D-serine levels contribute to psychiatric disorders. D-serine is produced through isomerization of L-serine by serine racemase (Srr), either in neurons or in astrocytes. It is released by astrocytes by an activity-dependent mechanism involving secretory vesicles. In the present study we generated transgenic mice (SrrTg) expressing serine racemase under a human GFAP promoter. These mice were biochemically and behaviorally analyzed using paradigms of anxiety, depression and cognition. Furthermore, we investigated the behavioral effects of long-term administration of D-serine added to the drinking water. Elevated brain D-serine levels in SrrTg mice resulted in specific behavioral phenotypes in the forced swim, novelty suppression of feeding and olfactory bulbectomy paradigms that are indicative of a reduced proneness towards depression-related behavior. Chronic dietary D-serine supplement mimics the depression-related behavioral phenotype observed in SrrTg mice. Our results suggest that D-serine supplementation may improve mood disorders.

Regional mRNA expression of GABAergic receptor subunits in brains of C57BL/6J and 129P3/J mice: strain and heroin effects

C57BL/6J and 129 substrains of mice are known to differ in their basal levels of anxiety and behavioral response to drugs of abuse. We have previously shown strain differences in heroin-induced conditioned place preference (CPP) between C57BL/6J (C57) and 129P3/J (129) mice, and in the regional expression of several receptor and peptide mRNAs. In this study, we examined the contribution of the GABAergic system in the cortex, nucleus accumbens (NAc), caudate putamen (CPu) and the region containing the substantia nigra and ventral tegmental area (SN/VTA) to heroin reward by measuring mRNA levels of 7 of the most commonly expressed GABA-A receptor subunits, and both GABA-B receptor subunits, in these same mice following saline (control) or heroin administration in a CPP design. Using real-time PCR, we studied the effects of strain and heroin administration on GABA-A α1, α2, α3, β2, and γ2 subunits, which typically constitute synaptic GABA-A receptors, GABA-A α4 and δ subunits, which typically constitute extrasynaptic GABA-A receptors, and GABA-B R1 and R2 subunits. In saline-treated animals, we found an experiment-wise significant strain difference in GABA-Aα2 mRNA expression in the SN/VTA. Point-wise significant strain differences were also observed in GABA-Aα2, GABA-Aα3, and GABA-Aα4 mRNA expression in the NAc, as well as GABA-BR2 mRNA expression in the NAc and CPu, and GABA-BR1 mRNA expression in the cortex. For all differences, 129 mice had higher mRNA expression compared to C57 animals, with the exception of GABA-BR1 mRNA in the cortex where we observed lower levels in 129 mice. Therefore, it may be possible that known behavioral differences between these two strains are, in part, due to differences in their GABAergic systems. While we did not find heroin dose-related changes in mRNA expression levels in C57 mice, we did observe dose-related differences in 129 mice. These results may relate to our earlier behavioral finding that 129 mice are hyporesponsive to the rewarding effects of heroin.

Distinct behavioral phenotypes in male mice lacking the thyroid hormone receptor α1 or β isoforms

Thyroid hormones influence both neuronal development and anxiety via the thyroid hormone receptors (TRs). The TRs are encoded by two different genes, TRα and TRβ. The loss of TRα1 is implicated in increased anxiety in males, possibly via a hippocampal increase in GABAergic activity. We compared both social behaviors and two underlying and related non-social behaviors, state anxiety and responses to acoustic and tactile startle in the gonadally intact TRα1 knockout (α1KO) and TRβ (βKO) male mice to their wild-type counterparts. For the first time, we show an opposing effect of the two TR isoforms, TRα1 and TRβ, in the regulation of state anxiety, with α1 knockout animals (α1KO) showing higher levels of anxiety and βKO males showing less anxiety compared to respective wild-type mice. At odds with the increased anxiety in non-social environments, α1KO males also show lower levels of responsiveness to acoustic and tactile startle stimuli. Consistent with the data that T4 is inhibitory to lordosis in female mice, we show subtly increased sex behavior in α1KO male mice. These behaviors support the idea that TRα1 could be inhibitory to ERα driven transcription that ultimately impacts ERα driven behaviors such as lordosis. The behavioral phenotypes point to novel roles for the TRs, particularly in non-social behaviors such as state anxiety and startle.

5-HT2 ligands in the treatment of anxiety and depression

INTRODUCTION

One third of depressed patients do not respond adequately to conventional antidepressants including the selective serotonin reuptake inhibitors (SSRIs). Therefore, multi-target drugs or augmentation strategies have been developed for the management of SSRIs-resistant patients. In this context, the 5-HT(2) receptor subtypes represent promising targets but their precise roles have yet to be determined.

AREAS COVERED

The aim of this review is to shed some light on the preclinical evidence supporting the use of 5-HT(2A) and/or 5-HT(2C) receptor antagonists such as antipsychotics, as potential effective adjuncts in SSRIs-resistant depression. This review synthesizes the current literature about the behavioral, electrophysiological and neurochemical effects of 5-HT(2) receptors ligands on the monoaminergic systems but also on adult hippocampal neurogenesis.

EXPERT OPINION

Although studies support the hypothesis that the inactivation of 5-HT(2A) and/or 5-HT(2C) receptors might be of interest to reinforce different facets of the therapeutic activity of SSRIs, this pharmacological strategy remains debatable notably because of the lack of chronic data in relevant animal models. Conversely, emerging evidence suggests that the activation of 5-HT(2B) receptor is required for antidepressant-like activity, opening the way to new therapeutic approaches. However, the potential risks related to the enhancement of monoaminergic neurotransmissions could represent a major concern.

Differential effects of diazepam and MPEP on habituation and neuro-behavioural processes in inbred mice

Background

Previous studies have demonstrated a profound lack of habituation in 129P3 mice compared to the habituating, but initially more anxious, BALB/c mice. The present study investigated whether this non-adaptive phenotype of 129P3 mice is primarily based on anxiety-related characteristics.

Methods

To test this hypothesis and extend our knowledge on the behavioural profile of 129P3 mice, the effects of the anxiolyticdiazepam (1, 3 and 5 mg/kg) and the putative anxiolytic metabotropic glutamate receptor 5 (mGlu5R) antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP, 3, 10 and 30 mg/kg) treatment on within-trial (intrasession) habituation, object recognition (diazepam: 1 mg/kg; MPEP 10 mg/kg) and on the central-nervous expression of the immediate early gene c-Fos (diazepam: 1 mg/kg; MPEP 10 mg/kg) were investigated.

Results

Behavioural findings validated the initially high, but habituating phenotype of BALB/c mice, while 129P3 mice were characterized by impaired intrasession habituation. Diazepam had an anxiolytic effect in BALB/c mice, while in higher doses caused behavioural inactivity in 129P3 mice. MPEP revealed almost no anxiolytic effects on behaviour in both strains, but reduced stress-induced corticosterone responses only in 129P3 mice. These results were complemented by reduced expression of c-Fos after MPEP treatment in brain areas related to emotional processes, and increased c-Fos expression in higher integrating brain areas such as the prelimbic cortex compared to vehicle-treated 129P3 mice.

Conclusions

These results suggest that the strain differences observed in (non)adaptive anxiety behaviour are at least in part mediated by differences in gamma-aminobutyric acid- A and mGluR5 mediated transmission.

Differential long term effects of early diisopropylfluorophosphate exposure in Balb/C and C57Bl/J6 mice

The long-term effect of postnatal administration of a sub-toxic dose of the irreversible acetylcholinesterase inhibitor diisopropylfluorophosphate (DFP) on depression and anxiety behavior was compared in two strains of inbred mice. C57BL/6J and Balb/C mice were injected for 7 consecutive days with either 1 mg/kg DFP or saline on postnatal days 14-20. Mice were tested at age 3-4 months for initial and learned anxiety using double-exposure elevated plus maze and to a novel enclosed environment. Depression was assayed using the sweet preference model of anhedonia and the forced swim test for despair. Postnatal DFP pretreatment led to less activity and more immobility in the elevated plus maze in both mouse strains in the first session. The effect was attenuated in the second session in the C57BL/6J strain but not the Balb/C strain. DFP did not affect the sweet preference or forced swim tests, suggesting a dissociation between the long-term effects of DFP on immobility in the context of approach-avoidance conflict (elevated plus maze) versus despair (forced swim).

The gene or not the gene--that is the question: understanding the genetically engineered mouse phenotype

Embryonic stem cells have had a significant impact on understanding gene function and gene interactions through the use of genetically engineered mice. However, the genetic context (ie, mouse strain) in which these modifications in alleles are made may have a considerable effect on the phenotypic changes identified in these mice. In addition, tissue- and time-specific gene expression systems may generate unanticipated outcomes. This article discusses the history of embryonic stem cells, reviews how mouse strain can affect phenotype (using specific examples), and examines some of the caveats of conditional gene expression systems.

Psychomotor stimulant effects of cocaine in rats and 15 mouse strains

Relative to intravenous drug self-administration, locomotor activity is easier to measure with high throughput, particularly in mice. Therefore its potential to predict differences in self-administration between genotypes (e.g., targeted mutations, recombinant inbred strains) is appealing, but such predictive value is unverified. The main goal of this study was to evaluate the utility of the locomotor assay for accurately predicting differences in cocaine self-administration. A second goal was to evaluate any correlation between activity in a novel environment, and cocaine-induced hyperactivity, between strains. We evaluated locomotor activity in male and female Sprague-Dawley rats and 15 mouse strains (129S1/SvImJ, 129S6/SvEvTac, 129X1/SvJ, A/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/EiJ, DBA/2J, FVB/NJ, SJL/J, SPRET/EiJ, and outbred Swiss Webster and CD-1/ICR), as well as cocaine self-administration in BALB substrains. All but BALB/cJ mice showed locomotor habituation and significant cocaine-induced hyperactivity. BALB/cJ mice also failed to self-administer cocaine. BALB/cByJ mice showed modest locomotor habituation, cocaine-induced locomotion, and cocaine self-administration. As previously reported, female rats showed greater cocaine-induced locomotion than males, but this was only observed in one of 15 mouse strains (FVB/NJ), and the reverse was observed in two strains (129X1/SvJ, BALB/cByJ). The intriguing phenotype of the BALB/cJ strain may indicate some correlation between all-or-none locomotion in a novel environment, and stimulant and reinforcing effects of cocaine. However, neither novelty- nor cocaine-induced activity offered a clear prediction of relative reinforcing effects among strains. Additionally, these results should aid in selecting mouse strains for future studies in which relative locomotor responsiveness to psychostimulants is a necessary consideration.

The clinical implications of mouse models of enhanced anxiety

Mice are increasingly overtaking the rat model organism in important aspects of anxiety research, including drug development. However, translating the results obtained in mouse studies into information that can be applied in clinics remains challenging. One reason may be that most of the studies so far have used animals displaying 'normal' anxiety rather than 'psychopathological' animal models with abnormal (elevated) anxiety, which more closely reflect core features and sensitivities to therapeutic interventions of human anxiety disorders, and which would, thus, narrow the translational gap. Here, we discuss manipulations aimed at persistently enhancing anxiety-related behavior in the laboratory mouse using phenotypic selection, genetic techniques and/or environmental manipulations. It is hoped that such models with enhanced construct validity will provide improved ways of studying the neurobiology and treatment of pathological anxiety. Examples of findings from mouse models of enhanced anxiety-related behavior will be discussed, as well as their relation to findings in anxiety disorder patients regarding neuroanatomy, neurobiology, genetic involvement and epigenetic modifications. Finally, we highlight novel targets for potential anxiolytic pharmacotherapeutics that have been established with the help of research involving mice. Since the use of psychopathological mouse models is only just beginning to increase, it is still unclear as to the extent to which such approaches will enhance the success rate of drug development in translating identified therapeutic targets into clinical trials and, thus, helping to introduce the next anxiolytic class of drugs.

Automated three-chambered social approach task for mice

Autism is diagnosed by three major symptom categories: unusual reciprocal social interactions, impaired communication, and repetitive behaviors with restricted interests. Direct social approach in mice has strong face validity to simple social approach behaviors in humans, which are frequently impaired in autism. This unit presents a basic protocol for a standardized, high-throughput social approach test for assaying mouse sociability. Our automated three-chambered social approach task quantifies direct social approach behaviors when a subject mouse is presented with the choice of spending time with either a novel mouse or a novel object. Sociability is defined as the subject mouse spending more time in the chamber containing the novel target mouse than in the chamber containing the inanimate novel object. The Basic Protocol describes procedures for testing one subject at a time in a single apparatus. A Support Protocol addresses data collection.

Metabolomic analysis of normal (C57BL/6J, 129S1/SvImJ) mice by gas chromatography-mass spectrometry: detection of strain and gender differences

Previous studies have shown that the C57 and 129 strains of mice display marked differences in behavioural performance, neuroanatomy, neurochemistry and synaptic plasticity. However, few metabolomic studies of their biofluids have been performed. As part of a series of metabolic phenotyping, the effects of gender and strain upon serum metabolite composition and variation are examined in this study using gas chromatography-mass spectrometry (GC-MS) in normal C57BL/6J and 129S1/SvImJ strains of mice. The 129S1/SvImJ strain is phenotypically distinct from the C57BL/6J strain and characteristic metabotypes are produced for both male and female mice of each strain. These data demonstrate that the C57BL/6J and 129S1/SvImJ strains of mice show a wide range of metabolic differences across glycine, serine and threonine metabolism; valine, leucine and isoleucine biosynthesis; and tricarboxylic acid cycle pathways. Remarkably, the concentration of glyceric acid in the 129S1/SvImJ strain is significantly increased compared to the C57BL/6J mouse strain, reflecting important considerations for studies that use the 129S1/SvImJ mouse as the human d-glycericaciduria model. We infer that a deficiency of d-glycerate kinase would explain such a glyceric acid accumulation in the 129S1/SvImJ strain. More importantly, this differential metabolite level data provide insight into specific metabolic pathways and lay the groundwork for integrated studies of the mouse models.

5-HT2C receptor activation prevents stress-induced enhancement of brain 5-HT turnover and extracellular levels in the mouse brain: modulation by chronic paroxetine treatment

Stress is known to activate the central 5-hydroxytryptamine (5-HT) system, and this is probably part of a coping response involving several 5-HT receptors. Although 5-HT(2C) receptors are well known to be implicated in anxiety, their participation in stress-induced changes had not been investigated in parallel at both behavioral and neurochemical levels. We show here that the preferential 5-HT(2C) receptor agonist, m-chlorophenylpiperazine, as well as restraint stress increased anxiety in the mouse social interaction test. The selective 5-HT(2C) receptor antagonist, SB 242,084, prevented both of these anxiogenic effects. Restraint stress increased 5-HT turnover in various brain areas, and this effect was prevented by the 5-HT(2B/2C) receptor agonist RO 60-0175 (1 mg/kg), but not the preferential 5-HT(2A) agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (1 mg/kg), and in contrast potentiated by SB 242,084 (1 mg/kg), which also blocked the effect of RO 60-0175. Using microdialysis, RO 60-0175 was shown to inhibit cortical 5-HT overflow in stressed mice when 5-HT reuptake was blocked locally. Chronic paroxetine prevented both the anxiogenic effect of m-chlorophenylpiperazine and the inhibitory effect of RO 60-0175 on locomotion and stress-induced increase in 5-HT turnover. The anxiolytic action of chronic paroxetine might be associated with an enhancement of 5-HT neurotransmission caused by a decreased 5-HT(2C) receptor-mediated inhibition of stress-induced increase in 5-HT release.

Fear learning and extinction are linked to neuronal plasticity through Rin1 signaling

The amygdala is known to have a crucial role in both the acquisition and extinction of conditioned fear, but the physiological changes and biochemical mechanisms underlying these forms of learning are only partly understood. The Ras effector Rin1 activates Abl tyrosine kinases and Rab5 GTPases and is highly expressed in mature neurons of the telencephalon including the amygdala, where it inhibits the acquisition of fear memories (Rin1(-/-) mice show enhanced learning of conditioned fear). Here we report that Rin1(-/-) mice exhibit profound deficits in both latent inhibition and fear extinction, suggesting a critical role for Rin1 in gating the acquisition and persistence of cue-dependent fear conditioning. Surprisingly, we also find that depotentiation, a proposed cellular mechanism of extinction, is enhanced at lateral-basolateral (LA-BLA) amygdaloid synapses in Rin1(-/-) mice. Inhibition of a single Rin1 downstream effector pathway, the Abl tyrosine kinases, led to reduced amygdaloid depotentiation, arguing that proper coordination of Abl and Rab5 pathways is critical for Rin1-mediated effects on plasticity. While demonstrating a correlation between amygdala plasticity and fear learning, our findings argue against models proposing a direct causative relationship between amygdala depotentiation and fear extinction. Taken together, the behavior and physiology of Rin1(-/-) mice provide new insights into the regulation of memory acquisition and maintenance. In addition, Rin1(-/-) mice should prove useful as a model for pathologies marked by enhanced fear acquisition and retention, such as posttraumatic stress disorder.

Impaired sociability and cognitive function in Nrcam-null mice

NRCAM (Neuronal Cell Adhesion Molecule) has an important role in axonal guidance and the organization of neural circuitry during brain development. Association analyses in human populations have identified NRCAM as a candidate gene for autism susceptibility. In the present study, we evaluated Nrcam-null mice for sociability, social novelty preference, and reversal learning as a model for the social deficits, repetitive behavior, and cognitive rigidity characteristic of autism. Prepulse inhibition of acoustic startle responses was also measured, to reflect sensorimotor-gating deficits in autism spectrum disorders. Assays for anxiety-like behavior in an elevated plus maze and open field, motor coordination, and olfactory ability in a buried food test were conducted to provide control measures for the interpretation of results. Overall, the loss of Nrcam led to behavioral alterations in sociability, acquisition of a spatial task, and reversal learning, dependent on sex. In comparison to male wild type mice, male Nrcam-null mutants had significantly decreased sociability in a three-chambered choice task. Low sociability in the male null mutants was not associated with changes in anxiety-like behavior, activity, or motor coordination. Male, but not female, Nrcam-null mice had small decreases in prepulse inhibition. Nrcam deficiency in female mice led to impaired acquisition of spatial learning in the Morris water maze task. Reversal learning deficits were observed in both male and female Nrcam-null mice. These results provide evidence that NRCAM mediates domains of function relevant to symptoms observed in autism.

Anti-depressant and anxiolytic like behaviors in PKCI/HINT1 knockout mice associated with elevated plasma corticosterone level

BACKGROUND

Protein kinase C interacting protein (PKCI/HINT1) is a small protein belonging to the histidine triad (HIT) family proteins. Its brain immunoreactivity is located in neurons and neuronal processes. PKCI/HINT1 gene knockout (KO) mice display hyper-locomotion in response to D-amphetamine which is considered a positive symptom of schizophrenia in animal models. Postmortem studies identified PKCI/HINT1 as a candidate molecule for schizophrenia and bipolar disorder. We investigated the hypothesis that the PKCI/HINT1 gene may play an important role in regulating mood function in the CNS. We submitted PKCI/HINT1 KO mice and their wild type (WT) littermates to behavioral tests used to study anti-depressant, anxiety like behaviors, and goal-oriented behavior. Additionally, as many mood disorders coincide with modifications of hypothalamic-pituitary-adrenal (HPA) axis function, we assessed the HPA activity through measurement of plasma corticosterone levels.

RESULTS

Compared to the WT controls, KO mice exhibited less immobility in the forced swim (FST) and the tail suspension (TST) tests. Activity in the TST tended to be attenuated by acute treatment with valproate at 300 mg/kg in KO mice. The PKCI/HINT1 KO mice presented less thigmotaxis in the Morris water maze and spent progressively more time in the lit compartment in the light/dark test. In a place navigation task, KO mice exhibited enhanced acquisition and retention. Furthermore, the afternoon basal plasma corticosterone level in PKCI/HINT1 KO mice was significantly higher than in the WT.

CONCLUSION

PKCI/HINT1 KO mice displayed a phenotype of behavioral and endocrine features which indicate changes of mood function, including anxiolytic-like and anti-depressant like behaviors, in conjunction with an elevated corticosterone level in plasma. These results suggest that the PKCI/HINT 1 gene could be important for the mood regulation function in the CNS.

Hypothalamic-pituitary-adrenal axis abnormalities in response to deletion of 11beta-HSD1 is strain-dependent

Inter-individual differences in hypothalamic-pituitary-adrenal (HPA) axis activity underlie differential vulnerability to neuropsychiatric and metabolic disorders, although the basis of this variation is poorly understood. 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) has previously been shown to influence HPA axis activity. 129/MF1 mice null for 11beta-HSD1 (129/MF1 HSD1(-/-)) have greatly increased adrenal gland size and altered HPA activity, consistent with reduced glucocorticoid negative feedback. On this background, concentrations of plasma corticosterone and adrenocorticotrophic hormone (ACTH) were elevated in unstressed mice, and showed a delayed return to baseline after stress in HSD1-null mice with reduced sensitivity to exogenous glucocorticoid feedback compared to same-background genetic controls. In the present study, we report that the genetic background can dramatically alter this pattern. By contrast to HSD1(-/-) mice on a 129/MF1 background, HSD1(-/-) mice congenic on a C57Bl/6J background have normal basal plasma corticosterone and ACTH concentrations and exhibit normal return to baseline of plasma corticosterone and ACTH concentrations after stress. Furthermore, in contrast to 129/MF1 HSD1(-/-) mice, C57Bl/6J HSD1(-/-) mice have increased glucocorticoid receptor expression in areas of the brain involved in glucocorticoid negative feedback (hippocampus and paraventricular nucleus), suggesting this may be a compensatory response to normalise feedback control of the HPA axis. In support of this hypothesis, C57Bl/6J HSD1(-/-) mice show increased sensitivity to dexamethasone-mediated suppression of peak corticosterone. Thus, although 11beta-HSD1 appears to contribute to regulation of the HPA axis, the genetic background is crucial in governing the response to (and hence the consequences of) its loss. Similar variations in plasticity may underpin inter-individual differences in vulnerability to disorders associated with HPA axis dysregulation. They also indicate that 11beta-HSD1 inhibition does not inevitably activate the HPA axis.

Behavioral phenotyping of neuropeptide S receptor knockout mice

Central administration of neuropeptide S (NPS) in rodents induces arousal and prolonged wakefulness as well as anxiolytic-like effects. NPS has also been implicated in modulation of cognitive functions and energy homeostasis. Here we present a comprehensive phenotypical analysis of mice carrying a targeted mutation in the NPS receptor (NPSR) gene. NPSR knockout mice were found to exhibit reduced exploratory activity when challenged with a novel environment, which might indicate attenuated arousal. We also observed attenuated late peak wheel running activity in NPSR knockout mice, representing reduced activity during the subjective evening. These mice also displayed increased anxiety-like behaviors when compared to their wildtype littermates, although analysis of anxiety behaviors was limited by genetic background influences. Unexpectedly, NPSR knockout mice showed enhanced motor performance skills. No phenotypical differences were detected in the forced-swim test, startle habituation and pre-pulse inhibition paradigms. Together, these data indicate that the endogenous NPS system might be involved in setting or maintaining behavioral arousal thresholds and that the NPS system might have other yet undiscovered physiological functions.

Identifying emotional adaptation: behavioural habituation to novelty and immediate early gene expression in two inbred mouse strains

Normal anxiety is an adaptive emotional response. However, when anxiety appears to lack adaptive value, it might be defined as pathological. Adaptation in animals can be assessed for example by changes in behavioural responses over time, i.e. habituation. We hypothesize that non-adaptive anxiety might be reflected by impaired habituation. To test our hypothesis, we repeatedly exposed male mice from two inbred strains to a novel environment, the modified hole board. BALB/cJ mice were found to be initially highly anxious, but subsequently habituated to the test environment. In contrast, 129P3/J mice initially showed less anxiety-related behaviour compared with the BALB/cJ mice but no habituation in anxiety-related behaviour was observed. Notably, anxiety-related behaviour even increased during the experimental period. Complementary, 129P3/J mice did not show habituation in other parameters such as locomotor and exploratory activity, whereas significant changes appeared in these behaviours in BALB/c mice. Finally, the expression of the immediate early gene c-fos differed between the two strains in distinct brain areas, known to regulate the integration of emotional and cognitive processes. These results suggest that 129P3/J mice might be a promising (neuro)-behavioural animal model for non-adaptive, i.e. pathological anxiety.

ABNORMAL BEHAVIORAL ORGANIZATION OF GROOMING IN MICE LACKING THE VITAMIN D RECEPTOR GENE

Vitamin D is a steroid hormone with several important functions in the nervous system. Numerous human and animal data link alterations in the vitamin D system to various behavioral disorders. Grooming is an important element of rodent behavior with a general pattern of cephalocaudal progression (paw licking - nose/face wash - body wash - tail/genitals wash). Here we studied whether genetic ablation of vitamin D nuclear receptors (VDR) in mice may be associated with altered behavioral sequencing of grooming. Overall, VDR null mutant mice showed abnormal grooming, including a higher percentage of "incorrect" transitions and longer duration of "incorrect" grooming (contrary to the cephalocaudal progression); a higher percentage of interrupted grooming bouts; and the atypical regional distribution of grooming (more leg grooming, less body and tail/genitals grooming), compared to their wild-type controls. Grooming of heterozygous mice was similar to the wild-type group, indicating that abnormal grooming patterning is inherited as a recessive. In contrast, behavioral sequencing of another complex behavior (mating with a female) was unaltered in all three genotypes, suggesting grooming-specific abnormal sequencing in these mutant mice. Our results suggest that a neurosteroid vitamin D and VDR may play an important role in controlling sequencing of grooming in mice, and further confirm the important role of the vitamin D system and VDR in the regulation of behavior.