Hypolocomotion, anxiety and serotonin syndrome-like behavior contribute to the complex phenotype of serotonin transporter knockout mice

Benefits of adversity?! How life history affects the behavioral profile of mice varying in serotonin transporter genotype

Behavioral profiles are influenced by both positive and negative experiences as well as the genetic disposition. Traditionally, accumulating adversity over lifetime is considered to predict increased anxiety-like behavior (“allostatic load”). The alternative “mismatch hypothesis” suggests increased levels of anxiety if the early environment differs from the later-life environment. Thus, there is a need for a whole-life history approach to gain a deeper understanding of how behavioral profiles are shaped. The aim of this study was to elucidate the effects of life history on the behavioral profile of mice varying in serotonin transporter (5-HTT) genotype, an established mouse model of increased anxiety-like behavior. For this purpose, mice grew up under either adverse or beneficial conditions during early phases of life. In adulthood, they were further subdivided so as to face a situation that either matched or mismatched the condition experienced so far, resulting in four different life histories. Subsequently, mice were tested for their anxiety-like and exploratory behavior. The main results were: (1) Life history profoundly modulated the behavioral profile. Surprisingly, mice that experienced early beneficial and later escapable adverse conditions showed less anxiety-like and more exploratory behavior compared to mice of other life histories. (2) Genotype significantly influenced the behavioral profile, with homozygous 5-HTT knockout mice displaying highest levels of anxiety-like and lowest levels of exploratory behavior. Our findings concerning life history indicate that the absence of adversity does not necessarily cause lower levels of anxiety than accumulating adversity. Rather, some adversity may be beneficial, particularly when following positive events. Altogether, we conclude that for an understanding of behavioral profiles, it is not sufficient to look at experiences during single phases of life, but the whole life history has to be considered.

Monoamine-sensitive developmental periods impacting adult emotional and cognitive behaviors

Development passes through sensitive periods, during which plasticity allows for genetic and environmental factors to exert indelible influence on the maturation of the organism. In the context of central nervous system development, such sensitive periods shape the formation of neurocircuits that mediate, regulate, and control behavior. This general mechanism allows for development to be guided by both the genetic blueprint as well as the environmental context. While allowing for adaptation, such sensitive periods are also vulnerability windows during which external and internal factors can confer risk to disorders by derailing otherwise resilient developmental programs. Here we review developmental periods that are sensitive to monoamine signaling and impact adult behaviors of relevance to psychiatry. Specifically, we review (1) a serotonin-sensitive period that impacts sensory system development, (2) a serotonin-sensitive period that impacts cognition, anxiety- and depression-related behaviors, and (3) a dopamine- and serotonin-sensitive period affecting aggression, impulsivity and behavioral response to psychostimulants. We discuss preclinical data to provide mechanistic insight, as well as epidemiological and clinical data to point out translational relevance. The field of translational developmental neuroscience has progressed exponentially providing solid conceptual advances and unprecedented mechanistic insight. With such knowledge at hand and important methodological innovation ongoing, the field is poised for breakthroughs elucidating the developmental origins of neuropsychiatric disorders, and thus understanding pathophysiology. Such knowledge of sensitive periods that determine the developmental trajectory of complex behaviors is a necessary step towards improving prevention and treatment approaches for neuropsychiatric disorders.

Serotonergic modulation of zebrafish behavior: towards a paradox

Due to the fish-specific genome duplication event (~320-350 mya), some genes which code for serotonin proteins were duplicated in teleosts; this duplication event was preceded by a reorganization of the serotonergic system, with the appearance of the raphe nuclei (dependent on the isthmus organizer) and prosencephalic nuclei, including the paraventricular and pretectal complexes. With the appearance of amniotes, duplicated genes were lost, and the serotonergic system was reduced to a more complex raphe system. From a comparative point of view, then, the serotonergic system of zebrafish and that of mammals shows many important differences. However, many different behavioral functions of serotonin, as well as the effects of drugs which affect the serotonergic system, seem to be conserved among species. For example, in both zebrafish and rodents acute serotonin reuptake inhibitors (SSRIs) seem to increase anxiety-like behavior, while chronic SSRIs decrease it; drugs which act at the 5-HT1A receptor seem to decrease anxiety-like behavior in both zebrafish and rodents. In this article, we will expose this paradox, reviewing the chemical neuroanatomy of the zebrafish serotonergic system, followed by an analysis of the role of serotonin in zebrafish fear/anxiety, stress, aggression and the effects of psychedelic drugs.

Developmental alterations in anxiety and cognitive behavior in serotonin transporter mutant mice

RATIONALE

A promoter variant of the serotonin transporter (SERT) gene is known to affect emotional and cognitive regulation. In particular, the "short" allelic variant is implicated in the etiology of multiple neuropsychiatric disorders. Heterozygous (SERT(+/-)) and homozygous (SERT(-/-)) SERT mutant mice are valuable tools for understanding the mechanisms of altered SERT levels. Although these genetic effects are well investigated in adulthood, the developmental trajectory of altered SERT levels for behavior has not been investigated.

OBJECTIVES

We assessed anxiety-like and cognitive behaviors in SERT mutant mice in early adolescence and adulthood to examine the developmental consequences of reduced SERT levels. Spine density of pyramidal neurons was also measured in corticolimbic brain regions.

RESULTS

Adult SERT(-/-) mice exhibited increased anxiety-like behavior, but these differences were not observed in early adolescent SERT(-/-) mice. Conversely, SERT(+/-) and SERT(-/-) mice did display higher spontaneous alternation during early adolescence and adulthood. SERT(+/-) and SERT(-/-) also exhibited greater neuronal spine densities in the orbitofrontal but not the medial prefrontal cortices. Adult SERT(-/-) mice also showed an increased spine density in the basolateral amygdala.

CONCLUSIONS

Developmental alterations of the serotonergic system caused by genetic inactivation of SERT can have different influences on anxiety-like and cognitive behaviors through early adolescence into adulthood, which may be associated with changes of spine density in the prefrontal cortex and amygdala. The altered maturation of serotonergic systems may lead to specific age-related vulnerabilities to psychopathologies that develop during adolescence.

Hope for the best or prepare for the worst? Towards a spatial cognitive bias test for mice

Cognitive bias, the altered information processing resulting from the background emotional state of an individual, has been suggested as a promising new indicator of animal emotion. Comparable to anxious or depressed humans, animals in a putatively negative emotional state are more likely to judge an ambiguous stimulus as if it predicts a negative event, than those in positive states. The present study aimed to establish a cognitive bias test for mice based on a spatial judgment task and to apply it in a pilot study to serotonin transporter (5-HTT) knockout mice, a well-established mouse model for the study of anxiety- and depression-related behavior. In a first step, we validated that our setup can assess different expectations about the outcome of an ambiguous stimulus: mice having learned to expect something positive within a maze differed significantly in their behavior towards an unfamiliar location than animals having learned to expect something negative. In a second step, the use of spatial location as a discriminatory stimulus was confirmed by showing that mice interpret an ambiguous stimulus depending on its spatial location, with a position exactly midway between a positive and a negative reference point provoking the highest level of ambiguity. Finally, the anxiety- and depression-like phenotype of the 5-HTT knockout mouse model manifested--comparable to human conditions--in a trend for a negatively distorted interpretation of ambiguous information, albeit this effect was not statistically significant. The results suggest that the present cognitive bias test provides a useful basis to study the emotional state in mice, which may not only increase the translational value of animal models in the study of human affective disorders, but which is also a central objective of animal welfare research.

Transient postnatal fluoxetine leads to decreased brain arachidonic acid metabolism and cytochrome P450 4A in adult mice

Fetal and perinatal exposure to selective serotonin (5-HT) reuptake inhibitors (SSRIs) has been reported to alter childhood behavior, while transient early exposure in rodents is reported to alter their behavior and decrease brain extracellular 5-HT in adulthood. Since 5-HT2A/2C receptor-mediated neurotransmission can involve G-protein coupled activation of cytosolic phospholipase A2 (cPLA2), releasing arachidonic acid (ARA) from synaptic membrane phospholipid, we hypothesized that transient postnatal exposure to fluoxetine would alter brain ARA metabolism in adult mice. Brain ARA incorporation coefficients k* and rates Jin were quantitatively imaged following intravenous [1-(14)C]ARA infusion of unanesthetized adult mice that had been injected daily with fluoxetine (10mg/kg i.p.) or saline during postnatal days P4-P21. Expression of brain ARA metabolic enzymes and other relevant markers also was measured. On neuroimaging, k* and Jin was decreased widely in early fluoxetine- compared to saline-treated adult mice. Of the enzymes measured, cPLA2 activity was unchanged, while Ca(2+)-independent iPLA2 activity was increased. There was a significant 74% reduced protein level of cytochrome P450 (CYP) 4A, which can convert ARA to 20-HETE. Reduced brain ARA metabolism in adult mice transiently exposed to postnatal fluoxetine, and a 74% reduction in CYP4A protein, suggest long-term effects independent of drug presence in brain ARA metabolism, and in CYP4A metabolites. These changes might contribute to reported altered behavior following early SSRI in rodents.

The murine serotonin syndrome - evaluation of responses to 5-HT-enhancing drugs in NMRI mice

In humans, the ingestion of the combination of two or more serotonin (5-HT)-enhancing drugs but also of a single drug in overdose can induce serious adverse effects, which are characteristics of the serotonin syndrome (SS). In mice, acute administration of direct and indirect 5-HT agonists also leads to behavioral and autonomic responses, but in literature different responses are thought to be essential. In order to detect common behavioral SS responses induced by 5-HT-enhancing drugs with different mechanisms of action, we investigated the effects of the 5-HT precursor 5-hydroxy-l-tryptophan (5-HTP), the selective serotonin reuptake inhibitor (SSRI) fluoxetine (FLX), and the monoaminooxidase (MAO) inhibitor tranylcypromine (TCP) in male NMRI mice. The drugs were administered alone or in combination to investigate additive effects or drug potentiation. Moreover, we compared the 5-HT responses to the effects induced by the dopamine, noradrenaline, and cholinergic agonists, apomorphine (APO), atomoxetine (ATO), and oxotremorine (OXO). Our results show that the studied 5-HT-enhancing drugs induced a different number of concomitant responses. The following five responses consistently and dose-dependently occurred in NMRI mice: flat body posture, hindlimb abduction, piloerection, tremor, and decreased rearings. Like in humans, the combination of 5-HT-enhancing drugs leads to a potentiation of drug effects. With the exception of flat body posture the responses are not specific for serotonergic hyperactivity. The findings demonstrate that the SS in NMRI mice is a suitable animal model for preclinical research, if it is taken into account that the spectrum of typical responses to 5-HT enhancing drugs may differ depending on drug and mouse strain and that some responses might be evoked by activation of other transmission systems, too.

Burrowing and nest building behavior as indicators of well-being in mice

The assessment of pain, distress and suffering, as well as evaluation of the efficacy of stress-reduction strategies, is crucial in animal experimentation but can be challenging in laboratory mice. Nest building and burrowing performance, observed in the home cage, have proved to be valuable and easy-to-use tools to assess brain damage or malfunction as well as neurodegenerative diseases. Both behaviors are used as parameters in models of psychiatric disorders or to monitor sickness behavior following infection. Their use has been proposed in more realistic and clinically relevant preclinical models of disease, and reduction of these behaviors seems to be especially useful as an early sign of dysfunction and to monitor disease progression. Finally, both behaviors are reduced by pain and stress. Therefore, in combination with specific disease markers, changes in nest building and burrowing performance may help provide a global picture of a mouse's state, and thus aid monitoring to ensure well-being in animal experimentation.

Differential postpartum sensitivity to the anxiety-modulating effects of offspring contact is associated with innate anxiety and brainstem levels of dopamine beta-hydroxylase in female laboratory rats

In female mammals, the postpartum period involves dramatic shifts in many socioemotional behaviors. This includes a suppression of anxiety-related behaviors that requires recent physical contact with offspring. Factors contributing to differences among females in their susceptibility to the anxiety-modulating effect of offspring contact are unknown, but could include their innate anxiety and brain monoaminergic activity. Anxiety behavior was assessed in a large group of nulliparous female rats and the least-anxious and most-anxious tertiles were mated. Anxiety was assessed again postpartum after females were permitted or prevented from contacting their offspring 4 h before testing. Levels of dopamine β-hydroxylase (DBH, norepinephrine synthesizing enzyme) and tryptophan hydroxylase-2 (TPH2, serotonin synthesizing enzyme) were measured in the brainstem and dorsal raphe, respectively. It was found that anxiety-related behavior in the two groups did not differ when dams were permitted contact with offspring before testing. Removal of the offspring before testing, however, differentially affected anxiety based on dams' innate anxiety. Specifically, dams reverted back to their pre-mating levels of anxiety such that offspring removal slightly increased anxiety in the most-anxious females but greatly lowered anxiety in the least-anxious females. This reduction in anxiety in the least-anxious females after litter removal was associated with lower brainstem DBH. There was no relationship between females' anxiety and dorsal raphe TPH2. Thus, a primary effect of recent contact with offspring on anxiety-related behavior in postpartum rats is to shift females away from their innate anxiety to a more moderate level of responding. This effect is particularly true for females with the lowest anxiety, may be mediated by central noradrenergic systems, and has implications for their ability to attend to their offspring.

Mutations in monoamine oxidase (MAO) genes in mice lead to hypersensitivity to serotonin-enhancing drugs: implications for drug side effects in humans

A possible side effect of serotonin-enhancing drugs is the serotonin syndrome, which can be lethal. Here we examined possible hypersensitivity to two such drugs, the serotonin precursor 5-hydroxy-L-tryptophan (5-HTP) and the atypical opioid tramadol, in mice lacking the genes for both monoamine oxidase A (MAOA) and MAOB. MAOA/B-knockout (KO) mice displayed baseline serotonin syndrome behaviors, and these behavioral responses were highly exaggerated following 5-HTP or tramadol versus baseline and wild-type (WT) littermates. Compared with MAOA/B-WT mice, baseline tissue serotonin levels were increased ∼2.6-3.9-fold in MAOA/B-KO mice. Following 5-HTP, serotonin levels were further increased ∼4.5-6.2-fold in MAOA/B-KO mice. These exaggerated responses are in line with the exaggerated responses following serotonin-enhancing drugs that we previously observed in mice lacking the serotonin transporter (SERT). These findings provide a second genetic mouse model suggestive of possible human vulnerability to the serotonin syndrome in individuals with lesser-expressing MAO or SERT polymorphisms that confer serotonergic system changes.

5-HTT deficiency affects neuroplasticity and increases stress sensitivity resulting in altered spatial learning performance in the Morris water maze but not in the Barnes maze

The purpose of this study was to evaluate whether spatial hippocampus-dependent learning is affected by the serotonergic system and stress. Therefore, 5-HTT knockout (-/-), heterozygous (+/-) and wildtype (+/+) mice were subjected to the Barnes maze (BM) and the Morris water maze (WM), the latter being discussed as more aversive. Additionally, immediate early gene (IEG) expression, hippocampal adult neurogenesis (aN), and blood plasma corticosterone were analyzed.

While the performance of 5-HTT-/- mice in the BM was undistinguishable from both other genotypes, they performed worse in the WM. However, in the course of the repeated WM trials 5-HTT-/- mice advanced to wildtype level. The experience of a single trial of either the WM or the BM resulted in increased plasma corticosterone levels in all genotypes. After several trials 5-HTT-/- mice exhibited higher corticosterone concentrations compared with both other genotypes in both tests. Corticosterone levels were highest in 5-HTT-/- mice tested in the WM indicating greater aversiveness of the WM and a greater stress sensitivity of 5-HTT deficient mice.

Quantitative immunohistochemistry in the hippocampus revealed increased cell counts positive for the IEG products cFos and Arc as well as for proliferation marker Ki67 and immature neuron marker NeuroD in 5-HTT-/- mice compared to 5-HTT+/+ mice, irrespective of the test. Most differences were found in the suprapyramidal blade of the dentate gyrus of the septal hippocampus. Ki67-immunohistochemistry revealed a genotype x environment interaction with 5-HTT genotype differences in naïve controls and WM experience exclusively yielding more Ki67-positive cells in 5-HTT+/+ mice. Moreover, in 5-HTT-/- mice we demonstrate that learning performance correlates with the extent of aN.

Overall, higher baseline IEG expression and increased an in the hippocampus of 5-HTT-/- mice together with increased stress sensitivity may constitute the neurobiological correlate of raised alertness, possibly impeding optimal learning performance in the more stressful WM.

Decynium-22 enhances SSRI-induced antidepressant-like effects in mice: uncovering novel targets to treat depression

Mood disorders cause much suffering and lost productivity worldwide, compounded by the fact that many patients are not effectively treated by currently available medications. The most commonly prescribed antidepressant drugs are the selective serotonin (5-HT) reuptake inhibitors (SSRIs), which act by blocking the high-affinity 5-HT transporter (SERT). The increase in extracellular 5-HT produced by SSRIs is thought to be critical to initiate downstream events needed for therapeutic effects. A potential explanation for their limited therapeutic efficacy is the recently characterized presence of low-affinity, high-capacity transporters for 5-HT in brain [i.e., organic cation transporters (OCTs) and plasma membrane monoamine transporter], which may limit the ability of SSRIs to increase extracellular 5-HT. Decynium-22 (D-22) is a blocker of these transporters, and using this compound we uncovered a significant role for OCTs in 5-HT uptake in mice genetically modified to have reduced or no SERT expression (Baganz et al., 2008). This raised the possibility that pharmacological inactivation of D-22-sensitive transporters might enhance the neurochemical and behavioral effects of SSRIs. Here we show that in wild-type mice D-22 enhances the effects of the SSRI fluvoxamine to inhibit 5-HT clearance and to produce antidepressant-like activity. This antidepressant-like activity of D-22 was attenuated in OCT3 KO mice, whereas the effect of D-22 to inhibit 5-HT clearance in the CA3 region of hippocampus persisted. Our findings point to OCT3, as well as other D-22-sensitive transporters, as novel targets for new antidepressant drugs with improved therapeutic potential.

Genetic and pharmacological manipulations of the serotonergic system in early life: neurodevelopmental underpinnings of autism-related behavior

Serotonin, in its function as neurotransmitter, is well-known for its role in depression, autism and other neuropsychiatric disorders, however, less known as a neurodevelopmental factor. The serotonergic system is one of the earliest to develop during embryogenesis and early changes in serotonin levels can have large consequences for the correct development of specific brain areas. The regulation and functioning of serotonin is influenced by genetic risk factors, such as the serotonin transporter polymorphism in humans. This polymorphism is associated with anxiety-related symptoms, changes in social behavior, and cortical gray and white matter changes also seen in patients suffering from autism spectrum disorders (ASD). The human polymorphism can be mimicked by the knockout of the serotonin transporter in rodents, which are as a model system therefore vital to explore the precise neurobiological mechanisms. Moreover, there are pharmacological challenges influencing serotonin in early life, like prenatal/neonatal exposure to selective serotonin reuptake inhibitors (SSRI) in depressed pregnant women. There is accumulating evidence that this dysregulation of serotonin during critical phases of brain development can lead to ASD-related symptoms in children, and reduced social behavior and increased anxiety in rodents. Furthermore, prenatal valproic acid (VPA) exposure, a mood stabilizing drug which is also thought to interfere with serotonin levels, has the potency to induce ASD-like symptoms and to affect the development of the serotonergic system. Here, we review and compare the neurodevelopmental and behavioral consequences of serotonin transporter gene variation, and prenatal SSRI and VPA exposure in the context of ASD.

Anxiolytic-like effect of lavender essential oil inhalation in mice: participation of serotonergic but not GABAA/benzodiazepine neurotransmission

ETHNOPHARMACOLOGICAL RELEVANCE

Lavandula angustifolia (lavender) inhalation has been used in folk medicine for the treatment of anxiety, and clinical and animal studies have corroborated its anxiolytic effect, although its mechanism of action is still not fully understood.

AIMS OF THE STUDY

The objective of the present study was to determine whether the GABAA/benzodiazepine complex or serotonin neurotransmission mediates the anxiolytic-like effect of lavender essential oil.

MATERIALS AND METHODS

Male Swiss mice were subjected to the marble-burying test after being exposed to the aroma of lavender essential oil (1-5%), amyl acetate (5%; used as a behaviorally neutral odor), or distilled water for 15 min via inhalation. Additionally, the effect of 5% lavender essential oil was also evaluated in mice subjected to the elevated plus maze. GABAA/benzodiazepine mediation was evaluated by pretreating the mice with the GABAA receptor antagonist picrotoxin before the marble burying test and [(3)H]flunitrazepam binding to the benzodiazepine site on the GABAA receptor. Serotonergic mediation was studied by pretreating the mice with O-methyl-[3H]-N-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride (WAY100635), a serotonin 5-HT1A receptor antagonist before the marble burying test. We also evaluated changes in the pharmacologically induced serotonin syndrome and the effects of combined administration of subeffective doses of lavender essential oil and the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT).

RESULTS

Lavender essential oil (1-5%) decreased the number of marbles buried compared with the control and amyl acetate groups. In the elevated plus maze, 5% lavender essential oil inhalation increased the percentage of time spent on and number of entries into the open arms compared with controls. No effect was seen in the number of closed arm entries or number of beam interruptions in the automated activity chamber. Pretreatment with the GABAA receptor antagonist picrotoxin (0.5mg/kg) did not modify the behavioral effect of 5% lavender essential oil in the marble-burying test. Lavender essential oil also did not alter [(3)H]flunitrazepam binding to the benzodiazepine site on the GABAA receptor. Pretreatment with the serotonin 5-HT1A receptor antagonist WAY100635 (3mg/kg) blocked the anxiolytic-like effect of lavender essential oil and the 5-HT1A receptor agonist 8-OH-DPAT (3mg/kg). A combination of ineffective doses of 8-OH-DPAT (0.5mg/kg) and lavender essential oil (0.1%) reduced the number of marbles buried. Finally, 5% lavender essential oil attenuated the serotonin syndrome induced by 40 mg/kg fluoxetine plus 80 mg/kg 5-hydroxytryptophan.

CONCLUSIONS

These results indicate an important role for the serotonergic system in the anxiolytic-like effect of lavender essential oil.

Transgenic mouse models for ADHD

Attention-deficit hyperactivity disorder (ADHD) is a developmental disorder characterized by symptoms of inattention, impulsivity and hyperactivity that adversely affect many aspects of life. Whereas the etiology of ADHD remains unknown, growing evidence indicates a genetic involvement in the development of this disorder. The brain circuits associated with ADHD are rich in monoamines, which are involved in the mechanism of action of psychostimulants and other medications used to treat this disorder. Dopamine (DA) is believed to play a major role in ADHD but other neurotransmitters are certainly also involved. Genetically modified mice have become an indispensable tool used to analyze the contribution of genetic factors in the pathogenesis of human disorders. Although rodent models cannot fully recapitulate complex human psychiatric disorders such as ADHD, transgenic mice offer an opportunity to directly investigate in vivo the specific roles of novel candidate genes identified in ADHD patients. Several knock-out and transgenic mouse models have been proposed as ADHD models, mostly based on targeting genes involved in DA transmission, including the gene encoding the dopamine transporter (DAT1). These mutant models provided an opportunity to evaluate the contribution of dopamine-related processes to brain pathology, to dissect the neuronal circuitry and molecular mechanisms involved in the antihyperkinetic action of psychostimulants and to evaluate novel treatments for ADHD. New transgenic models mouse models targeting other genes have recently been proposed for ADHD. Here, we discuss the recent advances and pitfalls in modeling ADHD endophenotypes in genetically altered animals.

Physiologically relevant changes in serotonin resolved by fast microdialysis

Online microdialysis is a sampling and detection method that enables continuous interrogation of extracellular molecules in freely moving subjects under behaviorally relevant conditions. A majority of recent publications using brain microdialysis in rodents report sample collection times of 20-30 min. These long sampling times are due, in part, to limitations in the detection sensitivity of high performance liquid chromatography (HPLC). By optimizing separation and detection conditions, we decreased the retention time of serotonin to 2.5 min and the detection threshold to 0.8 fmol. Sampling times were consequently reduced from 20 to 3 min per sample for online detection of serotonin (and dopamine) in brain dialysates using a commercial HPLC system. We developed a strategy to collect and to analyze dialysate samples continuously from two animals in tandem using the same instrument. Improvements in temporal resolution enabled elucidation of rapid changes in extracellular serotonin levels associated with mild stress and circadian rhythms. These dynamics would be difficult or impossible to differentiate using conventional microdialysis sampling rates.

Unexpected effects of early-life adversity and social enrichment on the anxiety profile of mice varying in serotonin transporter genotype

Developmental mechanisms that shape behaviour are under environmental as well as genetic influence, commonly referred to as gene-by-environment interaction (GxE). Here, we compared the role of different early environments - adverse, standard, and enriched - for the modulation of the anxiety profile in mice varying in serotonin transporter (5-HTT) genotype. Early-life adversity was simulated by exposing lactating 5-HTT +/- dams to soiled bedding of unfamiliar males (UMB), signalling the danger of infanticide. An enriched early environment was established by communal nesting (CN). 5-HTT +/- females of a third group were housed under standard nesting conditions (SN) of individual nesting. The offspring (5-HTT +/+, 5-HTT +/-, and 5-HTT -/-) were analyzed for anxiety-like and exploratory behaviour in a battery of tests. The main findings were: (1) Maternal care was reduced in UMB compared to CN dams. (2) There was no significant variation in state anxiety levels between UMB, SN, and CN offspring. (3) UMB offspring showed significantly lower levels of trait anxiety compared to CN offspring, while SN offspring were intermediate. (4) There was a significant main effect of genotype, with highest levels of state and trait anxiety in 5-HTT -/- mice. The findings corroborate that anxiety profiles in mice can be affected by both early environmental conditions and 5-HTT genotype. Notably, state and trait anxiety of an individual can independently be affected by the early environment.

Depression-related behaviours displayed by female C57BL/6J mice during abstinence from chronic ethanol consumption are rescued by wheel-running

Withdrawal from a chronic period of alcohol consumption is commonly associated with the manifestation of depression, potentially exerting a significant influence on treatment prospects and increasing the likelihood of relapse. Better therapeutic strategies need to be developed to assist with rehabilitation. Here, we report the detection of depression-related behaviours in a mouse model of 6-week free-choice ethanol (10%, v/v) consumption followed by 2-week abstinence. Mice abstinent from alcohol showed increased immobility time on the forced-swim test, reduced saccharin consumption and increased latency to feed in the novelty-suppressed feeding test. By comparison, there was no significant effect on anxiety-related behaviours as determined by testing on the light-dark box and elevated plus maze. We found that the provision of running-wheels through the duration of abstinence attenuated depressive behaviour in the forced-swim and novelty-suppressed feeding tests, and increased saccharin consumption. Given the link between withdrawal from addictive substances and depression, this model will be useful for the study of the pathophysiology underlying alcohol-related depression. The findings of this study establish an interaction between physical activity and the development of behavioural changes following cessation of alcohol consumption that could have implications for the development of rehabilitative therapies.

To attack, or not to attack? The role of serotonin transporter genotype in the display of maternal aggression

Aggressive behavior in males has been intensively investigated regarding the influence of the brain serotonergic system. Despite some inconsistencies, a general conclusion is that low levels of serotonin (5-HT) are associated with high levels of male aggression. The role of the serotonergic system for female aggression is less well researched. Female mice rarely show intraspecific aggressive behavior, except during lactation, when they may exhibit intense aggression towards intruders to protect their pups. The aim of the present study was to investigate the impact of 5-HT transporter (5-HTT) inactivation on maternal aggression in mice. Therefore, lactating homozygous and heterozygous 5-HTT knockout as well as wildtype mice were confronted with male intruders in their home cages. Homozygous 5-HTT knockout dams, which exhibit highest levels of extracellular 5-HT in the brain, were significantly less prone to initiate offensive aggression than wildtype controls. Moreover, they showed longer latencies to attack the intruder, attacked less often and displayed an overall lower frequency of offensive aggressive behavior patterns than wildtype dams. Heterozygous 5-HTT knockout mothers generally showed intermediate levels of aggressive behavior. Thus, our data indicate that higher extracellular including synaptic levels of 5-HT are associated with lower intensity of aggressive behavior in lactating mice, adding support to the inhibitory role of 5-HT in aggression also in females.

Identifying essential cell types and circuits in autism spectrum disorders

Autism spectrum disorder (ASD) is highly genetic in its etiology, with potentially hundreds of genes contributing to risk. Despite this heterogeneity, these disparate genetic lesions may result in the disruption of a limited number of key cell types or circuits-information which could be leveraged for the design of therapeutic interventions. While hypotheses for cellular disruptions can be identified by postmortem anatomical analysis and expression studies of ASD risk genes, testing these hypotheses requires the use of animal models. In this review, we explore the existing evidence supporting the contribution of different cell types to ASD, specifically focusing on rodent studies disrupting serotonergic, GABAergic, cerebellar, and striatal cell types, with particular attention to studies of the sufficiency of specific cellular disruptions to generate ASD-related behavioral abnormalities. This evidence suggests multiple cellular routes can create features of the disorder, though it is currently unclear if these cell types converge on a final common circuit. We hope that in the future, systematic studies of cellular sufficiency and genetic interaction will help to classify patients into groups by type of cellular disruptions which suggest tractable therapeutic targets.

Catecholamine-related gene expression in blood correlates with tic severity in tourette syndrome

Tourette syndrome (TS) is a heritable disorder characterized by tics that are decreased in some patients by treatment with alpha adrenergic agonists and dopamine receptor blockers. Thus, this study examines the relationship between catecholamine gene expression in blood and tic severity. TS diagnosis was confirmed using Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV criteria and tic severity measured using the Yale Global Tic Severity Scale (YGTSS) for 26 un-medicated subjects with TS. Whole blood was collected and Ribonucleic acid (RNA) processed on Affymetrix Human Exon 1.0 ST arrays. An Analysis of Covariance (ANCOVA) identified 3627 genes correlated with tic severity (p<0.05). Searches of Medical Subject Headings, Gene Ontology, Allen Mouse Brain Atlas, and PubMed determined genes associated with catecholamines and located in the basal ganglia. Using GeneCards, PubMed, and manual curation, seven genes associated with TS were further examined: DRD2, HRH3, MAOB, BDNF, SNAP25, SLC6A4, and SLC22A3. These genes are highly associated with TS and have also been implicated in other movement disorders, Attention Deficit Hyperactivity Disorder (ADHD), and Obsessive-Compulsive Disorder (OCD). Correlation of gene expression in peripheral blood with tic severity may allow inferences about catecholamine pathway dysfunction in TS subjects. Findings built on previous work suggest that at least some genes expressed peripherally are relevant for central nervous system (CNS) pathology in the brain of individuals with TS.

Influence of chronic amphetamine treatment and acute withdrawal on serotonin synthesis and clearance mechanisms in the rat ventral hippocampus

Amphetamine withdrawal in both humans and rats is associated with increased anxiety states, which are thought to contribute to drug relapse. Serotonin in the ventral hippocampus mediates affective behaviors, and reduced serotonin levels in this region are observed in rat models of high anxiety, including during withdrawal from chronic amphetamine. This goal of this study was to understand the mechanisms by which reduced ventral hippocampus serotonergic neurotransmission occurs during amphetamine withdrawal. Serotonin synthesis (assessed by accumulation of serotonin precursor as a measure of the capacity of in vivo tryptophan hydroxylase activity), expression of serotonergic transporters, and in vivo serotonergic clearance using in vivo microdialysis were assessed in the ventral hippocampus in adult male Sprague Dawley rats at 24 h withdrawal from chronic amphetamine. Overall, results showed that diminished extracellular serotonin at 24 h withdrawal from chronic amphetamine was not accompanied by a change in capacity for serotonin synthesis (in vivo tryptophan hydroxylase activity), or serotonin transporter expression or function in the ventral hippocampus, but instead was associated with increased expression and function of organic cation transporters (low-affinity, high-capacity serotonin transporters). These findings suggest that 24 h withdrawal from chronic amphetamine reduces the availability of extracellular serotonin in the ventral hippocampus by increasing organic cation transporter-mediated serotonin clearance, which may represent a future pharmacological target for reversing anxiety states during drug withdrawal.

The genetics of selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are among the most widely prescribed drugs in psychiatry. Based on the fact that SSRIs increase extracellular monoamine levels in the brain, the monoamine hypothesis of depression was introduced, postulating that depression is associated with too low serotonin, dopamine and noradrenaline levels. However, several lines of evidence indicate that this hypothesis is too simplistic and that depression and the efficacy of SSRIs are dependent on neuroplastic changes mediated by changes in gene expression. Because a coherent view on global gene expression is lacking, we aim to provide an overview of the effects of SSRI treatment on the final targets of 5-HT receptor signal transduction pathways, namely the transcriptional regulation of genes. We address gene polymorphisms in humans that affect SSRI efficacy, as well as in vitro studies employing human-derived cells. We also discuss the molecular targets affected by SSRIs in animal models, both in vivo and in vitro. We conclude that serotonin transporter gene variation in humans affects the efficacy and side-effects of SSRIs, whereas SSRIs generally do not affect serotonin transporter gene expression in animals. Instead, SSRIs alter mRNA levels of genes encoding serotonin receptors, components of non-serotonergic neurotransmitter systems, neurotrophic factors, hypothalamic hormones and inflammatory factors. So far little is known about the epigenetic and age-dependent molecular effects of SSRIs, which might give more insights in the working mechanism(s) of SSRIs.

High-throughput screening of stem cell therapy for globoid cell leukodystrophy using automated neurophenotyping of twitcher mice

Globoid cell leukodystrophy (Krabbe's disease) is an autosomal recessive neurodegenerative disorder that results from the deficiency of galactosylceramidase, a lysosomal enzyme involved in active myelination. Due to the progressive, lethal nature of this disease and the limited treatment options available, multiple laboratories are currently exploring novel therapies using the mouse model of globoid cell leukodystrophy. In order to establish a protocol for motor function assessment of the twitcher mouse, this study tested the capability of an automated system to detect phenotypic differences across mouse genotypes and/or treatment groups. The sensitivity of this system as a screening tool for the assessment of therapeutic interventions was determined by the administration of murine bone marrow-derived stem cells into twitcher mice via intraperitoneal injection. Animal behavior was analyzed using the Noldus EthoVision XT7 software. Novel biomarkers, including abnormal locomotion (e.g., velocity, moving duration, distance traveled, turn angle) and observed behaviors (e.g., rearing activity, number of defecation boli), were established for the twitcher mouse. These parameters were monitored across all mouse groups, and the automated system detected improved locomotion in the treated twitcher mice based on the correction of angular velocity, turn angle, moving duration, and exploratory behavior, such as thigmotaxis. Further supporting these findings, the treated mice showed improved lifespan, gait, wire hang ability, twitching severity and frequency, and sciatic nerve histopathology. Taken together, these data demonstrate the utility of computer-based neurophenotyping for motor function assessment of twitcher mice and support its utility for detecting the efficacy of stem cell-based therapy for neurodegenerative disorders.

Alterations in grooming activity and syntax in heterozygous SERT and BDNF knockout mice: the utility of behavior-recognition tools to characterize mutant mouse phenotypes

Serotonin transporter (SERT) and brain-derived neurotrophic factor (BDNF) are key modulators of molecular signaling, cognition and behavior. Although SERT and BDNF mutant mouse phenotypes have been extensively characterized, little is known about their self-grooming behavior. Grooming represents an important behavioral domain sensitive to environmental stimuli and is increasingly used as a model for repetitive behavioral syndromes, such as autism and attention deficit/hyperactivity disorder. The present study used heterozygous ((+/-)) SERT and BDNF male mutant mice on a C57BL/6J background and assessed their spontaneous self-grooming behavior applying both manual and automated techniques. Overall, SERT(+/-) mice displayed a general increase in grooming behavior, as indicated by more grooming bouts and more transitions between specific grooming stages. SERT(+/-) mice also aborted more grooming bouts, but showed generally unaltered activity levels in the observation chamber. In contrast, BDNF(+/-) mice displayed a global reduction in grooming activity, with fewer bouts and transitions between specific grooming stages, altered grooming syntax, as well as hypolocomotion and increased turning behavior. Finally, grooming data collected by manual and automated methods (HomeCageScan) significantly correlated in our experiments, confirming the utility of automated high-throughput quantification of grooming behaviors in various genetic mouse models with increased or decreased grooming phenotypes. Taken together, these findings indicate that mouse self-grooming behavior is a reliable behavioral biomarker of genetic deficits in SERT and BDNF pathways, and can be reliably measured using automated behavior-recognition technology.

Behavior in the open field predicts the number of KCl-induced cortical spreading depressions in rats

Anxiety disorders are known to be comorbid with migraine, and cortical spreading depression (CSD) is the most likely cause of the migraine aura. To search for possible correlations between susceptibility to CSD and anxiety we used the open field test in male Sprague-Dawley rats chronically treated with the preventive anti-migraine drugs valproate or riboflavin. Animals avoiding the central area of the open field chamber and those with less exploratory activity (i.e. rearing) were considered more anxious. After 4 weeks of treatment CSDs were elicited by application of 1M KCl over the occipital cortex and the number of CSDs occurring over a 2h period was compared to the previously assessed open field behavior. Higher anxiety-like behavior was significantly correlated with a higher frequency of KCl-induced CSDs. In saline-treated animals, fewer rearings were found in animals with more frequent CSDs (R=-1.00). The duration of ambulatory episodes in the open field center correlated negatively with number of CSDs in the valproate group (R=-0.83; p<0.005) and in riboflavin treated group (R=-0.69; p<0.05) as well as total time spent in the open field center in both groups (R=-0.75; p<0.05 and R=-0.58; p<0.1 respectively). These results suggest that anxiety symptoms are associated with susceptibility to CSD and might explain why it can be an aggravating factor in migraine with aura.

Reduced serotonin reuptake transporter (SERT) function causes insulin resistance and hepatic steatosis independent of food intake

Serotonin reuptake transporter (SERT) is a key regulator of serotonin neurotransmission and a major target of antidepressants. Antidepressants, such as selectively serotonin reuptake inhibitors (SSRIs), that block SERT function are known to affect food intake and body weight. Here, we provide genetic evidence that food intake and metabolism are regulated by separable mechanisms of SERT function. SERT-deficient mice ate less during both normal diet and high fat diet feeding. The reduced food intake was accompanied with markedly elevated plasma leptin levels. Despite reduced food intake, SERT-deficient mice exhibited glucose intolerance and insulin resistance, and progressively developed obesity and hepatic steatosis. Several lines of evidence indicate that the metabolic deficits of SERT-deficient mice are attributable to reduced insulin-sensitivity in peripheral tissues. First, SERT-deficient mice exhibited beta-cell hyperplasia and islet-mass expansion. Second, biochemical analyses revealed constitutively elevated JNK activity and diminished insulin-induced AKT activation in the liver of SERT-deficient mice. SERT-deficient mice exhibited hyper-JNK activity and hyperinsulinemia prior to the development of obesity. Third, enhancing AKT signaling by PTEN deficiency corrected glucose tolerance in SERT-deficient mice. These findings have potential implications for designing selective SERT drugs for weight control and the treatment of metabolic syndromes.

The deletion of STOP/MAP6 protein in mice triggers highly altered mood and impaired cognitive performances

The microtubule-associated Stable Tubulie Only Polypeptide (STOP; also known as MAP6) protein plays a key role in neuron architecture and synaptic plasticity, the dysfunctions of which are thought to be implicated in the pathophysiology of psychiatric diseases. The deletion of STOP in mice leads to severe disorders reminiscent of several schizophrenia-like symptoms, which are also associated with differential alterations of the serotonergic tone in somas versus terminals. In STOP knockout (KO) compared with wild-type mice, serotonin (5-HT) markers are found to be markedly accumulated in the raphe nuclei and, in contrast, deeply depleted in all serotonergic projection areas. In the present study, we carefully examined whether the 5-HT imbalance would lead to behavioral consequences evocative of mood and/or cognitive disorders. We showed that STOP KO mice exhibited depression-like behavior, associated with a decreased anxiety-status in validated paradigms. In addition, although STOP KO mice had a preserved very short-term memory, they failed to perform well in all other learning and memory tasks. We also showed that STOP KO mice exhibited regional imbalance of the norepinephrine tone as observed for 5-HT. As a consequence, mutant mice were hypersensitive to acute antidepressants with different selectivity. Altogether, these data indicate that the deletion of STOP protein in mice caused deep alterations in mood and cognitive performances and that STOP protein might have a crucial role in the 5-HT and norepinephrine networks development.

RETRACTED: Dysregulated glutamate and dopamine transporters in postmortem frontal cortex from bipolar and schizophrenic patients

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of The National Institutes of Health has found that the first author, Dr. Jagadeesh S. Rao engaged in research misconduct by falsifying data in “Dysregulated glutamate and dopamine transporters in postmortem frontal cortex from bipolar and schizophrenic patients”. Rao JS, Kellom M, Reese EA, Rapoport SI, Kim HW. J. Affect Disord. 136(1–2):63–71. 2012. Data in Figures 2A, 2B, 3A, 3B and 4A were falsified.

Animal models of depression and anxiety: What do they tell us about human condition?

While modern neurobiology methods are necessary they are not sufficient to elucidate etiology and pathophysiology of affective disorders and develop new treatments. Achievement of these goals is contingent on applying cutting edge methods on appropriate disease models. In this review, the authors present four rodent models with good face-, construct-, and predictive-validity: the Flinders Sensitive rat line (FSL); the genetically "anxious" High Anxiety-like Behavior (HAB) line; the serotonin transporter knockout 5-HTT(-/-) rat and mouse lines; and the post-traumatic stress disorder (PTSD) model induced by exposure to predator scent, that they have employed to investigate the nature of depression and anxiety.

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.

The winner and loser effect, serotonin transporter genotype, and the display of offensive aggression

Aggressive behaviour results from a complex interplay between genetic and environmental factors. Key modulators of aggression include the serotonergic system on the molecular level and experience in prior aggressive contests as an environmental factor. The aim of this study was to elucidate the effects of fighting experience on the display of offensive aggressive behaviour in adult male mice varying in serotonin transporter (5-HTT) genotype. 5-HTT +/+, 5-HTT +/- and 5-HTT -/- mice were given either a winning or a losing experience on each of three consecutive days and were subsequently observed for their offensive aggressive behaviour as residents against a docile intruder from the C3H strain in a resident-intruder paradigm. The main findings were: There was no significant difference between the amount of offensive aggressive behaviour displayed by the genotypes. Winners showed more engagement with the intruder, attacked him faster and exhibited overall higher aggression scores than losers. There was no significant genotype × social experience interaction: winning and losing had a similar effect on offensive aggressive behaviour in all three 5-HTT genotypes. We conclude that social experience in terms of having been a winner or having been a loser rather than the 5-HTT genotype determines the behaviour towards a docile intruder.

Annual Research Review: Transgenic mouse models of childhood-onset psychiatric disorders

Childhood-onset psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), mood disorders, obsessive compulsive spectrum disorders (OCSD), and schizophrenia (SZ), affect many school-age children, leading to a lower quality of life, including difficulties in school and personal relationships that persist into adulthood. Currently, the causes of these psychiatric disorders are poorly understood, resulting in difficulty diagnosing affected children, and insufficient treatment options. Family and twin studies implicate a genetic contribution for ADHD, ASD, mood disorders, OCSD, and SZ. Identification of candidate genes and chromosomal regions associated with a particular disorder provide targets for directed research, and understanding how these genes influence the disease state will provide valuable insights for improving the diagnosis and treatment of children with psychiatric disorders. Transgenic mouse models are one important approach in the study of human diseases, allowing for the use of a variety of experimental approaches to dissect the contribution of a specific chromosomal or genetic abnormality in human disorders. While it is impossible to model an entire psychiatric disorder in a single mouse model, these models can be extremely valuable in dissecting out the specific role of a gene, pathway, neuron subtype, or brain region in a particular abnormal behavior. In this review we discuss existing transgenic mouse models for childhood-onset psychiatric disorders. We compare the strength and weakness of various transgenic mouse models proposed for each of the common childhood-onset psychiatric disorders, and discuss future directions for the study of these disorders using cutting-edge genetic tools.

Away game or home match: the influence of venue and serotonin transporter genotype on the display of offensive aggression

Aggression can be modulated by both genetic and environmental factors. Here, we analyse how the serotonin transporter (5-HTT) genotype and the environmental situation in which a contest takes place shape the display of offensive aggression. Therefore, male wildtype, heterozygous, and homozygous 5-HTT knockout mice, which are known to differ in inborn levels of anxiety, were confronted three times with a docile opponent in one of three environmental situations: own territory, opponent's territory or neutral area. The main findings were: The frequency of approaching the contestant in order to gather information about him depended significantly on the venue but not on the genotype with lowest frequencies in the opponent's territory. The decision how quickly to attack the opponent was significantly influenced by the 5-HTT genotype but not by the venue: Homozygous 5-HTT knockout mice showed longest latencies. The sum of offensive aggression was significantly influenced by the 5-HTT genotype, the environmental situation, and a genotype by environment interaction. It is likely that, due to their varying genetic predisposition for anxiety, mice of the three genotypes were differentially affected by the aversiveness of the respective venue and the opponent's behaviour, which influenced their decision to display offensive aggression. As a consequence, the amount of aggression shown by homozygous 5-HTT knockout mice was influenced by the venue and the opponent's behaviour, whereas heterozygotes reacted only to the venue. Strikingly, wildtypes behaved always the same way, irrespective of venue and opponent.

Disturbed neurotransmitter transporter expression in Alzheimer's disease brain

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory loss and behavioral and psychological symptoms of dementia. An imbalance of different neurotransmitters--glutamate, acetylcholine, dopamine, and serotonin--has been proposed as the neurobiological basis of behavioral symptoms in AD. The molecular changes associated with neurotransmission imbalance in AD are not clear. We hypothesized that altered reuptake of neurotransmitters by vesicular glutamate transporters (VGLUTs), excitatory amino acid transporters (EAATs), the vesicular acetylcholine transporter (VAChT), the serotonin reuptake transporter (SERT), or the dopamine reuptake transporter (DAT) are involved in the neurotransmission imbalance in AD. We tested this hypothesis by examining protein and mRNA levels of these transporters in postmortem prefrontal cortex from 10 AD patients and 10 matched non-AD controls. Compared with controls, protein and mRNA levels of VGLUTs, EAAT1-3, VAChT, and SERT were reduced significantly in AD. Expression of DAT and catechol O-methyltransferase was unchanged. Reduced VGLUTs and EAATs may contribute to an alteration in glutamatergic recycling, and reduced SERT could exacerbate depressive symptoms in AD. The reduced VAChT expression could contribute to the recognized cholinergic deficit in AD. Altered neurotransmitter transporters could contribute to the pathophysiology of AD and are potential targets for therapy.

Monoamine transporters: vulnerable and vital doorkeepers

Transporters of dopamine, serotonin, and norepinephrine have been empirically used as medication targets for several mental illnesses in the last decades. These protein-targeted medications are effective only for subpopulations of patients with transporter-related brain disorders. Since the cDNA clonings in early 1990s, molecular studies of these transporters have revealed a wealth of information about the transporters' structure-activity relationship (SAR), neuropharmacology, cell biology, biochemistry, pharmacogenetics, and the diseases related to the human genes encoding these transporters among related regulators. Such new information creates a unique opportunity to develop transporter-specific medications based on SAR, mRNA, DNA, and perhaps transporter trafficking regulation for a number of highly relevant diseases including substance abuse, depression, schizophrenia, and Parkinson's disease.

Decreased exploratory activity in a mouse model of 15q duplication syndrome; implications for disturbance of serotonin signaling

Autism spectrum disorders (ASDs) have garnered significant attention as an important grouping of developmental brain disorders. Recent genomic studies have revealed that inherited or de novo copy number variations (CNVs) are significantly involved in the pathophysiology of ASDs. In a previous report from our laboratory, we generated mice with CNVs as a model of ASDs, with a duplicated mouse chromosome 7C that is orthologous to human chromosome 15q11-13. Behavioral analyses revealed paternally duplicated (patDp/+) mice displayed abnormal behaviors resembling the symptoms of ASDs. In the present study, we extended these findings by performing various behavioral tests with C57BL/6J patDp/+ mice, and comprehensively measuring brain monoamine levels with ex vivo high performance liquid chromatography. Compared with wild-type controls, patDp/+ mice exhibited decreased locomotor and exploratory activities in the open field test, Y-maze test, and fear-conditioning test. Furthermore, their decreased activity levels overcame increased appetite induced by 24 hours of food deprivation in the novelty suppressed feeding test. Serotonin levels in several brain regions of adult patDp/+ mice were lower than those of wild-type control, with no concurrent changes in brain levels of dopamine or norepinephrine. Moreover, analysis of monoamines in postnatal developmental stages demonstrated reduced brain levels of serotonin in young patDp/+ mice. These findings suggest that a disrupted brain serotonergic system, especially during postnatal development, may generate the phenotypes of patDp/+ mice.

Adaptive modulation of behavioural profiles by social stress during early phases of life and adolescence

The development of individual behavioural profiles can be powerfully influenced by stressful social experiences. Using a comparative approach, we focus on the role of social stressors for the modulation of behavioural profile during early phases of life and adolescence. For gregarious species, the stability of the social environment in which the pregnant and lactating female lives is of major importance for foetal brain development and the behavioural profile of the offspring in later life. Social instability during these critical periods of development generally brings about a behavioural and neuroendocrine masculinisation in daughters and a less pronounced expression of male-typical traits in sons. Moreover, when mothers live in a socially threatening world during this time, anxiety-like behaviour of their offspring often is elevated in adulthood. These effects of the social environment are likely to be mediated by maternal hormones and/or maternal behaviour. In addition, they can be modulated significantly by offspring genotype. We favour the hypothesis that the behavioural effects of social stress during this phase of life are not necessarily "pathological" (nonadaptive) consequences or constraints of adverse social conditions. Rather, mothers could be adjusting the offspring to their environment in an adaptive way. Adolescence is another period in which behavioural development is particularly susceptible to social influences. There is some evidence that stressful social events experienced at this time alter and canalize behaviour in an adaptive fashion, so that earlier influences on behavioural profile development can be complemented and readjusted, if necessary, to meet current environmental conditions. In terms of underlying neuroendocrine mechanism, a central role for the interaction of testosterone and stress hormones is suggested. In summary, the modulation of behavioural profiles by social stress from the prenatal phase through adolescence appears to represent an effective mechanism for repeated and rapid adaptation.

Forebrain glucocorticoid receptor overexpression increases environmental reactivity and produces a stress-induced spatial discrimination deficit

Reactivity to environmental stressors influences vulnerability to neurological and psychiatric illnesses, but little is known about molecular mechanisms that control this reactivity. Since mice with forebrain-specific glucocorticoid receptor overexpression (GRov mice) display anxiety-like behaviors in novel environments and have difficulty adjusting to change in memory tasks, we hypothesized that these may be facets of a broader phenotype of altered reactivity to environmental demands. Male GRov and wild-type mice were tested in a multiple-trial object interaction test comprising environmental and object habituation and spatial and object novelty trials. Half the mice received restraint stress before testing. GRov mice exhibited more locomotor activity and, without stress, more object interaction than wild-type mice. Following acute stress, GRov mice no longer showed increased object exploration. While stress dampened responses to object novelty in both groups, GRov mice were particularly impaired in discrimination of spatial novelty post-stress. These data demonstrate that GRov leads to increased environmental reactivity, responsiveness to salience, and vulnerability to stress-induced cognitive deficits. They implicate forebrain glucocorticoid receptor (GR) in fine-tuning interactions with the environment and the interplay of emotional salience, coping abilities, and cognitive function.

Exploratory, anxiety and spatial memory impairments are dissociated in mice lacking the LPA1 receptor

Lysophosphatidic acid (LPA) is a new, intercellular signalling molecule in the brain that has an important role in adult hippocampal plasticity. Mice lacking the LPA(1) receptor exhibit motor, emotional and cognitive alterations. However, the potential relationship among these concomitant impairments was unclear. Wild-type and maLPA(1)-null mice were tested on the hole-board for habituation and spatial learning. MaLPA(1)-null mice exhibited reduced exploration in a novel context and a defective intersession habituation that also revealed increased anxiety-like behaviour throughout the hole-board testing. In regard to spatial memory, maLPA(1) nulls failed to reach the controls' performance at the end of the reference memory task. Moreover, their defective working memory on the first training day suggested a delayed acquisition of the task's working memory rule, which is also a long term memory component. The temporal interval between trials and the task's difficulty may explain some of the deficits found in these mice. Principal components analysis revealed that alterations found in each behavioural dimension were independent. Therefore, exploratory and emotional impairments did not account for the cognitive deficits that may be attributed to maLPA(1) nulls' hippocampal malfunction.