Unaltered hormonal response to stress in a mouse model of fragile X syndrome

The Impact of Mild Chronic Stress and Maternal Experience in the Fmr1 Mouse Model of Fragile X Syndrome

Fragile X syndrome (FXS) is a pervasive developmental disorder and the most common monogenic cause of autism spectrum disorder (ASD). Female heterozygous (HET) carriers play a major role in the transmission of the pathology and present several FXS- and ASD-like behavioral alterations. Despite their clear genetic origins, FXS symptoms are known to be modulated by environmental factors, e.g., exposure to chronic stress, especially during critical life periods, such as pregnancy. Pregnancy, together with pups' care, constitutes maternal experience, i.e., another powerful environmental factor affecting several neurobehavioral functions in females. Here we investigated the impact of maternal experience on the long-term effects of stress in Fmr1-HET female mice. Our findings demonstrated that the behavioral abnormalities of HET females, i.e., hyperactivity and memory deficits, were unaffected by stress or maternal experience. In contrast, stress, independently of maternal experience, induced the appearance of cognitive deficits in WT mice. Maternal experience increased anxiety levels in all mice and enhanced their corticosterone levels, concomitantly promoting the effects of stress on social communication and adrenal glands. In translational terms, these results advance our understanding of the environmental modulation of the behavioral alterations observed in FXS female carriers and highlight the long-term impact of maternal experience and its interactions with chronic stress.

Prenatal valproic acid-induced autism marmoset model exhibits higher salivary cortisol levels

Individuals with autism spectrum disorder (ASD) are exposed to a variety of stressors owing to their behavioral traits. Cortisol is a hormone typically associated with stress, and its concentration and response to stress are higher in individuals with ASD than in controls. The mechanisms underlying cortisol dysregulation in ASD have been explored in rodents. Although rodent models have successfully replicated the major symptoms of autism (i.e., impaired vocal communication, social interaction deficits, and restricted/repetitive patterns of behavior), evidence suggests that the hypothalamic-pituitary-adrenal (HPA) axis system differs between rodents and primates. We developed an ASD model in the common marmoset (Callithrix jacchus), a New World monkey, utilizing prenatal exposure to valproic acid (VPA). In this study, we collected the salivary cortisol levels in VPA-exposed and unexposed marmosets in the morning and afternoon. Our results revealed that both VPA-exposed and unexposed marmosets showed similar diurnal changes in cortisol levels, which were lower in the afternoon than in the morning. However, heightened cortisol levels were observed throughout the day in VPA-exposed marmosets. These results are consistent with those of ASD in humans. Our results suggest that VPA-exposed marmosets show similarities not only in their behavioral patterns and brain pathologies, which we have reported previously, but also in hormonal regulation, validating the usefulness of VPA-exposed marmosets also as a tool for ASD stress research.

Evaluation of the neutrophil:lymphocyte ratio as an indicator of chronic distress in the laboratory mouse

When evaluating the effect of husbandry and biomethodologies on the well-being of laboratory mice, it is critical to utilize measurements that allow the distinguishing of acute stress from chronic stress. One of the most common measurements of stress in laboratory animals is the corticosterone assessment. However, while this measurement provides a highly accurate reflection of the animal's response to acute stressors, its interpretation is more prone to error when evaluating the effect of chronic stress. This study evaluated the use of the neutrophil:lymphocyte (NE:LY) ratio as an assessment of chronic stress in male and female C57Bl/6N mice as compared to serum corticosterone. One group of mice was exposed to mild daily stressors for 7 days, while the control group was handled with normal husbandry. The NE:LY ratio and serum corticosterone levels were significantly elevated in the chronically stressed mice, though a significant increase in corticosterone was only significant in males when compared by sex. The chronically stressed mice also demonstrated significantly fewer entries into the open arms and less time spent in the open arms of the elevated plus maze, suggesting that the mild daily stressors had induced a state of distress. The findings of this study confirm that the NE:LY ratio is a valid measurement for chronic stress in the laboratory mouse. However, these assays do not distinguish between distress or eustress, so behavioral and physiological assessments should always be included to determine a complete assessment of the well-being of the mouse.

Behavioral effects of chronic stress in the Fmr1 mouse model for fragile X syndrome

Fragile X Syndrome (FXS) is a pervasive developmental disorder due to a mutation in the FMR1 X-linked gene. Despite its clear genetic cause, the expression of FXS symptoms is known to be modulated by environmental factors, including stress. Furthermore, several studies have shown disturbances in stress regulatory systems in FXS patients and Fmr1 mice. These studies have mostly focused on the hormonal responses to stress, using the acute exposure to a single type of stressor. Hence, little is known about the behavioral effects of stress in FXS, and the importance of the nature of the stressing procedure, especially in the context of a repeated exposure that more closely resembles real life conditions. Here we evaluated the effects of chronic exposure to different types of stress (i.e., either repeated restraint or unpredictable stress) on the behavioral phenotype of adult Fmr1 mice. Our results demonstrated that chronic stress induced deficits in social interaction and working memory only in WT mice and the impact of stress depended on the type of stressors and the specific behavior tested. Our data suggest that the behavioral sensitivity to stress is dramatically reduced in FXS, opening new views on the impact of gene-environment interactions in this pathology.

GABA-B Agonist Baclofen Normalizes Auditory-Evoked Neural Oscillations and Behavioral Deficits in the Fmr1 Knockout Mouse Model of Fragile X Syndrome

Fragile X syndrome is a genetic condition resulting from FMR1 gene mutation that leads to intellectual disability, autism-like symptoms, and sensory hypersensitivity. Arbaclofen, a GABA-B agonist, has shown efficacy in some individuals with FXS but has become unavailable after unsuccessful clinical trials, prompting interest in publicly available, racemic baclofen. The present study investigated whether racemic baclofen can remediate abnormalities of neural circuit function, sensory processing, and behavior in Fmr1 knockout mice, a rodent model of fragile X syndrome. Fmr1 knockout mice showed increased baseline and auditory-evoked high-frequency gamma (30-80 Hz) power relative to C57BL/6 controls, as measured by electroencephalography. These deficits were accompanied by decreased T maze spontaneous alternation, decreased social interactions, and increased open field center time, suggestive of diminished working memory, sociability, and anxiety-like behavior, respectively. Abnormal auditory-evoked gamma oscillations, working memory, and anxiety-related behavior were normalized by treatment with baclofen, but impaired sociability was not. Improvements in working memory were evident predominantly in mice whose auditory-evoked gamma oscillations were dampened by baclofen. These findings suggest that racemic baclofen may be useful for targeting sensory and cognitive disturbances in fragile X syndrome.

Long-term continuous allopregnanolone elevation causes memory decline and hippocampus shrinkage, in female wild-type B6 mice

Chronic stress in various forms increases the risk for cognitive dysfunction, dementia and Alzheimer's disease. While the pathogenesis behind these findings is unknown, growing evidence suggests that chronic increase in neurosteroid levels, such as allopregnanolone, is part of the mechanism. We treated wild-type C57BL/6J mice with allopregnanolone for 5months, using osmotic pumps. This treatment led to moderately increased levels of allopregnanolone, equivalent to that of mild chronic stress. After an interval of no treatment for 1month, female mice showed impaired learning and memory function in the Morris water maze (MWM) in combination with diminished hippocampus weight and increased cerebellum weight, both correlating to MWM performance. Male mice showed a minor reduction in memory function and no differences in brain structure. We conclude that chronic allopregnanolone elevation can lead to cognitive dysfunction and negative brain alterations. We suggest that allopregnanolone could play a key role in the pathogenesis of stress-induced cognitive disturbances and perhaps dementia.

Cholesterol levels in fragile X syndrome

Fragile X syndrome (FXS) is associated with intellectual disability and behavioral dysfunction, including anxiety, ADHD symptoms, and autistic features. Although individuals with FXS are largely considered healthy and lifespan is not thought to be reduced, very little is known about the long-term medical health of adults with FXS and no systematically collected information is available on standard laboratory measures from metabolic screens. During the course of follow up of a large cohort of patients with FXS we noted that many patients had low cholesterol and high density lipoprotein (HDL) values and thus initiated a systematic chart review of all cholesterol values present in charts from a clinic cohort of over 500 patients with FXS. Total cholesterol (TC), low density lipoprotein (LDL) and HDL were all significantly reduced in males from the FXS cohort relative to age-adjusted population normative data. This finding has relevance for health monitoring in individuals with FXS, for treatments with cholesterol-lowering agents that have been proposed to target the underlying CNS disorder in FXS based on work in animal models, and for potential biomarker development in FXS.

Long-lasting effects of minocycline on behavior in young but not adult Fragile X mice

Fragile X Syndrome (FXS) is the most common single-gene inherited form of intellectual disability with behaviors characteristic of autism. People with FXS display childhood seizures, hyperactivity, anxiety, developmental delay, attention deficits, and visual-spatial memory impairment, as well as a propensity for obsessive-compulsive disorder. Several of these aberrant behaviors and FXS-associated synaptic irregularities also occur in "fragile X mental retardation gene" knock-out (Fmr1 KO) mice. We previously reported that minocycline promotes the maturation of dendritic spines - postsynaptic sites for excitatory synapses - in the developing hippocampus of Fmr1 KO mice, which may underlie the beneficial effects of minocycline on anxiolytic behavior in young Fmr1 KO mice. In this study, we compared the effectiveness of minocycline treatment in young and adult Fmr1 KO mice, and determined the dependence of behavioral improvements on short-term versus long-term minocycline administration. We found that 4- and 8-week-long treatments significantly reduced locomotor activity in both young and adult Fmr1 KO mice. Some behavioral improvements persisted in young mice post-treatment, but in adults the beneficial effects were lost soon after minocycline treatment was stopped. We also show, for the first time, that minocycline treatment partially attenuates the number and severity of audiogenic seizures in Fmr1 KO mice. This report provides further evidence that minocycline treatment has immediate and long-lasting benefits on FXS-associated behaviors in the Fmr1 KO mouse model.

Macrophage migration inhibitory factor (MIF) is essential for inflammatory and neuropathic pain and enhances pain in response to stress

Stress and glucocorticoids exacerbate pain via undefined mechanisms. Macrophage migration inhibitory factor (MIF) is a constitutively expressed protein that is secreted to maintain immune function when glucocorticoids are elevated by trauma or stress. Here we show that MIF is essential for the development of neuropathic and inflammatory pain, and for stress-induced enhancement of neuropathic pain. Mif null mutant mice fail to develop pain-like behaviors in response to inflammatory stimuli or nerve injury. Pharmacological inhibition of MIF attenuates pain-like behaviors caused by nerve injury and prevents sensitization of these behaviors by stress. Conversely, injection of recombinant MIF into naïve mice produces dose-dependent mechanical sensitivity that is exacerbated by stress. MIF elicits pro-inflammatory signaling in microglia and activates sensory neurons, mechanisms that underlie pain. These data implicate MIF as a key regulator of pain and provide a mechanism whereby stressors exacerbate pain. MIF inhibitors warrant clinical investigation for the treatment of chronic pain.

Genetic manipulation of STEP reverses behavioral abnormalities in a fragile X syndrome mouse model

Fragile X syndrome (FXS), the most common inherited form of intellectual disability and prevailing known genetic basis of autism, is caused by an expansion in the Fmr1 gene that prevents transcription and translation of fragile X mental retardation protein (FMRP). FMRP binds to and controls translation of mRNAs downstream of metabotropic glutamate receptor (mGluR) activation. Recent work shows that FMRP interacts with the transcript encoding striatal-enriched protein tyrosine phosphatase (STEP; Ptpn5). STEP opposes synaptic strengthening and promotes synaptic weakening by dephosphorylating its substrates, including ERK1/2, p38, Fyn and Pyk2, and subunits of N-methyl-d-aspartate (NMDA) and AMPA receptors. Here, we show that basal levels of STEP are elevated and mGluR-dependent STEP synthesis is absent in Fmr1(KO) mice. We hypothesized that the weakened synaptic strength and behavioral abnormalities reported in FXS may be linked to excess levels of STEP. To test this hypothesis, we reduced or eliminated STEP genetically in Fmr1(KO) mice and assessed mice in a battery of behavioral tests. In addition to attenuating audiogenic seizures and seizure-induced c-Fos activation in the periaqueductal gray, genetically reducing STEP in Fmr1(KO) mice reversed characteristic social abnormalities, including approach, investigation and anxiety. Loss of STEP also corrected select nonsocial anxiety-related behaviors in Fmr1(KO) mice, such as light-side exploration in the light/dark box. Our findings indicate that genetically reducing STEP significantly diminishes seizures and restores select social and nonsocial anxiety-related behaviors in Fmr1(KO) mice, suggesting that strategies to inhibit STEP activity may be effective for treating patients with FXS.

Fragile X syndrome: a psychiatric perspective

Fragile X syndrome (FXS) is associated with a complex but relatively consistent psychiatric phenotype. Recent research has suggested neural substrates for the behavioral abnormalities typically seen in FXS, and enhanced treatment strategies for managing disabling psychiatric comorbidity. While disease-specific, and possibly disease-modifying, therapeutics are being developed for FXS, currently available psychiatric medications can provide significant symptomatic relief of the hyperactivity, anxiety disorders, and affective disturbances often seen in the course of FXS. However, patients with fragile X may be especially susceptible to the psychiatric side effects of these medications, requiring particular care in prescribing. Recent findings concerning disease mechanisms and treatment strategies are reviewed from the perspective of a clinical psychiatrist, in an effort to enhance conventional pharmacotherapy of FXS.

Effects of chronic immobilization stress on anxiety-like behavior and basolateral amygdala morphology in Fmr1 knockout mice

Several lines of clinical evidence support the idea that fragile X syndrome (FXS) may involve a dysregulation of hypothalamic-pituitary-adrenal axis function [Wisbeck et al. (2000) J Dev Behav Pediatr 21:278-282; Hessl et al. (2002) Psychoneuroendocrinology 27:855-872]. We had tested this idea in a mouse model of FXS (Fmr1 KO) and found that the hormonal response to acute stress was similar to that of wild-type (WT) mice [Qin and Smith (2008) Psychoneuroendocrinology 33:883-889]. We report here responses to chronic stress (CS) in Fmr1 KO mice. Following restraint for 120 min/d, 10 consecutive days, we assessed dendrite and spine morphology in basolateral amygdala (BLA). We also monitored behavior in an elevated plus maze (EPM) and the hormonal response to this novel spatial environment. After CS, mice of both genotypes underwent adrenal hypertrophy, but effects were greater in WT mice. Behavior in the EPM indicated that only WT mice had the expected increase in anxiety following CS. Serum corticosterone and adrenocorticotropic hormone (ACTH) levels were both increased following the spatial novelty of EPM, and there were no differences between genotypes in the hormonal responses. BLA dendritic branching increased proximal to the soma in WT, but in Fmr1 KO mice branching was unaffected close to the soma and slightly decreased at one point distal to the soma. Similarly, spine density on apical and basal dendrites increased in WT but decreased in Fmr1 KO mice. Spine length on apical and basal dendrites increased in WT but was unaffected in Fmr1 KO mice. These differences in behavioral response and effects on neuron morphology in BLA suggest a diminished adaptive response of Fmr1 KO mice.

The psychiatric presentation of fragile x: evolution of the diagnosis and treatment of the psychiatric comorbidities of fragile X syndrome

Fragile X syndrome (FXS) is the leading inherited cause of mental retardation and autism spectrum disorders worldwide. It presents with a distinct behavioral phenotype which overlaps significantly with that of autism. Unlike autism and most common psychiatric disorders, the neurobiology of fragile X is relatively well understood. Lack of the fragile X mental retardation protein causes dysregulation of synaptically driven protein synthesis, which in turn causes global disruption of synaptic plasticity. Thus, FXS can be considered a disorder of synaptic plasticity, and a developmental disorder in the purest sense: mutation of the FMR1 (fragile X mental retardation 1) gene results in abnormal synaptic development in response to experience. Accumulation of this abnormal synaptic development, over time, leads to a characteristic and surprisingly consistent behavioral phenotype of attention deficit, hyperactivity, impulsivity, multiple anxiety symptoms, repetitive/perseverative/stereotypic behaviors, unstable affect, aggression, and self-injurious behavior. Many features of the behavioral and psychiatric phenotype of FXS follow a developmental course, waxing and waning over the life span. In most cases, symptoms present as a mixed clinical picture, not fitting established diagnostic categories. There have been many clinical trials in fragile X subjects, but no placebo-controlled trials of adequate size or methodology utilizing the most commonly prescribed psychiatric medications. However, large and well-designed trials of investigational agents which target the underlying pathology of FXS have recently been completed or are under way. While the literature offers little guidance to the clinician treating patients with FXS today, potentially disease-modifying treatments may be available in the near future.

Lithium ameliorates phenotypic deficits in a mouse model of fragile X syndrome

As our understanding of the underlying defects in fragile X syndrome (FXS) increases so does the potential for development of treatments aimed at modulating the defects and ameliorating the constellation of symptoms seen in patients. Symptoms of FXS include cognitive disability, hyperactivity, autistic behaviour, seizures and learning deficits. Lithium is a drug used clinically to treat bipolar disorder, and it has been used to treat mood dysregulation in individuals with FXS. We examined whether dietary lithium would alter behavioural and morphological abnormalities in fmr1 knockout (KO) mice. We studied wild-type (WT) and KO mice untreated (control chow) or treated with lithium (0.3% lithium-carbonate-containing chow) commenced at weaning and maintained throughout the experiment. At age 8-12 wk, mice were subjected to the following behavioural tests: open field, social interaction, elevated plus maze, elevated zero maze and passive avoidance. At 13 wk, brains were prepared for Golgi staining and analysis of dendritic spine morphology in medial prefrontal cortex. We found that compared to untreated WT, untreated KO mice were hyperactive and had reduced anxiety, impaired social interactions, and deficits on a learning test. Dendritic spines in medial prefrontal cortex were longer and increased in number. Lithium treatment ameliorated the hyperactivity and reversed impaired social interaction and deficits on the learning test. Lithium treatment also partially normalized general anxiety levels and dendritic spine morphology. Our findings and those from other laboratories on the efficacy of lithium treatment in animal models support further studies in patients with FXS.

Lithium ameliorates altered glycogen synthase kinase-3 and behavior in a mouse model of fragile X syndrome

Fragile X syndrome (FXS), the most common form of inherited mental retardation and a genetic cause of autism, results from mutated fragile X mental retardation-1 (Fmr1). This study examined the effects on glycogen synthase kinase-3 (GSK3) of treatment with a metabotropic glutamate receptor (mGluR) antagonist, MPEP, and the GSK3 inhibitor, lithium, in C57Bl/6 Fmr1 knockout mice. Increased mGluR signaling may contribute to the pathology of FXS, and the mGluR5 antagonist MPEP increased inhibitory serine-phosphorylation of brain GSK3 selectively in Fmr1 knockout mice but not in wild-type mice. Inhibitory serine-phosphorylation of GSK3 was lower in Fmr1 knockout, than wild-type, mouse brain regions and was increased by acute or chronic lithium treatment, which also increased hippocampal brain-derived neurotrophic factor levels. Fmr1 knockout mice displayed alterations in open-field activity, elevated plus-maze, and passive avoidance, and these differences were ameliorated by chronic lithium treatment. These findings support the hypothesis that impaired inhibition of GSK3 contributes to the pathogenesis of FXS and support GSK3 as a potential therapeutic target.

Dissociation of social and nonsocial anxiety in a mouse model of fragile X syndrome

Anxiety is a common symptom in fragile X patients. However, an anxiety-prone phenotype in mouse models of fragile X syndrome is not clear. In most studies of fmr1 knockout mice, decreased anxiety-like responses in exploratory-based models are found, but mice also exhibit abnormal social interactions. We hypothesize the coexistence of elevated social anxiety and reduced nonsocial anxiety in fmr1 knockout mice. In the present study, we applied an automated three-chambered social approach method and the elevated zero maze test to further investigate social interactions and general anxiety, respectively. Results indicate lower levels of both social approach behavior and response to social novelty in fmr1 knockout mice compared with wild-type littermates in the social interaction test. In the elevated zero maze, fmr1 knockout mice spent a greater percent time in open quadrants than wild-type mice, suggesting reduced nonsocial anxiety. These findings support the hypothesis that social and nonsocial anxiety can be dissociated and that in the fragile X mouse model, behavior consistent with hyper-social anxiety coexists with hypo-nonsocial anxiety.