Effects of the Female Estrous Cycle on the Sexual Behaviors and Ultrasonic Vocalizations of Male C57BL/6 and Autistic BTBR T+ tf/J Mice

The effects of 17β-trenbolone and bisphenol A on sexual behavior and social dominance via the hypothalamic-pituitary-gonadal axis in male mice

17β-Trenbolone (17-TB) is well documented as an environmental endocrine disruptor in aquatic biological studies, but its effects on mammals remain poorly understood. Furthermore, 17-TB acts as a hormone with properties similar to testosterone, and the consequences of juvenile exposure on adult social behavior remain uncertain. Bisphenol A (BPA) acts as an estrogen-like hormone, compared to 17-TB. Three-week-old male Balb/c mice were exposed orally to 17-TB (100 µg/(kg·day)) and BPA (4 mg/(kg·day)) for 28 days. Assessments of social interactions and a three-chamber test showed that 17-TB increased virility in male mice, intensified both male and female sexual behavior, and attracted and accepted female mice. It also increased social dominance through tube tests in male mice and markedly activated the c-Fos+ immune response in the medial prefrontal cortex (mPFC) and basal amygdala (BLA). ELISA data showed that 17-TB and BPA exposure significantly affected serum gonadotropin-releasing hormone (GnRH), growth hormone (GH), estradiol (E2), and luteinizing hormone (LH) levels, as well as testicular lesions and androgen receptor (ARβ) and estrogen receptor (ERα) synthesis. Testicular transcriptomic analysis further confirmed that could disrupt steroid synthesis and linoleic acid-related biometabolic processes. These findings suggest the influence of 17-TB and BPA exposure on sexual behavior and fertility in male mice, possibly through modulation of the hypothalamic-pituitary-gonadal axis. This study provides insights relevant to human reproductive health and neuro-social behavioral research, and the potential risk of environmental disturbances should not be overlooked.

Vocal communication in asocial BTBR mice is more malleable by a ketogenic diet in juveniles than adults

Deficits in social communication and language development are a hallmark of autism spectrum disorder currently with no effective approaches to reduce the negative impact. Interventional studies using animal models have been very limited in demonstrating improved vocal communication. Autism has been proposed to involve metabolic dysregulation. Ketogenic diet (KD) is a metabolism-based therapy for medically intractable epilepsy, and its applications in other neurological conditions have been increasingly tested. However, how KD would affect vocal communication has not been explored. The BTBR mouse strain is widely used to model asocial phenotypes. They display robust and pronounced deficits in vocalization during social interaction, and have metabolic changes implicated in autism. We investigated the effects of KD on ultrasonic vocalizations (USVs) in juvenile and adult BTBR mice during male-female social encounters. After a brief treatment with KD, the number, spectral bandwidth, and much of the temporal structure of USVs were robustly closer to control levels in both juvenile and adult BTBR mice. Composition of call categories and transitioning between individual call subtypes were more effectively altered to more closely align with the control group in juvenile BTBR mice. Together, our data provide further support to the hypothesis that metabolism-based dietary intervention could modify disease expression, including core symptoms, in autism. Future studies should tease apart the molecular mechanisms of KD's effects on vocalization.

Endogenous opioids facilitate stress-induced binge eating via an insular cortex-claustrum pathway

Stress has been shown to promote the development and persistence of binge eating behaviors. However, the neural circuit mechanisms for stress-induced binge-eating behaviors are largely unreported. The endogenous dynorphin (dyn)/kappa opioid receptor (KOR) opioid neuropeptide system has been well established to be a crucial mediator of the anhedonic component of stress. Here, we aimed to dissect the basis of dynorphinergic control of stress-induced binge-like eating behavior. We first established a mouse behavioral model for stress-induced binge-like eating behaviors. We found that mice exposed to stress increased their food intake of familiar palatable food (high fat, high sugar, HPD) compared to non-stressed mice. Following a brain-wide analysis, we isolated robust cFos-positive cells in the Claustrum (CLA), a subcortical structure with highly abundant KOR expression, following stress-induced binge-eating behavior. We report that KOR signaling in CLA is necessary for this elevated stress-induced binge eating behavior using local pharmacology and local deletion of KOR. In vivo calcium recordings using fiber photometry revealed a disinhibition circuit structure in the CLA during the initiation of HPD feeding bouts. We further established the dynamics of endogenous dynorphinergic control of this behavior using a genetically encoded dynorphin biosensor, Klight. Combined with 1-photon single-cell calcium imaging, we report significant heterogeneity with the CLA population during stress-induced binge eating and such behavior attenuates local dynorphin tone. Furthermore, we isolate the anterior Insular cortex (aIC) as the potential source of endogenous dynorphin afferents in the CLA. By characterizing neural circuits and peptidergic mechanisms within the CLA, we uncover a pathway that implicates endogenous opioid regulation stress-induced binge eating.

Influence of environmental enrichment on sexual behavior and the process of learning and memory in a rat model of autism with valproic acid

Autism spectrum disorder (ASD) is a psychiatric disorder with severe behavioral consequences and no specific therapy. Its etiology is multifactorial, as it is caused by a complex interaction of genetic and environmental factors. In rats, prenatal exposure to the antiepileptic drug valproic acid (VPA) has been associated with an increased risk of autistic-like behaviors in offspring, including social behavior deficits, increased repetitive behaviors, and cognitive impairments. In addition, VPA-treated rats have shown altered sociosexual behaviors. However, the mechanisms underlying these alterations in reproductive processes in VPA-treated rats are not fully understood. Interestingly some abnormal behaviors in VPA autism models are improved by an enriched environment (EE). In the present study, we examined the effects of EE on memory performance and sexual behavior in male rats. We found that on postnatal day 90, EE reduced the time it took for both control and VPA-treated groups to find a hidden platform in the Morris water maze. On PND 100, prenatal exposure to VPA reduced total exploring time in object recognition tests. On PND 110, EE reduced mount and intromission latency and increased ejaculatory frequency in VPA-treated male rats. These results suggest that environmental stimuli significantly influence the onset of sexual behavior in VPA-treated male rats and that EE may be a potential tool for improving a variety of behavioral deficiencies in rodent models of autism.

Listening to your partner: serotonin increases male responsiveness to female vocal signals in mice

The context surrounding vocal communication can have a strong influence on how vocal signals are perceived. The serotonergic system is well-positioned for modulating the perception of communication signals according to context, because serotonergic neurons are responsive to social context, influence social behavior, and innervate auditory regions. Animals like lab mice can be excellent models for exploring how serotonin affects the primary neural systems involved in vocal perception, including within central auditory regions like the inferior colliculus (IC). Within the IC, serotonergic activity reflects not only the presence of a conspecific, but also the valence of a given social interaction. To assess whether serotonin can influence the perception of vocal signals in male mice, we manipulated serotonin systemically with an injection of its precursor 5-HTP, and locally in the IC with an infusion of fenfluramine, a serotonin reuptake blocker. Mice then participated in a behavioral assay in which males suppress their ultrasonic vocalizations (USVs) in response to the playback of female broadband vocalizations (BBVs), used in defensive aggression by females when interacting with males. Both 5-HTP and fenfluramine increased the suppression of USVs during BBV playback relative to controls. 5-HTP additionally decreased the baseline production of a specific type of USV and male investigation, but neither drug treatment strongly affected male digging or grooming. These findings show that serotonin modifies behavioral responses to vocal signals in mice, in part by acting in auditory brain regions, and suggest that mouse vocal behavior can serve as a useful model for exploring the mechanisms of context in human communication.

Early Neurobehavioral Characterization of the CD Mouse Model of Williams-Beuren Syndrome

Williams-Beuren syndrome (WBS) is a neurodevelopmental disorder caused by a chromosomic microdeletion (7q11.23). WBS has been modeled by a mouse line having a complete deletion (CD) of the equivalent mouse locus. This model has been largely used to investigate the etiopathological mechanisms of WBS, although pharmacological therapies have not been identified yet. Surprisingly, CD mice were so far mainly tested in adulthood, despite the developmental nature of WBS and the critical relevance of early timing for potential treatments. Here we provide for the first time a phenotypic characterization of CD mice of both sexes during infancy and adolescence, i.e., between birth and 7 weeks of age. CD pups of both sexes showed reduced body growth, delayed sensory development, and altered patterns of ultrasonic vocalizations and exploratory behaviors. Adolescent CD mice showed reduced locomotion and acoustic startle response, and altered social interaction and communication, the latter being more pronounced in female mice. Juvenile CD mutants of both sexes also displayed reduced brain weight, cortical and hippocampal dendritic length, and spine density. Our findings highlight the critical relevance of early neurobehavioral alterations as biomarkers of WBS pathology, underlying the importance of adolescence for identifying novel therapeutic targets for this neurological disorder.

Deficits in Cerebellum-Dependent Learning and Cerebellar Morphology in Male and Female BTBR Autism Model Mice

Recently, there has been increased interest in the role of the cerebellum in autism spectrum disorder (ASD). To better understand the pathophysiological role of the cerebellum in ASD, it is necessary to have a variety of mouse models that have face validity for cerebellar disruption in humans. Here, we add to the literature on the cerebellum in mouse models of autism with the characterization of the cerebellum in the idiopathic BTBR T + Itpr3tf/J (BTBR) inbred mouse strain, which has behavioral phenotypes that are reminiscent of ASD in patients. When we examined both male and female BTBR mice in comparison to C57BL/6J (C57) controls, we noted that both sexes of BTBR mice showed motor coordination deficits characteristic of cerebellar dysfunction, but only the male mice showed differences in delay eyeblink conditioning, a cerebellum-dependent learning task that is known to be disrupted in ASD patients. Both male and female BTBR mice showed considerable expansion of, and abnormal foliation in, the cerebellum vermis—including a significant expansion of specific lobules in the anterior cerebellum. In addition, we found a slight but significant decrease in Purkinje cell density in both male and female BTBR mice, irrespective of the lobule. Finally, there was a marked reduction of Purkinje cell dendritic spine density in both male and female BTBR mice. These findings suggest that, for the most part, the BTBR mouse model phenocopies many of the characteristics of the subpopulation of ASD patients that have a hypertrophic cerebellum. We discuss the significance of strain differences in the cerebellum as well as the importance of this first effort to identify both similarities and differences between male and female BTBR mice with regard to the cerebellum.

Mistimed restricted feeding disrupts circadian rhythms of male mating behavior and female preovulatory LH surges in mice

In rodents, eating at atypical circadian times, such as during the biological rest phase when feeding is normally minimal, reduces fertility. Prior findings suggest this fertility impairment is due, at least in part, to reduced mating success. However, the physiological and behavioral mechanisms underlying this reproductive suppression are not known. In the present study, we tested the hypothesis that mistimed feeding-induced infertility is due to a disruption in the normal circadian timing of mating behavior and/or the generation of pre-ovulatory luteinizing hormone (LH) surges (estrogen positive feedback). In the first experiment, male+female mouse pairs, acclimated to be food restricted to either the light (mistimed feeding) or dark (control feeding) phase, were scored for mounting frequency and ejaculations over 96 h. Male mounting behavior and ejaculations were distributed much more widely across the day in light-fed mice than in dark-fed controls and fewer light-fed males ejaculated. In the second experiment, the timing of the LH surge, a well characterized circadian event driven by estradiol (E2) and the SCN, was analyzed from serial blood samples taken from ovariectomized and E2-primed female mice that were light-, dark-, or ad-lib-fed. LH concentrations peaked 2 h after lights-off in both dark-fed and ad-lib control females, as expected, but not in light-fed females. Instead, the normally clustered LH surges were distributed widely with high inter-mouse variability in the light-fed group. These data indicate that mistimed feeding disrupts the temporal control of the neural processes underlying both ovulation and mating behavior, contributing to infertility.

Ultrasonic Vocalizations in Adult C57BL/6J Mice: The Role of Sex Differences and Repeated Testing

Ultrasonic vocalizations (USVs) are a major tool for assessing social communication in laboratory mice during their entire lifespan. At adulthood, male mice preferentially emit USVs toward a female conspecific, while females mostly produce ultrasonic calls when facing an adult intruder of the same sex. Recent studies have developed several sophisticated tools to analyze adult mouse USVs, especially in males, because of the increasing relevance of adult communication for behavioral phenotyping of mouse models of autism spectrum disorder (ASD). Little attention has been instead devoted to adult female USVs and impact of sex differences on the quantitative and qualitative characteristics of mouse USVs. Most of the studies have also focused on a single testing session, often without concomitant assessment of other social behaviors (e.g., sniffing), so little is still known about the link between USVs and other aspects of social interaction and their stability/variations across multiple encounters. Here, we evaluated the USVs emitted by adult male and female mice during 3 repeated encounters with an unfamiliar female, with equal or different pre-testing isolation periods between sexes. We demonstrated clear sex differences in several USVs' characteristics and other social behaviors, and these were mostly stable across the encounters and independent of pre-testing isolation. The estrous cycle of the tested females exerted quantitative effects on their vocal and non-vocal behaviors, although it did not affect the qualitative composition of ultrasonic calls. Our findings obtained in B6 mice, i.e., the strain most widely used for engineering of transgenic mouse lines, contribute to provide new guidelines for assessing ultrasonic communication in male and female adult mice.

Prenatal exposure to valproic acid and treatment with intranasal oxytocin have sex-specific effects on behavior in Long Evans rats

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social behaviors and communication. In rodents and humans, prenatal exposure to antiepileptic valproic acid is associated with an increased risk for autistic-like characteristics. One potential treatment is oxytocin, a prosocial neuropeptide that can be delivered intranasally. However, the sex-specific effects of valproic acid exposure and intranasal oxytocin treatment on behavior have not been fully explored. Pregnant Long Evans rats were administered valproic acid (500 mg/kg) or saline midday on gestational day 12, and after weaning, male and female pups were assigned to control (saline-saline), valproic acid-saline, or valproic acid-oxytocin groups. Oxytocin (0.8 IU/kg) or saline was delivered intranasally 30-60 min before tests for anxiety-like behaviors (elevated plus maze), social interactions (sociability) and sociosexual behaviors (partner preference, 50 kHz vocalizations and scent marking). Prenatal exposure to valproic acid resulted in sex-specific differences in behavior. When compared to controls, valproic acid males showed enhanced anxiety-like behaviors in adolescence and fewer scent marks in adulthood, while valproic acid females showed reduced sexual (partner) preference as adults. Intranasal oxytocin was anxiolytic for valproic acid males, but moderately anxiogenic for valproic acid females, and in both sexes it surprisingly impaired social interactions in the sociability test. Furthermore, intranasal oxytocin failed to improve sociosexual deficits in valproic acid rats. These findings highlight the importance of conducting preclinical studies in both sexes, and suggest that oxytocin may be an effective treatment in animal models with heightened anxiety-like behaviors.

Prebiotic, Probiotic, and Synbiotic Consumption Alter Behavioral Variables and Intestinal Permeability and Microbiota in BTBR Mice

Given that prebiotics have been shown to improve gut microbiota composition, gastrointestinal symptoms and select behaviors in autism spectrum disorder (ASD), we hypothesized that prebiotic supplementation would improve sociability, communication, and repetitive behaviors in a murine model of ASD. We also examined the effect of a synbiotic (probiotic + prebiotic). Juvenile male BTBR mice were randomized to: (1) control; (2) probiotic (1 × 10¹⁰ CFU/d Lactobacillus reuteri RC-14^®; now known as Limosilactobacillus reuteri); (3) prebiotic (10% oligofructose-enriched inulin); (4) prebiotic + probiotic (n = 12/group) administered through food for 3 weeks. Sociability, communication, repetitive behavior, intestinal permeability and gut microbiota were assessed. Probiotic and symbiotic treatments improved sociability (92 s and 70 s longer in stranger than empty chamber) and repetitive behaviors (50% lower frequency), whereas prebiotic intake worsened sociability (82 s less in stranger chamber) and increased the total time spent self-grooming (96 s vs. 80 s CTR), but improved communication variables (4.6 ms longer call duration and 4 s higher total syllable activity). Mice consuming probiotics or synbiotics had lower intestinal permeability (30% and 15% lower than CTR). Prebiotic, probiotic, and symbiotic treatments shifted gut microbiota to taxa associated with improved gut health. L.reuteri may help alleviate ASD behavioral symptom severity and improve gut health. The potential use of prebiotics in an ASD population warrants further research.

Skin exposure to UVB light induces a skin-brain-gonad axis and sexual behavior

Ultraviolet (UV) light affects endocrinological and behavioral aspects of sexuality via an unknown mechanism. Here we discover that ultraviolet B (UVB) exposure enhances the levels of sex-steroid hormones and sexual behavior, which are mediated by the skin. In female mice, UVB exposure increases hypothalamus-pituitary-gonadal axis hormone levels, resulting in larger ovaries; extends estrus days; and increases anti-Mullerian hormone (AMH) expression. UVB exposure also enhances the sexual responsiveness and attractiveness of females and male-female interactions. Conditional knockout of p53 specifically in skin keratinocytes abolishes the effects of UVB. Thus, UVB triggers a skin-brain-gonadal axis through skin p53 activation. In humans, solar exposure enhances romantic passion in both genders and aggressiveness in men, as seen in analysis of individual questionaries, and positively correlates with testosterone level. Our findings suggest opportunities for treatment of sex-steroid-related dysfunctions.

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UVB exposure increases circulating sex-steroid levels in mice and humans

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UVB exposure enhances female attractiveness and receptiveness toward males

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UVB exposure increases females’ estrus phase, HPG axis hormones, and follicle growth

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Skin p53 regulates UVB-induced sexual behavior and ovarian physiological changes

Communication and social interaction in the cannabinoid-type 1 receptor null mouse: Implications for autism spectrum disorder

Clinical and preclinical findings have suggested a role of the endocannabinoid system (ECS) in the etiopathology of autism spectrum disorder (ASD). Previous mouse studies have investigated the role of ECS in several behavioral domains; however, none of them has performed an extensive assessment of social and communication behaviors, that is, the main core features of ASD. This study employed a mouse line lacking the primary endocannabinoid receptor (CB1r) and characterized ultrasonic communication and social interaction in CB1^-/- , CB1^+/- , and CB1^+/+ males and females. Quantitative and qualitative alterations in ultrasonic vocalizations (USVs) were observed in CB1 null mice both during early development (i.e., between postnatal days 4 and 10), and at adulthood (i.e., at 3 months of age). Adult mutants also showed marked deficits in social interest in the three-chamber test and social investigation in the direct social interaction test. These behavioral alterations were mostly observed in both sexes and appeared more marked in CB1^-/- than CB1^+/- mutant mice. Importantly, the adult USV alterations could not be attributed to differences in anxiety or sensorimotor abilities, as assessed by the elevated plus maze and auditory startle tests. Our findings demonstrate the role of CB1r in social communication and behavior, supporting the use of the CB1 full knockout mouse in preclinical research on these ASD-relevant core domains. LAY SUMMARY: The endocannabinoid system (ECS) is important for brain development and neural function and is therefore likely to be involved in neurodevelopmental disorders such as Autism Spectrum Disorder (ASD). Here we investigated changes in social behavior and communication, which are core features of ASD, in male and female mice lacking the chief receptor of this system. Our results show that loss of this receptor results in several changes in social behavior and communication both during early development and in adulthood, thus supporting the role of the ECS in these ASD-core behavioral domains.

Pharmacological inhibition of the primary endocannabinoid producing enzyme, DGL-α, induces autism spectrum disorder-like and co-morbid phenotypes in adult C57BL/J mice

Accumulating evidence links dysfunction in the endocannabinoid system (ECS) with the pathology of neurodevelopmental disorders, particularly autism spectrum disorder (ASD). Variants in ECS genes CNR1 and DAGLA are associated with neurological phenotypes in humans. The endocannabinoids (eCBs), 2-AG and AEA, which act at the primary cannabinoid receptor (CB1), mediate behaviors relevant to neurodevelopmental disorders. The overlap between these eCBs is poorly understood. Most ECS studies have focused on stress responses, anxiety, and epilepsy, however, its role in social behavior and communication has only recently come under investigation. This represents a critical gap in our understanding of the ECS and its relationship to ASD. Furthermore, the increasing prevalence of ASD and a lack of therapeutics emphasize a crucial need for novel therapeutic targets. To this aim, we used an inhibitor of the eCB producing enzyme DGL-α, DO34, and the CB1 inverse agonist, rimonabant, to evaluate the role of the primary eCB, 2-AG, in ASD. Adult male C57BL/6J mice were used in a series of behavioral paradigms which assessed social behavior, social communication, repetitive behaviors, anxiety and locomotor activity. DO34 and rimonabant increased anxiety-like behavior, while only DO34 induced hyperactivity, social deficits, and repetitive self-grooming behavior. These data indicate that reduced 2-AG bioavailability, or CB1 inhibition, each induce unique respective behavioral phenotypes relevant to neurodevelopmental disorders, particularly ASD. This suggests fundamental differences in CB1 signaling via 2-AG and the CB1 receptor itself, particularly for social behaviors, and that 2-AG signaling may represent a target for the development of novel therapeutics. LAY SUMMARY: Endocannabinoids play a critical role in the developing nervous system. Alterations in the endocannabinoid system are linked to neurodevelopmental disorders. Studies suggest these variants may play a critical role in the core symptoms of autism spectrum disorder. In this study, pharmacological inhibition of the primary endocannabinoid producing enzyme, DGL-α, induced a constellation of deficits in behavioral domains associated with autism.

Dysfunction of NMDA receptors in neuronal models of an autism spectrum disorder patient with a DSCAM mutation and in Dscam-knockout mice

Heterogeneity in the etiopathology of autism spectrum disorders (ASD) limits the development of generic remedies, requires individualistic and patient-specific research. Recent progress in human-induced pluripotent stem cell (iPSC) technology provides a novel platform for modeling ASDs for studying complex neuronal phenotypes. In this study, we generated telencephalic induced neuronal (iN) cells from iPSCs derived from an ASD patient with a heterozygous point mutation in the DSCAM gene. The mRNA of DSCAM and the density of DSCAM in dendrites were significantly decreased in ASD compared to control iN cells. RNA sequencing analysis revealed that several synaptic function-related genes including NMDA receptor subunits were downregulated in ASD iN cells. Moreover, NMDA receptor (R)-mediated currents were significantly reduced in ASD compared to control iN cells. Normal NMDA-R-mediated current levels were rescued by expressing wild-type DSCAM in ASD iN cells, and reduced currents were observed by truncated DSCAM expression in control iN cells. shRNA-mediated DSCAM knockdown in control iN cells resulted in the downregulation of an NMDA-R subunit, which was rescued by the overexpression of shRNA-resistant DSCAM. Furthermore, DSCAM was co-localized with NMDA-R components in the dendritic spines of iN cells whereas their co-localizations were significantly reduced in ASD iN cells. Levels of phospho-ERK1/2 were significantly lower in ASD iN cells, suggesting a potential mechanism. A neural stem cell-specific Dscam heterozygous knockout mouse model, showing deficits in social interaction and social memory with reduced NMDA-R currents. These data suggest that DSCAM mutation causes pathological symptoms of ASD by dysregulating NMDA-R function.

CD157 and Brain Immune System in (Patho)physiological Conditions: Focus on Brain Plasticity

Ectoenzyme and receptor BST-1/CD157 has been considered as a key molecule involved in the regulation of functional activity of cells in various tissues and organs. It is commonly accepted that CD157 catalyzes NAD+ hydrolysis and acts as a component of integrin adhesion receptor complex. Such properties are important for the regulatory role of CD157 in neuronal and glial cells: in addition to recently discovered role in the regulation of emotions, motor functions, and social behavior, CD157 might serve as an important component of innate immune reactions in the central nervous system. Activation of innate immune system in the brain occurs in response to infectious agents as well as in brain injury and neurodegeneration. As an example, in microglial cells, association of CD157 with CD11b/CD18 complex drives reactive gliosis and neuroinflammation evident in brain ischemia, chronic neurodegeneration, and aging. There are various non-substrate ligands of CD157 belonging to the family of extracellular matrix proteins (fibronectin, collagen I, finbrinogen, and laminin) whose activity is required for controlling cell adhesion and migration. Therefore, CD157 could control structural and functional integrity of the blood-brain barrier and barriergenesis. On the other hand, contribution of CD157 to the regulation of brain development is rather possible since in the embryonic brain, CD157 expression is very high, whereas in the adult brain, CD157 is expressed on neural stem cells and, presumably, is involved in the neurogenesis. Besides, CD157 could mediate astrocytes' action on neural stem and progenitor cells within neurogenic niches. In this review we will summarize how CD157 may affect brain plasticity acting as a molecule at the crossroad of neurogenesis, cerebral angiogenesis, and immune regulation.

Somatosensorimotor and Odor Modification, Along with Serotonergic Processes Underlying the Social Deficits in BTBR T+ Itpr3tf/J and BALB/cJ Mouse Models of Autism

Autism is a complex spectrum of disorders characterized by core behavioral deficits in social communicative behavior, which are also required for comprehensive analysis of preclinical mouse models. As animal models of the core behavioral deficits in autism, two inbred mouse strains, BTBR T+ Itpr3tf/J (BTBR) and BALB/cJ (BALB), were compared with the standard social strain, C57BL/6J (B6), regarding a variety of behavioral factors underlying social communicative interactions, including olfactory and tactile sensory processes, social recognition abilities and behavioral expression strategies. Although both female BTBR and BALB mice can express social recognition and approach behavior depending on the stimuli they encounter, the available sensory modalities, along with modulation of the serotonergic system, differ between the two strains. BALB mice have deficits in using volatile olfactory cues and tactile information in a social context; they fail to exhibit a social approach to volatile cues and seek nonvolatile cues by exhibiting substantial sniff/contact behavior when allowed direct contact with social opponents. Systemic injection of the serotonin (5-HT1A) agonist buspirone has little effect on these social deficits, suggesting a congenitally degraded serotonergic system in BALB mice. In contrast, BTBR mice exhibit impaired body coordination and social motivation-modified olfactory signals, which are relevant to a reduced social approach. A systemic injection of the 5-HT1A agonist restored these social deficits in BTBR mice, indicating that a downregulated serotonergic system is involved in the social deficits exhibited by BTBR mice.

The Stage of the Estrus Cycle Is Critical for Interpretation of Female Mouse Social Interaction Behavior

Female animals in biomedical research have traditionally been excluded from research studies due to the perceived added complexity caused by the estrus cycle. However, given the importance of sex differences in a variety of neurological disorders, testing female mice is critical to identifying sex-linked effects in diseases. To determine the susceptibility of simple behaviors to hormonal fluctuations in the estrus cycle, we studied the effects of sex and the estrus cycle on a variety of behavioral tasks commonly used in mouse phenotyping laboratories. Male and female C57BL/6J mice were tested in a small battery of short duration tests and, immediately on completion of each test, females were classified using cytology of vaginal lavages as sexually-receptive (proestrus and estrus) or non-receptive (NR; metestrus and diestrus). We showed that there was a significant difference in 3-chamber social interaction (SI) between female mice at different stages of their estrus cycle, with sexually-receptive mice showing no preferential interest in a novel female mouse compared with an empty chamber. NR female mice showed the same level of preference for a novel female mouse as male mice did for a novel male mouse. No differences between or within sexes were found for tests of anxiety elevated plus maze (EPM; Hole board), working memory [Novel object recognition (NOR)], and motor learning (repeated tests on rotarod). We conclude that the stage of the estrus cycle may impact SI between same-sex conspecifics, and does not impact performance in the elevated plus-maze, hole board, NOR, and rotarod.

Age-dependent involvement of gut mast cells and histamine in post-stroke inflammation

BACKGROUND

Risk of stroke-related morbidity and mortality increases significantly with age. Aging is associated with chronic, low-grade inflammation, which is thought to contribute to the poorer outcomes after stroke seen in the elderly. Histamine (HA) is a major molecular mediator of inflammation, and mast cells residing in the gut are a primary source of histamine.

METHODS

Stroke was induced in male C57BL/6 J mice at 3 months (young) and 20 months (aged) of age. Role of histamine after stroke was examined using young (Yg) and aged (Ag) mice; mice underwent MCAO surgery and were euthanized at 6 h, 24 h, and 7 days post-ischemia; sham mice received the same surgery but no MCAO. In this work, we evaluated whether worsened outcomes after experimental stroke in aged mice were associated with age-related changes in mast cells, histamine levels, and histamine receptor expression in the gut, brain, and plasma.

RESULTS

We found increased numbers of mast cells in the gut and the brain with aging. Using the middle cerebral artery occlusion (MCAO) model of ischemic stroke, we demonstrate that stroke leads to increased numbers of gut mast cells and gut histamine receptor expression levels. These gut-centric changes are associated with elevated levels of HA and other pro-inflammatory cytokines including IL-6, G-CSF, TNF-α, and IFN-γ in the peripheral circulation. Our data also shows that post-stroke gut inflammation led to a significant reduction of mucin-producing goblet cells and a loss of gut barrier integrity. Lastly, gut inflammation after stroke is associated with changes in the composition of the gut microbiota as early as 24-h post-stroke.

CONCLUSION

An important theme emerging from our results is that acute inflammatory events following ischemic insults in the brain persist longer in the aged mice when compared to younger animals. Taken together, our findings implicate mast cell activation and histamine signaling as a part of peripheral inflammatory response after ischemic stroke, which are profound in aged animals. Interfering with histamine signaling orally might provide translational value to improve stroke outcome.

Male mice adjust courtship behavior in response to female multimodal signals

Multimodal signaling is nearly ubiquitous across animal taxa. While much research has focused on male signal production contributing to female mate-choice or preferences, females often give their own multimodal signals during intersexual communication events. Multimodal signal components are often classified based on whether they contain redundant information (e.g., the backup hypothesis) or non-redundant information (e.g., the multiple messages hypothesis) from the perspective of the receiver. We investigated the role of two different female vocalizations produced by the female house mouse (Mus musculus): the broadband, relatively low-frequency squeaks (broadband vocalizations or BBVs,), and the higher-frequency ultrasonic vocalizations (USVs). These female vocalizations may convey differently valenced information to the male receivers. We paired these vocalizations with and without female urine to examine the influence of combining information across multiple modalities. We found evidence that female urine and vocalizations act as non-redundant multimodal cues as males responded with different behaviors and vocalization rates depending on the female signal presented. Additionally, male mice responded with greater courtship effort to the multimodal combination of female USVs paired with female urine than any other signal combination. These results suggest that the olfactory information contained in female urine provides the context by which males can then evaluate potentially ambiguous female vocalizations.

Effect of rutin on anxiety-like behavior and activity of acetylcholinesterase isoforms in specific brain regions of pentylenetetrazol-treated mice

The aim of the present study was to investigate the effect of rutin administration (100 mg/kg/day) to pentylenetetrazol (PTZ)-treated Balb-c mice (60 mg/kg/day), with respect to anxiety-like behavior using both open-field and elevated plus-maze (EPM) tests, and acetylcholinesterase (AChE) activity in salt-soluble (SS) fraction and detergent-soluble (DS) fraction of the cerebral cortex, hippocampus, striatum, midbrain, and diencephalon. Our results demonstrated that the administration of PTZ in 3 doses and the induction of seizures increased significantly anxiety behavior of mice and reduced significantly DS-AChE activity in all brain regions examined, while the reduction in the SS fraction was brain region-specific. Rutin administration to normal mice did not affect their behavior, while it induced a brain region-specific reduction in SS-AChE and a significant decrease in DS-AChE in all brain regions. We demonstrated for the first time that pretreatment of PTZ-mice with rutin (PTZ + Rutin group) prevented the manifestation of anxiety and induced interestingly a further significant reduction on the SS- and DS-AChE activities only in the cerebral cortex and striatum, in comparison with PTZ group. Our results show that rutin exhibits an important anxiolytic effect and an anticholinesterase activity in specific brain areas in the seizure model of PTZ.

Sex differences in vocal communication of freely interacting adult mice depend upon behavioral context

Ultrasonic vocalizations (USVs) are believed to play a critical role in mouse communication. Although mice produce USVs in multiple contexts, signals emitted in reproductive contexts are typically attributed solely to the male mouse. Only recently has evidence emerged showing that female mice are also vocally active during mixed-sex interactions. Therefore, this study aimed to systematically quantify and compare vocalizations emitted by female and male mice as the animals freely interacted. Using an eight-channel microphone array to determine which mouse emitted specific vocalizations during unrestrained social interaction, we recorded 13 mixed-sex pairs of mice. We report here that females vocalized significantly less often than males during dyadic interactions, with females accounting for approximately one sixth of all emitted signals. Moreover, the acoustic features of female and male signals differed. We found that the bandwidths (i.e., the range of frequencies that a signal spanned) of female-emitted signals were smaller than signals produced by males. When examining how the frequency of each signal changed over time, the slopes of male-emitted signals decreased more rapidly than female signals. Further, we revealed notable differences between male and female vocal signals when the animals were performing the same behaviors. Our study provides evidence that a female mouse does in fact vocalize during interactions with a male and that the acoustic features of female and male vocalizations differ during specific behavioral contexts.

Conditional deletion of Cadherin 13 perturbs Golgi cells and disrupts social and cognitive behaviors

Inhibitory interneurons mediate the gating of synaptic transmission and modulate the activities of neural circuits. Disruption of the function of inhibitory networks in the forebrain is linked to impairment of social and cognitive behaviors, but the involvement of inhibitory interneurons in the cerebellum has not been assessed. We found that Cadherin 13 (Cdh13), a gene implicated in autism spectrum disorder and attention-deficit hyperactivity disorder, is specifically expressed in Golgi cells within the cerebellar cortex. To assess the function of Cdh13 and utilize the manipulation of Cdh13 expression in Golgi cells as an entry point to examine cerebellar-mediated function, we generated mice carrying Cdh13-floxed alleles and conditionally deleted Cdh13 with GlyT2::Cre mice. Loss of Cdh13 results in a decrease in the expression/localization of GAD67 and reduces spontaneous inhibitory postsynaptic current (IPSC) in cerebellar Golgi cells without disrupting spontaneous excitatory postsynaptic current (EPSC). At the behavioral level, loss of Cdh13 in the cerebellum, piriform cortex and endopiriform claustrum have no impact on gross motor coordination or general locomotor behaviors, but leads to deficits in cognitive and social abilities. Mice lacking Cdh13 exhibit reduced cognitive flexibility and loss of preference for contact region concomitant with increased reciprocal social interactions. Together, our findings show that Cdh13 is critical for inhibitory function of Golgi cells, and that GlyT2::Cre-mediated deletion of Cdh13 in non-executive centers of the brain, such as the cerebellum, may contribute to cognitive and social behavioral deficits linked to neurological disorders.

Importance of adiponectin activity in the pathogenesis of Alzheimer's disease

A recent study suggested that insulin resistance may play a central role in the pathogenesis of Alzheimer's disease (AD). In this regard, it is of note that upregulation of plasma adiponectin (APN), a benign adipokine that sensitizes the insulin receptor signaling pathway and suppresses inflammation, has recently been associated with the severities of amyloid deposits and cognitive deficits in the elderly, suggesting that APN may enhance the risk of AD. These results are unanticipated because AD has been linked to type II diabetes and other metabolic disorders in which hypoadiponectinemia has been firmly established, and because APN ameliorated neuropathological features in a mouse model of neurodegeneration. Therefore, the objective of this study is to discuss the possible mechanisms underlying the biological actions of APN in the context of AD. Given that insulin receptor signaling is required for normal function of the nervous system, we predict that APN may be upregulated to compensate for compromised activity of the insulin receptor signaling pathway. However, increased APN might be sequestered by tau in the brain, leading to neurotoxic protein aggregation in AD. Alternatively, misfolding of APN may result in downregulation of the insulin/APN signal transduction network, leading to decreased neuroprotective and neurotrophic activities. Thus, it is possible that both ‘gain of function’ and ‘loss of function’ of APN may underlie synaptic dysfunction and neuronal cell death in AD. Such a unique biological mechanism underlying APN function in AD may require a novel therapeutic strategy that is distinct from previous treatment for metabolic disorders.

Autism-like behavior in the BTBR mouse model of autism is improved by propofol

Autism spectrum disorder (ASD) is a developmental disorder that is characterized by symptoms of impaired social interactions, restricted interests and repetitive behaviors. Recent studies in humans and animal-models suggest that reduced GABAergic neurotransmission in the brain may underlie autism-related behavioral symptoms. It has been shown that propofol, a commonly used anesthetic, facilitates γ-aminobutyric acid-mediated inhibitory synaptic transmission. The present study investigated whether propofol improved autistic phenotypes in BTBR T + Itpr3tf/J (BTBR) mice, a model of idiopathic autism. We found that i.p. injection of propofol in BTBR mice significantly improved aspects of social approach and repetitive behaviors without affecting reciprocal social interactions and without any detrimental effects in C57BL/6J mice. The ability of propofol to improve autistic phenotypes in BTBR mice through GABAergic neurotransmission suggests a potential pharmacological target for interventions to treat symptoms of autism.

Social Ultrasonic Vocalization in Awake Head-Restrained Mouse

Numerous animal species emit vocalizations in response to various social stimuli. The neural basis of vocal communication has been investigated in monkeys, songbirds, rats, bats, and invertebrates resulting in deep insights into motor control, neural coding, and learning. Mice, which recently became very popular as a model system for mammalian neuroscience, also utilize ultrasonic vocalizations (USVs) during mating behavior. However, our knowledge is lacking of both the behavior and its underlying neural mechanism. We developed a novel method for head-restrained male mice (HRMM) to interact with non-restrained female mice (NRFM) and show that mice can emit USVs in this context. We first recorded USVs in a free arena with non-restrained male mice (NRMM) and NRFM. Of the NRMM, which vocalized in the free arena, the majority could be habituated to also vocalize while head-restrained but only when a female mouse was present in proximity. The USVs emitted by HRMM are similar to the USVs of NRMM in the presence of a female mouse in their spectral structure, inter-syllable interval distribution, and USV sequence length, and therefore are interpreted as social USVs. By analyzing the vocalizations of NRMM, we established criteria to predict which individuals are likely to vocalize while head fixed based on the USV rate and average syllable duration. To characterize the USVs emitted by HRMM, we analyzed the syllable composition of HRMM and NRMM and found that USVs emitted by HRMM have a higher proportion of USVs with complex spectral representation, supporting previous studies showing that mice social USVs are context dependent. Our results suggest a way to study the neural mechanisms of production and control of social vocalization in mice using advanced methods requiring head fixation.