Nest building is impaired in the Ts65Dn mouse model of Down syndrome and rescued by blocking 5HT2a receptors

The mouse Social Frailty Index (mSFI): a novel behavioral assessment for impaired social functioning in aging mice

Various approaches exist to quantify the aging process and estimate biological age on an individual level. Frailty indices based on an age-related accumulation of physical deficits have been developed for human use and translated into mouse models. However, declines observed in aging are not limited to physical functioning but also involve social capabilities. The concept of "social frailty" has been recently introduced into human literature, but no index of social frailty exists for laboratory mice yet. To fill this gap, we developed a mouse Social Frailty Index (mSFI) consisting of seven distinct assays designed to quantify social functioning which is relatively simple to execute and is minimally invasive. Application of the mSFI in group-housed male C57BL/6 mice demonstrated a progressively elevated levels of social frailty through the lifespan. Conversely, group-housed females C57BL/6 mice manifested social frailty only at a very old age. Female mice also showed significantly lower mSFI score from 10 months of age onward when compared to males. We also applied the mSFI in male C57BL/6 mice under chronic subordination stress and in chronic isolation, both of which induced larger increases in social frailty compared to age-matched group-housed males. Lastly, we show that the mSFI is enhanced in mouse models that show accelerated biological aging such as progeroid Ercc1-/Δ and Xpg-/- mice of both sexes compared to age matched littermate wild types. In summary, the mSFI represents a novel index to quantify trajectories of biological aging in mice and may help elucidate links between impaired social behavior and the aging process.

Mice lacking Ptprd exhibit deficits in goal-directed behavior and female-specific impairments in sensorimotor gating

Protein Tyrosine Phosphatase receptor type D (PTPRD) is a member of the protein tyrosine phosphatase family that mediates cell adhesion and synaptic specification. Genetic studies have linked Ptprd to several neuropsychiatric phenotypes, including Restless Leg Syndrome (RLS), opioid abuse disorder, and antipsychotic-induced weight gain. Genome-wide association studies (GWAS) of either pediatric obsessive-compulsive traits, or Obsessive-Compulsive Disorder (OCD), have identified loci near PTPRD as genome-wide significant, or strongly suggestive for this trait. We assessed Ptprd wild-type (WT), heterozygous (HT), and knockout (KO) mice for behavioral dimensions that are altered in OCD, including anxiety and exploration (open field test, dig test), perseverative behavior (splash-induced grooming, spatial d), sensorimotor gating (prepulse inhibition), and home cage goal-directed behavior (nest building). No effect of genotype was observed in any measure of the open field test, dig test, or splash test. However, Ptprd KO mice of both sexes showed impairments in nest building behavior. Finally, female, but not male, Ptprd KO mice showed deficits in prepulse inhibition, an operational measure of sensorimotor gating that is reduced in female, but not male, OCD patients. Our results indicate that constitutive lack of Ptprd may contribute to the development of certain domains that are altered OCD, including goal-directed behavior, and reduced sensorimotor gating specifically in females.

Ts66Yah, a mouse model of Down syndrome with improved construct and face validity

Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21). The understanding of genotype-phenotype relationships, the identification of driver genes and various proofs of concept for therapeutics have benefited from mouse models. The premier model, named Ts(1716)65Dn/J (Ts65Dn), displayed phenotypes related to human DS features. It carries an additional minichromosome with the Mir155 to Zbtb21 region of mouse chromosome 16, homologous to Hsa21, encompassing around 90 genes, fused to the centromeric part of mouse chromosome 17 from Pisd-ps2/Scaf8 to Pde10a, containing 46 genes not related to Hsa21. Here, we report the investigation of a new model, Ts66Yah, generated by CRISPR/Cas9 without the genomic region unrelated to Hsa21 on the minichromosome. As expected, Ts66Yah replicated DS cognitive features. However, certain phenotypes related to increased activity, spatial learning and molecular signatures were changed, suggesting genetic interactions between the Mir155-Zbtb21 and Scaf8-Pde10a intervals. Thus, Ts66Yah mice have stronger construct and face validity than Ts65Dn mice for mimicking consequences of DS genetic overdosage. Furthermore, this study is the first to demonstrate genetic interactions between triplicated regions homologous to Hsa21 and others unrelated to Hsa21. This article has an associated First Person interview with the first author of the paper.

Targeting increased levels of APP in Down syndrome: Posiphen-mediated reductions in APP and its products reverse endosomal phenotypes in the Ts65Dn mouse model

OBJECTIVE

Recent clinical trials targeting amyloid beta (Aβ) and tau in Alzheimer's disease (AD) have yet to demonstrate efficacy. Reviewing the hypotheses for AD pathogenesis and defining possible links between them may enhance insights into both upstream initiating events and downstream mechanisms, thereby promoting discovery of novel treatments. Evidence that in Down syndrome (DS), a population markedly predisposed to develop early onset AD, increased APP gene dose is necessary for both AD neuropathology and dementia points to normalization of the levels of the amyloid precursor protein (APP) and its products as a route to further define AD pathogenesis and discovering novel treatments.

BACKGROUND

AD and DS share several characteristic manifestations. DS is caused by trisomy of whole or part of chromosome 21; this chromosome contains about 233 protein-coding genes, including APP. Recent evidence points to a defining role for increased expression of the gene for APP and for its 99 amino acid C-terminal fragment (C99, also known as β-CTF) in dysregulating the endosomal/lysosomal system. The latter is critical for normal cellular function and in neurons for transmitting neurotrophic signals.

NEW/UPDATED HYPOTHESIS

We hypothesize that the increase in APP gene dose in DS initiates a process in which increased levels of full-length APP (fl-APP) and its products, including β-CTF and possibly Aβ peptides (Aβ42 and Aβ40), drive AD pathogenesis through an endosome-dependent mechanism(s), which compromises transport of neurotrophic signals. To test this hypothesis, we carried out studies in the Ts65Dn mouse model of DS and examined the effects of Posiphen, an orally available small molecule shown in prior studies to reduce fl-APP. In vitro, Posiphen lowered fl-APP and its C-terminal fragments, reversed Rab5 hyperactivation and early endosome enlargement, and restored retrograde transport of neurotrophin signaling. In vivo, Posiphen treatment (50 mg/kg/d, 26 days, intraperitoneal [i.p.]) of Ts65Dn mice was well tolerated and demonstrated no adverse effects in behavior. Treatment resulted in normalization of the levels of fl-APP, C-terminal fragments and small reductions in Aβ species, restoration to normal levels of Rab5 activity, reduced phosphorylated tau (p-tau), and reversed deficits in TrkB (tropomyosin receptor kinase B) activation and in the Akt (protein kinase B [PKB]), ERK (extracellular signal-regulated kinase), and CREB (cAMP response element-binding protein) signaling pathways. Remarkably, Posiphen treatment also restored the level of choline acetyltransferase protein to 2N levels. These findings support the APP gene dose hypothesis, point to the need for additional studies to explore the mechanisms by which increased APP gene expression acts to increase the risk for AD in DS, and to possible utility of treatments to normalize the levels of APP and its products for preventing AD in those with DS.

MAJOR CHALLENGES FOR THE HYPOTHESIS

Important unanswered questions are: (1) When should one intervene in those with DS; (2) would an APP-based strategy have untoward consequences on possible adaptive changes induced by chronically increased APP gene dose; (3) do other genes present on chromosome 21, or on other chromosomes whose expression is dysregulated in DS, contribute to AD pathogenesis; and (4) can one model strategies that combine the use of an APP-based treatment with those directed at other AD phenotypes including p-tau and inflammation.

LINKAGE TO OTHER MAJOR THEORIES

The APP gene dose hypothesis interfaces with the amyloid cascade hypothesis of AD as well as with the genetic and cell biological observations that support it. Moreover, upregulation of fl-APP protein and products may drive downstream events that dysregulate tau homeostasis and inflammatory responses that contribute to propagation of AD pathogenesis.

Assessment of nest building and social interaction behavior in mice exposed to acute social defeat stress using a three-dimensional depth camera

Nest building is an instinctive behavior toward protection from predators, body temperature regulation, and courtship. Previously, we discovered that acute and chronic social defeat stress suppresses the onset of nest-building behavior in male mice (C57BL/6J). Here, we analyzed nest building and other behavioral deficits induced by acute social defeat stress (ASDS). We utilized a customized cage and specifically developed observational programs for nest building, social avoidance, and other behaviors using an infrared depth camera to acquire three-dimensional (3D) data of animal behavior (Negura system). We determined the volume of nesting materials from these 3D depth images. Mice exposed to ASDS showed increased spontaneous activities, decreased rearing, and delayed nest building; however, nest-building activity was gradually recovered during the dark period of the 24 hr observation interval. At the endpoint following 24 hr, the ASDS and control groups showed no differences in nest volumes. Furthermore, we observed the time courses of both nest building and social avoidance behaviors and their relationship using the Negura system. Our data demonstrated a weak positive correlation between nest-building delay and social avoidance in ASDS mice. The Negura system can observe various behaviors that reflect the effects of social defeat stress.

Sex differences in the modulation of mouse nest building behavior by kappa opioid receptor signaling

Emerging evidence suggests that females are less sensitive than males to the effects of kappa opioid receptor (KOR) ligands across multiple behavioral measures. The effects of the KOR agonist U50,488 and the KOR antagonist aticaprant were assessed on nest building behavior, an ethologically relevant indicator of overall well-being and affect, in adult male and female C57BL/6J mice. Females required a higher dose of U50,488 to suppress nesting, and a higher dose of aticaprant to restore U50,488-induced impairment of nesting. Females also required a higher dose of aticaprant to decrease immobility scores in the forced swim test. Pretreatment with the estrogen receptor modulator tamoxifen, at a dose which blocked estrogen receptors, augmented the effect of U50,488 on nesting in female mice, suggesting that estrogen receptors play a key role in attenuating the effects of KOR ligands in female mice. Together, these results suggest that females are less sensitive to KOR mediation, requiring a higher dose to achieve comparable results to males. This behavioral sensitivity, as measured by nesting, may be mediated by estrogen receptors. Together these studies highlight the importance of comparing sex differences in response to KOR regulation on behaviors related to affective states.

Behavioral Phenotyping for Down Syndrome in Mice

Down syndrome (DS) is the most frequent genetic cause of intellectual disability, characterized by alterations in different behavioral symptom domains: neurodevelopment, motor behavior, and cognition. As mouse models have the potential to generate data regarding the neurological basis for the specific behavioral profile of DS, and may indicate pharmacological treatments with the potential to affect their behavioral phenotype, it is important to be able to assess disease-relevant behavioral traits in animal models in order to provide biological plausibility to the potential findings. The field is at a juncture that requires assessments that may effectively translate the findings acquired in mouse models to humans with DS. In this article, behavioral tests are described that are relevant to the domains affected in DS. A neurodevelopmental behavioral screen, the balance beam test, and the Multivariate Concentric Square Field test to assess multiple behavioral phenotypes and locomotion are described, discussing the ways to merge these findings to more fully understand cognitive strengths and weaknesses in this population. New directions for approaches to cognitive assessment in mice and humans are discussed. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Preweaning neurodevelopmental battery Basic Protocol 2: Balance beam Basic Protocol 3: Multivariate concentric square field test (MCSF).

Reduction in BDNF from Inefficient Precursor Conversion Influences Nest Building and Promotes Depressive-Like Behavior in Mice

We generated a knock-in mouse line in which the gene encoding brain-derived neurotrophic factor (Bdnf) was replaced with a sequence for proBDNF containing human single nucleotide polymorphisms encoding arginines proximal to the cleavage site (R125M and R127L). The ratio of the mature form of BDNF (mBDNF) to precursor BDNF (proBDNF) in hippocampal tissue lysates was decreased in a manner dependent on the number of copies of the mutant gene, indicating that the mutations inhibited proteolytic conversion of proBDNF into mBDNF. Although homozygous mice had a proBDNF/mBDNF ratio of ~9:1, they survived until adulthood. The levels of mBDNF were reduced by 57% in heterozygous mutant mice, which exhibited a depressive-like behavior in the tail suspension test and weight gain when housed in social isolation, showing that impaired proBDNF cleavage contributes to stress-induced depressive-like phenotypes. Furthermore, socially isolated heterozygous mice displayed a pronounced deficit in daily nest-building behaviors. These findings suggest that the decreased production of mBDNF by impaired proBDNF cleavage disturbs daily activities in mice.

Prefrontal-hippocampal functional connectivity encodes recognition memory and is impaired in intellectual disability

Down syndrome (DS) is the most common form of intellectual disability. The cognitive alterations in DS are thought to depend on brain regions critical for learning and memory such as the prefrontal cortex (PFC) and the hippocampus (HPC). Neuroimaging studies suggest that increased brain connectivity correlates with lower intelligence quotients (IQ) in individuals with DS; however, its contribution to cognitive impairment is unresolved. We recorded neural activity in the PFC and HPC of the trisomic Ts65Dn mouse model of DS during quiet wakefulness, natural sleep, and the performance of a memory test. During rest, trisomic mice showed increased theta oscillations and cross-frequency coupling in the PFC and HPC while prefrontal-hippocampal synchronization was strengthened, suggesting hypersynchronous local and cross-regional processing. During sleep, slow waves were reduced, and gamma oscillations amplified in Ts65Dn mice, likely reflecting prolonged light sleep. Moreover, hippocampal sharp-wave ripples were disrupted, which may have further contributed to deficient memory consolidation. Memory performance in euploid mice correlated strongly with functional connectivity measures that indicated a hippocampal control over memory acquisition and retrieval at theta and gamma frequencies, respectively. By contrast, trisomic mice exhibited poor memory abilities and disordered prefrontal-hippocampal functional connectivity. Memory performance and key neurophysiological alterations were rescued after 1 month of chronic administration of a green tea extract containing epigallocatequin-3-gallate (EGCG), which improves executive function in young adults with DS and Ts65Dn mice. Our findings suggest that abnormal prefrontal-hippocampal circuit dynamics are candidate neural mechanisms for memory impairment in DS.

Btbd3 expression regulates compulsive-like and exploratory behaviors in mice

BTB/POZ domain-containing 3 (BTBD3) was identified as a potential risk gene in the first genome-wide association study of obsessive-compulsive disorder (OCD). BTBD3 is a putative transcription factor implicated in dendritic pruning in developing primary sensory cortices. We assessed whether BTBD3 also regulates neural circuit formation within limbic cortico-striato-thalamo-cortical circuits and behaviors related to OCD in mice. Behavioral phenotypes associated with OCD that are measurable in animals include compulsive-like behaviors and reduced exploration. We tested Btbd3 wild-type, heterozygous, and knockout mice for compulsive-like behaviors including cage-mate barbering, excessive wheel-running, repetitive locomotor patterns, and reduced goal-directed behavior in the probabilistic learning task (PLT), and for exploratory behavior in the open field, digging, and marble-burying tests. Btbd3 heterozygous and knockout mice showed excessive barbering, wheel-running, impaired goal-directed behavior in the PLT, and reduced exploration. Further, chronic treatment with fluoxetine, but not desipramine, reduced barbering in Btbd3 wild-type and heterozygous, but not knockout mice. In contrast, Btbd3 expression did not alter anxiety-like, depression-like, or sensorimotor behaviors. We also quantified dendritic morphology within anterior cingulate cortex, mediodorsal thalamus, and hippocampus, regions of high Btbd3 expression. Surprisingly, Btbd3 knockout mice only showed modest increases in spine density in the anterior cingulate, while dendritic morphology was unaltered elsewhere. Finally, we virally knocked down Btbd3 expression in whole, or just dorsal, hippocampus during neonatal development and assessed behavior during adulthood. Whole, but not dorsal, hippocampal Btbd3 knockdown recapitulated Btbd3 knockout phenotypes. Our findings reveal that hippocampal Btbd3 expression selectively modulates compulsive-like and exploratory behavior.

Luteolin induces hippocampal neurogenesis in the Ts65Dn mouse model of Down syndrome

Studies have shown that the natural flavonoid luteolin has neurotrophic activity. In this study, we investigated the effect of luteolin in a mouse model of Down syndrome. Ts65Dn mice, which are frequently used as a model of Down syndrome, were intraperitoneally injected with 10 mg/kg luteolin for 4 consecutive weeks starting at 12 weeks of age. The Morris water maze test was used to evaluate learning and memory abilities, and the novel object recognition test was used to assess recognition memory. Immunohistochemistry was performed for the neural stem cell marker nestin, the astrocyte marker glial fibrillary acidic protein, the immature neuron marker DCX, the mature neuron marker NeuN, and the cell proliferation marker Ki67 in the hippocampal dentate gyrus. Nissl staining was used to observe changes in morphology and to quantify cells in the dentate gyrus. Western blot assay was used to analyze the protein levels of brain-derived neurotrophic factor (BDNF) and phospho-extracellular signal-regulated kinase 1/2 (p-ERK1/2) in the hippocampus. Luteolin improved learning and memory abilities as well as novel object recognition ability, and enhanced the proliferation of neurons in the hippocampal dentate gyrus. Furthermore, luteolin increased expression of nestin and glial fibrillary acidic protein, increased the number of DCX⁺ neurons in the granular layer and NeuN⁺ neurons in the subgranular region of the dentate gyrus, and increased the protein levels of BDNF and p-ERK1/2 in the hippocampus. Our findings show that luteolin improves behavioral performance and promotes hippocampal neurogenesis in Ts65Dn mice. Moreover, these effects might be associated with the activation of the BDNF/ERK1/2 pathway.

Effect of Continuous Trio Breeding Compared with Continuous Pair Breeding in 'Shoebox' Caging on Measures of Reproductive Performance in Estrogen Receptor Knockout Mice

Some performance standards for continuous trio breeding in 'shoebox' cages for inbred stocks and outbred strains of mice challenge the minimum floor space recommendations in the 8th edition of the Guide for the Care and Use of Laboratory Animals. In our study, we evaluated whether continuous trio breeding could be successfully applied to a breeding colony of genetically engineered mice housed in shoebox cages with a floor area of 67.6 in2. Mice heterozygous for genetically engineered mutations to estrogen receptors and their wildtype counterparts were continuously bred as trios or pairs. Confounding environmental factors were controlled through standardized husbandry practices and husbandry, and all mice were bred simultaneously to control for temporal factors. Several measures of reproductive performance-including number of litters per female, production index, interlitter interval, litter size at birth, litter size at weaning, weaning rate, and body weight of pups at weaning- were evaluated over approximately 6 mo. Regardless of genotype, interlitter interval, litter size at birth, and litter size at weaning were significantly lower for trio-bred mice than for pair-bred mice. In addition, significant interactions emerged between genotype and breeding strategy for these reproductive measures. Furthermore, significant differences between genotypes occurred for interlitter interval and weaning rate, regardless of breeding strategy. Underlying mechanisms to account for effects of genotype on interlitter interval and the interaction of genotype with breeding strategy were unclear but may reflect effects of overcrowding and reproductive suppression.

Overexpression of the DYRK1A Gene (Dual-Specificity Tyrosine Phosphorylation-Regulated Kinase 1A) Induces Alterations of the Serotoninergic and Dopaminergic Processing in Murine Brain Tissues

Trisomy 21 (T21) or Down syndrome (DS) is the most common genetic disorder associated with intellectual disability and affects around 5 million persons worldwide. Neuroanatomical phenotypes associated with T21 include slight reduction of brain size and weight, abnormalities in several brain areas including spines dysgenesis, dendritic morphogenesis, and early neuroanatomical characteristics of Alzheimer's disease. Monoamine neurotransmitters are involved in dendrites development, functioning of synapses, memory consolidation, and their levels measured in the cerebrospinal fluid, blood, or brain areas that are modified in individuals with T21. DYRK1A is one of the recognized key genes that could explain some of the deficits present in individuals with T21. We investigated by high-performance liquid chromatography with electrochemical detection the contents and processing of monoamines neurotransmitters in four brain areas of female and male transgenic mice for the Dyrk1a gene (mBactgDyrk1a). DYRK1A overexpression induced dramatic deficits in the serotonin contents of the four brain areas tested and major deficits in dopamine and adrenaline contents especially in the hypothalamus. These results suggest that DYRK1A overexpression might be associated with the modification of monoamines content found in individuals with T21 and reinforce the interest to target the level of DYRK1A expression as a therapeutic approach for persons with T21.

Blood phenylalanine reduction corrects CNS dopamine and serotonin deficiencies and partially improves behavioral performance in adult phenylketonuric mice

Central nervous system (CNS) deficiencies of the monoamine neurotransmitters dopamine and serotonin have been implicated in the pathophysiology of neuropsychiatric dysfunction in human phenylketonuria (PKU). In this study, we confirmed the occurrence of brain dopamine and serotonin deficiencies in association with severe behavioral alterations and cognitive impairments in hyperphenylalaninemic C57BL/6-Pah^enu2/enu2 mice, a model of human PKU. Phenylalanine-reducing treatments, including either dietary phenylalanine restriction or liver-directed gene therapy, initiated during adulthood were associated with increased brain monoamine content along with improvements in nesting behavior but without a change in the severe cognitive deficits exhibited by these mice. At euthanasia, there was in Pah^enu2/enu2 brain a significant reduction in the protein abundance and maximally stimulated activities of tyrosine hydroxylase (TH) and tryptophan hydroxylase 2 (TPH2), the rate limiting enzymes catalyzing neuronal dopamine and serotonin synthesis respectively, in comparison to levels seen in wild type brain. Phenylalanine-reducing treatments initiated during adulthood did not affect brain TH or TPH2 content or maximal activity. Despite this apparent fixed deficit in striatal TH and TPH2 activities, initiation of phenylalanine-reducing treatments yielded substantial correction of brain monoamine neurotransmitter content, suggesting that phenylalanine-mediated competitive inhibition of already constitutively reduced TH and TPH2 activities is the primary cause of brain monoamine deficiency in Pah^enu2 mouse brain. We propose that CNS monoamine deficiency may be the cause of the partially reversible adverse behavioral effects associated with chronic HPA in Pah^enu2 mice, but that phenylalanine-reducing treatments initiated during adulthood are unable to correct the neuropathology and attendant cognitive deficits that develop during juvenile life in late-treated Pah^enu2/enu2 mice.

Deleterious Effects of Chronic Folate Deficiency in the Ts65Dn Mouse Model of Down Syndrome

Folate is an important B vitamin naturally found in the human diet and plays a critical role in methylation of nucleic acids. Indeed, abnormalities in this major epigenetic mechanism play a pivotal role in the pathogenesis of cognitive deficit and intellectual disability in humans. The most common cause of cognitive dysfunction in children is Down syndrome (DS). Since folate deficiency is very common among the pediatric population, we questioned whether chronic folate deficiency (CFD) exacerbates cognitive dysfunction in a mouse model of DS. To test this, adult Ts65Dn mice and their disomic littermates were chronically fed a diet free of folic acid while preventing endogenous production of folate in the digestive tract for a period of 8 weeks. Our results show that the Ts65Dn mouse model of DS was significantly more vulnerable to CFD in terms of plasma homocysteine and N5-methyltetrahydrofolate (5-MTHF) levels. Importantly, these changes were linked to degenerative alterations in hippocampal dendritic morphology and impaired nest building behavior in Ts65Dn mice. Based on our results, a rigorous examination of folate intake and its metabolism in individuals with DS is warranted.

Social defeat models in animal science: What we have learned from rodent models

Studies on stress and its impacts on animals are very important in many fields of science, including animal science, because various stresses influence animal production and animal welfare. In particular, the social stresses within animal groups have profound impact on animals, with the potential to induce abnormal behaviors and health problems. In humans, social stress induces several health problems, including psychiatric disorders. In animal stress models, social defeat models are well characterized and used in various research fields, particularly in studies concerning mental disorders. Recently, we have focused on behavior, nutrition and metabolism in rodent models of social defeat to elucidate how social stresses affect animals. In this review, recent significant progress in studies related to animal social defeat models are described. In the field of animal science, these stress models may contribute to advances in the development of functional foods and in the management of animal welfare.

Ts1Cje Down syndrome model mice exhibit environmental stimuli-triggered locomotor hyperactivity and sociability concurrent with increased flux through central dopamine and serotonin metabolism

Ts1Cje mice have a segmental trisomy of chromosome 16 that is orthologous to human chromosome 21 and display Down syndrome-like cognitive impairments. Despite the occurrence of affective and emotional impairments in patients with Down syndrome, these parameters are poorly documented in Down syndrome mouse models, including Ts1Cje mice. Here, we conducted comprehensive behavioral analyses, including anxiety-, sociability-, and depression-related tasks, and biochemical analyses of monoamines and their metabolites in Ts1Cje mice. Ts1Cje mice showed enhanced locomotor activity in novel environments and increased social contact with unfamiliar partners when compared with wild-type littermates, but a significantly lower activity in familiar environments. Ts1Cje mice also exhibited some signs of decreased depression like-behavior. Furthermore, Ts1Cje mice showed monoamine abnormalities, including increased extracellular dopamine and serotonin, and enhanced catabolism in the striatum and ventral forebrain. This study constitutes the first report of deviated monoamine metabolism that may help explain the basis for abnormal behaviors, including the environmental stimuli-triggered hyperactivity, increased sociability and decreased depression-like behavior in Ts1Cje mice.

The acute social defeat stress and nest-building test paradigm: A potential new method to screen drugs for depressive-like symptoms

Psychosocial stress can cause mental conditions such as depression in humans. To develop drug therapies for the treatment of depression, it is necessary to use animal models of depression to screen drug candidates that exhibit anti-depressive effects. Unfortunately, the present methods of drug screening for antidepressants, the forced-swim test and tail-suspension test, are limiting factors in drug discovery because they are not based on the constructive validity of objective phenotypes in depression. Previously, we discovered that the onset of nest building is severely delayed in mice exposed to subchronic mild social defeat stress (sCSDS). Therefore, a novel paradigm combining acute social defeat stress (ASDS) and the nest-building test (SNB) were established for the efficient screening of drugs for depressive-like symptoms. Since ASDS severely delayed the nest-building process as shown in chronically social defeated mice, we sought to rescue the delayed nest-building behavior in ASDS mice. Injecting a specific serotonin 2a receptor antagonist (SR-46349B), the nest-building deficit exhibited by ASDS mice was partially rescued. On the other hand, a selective serotonin reuptake inhibitor (fluoxetine) did not rescue the nest-building deficit in ASDS mice. Therefore, we conclude that the SNB paradigm is an another potential behavioral method for screening drugs for depressive-like symptoms including attention deficit, anxiety, low locomotion, and decreased motivation.

Transcriptional dysregulation causes altered modulation of inhibition by haloperidol

Many neuropsychiatric and neurodevelopmental disorders such as schizophrenia and autism involve interneuron transcriptional dysregulation. The transcriptional coactivator PGC-1α regulates gene expression in GABAergic interneurons, which are important for regulating hippocampal network activity. Genetic deletion of PGC-1α causes a decrease in parvalbumin expression, similar to what is observed in schizophrenia postmortem tissue. Our lab has previously shown that PGC-1α-/- mice have enhanced GABAergic inhibition onto CA1 pyramidal cells, which increases the inhibition/excitation (I/E) ratio, alters hippocampal circuit function, and impairs hippocampal dependent behavior. The typical antipsychotic haloperidol, a dopamine receptor antagonist with selectivity for D2-like receptors, has previously been shown to increase excitation in the CA1 region of hippocampus. We therefore tested whether haloperidol could normalize the I/E balance in CA1 of PGC-1α-/- mice, potentially improving circuit function and behavior. Surprisingly, we discovered instead that interneuron transcriptional dysregulation caused by loss of PGC-1α alters the effects of haloperidol on hippocampal synaptic transmission and circuit function. Acute administration of haloperidol causes disinhibition in CA1 and decreases the I/E ratio onto CA1 pyramidal cells in slices from PGC-1α+/+ mice, but not PGC-1α-/- mice. The spread of activity in CA1, assessed by voltage sensitive dye imaging, is increased by haloperidol in slices from PGC-1α+/+ mice; however haloperidol decreases the spread of activity in slices from PGC-1α-/- mice. Haloperidol increased the power of hippocampal gamma oscillation in slices from PGC-1α+/+ mice but reduced the power of gamma oscillations in slices from PGC-1α-/- mice. Nest construction, an innate hippocampal-dependent behavior, is inhibited by haloperidol in PGC-1α+/+ mice, but not in PGC-1α-/- mice, which already have impaired nest building. The effects of haloperidol are mimicked and occluded by a D2 receptor antagonist in slices from PGC-1α+/+ mice, and the effects of blocking D2 receptors are lost in slices from PGC-1α-/- mice, although there is no change in D2 receptor transcript levels. Together, our results show that hippocampal inhibitory synaptic transmission, CA1 circuit function, and hippocampal dependent behavior are modulated by the antipsychotic haloperidol, and that these effects of haloperidol are lost in PGC-1α-/- mice. These results have implications for the treatment of individuals with conditions involving PGC-1α deficiency.

Effects of acute alcohol withdrawal on nest building in mice selectively bred for alcohol withdrawal severity

Nest building has been used to assess thermoregulatory behavior and positive motivational states in mice. There are known genetic influences on ethanol withdrawal severity as well as individual/thermoregulatory nest building. Withdrawal Seizure-Prone (WSP-1, WSP-2) and Withdrawal Seizure-Resistant (WSR-1, WSR-2) mice were selectively bred for high vs low handling-induced convulsion (HIC) severity, respectively, during withdrawal from chronic ethanol vapor inhalation. They also differ in HIC severity during withdrawal from an acute, 4g/kg ethanol injection. In our initial study, withdrawal from an acute dose of ethanol dose-dependently impaired nest building over the initial 24h of withdrawal in genetically segregating Withdrawal Seizure Control (WSC) mice. In two further studies, acute ethanol withdrawal suppressed nest building for up to two days in WSP-1 females. Deficits in nest building from ethanol were limited to the initial 10h of withdrawal in WSR-1 females and to the initial 24h of withdrawal in WSP-1 and WSR-1 males. Effects of ethanol on nest building for up to two days were found in WSP-2 and WSR-2 mice of both sexes. Nest building deficits in female mice from the first replicate could not be explained by a general decrease in locomotor behavior. These results suggest that nest building is a novel behavioral phenotype for indexing the severity of acute ethanol withdrawal, and that genes contributing to this trait differ from those affecting acute withdrawal HIC severity.

Expression of A152T human tau causes age-dependent neuronal dysfunction and loss in transgenic mice

A152T-variant human tau (hTau-A152T) increases risk for tauopathies, including Alzheimer's disease. Comparing mice with regulatable expression of hTau-A152T or wild-type hTau (hTau-WT), we find age-dependent neuronal loss, cognitive impairments, and spontaneous nonconvulsive epileptiform activity primarily in hTau-A152T mice. However, overexpression of either hTau species enhances neuronal responses to electrical stimulation of synaptic inputs and to an epileptogenic chemical. hTau-A152T mice have higher hTau protein/mRNA ratios in brain, suggesting that A152T increases production or decreases clearance of hTau protein. Despite their functional abnormalities, aging hTau-A152T mice show no evidence for accumulation of insoluble tau aggregates, suggesting that their dysfunctions are caused by soluble tau. In human amyloid precursor protein (hAPP) transgenic mice, co-expression of hTau-A152T enhances risk of early death and epileptic activity, suggesting copathogenic interactions between hTau-A152T and amyloid-β peptides or other hAPP metabolites. Thus, the A152T substitution may augment risk for neurodegenerative diseases by increasing hTau protein levels, promoting network hyperexcitability, and synergizing with the adverse effects of other pathogenic factors.

Interneuron Transcriptional Dysregulation Causes Frequency-Dependent Alterations in the Balance of Inhibition and Excitation in Hippocampus

Circuit dysfunction in complex brain disorders such as schizophrenia and autism is caused by imbalances between inhibitory and excitatory synaptic transmission (I/E). Short-term plasticity differentially alters responses from excitatory and inhibitory synapses, causing the I/E ratio to change as a function of frequency. However, little is known about I/E ratio dynamics in complex brain disorders. Transcriptional dysregulation in interneurons, particularly parvalbumin interneurons, is a consistent pathophysiological feature of schizophrenia. Peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α) is a transcriptional coactivator that in hippocampus is highly concentrated in inhibitory interneurons and regulates parvalbumin transcription. Here, we used PGC-1α(-/-) mice to investigate effects of interneuron transcriptional dysregulation on the dynamics of the I/E ratio at the synaptic and circuit level in hippocampus. We find that loss of PGC-1α increases the I/E ratio onto CA1 pyramidal cells in response to Schaffer collateral stimulation in slices from young adult mice. The underlying mechanism is enhanced basal inhibition, including increased inhibition from parvalbumin interneurons. This decreases the spread of activation in CA1 and dramatically limits pyramidal cell spiking, reducing hippocampal output. The I/E ratio and CA1 output are partially restored by paired-pulse stimulation at short intervals, indicating frequency-dependent effects. However, circuit dysfunction persists, indicated by alterations in kainate-induced gamma oscillations and impaired nest building. Together, these results show that transcriptional dysregulation in hippocampal interneurons causes frequency-dependent alterations in I/E ratio and circuit function, suggesting that PGC-1α deficiency in psychiatric and neurological disorders contributes to disease by causing functionally relevant alterations in I/E balance.

SIGNIFICANCE STATEMENT

Alteration in the inhibitory and excitatory synaptic transmission (I/E) balance is a fundamental principle underlying the circuit dysfunction observed in many neuropsychiatric and neurodevelopmental disorders. The I/E ratio is dynamic, continuously changing because of synaptic short-term plasticity. We show here that transcriptional dysregulation in interneurons, particularly parvalbumin interneurons, causes frequency-dependent alterations in the I/E ratio and in circuit function in hippocampus. Peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α-deficient) mice have enhanced inhibition in CA1, the opposite of what is seen in cortex. This study fills an important gap in current understanding of how changes in inhibition in complex brain disorders affect I/E dynamics, leading to region-specific circuit dysfunction and behavioral impairment. This study also provides a conceptual framework for analyzing the effects of short-term plasticity on the I/E balance in disease models.

Longitudinal measures of cognition in the Ts65Dn mouse: Refining windows and defining modalities for therapeutic intervention in Down syndrome

Mouse models have provided insights into adult changes in learning and memory in Down syndrome, but an in-depth assessment of how these abnormalities develop over time has never been conducted. To address this shortcoming, we conducted a longitudinal behavioral study from birth until late adulthood in the Ts65Dn mouse model to measure the emergence and continuity of learning and memory deficits in individuals with a broad array of tests. Our results demonstrate for the first time that the pace at which neonatal and perinatal milestones are acquired is correlated with later cognitive performance as an adult. In addition, we find that life-long behavioral indexing stratifies mice within each genotype. Our expanded assessment reveals that diminished cognitive flexibility, as measured by reversal learning, is the most robust learning and memory impairment in both young and old Ts65Dn mice. Moreover, we find that reversal learning degrades with age and is therefore a useful biomarker for studying age-related decline in cognitive ability. Altogether, our results indicate that preclinical studies aiming to restore cognitive function in Ts65Dn should target both neonatal milestones and reversal learning in adulthood. Here we provide the quantitative framework for this type of approach.

Early environmental therapy rescues brain development in a mouse model of Down syndrome

Down syndrome (DS), the most common genetic disorder associated with intellectual disabilities, is an untreatable condition characterized by a number of developmental defects and permanent deficits in the adulthood. Ts65Dn mice, the major animal model for DS, display severe cognitive and synaptic plasticity defects closely resembling the human phenotype. Here, we employed a multidisciplinary approach to investigate, for the first time in developing Ts65Dn mice, the effects elicited by early environmental enrichment (EE) on brain maturation and function. We report that exposure to EE resulted in a robust increase in maternal care levels displayed by Ts65Dn mothers and led to a normalization of declarative memory abilities and hippocampal plasticity in trisomic offspring. The positive effects of EE on Ts65Dn phenotype were not limited to the cognitive domain, but also included a rescue of visual system maturation. The beneficial EE effects were accompanied by increased BDNF and correction of over-expression of the GABA vesicular transporter vGAT. These findings highlight the beneficial impact of early environmental stimuli and their potential for application in the treatment of major functional deficits in children with DS.

Assessing nest-building behavior of mice using a 3D depth camera

We developed a novel method to evaluate the nest-building behavior of mice using an inexpensive depth camera. The depth camera clearly captured nest-building behavior. Using three-dimensional information from the depth camera, we obtained objective features for assessing nest-building behavior, including "volume," "radius," and "mean height". The "volume" represents the change in volume of the nesting material, a pressed cotton square that a mouse shreds and untangles in order to build its nest. During the nest-building process, the total volume of cotton fragments is increased. The "radius" refers to the radius of the circle enclosing the fragments of cotton. It describes the extent of nesting material dispersion. The "radius" averaged approximately 60mm when a nest was built. The "mean height" represents the change in the mean height of objects. If the nest walls were high, the "mean height" was also high. These features provided us with useful information for assessment of nest-building behavior, similar to conventional methods for the assessment of nest building. However, using the novel method, we found that JF1 mice built nests with higher walls than B6 mice, and B6 mice built nests faster than JF1 mice. Thus, our novel method can evaluate the differences in nest-building behavior that cannot be detected or quantified by conventional methods. In future studies, we will evaluate nest-building behaviors of genetically modified, as well as several inbred, strains of mice, with several nesting materials.