Digging and marble burying in mice: simple methods for in vivo identification of biological impacts

Maternal immune activation modifies the course of Niemann-pick disease, type C1 in a gender specific manner

Niemann-Pick disease, type C1 (NPC1) is a rare neurodegenerative lysosomal storage disease with a wide spectrum of clinical manifestation. Multiple genetic factors influence the NPC1 mouse phenotype, but very little attention has been given to prenatal environmental factors that might have long-term effects on the neuroinflammatory component of NPC1 pathology. Studies in other mouse models of cerebellar ataxia have shown that developmental exposures lead to Purkinje neuron degeneration later in life, suggesting that environmental exposures during development can impact cerebellar biology. Thus, we evaluated the potential effect of maternal immune activation (MIA) on disease progression in an Npc1 mouse model. The MIA paradigm used mimics viral infection using the toll like receptor 3 agonist polyinosinic-polycytidilic acid during gestation. Through phenotypic and pathologic tests, we measured motor and behavioral changes as well as cerebellar neuroinflammation and neurodegeneration. We observed a gender and genotype dependent effect of MIA on the cerebellum. While the effects of MIA have been previously shown to primarily affect male progeny, we observed increased sensitivity of female mutant progeny to prenatal exposure to treatment with polyinosinic-polycytidilic acid. Specifically, prenatal MIA resulted in female NPC1 mutant progeny with greater motor deficits and a corresponding decrease in cerebellar Purkinje neurons. Our data suggest that prenatal environmental exposures may be one factor contributing to the phenotypic variability observed in individuals with NPC1.

Environmental Enrichment: Disentangling the Influence of Novelty, Social, and Physical Activity on Cerebral Amyloid Angiopathy in a Transgenic Mouse Model

Cerebral amyloid angiopathy (CAA) is the deposition of amyloid protein in the cerebral vasculature, a common feature in both aging and Alzheimer's disease (AD). However, the effects of environmental factors, particularly cognitive stimulation, social stimulation, and physical activity, on CAA pathology are poorly understood. These factors, delivered in the form of the environmental enrichment (EE) paradigm in rodents, have been shown to have beneficial effects on the brain and behavior in healthy aging and AD models. However, the relative importance of these subcomponents on CAA pathology has not been investigated. Therefore, we assessed the effects of EE, social enrichment (SOC), and cognitive enrichment (COG) compared to a control group that was single housed without enrichment (SIN) from 4 to 8 months of age in wild-type mice (WT) and Tg-SwDI mice, a transgenic mouse model of CAA that exhibits cognitive/behavioral deficits. The results show that individual facets of enrichment can affect an animal model of CAA, though the SOC and combined EE conditions are generally the most effective at producing physiological, cognitive/behavioral, and neuropathological changes, adding to a growing literature supporting the benefits of lifestyle interventions.

Brain-wide functional architecture remodeling by alcohol dependence and abstinence

Alcohol abuse and alcohol dependence are key factors in the development of alcohol use disorder, which is a pervasive societal problem with substantial economic, medical, and psychiatric consequences. Although our understanding of the neurocircuitry that underlies alcohol use has improved, novel brain regions that are involved in alcohol use and novel biomarkers of alcohol use need to be identified. The present study used a single-cell whole-brain imaging approach to 1) assess whether abstinence from alcohol in an animal model of alcohol dependence alters the functional architecture of brain activity and modularity, 2) validate our current knowledge of the neurocircuitry of alcohol abstinence, and 3) discover brain regions that may be involved in alcohol use. Alcohol abstinence resulted in the whole-brain reorganization of functional architecture in mice and a pronounced decrease in modularity that was not observed in nondependent moderate drinkers. Structuring of the alcohol abstinence network revealed three major brain modules: 1) extended amygdala module, 2) midbrain striatal module, and 3) cortico-hippocampo-thalamic module, reminiscent of the three-stage theory. Many hub brain regions that control this network were identified, including several that have been previously overlooked in alcohol research. These results identify brain targets for future research and demonstrate that alcohol use and dependence remodel brain-wide functional architecture to decrease modularity. Further studies are needed to determine whether the changes in coactivation and modularity that are associated with alcohol abstinence are causal features of alcohol dependence or a consequence of excessive drinking and alcohol exposure.

Behavioral adaptations in a relapsing mouse model of colitis

Inflammatory bowel disease (IBD) is characterized by relapsing periods of gut inflammation, and is comorbid with depression, anxiety, and cognitive deficits. Animal models of IBD that explore the behavioral consequences almost exclusively use acute models of gut inflammation, which fails to recapitulate the cyclic, chronic nature of IBD. This study sought to identify behavioral differences in digging, memory, and stress-coping strategies in mice exposed to one (acute) or three (chronic) cycles of gut inflammation, using the dextran sodium sulfate (DSS) model of colitis. Similar levels of gut pathology were observed between acute and chronically exposed mice, although mice in the chronic treatment had significantly shorter colons, suggesting more severe disease. Behavioral measures revealed an unexpected pattern in which chronic treatment evoked fewer deficits than acute treatment. Specifically, acutely-treated mice showed alterations in measures of object burying, novel object recognition, object location memory, and stress-coping (forced swim task). Chronically-treated animals, however, showed similar alterations in object burying, but not the other measures. These data suggest an adaptive or tolerizing effect of repeated cycles of peripheral gut inflammation on mnemonic function and stress-coping, whereas some other behaviors continue to be affected by gut inflammation. We speculate that the normalization of some functions may involve the reversion to the baseline state of the hypothalamic-pituitary-adrenal axis and/or levels of neuroinflammation, which are both activated by the first exposure to the colitic agent.

Early-life stress impairs postnatal oligodendrogenesis and adult emotional behaviour through activity-dependent mechanisms

Exposure to stress during early life (infancy/childhood) has long-term effects on the structure and function of the prefrontal cortex (PFC), and increases the risk for adult depression and anxiety disorders. However, little is known about the molecular and cellular mechanisms of these effects. Here, we focused on changes induced by chronic maternal separation during the first 2 weeks of postnatal life. Unbiased mRNA expression profiling in the medial PFC (mPFC) of maternally separated (MS) pups identified an increased expression of myelin-related genes and a decreased expression of immediate early genes. Oligodendrocyte lineage markers and birthdating experiments indicated a precocious oligodendrocyte differentiation in the mPFC at P15, leading to a depletion of the oligodendrocyte progenitor pool in MS adults. We tested the role of neuronal activity in oligodendrogenesis, using designed receptors exclusively activated by designed drugs (DREADDs) techniques. hM4Di or hM3Dq constructs were transfected into mPFC neurons using fast-acting AAV8 viruses. Reduction of mPFC neuron excitability during the first 2 postnatal weeks caused a premature differentiation of oligodendrocytes similar to the MS pups, while chemogenetic activation normalised it in the MS animals. Bidirectional manipulation of neuron excitability in the mPFC during the P2-P14 period had long lasting effects on adult emotional behaviours and on temporal object recognition: hM4Di mimicked MS effects, while hM3Dq prevented the pro-depressive effects and short-term memory impairment of MS. Thus, our results identify neuronal activity as a critical target of early-life stress and demonstrate its function in controlling both postnatal oligodendrogenesis and adult mPFC-related behaviours.

Involvement of oxidative stress and mitochondrial mechanisms in air pollution-related neurobiological impairments

Background

Vehicle exhaust emissions are known to be significant contributors to physical and psychological stress. Vehicle exhaust-induced stress and associated respiratory and cardiovascular complications are well-known, but the impact of this stress on the brain is unclear. Simulated vehicle exhaust exposure (SVEE) in rats causes behavioral and cognitive deficits. In the present study, the underlying mechanisms were examined. Our postulation is that SVEE, a simulation of physiologically relevant concentrations of pro-oxidants (0.04% carbon dioxide, 0.9 ppm nitrogen dioxide, 3 ppm carbon monoxide) creates a toxic stress environment in the brain that results in an imbalance between production of reactive oxygen species and the counteracting antioxidant mechanisms. This impairs mitochondrial function in the high bioenergetic demand areas of the brain including the hippocampus (HIP), amygdala (AMY) and the prefrontal cortex (PFC), disrupting neuronal network, and causing behavioral deficits. Mitochondria-targeted antioxidant Mito-Q protects against these impairments.

Methods

Sprague Dawley rats were provided with Mito-Q (250 μM) in drinking water for 4 weeks followed by SVEE 5 h/day for 2 weeks, followed by behavioral and biochemical assessments.

Results

SVEE resulted in anxiety- and depression-like behavior, accompanied with increased oxidative stress, diminished antioxidant response and mitochondrial impairment reflected from electron transport chain (ETC) disruption, reduced oxygen consumption, low adenosine tri-phosphate (ATP) synthesis and an alteration in the mitochondrial biochemical dynamics assessed via protein expression profiles of mitochondrial fission marker, dynamin-related protein-1 and fusion markers, mitofusin-1/2 in the HIP, AMY and the PFC. Mito-Q treatment prevented SVEE-induced behavioral deficits, attenuated rise in oxidative stress and also prevented SVEE-induced mitochondrial impairment.

Conclusion

This study demonstrates a causal mechanism mediating SVEE-induced behavioral deficits in rats. We further established that SVEE is a toxicological stressor that induces oxidative stress and results in mitochondrial impairment, which by disrupting neural circuitry impairs cognitive and behavioral functions.

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Simulated vehicle exhaust exposure is a source of toxicological stress.

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Prolonged exposure leads to behavioral deficits and elevated oxidative stress.

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Oxidative stress elevation triggers mitochondrial impairment in the brain.

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Mito-Q prevents exhaust-associated behavioral and biochemical alterations.

Bridging the species gap in translational research for neurodevelopmental disorders

The prevalence and societal impact of neurodevelopmental disorders (NDDs) continue to increase despite years of research in both patient populations and animal models. There remains an urgent need for translational efforts between clinical and preclinical research to (i) identify and evaluate putative causes of NDD, (ii) determine their underlying neurobiological mechanisms, (iii) develop and test novel therapeutic approaches, and (iv) translate basic research into safe and effective clinical practices. Given the complexity behind potential causes and behaviors affected by NDDs, modeling these uniquely human brain disorders in animals will require that we capitalize on unique advantages of a diverse array of species. While much NDD research has been conducted in more traditional animal models such as the mouse, ultimately, we may benefit from creating animal models with species that have a more sophisticated social behavior repertoire such as the rat (Rattus norvegicus) or species that more closely related to humans, such as the rhesus macaque (Macaca mulatta). Here, we highlight the rat and rhesus macaque models for their role in previous psychological research discoveries, current efforts to understand the neurobiology of NDDs, and focus on the convergence of behavior outcome measures that parallel features of human NDDs.

Prokineticin 2 promotes and sustains neuroinflammation in vincristine treated mice: Focus on pain and emotional like behavior

Vincristine (VCR) treatment is often associated to painful neuropathy. Its development is independent from antitumoral mechanism and involves neuroinflammation. We investigated the role of the chemokine prokineticin (PK)2 in a mouse model of VCR induced neuropathy using a PK-receptors (PK-R) antagonist to counteract its development. We also evaluated emotional like deficits in VCR mice. VCR (0,1 mg/kg) was i.p. injected in C57BL/6J male mice once a day for 14 consecutive days. Pain, anxiety and depressive like behaviors were assessed in animals. PK2, PK-Rs, cytokines, neuroinflammatory markers (CD68, CD11b, GFAP, TLR4) and ATF3 were evaluated in DRG, spinal cord, prefrontal cortex and hippocampus. The PK-Rs antagonist PC1, was s.c. injected (150 μg/kg) twice a day from day 7 (hypersensitivity state) until day 14. Its effect on pain and neuroinflammation was evaluated. VCR mice developed neuropathic pain but not mood alterations. After 7 days of VCR treatment we observed a neuroinflammatory condition in DRG with high levels of PK-Rs, TLR4, CD68, ATF3 and IL-1β without relevant alterations in spinal cord. At day 14, an upregulation of PK system and a marked neuroinflammation was evident also in spinal cord. Moreover, at the same time, we observed initial alterations in supraspinal brain areas. PC1 treatment significantly counteracted neuropathic pain and blunted neuroinflammation.

Increased IL-6 expression in astrocytes is associated with emotionality, alterations in central amygdala GABAergic transmission, and excitability during alcohol withdrawal

Accumulating evidence from preclinical and clinical studies has implicated a role for the cytokine IL-6 in a variety of CNS diseases including anxiety-like and depressive-like behaviors, as well as alcohol use disorder. Here we use homozygous and heterozygous transgenic mice expressing elevated levels of IL-6 in the CNS due to increased astrocyte expression and non-transgenic littermates to examine a role for astrocyte-produced IL-6 in emotionality (response to novelty, anxiety-like, and depressive-like behaviors). Our results from homozygous IL-6 mice in a variety of behavioral tests (light/dark transfer, open field, digging, tail suspension, and forced swim tests) support a role for IL-6 in stress-coping behaviors. Ex vivo electrophysiological studies of neuronal excitability and inhibitory GABAergic synaptic transmission in the central nucleus of the amygdala (CeA) of the homozygous transgenic mice revealed increased inhibitory GABAergic signaling and increased excitability of CeA neurons, suggesting a role for astrocyte produced IL-6 in the amygdala in exploratory drive and depressive-like behavior. Furthermore, studies in the hippocampus of activation/expression of proteins associated with IL-6 signal transduction and inhibitory GABAergic mechanisms support a role for astrocyte produced IL-6 in depressive-like behaviors. Our studies indicate a complex and dose-dependent relationship between IL-6 and behavior and implicate IL-6 induced neuroadaptive changes in neuronal excitability and the inhibitory GABAergic system as important contributors to altered behavior associated with IL-6 expression in the CNS.

Vortioxetine Reduces Marble Burying but Only Transiently Enhances Social Interaction Preference in Adult Male BTBR T+Itpr3tf/J Mice

Vortioxetine is a multimodal antidepressant with agonist activity at serotonin (5-HT)_1A and 5-HT_1B receptors that blocks the 5-HT transporter (SERT). Previously in male BTBR T⁺Itpr3^tf/J (BTBR) mice, the 5-HT_1A partial agonist buspirone and SERT blocker fluoxetine enhanced social interaction but did not reduce marble burying. We hypothesized that vortioxetine through its actions at SERT and 5-HT_1A could improve BTBR sociability and via 5-HT_1B could reduce burying better than sertraline, a selective SERT blocker. Vortioxetine (5-10 mg/kg) or sertraline (2 mg/kg) was administered 30 min presociability and 75 min prior to marble burying tests. Vortioxetine (10 mg/kg) occupancy (%) was 84 ± 1 for SERT, 31 ± 12 for 5-HT_1A, and 80 ± 5 for 5-HT_1B in brain at 110 min postinjection, and serum oxytocin was 24% lower (p < 0.01) in vortioxetine-treated mice. Vortioxetine reduced novel object investigation, whereas sertraline enhanced overall sociability. However, the vortioxetine-induced increase in social sniffing was transient, as it was lost with 60-120 min presociability test delays in subsequent experiments. Vortioxetine and sertraline both reduced BTBR marble burying. Based on vortioxetine occupancy, actions at SERT and/or 5-HT_1B are more likely to underlie its behavioral effects than 5-HT_1A. Overall, vortioxetine has great potential for suppressing restrictive-repetitive behaviors, but it appears less promising as a sociability enhancer.

Increased interactions and engulfment of dendrites by microglia precede Purkinje cell degeneration in a mouse model of Niemann Pick Type-C

Niemann Pick Type-C disease (NPC) is an inherited lysosomal storage disease (LSD) caused by pathogenic variants in the Npc1 or Npc2 genes that lead to the accumulation of cholesterol and lipids in lysosomes. NPC1 deficiency causes neurodegeneration, dementia and early death. Cerebellar Purkinje cells (PCs) are particularly hypersensitive to NPC1 deficiency and degenerate earlier than other neurons in the brain. Activation of microglia is an important contributor to PCs degeneration in NPC. However, the mechanisms by which activated microglia promote PCs degeneration in NPC are not completely understood. Here, we are demonstrating that in the Npc1^nmf164 mouse cerebellum, microglia in the molecular layer (ML) are activated and contacting dendrites at early stages of NPC, when no loss of PCs is detected. During the progression of PCs degeneration in Npc1^nmf164 mice, accumulation of phagosomes and autofluorescent material in microglia at the ML coincided with the degeneration of dendrites and PCs. Feeding Npc1^nmf164 mice a western diet (WD) increased microglia activation and corresponded with a more extensive degeneration of dendrites but not PC somata. Together our data suggest that microglia contribute to the degeneration of PCs by interacting, engulfing and phagocytosing their dendrites while the cell somata are still present.

NGL-1/LRRC4C-Mutant Mice Display Hyperactivity and Anxiolytic-Like Behavior Associated With Widespread Suppression of Neuronal Activity

Netrin-G ligand-1 (NGL-1), encoded by Lrrc4c, is a post-synaptic adhesion molecule implicated in various brain disorders, including bipolar disorder, autism spectrum disorder, and developmental delay. Although previous studies have explored the roles of NGL-1 in the regulation of synapse development and function, the importance of NGL-1 for specific behaviors and the nature of related neural circuits in mice remain unclear. Here, we report that mice lacking NGL-1 (Lrrc4c^–/–) show strong hyperactivity and anxiolytic-like behavior. They also display impaired spatial and working memory, but normal object-recognition memory and social interaction. c-Fos staining under baseline and anxiety-inducing conditions revealed suppressed baseline neuronal activity as well as limited neuronal activation in widespread brain regions, including the anterior cingulate cortex (ACC), motor cortex, endopiriform nucleus, bed nuclei of the stria terminalis, and dentate gyrus. Neurons in the ACC, motor cortex, and dentate gyrus exhibit distinct alterations in excitatory synaptic transmission and intrinsic neuronal excitability. These results suggest that NGL-1 is important for normal locomotor activity, anxiety-like behavior, and learning and memory, as well as synapse properties and excitability of neurons in widespread brain regions under baseline and anxiety-inducing conditions.

Epilepsy and neuropsychiatric comorbidities in mice carrying a recurrent Dravet syndrome SCN1A missense mutation

Dravet Syndrome (DS) is an encephalopathy with epilepsy associated with multiple neuropsychiatric comorbidities. In up to 90% of cases, it is caused by functional happloinsufficiency of the SCN1A gene, which encodes the alpha subunit of a voltage-dependent sodium channel (Nav1.1). Preclinical development of new targeted therapies requires accessible animal models which recapitulate the disease at the genetic and clinical levels. Here we describe that a C57BL/6 J knock-in mouse strain carrying a heterozygous, clinically relevant SCN1A mutation (A1783V) presents a full spectrum of DS manifestations. This includes 70% mortality rate during the first 8 weeks of age, reduced threshold for heat-induced seizures (4.7 °C lower compared with control littermates), cognitive impairment, motor disturbances, anxiety, hyperactive behavior and defects in the interaction with the environment. In contrast, sociability was relatively preserved. Electrophysiological studies showed spontaneous interictal epileptiform discharges, which increased in a temperature-dependent manner. Seizures were multifocal, with different origins within and across individuals. They showed intra/inter-hemispheric propagation and often resulted in generalized tonic-clonic seizures. ¹⁸F-labelled flourodeoxyglucose positron emission tomography (FDG-PET) revealed a global increase in glucose uptake in the brain of Scn1a^WT/A1783V mice. We conclude that the Scn1a^WT/A1783V model is a robust research platform for the evaluation of new therapies against 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.

Comprehensive Characterization of the Pyroglutamate Amyloid-β Induced Motor Neurodegenerative Phenotype of TBA2.1 Mice

Alzheimer's disease (AD) is the most common neurodegenerative disorder and is being intensively investigated using a broad variety of animal models. Many of these models express mutant versions of human amyloid-β protein precursor (AβPP) that are associated with amyloid-β protein (Aβ)-induced early onset familial AD. Most of these models, however, do not develop bold neurodegenerative pathology and the respective phenotypes. Nevertheless, this may well be essential for their suitability to identify therapeutically active compounds that have the potential for a curative or at least disease-modifying therapy in humans. In this study, the new transgenic mouse model TBA2.1 was explored in detail to increase knowledge about the neurodegenerative process induced by the presence of pyroglutamate modified human Aβ3-42 (pEAβ3-42). Analysis of the sensorimotor phenotype, motor coordination, Aβ pathology, neurodegeneration, and gliosis revealed formation and progression of severe pathology and phenotypes including massive neuronal loss in homozygous TBA2.1 mice within a few months. In contrast, the start of a slight phenotype was observed only after 21 months in heterozygous mice. These data highlight the role of pEAβ3-42 in the disease development and progression of AD. Based on the findings of this study, homozygous TBA2.1 mice can be utilized to gain deeper understanding in the underlying mechanisms of pEAβ3-42 and might be suitable as an animal model for treatment studies targeting toxic Aβ species, complementary to the well described transgenic AβPP mouse models.

Leptin deficiency reverses high metabolic state and weight loss without affecting central pathology in the R6/2 mouse model of Huntington's disease

Body weight has been shown to be a predictor of clinical progression in Huntington's disease (HD). Alongside widespread neuronal pathology, both HD patients and the R6/2 mouse model of HD exhibit weight loss and increased energy expenditure, providing a rationale for targeting whole-body energy metabolism in HD. Leptin-deficient mice display low energy expenditure and increased body weight. We therefore hypothesized that normalizing energy metabolism in R6/2 mice, utilizing leptin- deficiency, would lead to a slower disease progression in the R6/2 mouse. In this study, we show that R6/2 mice on a leptin-deficient genetic background display increased body weight and increased fat mass compared to R6/2 mice, as well as wild type littermates. The increased body weight was accompanied by low energy expenditure, illustrated by a reduction in respiratory exchange rate. Leptin-deficient R6/2 mice had large white adipocytes with white adipocyte gene expression characteristics, in contrast to white adipose tissue in R6/2 mice, where white adipose tissue showed signs of browning. Leptin-deficient R6/2 mice did not exhibit improved neuropathological measures. Our results indicate that lowering energy metabolism in HD, by increasing fat mass and reducing respiratory exchange rate, is not sufficient to affect neuropathology. Further studies targeting energy metabolism in HD are warranted.

Characterization of the sensory, affective, cognitive, biochemical, and neuronal alterations in a modified chronic constriction injury model of neuropathic pain in mice

The chronic constriction injury (CCI) of the sciatic nerve is a nerve injury-based model of neuropathic pain (NP). Comorbidities of NP such as depression, anxiety, and cognitive deficits are associated with a functional reorganization of the medial prefrontal cortex (mPFC). Here, we have employed an adapted model of CCI by placing one single loose ligature around the sciatic nerve in mice for investigating the alterations in sensory, motor, affective, and cognitive behavior and in electrophysiological and biochemical properties in the prelimbic division (PrL) of the mPFC. Our adapted model of CCI induced mechanical allodynia, motor, and cognitive impairments and anxiety- and depression-like behavior. In the PrL division of mPFC was observed an increase in GABA and a decrease in d-aspartate levels. Moreover an increase in the activity of neurons responding to mechanical stimulation with an excitation, mPFC (+), and a decrease in those responding with an inhibition, mPFC (-), was found. Altogether these findings demonstrate that a single ligature around the sciatic nerve was able to induce sensory, affective, cognitive, biochemical, and functional alterations already observed in other neuropathic pain models and it may be an appropriate and easily reproducible model for studying neuropathic pain mechanisms and treatments.

Loss of serum response factor in mature neurons in the dentate gyrus alters the morphology of dendritic spines and hippocampus-dependent behavioral tasks

Serum response factor (SRF) is a major transcription factor that regulates the expression of several plasticity-associated genes in the brain. Although the developmental expression of SRF in excitatory neurons is crucial for establishing proper hippocampal circuitry, no substantial evidence of its role in unstimulated mature neurons has been provided. The present study used time-controlled, conditional SRF knockout mice and found that the lack of SRF in adult neurons led to decreased actin levels and inactivation of the actin-severing protein cofilin 1 through its increase in phosphorylation at Ser3. The augmentation of cofilin 1 phosphorylation correlated with an alteration of dendritic spine morphology in the dentate gyrus, which was reflected by an increase in the number of spines that clustered into the long-spine category. The changes in spine morphology coincided with a lower amplitude and frequency of miniature excitatory postsynaptic currents. Moreover, SRF knockout animals were hyperactive and exhibited impairments in hippocampus-dependent behaviors, such as digging, marble burying, and nesting. Altogether, our data indicate that the adult deletion of neuronal SRF leads to alterations of spine morphology and function and hippocampus-dependent behaviors. Thus, SRF deletion in adult neurons recapitulates some aspects of morphological, electrophysiological, and behavioral changes that are observed in such psychiatric disorders as schizophrenia and autism spectrum disorders.

Multi-hit early life adversity affects gut microbiota, brain and behavior in a sex-dependent manner

The accumulation of adverse events in utero and during childhood differentially increases the vulnerability to psychiatric diseases in men and women. Gut microbiota is highly sensitive to the early environment and has been recently hypothesized to affect brain development. However, the impact of early-life adversity on gut microbiota, notably with regards to sex differences, remains to be explored. We examined the effects of multifactorial early-life adversity on behavior and microbiota composition in C3H/HeN mice of both sexes exposed to a combination of maternal immune activation (lipopolysaccharide injection on embryonic day 17, 120 µg/kg, i.p.), maternal separation (3hr per day from postnatal day (PND)2 to PND14) and maternal unpredictable chronic mild stress. At adulthood, offspring exposed to multi-hit early adversity showed sex-specific behavioral phenotypes with males exhibiting deficits in social behavior and females showing increased anxiety in the elevated plus maze and increased compulsive behavior in the marble burying test. Early adversity also differentially regulated gene expression in the medial prefrontal cortex (mPFC) according to sex. Interestingly, several genes such as Arc, Btg2, Fosb, Egr4 or Klf2 were oppositely regulated by early adversity in males versus females. Finally, 16S-based microbiota profiling revealed sex-dependent gut dysbiosis. In males, abundance of taxa belonging to Lachnospiraceae and Porphyromonadaceae families or other unclassified Firmicutes, but also Bacteroides, Lactobacillus and Alloprevotella genera was regulated by early adversity. In females, the effects of early adversity were limited and mainly restricted to Lactobacillus and Mucispirillum genera. Our work reveals marked sex differences in a multifactorial model of early-life adversity, both on emotional behaviors and gut microbiota, suggesting that sex should systematically be considered in preclinical studies both in neurogastroenterology and psychiatric research.

Persistent central inflammation and region specific cellular activation accompany depression- and anxiety-like behaviours during the resolution phase of experimental colitis

Depression and anxiety-related psychological symptoms are increasingly recognised as important co-morbidities in patients with inflammatory bowel disease (IBD). Dextran sulfate sodium (DSS) -induced colitis is an animal model of IBD in which afferent activation of the gut-brain axis can be assessed and explored as a source of behavioural change. Exposure of adult male Wistar rats to DSS (5%) in drinking water induced distal colitis. In parallel to local inflammatory responses in the gut wall, increased expression of IL-6 and iNOS was found in the cerebral cortex and an increase in ventricular volume. Immunoreactivity of immediate early gene FosB/ΔFosB activation was measured as an index of cellular activation and was increased in the nucleus accumbens and dorsal raphe nucleus in acutely colitic animals. Following resolution of the acute colitic response, sustained anhedonia in the saccharin preference test, immobility in the forced swim test, reduced burying behaviour in the marble burying test, and mild signs of anxiety in the elevated plus maze and light/dark box were observed. Central increases in iNOS expression persisted during the recovery phase and mapped to reactive microglia, particularly those found in the parenchyma surrounding circumventricular regions. Evidence of associated nitration was also found. Sustained increases in ventricular volume and reduced T2 magnetic resonance relaxometry time in cortical regions were observed during the recovery period. FosB/ΔFosB activation was evident in the dorsal raphe during recovery. Persistent central inflammation and cellular activation may underpin the emergence of symptoms of depression and anxiety in experimental colitis.

Astrogliosis Associated With Behavioral Abnormality in a Non-anaphylactic Mouse Model of Cow's Milk Allergy

Etiology of neuropsychiatric disorders is complex, involving multiple factors that can affect the type and severity of symptoms. Although precise causes are far from being identified, allergy or other forms of hypersensitivity to dietary ingredients have been implicated in triggering or worsening of behavioral and emotional symptoms, especially in patients suffering from depression, anxiety, attention-deficit hyperactivity, and/or autism. Among such ingredients, cow's milk, along with wheat gluten, is commonly suspected. However, the contributory role of cow's milk in these disorders has not been elucidated due to insufficient pathophysiological evidence. In the present study, we therefore investigated neuroinflammatory changes that are associated with behavioral abnormality using a non-anaphylactic mouse model of cow's milk allergy (CMA). Male and female C57BL/6J mice were subjected to a 5-week oral sensitization procedure without or with a major milk allergen, beta-lactoglobulin (BLG). All mice were then later challenged with BLG, and their anxiety- and depression-associated behaviors were subsequently assessed during the 6th and 7th weeks. We found that BLG-sensitized male mice exhibited significantly increased anxiety- and depression-like behavior, although they did not display anaphylactic reactions when challenged with BLG. Female behavior was not noticeably affected by BLG sensitization. Upon examination of the small intestines, reduced immunoreactivity to occludin was detected in the ileal mucosa of BLG-sensitized mice although the transcriptional expression of this tight-junction protein was not significantly altered when measured by quantitative RT-PCR. On the other hand, the expression of tumor necrosis factor alpha (TNFα) in the ileal mucosa was significantly elevated in BLG-sensitized mice, suggesting the sensitization had resulted in intestinal inflammation. Inflammatory responses were also detected in the brain of BLG-sensitized mice, determined by the hypertrophic morphology of GFAP-immunoreactive astrocytes. These reactive astrocytes were particularly evident near the blood vessels in the midbrain region, resembling the perivascular barrier previously reported by others in experimental autoimmune encephalitis (EAE) mouse models. Interestingly, increased levels of COX-2 and TNFα were also found in this region. Taken together, our results demonstrated that BLG sensitization elicits inflammatory responses in the intestine and brain without overt anaphylactic signs of milk allergy, signifying food allergy as a potential pathogenic factor of neuropsychiatric disorders.

Long-term voluntary wheel running does not alter vascular amyloid burden but reduces neuroinflammation in the Tg-SwDI mouse model of cerebral amyloid angiopathy

BACKGROUND

Cardiovascular exercise (CVE) has been shown to be protective against cognitive decline in aging and the risk for dementias, including Alzheimer's Disease (AD). CVE has also been shown to have several beneficial effects on brain pathology and behavioral impairments in mouse models of AD; however, no studies have specifically examined the effects of CVE on cerebral amyloid angiopathy (CAA), which is the accumulation of amyloid-beta (Aβ) in the cerebral vasculature. CAA may be uniquely susceptible to beneficial effects of CVE interventions due to the location and nature of the pathology. Alternatively, CVE may exacerbate CAA pathology, due to added stress on already compromised cerebral vasculature.

METHODS

In the current study, we examined the effects of CVE over many months in mice, thereby modeling a lifelong commitment to CVE in humans. We assessed this voluntary CVE in Tg-SwDI mice, a transgenic mouse model of CAA that exhibits behavioral deficits, fibrillar vascular Aβ pathology, and significant perivascular neuroinflammation. Various "doses" of exercise intervention (0 h ("Sedentary"), 1 h, 3 h, 12 h access to running wheel) were assessed from ~ 4 to 12 months of age for effects on physiology, behavior/cognitive performance, and pathology.

RESULTS

The 12 h group performed the greatest volume of exercise, whereas the 1 h and 3 h groups showed high levels of exercise intensity, as defined by more frequent and longer duration running bouts. Tg-SwDI mice exhibited significant cerebral vascular Aβ pathology and increased expression of pro-inflammatory cytokines as compared to WT controls. Tg-SwDI mice did not show motor dysfunction or altered levels of anxiety or sociability compared to WT controls, though Tg-SwDI animals did appear to exhibit a reduced tendency to explore novel environments. At all running levels, CAA pathology in Tg-SwDI mice was not significantly altered, but 12-h high-volume exercise showed increased insoluble Aβ burden. However, CVE attenuated the expression of pro-inflammatory cytokines TNF-α and IL-6 and was generally effective at enhancing motor function and reducing anxiety-like behavior in Tg-SwDI mice, though alterations in learning and memory tasks were varied.

CONCLUSIONS

Taken together, these results suggest that CAA can still develop regardless of a lifespan of substantial CVE, although downstream effects on neuroinflammation may be reduced and functional outcomes improved.

Behavioural and biochemical effects of one-week exposure to aflatoxin B1 and aspartame in male Wistar rats

Food products are susceptible to contamination by mycotoxins, and aflatoxin B1 (AFB1) stands as the most toxic among them. AFB1 intoxication results in distinct signs, including widespread systemic toxicity. Aspartame (ASP) is an artificial sweetener used as a sugar substitute in many products, and compelling evidence indicates ASP can be toxic. Interestingly, mechanisms underlying ASP and AFB1 toxicity involve oxidative stress. In this context, concomitant use of ASP and AFB1 in a meal may predispose to currently unidentified behavioural and biochemical changes. Therefore, we evaluated the effect of AFB1 (250 μg/kg, intragastrically (i.g.)) and/or ASP (75 mg/kg, i.g.) exposure for 7 days on behavioural and biochemical markers of oxidative stress in male Wistar rats. AFB1 and/or ASP increased hepatic glutathione S-transferase (GST) activity when compared to controls. In the kidneys, increased GST activity was detected in AFB1 and AFB1+ASP groups. In addition, AFB1 and or ASP elicited behavioural changes in the open field, marble burying and splash tests, however no additive effects were detected. Altogether, present data suggest AFB1 and ASP predispose to anxiety- and obsessive-compulsive-like symptoms, as well as to enzymatic defence system imbalance in liver and kidney of Wistar rats.

Developmental Vitamin D Deficiency Produces Behavioral Phenotypes of Relevance to Autism in an Animal Model

Emerging evidence suggests that gestational or developmental vitamin D (DVD) deficiency is associated with an increased risk of autism spectrum disorder (ASD). ASD is a neurodevelopmental disorder characterized by impairments in social interaction, lack of verbal and non-verbal communications, stereotyped repetitive behaviors and hyper-activities. There are several other clinical features that are commonly comorbid with ASD, including olfactory impairments, anxiety and delays in motor development. Here we investigate these features in an animal model related to ASD-the DVD-deficient rat. Compared to controls, both DVD-deficient male and female pups show altered ultrasonic vocalizations and stereotyped repetitive behavior. Further, the DVD-deficient animals had delayed motor development and impaired motor control. Adolescent DVD-deficient animals had impaired reciprocal social interaction, while as adults, these animals were hyperactive. The DVD-deficient model is associated with a range of behavioral features of interest to ASD.

Neuroplastin 65 modulates anxiety- and depression-like behavior likely through adult hippocampal neurogenesis and central 5-HT activity

Neuroplastin 65 (Np65) is a brain-specific cell adhesion molecule that is highly expressed in the hippocampus, amygdala, and cortex, regions of the brain that are associated with memory and emotions. However, the role of Np65 in regulation of emotional behavior is still unclear. In the present study, we show that Np65 knock-out (Np65 KO) mice display enhanced anxiety-like behavior, a reduction in some aspects of depressive-like behaviors, and increased sociability and memory. Biochemical investigations revealed that Np65 KO mice show increased adult-born neurons and proliferation in the hippocampus. In addition, the level of 5-hydroxytryptamine (5-HT) in the hippocampus was reduced. The expression of tryptophan hydroxylase 2 in the brainstem and the expression of the 5-HT_3A receptor were also decreased. Electrophysiological recordings confirmed an impaired maintenance of long-term potentiation in the hippocampus of Np65 KO mice. Together, our findings uncover a role for Np65 in regulating anxiety- and depressive-like behaviors and suggest that Np65 may be essential for the maintenance of emotional stability, indicating that it might be an attractive potential target for treatment of psychiatric disorders.

A farnesyltransferase inhibitor activates lysosomes and reduces tau pathology in mice with tauopathy

Tau inclusions are a shared feature of many neurodegenerative diseases, among them frontotemporal dementia caused by tau mutations. Treatment approaches for these conditions include targeting posttranslational modifications of tau proteins, maintaining a steady-state amount of tau, and preventing its tendency to aggregate. We discovered a new regulatory pathway for tau degradation that operates through the farnesylated protein, Rhes, a GTPase in the Ras family. Here, we show that treatment with the farnesyltransferase inhibitor lonafarnib reduced Rhes and decreased brain atrophy, tau inclusions, tau sumoylation, and tau ubiquitination in the rTg4510 mouse model of tauopathy. In addition, lonafarnib treatment attenuated behavioral abnormalities in rTg4510 mice and reduced microgliosis in mouse brain. Direct reduction of Rhes in the rTg4510 mouse by siRNA reproduced the results observed with lonafarnib treatment. The mechanism of lonafarnib action mediated by Rhes to reduce tau pathology was shown to operate through activation of lysosomes. We finally showed in mouse brain and in human induced pluripotent stem cell-derived neurons a normal developmental increase in Rhes that was initially suppressed by tau mutations. The known safety of lonafarnib revealed in human clinical trials for cancer suggests that this drug could be repurposed for treating tauopathies.

Supplementation of dietary non-digestible oligosaccharides from birth onwards improve social and reduce anxiety-like behaviour in male BALB/c mice

Objective: The intestinal microbiota is acknowledged to be essential in brain development and behaviour. Their composition can be modulated by prebiotics such as short-chain galacto-oligosaccharides (scGOS) and long-chain fructo-oligosaccharide (lcFOS). Several studies reported potential health benefit of prebiotics on behaviour. As the prebiotic mixture of scGOS and lcFOS is included in infant formula, we investigated the effects of dietary supplementation with this specific mixture from the day of birth onwards on behaviour and intestinal microbiota development in mice. Method: Healthy male BALB/cByJ mice received, from day of birth, a dietary supplement with or without 3% scGOS:lcFOS (9:1). Behavioural tests were performed pre-weaning, in adolescence, early adulthood and adulthood. We assessed faecal microbiota compositions over time, caecal short-chain fatty acids as well as brain mRNA expression of Htr1a, Htr1b and Tph2 and monoamine levels. Results: Compared to control fed mice, scGOS:lcFOS fed mice showed reduced anxiety-like and repetitive behaviour over time and improved social behaviour in adulthood. The serotonergic system in the prefrontal cortex (PFC) and somatosensory cortex (SSC) was affected by the scGOS:lcFOS. In the PFC, mRNA expression of brain-derived neurotrophic factor (Bdnf) was enhanced in scGOS:lcFOS fed mice. Although the bacterial diversity of the intestinal microbiota was unaffected by the scGOS:lcFOS diet, microbiota composition differed between the scGOS:lcFOS and the control fed mice over time. Moreover, an increased saccharolytic and decreased proteolytic fermentation activity were observed in caecum content. Discussion: Supplementing the diet with scGOS:lcFOS from the day of birth is associated with reduced anxiety-like and improved social behaviour during the developmental period and later in life, and modulates the composition and activity of the intestinal microbiota in healthy male BALB/c mice. These data provide further evidence of the potential impact of scGOS:lcFOS on behaviour at several developmental stages throughout life and strengthen the insights in the interplay between the developing intestine and brain.

The Effect of ASIC3 Knockout on Corticostriatal Circuit and Mouse Self-grooming Behavior

Stereotypic and/or repetitive behavior is one of the major symptoms of autism spectrum disorder (ASD). Increase of self-grooming behavior is a behavioral phenotype commonly observed in the mouse models for ASD. Previously, we have shown that knockout of acid-sensing ion channel 3 (ASIC3) led to the increased self-grooming behavior in resident-intruder test. Given the facts that ASIC3 is mainly expressed in the peripheral dorsal root ganglion (DRG) and conditional knockout of ASIC3 in the proprioceptors induced proprioception deficits. We speculate a hypothesis that stereotypic phenotype related to ASD, pararalled with striatal dysfunction, might be caused by proprioception defect in the peripheral sensory neuron origin. Herein, we investigate in depth whether and how ASIC3 is involved in the regulation of self-grooming behavior. First, we observed that Asic3 null mutant mice exhibited increased self-grooming in social interaction during juvenile stage. Similarly, they displayed increased self-grooming behavior in a novel cage in the absence of cagemate. To further understand the mechanism by which ASIC3 affects grooming behavior, we analyzed neurochemical, neuropathological and electrophysiological features in the dorsal striatum of Asic3 null mutant mice. Knockout of Asic3 increased dopamine (DA) activity and phospho-ERK immunoreactivities in the dorsal striatum. Furthermore, we detected a lower paired-pulse ratio (PPR) and impaired long-term potentiation (LTP) in corticostriatal circuits in Asic3 null mutant mice as compared with wild-type (WT) littermates. Moreover, knockout of Asic3 altered the medial spiny neurons in the striatum with defects in presynaptic function and decrease of dendritic spines. Lastly, genetic ablation of Asic3 specifically in parvalbumin-positive (PV+) cells resulted in the increase of self-grooming behavior in mice. These findings suggest knockout of Asic3 in the PV+ neurons alters grooming behavior by co-opting corticostriatal circuits.

CDKL5 protein substitution therapy rescues neurological phenotypes of a mouse model of CDKL5 disorder

Cyclin-dependent kinase like-5 (CDKL5) disorder is a rare neurodevelopmental disease caused by mutations in the CDKL5 gene. The consequent misexpression of the CDKL5 protein in the nervous system leads to a severe phenotype characterized by intellectual disability, motor impairment, visual deficits and early-onset epilepsy. No therapy is available for CDKL5 disorder. It has been reported that a protein transduction domain (TAT) is able to deliver macromolecules into cells and even into the brain when fused to a given protein. We demonstrate that TAT-CDKL5 fusion protein is efficiently internalized by target cells and retains CDKL5 activity. Intracerebroventricular infusion of TAT-CDKL5 restored hippocampal development, hippocampus-dependent memory and breathing pattern in Cdkl5-null mice. Notably, systemically administered TAT-CDKL5 protein passed the blood-brain-barrier, reached the CNS, and rescued various neuroanatomical and behavioral defects, including breathing pattern and visual responses. Our results suggest that CDKL5 protein therapy may be an effective clinical tool for the treatment of CDKL5 disorder.

Sex-Dependent Sensory Phenotypes and Related Transcriptomic Expression Profiles Are Differentially Affected by Angelman Syndrome

Angelman syndrome (AS) is a genetic disorder which entails autism, intellectual disability, lack of speech, motor deficits, and seizure susceptibility. It is caused by the lack of UBE3A protein expression, which is an E3-ubiquitin ligase. Despite AS equal prevalence in males and females, not much data on how sex affects the syndrome was reported. In the herein study, we thoroughly characterized many behavioral phenotypes of AS mice. The behavioral data acquired was analyzed with respect to sex. In addition, we generated a new mRNA sequencing dataset. We analyzed the coding transcriptome expression profiles with respect to the effects of genotype and sex observed in the behavioral phenotypes. We identified several neurobehavioral aspects, especially sensory perception, where AS mice either lack the male-to-female differences observed in wild-type littermates or even show opposed differences. However, motor phenotypes did not show male-to-female variation between wild-type (WT) and AS mice. In addition, by utilizing the mRNA sequencing, we identified genes and isoforms with expression profiles that mirror the sensory perception results. These genes are differentially regulated in the two sexes with inverse expression profiles in AS mice compared to WT littermates. Some of these are known pain-related and estrogen-dependent genes. The observed differences in sex-dependent neurobehavioral phenotypes and the differential transcriptome expression profiles in AS mice strengthen the evidence for molecular cross talk between Ube3a protein and sex hormone receptors or their elicited pathways. These interactions are essential for understanding Ube3a deletion effects, beyond its E3-ligase activity.

Vibrating Tail, Digging, Body/Face Interaction, and Lack of Barbering: Sex-Dependent Behavioral Signatures of Social Dysfunction in 3xTg-AD Mice as Compared to Mice with Normal Aging

Modeling of Alzheimer's disease (AD), classically focused on the subject-environment interaction, foresees current social neuroscience efforts as improving the predictive validity of new strategies. Here we studied social functioning among congeners in 13-14-month-old mice with normal aging in naturalistic and experimental conditions and depicted behavioral signatures of dysfunction in age-matched 3xTg-AD mice. The most sensitive variables were vibrating tail, digging, body/face and self-grooming, that can be easily used in housing routines and the assessment of strategies. Sex-specific signatures (vibrating tail, digging, and grooming) defined female 3xTg-AD mice ethogram. All animals sleep huddled while barbering was only found in females with normal aging.

Sex-Dependent Motor Deficit and Increased Anxiety-Like States in Mice Lacking Autism-Associated Gene Slit3

Altered neuronal connectivity has been implicated in the pathophysiology of Autism Spectrum Disorder (ASD). SLIT/ROBO signaling plays an important role in developmental processes of neuronal connectivity, including axon guidance, neuronal migration, and axonal and dendritic branching. Genetic evidence supports that SLIT3, one of the genes encoding SLITs, is associated with ASD. Yet the causal link between SLIT3 mutation and autism symptoms has not been examined. Here we assessed ASD-associated behaviors in Slit3 knockout (KO) mice. Our data showed that Slit3-KO mice exhibited reduced marble burying behaviors but normal social behaviors. In addition, Slit3-KO mice displayed hypolocomotion in the open field test and impaired motor coordination in the rotarod test. Anxiety-like behaviors were mainly observed in female KO mice assessed by three types of behavioral tests, namely, the open field test, elevated plus maze test, and light/dark box test. No differences were observed between KO and wildtype mice in recognition memory in the novel object recognition test or depression-like behavior in the tail suspension test. Taken together, loss of Slit3 may result in disrupted neural circuits related to motor function and increased anxiety-like states, which are co-occurring symptoms in ASD.

Genetic differences in the behavioral organization of binge eating, conditioned food reward, and compulsive-like eating in C57BL/6J and DBA/2J strains

Binge eating (BE) is a heritable symptom of eating disorders associated with anxiety, depression, malnutrition, and obesity. Genetic analysis of BE could facilitate therapeutic discovery. We used an intermittent, limited access BE paradigm involving sweetened palatable food (PF) to examine genetic differences in BE, conditioned food reward, and compulsive-like eating between C57BL/6J (B6J) and DBA/2J (D2J) inbred mouse strains. D2J mice showed a robust escalation in intake and conditioned place preference for the PF-paired side. D2J mice also showed a unique style of compulsive-like eating in the light/dark conflict test where they rapidly hoarded and consumed PF in the preferred unlit environment. BE and compulsive-like eating exhibited narrow-sense heritability estimates between 56 and 73%. To gain insight into the genetic basis, we phenotyped and genotyped a small cohort of 133 B6J × D2J-F₂ mice at the peak location of three quantitative trait loci (QTL) previously identified in F₂ mice for sweet taste (chromosome 4: 156 Mb), bitter taste (chromosome 6: 133 Mb) and behavioral sensitivity to drugs of abuse (chromosome 11: 50 Mb). The D2J allele on chromosome 6 was associated with greater PF intake on training days and greater compulsive-like PF intake, but only in males, suggesting that decreased bitter taste may increase BE in males. The D2J allele on chromosome 11 was associated with an increase in final PF intake and slope of escalation across days. Future studies employing larger crosses and genetic reference panels comprising B6J and D2J alleles will identify causal genes and neurobiological mechanisms.

Acute inflammation sensitizes knee-innervating sensory neurons and decreases mouse digging behavior in a TRPV1-dependent manner

Ongoing, spontaneous pain is characteristic of inflammatory joint pain and reduces an individual's quality of life. To understand the neural basis of inflammatory joint pain, we made a unilateral knee injection of complete Freund's adjuvant (CFA) in mice, which reduced their natural digging behavior. We hypothesized that sensitization of knee-innervating dorsal root ganglion (DRG) neurons underlies this altered behavior. To test this hypothesis, we performed electrophysiological recordings on retrograde labeled knee-innervating primary DRG neuron cultures and measured their responses to a number of electrical and chemical stimuli. We found that 24-h after CFA-induced knee inflammation, knee neurons show a decreased action potential generation threshold, as well as increased GABA and capsaicin sensitivity, but have unaltered acid sensitivity. The inflammation-induced sensitization of knee neurons persisted for 24-h in culture, but was not observed after 48-h in culture. Through immunohistochemistry, we showed that the increased knee neuron capsaicin sensitivity correlated with enhanced expression of the capsaicin receptor, transient receptor potential vanilloid 1 (TRPV1) in knee-innervating neurons of the CFA-injected side. We also observed an increase in the co-expression of TRPV1 with tropomyosin receptor kinase A (TrkA), which is the receptor for nerve growth factor (NGF), suggesting that NGF partially induces the increased TRPV1 expression. Lastly, we found that systemic administration of the TRPV1 antagonist, A-425619, reversed the decrease in digging behavior induced by CFA injection, further confirming the role of TRPV1, expressed by knee neurons, in acute inflammatory joint pain.

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Knee inflammation decreases digging behavior in mice.

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Knee-innervating dorsal root ganglion neurons are hyperexcitable after inflammation.

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NGF-mediated increase in TRPV1 expression is observed in knee-innervating neurons.

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Systemic TRPV1 antagonist administration normalises digging behavior in mice.

A high-refined carbohydrate diet facilitates compulsive-like behavior in mice through the nitric oxide pathway

Obesity is characterized by abnormal adipose tissue expansion and is associated with chronic inflammation. Obesity itself may induce several comorbidities, including psychiatric disorders. It has been previously demonstrated that proinflammatory cytokines are able to up-regulate inducible nitric oxide synthase (iNOS) and nitric oxide (NO) release, which both have a role in compulsive related behaviors.

OBJECTIVE

To evaluate whether acute or chronic consumption of a high-refined carbohydrate-containing (HC) diet will modify burying-behavior in the Marble Burying Test (MBT) through augmentation of NO signaling in the striatum, a brain region related to the reward system. Further, we also verified the effects of chronic consumption of a HC diet on the reinforcing effects induced by cocaine in the Conditioned Place Preference (CPP) test.

METHODS

Male BALB/c mice received a standard diet (control diet) or a HC diet for 3 days or 12 weeks.

RESULTS

An increase in burying behavior occurred in the MBT after chronic consumption of a HC diet that was associated with an increase of nitrite levels in the striatum. The pre-treatment with Aminoguanidine (50 mg/kg), a preferential inhibitor of iNOS, prevented such alterations. Additionally, a chronic HC diet also induced a higher expression of iNOS in this region and higher glutamate release from striatal synaptosomes. Neither statistical differences were observed in the expression levels of the neuronal isoform of NOS nor in microglia number and activation. Finally, the reinforcing effects induced by cocaine (15 mg/kg, i.p.) during the expression of the conditioned response in the CPP test were not different between the chronically HC diet fed mice and the control group. However, HC diet-feeding mice presented impairment of cocaine-preference extinction.

CONCLUSION

Altogether, our results suggest that the chronic consumption of a HC diet induces compulsive-like behavior through a mechanism possibly associated with NO activation in the striatum.

Autism-related behaviors in the cyclooxygenase-2-deficient mouse model

Prostaglandin E2 (PGE2) is an endogenous lipid molecule involved in normal brain development. Cyclooxygenase-2 (COX2) is the main regulator of PGE2 synthesis. Emerging clinical and molecular research provides compelling evidence that abnormal COX2/PGE2 signaling is associated with autism spectrum disorder (ASD). We previously found that COX2 knockout mice had dysregulated expression of many ASD genes belonging to important biological pathways for neurodevelopment. The present study is the first to show the connection between irregular COX2/PGE2 signaling and autism-related behaviors in male and female COX2-deficient knockin, (COX)-2^- , mice at young (4-6 weeks) or adult (8-11 weeks) ages. Autism-related behaviors were prominent in male (COX)-2^- mice for most behavioral tests. In the open field test, (COX)-2^- mice traveled more than controls and adult male (COX)-2^- mice spent less time in the center indicating elevated hyperactive and anxiety-linked behaviors. (COX)-2^- mice also buried more marbles, with males burying more than females, suggesting increased anxiety and repetitive behaviors. Young male (COX)-2^- mice fell more frequently in the inverted screen test revealing motor deficits. The three-chamber sociability test found that adult female (COX)-2^- mice spent less time in the novel mouse chamber indicative of social abnormalities. In addition, male (COX)-2^- mice showed altered expression of several autism-linked genes: Wnt2, Glo1, Grm5 and Mmp9. Overall, our findings offer new insight into the involvement of disrupted COX2/PGE2 signaling in ASD pathology with age-related differences and greater impact on males. We propose that (COX)-2^- mice might serve as a novel model system to study specific types of autism.

Altered Trek-1 Function in Sortilin Deficient Mice Results in Decreased Depressive-Like Behavior

The background potassium channel TREK-1 has been shown to be a potent target for depression treatment. Indeed, deletion of this channel in mice resulted in a depression resistant phenotype. The association of TREK-1 with the sorting protein sortilin prompted us to investigate the behavior of mice deleted from the gene encoding sortilin (Sort1^−/−). To characterize the consequences of sortilin deletion on TREK-1 activity, we combined behavioral, electrophysiological and biochemical approaches performed in vivo and in vitro. Analyses of Sort1^−/− mice revealed that they display: (1) a corticosterone-independent anxiety-like behavior, (2) a resistance to depression as demonstrated by several behavioral tests, and (3) an increased activity of dorsal raphe nucleus neurons. All these properties were associated with TREK-1 action deficiency consequently to a decrease of its cell surface expression and to the modification of its electrophysiological activity. An increase of BDNF expression through activation of the furin-dependent constitutive pathway as well as an increase of the activated BDNF receptor TrkB were in agreement with the decrease of depressive-like behavior of Sort1^−/− mice. Our results demonstrate that the TREK-1 expression and function are altered in the absence of sortilin confirming the importance of this channel in the regulation on the mood as a crucial target to treat depression.

Anxiety-like behavior and other consequences of early life stress in mice with increased protein kinase A activity

Anxiety disorders are associated with abnormalities in fear-learning and bias to threat; early life experiences are influential to the development of an anxiety-like phenotype in adulthood. We recently reported that adult mice (Prkar1a+/-) with haploinsufficiency for the main regulatory subunit of the protein kinase A (PKA) exhibit an anxiety-like phenotype associated with increased PKA activity in the amygdala. PKA is the main effector of cyclic adenosine mono-phosphate signaling, a key pathway involved in the regulation of fear learning. Since anxiety has developmental and genetic components, we sought to examine the interaction of a genetic defect associated with anxiety phenotype and early life experiences. We investigated the effects of neonatal maternal separation or tactile stimulation on measures of behavior typical to adolescence as well as developmental changes in the behavioral phenotype between adolescent and adult wild-type (WT) and Prkar1a+/- mice. Our results showed developmental differences in assays of anxiety and novelty behavior for both genotypes. Adolescent mice showed increased exploratory and novelty seeking behavior compared to adult counterparts. However, early life experiences modulated behavior in adolescent WT differently than in adolescent Prkar1a+/- mice. Adolescent WT mice exposed to early life tactile stimulation showed attenuation of anxiety-like behavior, whereas an increase in exploratory behavior was found in Prkar1a+/- adolescent mice. The finding of behavioral differences that are apparent during adolescence in Prkar1a^+/- mice suggests that long-term exposure of the brain to increased PKA activity during critical developmental periods contributes to the anxiety-like phenotype noted in the adult animals with increased PKA activity.

Distinct Phenotypes of Shank2 Mouse Models Reflect Neuropsychiatric Spectrum Disorders of Human Patients With SHANK2 Variants

The SHANK scaffolding proteins are important organizers for signaling proteins in the postsynapse of excitatory neurons. The functional significance of SHANK proteins becomes apparent by the wide spectrum of neurodevelopmental and neuropsychiatric disorders associated with SHANK variants in human patients. A similar diversity of neuropsychiatric-like phenotypes is described for numerous Shank2 and Shank3 knockout (KO) mouse lines. In this review, we will focus on and discuss the experimental results obtained from different, but genetically related and therefore comparable, Shank2 mouse models. First, we will describe the distinct SHANK2 variant-mediated neurodevelopmental and neuropsychiatric disorders in human patients. Then we will discuss the current knowledge of the expressed SHANK2 isoforms in the mouse, and we will describe the genetic strategies used for generating three conventional and seven conditional Shank2 mouse lines. The distinct impairments i.e., autistic-like and mania-like behavior and the alterations on the molecular, electrophysiological and behavioral levels will be compared between the different Shank2 mouse models. We will present our view as to why in these mouse models a spectrum of phenotypes can arise from similar Shank2 gene manipulations and how Shank2 mutant mice can be used and should be analyzed on the behavioral level in future research.

Aβ Oligomer Elimination Restores Cognition in Transgenic Alzheimer's Mice with Full-blown Pathology

Oligomers of the amyloid-β (Aβ) protein are suspected to be responsible for the development and progression of Alzheimer’s disease. Thus, the development of compounds that are able to eliminate already formed toxic Aβ oligomers is very desirable. Here, we describe the in vivo efficacy of the compound RD2, which was developed to directly and specifically eliminate toxic Aβ oligomers. In a truly therapeutic, rather than a preventive study, oral treatment with RD2 was able to reverse cognitive deficits and significantly reduce Aβ pathology in old-aged transgenic Alzheimer’s Disease mice with full-blown pathology and behavioral deficits. For the first time, we demonstrate the in vivo target engagement of RD2 by showing a significant reduction of Aβ oligomers in the brains of RD2-treated mice compared to placebo-treated mice. The correlation of Aβ elimination in vivo and the reversal of cognitive deficits in old-aged transgenic mice support the hypothesis that Aβ oligomers are relevant not only for disease development and progression, but also offer a promising target for the causal treatment of Alzheimer’s disease.